2022-12-14: How Can Matter Be BOTH Liquid AND Gas?
- 00:03: ... is made of, or at extreme densities we get the nuclear matter of neutron stars. ...
- 03:45: To start with, both are fluids - they flow.
- 11:28: ... is to send it out into outerspace to catch cosmic dust, as in NASA’s Stardust ...
- 14:26: ... to think of it, let’s not review all the states of matter, because I’m starting to think there may be no end to the weird ways that matter can ...
- 16:31: Let’s start with quasiparticles.
2022-12-08: How Are Quasiparticles Different From Particles?
- 00:44: Let’s start our discussion of quasiparticles by talking about the particular quasiparticle that lets me talk to you about quasiparticles right now.
2022-11-23: How To See Black Holes By Catching Neutrinos
- 04:17: ... are not slowed down, so the electron or muon that it creates also start out with a speed faster than the reduced speed of light in the ...
- 05:01: A grid of over 5000 photomultiplies spans a cubic kilometer of the glacier, starting at a depth of 1.5km.
- 07:49: ... patch of sky in the constellation of cetus includes a lot of Milky Way stars, a lot of very distant galaxies, but there’s only one thing that is a ...
- 11:09: So that means we can finally start doing real neutrino astrophysics.
- 11:35: Supernovae, colliding neutron stars and black holes, tidal disruption events when black holes rip apart stars, you name it.
- 15:40: And by the way kids - if you start seeing mysterious flashes, you might be one of those lucky few, but you should talk to your doctor anyway.
- 16:33: ... heavy elements are produced in supernovae or in colliding neutron stars by the R-process - basically bombarding lighter elements with ...
2022-11-16: Are there Undiscovered Elements Beyond The Periodic Table?
- 00:26: ... elements whose incredible properties will propel us into our star-faring ...
- 01:17: To understand the possibility of new artificial elements let's start with the story of the first artificial element.
- 01:38: ... time you add a proton to the nucleus, until the shell fills and you start over, filling the next shell ...
- 03:28: Well, actually technetium is produced in nature - just like other heavy elements, in the core of massive stars.
- 03:36: Those elements eventually find their way into planets, which form from the guts of those stars after they explode as supernovae.
- 03:43: But technetium is so unstable that by the time the Earth pulled itself together from the detritus of dead stars, all the technetium was long gone.
- 18:57: ... times on early, except for the fact that once one incident of life got started and made progress, it would be very difficult for it to happen a second ...
2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations?
- 00:38: ... Stars will continue burning for another hundred trillion years, and the heat ...
- 00:52: At the same time, when we look at the sky we see… stars.
- 01:30: We are in fact on a typical planet, orbiting a typical star in a typical galaxy.
- 03:32: ... start with a function called the appearance rate, which tells us how ...
- 04:05: ... figure out the appearance rate function, the researchers start with what we know about when habitable worlds formed in the past or when ...
- 04:16: It turns out that most habitable stars are formed in a pretty short period of cosmic history.
- 04:29: And around 20 billion years in the future, there won’t be enough interstellar material left to form new stars.
- 04:36: Habitable star formation will peak at around 15 billion years, not so far away from our current date.
- 04:50: Once a habitable star along with its habitable planets have formed, life needs time to evolve.
- 05:51: If there are few hard steps, then civilizations emerge soon after their stars are formed.
- 07:23: ... would mostly stop appearing 5 billion years after the peak of habitable star formation - which, if you remember, is 20 billion years ...
- 07:49: ... stars, also known as red dwarfs, can live for thousands of times longer than ...
- 08:16: Since they’re very dim, orbiting planets need to be very close to the star in order to have liquid water, which may be necessary for life.
- 08:23: But planets closer to their star are more likely to be tidally locked.
2022-10-26: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
- 01:22: Let’s start with a simple thought experiment.
- 15:43: We hope you find peace among the stars.
- 16:01: Let’s start with the solar gravitational lens.
- 17:37: The report talks about Earth-mass planets around Sun-like stars, of which there are plenty.
- 18:21: The idea here was to give you a taste of its contents, and perhaps a starting point for further investigation.
- 20:06: Although, to be fair, each of the 3 readings took like 20 minutes while staring at my own face, so it could be I hallucinated the whole thing.
2022-10-19: The Equation That Explains (Nearly) Everything!
- 01:02: ... Standard Model. We finally have what we need to bring it together. Let’s start by recalling how the standard model itself got started. One of the most ...
2022-10-12: The REAL Possibility of Mapping Alien Planets!
- 00:33: ... reveal anything more than a single dot in orbit around a star. If we find evidence for life, we’re going to want to ...
- 01:25: ... a New York sized telescope - at this spot, we have a star-sized telescope. The result is an amplification of the brightness of the ...
- 07:45: ... the Sun. To reach the speeds we need, our spacecraft can’t start their outward journey from the Earth - they needs to get closer to ...
- 09:31: ... spacecraft starts out by launching backwards compared to Earth’s orbital ...
- 10:07: ... the Sun’s gravitational field creates a focal line, starting at 550 astronomical units, and extending indefinitely, with ...
- 15:45: ... 1/137 as the universe cooled. By the time fhe first stars were formed ti was essentially as it is today. Radoslaw Garbacz ask What ...
- 18:29: ... the universe where this happens today. Not in the centers of stars or accretion disks. But perhaps in the cores of neutron stars ...
2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?
- 01:34: As with much of quantum mechanics, it started with us watching the light produced as electrons flicked between energy levels in atoms.
- 03:54: ... splitting of spectral lines it would be just a fun oddity, except this started to show up ...
- 06:37: So it’s starting to make sense why the fine structure constant appears in all of these formulas that depend on the electromagnetic force.
- 08:22: ... a few percent different, carbon would never have formed inside stars, making life ...
- 11:03: Let’s start by thinking about the similarly prolific constants of nature - the ones that actually have units.
2022-09-21: Science of the James Webb Telescope Explained!
- 01:52: ... planning picked up over the 90s, and pretty quickly core properties started to crystalize for what was then the “Next Generation Space Telescope” ...
- 04:03: The very first galaxies shone with intense ultraviolet light as the dense, young gas of the early universe collapsed into the first stars.
- 04:40: ... allows it to see the cool dust and gas that lives between the stars, as well as peer through that dust which normally blocks shorter ...
- 05:01: IR sensitivity lets us peer into the dusty whirlpools around new stars and watch the formation of planets in action.
- 05:32: ... objects at once; or using a coronagraph to block the bright light of a star to better see its planets, to name just a ...
- 05:52: Let’s start by looking at how most working astrophysicists hope to use JWST.
- 09:49: And this bright star is, well, a star - in the milky Way galaxy.
- 10:41: How could YOU get started doing something with this telescope?
- 12:34: Let’s start with the strong force.
- 14:20: Quantum chromodynamics actually started to explain was going on, so it suplanted hadronic string theory.
- 14:45: ... still failing to produce a slam-dunk testable prediciton, people are starting to take the prodigious math developed for the theory and apply it to ...
2022-09-14: Could the Higgs Boson Lead Us to Dark Matter?
- 02:05: Let’s start by looking at how we detect new particles in general.
2022-08-24: What Makes The Strong Force Strong?
- 01:29: ... came in the 1940s when we switched on our first particle colliders and started to detect a veritable zoo of new ...
- 16:52: Starting with Lattice QCD, although the questions are more generally about particle physics.
2022-08-17: What If Dark Energy is a New Quantum Field?
- 03:33: ... but also the positive gravity of all other matter. And it’s only getting started. As the universe gets bigger and galaxies get further and further apart, ...
- 10:55: ... the density of matter. And it only becomes dark-energy-like when matter starts to thin out. That provides a natural explanation for why dark energy ...
2022-08-03: What Happens Inside a Proton?
- 00:00: ... we ever want to simulate a universe, we should probably start by learning to simulate even a single atomic nucleus. But ...
- 06:37: ... even with computers. Now Before any particle physicists start shouting at me, I’ll quickly add the caveat that there are ...
- 07:53: ... need to account for all possible paths between the starting and final field configuration to get the probability of that ...
- 10:18: ... number of ways that the field can move from the starting to final configuration. And because these configurations are ...
- 10:43: ... configurations of a pixelated space that get us from the start to the end of our interaction. But these can’t be ...
- 19:17: ... can I abuse the rules of reality to survive past the death of the stars and live to see the release of half life 3?” The ...
2022-07-27: How Many States Of Matter Are There?
- 04:55: Let’s start our search for some new states of matter by exploring in the direction we started.
- 06:10: However in the very early universe everything was a quark-gluon plasma, and that may also be true in the cores of massive neutron stars.
- 07:34: If you want to see what it’s like to move to right on this diagram, just burrow into a neutron star.
- 09:30: ... how those grains of sand interact with each other, and the sand will start acting like a ...
- 10:21: It starts behaving like a liquid.
- 10:57: Astrophysicists routinely model the galaxies as a sort of fluid of stars, where the interactions are not electromagnetic, but gravitational.
- 11:05: So, galaxies are fluids of stars which themselves are made of plasmas of hydrogen made of frozen nuggets of quark matter.
2022-07-20: What If We Live in a Superdeterministic Universe?
- 08:28: Alice and Bob start out together, acquire their entangled electrons, and then move sideways in space and up in time.
- 08:56: Now let’s look at the case where the electrons start out with defined spins.
- 12:29: Their first effort used the light from a pair of distant stars as proxies for Alice and Bob.
- 12:53: ... and Bob’s decisions except in the seemingly implausible scenario of stars talking to each other and conspiring against ...
- 18:30: No Star Trek future unless you can assemble furniture without destroying your planet.
2022-06-30: Could We Decode Alien Physics?
- 00:00: ... - I mean, we live in the same universe after all. We start by noticing that the alien technology seems to use good ol’ ...
- 10:41: ... - appears to bring our equations back to where they started. This is CP symmetry. A mirror-reflected, antimatter universe has ...
- 15:07: ... speeds through the dust and gas that lives between the stars. ...
- 16:39: ... in the light and wind and magnetic field of the destination star, or Bussard ramjets - vast scoops that collect diffuse ...
2022-06-22: Is Interstellar Travel Impossible?
- 01:31: But none ever manage to populate the galaxy because sending living creatures between the stars is so difficult that it’s just not worth it.
- 02:01: The nearest star, Proxima centauri, is 4.2 light years away.
- 02:19: ... humans to travel the stars, travel time needs to at least be of order a human lifetime, which means ...
- 02:35: ... Breakthrough Starshot program proposes to send a train of tiny craft powered by solar sails, ...
- 03:36: The space between the stars in our galaxy is far from empty.
- 04:02: ... glorious star-spanning future depends on the answer to a rather mundane question: can a ship ...
- 04:38: We’re going to send a starship to the Proxima Centauri with the aim of getting them there in a generation, and hopefully alive.
- 06:41: This stuff comes from heavy elements that are fused in the cores of massive stars and ejected in supernovae or in the winds from giant stars.
- 07:38: They start to burn up almost as soon as they enter its upper layers, where the air is only a millionth the density of sea-level.
- 09:49: So we can minimise the additional weight by making our starship as long and narrow as possible.
- 09:56: ... viability of crewed missions, but rather on missions like Breakthrough Starshot where the “spaceship” is a wafer-thin chip for which a millimeter ...
- 10:30: Moderate shielding is sufficient for nearby stars, and the ability to repair shielding might get us to more distant parts of the galaxy.
- 10:56: One that could result in our starship reaching its destination perfectly intact, but carrying a dead crew.
- 13:09: ... accelerate txo relativistic speeds, at least for our early iterations of starship propulsion ...
- 15:02: Amy, thanks for helping us reach for the stars.
2022-06-15: Can Wormholes Solve The Black Hole Information Paradox?
- 05:20: ... radiation is produced, but then at some point the entropy starts to drop again because the information from past ...
2022-06-01: What If Physics IS NOT Describing Reality?
- 01:41: ... a recent episode we started talking about informational interpretations of quantum ...
- 04:56: ... simplest way to start is to look at a quantum system where the answer to a ...
- 05:53: ... rotating the Stern Gerlach apparatus 90 degrees. You started out with one bit of knowledge about the particle’s up-down ...
- 13:41: ... within our galaxy’s gravitational well. It’ll interact with stars, kicking them up to higher orbits while its own orbit decays. In ...
- 14:22: ... better and worse parts of this ring, but remember that a star will move through many different regions as it orbits the ...
- 15:25: ... Kosa asks about actual collisions between stars when galaxies merge. Given that most of the galaxy is empty ...
2022-05-25: The Evolution of the Modern Milky Way Galaxy
- 00:00: ... in the southern hemisphere and you’ll see too: the several billion stars of the large and small magellanic clouds in their slow death ...
- 01:41: ... tracked the positions and motions of more than a billion Milky Way stars. We’re now able to calculate a detailed and dynamical map of ...
- 02:19: ... arms. It orbits in the same direction as all the disk stars once every 230 Million years. In the center we have the bulge ...
- 03:22: ... big bang. Back then, galaxies were raging storms of star formation due to the abundance of gas back then. We only see ...
- 04:41: ... reconstruct the details of such a chaotic process? The stars from every previous merger are mixed all across the ...
- 05:11: ... review the evidence. Item 1: Stars that join the Milky Way at the same time, like during ...
- 05:58: ... on their own aren’t really enough to tell if two stars came from the same galactic snack. So Evidence item number 2: If ...
- 06:57: ... Telescope which was used to discover the event by identifying star from this devoured galaxy in the Milky Way’s halo. The ...
- 07:58: ... disk, which is a few hundred lightyears thick, and is the main star factory of the Milky way. It’s home to the spiral arms and the ...
- 08:29: ... special happened to the Milky Way to create it. It’s made of stars, not gas, and these stars orbit just a little faster on ...
- 09:11: ... during the merger with Gaia-Enceladus. While the stars of Gaia Enceladus got mixed into the halo, the crazy gravitational ...
- 10:12: ... easy for astronomers to pick out the little stripe of stars, like GD-1: a globular cluster that’s in the process of being ...
- 11:10: ... Like beating a drum or plucking a guitar string, the stars oscillate up and down in the galactic plane, making a very faint ...
- 12:11: ... a fresh infusion of gas, probably triggering another bout of star formation in about 2 billion years. The accompanying supernova ...
- 14:08: ... work. There’s a link in the description, so everyone can start exploring Search.pbsspacetime.com right ...
- 14:38: ... bound systems like the Milky Way. Let's start with the habitable zone: In that episode I said that parts of the ...
- 16:41: ... of heavy elements - which was perhaps necessary for life to get started. The late heavy bombardment was a massive meteor shower that lasted ...
2022-05-18: What If the Galactic Habitable Zone LIMITS Intelligent Life?
- 01:07: ... mysteries of the universe? In a galaxy of 200+ billion stars, why don’t we see any other signs of technological life? This is ...
- 03:34: But pf course, modern science has its own origin story for our nearest and dearest star, the sun.
- 04:32: ... our home star has a pretty cool backstory, but hardly a unique one. Our Sun is a ...
- 05:24: ... not so fast. There is another factor to consider. Stars have habitable zones, but so do galaxies. There are huge regions ...
- 05:52: ... Stars are mostly made out of hydrogen and helium, with trace amounts of ...
- 06:28: ... of these heavy elements are produced in massive stars and then spread through the galaxy in supernova explosions. ...
- 06:56: ... systems could have formed in the first place. Our galaxies started like all galaxies - as a slightly overdense spot in the near ...
- 07:36: ... primordial generation of stars were unpolluted by heavy elements, which means they couldn’t ...
- 08:01: ... next generation of stars had some metals, and so for the first time had the chance to ...
- 09:26: ... the core the worst place in the galaxy. The extreme density of stars will have led to frequent close encounters between ...
- 10:04: ... Eventually the disk of gas converted itself into a disk of stars. It took some time for the emerging spiral disk to seed itself with ...
- 10:48: ... Galactic habitable zone. It emerged around 8 billion years ago, starting out as a band between around 20 and 30 thousand light years ...
- 11:12: ... on the Milky Way’s formation history, our starting intuition seems right: the Sun and solar system are NOT ...
- 12:04: ... but it’s also not the most typical. Fewer than 10% of stars formed in the Milky Way have optimal conditions for the ...
- 13:03: ... probes. But it seems that most earth-analogs have a head start of a billion years - more than enough time to establish galactic ...
2022-05-04: Space DOES NOT Expand Everywhere
- 01:24: ... to move around due to nearby gravitational influences - planets orbit stars, stars orbit in the mutual gravity of their galaxies, galaxies whirl and ...
- 05:19: ... galaxy growing but overcome by the gravitational attraction between the stars? ...
- 09:16: ... general relativity, space can be infinitely divided. That means we can start with a universe that’s small and grid it up and watch it expand. The ...
- 09:38: ... one of those points traces a path back to the big bang. We can make the starting grid as fine as we like and get the same result. Every point in the ...
- 14:34: ... logical inference in the style of Descartes. They felt it dishonest to start their train of reasoning with statements about external factors that ...
2022-04-27: How the Higgs Mechanism Give Things Mass
- 05:38: ... and they end up all aligning. The equations of magnetism don’t start out with a preferred orientation, but in certain conditions ...
- 06:43: ... middle. The system is still symmetric, but if the ball starts at the top of the hill it will randomly roll down into one ...
2022-04-20: Does the Universe Create Itself?
- 01:59: ... to explain the universe, let’s review some quantum weirdness. We’ll start with the good ol’ Schrodinger’s cat thought experiment, devised by ...
- 04:14: ... satisfied with any of the proposed quantum interpretations. Although he started out as a pure realist, he came to believe that the observer must in some ...
- 17:39: ... hole with the mass of our observable universe - adding together all the stars, dark matter, other black holes, etc - then it’s event horizon is the same ...
2022-03-30: Could The Universe Be Inside A Black Hole?
- 05:19: ... outside universe. So the black hole and the big bang singularities are starting to look more alike. With the difference being, their residence in the ...
- 06:28: That’s starting to look like our universe - a past, space-like singularity and an event horizon that can’t be crossed from the outside.
- 08:15: ... with his student Hartland Snyder They approximated the collapse of a star by modeling it as a spherical cloud of matter with a perfectly ...
- 08:51: Now real stars don’t look like this.
- 09:20: In fact you can describe the spacetime of a collapsing star by patching an FLRW metlric inside a Schwarzschild metric.
- 09:35: So you can have what looks like a black hole from the inside, but looks like comfortably flat space inside the still-collapsing star.
- 10:40: OK, so we need one last ingredient to be able to answer “maybe” to the question we started with: Are we in a black hole?
2022-03-23: Where Is The Center of The Universe?
- 00:25: ... us from our pedestal onto a random rocky planet orbiting an ordinary star in the outskirts of an unremarkable ...
- 02:55: As with much, it starts with Einstein.
- 06:21: In the case of the closed universe, that means it started out as a very, very tiny hypersphere surface and got bigger.
- 09:40: ... - if all geodesics emerged from that point - does that mean the universe started out ...
- 10:16: So did the universe start out pointlike at t=0 and then suddenly become infinite in size?
- 14:27: ... starts out explaining relativity in terms of boats passing by each other on a ...
- 14:58: Starting with Proxima.
- 15:27: But even if life didn’t start in tidal pools on Earth, who’s to say it couldn’t have happened that way elsewhere?
- 16:11: A hot interior may also have been essential for abiogenesis - if life really did first start around geothermal vents or hot springs.
- 18:31: ... found around 60 similar signals that were not clearly associated with stars and had radio frequency spacing similar to Earthly ...
2022-03-16: What If Charge is NOT Fundamental?
- 03:23: By introducing this new conserved quantity, Heisenberg started to make sense of the relationship between protons and neutrons.
- 08:03: Starting with experiments at the Stanford Linear Accelerator Center in 1968, the reality of quarks quickly became conclusive.
- 09:32: ... to connect all of this back to quantum spin, which is sort of where we started. ...
2022-03-08: Is the Proxima System Our Best Hope For Another Earth?
- 00:11: He made careful note of the position of a bright star that hung just above the southern horizon.
- 00:25: A world that would be humanity’s first destination when we would finally venture to the stars.
- 00:37: Alpha Centauri is the first and brightest of the constellation of the centaur, and the nearest star in our galaxy of 200 billion.
- 00:46: ... Almagest, more than a millennium and a half passed before we started to realize its incredible ...
- 00:57: By the end of the 17th century, the star had long since slipped below the horizon of Alexandria in its galactic wanderings.
- 01:15: Father Jean Richaud saw two stars instead of one, these days dubbed Rigel Kentaurus and Tolimar, a binary pair bound in an 80 year waltz.
- 01:28: ... allowing astronomers to watch alpha-cen sway relative to the background stars as Earth orbited the ...
- 01:47: The two stars were so near and so familiar - both within 10% or so of our own Sun’s mass.
- 02:00: Dreams of an interstellar humanity started with the twins at the centaur’s foot.
- 02:10: Forward another century, and a Scotsman named Robert Innes photographed the southern stars from Johannesburg to track their galactic wanderings.
- 02:33: A faint red star crawled on a vast, half-million year orbit around its brighter siblings.
- 03:05: This one was barely a star at all, really, at only 12% of the Sun’s mass and only a little larger than Jupiter.
- 03:22: ... resulting from electron transitions in the atoms and molecules of the star’s ...
- 04:05: Planets don’t really orbit stars.
- 04:08: A planet-star pair mutually orbits its shared center of mass - its barycenter - which is usually deep inside the star.
- 04:15: Planets make stars wobble, and that motion induces something called Doppler shift in the star’s emission lines.
- 04:22: ... the wavelengths of all the star’s light are stretched as the star moves away from us and compressed as it ...
- 04:42: ... the Doppler effect is only produced by the component of the star’s velocity that’s either directly towards us or away from us - in the ...
- 05:07: ... in which planets are identified by their dimming of their parent star as they cross or transit the face of that star from our ...
- 05:26: Nonetheless the Kepler mission found 2600+ exoplanets this way, and extrapolating from that revealed that most stars host planetary systems.
- 05:56: ... realized that Proxima’s shifting emission lines made sense if the star was wobbling in a tight circle, moving at about a mile per hour over a ...
- 06:18: Such a short orbital period, combined with the star’s mass, gave them an orbital radius for the exoplanet of around 20 times smaller than the Earth’s.
- 06:37: ... places the new exoplanet exactly in the habitable zone of the star - just the right distance for the intensity of the star’s radiation to ...
- 06:50: ... stunning calculation to come: with the distance between exoplanet and star combined with the speed of the wobble, astronomers could calculate its ...
- 07:18: The nearest habitable exoplanet orbited the nearest star.
- 07:28: The discovery of this exoplanet - Proxima Centauri B - or Proxima-B - was just the first of this little star’s surprises.
- 08:30: We have a bona fide planetary system in at least one of the stars in the Alpha-Cen system.
- 09:12: One very important point is that Proxima B is probably tidally locked to its star.
- 09:17: ... close proximity to the star means strong tidal forces, which will have forced the planet’s rotation ...
- 09:34: That would keep the same side of the planet facing the star at all times.
- 10:34: ... the exoplanet has an ocean to be pulled and squeezed by the nearby star. ...
- 11:03: In order for life to have a chance in this system, it needs to be protected from the star itself.
- 11:20: It’s what’s known as a flare star.
- 11:22: ... convection through the star’s body generates crazy magnetic storms, which can cause the star to have ...
- 12:12: There’s far less visible light, so to our eyes the star would appear very dim.
- 12:50: ... indicate that there wouldn’t have been enough material so close to the star for it to have formed in that ...
- 13:51: It’s the breakthrough Starshot program - something we’ve discussed previously.
- 14:56: But there’s another white star on the horizon, but it’s slowly slipping away on its own orbit around the Milky Way.
- 16:27: ... it’s yours to do with it as you wish - name it, claim lordship over it, start your galactic empire there, or just use it for weekend ...
2022-02-23: Are Cosmic Strings Cracks in the Universe?
- 00:00: ... from a single surface. If the crystallization process starts from multiple nucleation points then there’ll be ...
- 04:51: ... Here and there across the universe, the Higgs field started falling towards the new vacuum state - we call this ...
- 08:50: ... these things are long. They started as long as light can travel between the nucleation ...
- 10:09: ... do. Now, how do we find them, assuming they exist? Well let’s start with these gravitational waves. That radiation should be emitted ...
2022-02-16: Is The Wave Function The Building Block of Reality?
- 04:17: ... story starts in 1986 when three Italian physicists, Giancarlo Ghirardi, Alberto ...
2022-02-10: The Nature of Space and Time AMA
- 00:03: ... the day is the nature of space and the nature of time now i should start out by pointing out that no one knows what the nature of space and ...
2022-01-27: How Does Gravity Escape A Black Hole?
- 02:08: ... that’s been confirmed when gravitational waves from colliding neutron stars reach us at about the same time the corresponding electromagnetic ...
- 03:25: Starting with good old fashioned general relativity.
- 09:24: Think about a star collapsing into a black hole.
- 09:46: ... star does appear to go black, but really the faintest signals of that ...
- 12:41: In one of those simulations you live 3000 years and become emperor of space, and in another you star in Interstellar instead of Matthew McConaughey.
- 13:25: Starting with the quantum, manonthedollar asks - given the incredible amount of power required to simulate quantum interactions...
- 14:21: We said that in density function theory you start with a make-believe system of non-interacting electrons.
- 16:14: ... unless they’re close together, then the magnets will obviously form stars and ...
2022-01-19: How To Build The Universe in a Computer
- 00:47: ... chaotic gravitational and hydrodynamic interactions of countless stars and gas and dark matter particles over billions of future ...
- 01:40: He arrayed 37 light bulbs on a plane, each one representing billions of stars in a spiral galaxy disk.
- 02:04: ... the simulation went like this: Holmberg started with a pair of these light-bulb-galaxies next to each other, with the ...
- 02:15: He would then measure light at each bulb, which told him the summed “gravitational” pull on that group of stars.
- 02:33: Then, from that new configuration he’d start the process again.
- 04:37: But if we want realistic simulations of say, a galaxy with its billions of stars, we need to do a bit better.
- 05:14: For a modern one-million particle simulation of a star cluster, that’s a trillion computations per time step.
- 06:16: It works like this: you start with a volume full of particles, each with its starting position and velocity.
- 07:24: Adaptive particle meshes can be used to add higher resolution where needed - say, where the stars have higher density or structure.
- 07:52: The universe started as an ocean of gas a few hundred thousand years after the Big Bang.
- 07:57: ... from beyond, where it rides the disk, fragments and collapses into stars, it forms whirlpools and jets around new stars and black ...
- 08:08: All of these processes are key parts of galaxy evolution and of star and planet formation, and so we’d better be able to simulate this too.
- 08:45: ... the flows of gas in galaxies and around quasars, used to simulate star and planet formation, and even star and planet ...
- 08:58: SPH can even be used to do galaxy formation, where the stars themselves are treated as a type of fluid.
- 09:22: In your galaxy simulation you might need a separate prescription to describes how stars age and die.
- 09:34: ... don’t get me started about the complexity of including magnetic fields, or of ...
- 09:53: We can see how stars form in multitudes from collapsing gas clouds, and how planets then coalesce in the disks surrounding those stars.
- 10:02: ... galaxies form, with gas and dark matter interacting to produce waves of star formation and supernovae, settling into spiral structures - just like we ...
2022-01-12: How To Simulate The Universe With DFT
- 02:39: But it’s where we start learning quantum mechanics, and it works for a lot of simple cases.
- 05:52: ... the impossible case of many interacting quantum particles, we should start by thinking about the completely solvable case of many non-quantum or ...
- 10:42: ... we start with a bad guess at the ground state charge distribution and then ...
- 11:37: ... according to the theorem that we started with, that ground state charge distribution is unique - it corresponds ...
- 16:50: I did see a paper that claimed we might be able see the high-frequency seismic fluctuations set up inside a star after a black hole passage.
2021-12-29: How to Find ALIEN Dyson Spheres
- 01:20: It was first proposed by British author Olaf Stapledon in his 1937 story Star Maker.
- 01:38: ... might expand to occupy an entire sphere surrounding its home star at the radius of its planet of origin, for the purpose of both ...
- 02:01: ... actually as a swarm of independent craft, either in orbit around the star or kiting in place on the solar ...
- 03:36: ... spot this spectral shift from another star you’d have to have an incredibly sensitive telescope to pick the Earth’s ...
- 03:47: ... has expanded to reprocess a significant fraction of its home star’s light, then not only could we detect that shift with our current ...
- 04:10: Dyson’s original notion was simply to search for points of light with temperatures of a few hundred Kelvin, but emitting the power of an entire star.
- 04:54: Surveys started to find many, many objects that fit the description.
- 05:06: ... protostars - the clouds of gas in the process of collapsing into a new star, circumstellar disks - the luke-warm disk of gas surrounding a new-born ...
- 05:48: Dyson and Sagan etc’s calculations were for a full Dyson sphere - one that reprocesses all of their star’s light.
- 05:56: But many civilizations may find it totally adequate to only partially harvest their star’s light.
- 06:11: Or really any so-called megastructure that intercepts a decent fraction of the star’s light.
- 06:24: To understand how to spot such a thing, let’s learn a thing or two about stars.
- 06:30: Stars are surprisingly simple beasts, for the most part ruled by laws of physics that we’ve understood for centuries.
- 06:37: ... star in the prime of its life settles into an equilibrium state in which the ...
- 06:47: If you know the mass of such a star, you can predict its size, its temperature, its brightness, its lifespan, and so on.
- 06:54: If a star deviates from the tight relationships between these properties then we quickly know that something is up.
- 07:11: It would be an unnatural combination of a large, hot object - the central star, and a gigantic cool object - the partial sphere.
- 07:24: But from our great distance the light from the star and the sphere would be blended into a point.
- 07:41: If we carefully broke up the star’s light with spectrographs spanning a huge wavelength range, we might be able to see two distinct thermal spectra.
- 07:52: But that’s a lot of work even for a single star, and we probably need to search a huge number of stars to hope to find even a single Dyson sphere.
- 08:03: Fortunately, even a crude observation of a star’s color and brightness can tell us that something is up.
- 08:27: I mentioned that most stars show a tight relationship between certain properties.
- 08:31: For example, the higher the surface temperature of a star, the higher its total power output - it’s luminosity.
- 08:50: ... stars that are in the primes of their lives - those powered by fusing hydrogen ...
- 09:03: ... Stars drive off the main sequence when they expand into giants at the ends of ...
- 09:14: Let’s see what a Dyson sphere would actually do to a star on the HR diagram.
- 09:20: At visible wavelengths a star’s color might not change much - it’ll just look dimmer.
- 09:25: So a star might appear too faint for its apparent temperature - dropping below the main sequence.
- 09:40: The star would look cooler - lower temperature than suggested by its visible color alone.
- 09:46: ... years, calculate that a partial sphere that intercepts only 1% of its star's light could shift the visible-to-infrared color by a factor of more than ...
- 10:01: ... teams have used successively more advanced instruments to look for stars that were both too dim and too infrared, time and again they came up ...
- 10:28: The team started by looking for stars that were a little too faint for their visible-light color - below the main sequence.
- 10:39: Then they checked whether these stars had an excess of light in the infrared.
- 10:56: ... might be expected if a giant orbiting structure partially eclipses the star in an irregular ...
- 11:09: And that’s exactly what happened with the famed Tabby's Star.
- 11:13: This weird star discovered by Tabetha Boyajian, exhibited complex dips in brightness, causing rumours of alien megastructures to abound.
- 11:33: At this point, our surveys have found no evidence for star-spanning megastructures.
- 11:54: It would be incredibly difficult to detect such an object around a low mass star if it’s on the other side of the galaxy.
- 12:12: ... we can't identify a single Dyson sphere's effects around individual stars at distant galaxies. But what if a civilization in one of those has ...
- 12:44: Now this is a bit tougher, because galaxies aren’t as simple as stars.
- 13:19: And about the effect on the enclosed star due to a partial Dyson sphere.
- 13:31: But some very serious scientists - starting with Freeman Dyson and Carl Sagan - take the question very seriously.
2021-12-20: What Happens If A Black Hole Hits Earth?
- 00:29: ... 1000 light years distant. It’s currently devouring its binary companion star, which is how we see it - but there’s no possibility of it ever coming ...
- 01:23: ... and those little fluctuations in density eventually collapsed into stars and galaxies instead of black ...
- 01:49: ... at the earliest of times, while still leaving plenty of matter left for stars. ...
- 02:50: ... these black holes then they’d frequently pass in front of more distant stars, magnifying those stars’ light with gravitational ...
- 03:25: ... to the masses of large asteroids. Black holes this big don’t devour stars like Cygnus X-1, and they don’t warp the passage of light from distant ...
- 06:02: ... hilariously high temperatures - much hotter than the cores of a star. This is how we “see” black holes like Cygnus X-1 or the supermassive ...
- 06:35: ... black hole’s intense gravity. Try to feed a black hole too fast and it starts to blast away its own food. The bigger the black hole the faster it can ...
- 07:29: ... passed into our atmosphere, it would look like the brightest shooting star you’ve ever seen, producing a destructive shockwave before hitting the ...
2021-12-10: 2021 End of Year AMA!
- 00:02: ... we're gonna spend about 30 minutes so without further ado i will get started first question uh let's start by making this all about me because ...
2021-11-17: Are Black Holes Actually Fuzzballs?
- 05:09: ... gravity starts to get quantum even above the event horizon, then it may be possible to ...
- 06:12: Lose that pesky infinite density and we can start making sense of physics again.
- 09:25: ... as the neutron star’s gravitational field is so intense that atomic nuclei are crushed into a ...
- 11:07: But if you approach the fuzzball you start to see this surface of stringy material with a thickness of about a Planck length.
- 14:10: ... starts out explaining relativity in terms of boats passing each other on a ...
- 15:45: So it is our honor to honor Ernest H Anderson Jr., who passed away in 2018, and has returned to the stars.
2021-11-10: What If Our Understanding of Gravity Is Wrong?
- 02:11: In most galaxies, stars are somewhat concentrated towards the centers, which means gravity should weaken towards the outskirts.
- 02:18: That means the orbital velocities of stars out there should be lower in order to keep them in orbit.
- 03:44: In MOND, force or acceleration drop off with distance squared until, at very low values they start to plateau out.
- 06:47: ... on the dark matter halo while the luminosity depends on the stars. ...
- 08:50: ... it was a good start - the resulting “AQuaL - for “a quadratic Lagrangian” gave the ...
- 10:01: ... of matter, which would, for example, make long-lived stars ...
- 12:07: ... RelMOND - relativistic MOND - works for galaxy clusters and keeps stars from exploding - but the authors are ...
2021-11-02: Is ACTION The Most Fundamental Property in Physics?
- 02:21: ... ball starts out moving fast - it has a lot of kinetic energy, which it trades for ...
- 05:52: ... start with Einstein’s General Theory of Relativity, which, as we’ve discussed ...
- 07:09: ... valid even in the shifting frames of Einstein’s relativity. And we also start to learn something about the nature of the Action. Once we apply the ...
- 08:39: ... start with the famous double slit experiment, as we so often do when talking ...
- 11:59: ... Dirac started to guess, particles tend to end up near the stationary points of the ...
- 13:46: ... remember, this all started with Heron of Alexandria studying light two thousand years ago. He found ...
- 15:27: ... that constructor theory really offers anything new. And honestly, I started out wondering the same and it took me a lot of time to get an inkling ...
2021-10-20: Will Constructor Theory REWRITE Physics?
- 00:51: Based on some initial state - a starting set of these numbers predict how the system will evolve at all future times Step 4.
- 02:10: Some are starting to wonder if we need to rethink how we do physics at the fundamental level.
- 04:55: ... mechanistic philosophy that dominates physics really started with Isaac Newton, so it’s appropriate to start with the falling apple ...
- 14:00: ... a tunneling event be considered travel at all. Does it just start existing on the other side of the barrier without crossing the ...
- 14:48: ... These comments are telling me that you lot are really starting to get a sense of how far our perception of reality is ...
2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light
- 05:48: If the position of the tunneling particle isn’t perfectly known, how do we know when to start and stop our tunneling stopwatch?
- 05:56: It seems natural to define those times as whenever the center of the wavefunction passes the start and end points.
- 06:45: It’s hard to measure the travel time of a quantum train OR a quantum wavefunction because it’s hard to define the start and end points.
- 07:01: Launch a particle through empty space with a well defined starting position, and it’s position wavefunction will spread out before the finish line.
- 13:06: ... starts out explaining relativity in terms of boats passing by each other on a ...
2021-10-05: Why Magnetic Monopoles SHOULD Exist
- 05:37: The great Paul Dirac had a habit of discovering particles just by staring at the math.
- 06:00: ... you start with a dipole magnetic field, you can approximate a monopole by moving ...
- 16:32: ... it smashes through the degeneracy pressure that supports white dwarf stars and instead produces a black hole or neutron ...
- 16:57: In the case of the collapsing star, densities and energies become high enough for electrons to be captured by protons, converting them to neutrons.
2021-09-21: How Electron Spin Makes Matter Possible
- 00:26: ... to turn an electron around twice - 720 degrees - to get it back to its starting position. They are, we say, spin-½ - because one normal rotation only ...
- 01:13: ... the much more sensible case of a single 360 degrees rotation back to the starting point. Integer-spin particles are bosons, and they are the force ...
- 02:59: ... that fermions have, and has this property that it returns to its starting state with a 720 degree rotation, not ...
- 06:49: ... 360 degree rotation puts a spinor perfectly out of phase compared to its starting point. So a 360 rotation introduces a negative sign to the spinor ...
- 15:42: And the episode where we took a journey into the weird, pasta-filled core of a neutron star.
- 15:48: ... Gorman says that he imagined that black holes would look more like dim stars rather than, well, black holes because they slingshot light around from ...
- 16:27: ... times! There was speculation that quasars could be swarms of neutron stars or supernova cascades or even bizarre objects flying at crazy speeds out ...
- 17:29: ... of the weird gridlocked plasma crystal lattice of the crust of a neutron star. And then my favorite thing happened - someone who knows more than me ...
2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe
- 00:00: ... heard of. Today we take a journey to the center of the neutron star. ...
- 00:25: ... stars are arguably the strangest objects in the universe - if we don’t ...
- 01:42: ... this is going to come in handy as soon as we approach the neutron star. The first thing we encounter is its magnetosphere. This is ...
- 02:35: ... through the magnetosphere we start to notice that the neutron star’s surface is a little fuzzy. We’re seeing the star’s ...
- 03:07: ... the neutron star’s atmosphere is not made of atoms, rather it's a plasma, ...
- 03:27: ... depending on how you define the edge of space, the neutron star’s atmosphere is barely a meter thick, with most of the plasma ...
- 04:04: ... we start to encounter the first truly strange states of matter. See, the ...
- 04:39: ... landed on the neutron star, we actually do have a solid surface below our feet. It ...
- 05:48: ... the real journey can begin as we start to tunnel into the star’s interior. We enter the outer crust ...
- 06:38: ... see nuclei that can’t even exist outside a neutron star. Where the star is 50 billion times the density of earth, we might ...
- 07:06: ... for the inner crust, our nuclei become so neutron-rich that they start to fall apart. We call this “neutron drip” - neutrons leak from ...
- 07:43: ... due to the electron capture process. In fact the neutron gas starts to take over the role of the electrons. Neutrons are also ...
- 08:15: ... down the nuclei themselves start to get fuzzy as protons are outnumbered by neutrons 5 to 1. ...
- 10:06: ... sort of like nuclear pasta mountains buried beneath the star’s surface. These could be as tall as 10 centimeters. which doesn’t ...
- 11:14: ... time we reach the bottom of the pasta layer, just above the neutron star core, all that matter has been smooshed together into ...
- 11:29: ... which is probably an essential part of maintaining the neutron star’s enormous magnetic ...
- 12:23: ... the dead center of the neutron star and even the protons and neutrons start to lose structure ...
- 13:06: ... storms raging above us on the surface. It seems our neutron star has started accreting matter from a binary partner ...
2021-09-07: First Detection of Light from Behind a Black Hole
- 04:57: This gas starts to glow in a different way - not from heat, but from the motion of electrons between their atomic energy levels.
- 09:23: OK, it’s time we got back to the discovery that started our little journey - the light that was detected from behind a black hole.
- 11:47: After decades of practice, and inventing better and better telescopes, we’re starting to get good at this game.
2021-08-18: How Vacuum Decay Would Destroy The Universe
- 00:21: ... expansion rate, and has just the right particle properties to allow stars and planets and people to exist. The habitability ...
- 04:00: ... that's where the trouble starts. The Higgs field may have yet another weird property. It ...
- 07:01: ... phase transition to water vapor - that phase transition also starts in small bubbles that grow into its surroundings. The formation ...
- 08:30: ... the masses of the elementary particles. The ability for stars to form and undergo nuclear fusion, and the ability for ...
- 11:34: ... or sufficiently large universe then vacuum decay has definitely started somewhere. But as long as we’re far enough away we’re ...
2021-08-10: How to Communicate Across the Quantum Multiverse
- 09:23: ... he was only getting started. He follows up by finding a way to write one non-linear Schrodinger ...
- 14:02: ... episode we talked about this one very weird white dwarf star that scientists think may be the first observation of the result of the ...
- 14:53: ... out there, a common envelope binary system is one where the stars are so close together that they share an envelope - you can also ...
- 15:46: ... enough gas to spin up the white dwarf while still allowing the partner star to explode? Well, I'm not sure - but it seems these scientists think ...
- 16:27: ... Persona asks what happens to the star’s magnetic fields after it goes supernova. And then guesses the correct ...
- 17:12: ... I started that episode with a mangled quote - scientific progress is accompanied ...
2021-08-03: How An Extreme New Star Could Change All Cosmology
- 00:21: ... particular “huh, that’s weird” takes the form of a white dwarf star that’s doing some stuff that no white dwarf should ever be able to do. ...
- 01:45: ... - or at least, what we thought we knew. When all but the most massive stars end their lives, they blast off their outer layers in their final fits ...
- 02:13: ... fast it’s spinning. Now we do expect white dwarfs to rotate. After all, stars rotate and so should their remnant cores. That spin should also increase ...
- 02:47: Such a parent star should have torn itself to pieces.
- 03:58: ... so far so weird. The next step in the star-sleuth’s playbook is to get an accurate measure of size. Size is hard to measure ...
- 04:37: ... measure, but luminosity is less so. Luminosity determines how bright the star appears to us - but there’s another factor at play there - how far away ...
- 05:01: ... thing we’re missing from this equation for size is the distance to this star - and of all of these things distance is the hardest to measure. The ...
- 05:24: ... GAIA satellite changed that by measuring parallaxes for a billion stars across the Milky Way, and Zee was one of them. So we have its distance - ...
- 06:17: That’s true of planets and regular stars, but it’s not true of white dwarfs.
- 06:21: ... that the inward gravitational pull is insane. The only thing holding the star up from absolute collapse is the fact that if it got any smaller, its ...
- 07:24: ... happens when you add mass to less weird space-stuff, say a planet or a star. The matter inside is crushed closer together until there’s enough ...
- 08:29: ... gets packed so close together that one of two things happen. If a dying star’s core exceeds the Chandrasekhar limit then it collapses into a neutron ...
- 08:48: ... just don’t see these extreme properties in the white dwarfs produced as stars ...
- 09:18: ... energy. We’ve seen the result of this with black holes and neutron stars when LIGO detected the gravitational waves from the last moment of those ...
- 09:51: ... it adds up to less and we get a bigger, much weirder white dwarf. That star would be spinning really really fast because it doesn’t just have the ...
- 12:50: ... into protons, which would turn those protons into neutrons. If that starts to happen then you get a chain reaction of so-called electron capture ...
- 13:30: ... path to supernova, and a bad end for our highly suspicious little star. ...
- 15:55: ... asks whether magnetic fields have any measurable effect on the orbits of stars around the galaxy. Not directly. The galactic magnetic field is very ...
- 16:19: So the locations that stars formed may be influenced by magnetic fields, which in turn affects their orbits. So the answer is yes, sort of.
- 17:08: ... is no, although magnetic fields do have important effects on scales from stars to galaxies - they’re still much, much weaker than gravity. Some people ...
2021-07-21: How Magnetism Shapes The Universe
- 00:02: As far as the north magnetic pole, where the needle starts spinning wildly?
- 06:00: The interstellar medium - the space between the stars - is scattered with tiny specks of dust produced in past supernova explosions.
- 09:10: These amplify what starts out as a very weak and disordered field into the ordered and powerful field that surrounds the Earth.
- 10:00: Without that, those clouds would never be able to collapse all the way into stars.
- 10:05: And magnetic fields also facilitate star formation after stars die.
- 10:09: ... to compress gas in the path of that explosion, triggering bursts of new star ...
- 10:44: Their material tends to spill into the space around the galaxy before slowly raining back in, where it can be used for new star formation.
2021-07-13: Where Are The Worlds In Many Worlds?
- 10:38: And, I don’t know, maybe next to the love of your life, who convinces you to leave research and start a small bed and breakfast in Argentina.
2021-07-07: Electrons DO NOT Spin
- 00:47: ... thread and switch on a vertical magnetic field. The cylinder immediately starts rotating with a constant speed. At first glance this appears to violate ...
- 08:50: ... familiar objects, a rotation of 360 degrees gets it back to its starting point. That’s also true of vectors - which are just arrows pointing in ...
- 09:30: ... If we rotate the cube by 360 degrees, the cube itself is back to the starting point, but the ribbons have a twist compared to how they started. ...
- 09:59: ... angle - and a 360 rotation pulls it out of phase compared to its starting ...
- 16:27: ... point, asking if the conditions of the Big Bang meant everything started out entangled. You’d think so - but that’s not necessarily the ...
- 17:20: In other words, the universe - or our patch of it - may have started out unentangled and at low entropy, even if it was at thermal equilibrium.
2021-06-23: How Quantum Entanglement Creates Entropy
- 02:48: ... the more common configurations. Hence, entropy increases. Here we can start to see the connection between entropy and information. ...
- 04:50: ... As the (perhaps apocryphal) origin story goes, he only started calling his invention “entropy” after talking to the great ...
2021-06-16: Can Space Be Infinitely Divided?
- 03:14: ... start, let’s say you’re trying to measure the distance to an object. You ...
- 06:02: ... and momentum. As we crank up the energy even further we start to notice something. The photon is starting to produce an ...
2021-06-09: Are We Running Out of Space Above Earth?
- 10:18: This is where StarLink deserves a mention.
- 10:53: I should add that StarLink will be in very low orbit, and so has a fast decay time - under 5 years.
- 11:03: ... StarLink isn’t going to be the last giant swarm of internet satellites - in fact, ...
- 12:47: Or we could start taking more care right now.
- 14:49: ... within that range then perhaps it would be absorbed and the relic would start to ...
2021-05-25: What If (Tiny) Black Holes Are Everywhere?
- 03:02: For the black hole left behind when a massive star dies, the event horizon is several kilometers in radius.
- 03:45: ... gives us this nice picture of a far, far distant future in which the stars have gone out and we only have black holes, which one by one vanish in ...
- 05:45: But as the black hole gets very small, the allowed vibrational modes start to get restricted.
- 07:04: ... let me start by saying that we know for sure that general relativity doesn’t work on ...
- 07:22: The only way to make black holes in the modern universe is in the deaths of massive stars.
- 07:45: For Planck relics to exist now we need a way to make black holes that are much smaller than a star.
2021-05-19: Breaking The Heisenberg Uncertainty Principle
- 00:47: ... measurements have become so precise that we’re starting to run up against the absolute quantum limit - the limit defined by the ...
- 09:13: ... away, and involving lower-mass mergers of black holes and neutron stars. ...
2021-05-11: How To Know If It's Aliens
- 01:55: ... start - or rather continue with our quest to find evidence of primitive life ...
- 09:21: ... Star is another good example of this. Perhaps you recall - the crazily ...
- 11:24: ... of Proximans? More plausibly from the motion of a planet around the star. Now there are very good reasons to think that this signal isn't aliens. ...
2021-04-21: The NEW Warp Drive Possibilities
- 00:00: That Einstein guy was a real bummer for our hopes of a star-hopping, science-fiction-y future.
- 00:51: And only 15 years after general relativity’s debut, the warp drive was invented, propelling humanity on its first journeys to the stars.
- 01:34: ... pretend technology really took off with Star Trek in the 60s - and Star Trek inspired the very first real warp field ...
- 01:44: That’s the Alcubierre warp field, derived by Mexican physicist and star trek aficionado Miguel Alcubierre.
- 02:12: Today we’re going to pull them apart two new papers on warp drives and see if it’s really time to don our Star Trek cosplay and warp out of here.
- 05:11: ... in all the matter in the visible universe to move a moderate-sized starship. ...
- 06:35: But I guess the dreams of wannabe starship captains are strong - because the work continued, and just recently two papers have claimed breakthroughs.
- 06:44: We’ll start with the paper entitled Introducing Physical Warp Drives by Alexey Bobrick and Gianni Martire.
- 07:16: All of them, including Alcubierre’s, move with whatever velocity they started at.
- 08:02: A superluminal warp bubble has to have started out superluminal.
- 09:04: This one is a little more star trek friendly than, well, pretty much every prior effort.
- 12:18: Einstein and the universe appear to be trolling us - alternately inspiring and crushing our hopes for a star-hopping future.
- 12:37: They’ll continue to try to “make it so” by exploring Einstein’s theory - hoping to build starship, but in the process learning how our universe works.
- 12:47: And possibly also building a starship, to propel humanity into the galaxy on waves of warped space time.
- 14:04: We’ll start with the muon g-2 result, which revealed a possible a crack in the standard model of particle physics.
2021-04-13: What If Dark Matter Is Just Black Holes?
- 00:00: ... may be that for every star in the universe there are billions of microscopic black holes streaming ...
- 01:39: ... twice the diameter of the Milky Way’s spiral disk, where most of the stars are ...
- 03:06: ... before we start eliminating specific black holes masses, let’s rule out an entire class ...
- 03:16: We know black holes form from the remaining cores of the most massive stars, after they explode as supernovae.
- 03:21: ... maximum possible number of these black holes by estimating the number of stars that formed and died through cosmic ...
- 03:31: When we look into the distance we’re actually looking back in time, so we can literally see star formation happening in the early universe.
- 03:37: ... in those explosions, but the heavy elements forged in the cores of these stars during their ...
- 03:47: ... star formation history and heavy element abundance tells us there haven’t ...
- 03:57: Also, if dark matter is produced as stars die, you’d expect its influence to increase over time.
- 04:07: ... gravity of dark matter was pulling matter together long before the first stars ever ...
- 05:36: OK, let’s get started.
- 06:30: I’m talking somewhere between a billion to a billion billion times more of them than there are stars in the universes..
- 06:48: For example, they’d puncture white dwarfs and neutron stars on a regular basis.
- 06:53: ... through a white dwarf, but it would deposit enough heat to allow the stars' ultra dense carbon and oxygen to undergo nuclear ...
- 07:04: Like striking a match, this would ignite a cataclysmic chain reaction, exploding the star as a type 1a supernova.
- 07:12: Neutron stars are a bit different.
- 07:18: The black hole would then swallow the neutron star from the inside out.
- 07:22: But we see too few type 1a supernova and too many neutron stars for this to be a common phenomenon.
- 07:58: ... is a black hole or some other dark compact mass like a brown dwarf star, neutron star, Dyson sphere or a cluster of Reaper capital ships - as ...
- 08:24: ... best way to search for MACHOs in our galaxy is to monitor the stars in the galactic bulge or in our neighboring galaxies to see if they ...
- 08:52: ... Clouds are especially good for this - the low level of microlensing of stars in these mini-galaxies has allowed us to rule out MACHOs between roughly ...
- 09:07: ... Milky Way halo may be dark, compact objects with the masses of a small star. ...
- 10:01: ... trickled to the center by now, and in the process flung less massive stars into higher ...
- 10:20: ... existence of loosely bound binary star systems throughout our galaxy gives us similar constraints - if there ...
2021-04-07: Why the Muon g-2 Results Are So Exciting!
- 02:44: Starting in 20 years ago, experimental measurements of the Muon g-factor did not agree with the QED calculation.
- 03:01: Let's start by talking about quantum spin.
2021-03-23: Zeno's Paradox & The Quantum Zeno Effect
- 02:04: In this case let’s say our quantum arrow’s position is quantized - it can exist only at the start and end of its path, but not in between.
- 02:13: In order to travel from start to end, it has to flick between these states without occupying intervening space.
- 02:32: That means it can be at the start and end of its path simultaneously.
- 02:58: ... amplitudes of its position; its wavefunction is spread between the start and end of the ...
- 03:36: ... begins in the pure state of being entirely at the start of its journey, but then it enters a superposition of states - mostly at ...
- 03:47: ... you observe the arrow now, most likely it’ll “collapse” to the starting position, but there’s a small chance it would suddenly appear at the ...
- 03:58: ... no observation the wavefunction evolves - less and less amplitude at the starting state and more and more at the end state - until it finally enters the ...
- 04:28: Every observation you make of the arrow collapses its wavefunction into one of its possible positions - start or end.
- 04:34: But because you start watching it close to the beginning of its journey, there’s very little probability of it collapsing to the end.
- 04:41: ... observation resets the trajectory to the start, at which point the wavefunction has to start evolving from scratch - but ...
- 07:15: To test this, the researchers start the atoms all in state one, and then hit them with a series of very rapid laser pulses.
- 08:54: Let’s start with measurement.
- 09:11: ... a way that the electron had an increased chance to jiggle back to its starting ...
- 10:32: In fact, as argued by Ballentine, you can force a quantum system back to its starting state without true decoherence.
- 11:18: But in this case, you’re not forcing the wavefunction to collapse back to its starting position through the power of observation.
- 11:42: If you do it right you’ll produce more “worlds” in which the system goes back to its starting state.
- 11:48: And then you enter the world of of the possible outcome states - again, most likely the starting position.
- 11:54: But if your observation wasn’t perfect, there’ll be some worlds in which the final state is chosen rather than the starting state.
- 13:13: To learn more, check out TheGreatCoursesPlus.com/spacetimepbs or click on the link in the description below to start your trial today.
- 15:56: I said at the start of the episode that it's exciting for scientists to be proven wrong.
- 16:44: Whether it's a full blown existential crisis, or just a little radiating Hubble tension in your neck from staring at too much supernova data.
2021-03-16: The NEW Crisis in Cosmology
- 00:22: ... be wrong. So it’s no wonder that many cosmologists are starting to get excited by what has become known as the Hubble ...
- 02:07: ... in the solar system - then use those to measure distances to nearby stars, then more distant stars, then nearby galaxies, then distant ...
- 02:36: ... distance. Swan Leavitt realized that a type pulsating star known as a Cepheid variable has a rate of pulsation ...
- 03:13: ... variables are great standard candles, but they’re just stars, and are too faint to see beyond a certain distance. In the ...
- 07:28: ... can use this same trick to measure the distance to stars. As the earth orbits the sun over the course of the year, ...
- 08:03: ... measurements of Cepheids in the Milky Way to turn these stars into standard candles and so founded our distance ...
- 09:50: ... we start jumping up and down and yelling about new physics, ...
- 17:08: ... guys have to fight in so many different gravitational fields - star destroyers, the death star, forest moons, ice planets - ...
2021-03-09: How Does Gravity Affect Light?
- 00:38: ... of light gripped by the gravitational field of a sufficiently massive star would slow down, stop, and fall back - and so was the first to predict ...
- 02:09: In general relativity, the best place to start is always the equivalence principle.
- 05:13: Let’s start with the good-old equivalence principle again, and a spaceship attacked by giant alien spiders.
- 11:43: ... enabled him to measure the slight offset in the apparent positions of stars around the sun, due to their light rays being “refracted” in the Sun’s ...
- 12:38: ... our guiding star is that the universe is deeply self-consistent, our explanatory stories ...
2021-02-24: Does Time Cause Gravity?
- 01:48: Let’s start with … a teapot.
- 01:56: Absent a gravitational field or any forces, if the teapot starts motionless it stays that way.
- 04:47: All individual 4-velocities start out being purely in time, but the sum is rotated partially into space.
2021-02-17: Gravitational Wave Background Discovered?
- 00:00: ... have detected 50 similar signals from merging black holes and neutron stars across the universe these sweep past the earth every few days causing ...
2021-02-10: How Does Gravity Warp the Flow of Time?
- 01:13: Einstein had his happy thought in 1907, a couple of years after he started his scientific revolution with the special theory of relativity.
- 03:07: ... going to start out by me totally convincing you that time must run slow in a ...
- 07:27: In the twin paradox, the twin traveling to a nearby star and back has aged less even though both could see the other’s clock ticking slowly.
2021-01-26: Is Dark Matter Made of Particles?
- 00:23: ... see the influence of dark matter in the orbits of stars and galaxies, in way light bends around galaxies and clusters, in the ...
- 01:13: Now it’s possible that dark matter is not particles - it could be black holes or failed stars or even weirder so-called “compact objects”.
- 04:21: They might collapse into dark matter galaxies or dark matter stars or dark matter people.
- 04:34: In fact, galaxies are really just shiny dustings of stars, sprinkled deep in the gravitational wells of massive reservoirs of dark matter.
2021-01-19: Can We Break the Universe?
- 00:09: ... back in 1905, when Einstein was just getting started - he was already rocking our understanding of the universe with his ...
- 00:17: ... theory started with the simple assumption that the speed of light was the fastest speed ...
- 01:04: Say we have a spaceship traveling from Earth to a nearby star at a good fraction of the speed of light.
- 01:28: The spaceship can think of itself as stationary - it perceives the Earth as racing away from it and its destination star racing towards it.
- 02:33: ... back on itself, so by traveling far enough you can get back to where you started. ...
- 03:21: Let’s start with the twin paradox.
- 03:24: ... and travels at a good fraction of the speed of light to a nearby star and then turns around and heads back to ...
- 09:04: If the ladder didn’t fit in the barn to start with, it most certainly doesn’t fit now.
- 10:03: ... spatial direction - initially longer than the barn, but when the ladder starts moving it shortens so that it neatly fits inside the barn before ...
- 13:17: We'll start with the latter.
2021-01-12: What Happens During a Quantum Jump?
- 01:12: ... all started back in 1913, when the great Danish physicist Niels Bohr set about to ...
- 07:52: Then, after a period of time, the electron decays and fluorescence starts again.
- 10:02: But just prior to each jump the system started to shift in a way that enabled the researchers to predict the oncoming jump.
- 12:06: ... a century after Bohr and Schrodinger started the argument, we may be on the verge of the next quantum leap - to ...
2020-12-22: Navigating with Quantum Entanglement
- 02:04: Across long distances, birds often rely on the sun or even the stars.
- 13:08: ... talked about a possible new type of supernova - the black dwarf or iron star supernova, which may be the very last explosions at the end of our ...
- 13:47: ... really there are two main scenarios - either the core of a very massive star collapses after expending its fuel - that’s a type 2 supernova - or the ...
- 14:02: For more detail we would indeed need a whole episode Quantum fields asks what about neutron stars.
- 14:12: ... if protons do NOT decay then quantum tunneling will cause the neutron star to collapse into a black hole over an absurdly long timescale of ...
- 14:34: ... other hand if protons DO decay then the small proton content of neutron stars will decay into pions and neutrinos, leaking away some of the mass of ...
- 14:44: The neutron star will then expand, allowing some neutrons to convert back into protons, which can themselves decay.
- 14:50: The Star may go through a phase as a white - or perhaps now black dwarf and will continue to evaporate due to proton decay.
- 15:57: Easy, start by imagining 10^31998 years and then do THAT 10 times.
2020-12-15: The Supernova At The End of Time
- 01:24: Let’s actually start our story at the end.
- 01:28: In roughly 10^32000 years from now, give or take several orders of magnitude, the last iron star will be teetering on the edge of catastrophe.
- 01:52: ... one too many vanish, the entire star will undergo catastrophic collapse, and then rebound as a spectacular ...
- 02:20: But first, there are many questions to be answered - like how do stars including our Sun end up as one of these “iron stars” in the first place?
- 02:33: Well not quite the very beginning, but on the timescales of iron stars pretty close to it.
- 02:39: ... a mere 13.7 billion years after the big bang, when one of these iron stars was in its extremely brief phase as a bright ball of hydrogen, bathing a ...
- 03:03: ... - Chandra to his friends - was pondering the far future of the star whose warm light now bathed the ...
- 04:18: A new type of star had been discovered - white dwarfs.
- 04:22: These faint but searing-hot stars appeared to have densities so high that a single cubic centimeter of their material weighed a literal ton.
- 05:05: Most eminent physicists of the era were coming to believe that the white dwarf should be the fate of all stars.
- 05:49: ... this degeneracy pressure could support a dead star up to a point - if that stellar remnant’s mass was too high then a new ...
- 05:59: The star’s own electrons would be driven into its nuclei in a process called electron capture.
- 06:06: ... fewer electrons means less electron degeneracy pressure, which means the star begins to collapse, which means more electrons driven into nuclei, and ...
- 06:17: We now know that the end result is either a neutron star or a black hole, accompanied by a powerful supernova explosion.
- 06:24: ... the Chandrasekhar limit. For the stellar core left behind by an ordinary star that should be 1.44 times the mass of the ...
- 06:39: Not a bad start to graduate school - showing up on your professor’s doorstep having already improved one of your prof’s major life achievements.
- 06:54: They start out hot and bright, but with no capacity to generate new energy, they slowly radiate away the heat of their youth.
- 07:08: The star crystalizes.
- 07:20: The electrons remain as a hot, degenerate plasma and continue their work of keeping the star from collapsing.
- 07:29: They become almost motionless within the star, and slip into a regular grid pattern.
- 08:46: The result is an iron star - or an iron black dwarf - the hypothetical fate of all stars whose cores are beneath the Chandrasekhar limit.
- 09:02: ... mist in a mere 10^32 or so years, long before it could become an iron star. ...
- 09:13: But assuming protons are stable, we’ll reach a point where the universe consists of only iron stars and radiation.
- 09:20: ... those iron stars are also doomed - they’ll quietly become black holes themselves through ...
- 09:45: ... published in August this year, has found a way for some of these iron stars to end on a brighter note - as black dwarf ...
- 10:02: It depends on the number of electrons relative to the mass of the star.
- 10:06: But Caplan performed a detailed analysis of the nuclear reactions that lead to an iron star, and found that the delicate balance is threatened.
- 10:29: But that emitted positron is the antimatter counterpart of the electrons that are supporting the star from the collapse.
- 10:36: It immediately annihilates with one of those electrons, depleting the star’s supply.
- 10:41: By the time the iron star is fully formed, its Chandresekhar mass has dropped from around 1.44 to less than 1.2.
- 11:12: They’ll leave behind smaller iron cores or a neutron stars.
- 11:16: ... the largest such stars, you should expect the first explosions to begin in 10^1100 years or so, ...
- 11:45: ... be at least one more interesting thing to look forward to - Iron stars exploding in unimaginably distant future of space ...
2020-12-08: Why Do You Remember The Past But Not The Future?
- 07:18: It’s fully formed but hasn’t started to decay yet.
- 09:54: ... universe started in a state of extremely low entropy - spatially separated regions were ...
- 10:53: ... in one direction and not the other is because the early universe started out with this incredibly rich resource of correlation-lite states, which ...
2020-11-18: The Arrow of Time and How to Reverse It
- 04:13: ... if you start from a situation where energy is not perfectly randomly spread out, then ...
- 05:10: ... start with a handful of particles with low entropy. You can do low entropy by ...
- 06:19: ... if you live on either side of the starting, low-entropy point, you perceive an asymmetry in time - particles ...
2020-11-11: Can Free Will be Saved in a Deterministic Universe?
- 03:21: These may transform and become entangled with each other, but if quantum information is conserved, a thread can never vanish nor start out of nothing.
- 05:28: Let's start with one and two.
- 06:21: Think about a new thread of quantum information starting from nothing, let's say emerging from a packet of space time where no information enters.
2020-11-04: Electroweak Theory and the Origin of the Fundamental Forces
- 00:57: Let’s start with the mysterious and often misunderstood weak interaction.
- 10:13: However, if we cool the material down, the interactions between magnetic particles can start to come into play.
- 14:51: ... showed that at least some light rays - null geodesics - that start parallel from any trapped surface must converge in any positively curved ...
- 15:24: Start at Specialist Relativity and work your way up.
2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time
- 00:34: ... gravitation, they realized the possibility of a star so massive that it would prevent even light from escaping ...
- 02:48: ... flying back outwards again. So, for example, a star that collapses at the end of its life might entirely rebound as a ...
- 07:05: ... extending one of those paths just a little. The distance from the starting point to the end of that extension is still the same ...
- 08:11: ... you reached the end of north - maxed your northness - and started traveling south again. Well, in a black hole you don’t reach the end ...
- 10:36: ... beyond this point - which suggested that time really started at the Big Bang. Hawking and Penrose further developed these ...
- 12:11: ... supermassive black hole by monitoring the crazy orbits of stars in the galactic core. The work of Ghez and Genzel and other ...
- 13:38: ... though we can only see the universe of the past - e.g. a star 100 light years away being a century in the past. Surely if we ...
2020-10-20: Is The Future Predetermined By Quantum Mechanics?
- 05:39: Let's start with Copenhagen.
2020-10-13: Do the Past and Future Exist?
- 00:22: ... we’re starting a deep dive into the nature of time - and down that rabbit hole we’ll ...
- 08:44: Start moving forward and your slice of “now” will skew.
2020-10-05: Venus May Have Life!
- 01:55: To the outer solar system - Mars, Enceladus and Europa in particular, and ultimately to planets around other stars.
- 03:44: There are lots of ways to do this - for example seeing the effect on a star’s light as it passes through its own planets atmospheres.
- 03:58: This can be done at far infrared and submillimeter radio wavelengths where the star’s own glare doesn’t kill the signal.
2020-09-28: Solving Quantum Cryptography
- 03:23: Let’s start with a more visual example.
- 14:24: Last week we talked about a highly speculative idea - lifeforms inside stars, formed from cosmic strings and magnetic monopoles.
- 14:52: ... destruction is actually slower inside a star than outside - cosmic necklaces can be locked into the magnetic fields ...
- 15:10: Timescales may be driven by the timescale of the motion of plasma in the stars and by the size of these critters.
- 16:01: There was Frederik Pohl's "The world at the end of time" has a Plasma creature living in a star at war with copies of itself.
- 16:08: There’s david brin’s sundiver, and Frank Herbert's "Whipping Star", and several more.
2020-09-21: Could Life Evolve Inside Stars?
- 00:08: There’s Stanislaw Lem’s sentient ocean in Solaris, or the neutron star civilization made of nuclear matter in Robert L Forward’s Dragon’s Egg.
- 00:16: Oh, and here’s an extra crazy one - life composed of cosmic strings and magnetic monopoles, evolving in the hearts of stars.
- 01:03: ... monopoles - may evolve into complex structures, and even life, within stars. ...
- 06:58: And this is where stars come in.
- 07:00: Others have speculated that cosmic strings may get trapped inside stars in the process of star formation.
- 07:13: Depending on the stellar type and region, the insides of stars can be very turbulent places.
- 07:34: ... say that it might be catalyzed by interactions with atomic nuclei in the star. ...
- 09:02: OK, so inside a star there’s definitely free energy.
- 09:18: Energy could be spread more evenly across the electromagnetic spectrum, which would look like cooling - the star might appear cooler than it should.
- 09:27: Or perhaps the nuclear reactions in the core proceed faster, hastening the dissipation of the star’s energy through space.
- 09:34: At any rate, the star should behave differently to what our stellar physics models predict.
- 09:40: ... are a few stars in our modern surveys that don’t quite act as they should, however there ...
- 10:14: So are the stars filled with thriving ecosystems of critters built from fractured quantum fields?
2020-09-08: The Truth About Beauty in Physics
- 13:34: So today we're covering our episode on the future circular collider and on how we know the composition of stars.
- 13:42: In fact let's start with the stars.
- 13:50: Basically, why do we see specific wavelengths missing from starlight due to electrons absorbing those wavelengths in atoms?
- 14:47: ... of gas hanging out in space like a nebula - it will be illuminated by stars but you're not looking directly AT those stars through the ...
- 15:05: You won't see absorption unless you look directly through the cloud at one of those stars.
- 15:22: The Belle II experiment that just started taking data on Japan's superKEKB electron-positron collider.
2020-09-01: How Do We Know What Stars Are Made Of?
- 00:17: Science has long pondered the mysteries of the stars.
- 00:28: ... first thing you learn in astronomy is that the sun and the other stars are giant balls of fiery hydrogen and helium, powered by raging nuclear ...
- 00:39: A hundred years ago, we were starting to plumb the deepest mysteries of the universe with Einstein’s relativity and with quantum theory.
- 00:51: We didn’t know what stars were made of nor where their energy came from.
- 00:56: ... that we figured it out at all - afterall, we’ve never been to a star, never sampled its stuff to put under a ...
- 01:24: She not only revolutionized our understanding of the stars, but she helped blaze a trail in astronomy and physics for the women who would come after.
- 02:45: Enough so that she knew what she wanted to research - she wanted to unlock the mysteries of the stars.
- 02:57: The secret to understanding the stars is not exactly in the light they send to us.
- 03:26: The colour of a star depends on that temperature - blue for hot stars, red for cooler stars, and sort of greenish-yellow for stars like our Sun.
- 05:48: ... - was going to take some serious advances in understanding how both stars and atoms work Fortunately help was at ...
- 06:13: ... that she could use to decode the complex patterns of absorption lines in stars. ...
- 07:00: ... long before Celilia Payne started her research, Indian astrophysicist Meghdad Saha had used early ideas in ...
- 07:27: Payne realized that it should be possible to translate a star’s absorption line pattern into measures of temperature and composition.
- 08:36: Cecilia Payne set about analyzing the many spectra of stars that had been observed at Harvard Observatory.
- 08:43: ... the relative abundances of the elements and found they varied between stars, but were generally similar to what we find on Earth’s surface - but with ...
- 09:13: Cecilia Payne had discovered what the sun and stars were made of.
- 09:50: By the way, the whole finding out what stars are made of thing wasn’t even the main point of Payne’s thesis.
- 09:56: She also developed a way to calculate the temperatures of stars just based on the absorption lines.
- 10:08: So, yeah, that’s how we know what the stars are made of.
- 10:13: At around the same time as Ceclia Payne was doing all of this, other scientists were figuring out the rest of the mysteries of the stars.
- 10:20: ... fusion thing just a few years earlier in 1920, but now knowing what stars are made of, he and others were able to develop a detailed theory of ...
- 10:33: Stars went from being utterly mysterious to one of the best-understood denizens of the universe.
- 10:46: ... here’s to the stars - both types - Cecilia Payne-Gaposchkin, star astrophysicist, and also ...
- 12:17: Mark, we've talked about a lot of stars today, so it’s fitting we end on you, the starriest star of all.
- 12:24: Thanks for helping us to .... shoot for the stars?
2020-08-24: Can Future Colliders Break the Standard Model?
- 03:40: Graduating from electrons and positrons, in 1971 physicists started smashing protons together at CERN’s Intersecting Storage Rings facility.
- 07:57: Let’s start with better before we move to bigger.
- 09:11: ... the FCC will be smashing protons like the LHC does, but to start with it’ll collide electrons and positrons with the express intention of ...
- 11:34: ... if it does happen it’ll be at Brookhaven National Labs on Long Island, starting in around 10 ...
- 14:19: ... parasitic, and generally unhealthy relationships between the stars - from novae to black widow ...
- 15:16: They start separate, and the event horizons move towards each other as they join, and at some point the event horizons touch and then merge.
- 15:53: David Kosa asks how would we describe the interaction of two merging stars of equal mass whose combined mass exceeds the Chandrashekar limit?
- 15:59: ... protons to form neutrons, causing the thing to collapse into a neutron star. ...
- 16:17: That happens in the cores of massive stars when they die.
- 16:27: Well, the limit still applies, but typically you don’t get a neutron star.
- 16:32: In order to get a neutron star, you need a very symmetrical, clean application of pressure.
- 16:36: ... the white dwarf exceeds the limit by cannibalizing a companion star, and also presumably if it collides with another star, then the process ...
2020-08-17: How Stars Destroy Each Other
- 00:02: Forget TMZ - Here on Space Time we have all the latest details on the dysfunctional, explosive relationships between the stars.
- 00:15: Let me tell you a tale of a pair of star-crossed … well, stars.
- 00:20: When our galaxy was a little younger there were two ordinary stars - perhaps not unlike our sun, and they danced together in binary orbit.
- 00:33: After a billion or so years, one star died.
- 01:02: A stream dull, red gas now connected the two - the outer envelope of the star falling into the intense gravitational embrace of its old companion.
- 01:50: They named it a guest star.
- 01:53: We now call this phenomenon a nova, from stella nova, or new star.
- 02:07: ... more than half of all stars existing in binary orbits, it’s inevitable that many stellar remnants ...
- 02:16: ... the novae produced by white dwarfs, to X-ray binaries created by neutron stars and black holes - and much weirder things ...
- 02:28: ... at the same spot where the royal Korean astronomers saw their guest star … you see ...
- 04:13: After which they start the whole process all over again.
- 04:59: Just replace the white dwarf with a neutron star or black hole.
- 05:02: Those are what you get when the most massive stars die.
- 05:23: This is all stuff we’ve talked about before - be we haven’t seen the effect on a hapless companion star of having one of these as its binary partner.
- 05:33: Once again, if the two are close enough, gas is syphoned from the star onto the black hole or neutron star.
- 06:03: ... the case of neutron star X-ray binaries, that fluctuation includes powerful flares, resulting ...
- 06:14: Sometimes we also see the neutron star as a pulsar.
- 06:42: The nearest such system is the famous Cynus X1 X-ray binary, where a black hole the mass of 15 Suns is busy gorging on a blue giant star.
- 07:09: ... start, you need to know that when you look at our galaxy in gamma rays - the ...
- 07:58: ... turns out this object is a pulsar, and it’s in orbit around a companion star - in this case a brown dwarf, which is a star not quite massive enough ...
- 08:10: In this case the companion didn’t start out as a brown dwarf - it became one after losing most of its mass to its ravenous partner.
- 08:18: That brown dwarf orbits perilously close to the neutron star.
- 08:23: The neutron star’s jets sweep it hundreds of times per second, slowly blasting away its gas.
- 08:29: That gas forms an enveloping ring around the whole system, which then falls onto the neutron star.
- 09:04: Sticking with the deadly spider motif, if that second star is a red dwarf we have a red back.
- 09:09: That second star is doomed to an ignominious end.
- 09:14: ... its whittled away until its not a star any more, and eventually we expect it to become to become more and more ...
- 09:25: Finally that core is expected to break up in the neutron star’s tidal field and be scattered into the void.
- 09:51: Eventually, the core of the white dwarf reaches a temperature of hundred of millions of Kelvin, and the star’s carbon and oxygen can begin to fuse.
- 09:59: A runaway fusion reaction rips through the star, which explodes as a Type 1 supernova.
- 10:25: As you know, at the start of the pandemic we all had to quarantine on Earth to avoid contaminating space with the virus.
- 10:54: ... that seemed to straddle the mass between black holes and neutron stars, and which will change the way we think about whichever of those it turns ...
- 11:04: Zack Hamburg asks how we know that a black hole isn’t just a neutron star behind an event horizon.
- 11:10: Why should the star have crushed down into a point-like singularity at all?
- 11:14: ... give everyone some context: When a massive star dies, its core becomes a neutron star - but if that core is above a ...
- 11:27: So what happens to the neutron star after it collapses enough to form an event horizon?
- 11:39: That means the neutron star has no choice but to contract until no more contraction is possible - when it has zero size.
- 11:50: ... gravity effects would not kick in soon enough to save the neutron star. ...
- 12:10: Dead stars aren’t the only way to make black holes.
- 12:32: ... black holes could be less massive than black holes that come from stars, so might explain this weird teensy possible black ...
- 13:12: Some of you also asked why the less massive object can't just be a regular star.
- 13:27: Compared to a black hole or neutron star, regular stars are giant puffed up balls.
2020-08-10: Theory of Everything Controversies: Livestream
- 00:00: ... had james beach and stefan alexander and i think we really you know started to converge on on some some useful thoughts uh i really encourage you ...
2020-07-28: What is a Theory of Everything: Livestream
- 00:00: ... nature and the inner workings of the universe and be a really good starting point perhaps to kick off many more great discussions uh this year in ...
2020-07-20: The Boundary Between Black Holes & Neutron Stars
- 00:10: And we just did - an object on the boundary between neutron stars and black holes, which promises to reveal the secrets of both.
- 01:29: ... mass, it’s pushing the limit for what was thought possible for a neutron star, and it’s lighter than what was thought possible for a black ...
- 03:04: Unfortunately, there are countless galaxies in a region that size, so to start with we have no idea in which galaxy the merger happened.
- 03:26: Now that’s only been seen once before - with the merger of two neutron stars in 2017 - which we obviously covered back then.
- 03:34: ... across the electromagnetic spectrum - energy released as the neutron stars tore themselves apart in their collision before they collapsed into a ...
- 03:47: ... it an enormous amount of information about what happens when neutron stars collide - and we’re going to be using that information in just a ...
- 04:04: ... surprising - that event was 6 times further away than the 2017 neutron star merger, so would probably have been too faint to see ...
- 04:18: ... objects were black holes, but even if the smaller object was a neutron star it could well have been swallowed whole by the larger black hole without ...
- 04:39: To understand that, we have to understand a bit more about black holes and neutron stars.
- 04:44: A neutron star is what’s left after some massive stars explode as supernovae.
- 04:50: Once it was the burning heart of the star - a fusion engine that allowed the star to resist the inward crush of gravity.
- 04:57: But when it ran out of fuel, gravity took over and the entire star collapsed.
- 05:20: That insane density gives the neutron star a surface gravity around 100 billion times stronger than the surface of the Earth.
- 05:28: Scientists believe that it would be very difficult to get out of bed on the surface of a neutron star.
- 05:34: And much more difficult to escape the neutron star - the escape velocity at the surface is up to half the speed of light.
- 05:42: ... fact neutron stars are on the verge of being black holes, which by definition have an ...
- 05:51: If only you could cram a little more matter into the neutron star, the escape velocity would increase and it would become a black hole.
- 06:13: But neutron stars are NOT made of normal matter.
- 06:36: So more mass in a neutron star means higher surface gravity means higher escape velocity.
- 06:57: In the case of a neutron star it’s several kilometers.
- 07:00: As you increase a neutron star’s mass, its phantom event horizon grows while its actual surface shrinks.
- 07:11: This basic picture is pretty well accepted, but we still aren’t sure just how massive a neutron star can be before becoming a black hole.
- 07:19: ... required to understand the bizarre states of matter in a neutron star are horrendous, and there’s still some stuff that we don’t ...
- 07:31: That’s especially true towards the center of the neutron star, where the neutrons themselves probably break down into different types of quark matter.
- 07:49: ... details of the state of matter in the neutron star determines how a neuron star’s size changes with mass - and that’s what ...
- 08:05: Now, we can do better at making this theoretical prediction if we can catch a glimpse of the innards of a neutron star.
- 08:16: ... the 2017 neutron star merger we learned a lot about the structure of these objects by the way ...
- 08:34: We’ve estimated a maximum neutron star mass of between 2.2 to 2.4 solar masses.
- 08:43: ... direct measurements of neutron star masses come from pulsars - cosmic lighthouses that result from a neutron ...
- 08:53: Most pulsars are closer to the minimum neutron star mass of around 1.4 solar masses.
- 09:12: If it IS a neutron star then it puts us at the theoretical limit, and can tell us a lot about the crazy states of matter inside.
- 09:23: That’s if it’s a neutron star at all.
- 09:40: We see those in X-ray binaries - when a black hole is orbiting and cannibalizing another star.
- 09:47: ... weird that there seems to be a gap in masses between the biggest neuron stars and the smallest black holes, but actually we very much expect ...
- 09:58: New black holes are formed when the most massive stars die and the core is too big to become a neutron star.
- 10:04: But you don’t get this smooth transition from neutron stars to black holes.
- 10:08: Like I said earlier, a neutron star forms when a star’s core collapses, but most of the material rebounds as a supernova explosion.
- 10:17: But if that neutron star then becomes a black hole, some of the infalling material just gets sucked into the black hole.
- 10:28: Based on our calculations and simulations of how stars die, that minimum black hole mass of 5 Suns seems about right.
- 10:41: ... we figure out that this object CAN’T be a neutron star then we’re going to have to rework our models of how stars die - or find ...
- 10:52: But if it IS a neutron star then we’ve learned a ton about the most extreme states of matter in the universe.
- 11:08: Each will be rich in information on the nature of stars, and gravity, and strange quantum states of matter.
- 12:03: We’re shipping it to you from a little star cluster in Sagittarius - made locally from humanely sourced o-giant star of course.
2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing?
- 01:25: ... most likely answer seems to be that the universe started out with a little more matter compared to anti-matter. If there were ...
- 06:27: ... thought gas was expensive. So we’re going to wait a while to be powering starships with antimatter engines. Fortunately, you don’t need anything like a ...
2020-06-30: Dissolving an Event Horizon
- 07:42: By the time the gas reaches the black hole it has lost much of the angular momentum it started with.
- 12:25: ... a 3-D space, but travel around the tube and you’d get back to where you started. ...
2020-06-22: Building Black Holes in a Lab
- 00:16: ... one. Nonetheless, the evidence for their reality is overwhelming. Stars orbiting in crazy slingshot orbits around a patch of nothingness in the ...
- 01:29: ... it turns out we don’t need to make a real black hole to at least get started with the lab work. We can instead study analog black holes - and by ...
- 01:54: ... whole idea of analog black holes was started in 1972 by Bill Unruh - most known for his Unruh radiation, which we’ve ...
- 12:23: ... until we’re able to travel to the stars, or to build - and hopefully control - real black holes in the lab, the ...
2020-06-15: What Happens After the Universe Ends?
- 07:06: ... all stars will die and their remnants will decay - black holes will evaporate by ...
- 11:39: If entropy can only rise over time, per the second law of thermodynamics, how did it get so low at the start?
- 17:44: ... Stark realizes we can have an asteroid impact and alien virus wrapped up in ...
2020-06-08: Can Viruses Travel Between Planets?
- 01:08: I’m going to start with this absolute statement, because you know how the internet can be.
- 04:43: ... before - but in short, when an alien world passes in front of its home star, we can see signatures frequencies plucked from the starlight due to it ...
- 07:26: ... into interplanetary or even interstellar space by the radiation from the star. ...
- 08:01: So yeah, stars sneeze, you might want to maintain 6 light years distance.
- 10:24: All of that said, radiation from stars is probably our best hope for obliterating space viruses.
- 14:44: ... cluster where it seems like that the dark matter is separated from the stars and therefore can’t be due to just having the wrong theory of ...
2020-05-18: Mapping the Multiverse
- 00:09: ... can be traced out again but you do not end up in the universe that you started ...
- 04:06: But now as we fall the outward pressure due to the black hole’s rotation starts to win against that inward flow.
- 05:53: ... field is according to the geodesics of objects in freefall that start motionless relative to the gravitational ...
- 08:13: There are trajectories in this torus that lead you back to your starting location - in both space AND time.
- 10:37: ... universe either - here, the laws of physics are the same as where you started - at least as far as general relativity is ...
2020-05-11: How Luminiferous Aether Led to Relativity
- 09:26: ... say you set up the interferometer and see your interference pattern. To start with you wouldn’t know whether the arms were exactly equal lengths or ...
- 11:42: ... published 8 years after the Michelson-Morley experiment. Now Einstein’s starting motivation seems to have been the fact that the Maxwell equations are ...
- 13:18: ... his deathbed in 1931 Michelson's daughter begged Einstein “not get him started on the subject of the aether.” Michelson may have mourned the death of ...
- 14:06: ... is infinite in size" and "the universe has a finite age" if the universe started from a singularity. How do you go from infinitessimally small to ...
2020-05-04: How We Know The Universe is Ancient
- 00:17: ... on the night sky as did our astronomer ancestors. Familiar star-maps are recorded in cave paintings tens of thousands of years old. We could ...
- 01:35: ... Were they blobs of gas in the Milky Way, or vast, distant groups of stars - other “Milky Ways”, or as Immanuel Kant called them, island universes. ...
- 07:07: ... the distances to the galaxies wrong. It turns out that Cepheid variable stars come in two types, with two different period-luminosity ...
- 08:58: ... because it’s based on comparing the expected, true brightnesses of stars with the apparent, distance-dimmed brightness. It seems fair to assume ...
- 09:39: ... been counting bright clouds of hydrogen gas - so-called HII regions - as stars, which threw their numbers off. It was a young astronomer named Alan ...
- 11:07: ... discovered the anti-gravitational effect of dark energy, and had to start adding that into their equations also. But that’s a story for another ...
2020-04-28: Space Time Livestream: Ask Matt Anything
- 00:00: ... lots of types of questions we could we could go through I'm gonna just start by talking about the show and we'll get into some science and we'll ...
2020-04-22: Will Wormholes Allow Fast Interstellar Travel?
- 00:00: ... Stargate to Interstellar, wormholes have long been one of our favorite method for ...
- 13:26: ... to create a traversable wormhole. For the first many millennia of our star-faring future we’ll have to take the long way around the universe. But even if ...
- 15:35: ... Belhaj asks about the interstellar medium - isn't the space between the stars and galaxies an empty void? Actually no. Particularly within a galaxy, ...
2020-04-14: Was the Milky Way a Quasar?
- 00:47: ... also swarms with smaller black holes, searing hot clouds of gas, massive stars right on the edge of going supernova, and some of the most energetic ...
- 02:19: ... start in 2010, when a team of astronomers from the Harvard-Smithsonian Centre ...
- 04:06: These “cosmic rays” can then collide with nuclei in the gas between the stars - again, mostly the protons of hydrogen.
- 05:59: Let’s start with “when” - it’s a bit more straightforward.
- 06:47: ... or close interaction with another galaxy - then that gas can form stars at a really insane rate across the galaxy. We call these events ...
- 07:09: ... star formation part of a starburst isn’t energetic enough to produce the ...
- 07:25: ... shock waves created by the supernovae from a starburst in the Milky Way could literally punch a hole through the interstellar ...
- 07:43: All of those supernovae would have had to leave remnants behind - neutron stars and black holes.
- 07:49: The neutron stars should be seen as pulsars, and there just aren’t enough in that region to account for a starburst of the required magnitude.
- 08:42: ... Bubbles, Sag A* would have needed to devour - a single 50 solar mass star that happened to wander too ...
- 09:54: A mini AGN phase is triggered either by an influx of gas or by a random massive star getting too close to the black hole.
- 10:02: ... outflows would be compressed by shocks, provoking a sudden burst of star formation like we described ...
- 10:17: This starburst and the subsequent supernova barrage smooths out the energy in the bubbles.
- 10:23: AGN activity and starburst activity are very commonly seen together - in fact M82 that we saw previously harbours an AGN in its core.
- 10:34: The energy from those outflows will eventually shut down the star formation, but in the early phase it can help kick it off.
- 11:41: ... of accretion onto the Milky Way’s central black hole and a flurry of star formation egging each other ...
- 12:21: ... researchers believe that the starburst and accompanying supernova cascade that may have helped forged the Fermi ...
- 15:12: ... of the Universe state that, if it was created at all and didn't just start, as it were, unofficially, it came into being between ten and twenty ...
2020-04-07: How We Know The Earth Is Ancient
- 01:48: ... his result in 1778. It was ingenious really. He assumed the Earth started as a ball of molten rock, which subsequently cooled down to its current ...
- 02:38: ... around the same time as Buffon was staring at warm lumps of iron, the Scottish geologist James Hutton wandered ...
- 07:17: ... to decay. In principle, if you know how much of the stuff there was to start with you can figure out how long the radioactive material has been ...
- 09:33: ... can figure out how much uranium a given sample had to start with by looking at the proportion of uranium to lead. This only works if ...
- 11:02: ... back Earth’s age further and further. But beyond a few billion years it starts to get tricky. There aren’t many patches of land left from way back ...
- 12:35: ... but perhaps we’ve become a bit too comfortable with it. These days we stare down at the unfathomable gulf of the past and shrug, and we forget that ...
2020-03-31: What’s On The Other Side Of A Black Hole?
- 07:10: We’ll see later how things change in the case of a black hole born of the collapse of a star.
- 10:35: ... have somewhere to come from. But real black holes form from collapsing stars - there’s no white hole in their past. And within those black holes, any ...
2020-03-24: How Black Holes Spin Space Time
- 01:44: ... everything that went into forming it. That includes the rotation of the star’s core that collapsed into the black hole in the first place, and the ...
- 03:54: ... start by talking about what is actually rotating in a Kerr black hole. It’s ...
- 06:48: ... a black hole that is currently feeding - perhaps devouring a companion star or, in the case of quasars, a bunch of its host galaxy’s gas - the ISCO ...
- 11:31: ... astrophysical phenomenon - gamma ray bursts. When a truly gigantic star collapses at the end of its life, and if its core was rotating fast ...
2020-03-16: How Do Quantum States Manifest In The Classical World?
- 02:39: ... quantum darwinism - and you’ll see why. To get there we need to start by talking about quantum ...
- 04:28: ... superposition of states - measured in the vertical basis, each particle starts in a state of both up AND down, while in the horizontal each is left AND ...
- 07:37: ... so, we put this atom along the up path of our device, and we start it out in the off state. If our electron takes the up path it flips the ...
- 15:22: To learn more www.thegreatcoursesplus.com/spacetime or click on the link in the description to start your trial today.
2020-03-03: Does Quantum Immortality Save Schrödinger's Cat?
- 08:03: So more likely near the middle of our species existence rather than right at the start or right at the end.
2020-02-24: How Decoherence Splits The Quantum Multiverse
- 00:35: ... last week’s episode we started down this rabbit hole exploring the measurement problem - the question ...
- 13:47: In fact the details have been worked out with mathematical rigor - starting with H. Dieter Zeh’s foundational paper in 1970.
2020-02-18: Does Consciousness Influence Quantum Mechanics?
- 01:32: ... start, we're going to need to go back to one of the earliest interpretations of ...
- 08:09: ... perhaps the first to assert the connection, and his influence may have started the development of the Copenhagen interpretation - later attributed ...
- 14:26: ... Predmyrskyy also asked about this in the comments: if axions come from stars, would galaxies lose their dark matter and fly apart once the stars ...
- 14:51: ... axions produced in stars now would be a tiny fraction of the mass we see in dark matter - in fact ...
2020-02-11: Are Axions Dark Matter?
- 15:20: ... Let's say 10^10^60-ish times the diameter of our universe until things start to repeat ...
2020-02-03: Are there Infinite Versions of You?
- 01:08: To start with we need though we need some monkeys.
- 03:13: Perhaps you can start to see how this applies to there being infinite yous in an infinite universe.
- 03:19: ... a perfectly deterministic universe, the starting conditions in any given region - like positions, velocities, etc of all ...
- 05:24: If there are infinite possible starting configurations for any one region of the universe, then there can be infinite regions without any doubling up.
- 05:32: But if there are finite starting points then at least SOME of those starting configurations have to be repeated infinite times.
- 05:54: So if there really are finite possible starting conditions then this region is probably repeated.
- 06:02: So what does it mean for two regions of the universe to have the same starting conditions?
- 06:31: In such a chaotic system, even tiny differences in the starting conditions will lead to massive divergences in that future history.
- 06:39: ... there is an allowable level of ridiculously tiny deviation in the starting conditions between two regions that would still lead near-identical 13.5 ...
- 06:53: We can’t tune the starting conditions to an infinite degree and still get different results - and that’s the key point.
- 07:01: It seems there must be finite possible starting configurations.
- 07:12: I should also note that it’s not just the particles that define starting conditions, there’s also the laws of physics themselves.
- 08:40: For example, you could argue that fundamental quantum randomness will cause even identical starting configurations to produce different results.
- 09:00: In fact, quantum randomness could allow different starting conditions to evolve into a universe that looks like this one.
- 11:59: Honestly, I was dismissive of the idea before I started writing this script.
- 14:37: Well to start with, there is a causal order for the incoming and outgoing particles - the former cause the latter, and so they must come first.
2020-01-27: Hacking the Nature of Reality
- 01:30: ... it, insisting that matters are the observables - the measurable start and end points of an ...
- 03:10: But problems returned when we started to peer into the atomic nucleus.
- 06:04: At the time, nuclear scattering experiments were producing a startling variety of different particles.
- 09:11: ... up by the bootstraps” - the idea of raising yourself up without concrete starting point to push off ...
- 15:30: It may be easier with neutron star mergers, which we see a LIGO signal up to a minute before the merger.
2020-01-20: Solving the Three Body Problem
- 01:24: ... Plug numbers into that equation and its solved. Those numbers are the starting positions and velocities of your gravitating bodies, plus a value for ...
- 03:18: ... reality of the three-body problem is that the evolution of almost all starting configurations is dominated by chaotic dynamics. Future states are ...
- 07:56: ... motion - they evolve - sometimes in complex ways - back to their starting configuration. In the 70s, Michel Henon and Roger Broucke found a family ...
- 11:21: ... evolution of dense regions of the universe, where three-body systems of stars or black holes may form and then disintegrate very ...
- 15:31: ... we hadn’t met before we started filming, we are kindred spirits, interested both in cutting edge science ...
2020-01-13: How To Capture Black Holes
- 00:59: ... and astrophysics predicted black hole mergers. When two very massive stars are in binary orbit with each other, they may end their lives to leave a ...
- 02:50: ... of thousands of stellar-mass black holes. These are the remnants of dead stars, typically a few to a few tens times the mass of the Sun. They rained ...
- 03:34: ... in such a dense environment. Regular glancing encounters with other stars or black holes can tear binary pairs apart before they can spiral ...
- 07:17: ... planetary systems, a disk of gas and dust surrounds the newly-formed star - a protoplanetary disk. Lumps of coagulated ice and dust migrate to ...
- 10:40: ... since LIGO started operation we now have advanced follow-up systems in place. As soon as a ...
2020-01-06: How To Detect a Neutrino
- 07:51: ... 𝘩𝘪𝘨𝘩 𝘴𝘺𝘯𝘵𝘩) ♪ enough to leave a bit of leftover stuff to produce the stars and galaxies and ♪ ♪ particle physicists that we see around us ...
2019-12-17: Do Black Holes Create New Universes?
- 00:37: Tweak them too much and life, stars, galaxies, the universe as we know it wouldn’t exist.
- 02:43: Now by happy chance there’s a correlation between making lots of black holes and making life - both require stars.
- 02:52: The universe that is better at making stars is better at making planetary systems is better at making us.
- 05:49: In our modern universe, black holes are made when the most massive stars explode as supernovae.
- 05:59: So we should expect our universe to be optimized for producing as many of the most massive stars as possible.
- 06:13: Stars are formed when giant clouds of gas collapse under their own gravity.
- 06:37: ... elements and molecules allow clouds to cool and stars to form much more quickly, and of these, carbon monoxide is by far the ...
- 06:48: ... addition, gas needs to be shielded from the heating effect of other stars - and that seems to require the presence of tiny particles of ice and ...
- 07:00: ... without carbon, oxygen, water, and chemistry in general, far fewer stars and so far fewer black holes would form - and of course these factors ...
- 07:16: ... given infinite time these will eventually outnumber those produced by stars or stellar black ...
- 09:09: ... massive stars die, they actually mostly produce neutron stars - planet sized balls of ...
- 09:20: Black holes only form when the neutron stars is above a certain mass limit.
- 09:25: Now it may be that in the cores of the most massive neutron stars, some particles can convert into strange quarks.
- 09:34: The resulting material is even denser than the original neutron star, and so brings the star closer to collapse.
- 09:48: That in turn means less massive neutron stars would be able to collapse into black holes.
- 09:54: ... quark mass should be optimized to make the cutoff between neutron stars and black holes as low as ...
- 10:14: So, if this universe is optimized for black hole production then there should be no neutron stars more massive than 2 solar masses.
- 10:24: Well, the most massive known neutron star is 2.17 solar masses, discovered just this year.
- 11:13: ... ... but what if it was, I dunno, beryllium and boron that helped stars form - or other elements that were useless to ...
- 15:20: ... about the doomsday argument then chances are they didn't come near the start of their ...
2019-12-09: The Doomsday Argument
- 02:24: But it’s a good thing ours IS low because otherwise our universe would have blown itself up too quickly for stars and life to ever form.
- 05:07: And that’s the same guy who brought to popular attention and in fact named the anthropic principle to start with.
- 05:13: To start, let’s try a thought experiment.
- 06:07: ... a galactic civilization that last a million of years across a million star system, and ultimately gives rise to a hundred trillion trillion ...
- 13:39: ... start with a question from the discord: Habunelahack asks if it's ever be ...
- 14:57: ... most obvious example is that regular gravitational fields around stars and galaxies can be positively curved patches in a flat or hyperbolic ...
2019-12-02: Is The Universe Finite?
- 02:02: But more detailed study of the Planck data has started to reveal tensions.
- 03:19: Just like with the 2-D spherical analog, lines that start parallel in such a universe eventually come together.
- 03:32: If you travel far enough around you'll get back to where you started.
- 07:57: And can we find a faster route to India by traveling all the way around the cosmos to get back to where we started?
2019-11-18: Can You Observe a Typical Universe?
- 00:00: The moment you started observing reality, you hopelessly polluted any conclusions you might make about it.
- 00:45: ... we realized that our sun is a typical example out of 100s of billions of stars in the Milky Way, and that the Milky Way is an ordinary galaxy among ...
- 01:00: ... in the universe is called the Copernican principle after the guy who started it ...
- 05:50: ... interesting that's happened since - from the formation of stars and galaxies to the evolution of life - has been powered by the slow ...
- 06:01: ... life in a state of extreme disorder and high entropy - iron stars, black holes, and a mist of cold elementary particles, not very ...
- 09:46: If we then assume that the starting conditions for our universe were typical, that can tell us something about the physics of how universes are born.
- 13:39: ... their vast knowledge of physics across the multi-verse and unleash a Star Trek-esque science utopia here on ...
2019-11-11: Does Life Need a Multiverse to Exist?
- 01:44: ... would be vastly different - and probably unable to produce galaxies, or stars, or ...
- 04:01: Let’s start with chemistry.
- 05:05: The vast majority of carbon in the universe is produced in the cores of massive stars.
- 05:36: Other slight changes in nuclear fine tuning would also massively reduce the amount of oxygen that stars produce.
- 06:12: ... if it were stable, this stuff would be like superfuel for stars - meaning all stars in the universe would have burned out before life ...
- 06:21: ... unstable, eliminating one of the key steps in the fusion process inside stars - so stars like our sun wouldn’t burn at ...
- 06:42: With weaker gravity, diproton-burning stars could last longer, and with stronger gravity, fusion could skip the deuterium step.
- 07:05: The stability of atoms and the rate of fusion in stars and in the early universe depends on the balance between electromagnetism and the strong force.
- 08:25: ... the masses of the elementary particles, is just right for things like stars and complex matter to form in our ...
- 16:33: ... civilization, seems like such a huge responsibility that maybe we should start acting as though the stakes really are that high and not screw it all ...
- 16:59: Actually these just came in while I was writing the rare earth episode, as soon as I started thinking about how we're totally screwing it all up.
2019-11-04: Why We Might Be Alone in the Universe
- 04:23: Actually, let’s start by something that is NOT rare about the Earth.
- 04:31: ... I mean rocky planets about the size of the Earth in orbit around stars very similar to the Sun at the right distance to sustain liquid water on ...
- 04:45: The Kepler mission has revealed there should be 10 billion or so in our galaxy - 40 billion if we permit other star types.
- 04:53: ... billions of potential starting points for life in the Milky Way alone, even if we restrict ourselves to ...
- 05:02: ... stewing for billions of years - if only one civilization had a tiny head start on us then it could have colonized the galaxy by ...
- 05:41: We’ll start by comparing planets of our solar system, because our ability to probe extra-solar planets is still in its infancy.
- 14:22: ... long cylinder that you can travel around to end up back where you started - in both time and ...
2019-10-21: Is Time Travel Impossible?
- 05:59: And in fact we'd need entire planets – perhaps entire stars converted to negative energy to do this.
- 07:26: This generates sub-lightspeed paths through spacetime that form closed loops, ending up back where they started in both space and time.
2019-10-15: Loop Quantum Gravity Explained
- 06:07: ADM starts by defining this abstract space of spaces - 3-D spatial metrics, 3-D space slices cut out of 4-D spacetime.
2019-10-07: Black Hole Harmonics
- 01:00: But real black holes are created in the violent deaths of massive stars, and there’s nothing clean about that.
- 11:09: The last was the incredible binary neutron star merger that was also detected across the electromagnetic spectrum as a giant explosion.
- 12:00: ... around 20 new black hole-black hole mergers, a few black hole-neutron star, and neutron star-neutron star ...
- 12:52: We’re seeing many, many mergers of black holes and neutron stars, and we’re learning an awful lot about these objects.
2019-09-30: How Many Universes Are There?
- 02:35: Let’s start with the first two, because these are basically our challenge question.
- 06:19: ... of the vacuum should be so low without being exactly zero given that it started out so ...
- 06:31: ... have restarted its accelerating expansion too quickly for galaxies and stars and life to ever ...
- 11:46: Let’s start by answering the extra credit question: how close to bubbles need to be in order to collide?
- 17:20: But what about around other stars?
- 17:29: That's right, other stars don't have planets - they have exoplanets.
2019-09-23: Is Pluto a Planet?
- 00:02: A big round thing that orbits a star.
- 01:00: ... shape, black holes based on how they feed and how they're oriented, stars based on their color and brightness, and planets by… well, by a set of ...
- 01:36: If you were an ancient astronomer like say, Ptolemy, the planets were the asteres planetai, the wandering stars.
- 01:44: ... and the moon - basically anything that moved relative to the background stars. ...
- 03:06: New wandering stars were discovered in the centuries following Newton.
- 06:54: ... massive enough to ignite nuclear fusion in their cores like a true star, but still seemed too massive to be called ...
- 07:04: And yet some brown dwarfs orbit other, more massive stars just like planets do.
- 14:30: ... also starting a newsletter that's open to everyone to make sure you get notified when ...
2019-09-16: Could We Terraform Mars?
- 09:42: ... cover the entire surface to about 30 meters – which is not enough to start a proper water cycle or have oceans, but there may be a lot more water ...
- 15:42: It started out with one small step for man and now the journey to Mars is right around the corner!
2019-09-03: Is Earth's Magnetic Field Reversing?
- 03:48: Let’s start with a quick review of what the interior of the Earth look like.
- 05:55: For now, let’s say that we start with some weak dipole field.
- 06:21: As a result, the starting magnetic field gets wound up into rings around the axis of rotation – into a torus shape.
- 07:05: OK, so start with a weak dipole field and you get a strong one.
- 07:23: Once started, the field builds to maximum strength.
- 09:21: ... and when the field just glitches but ends up in the same direction it started we call it a geomagnetic ...
- 11:36: We’ll need to see a lot more disruption before we start to worry.
2019-08-26: How To Become an Astrophysicist + Challenge Question!
- 00:00: ... for our recent episodes on the eternally inflating universe Let me start by telling you about my own path. It was typical enough I started out ...
- 03:35: ... where I thought I might be able to stick with this gig. Oh And then I started making YouTube videos because God forbid I take it easy for a bit if ...
2019-08-19: What Happened Before the Big Bang?
- 02:03: ... we probably should know more about the field that drives it. To start with, you need a particular type of field to cause inflation, something ...
- 05:07: But it wouldn't end as a random process, it wouldn't require quantum tunneling to get started.
- 09:18: And to get this started, you need a speck.
- 09:34: Assuming a quantum field of the right type and that speck will start inflating.
- 10:33: ... time start at the Big Bang" and "What caused the Big Bang, the real physics of ...
- 12:29: ... actually gives a physical reason for the universe to have started with a rapid outward expansion rate in terms of pretty well understood ...
- 12:50: Dominic H quips "Did time start at the Big Bang? Let me guess depends on your definitions of "Did", "Time", "Start" and "Big Bang" " Ah...
- 13:01: Bad science starts with bad questions.
2019-08-12: Exploring Arecibo in VR 180
- 01:02: ... off planets and asteroids as far as Jupiter Or send messages to the stars. Let's check out the dish below We're now directly beneath the dish at ...
2019-08-06: What Caused the Big Bang?
- 01:56: But physicists are a skeptical bunch and most of the time they don't just make up stories and start believing them without good reason.
- 08:51: ... a deeper truer minimum - perhaps the true vacuum state - and suddenly starts to lose energy again racing towards that ...
- 09:35: And just like a growing ice crystal, this effect will propagate outwards from the starting point, which we call a nucleation point, by analogy.
- 11:17: But, right from the start Guth admits a number of problems with his story. The big one is about how inflation stops.
- 12:41: If inflation happened at all, that it's hard to avoid two conclusions: Once started, inflation should continue...
- 12:49: eternally - Only stopping in patches where a bubble universe forms. And once started, inflation should produce infinite such universes.
2019-07-25: Deciphering The Vast Scale of the Universe
- 00:25: That’s a quadrillion stars, and as many planetary systems.
- 03:07: For example, consider two stars – one bright one dim to our eyes.
- 03:14: Now, perhaps those stars are identical, and the bright one is just closer to us.
- 03:18: Or perhaps the bright one is truly much more luminous – and is at the same distance or even further away than the dim star.
- 03:25: Now there are some clever ways to measure distances to stars within the Milky Way galaxy.
- 03:39: ... Hubble made his discovery, Leavitt discovered that a certain type of star, Cepheid variables, brightened and dimmed with a repeating period that is ...
- 04:50: ... the discovery that the universe is expanding, meaning it must once have started with the Big ...
- 06:23: ... our solar system behind, we’re zipping past the hundreds of billions of stars of our Milky Way galaxy at a few hundred billion times the speed of ...
- 06:34: ... we’ve only mapped the locations and velocities of around 1% of those stars, that gives us an incredible understanding of the shape and motion of our ...
- 06:57: There’s Andromeda, its incredible distance first revealed to Hubble through its pulsing Cepheid variable stars.
- 08:16: ... well as the earliest galaxies or even black holes or worlds around other stars, Mt. Wilson's Hooker Telescope wouldn't cut ...
2019-07-18: Did Time Start at the Big Bang?
- 00:00: Thank you to LastPass for sponsoring PBS Digital Studios Our universe started with the Big Bang.
- 00:05: But only for the right definition of our universe and "started" for that matter. In fact, the Big Bang is probably nothing like what you were taught.
- 00:25: ... small point - a singularity. It's often said that the universe started with this singularity and the Big Bang is thought of as the explosive ...
- 01:22: ... cooler, at least as far as we understand it Now, before a certain crowd starts with "all the scientists keep changing their minds - they don't know ...
- 07:22: ... at the Big Bang singularity and their timelines end with them Or they start depending on how you want to think about it The point is that in the ...
- 08:52: ... all space was compacted into a single point and that this is where Time started. Ok. So what are the ...
- 12:30: ... service options available. Click on the link in description below to start ...
2019-07-15: The Quantum Internet
- 01:21: ... Shannon started it all with his 1948 paper “A Mathematical Theory of Communication”, ...
- 07:50: ... qubit B, after which that qubit will be in the state qubit C was at the start. ...
2019-07-01: Thorium and the Future of Nuclear Energy
- 02:49: ... or natural gas plants or you know on a Lunar or Martian settlement or a starship that same modularity Poses perhaps the biggest risk if small thorium ...
- 15:29: ... what you had to say Steve C comments that this whole black hole killing star formation thing seems like a negative feedback Interaction more gas ...
2019-06-20: The Quasar from The Beginning of Time
- 03:40: For example, viewed in visible light, the Andromeda galaxy shows us newborn stars.
- 03:57: The infrared Andromeda is a swirl of star-forming clouds and gas.
- 04:20: ... light. To do this in real time, Gemini creates its own artificial guide star by shooting lasers to twinkle off sodium atoms at 90km height, right ...
- 05:53: Now, that gas collapsed into the very first stars, then the very first galaxies.
- 05:58: Those stars eventually melted away the remaining hydrogen in a process called reionization, leaving a crystal-clear universe.
- 06:07: But this quasar shines out from the era of those first stars before they'd finished the job of reionization.
2019-06-17: How Black Holes Kill Galaxies
- 00:08: ... turns out that they may be responsible for ending Star formation across the entire Universe When we first realized that Black ...
- 01:35: ... they live in their Gravitational influence should only extend to the stars right at the very centre of the galaxy they definitely aren't directly ...
- 02:54: ... into the clusters from outside of the Universe igniting bouts of extreme star formation called Star Busts as galaxies grew so did their Black Holes ...
- 05:24: ... in Astronomy, a dead galaxy refers to its current star formation activity in particular, the largest galaxies in the Universe ...
- 07:21: ... prevent new gas arriving or it can heat the gas either case is bad for star formation in the later case is because hot gas can't form new stars gas ...
- 10:49: ... a feedback cycle of growth and quenching that neither quasar nor star forming galaxy would survive and perhaps for the best - for the comfort ...
- 11:24: ... time we talked about all the cool elements that get made when neutron stars ...
- 12:04: ... whether the Fermi Paradox might be explained by the fact that neutron star collisions are rare so that only lucky parts of the galaxies have a high ...
- 12:17: ... of the galaxy gets a decent amount of all the stable products of neutron star ...
- 13:04: Tricky asks us why we don't see more strange matter from neutron star collisions.
- 13:12: ... may be that some neutron stars are actually "Strange Stars" whose nuclear material is composed of ...
- 13:24: If such a star was disrupted, then we would expect to see blobs of strange matter in the debris.
- 13:30: ... stable under extreme pressure Release it from the embrace of the neutron star and all the strange quarks probably decay into boring old up and down ...
2019-06-06: The Alchemy of Neutron Star Collisions
- 00:00: ... Sagan's famous words: "We are star stuff", refers to a mind-blowing idea that most atomic nuclei in our ...
- 00:34: ... produced in onion shells by nuclear fusion in the cores of very massive stars during the last phases of their lives and that elements heavier than ...
- 02:47: ... spotted the space-time ripples from the merger of a pair of neutron stars many of the world's great telescopes monitored the subsequent ...
- 13:02: ... the dark ages would have actually been dark at least to us the dark ages started following recombination and then the cosmic background would still have ...
2019-05-16: The Cosmic Dark Ages
- 00:04: ... in the stelliferous era. Somewhere between 10 and 1000 billion trillion stars fill the observable universe with light. But there was a time before the ...
- 00:24: ... see the past in motion. In fact we’re able to see some of the first stars and galaxies to ever form. But if we look beyond, both in distance and ...
- 02:31: ... Stars that formed from that gas would be the next source of light, and those ...
- 02:52: ... believed that the first stars formed around 150 million years after recombination when tiny ...
- 03:52: ... galaxies – proto-galaxies – formed stars at a prodigious rate, and around these galaxies bubbles of ionized ...
- 04:29: ... size. It expanded by a factor of 100 before the epoch of reionization started, and it’s expanded by a factor of 10 since ...
- 05:45: ... or emits a radio photon with a wavelength of 21cm. When the first stars ignited they heated the surrounding gas, which caused it to absorb more ...
- 06:54: ... that first generation of giant stars? They did more than kickstart reionization and produce the first ...
- 11:17: ... track the progress of reionization and even figure out when it must have started. ...
2019-05-09: Why Quantum Computing Requires Quantum Cryptography
- 04:34: We’ll start with Heisenberg, which of course we’ve done an episode on already.
- 10:21: Man-in-the-middle attacks are in principle still possible because Werner could impersonate Albert and Niels from the very start.
2019-05-01: The Real Science of the EHT Black Hole
- 00:38: ... has subsided and I personally have stopped spending hours on end staring at a black spot, we can take a breath and actually look at the real ...
- 04:16: You need a minimum of three telescopes to start to form an image.
2019-04-24: No Dark Matter = Proof of Dark Matter?
- 00:03: ... as with many of his wiki's predictions like the existence of neutron stars and gravitational lensing this wasn't taken seriously until decades ...
2019-04-10: The Holographic Universe Explained
- 00:24: ... of the most startling possibilities is that our 3+1 dimensional universe may better described ...
- 01:07: We’ve made a background playlist if you want to start from scratch, and I especially recommend catching last week’s episode.
- 01:19: The story started with black holes, and with Jacob Bekenstein, who derived an equation to describe their entropy.
- 04:32: Let’s say we start with a plane – a flat, 2-D spacetime.
- 09:57: These are like multidimensional strings that can serve as start and end points for strings, but also as spaces embedded within higher-dimensions.
- 12:29: But the more startling implication of AdS/CFT is that it’s the first concrete realization of a holographic universe.
2019-04-03: The Edge of an Infinite Universe
- 02:26: Let’s start with a quick review of types of universe.
- 02:48: Travel far enough and you get back where you started.
- 05:40: As a quick review: start with a graph of space versus time – a spacetime diagram – then compactify.
- 09:26: Let’s start with another map.
- 10:11: The basic construction is straightforward enough – start with a circle.
- 17:49: ... I guess the painful part would be when expansion is fast enough that it starts to disrupt the way chemistry works, without actually ripping matter ...
- 17:58: ... so there would be some minutes to hours of bad times as our molecules start to betray ...
2019-03-28: Could the Universe End by Tearing Apart Every Atom?
- 00:05: ... ripped to shreds, Stars obliterated cats and dogs living together and then tragically separated ...
- 09:26: ... the effect of phantom energy is stronger than the gravity binding the stars ...
- 09:48: There are some millions of years of fun as we watch those galaxies disassemble and the constellations of stars in the Milky Way fly apart.
- 12:53: ... - the universe will still end in a long cold heat death in which the stars of our galaxy wink out become black holes and then evaporate over an ...
- 14:34: ... Stark asks, "if dark energy changed in the past, can it also change in the ...
2019-03-20: Is Dark Energy Getting Stronger?
- 03:19: ... observations of the cosmic microwave background reveal the starting conditions of the universe – the balance of dark energy, dark matter, ...
- 03:36: ... we apply the Concordance model to these starting conditions to calculate how the universe should have evolved from those ...
- 04:02: Type-1a supernovae– which result from exploding white dwarf stars.
- 05:21: It may be an issue with how we determine the starting conditions of the universe, or it may be our measurements of supernovae.
- 11:57: Let’s start with the latter, just in case.
- 13:07: ... example, there’s the idea that dark energy that started out much stronger dropped off rapidly, or even that it oscillates over ...
- 15:30: ... you have to do is click on the link the description below, to start today Last week we had a conversation with Richard Branson about his ...
2019-03-13: Will You Travel to Space?
- 03:29: ... check out on illegal fishing boats that are ravaging the ocean. We can start monitoring the reefs in a systematic ...
- 03:49: ... This is a stark difference to the motivations of Musk & Bezos, who have talked many ...
- 04:47: And that means we can we hope we can generate funds where we can then start thinking about point-to-point travel at great speeds.
- 09:17: ... the quarter of a million dollars that we currently charge, then we can start building more and more spaceships. And as you build more spaceships the ...
- 10:16: [RICHARD] You know, my dream will be to let me start the Virgin Hotel.
2019-03-06: The Impossibility of Perpetual Motion Machines
- 06:36: Like a perfect Carnot engine, or a frictionless wheel – with or without magnets and mercury tubes – or a planet orbiting a star.
- 13:47: ... mostly come from our galaxy - there's a lot from the dust in between the stars, and also from individual electrons either bumping into other charged ...
- 14:50: More dense regions were a little hotter, so recombination started later in those.
2019-02-20: Secrets of the Cosmic Microwave Background
- 07:42: ... represent the top of the spring's rise which is just determined by its starting position What does this have to do with the second ...
- 12:34: ... about 5% of the mass and energy that's all of the atoms in all of the stars in all of the galaxies basically everything you can see The remaining ...
- 14:23: ... learn more at curiositystream.com/spacetime In our previous episode we started our discussion of the baryon-acoustic oscillation the actual source or ...
2019-02-07: Sound Waves from the Beginning of Time
- 00:11: ... the stars, these galaxies form constellations, Hidden patterns that echo the ...
- 01:34: Let's start at the beginning.
- 05:01: At 380,000 years, the plasma hit a critical temperature of 3000 Kelvin, around the surface temperature of the coolest red dwarf stars.
- 06:46: ... matter, hydrogen and helium could begin the long work of collapsing into stars and galaxies work of collapsing into stars and galaxies as the universe ...
- 13:58: ... to wait 10^(10^25) years for the first quantum tunneling to turn iron stars into black holes, and way, way longer than that for anything ...
2019-01-30: Perpetual Motion From Negative Mass?
- 01:24: Let’s start with mass in Newton’s physics.
- 06:56: At first glance this tells us that any object, no matter its mass, will follow the geodesic determined by its starting position and velocity.
- 07:40: But those trajectories only depend on the active gravitational mass of the central object, and on the velocity and starting position of the apple.
- 13:43: Let’s say the two objects are about the size of apples, but to get some decent power output make them the density of a neutron star.
- 14:17: Link to that in the description if you want to start choosing your prize.
2019-01-24: The Crisis in Cosmology
- 03:18: ...giant stars, during the last phases of their lives.
- 04:41: These result when white dwarfs, ancient remnants of dead stars,...
- 09:15: Well, first you figure out what starting cosmological parameters...
- 09:21: Those parameters include the starting combination of both dark and light matter, and radiation,...
- 11:32: So let's start a new list.
- 17:07: ...and presumably reassemble itself into the stars, spaceships, monkeys,... that originally fell in.
2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe
- 03:02: ... that's not just intuitively expected but also theoretically required. Starting with Julian Schwinger's "Spin statistics theorem" in 1951 it became ...
- 08:43: ... as a literal rewind. Rewind the universe and you get back to where you started pretty much by definition so presumably quantum information is conserved ...
- 10:54: ... and then a simple T transformation and you get back to where you started. If CP is violated then this simple time reversal is also violated and we ...
2019-01-09: Are Dark Matter And Dark Energy The Same?
- 01:28: They should scatter their stars into the void.
- 06:11: In fact let’s start with dark matter because that’s a bit more straightforward.
- 10:31: Those supernova results suggest a universe that started expanding rapidly and then slowed down due to the gravity of matter – mostly dark matter.
2018-12-20: Why String Theory is Wrong
- 02:14: ... fails, we need to rewind to look at some of these a bit closer, to start with, to a precursor to string theory and the origin of all this extra ...
- 05:18: So, start with Kaluza-Klein, add vibrating strings and exactly the right extra special dimensions, and you have string theory.
- 06:03: Superstring started out with incredible promise, and so there was a proliferation of different versions of super string theory.
2018-12-12: Quantum Physics in a Mirror Universe
- 00:02: ... just as a reflection in two directions will get you back to where you started a parity transformation followed by a flipping of electric charge ...
2018-12-06: Did Life on Earth Come from Space?
- 00:37: ... eyeblink well maybe but it's also possible that life on Earth didn't start on earth at all perhaps it started on a distant world somewhere in the ...
2018-11-21: 'Oumuamua Is Not Aliens
- 00:24: To us, it looked like a faint spot of light moving quickly relative to the fixed stars.
- 02:26: ... certainly expect there to be a bunch of space junk floating between the stars, probably ejected in the violent early stages of formation of planetary ...
- 02:46: Those things are odd, but not odd enough to start assuming aliens.
- 05:27: And the breakthrough starship program is planning to use a lightsail as our first interstellar probe.
- 05:37: It may also explain why we saw something at all given that natural space debris the size of Oumuamua should be much rarer between the stars.
- 06:39: The acceleration is the weirdest thing so we'll start there.
- 07:59: ... it was tidily disrupted, pulled apart by the star or a gas giant from its home system, much like the comet Shoemaker Levy, ...
- 08:56: For example, it may be that stars release their Oort Clouds, when they die.
- 09:01: ... every star that passed before us shed its vast cloud of comets into the galaxy, ...
- 09:22: ... or gravitational interaction into a trajectory that will send it to the stars. ...
- 10:06: Interstellar space would need to be filled with broken lightsails, something like 10 to the power of 15 probes per star in the Milky Way.
- 10:29: On the other hand, the breakthrough starshot lightsails are aiming at 20% light speed for a 20 year journey to the Alpha Cen system.
- 15:19: tu_nonna_emiliana asks, if SUSY is easy, just add an s to the start, then how about Sstring?
2018-11-14: Supersymmetric Particle Found?
- 11:48: IceCube will start carefully scrutinizing its data.
2018-11-07: Why String Theory is Right
- 01:32: It's pretty, or at least it started out that way.
- 02:41: But the fact is when you start to work out the math of string theory, gravity appears like magic.
- 03:24: Let's actually start with the regular old point particles of the standard model.
- 04:06: More technically, you start to get runaway self-interactions, infinite feedback effects between the graviton and its own field.
- 07:17: Quantizing the motion of strings also starts out ugly, but there are also some math tricks to make it work.
- 12:18: And this is where string theory starts to look less attractive.
2018-10-31: Are Virtual Particles A New Layer of Reality?
- 01:30: ... started out as a trick to make impossible calculations in quantum field theory ...
- 03:25: ... the case of the interacting electrons, you start by saying each electron interacts once with the EM field, transferring ...
- 04:53: All those that both start and end within the diagram are virtual particles.
- 08:03: ... a bit like the photon starts out moving in the wrong direction and then quantum tunnels between the ...
- 16:48: A few of you pointed out that our depiction of the binary star system was wrong.
- 16:52: They were apparently orbiting a center of mass that wasn't even between the stars.
- 16:58: So that was actually a three star system.
- 17:02: One star had collapsed into a black hole, which is why you couldn't see it.
2018-10-25: Will We Ever Find Alien Life?
- 00:36: ... short, in a galaxy of hundreds of billions of stars, each of which having billions of years to spawn life and civilization, ...
- 00:54: If aliens can travel between the stars, why haven't they visited?
- 01:02: ... could give away their presence; radio transmissions, robotic probes, or star-blotting solar ...
- 01:43: ... worlds to date, spotted as they marched across the face of their parent star in chance transit ...
- 01:55: This number allows us to figure out the fraction of stars that have planets.
- 01:59: Essentially, all stars do.
- 02:07: By habitable, I mean rocky planets the right distance from their star to have liquid water.
- 02:32: We have no way to even start to guess that yet.
- 03:24: That said, our search hasn't even been sensitive enough to see human level transmission in the nearest star system.
- 03:52: And because they almost certainly have a head start on us of at least thousands of years, that galactic gentrification might be visible to us.
- 04:01: You might remember Tabby's Star, the strange star in the Kepler field that showed these bizarre dips in brightness.
- 04:09: Some very large collection of something is passing in front of the star.
- 04:52: An advance civilization may launch so many solar satellites that they substantially block the light from their own star.
- 05:00: Let's call such a solar fleet a Dyson swarm after the Dyson sphere, which is the next level up, a structure that completely encases a star.
- 05:10: ... Dyson swarm would cause an unusual dimming of its parent star and also cause an unusual increase in infrared light due to waste heat ...
- 05:33: A team of astronomers scoured the GAIA data looking for stars that were unusually faint for their stellar type.
- 05:40: They looked at 8,000 stars and exactly one of those stars had a brightness significantly lower than expected.
- 05:47: ... they also figured out that the offending star has a binary companion which may have caused a wobble in the star's ...
- 06:09: But GAIA's upcoming third data release will expand this study from 8,000 to a million stars.
- 06:32: That still seems surprising given those 40 billion possible starting points for life in the Milky Way.
- 06:51: ... them a million year head start on us, just one 10,000th of the age of the Milky Way, and someone should ...
- 07:23: ... are astrophysical factors like the rate of star formation and the fraction of these stars that form habitable worlds, ...
- 07:57: ... there aren't tens of thousands of advance civilizations, we can actually start to constrain those biological and sociological ...
- 08:46: ... gets wiped out by gamma ray bursts, a type of cataclysmically exploding star. ...
2018-10-18: What are the Strings in String Theory?
- 01:52: The idea started in the 60s with efforts to understand the behavior of hadrons, collections of quarks bound by the gluons of the strong nuclear force.
- 10:01: ... the strings themselves are 1-D, but to even start to produce the properties of known particles, they need to vibrate in ...
- 11:11: Travel the tiny width of this dimension and you'll find yourself back where you started.
- 14:22: ... result in Hawking radiation, which would take until long after the last star in universe has died to even give you a small fraction of that ...
2018-10-10: Computing a Universe Simulation
- 05:40: ... the size of a picturesque European nation with the mass of the heaviest stars in the universe and with the storage capacity to register every atom in ...
- 09:33: Protons will have started to decay by the time we simulate last Monday.
- 12:21: Glenn Stern asks about the fact that the gravitational waves from this neutron star merger arrived two seconds before the light from the merger.
- 13:30: ... actually due to the fact that the kilonova explosion from the neutron star merger started slightly after the gravitational wave ...
- 13:41: The gravitational waves start to get strong before the neutron stars even make contact.
2018-10-03: How to Detect Extra Dimensions
- 00:34: When does all of that start to happen?
- 01:07: A pair of neutron stars spiralled together and merged.
- 01:11: These superdense remnants of dead stars churned the fabric of space and time in their death spiral.
- 01:22: Unlike merging black holes, which are invisible, merging neutron stars explode spectacularly.
- 08:10: But it starts to obey the inverse cubed law on much larger scales.
- 09:58: ... electromagnetic signal from these merging exploding neutron stars allowed us to measure its distance completely independently to the ...
- 10:10: ... by the gravitational wave, we need to know how intense it was when it started its ...
2018-09-20: Quantum Gravity and the Hardest Problem in Physics
- 01:38: Let's start with summaries.
- 02:41: That math started with the Schrodinger equation, which tracks these probability waves through space and time.
- 03:27: Starting with the mild, we have the black hole information paradox.
- 05:08: ... start by thinking about what it means to define a location in a gravitational ...
- 11:27: Generations of physicists, starting with Einstein himself, spent their lives trying to fix this to unite quantum mechanics and general relativity.
- 14:53: I said "observable" near the start of the episode.
2018-09-12: How Much Information is in the Universe?
- 00:19: Hundreds of billions of galaxies, each with hundreds of billions of stars, each with rather a lot of particles in them.
- 00:25: ... then there's all the stuff that isn't stars-- the dark matter, black holes, planets, and the particles, and radiation ...
- 03:20: This probably way underistimates how much info you really need to describe the universe, but let's start with this anyway.
- 07:48: Sagittarius A star in the center of the Milky Way, which has a mass of four million suns.
- 08:55: ... if we started to fill up those empty Planck-sized cubes of space throughout the ...
- 11:40: ... Starting with our episode on the history of life on Mars, sdushdiu says, Cool, ...
2018-09-05: The Black Hole Entropy Enigma
- 03:04: But in our previous episodes we skipped the key insight that started all of this.
- 03:19: You know, it's almost like all those episodes are starting to come together, almost like we planned this.
- 04:32: We start, as usual, by collapsing the core of a dead star.
- 04:49: At the instant the star collapses far enough to form an event horizon, it becomes a black hole.
- 11:26: It's a hell of a conceptual leap given it started with Jacob Bekenstein noticing a peculiar similarity between some formulae.
2018-08-30: Is There Life on Mars?
- 09:56: As of the filming of this video, the storm is only starting to settle down.
- 11:37: But perhaps the coolest recent discovery is this giant underground lake I mentioned at the start of the episode.
- 12:57: It didn't take life that long to get started on Earth.
2018-08-23: How Will the Universe End?
- 00:06: We live in an unusual age, the age when the stars still shine.
- 00:27: ... MUSIC] In 100 trillion years, the last star in the universe will expand, the final atoms of hydrogen fuel and settle ...
- 00:47: The Era of Stars will be over.
- 00:55: And so the days of starlight and warmth have a way to go.
- 02:13: ... merger with the Andromeda Galaxy, and, finally, to the death of the last stars in the ...
- 02:32: ... Galaxy comprised of nothing but stellar remnants, the ultradense neutron stars and black holes from long-extinct massive stars, as well as the white ...
- 02:51: Those white dwarfs will fade to black in only several billion years, far shorter than the several trillion-year lives of those stars.
- 03:03: Civilizations may have persisted or even started from scratch in the Red Dwarf Era.
- 03:48: So at this point in the universe's future history, the Age of Stars has passed and no starlight will ever shine again.
- 04:05: But neutron stars and white-- or, by now, black-- dwarfs are made of degenerate matter.
- 04:23: Believe it or not, many of those black dwarfs will still have planetary systems from their days as regular stars.
- 04:49: As stars randomly pass close to each other, planets are flung into the blackness.
- 05:13: As dark star remnants rotate through countless galactic orbits, they interact with each other gravitationally.
- 05:28: Heavier bodies, mostly neutron stars and black holes, sink towards the center.
- 05:33: ... to an estimate by Freeman Dyson, 90% to 99% of our galaxy's stars will be scattered into the void in something like 10 to the power of 18 ...
- 07:13: Some will be the remnant black holes of individual stars that were flung from galaxies long ago.
- 10:11: Black dwarfs decay into iron stars-- still degenerate and insanely dense, but now perfect balls of iron.
- 10:23: But even iron stars can't last forever.
- 10:26: The same process of quantum tunneling eventually transport a star's material toward its center.
- 10:32: Iron stars evolve into neutron stars.
- 11:27: This same process will nail all of the neutron stars too.
- 13:55: ... start with, a few of you asked how we know that the g-factor of the electron ...
2018-08-15: Quantum Theory's Most Incredible Prediction
- 00:59: We've talked about QFT many times before, starting with the very first quantum field theory, quantum electrodynamics.
- 04:49: Thinking of electrons as little bar magnets or as rotating balls of charge is a nice starting point.
2018-08-01: How Close To The Sun Can Humanity Get?
- 08:41: This time if our luck holds, we'll come close to touching our home star to unlock the mysteries of our closest stellar neighbor in space time.
2018-07-25: Reversing Entropy with Maxwell's Demon
- 06:08: We are no longer in thermal equilibrium, and the entropy is lower than before the demon started.
- 07:22: ... demon, or the particle sorting system it represents, must start in some known predictable state, which is altered by interaction with a ...
- 12:01: Starting with this assumption gets you to the Boltzmann equation, and it's a nice, relatively simple way to understand entropy.
2018-07-18: The Misunderstood Nature of Entropy
- 01:43: Let's start from the beginning.
2018-07-04: Will A New Neutrino Change The Standard Model?
- 03:43: To explain, we need to start with helicity.
- 04:14: It flips direction if you start moving faster than the particle.
- 07:44: So the MiniBooNE experiment starts with muon neutrinos, and some of these transform into electron neutrinos by the time they hit the vat.
- 11:41: The idea is that if the information is still existent somewhere, then the universe could be put in rewind and it would end up back where it started.
- 13:22: Weird thing, that's actually how I got started.
- 13:33: I heard this one guy, he started out memorizing pi to impress chicks, ended up inventing the atomic bomb.
2018-06-27: How Asteroid Mining Will Save Earth
- 03:53: Let's start with the good stuff.
- 06:49: ... in the actual asteroid belt where useful rocks are plentiful, but to start with, it's much easier if the asteroid comes to ...
- 10:51: ... to complement your hikes, road trips, beach days, and those long starry night when you contemplate the ...
- 11:14: So, start a 30-day trial and your first audiobook is free.
2018-06-20: The Black Hole Information Paradox
- 07:14: Let's start with the second point.
- 11:54: They were glimpsed as dark stars in the mathematics of Isaac Newton's law of universal gravitation.
- 12:01: So, to continue your own mathematical journey into black holes, Newton's gravity is the place to start.
2018-06-13: What Survives Inside A Black Hole?
- 02:28: ... black hole could have formed from a collapsed star or entirely out of antimatter or photons or monkeys, but the only thing ...
- 09:19: ... with angular momentum falls into a black hole, whether it's a spinning star or a whirlpool of gas, it will either add or subtract from this flow of ...
2018-05-23: Why Quantum Information is Never Destroyed
- 02:23: ... symmetric if its equations of motion allow us to perfectly predict the starting point simply by knowing the state of the system at any later ...
2018-05-16: Noether's Theorem and The Symmetries of Reality
- 11:49: ... do better than that off the bat by analyzing the way the light from each star spreads into neighboring pixels by fitting the so-called point spread ...
- 12:05: Each time, stars will have moved slightly, but they'll have moved in extremely predictable ways.
- 12:10: ... fitting laws of motion to the stars' five-year trajectory, there's only a very narrow trajectory of extremely ...
- 12:47: ... people, on "Space Time," we only ask that you start with a passing familiarity with quantum physics and the etymological ...
2018-05-09: How Gaia Changed Astronomy Forever
- 00:34: Its primary goal is to map the stars of the Milky Way with a scale and precision orders of magnitude greater than ever before.
- 00:42: Gaia's predessecor, Hipparcos, cataloged 120,000 stars.
- 00:46: Gaia blows this out of the water, with positions, colors, and brightnesses of nearly 1.7 billion stars.
- 01:04: Gaia can pin down a star's position to the equivalent of a human hairs width at 1,000 kilometers.
- 01:15: As we'll see, this precision allows Gaia to measure true distances and true velocities for 1.3 billion of its stars.
- 01:33: Let's start with distances.
- 01:44: From there, it stares outwards to the galaxy.
- 01:47: As it traverses its orbit, Gaia detects the tiny shifts in the positions of stars due to this motion, a phenomenon called stellar parallax.
- 02:07: Coupled with its incredible position measurements, this enables Gaia to measure distances to stars as far away as the galactic center.
- 02:15: Knowing the distance to a star is critical for determining its other physical properties.
- 02:19: For example, combining distance with a star's apparent brightness gives us its true to luminosity.
- 02:33: Now, combining those gives us the color of the star, which, in turn, gives us its surface temperature.
- 02:50: Location on this diagram can tell us about a star's mass, size, fusion activity, and even its past and future evolution.
- 02:58: For example, stars on this diagonal band-- the so-called, main sequence-- are in the primes of their lives, fusing hydrogen into helium.
- 03:06: After which, lower mass stars will become red giants, before leaving behind white dwarf remnants.
- 03:51: We see hot, newly formed white dwarfs, some of which are still embedded in the nebula of gas injected in the death of their star.
- 04:04: These are stars near the ends of their lives, now burning helium in their.
- 04:09: We can even watch variable stars dance along the HR diagram as their brightness' change.
- 04:20: We are barely getting started.
- 04:28: The stars all move in their own orbits around the galactic core.
- 04:36: ... but Gaia's incredible astrometry revealed the change in positions of stars over the five years of its ...
- 04:45: This gives the velocities of the stars in the plane of the sky.
- 04:49: ... tiny Doppler shift-- the stretching or compression of the wavelength of starlight due to the motion towards or away from ...
- 05:00: Combining motion on the sky and Doppler shift, gives the full three-dimensional velocities for these billion stars.
- 05:22: We can see the rotation of the Milky Way through the red and blue Doppler shift of the stars.
- 05:53: ... the current velocities and positions of the stars, we can actually wind the clocks backwards and forwards, to see where ...
- 06:00: For example, this is the field of stars of the planet hunting, Kepler telescope.
- 06:14: We can now study the kinematics of stars that have cumulatively, thousands of confirmed planets.
- 06:20: We can potentially, trace the origins of these stars, allowing us to find solar systems that came from the same stellar nurseries.
- 06:27: ... by constraining the distances to stars, we can get better measurements on the sizes of those stars, and thus, ...
- 06:46: We can even potentially, detect exoplanets by looking at the star's radial velocities and measuring shifts to a planet tugging on the star.
- 06:55: New binary star systems can also be found with these same methods.
- 07:06: For example, we can study stretched out groups of stars, called stellar streams.
- 07:11: These dynamically connected flows of stars, once bound together as a globular clusters or dwarf galaxies.
- 07:34: And on top of all of this, Gaia doesn't only study stars.
- 08:33: Every dot of light in this picture is a star, with its past and future motion now known.
- 08:48: Last week, we talked about the last stars that will shine in our universe-- the humble, red dwarf.
- 09:03: A white dwarf is the remnant core of a low to mid-mass star after it burns out and ejects its outer layers, leaving only the hot core.
- 09:13: They start out blue and are expected to eventually fade, through white to red to black, but we always call them, white dwarfs.
- 09:21: Red dwarfs are just a very low mass stars.
- 09:23: They start out red, but heat up over time.
- 10:08: Craig Harrison asks about the accuracy of this statement, the star that burns twice as bright, burns half as long.
- 10:23: A star that burns twice as bright does burn half as long-- actually, slightly longer-- because that star will have a more massive core.
- 10:29: On the other hand, a star that weighs twice as much as the sun, burns about 25 times brighter and burns out 10 times faster.
2018-05-02: The Star at the End of Time
- 00:10: How long will life persist as the stars begin to die?
- 00:47: And finally, our heirs or successors find new homes among the stars after the Sun's final death and transformation into a dim white dwarf.
- 01:20: And the deepest wells of accessible energy in the universe are stars.
- 01:25: When the last star blinks out, life must soon follow.
- 01:29: To know the future of life, we must understand the life cycles of the longest-lived stars in the universe.
- 01:38: And don't be scornful of this little star.
- 01:51: Stars generate energy, fusing hydrogen into helium in their cores.
- 02:21: ... the rate of fusion depends very sensitively on temperature, more massive stars with their hotter cores burn through their fuel much, much more ...
- 02:31: The most massive stars live only a few million years.
- 02:36: Stars less massive than the Sun burn through their fuel much more slowly.
- 02:41: ... so let's get a little crunchy and figure out the lifespan of red dwarf stars, also known as "M dwarfs." We observe that a red dwarf with 10% of the ...
- 03:04: Actually, wrong-- stars like our Sun can only burn the hydrogen in their cores.
- 03:48: That helium gets mixed through the star, while new hydrogen is brought to the core for fusion.
- 04:20: Just like the Sun, the cores of red dwarf stars shrink and heat up over time.
- 04:37: An interesting thing about red dwarfs is they don't expand as they brighten, unlike more massive stars.
- 04:43: If you increase the energy output but keep the size of the star the same, then you necessarily increase the surface temperature of the star.
- 04:52: This is because the light produced by stars comes from the heat glow of their surfaces.
- 05:42: But as these stars heat up, their spectrum shifts.
- 06:00: ... with the last hydrogen fuel spent, the entire star will become composed of helium and will quietly contract into a helium ...
- 06:26: Well, long before the first red dwarfs approach the ends of their lives, there will be no other living stars left in the galaxy.
- 06:33: ... new Sun-like stars will be born in the Milky Way/Andromeda collision four billion years ...
- 07:19: ... age of the universe, Red dwarfs will surely be the places our own starfaring descendants will wait out ...
- 07:35: Just look at TRAPPIST-1 with its seven terrestrial worlds, two of which are at the right distance from the star to have liquid water.
- 07:43: We don't know yet whether life can evolve around red dwarf stars.
- 08:06: This period could last for up to five billion years, during which the star will shine almost as bright as the Sun and quite a bit hotter.
- 08:15: Those stars will have long-frozen worlds in the outer parts of their solar systems.
- 08:20: Those planets will thaw as their star brightens and may enjoy billions of years of stable warmth.
- 08:38: ... one last long renaissance of life as we huddle in the warmth of the last stars to burn in the darkening end of space ...
- 09:34: Yeah, dark matter is expected to be more evenly spread through the galaxy than things like stars and black holes.
- 10:06: Well, the answer is that we can constrain the size of the Milky Way central black hole, Sagittarius A*, because we can see stars in orbit around it.
2018-04-25: Black Hole Swarms
- 00:24: The stars are so densely packed that the night sky would be 500 times brighter than our own.
- 00:35: It flings nearby stars into extreme slingshot orbits.
- 01:56: And the densest, stellar objects, like black holes, sink to the centers of galaxies or star clusters.
- 02:11: Black holes form when the most massive stars end their lives in spectacular supernova explosions.
- 02:37: Even after blowing off most of their mass in a supernova, these black holes are still heavier than most stars.
- 02:51: As a black hole orbits the galaxy, it tugs on its neighboring stars.
- 02:55: Those stars are accelerated towards the black hole and can gather behind it in a gravitational wake.
- 03:07: The black hole can also slingshot stars outwards, losing momentum in that process, too.
- 03:50: They're like ancient, extremely dense mini-galaxies, containing millions of stars.
- 04:15: Over the life of the Milky Way, they have piled up in the galactic core, forming a giant nucleus star cluster.
- 04:49: Black holes are effectively invisible, but things can be different if a black hole and a companion star are in a binary orbit around each other.
- 04:57: If the companion star gets too close, its outer regions can fall into the gravitational influence of the black hole.
- 05:03: Gas is siphoned off the star into a whirlpool, an accretion disk around the black hole.
- 05:25: By the way, X-ray binaries can also result from a neutron star rather than a black hole cannibalizing its companion.
- 05:35: The brightest X-ray binaries are aggressively gobbling up their companion stars, but that ravenous phase probably doesn't last all that long.
- 05:44: X-ray binaries likely spend most of the time in a quieter phase, with the gas just trickling slowly from the companion star.
- 06:32: Polars are a bit like X-ray binaries, except instead of a black hole or a neutron star, you have a white dwarf with a powerful magnetic field.
- 06:39: ... magnetic fields act like a dam, allowing gas from the companion star to build up and then, fall very suddenly onto the white dwarf, producing ...
- 10:00: Juxtaposed stars asks whether, theoretically, you could build an engine to extract power from gravitational waves via the sticky bead method?
- 11:05: I don't know, maybe a cosmic scale wall of neutron stars with two gaps in it?
2018-04-18: Using Stars to See Gravitational Waves
- 01:07: ... if these black holes formed in the deaths of massive stars, which we think they must, then they should weigh in at between 5 and 15 ...
- 02:34: Of course, the really big recent news was the observation of a neutron star-neutron star merger.
- 02:59: ... what they tell us about neutron stars, more observations like this should allow us to figure out where the ...
- 03:10: ... Italian-based gravitational wave observatory, was online for the neutron star merger, and was extremely important in narrowing down its ...
- 03:35: ... the binary orbits just before merger, which for black holes and neutron stars clocks in at a few to maybe 1,000 orbits per second in the last ...
- 04:34: ... as the faint hum of thousands of binary pairs of white dwarfs, neutron stars, and black holes long before they ...
- 05:41: ... pulsars, neutron stars with jets that sweep past the Earth as the star processes, resulting in ...
- 06:44: Some scientists are even trying to see how gravitational waves should interact with stars.
- 07:21: ... be able to dump some of their energy into matter, for example, into stars. ...
- 07:32: Stars oscillate at particular frequencies.
- 07:38: If a gravitation wave frequency matches the natural resonant frequency of a star, oscillations can be set up inside the star.
- 07:50: The star should then brighten.
- 07:52: ... it may be possible to observe this effect in the dense star fields of galactic cores if those galaxies also contain binary ...
- 08:03: A similar effect may cause white dwarf stars in binary orbits to explode as they absorb gravitational radiation from their own orbits.
2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)
- 01:04: Stars always burn out.
- 05:15: We think it started with a self-replicating molecule similar to RNA.
- 10:10: ... the most random possible state, little eddies of order, like galaxies, stars, planets, and life naturally ...
2018-04-04: The Unruh Effect
- 03:42: Just before they reach my space-time location, that constant acceleration brings them to a halt, and they start moving back in the opposite direction.
2018-03-28: The Andromeda-Milky Way Collision
- 00:33: It's two and 1/2 million light years away and host to a trillion stars.
- 01:35: But being so far away, you can't see individual stars in Andromeda without a good size scope.
- 02:01: In the mid 1700s, he hypothesized that Andromeda was an island universe, a vast sea of stars distant to our own.
- 02:27: The first incontrovertible evidence came when Edwin Hubble calculated its distance by watching the pulsation of stars in Andromeda.
- 02:41: Time the pulsation rate, and you know how luminous the star is.
- 04:32: They mapped the locations of thousands of stars in Andromeda between 2002 and 2010 and compared them to background galaxies.
- 04:40: Then they averaged the observed motion of all of those stars and removed the effects due to the rotation of Andromeda and the motion of the sun.
- 05:06: They used simulations of the gravitational interactions of millions of particles representing groups of stars and dark matter.
- 06:09: Gravitational interactions with stars slingshots those stars into larger orbits or even completely out of the galaxy.
- 06:20: When those black holes are around a light year apart, they'll start losing orbital energy to gravitational waves.
- 06:37: There's also a chance that gas throughout the galaxy will be shocked into a storm of new star formation.
- 06:52: Well, for one thing, we don't expect any collisions between stars.
- 06:56: The average distance between stars is around 100 billion times greater than the average size of a star.
- 07:03: There's a higher chance of another star passing inside Neptune's orbit, which might cause some gravitational disruption.
- 08:37: ... our dynamical evolving universe, when we have a neighbor whose visible stars revealed its great distance, and whose spiral structure helped us guess ...
- 09:15: Last week, we talked about a stunning new result in astrophysics, the detection of the first stars to ever form.
- 09:40: ... the radio signal from the whole sky to measure their signal of the first stars. ...
- 09:49: ... the sky and so create images of the structures in which those first stars were forming, presumably some sort of proto-galactic ...
2018-03-21: Scientists Have Detected the First Stars
- 00:00: [MUSIC PLAYING] What do the first stars in the universe, dark matter, and superior siege engines have in common?
- 00:28: That's the case with the recent discovery of the earliest stars in the universe.
- 00:34: In a nature paper published just a few weeks ago, Judd Bowman and collaborators, report a signal from the very first stars to form in our universe.
- 02:11: At least to start with.
- 02:13: Before long, some of that early hydrogen gas collapsed to form the very first stars, long before the first galaxies formed.
- 02:20: ... ultraviolet light from those stars shifted the equilibrium so that the electron spin temperature became ...
- 02:38: ... a while, the first black holes formed, and started to spew out x-rays, as they gobbled up hydrogen. This heated the gas and ...
- 04:03: That period represents the time between the birth of the very first stars to the onset of very active black hole growth.
- 06:26: In both cases, the trebuchet counterweight started at the same height and also, reached the same height at the end of its swing.
- 06:41: To answer this, we need to know how much of the counterweights starting potential energy ends up in the projectile.
- 06:49: We know that the counterweights height in both shots was the same at the start and at the end of the swing.
- 07:47: ... only things you needed to know where the starting and final heights of the counterweight and projectile and the mass of ...
2018-03-15: Hawking Radiation
- 00:50: ... places of extreme density like the dead core of a massive star, space and time could be dragged inwards to create a hole in the ...
2018-03-07: Should Space be Privatized?
- 06:17: Then, there's Russian billionaire Yuri Milner with his breakthrough Starshot Program.
- 06:23: His seed funding may put the first robotic probe in another star system.
- 09:34: The future of human space travel is starting to look promising.
- 10:19: Roman, we're channeling your contributions towards starting our own aerospace company.
- 10:23: We'll start small, maybe a skateboard tied to a weather balloon and work up to launching sportscast to the asteroid belt. Baby steps, right?
- 10:37: Stimuli asked why stars get brighter as they age if their fuel is depleting.
- 10:54: In fact, to support the increased gravitational crush of the smaller core, the fusion rate has to be even higher than when it started.
- 11:02: [INAUDIBLE] wants to know how the least mass of stars, red dwarfs, die.
- 11:12: That means new hydrogen flows down to the core, while the helium produced in core fusion is mixed through the star.
- 11:36: But by the time a red dwarf finishes using its fuel, the entire star is made of helium.
- 11:42: When fusion switches off, the star contracts, until electron degeneracy pressure stops the collapse.
- 12:04: ... stars consume their fuel thousands of times more slowly than the sun, which ...
- 12:18: ... their frictionless trebuchets in a vacuum, while Don Sample suggests we start by assuming a spherical ...
2018-02-28: The Trebuchet Challenge
- 01:06: Before we get started, you should pause here and watch the previous episode if you haven't already.
- 01:31: The change in speed for a given object will be the same as long as the start and end points are the same.
- 07:40: It's enough to know the start and end locations of the counterweight and projectile, along with their masses.
2018-02-21: The Death of the Sun
- 00:21: In just a moment, our star will fuse the last of the hydrogen in its core, triggering a cataclysmic sequence of events.
- 00:43: Like living things, stars have a life cycle.
- 01:02: How a star dies depends on its mass.
- 01:09: The most massive stars live only for hundreds of thousands to millions of years, and die in spectacular explosions called supernovae.
- 03:52: While the stars outer layers of hydrogen are expanding and cooling, the core continues to collapse until it hits a quantum mechanical limit.
- 04:57: The entire star dims and shrinks to around 10 times the current radius.
- 09:18: ... sports cars and, perhaps, safer vessels to the planets and even to the stars. ...
2018-02-14: What is Energy?
- 03:22: It starts moving up with the same speed and kinetic energy it landed with.
- 04:42: As long as the ball ends up back where it started, it will always have the same combination of kinetic and potential energy as when it left.
- 12:10: Help support pull the series, and start your free trial by clicking on the link below or going to thegreatcoursesp lus.com/spacetime.
- 12:19: In our recent Space Time journal club, we talked about the discovery of the amazing Chronos, the planet eating star.
- 12:28: Sebry asked whether it's possible for different parts of a star-forming nebula to have different ratios of elements?
- 12:40: These star-forming clouds can vary in metallicity across their vast widths, which are often hundreds of light years.
- 12:58: ... out that 15 Earth masses of terrestrial material is a lot a planet for a star to consume, at least compared to our solar system, which only has little ...
- 13:14: In other star systems, we frequently see one or more super-Earths with several Earth masses each.
- 13:24: And that's around a tiny red dwarf star.
2018-01-31: Kronos: Devourer Of Worlds
- 00:00: ... PLAYING] A team of scientists recently discovered a star that appears to have consumed its own planets like some sort of ...
- 00:41: It's here that stars are born.
- 00:45: So in short, essentially all stars form in these stellar nurseries.
- 00:58: And we have no idea where its sibling stars might be.
- 01:02: However, if the gravitational connection between a pair of stars is strong enough, they might be ejected from the cluster as a binary pair.
- 01:12: Around half of all stars are binaries.
- 01:14: Binary stars typically have the same chemical composition as each other, having formed from the same cloud.
- 01:32: These wide binaries are actually extremely useful tools for understanding star formation and the environment of the galaxy they live in.
- 01:49: ... numbers of near-invisible stellar objects like black holes and neutron stars, as well as the distribution of gas and dark ...
- 02:06: They also allow us to test to what degree stars that formed in the same cloud share a chemical signature.
- 02:26: They're so, well, widely separated that it's hard to tell if a given pair of stars is actually gravitationally bound.
- 02:52: They identified plenty of stars that are close enough together that they could be gravitationally bound.
- 03:10: ... how the team came upon HD240430 and HD240429, Kronos and Krios, two stars nearly two light-years apart from each other, about 326 light-years from ...
- 03:24: They're both G-type stars like our sun.
- 03:29: The stars' velocities tell us that they're moving in lockstep together around the galaxy.
- 03:49: Stellar spectra are thick, with sharp emission and absorption features that result from electron transitions in atoms in the star's atmosphere.
- 03:57: And the strength of these lines can tell us the relative abundance of non-hydrogen and helium elements within the star.
- 04:04: In astro-speak, they tell us the star's metallicity, although for an astronomer, anything heavier than helium is called a metal.
- 04:43: These stars definitely formed from the same molecular cloud.
- 05:24: The extra elements found in Kronos are pretty much exactly what you'd expect from a star nomming on a bunch of terrestrial planets.
- 05:54: The researchers tested the hypothesis by throwing a bunch of Earth-like planets into a sun-like star-- mathematically, I mean.
- 06:18: Lithium gets depleted in the early years of stars like the sun.
- 06:27: Kronos has an unreasonably high lithium abundance for a star of its age, while Krios has the expected amount.
- 06:51: We now know that binary stars can have very different metallicities to each other.
- 07:02: Well, computer simulations of planet formation do show that planets can fall into their home stars.
- 07:08: ... between planets or if the gas giant is perturbed by a passing star into an elliptical ...
- 07:30: And it may also reveal other planet-eating stars, which will shed light on the whole planet formation process.
- 07:57: ... of you mentioned the idea of star lifting, of actually reducing the mass of the sun to reduce its ...
2018-01-24: The End of the Habitable Zone
- 01:00: All stars brighten as they age and they deplete their fuel.
- 01:06: Why does less fuel mean a brighter star?
- 01:53: But as soon as that starts to happen, the drop in energy production disrupts the delicate balance between outward pressure and gravity.
- 02:30: So over time, the sun's core shrinks and heats up, brightening the entire star.
- 05:48: But planet surface temperature and the location of the habitable zone depends on the planet's atmosphere as well as the star's brighteners.
- 10:09: To really gain intuition about our often very unintuitive universe, you need to start solving problems in physics, math, and astronomy.
2018-01-17: Horizon Radiation
- 01:34: ... laws of physics shouldn't change if we go near a black hole or if we start accelerating, but enforcing this isn't automatic, and something has to ...
- 06:59: Now it starts out with no oscillations, analogous to the vacuum state in quantum field theory.
- 12:28: Last week, we talked about the sounds that stars make-- the wonderful worlds of helio and asteroseismology.
- 12:38: Loki and Alex ask whether seismic activity in neutron stars can be used to probe their interior properties.
- 12:46: Neutron stars certainly seem to experience star quakes-- massive releases of energy, as the star's ion crust cracks.
- 12:56: Extremely large quakes can set the entire star ringing, which is observable in its effect on the extremely regular flashes of its pulsar jet.
- 13:11: Several of you asked where the sounds of stars we played at the end of the last episode came from.
- 13:32: The frequency spectra for resonant oscillations of several stars were shifted to a range audible to human hearing.
- 13:44: ... Justice, No Peace wonders whether stars may actually be speaking, considering Penrose's quantum brain ...
- 14:30: Second, stars aren't complex in the sense that Penrose means.
- 14:45: All that said, I love the idea of stars twinkling meaningfully at each other from across the galaxy.
2018-01-10: What Do Stars Sound Like?
- 00:08: Twinkle, twinkle little star, how I wonder about your interior structure and dynamical properties.
- 00:14: Believe it or not, we can now map the interiors of stars by listening to their harmonies as they vibrate with seismic waves.
- 00:22: [MUSIC PLAYING] Stars are among the best understood objects in astrophysics.
- 00:49: ... the core, the way energy flows to the surface, and even the life span of stars. ...
- 01:00: These models are largely built around what little we can learn from the light we receive directly from the surface of stars.
- 01:13: Well, we may not see light from beneath the stellar surface, but another type of wave travels freely through stars.
- 01:23: You see, stars have a dynamical complexity far exceeding the simplest predictions of the equations describing stellar structure.
- 01:33: ... oscillations, natural resonant frequencies that carry information about stars impenetrable ...
- 01:44: Stars ring like bells.
- 01:54: The fast-growing field of asteroseismology uses these oscillations to probe the interiors of the distant stars.
- 02:03: When we try to understand other stars, we always start with our sun.
- 02:07: While the distance stars are infinitesimal points of light to even our best telescopes, the surface of the sun can be resolved in incredible detail.
- 02:20: Understanding asteroseismology starts with understanding helioseismology.
- 02:27: Understanding helioseismology starts with regular old seismology on earth-- geoseismology.
- 02:46: Stars also support p-waves.
- 02:53: Because stars are fluid rather than solid, they don't support shear waves.
- 03:14: In stars, these waves occur below the surface, g-waves, and on the surface, f-waves.
- 03:24: However, it's the pressure waves-- the p-waves-- that really dominate in stars like the sun.
- 03:30: ... acoustic waves are generated by turbulence just below the surface of a star, just as seismic waves on earth are created by earthquakes just below the ...
- 03:41: They start as traveling waves that can move throughout the stars in a structure.
- 03:45: ... wave feeds its energy into standing pressure waves that cause the entire star to ...
- 03:58: These p-mode oscillations follow the rules of spherical harmonics, taking the form of regular patterns of density oscillations throughout the star.
- 05:13: ... many overlapping modes form complex oscillations on the surface of the star, but these can be deconstructed into simple sinusoidal oscillations, each ...
- 05:29: Helio- and asteroseismology are all about determining and modeling the resident modes within a star.
- 05:35: See, the nature of these modes depends on the internal structure, specifically on how the speed of sound changes throughout the star.
- 05:48: The internal rotation of the star is also a key factor.
- 06:46: Seismological studies of distance stars-- asteroseismology-- is much more difficult.
- 07:17: ... red giant stars, asteroseismology has been used to determine the fusion activity in their ...
- 07:45: Future planet hunting satellites, like Tess and Plato, will continue this work with higher precision and for many more stars.
- 07:52: Most stellar seismology is focused on learning about the average global structure of stars.
- 08:41: Stars sing.
- 09:04: Twinkle, twinkle little star, and in doing so, you give up your secrets.
- 09:09: Because the science of asteroseismology can now translate the messages of stars twinkling at us from across space time.
- 09:32: To really gain intuition about our often very unintuitive universe, you need to start solving problems in physics, math, and astronomy.
- 11:24: Because there are no stars that could possibly explode that way for hundreds of light years.
- 11:45: GRBs from exploding stars are estimated to have jets with conical opening angles of between 2 and 20 degrees.
- 12:39: In fact, the magnetic field of a gamma ray burst focuses charged particles-- electrons and the nuclei of the exploding star.
2017-12-20: Extinction by Gamma-Ray Burst
- 00:53: Hopefully, our super advanced and probably not-quite-human descendants will be able to escape those by traveling to other star systems.
- 01:01: ... collision with Andromeda, or the final burning out of the last stars, or the evaporation of the last black hole and decay of the last ...
- 01:17: ... get to each of these inevitable cosmic catastrophes, but let's start with the one that could happen any time-- a supernova or gamma-ray burst ...
- 02:05: ... being blasted by the intense radiation jets from a distant exploding star. ...
- 02:34: As many of you know, a supernova is the explosion that follows the catastrophic collapse of a massive star at the end of its life.
- 02:41: Now, some won't die that way, but any star more than around eight times the Sun's mass will.
- 03:03: It's even more dangerous if the star was rapidly rotating before it exploded.
- 03:25: The observed faint flash of gamma rays from exploding stars can last anywhere from a couple of seconds to a few minutes.
- 03:34: Short-duration bursts that last less than two seconds are caused by merging neutron stars.
- 06:29: Also, extinctions appear to have started before that ice age really got under way.
- 06:36: Extinction started due to the sudden UV exposure and continued due to climate change.
- 06:50: ... on the rates of GRBs we see in other galaxies and on the population of stars in the Milky Way, it's estimated that every billion years, Earth finds ...
- 07:17: This is a Wolf-Rayet star, WR 104.
- 07:20: It's a massive star in the last phase of its life, currently blasting off its outer shells into a pinwheel-like nebula.
- 07:27: The exposed inner star shines several times hotter and hundreds of thousands of times brighter than the Sun.
- 07:34: This star is part of a binary system, and it's this binary orbit that produces the spiraling nebula.
- 07:48: The rotational axis of the star will define the direction of the jet in the event that this Wolf-Rayet star does produce a gamma-ray burst.
- 08:11: Although, it's hard to tell exactly how close a star like this is to exploding.
- 08:26: It's the star's rotational axis that defines the direction of the jet.
- 08:30: But the orbital axis of a binary system and the rotational axis of its stars are often correlated, so we may have dodged a bullet in this case.
- 08:53: There are definitely no stars in that range that could explode anytime soon.
- 11:53: ... asks whether there's a chance that some stars/solar systems will be ejected from the galaxy when the Milky Way collides with ...
- 12:16: And some stars will be sling-shotted out of the galaxy by the two supermassive black holes of Andromeda and the Milky Way as they fall together.
2017-12-13: The Origin of 'Oumuamua, Our First Interstellar Visitor
- 00:36: ... discovery was made by Pan Starrs, the panoramic survey telescope and rapid response system, a group of ...
- 04:44: Now objects falling in from these regions, like comets, only pick up enough speed to bring them back to where they started.
- 05:18: So, hypothesis number two is that the object was ejected and flung towards us from a nearby star system.
- 05:25: PZ 17 performed more computer simulations to rewind the motion of both Oumuamua and the 3,700 stars within 100 light years of the sun.
- 05:35: They found that the object passed through the Oort cloud of another star, the unpoetically named TYC4742-102701 around 1.3 million years ago.
- 05:47: ... its speed relative to that star would have been over 100 kilometers per second, higher than the escape ...
- 06:38: Given how many stars there are, there should be a ton of asteroidal objects floating around in interstellar space.
- 07:11: ... that we've found so far, and on the volume of space scanned by Pan Starrs, PZ 17 extrapolate to estimate the density of the debris ...
- 07:23: ... have seen this one object in the five years we've been watching with Pan Starrs, there must be roughly 700 trillion objects per cubic parsec in the solar ...
- 07:49: The main reason we've only spotted one so far is that most don't get close enough to the earth for Pan Starrs to detect.
- 08:02: But even then, Pan Starrs was only just able to spot it.
- 08:30: LSST will be able to see objects around 14 times fainter than Pan Starrs.
- 08:53: Its trajectory we'll send it towards the constellation Pegasus, perhaps to find a new star system there to visit.
2017-12-06: Understanding the Uncertainty Principle with Quantum Fourier Series
- 02:16: To understand the origin of the uncertainty principle, we don't need to know any quantum mechanics, at least not to start with.
- 12:08: Help support the series and start your free one-month trial by clicking on the link below or going to the greatcoursesplus.com/spacetime.
- 13:13: ... kill time during warp journeys by scanning light curves of distant stars for the characteristic dips in brightness due to transiting alien ...
2017-11-29: Citizen Science + Zero-Point Challenge Answer
- 00:33: ... astronomer, he discovered Uranus and was the first to observe binary star systems, among other ...
- 01:05: ... sky, spotting things like comets and supernovae or monitoring variable stars. ...
- 01:52: These exploding stars show up as transient point of light, typically in very distant galaxies.
- 02:20: ... American Association of Variable Star Observers, founded in 1911, has generated an archive of variable star ...
- 02:32: This international database houses over 20 million variable star brightness measurements dating back over 100 years.
- 02:39: ... started with this sort of citizen science takes a bit of dedication and cash, ...
- 04:19: ... ninth planet, as well as looking for brown dwarfs-- cool, faint, failed stars-- that live, well, right now in ...
- 05:08: This all started with the City at Home program, which looks through radio data for signs of signals from intelligent life.
- 05:15: But there's also Einstein at Home, which searches for LIGO gravitational wave data for signals produced by rotating neutron stars.
- 05:21: And Milky Way at Home, which generates 3D dynamical models of streams of stars using data from the Sloan Digital Sky Survey.
2017-11-22: Suicide Space Robots
- 00:35: But we have few qualms about sending robots on one-way suicide missions to the stars.
- 09:17: After that, Voyager 1 will meet its very lonely doom, perhaps floating forever in the coldness between the stars.
2017-11-08: Zero-Point Energy Demystified
- 02:00: Let's start with the physics.
2017-11-02: The Vacuum Catastrophe
- 10:55: ... zero point energy or dark energy, like with the zero point modules in "Stargate." The answer is absolutely ...
2017-10-25: The Missing Mass Mystery
- 00:18: ... full of hundreds of billions of galaxies, each of them with as many stars. ...
- 00:33: The shining light of these stars illuminates or is conspicuously absorbed by gas and dust within those galaxies.
- 01:12: Yet, what if I told you that all of the stars and galaxies and galaxy clusters only comprise 10% of the light sector?
- 02:38: It's the stuff of stars, planets, gas, dust, you, me.
- 03:23: ... today tells us that there should have been 10 times as much hydrogen to start with than we actually see today in galaxies and ...
- 10:35: As those baryons fall into the dense nexuses of the cosmic web, they'll feed galaxies with material to form new stars.
- 10:44: In fact, this verifies that the epoch of star formation in our universe is far from over.
- 12:37: TS1336 was expecting last week's episode to be about the discovery of gravitational waves from merging neutron stars.
2017-10-19: The Nature of Nothing
- 12:22: Help support the series and start your free one-month trial by clicking on the link below, or going to thegreatcoursesp lus.com/spacetime.
2017-10-11: Absolute Cold
- 07:53: We never would've guessed we'd reach this point when we started making Space Time early in 2015.
- 09:21: Well, the answer is stars, lots and lots of stars.
- 09:25: The density of stars in the Milky Way core is around 100 times that of the Milky Way disk.
- 09:31: ... also expect there to be a good number of stellar remnants, like neutron stars and black holes, that have fallen towards the center from the ...
2017-10-04: When Quasars Collide STJC
- 00:08: Red giant stars incinerate planetary systems, but neutron stars cannibalize their red giant neighbors.
- 00:15: And stellar mass black holes rip neutron stars to shreds.
- 01:36: Now, we've he talked about the black hole that form in the deaths of massive stars.
- 01:40: They start with masses of up to 10 or so Suns.
- 01:59: Did they get most of their mass from eating gas and stars from their surrounding galaxy?
- 07:30: Basically, the black holes slingshot stars outwards through gravitational interactions.
- 07:51: However, by the time the black holes are only a few light-years apart, there shouldn't be any stars left in between them.
- 09:54: However, careful observations of the stars in the galaxy can help us figure out the masses of the black holes and look for signs of galaxy mergers.
- 12:27: WispXLegend asks where a 15-year-old Australian should start to pursue a career as a physicist.
- 12:49: Start a Bachelor of Science degree someone with a decent physics program.
2017-09-28: Are the Fundamental Constants Changing?
- 10:13: The stars themselves would never have formed.
- 10:16: It might seem lucky that Alpha is fine tuned for a universe with the warmth of stars, and a rich and complex chemistry-- both essential for life.
- 10:25: ... surprising that we find ourselves in a part of the universe conducive to stars, and to planets, and to ...
- 12:09: Help support the series and start your free one month trial by clicking on the link below, or going to the TheGreatCoursesP lus.com/SpaceTime.
- 14:34: A few of you noticed that star shades look a lot like Thargoids from Elite Dangerous.
2017-09-20: The Future of Space Telescopes
- 01:14: ... rocky planets like our Earth-- are extremely common and may orbit most stars in the Milky ...
- 01:27: ... and water, terrestrial planets tend to form close to their parent star. ...
- 01:49: So how can we find a terrestrial planet around a star light years away?
- 01:55: Maybe it's simple-- blot out the star.
- 01:58: ... decades with the coronagraph, a disk inside a telescope that occludes a star, blocking its light so that any planets can be seen more ...
- 02:21: This means it's never possible to completely block the star's light.
- 02:24: ... of objects from 100,000 to a million times fainter than the central star, but no where near the factor of 10 billion difference between the Earth ...
- 02:36: In 2005, Dr. Webster Cash proposed a successor to the coronagraph-- the starshade.
- 02:43: It's actually a spacecraft outfitted with thrusters to align itself between a space telescope and a star.
- 02:50: ... starshade will be up to 50 meters in diameter and hover 80,000 kilometers in front ...
- 02:59: At that distance, the starshade acts like an artificial eclipse.
- 03:09: But the starshade goes much further.
- 03:27: The number and length of pedals optimizes each starshade for a particular wavelength of light.
- 03:46: The main motivation for building starshades is to suppress the glare of stars enough to see the planets that orbit them.
- 03:54: Configured right, glare is suppressed by a factor of 10 billion at 50 milliarcseconds from the star.
- 04:08: There are a couple of thousand stars within that range, and hundreds of sun-like stars, many of which certainly have Earth-like planets.
- 04:18: With the starshade, we may soon directly observe terrestrial exoplanets with cameras and spectrographs.
- 04:30: Besides Earth-like exoplanets, the starshade would also be an enormous help in studying quasars and other high-contrast phenomena.
- 04:39: The first starshade may launch with NASA's WFIRST mission in the 2020s for a budget of around $750 million and a runtime of five years.
- 05:00: Oh, and one starshade could theoretically serve multiple telescopes.
- 07:41: ... and even map the cloud structure of a gas giant, especially if you add a starshade to the aragoscope-- because why ...
- 08:15: So it would be an independent spacecraft, just like the starshade.
- 09:49: Results probably won't top those of the magnificent starshade and aragoscope, but the orbiting rainbow is cheap.
- 11:00: ... had detected gravitational waves from the merger of a pair of neutron stars. ...
- 11:11: Kai Whitman would like to know what would happen if a black hole merges with a neutron star.
- 11:19: The neutron star would be totally disrupted when it got very close to the black hole, producing a blast of observable radiation.
- 11:52: Feinstein 100 asks whether a black hole forming in the death of a massive star first goes through a neutron star-like phase.
- 12:00: Well, in a way, yes, but it's never actually a neutron star.
- 12:04: The final phase of the core of such a star is a giant ball of nickel and iron, held up briefly by electron degeneracy pressure.
- 12:33: During that collapse, the core looks more and more like a neutron star, basically a giant ball of neutrons with the density of an atomic nucleus.
- 12:42: ... a neutron star holds this collapse, when they hit neutron degeneracy pressure, the most ...
- 12:56: So it's reasonable to imagine that neutron star-like conditions exist extremely briefly before the event horizon forms.
- 13:14: [INAUDIBLE] wants to confirm that the gold in their ring may have been created in the collision of two neutron stars.
- 13:25: And if not merging neutron stars, then it was likely a supernova explosion.
- 13:29: So yeah, your ring was forged in the death of a star or the birth of a black hole.
2017-09-13: Neutron Stars Collide in New LIGO Signal?
- 00:15: ... time spotted gravitational waves from the collision of a pair of neutron stars. ...
- 01:04: As the data comes in, we're learning a ton about black holes, how they grow, and the stars that produce them.
- 01:15: LIGO was supposed to also detect some other crazy stuff like certain types of supernova explosion and the merger of binary neutron stars.
- 01:27: ... abound that LIGO has finally spotted the long expected neutron star, neutron star merger, and that the event was accompanied by a bright ...
- 01:45: ... about the supposed signal at all, let's refresh our memory on neutron stars. ...
- 01:54: When a massive star ends its life in a supernova explosion, it leaves behind an ultra dense core.
- 02:00: For the most massive stars, that core will collapse into a black hole.
- 02:06: A remnant core between 1.4 and around 3 times the mass of our sun instead ends up as a neutron star.
- 02:14: These insane objects carry the mass of a star within a sphere the size of a city, around 18 kilometers in diameter.
- 02:39: ... stars can rotate up to thousands of times per second and have enormous ...
- 03:01: This was the Hulse-Taylor binary, two neutron stars in orbit around each other, one of which is visible to us as a pulsar.
- 03:17: And that gravitational radiation sucks energy from the orbiting system, causing the neutron stars to spiral inwards.
- 03:25: By monitoring the pulses of one of those stars, this inspiral was measured.
- 03:38: Any neutron stars or black holes in close orbit with each other will eventually collide as they leave gravitational radiation.
- 03:46: We now know of plenty of neutron star pairs in binary orbits.
- 03:56: Well, because the universe makes far more neutron stars than black holes.
- 04:00: See, black holes only form in the deaths of the most massive stars, those over approximately 20 times the Sun's mass.
- 04:09: But these are also the rarest of stars.
- 04:12: Neutron stars form from the not quite as rare stars of around 8 to 20 solar masses.
- 04:18: That means neutron stars should be more common than black holes and neutron star binary systems should merge more often than black whole binaries.
- 04:32: The remnant core of a dead star must be less than 3 solar masses to make a neutron star.
- 04:49: In fact, a typical neutron star merger needs to be about 10 times closer to us than a typical black whole merger for LIGO to be able to see it.
- 04:59: If we can see neutron star mergers only out to 1/10 the distance, then that translates to being sensitive to 1/1,000 of the volume.
- 05:10: We can see black hole merges across 1,000 times more universe compared to neutron star mergers.
- 05:25: Neutron star mergers do have one advantage over black hole mergers.
- 05:37: ... only hit that range in the final second before merger, while neutron stars ring at audible gravitational wave frequencies for at least several ...
- 05:48: If we did spot a neutron star merger as rumored, we'll have a lot more juicy data to analyze compared to a black hole merger.
- 05:59: It was started by a tweet from astronomer J Craig Wheeler about a LIGO detection with an optical counterpart.
- 07:01: But around 30% of them, the short-lived ones which last for less than 2 seconds, are believed to come from merging neutron stars.
- 08:03: We rarely see supernovae from this galaxy type because their most massive stars have long since exploded to leave neutron stars and black holes.
- 08:12: But that makes them the perfect environment for neutron star mergers.
- 08:16: NGC 4993 is 130 million light-years away, which is about at the limit for LIGO sensitivity to neutron star mergers.
- 08:36: Well, beyond raw curiosity, it may be that neutron star collisions produce many of the heavier elements of the periodic table.
- 09:02: But it turns out that merging neutron stars can do this too.
- 09:07: As these stars coalesce, most of their material goes into forming a new black hole.
- 09:12: But the neutron stars' thin iron crust is likely bombarded with neutrons and blasted outwards, spraying a ton of r-process elements into the galaxy.
- 09:22: Depending on how much of the outer layer is ejected, neutron star mergers could produce most of the heavy r-process elements that exist.
- 09:32: Seeing a gravitational wave signal from merging neutron stars would allow us to determine pretty exactly how much mass is lost in the merger.
- 09:49: Besides their importance to nucleosynthesis, the simple fact that we can see neutron star mergers in regular light is extremely powerful.
- 10:06: But colliding neutron stars are bright across the electromagnetic spectrum.
- 10:35: ... more black hole, black hole mergers in addition to this rumored neutron star ...
- 12:22: ... arrangements for half a planet's worth of gold from the next neutron star merger to be shipped directly to your address, priority ...
- 12:59: Well, the answer is no, thank the stars.
- 14:10: That method is to watch the effect on the parent stars' light as it passes through the planet's atmosphere.
- 14:16: And for that to happen, the planet needs to pass directly in front of its star from our perspective.
- 14:38: ... found by the Doppler method, which can measure the tiny wobble in a star's motion caused by the planet's gravitational ...
- 15:39: No wonder he's such a Star Trek fan.
2017-08-30: White Holes
- 03:49: Now, a real black hole forms from the gravitational collapse of a massive star's core.
- 03:55: ... singularity comes into being, and in the past, well, there's just a star, but what does this idealized eternal black hole look like in the ...
2017-08-24: First Detection of Life
- 00:25: Now, a quarter of a century later, we're on the verge of conducting that same experiment on a world orbiting another star.
- 06:44: ... however this experiment gives us a roadmap for what to look for in other star systems, decades before it became possible to do ...
- 07:03: Programs like Breakthrough Starshot, as discussed in this video, promise the first close-up observations of a new world in several decades time.
- 07:26: To be more precise, we analyze the light of a distant star as it passes through the atmosphere of one of its planets.
- 07:33: This only happens for transiting exoplanets, those that happen to be aligned so that they pass in front of their parent star from our point of view.
- 07:42: ... a tiny fraction of the star's light passes through the planet's atmosphere when this happens, but by ...
- 07:55: ... hot Jupiter, a gas giant, even larger than Jupiter, that orbits its star closer than the orbit of ...
- 08:06: The parent star was observed using the Hubble and Spitzer Space Telescopes during a transit.
- 08:37: We've even started to look at super-Earths, like in 55 Cancri e, detecting hydrogen and helium.
- 09:32: This is facilitated by the fact that the star itself is very dim, making subtraction of its light easier.
- 09:38: Three of these worlds-- e, f, and g-- lie in the habitable zone, the distance from the star where liquid water is possible.
2017-08-16: Extraterrestrial Superstorms
- 01:22: In fact, let's start with those found on Earth.
- 12:51: Start moving upwards and end moving downwards.
2017-08-10: The One-Electron Universe
- 05:27: ... invert the parity, reverse time-- a particle should end up back where it started. ...
- 05:37: But if you just flip the charge and in parity-- so do a CP transformation-- you still have to reverse time again to get back where you started.
2017-08-02: Dark Flow
- 00:26: Planets orbit stars.
- 00:28: Stars orbit within galaxies.
- 03:33: And actually, let's just start with the regular old thermal Sunyaev-Zeldovich effect.
- 12:14: Squid Master started studying physics and got a tattoo of a Feynman diagram, then switched majors to economics.
2017-07-26: The Secrets of Feynman Diagrams
- 02:55: This is where we start to see the power and simplicity of this approach.
- 07:47: To start with, each of the particle paths are actually infinite paths.
- 14:07: ... inexcusable failure to nickname the Strategic Defense Initiative not Star Wars, but Ronald ...
2017-07-19: The Real Star Wars
- 00:33: ... us, science was making incredible bounds, and our sights were set on the stars. ...
- 04:02: But if we're talking about satellite weapons platforms, we should talk about Star Wars.
- 05:45: So a powerful x-ray laser needs to start with a powerful x-ray source.
- 06:18: ... media derisively nicknamed the Strategic Defense Initiative "Star Wars." It absorbed many hundreds of millions in funding from 1983 to ...
- 13:38: Help support the series and start your free one-month trial by clicking on the link below, or going to thegreatcoursesp lus.com/spacetime.
2017-07-12: Solving the Impossible in Quantum Field Theory
- 05:18: And this is where Feynman diagrams start to come in handy, because they keep track of the different families of possibilities.
- 10:05: ... of trying to start with the unmeasurable fundamental mass of the electron and solve the ...
2017-07-07: Feynman's Infinite Quantum Paths
- 06:44: The length of the arrow connecting the start and the end of this chain represents the total probability from all paths.
- 09:26: Let's not even get started with the complexity of two or more particles interacting.
- 12:49: And this is a really great way to simultaneously support the show and to not burn your eyes out staring at the sun.
2017-06-28: The First Quantum Field Theory
- 01:55: Now before we start thinking about vibrating quantum fields or even fields at all, let's talk about vibrations.
- 04:51: Quantum physics may have started with Planck's discovery of the quantum nature of light.
- 13:12: Help support the series and start your free one-month trial by clicking on the link below or going to TheGreatCoursesP lus.com/SpaceTime.
- 13:44: In fact, Schrodinger followed the same approach, starting with Einstein's mass energy momentum equation.
2017-06-21: Anti-Matter and Quantum Relativity
- 03:00: The discovery of quantum spin starts with an Austrian physicist named Wolfgang Pauli.
- 04:51: In a way, he started with relativity.
- 11:33: Premium membership includes unlimited access to thousands of classes and is available starting at $10 a month.
- 11:53: This is so cool because it shows us how to produce beautiful starscape photographs using some pretty simple camera equipment.
2017-06-07: Supervoids vs Colliding Universes!
- 06:03: ... of the cold spot all the way out to the point where dark energy started to dominate the ...
- 06:38: McKenzie et al. also observed a control region, G23, in the direction of the star [INAUDIBLE]..
- 09:18: At that point, it stops inflating and starts expanding normally.
- 12:10: Last week we talked about the mysterious population three stars, the very first generation of stars that appeared soon after the Big Bang.
- 12:22: A few of you asked about looking back into the old universe to find population three stars, and that is indeed where we focus our search.
- 12:41: And we need the largest telescopes in the world to even detect the entire galaxy, let alone any individual stars.
- 12:48: ... measure the metallicity of a star or a galaxy, you need to be able to split the light into a spectrum and ...
- 13:04: Right now, efforts are focused on computational modeling of populations of stars to predict the overall light that we expect to come from a galaxy.
- 13:13: Add population three stars to those models and the light looks very different.
- 13:17: [INAUDIBLE] et al., 2015, found a galaxy in the old universe whose light is very hard to explain without a lot of pop three stars.
2017-05-31: The Fate of the First Stars
- 00:05: Soon after the Big Bang, the first generation of monstrously large stars ignited, lit up the universe, and then died.
- 00:24: These were the stars of population three.
- 00:39: In its light, we see telltale signs of the generations of stars that came before it.
- 00:45: See, the sun and all stars are made of the raw material forged in the heat of the Big Bang itself-- hydrogen and helium, mostly.
- 01:01: ... elements were forged in the cores of earlier generations of stars-- stars that exploded as supernovae, and spread their element-enriched ...
- 01:19: Astronomers categorize stars according to the relative quantity of heavy elements that they possess.
- 01:30: And the relative quantity of metals versus hydrogen and helium is a star's metalicity.
- 01:36: Stars that formed will recently tend to have the highest metalicities, because they contain the dust of more stellar generations past.
- 01:45: We divide stars up into three populations.
- 01:47: The sun is a population one star, meaning 2% to 3% of its mass is metals.
- 01:54: Pop one stars formed the most recently, and are still forming today, typically in the disks of spiral galaxies.
- 02:02: Population two stars are metal pore, with metalicities around 0.1% or even lower.
- 02:08: These are the oldest stars that we see in the Milky Way.
- 02:18: Today, they're found in the galactic bulge or in globular clusters, which are ancient, dense islands of stars that orbit far out in the galactic halo.
- 02:27: Population three stars have no heavier elements whatsoever.
- 02:32: ... were the first ever stars, shining in the first ever proto galaxies, born of the pristine hydrogen ...
- 02:59: We're starting to think they may be all long dead.
- 03:08: Except that the longest lived stars-- red dwarfs-- have lifespans of trillions of years.
- 03:17: Even stars a little smaller than our sun-- the orangish K-type stars-- live for longer than the current age of the universe.
- 03:25: Star lifespan gets shorter the more massive the spar.
- 03:31: But stars of the sun's mass and higher that formed over 13 billion years ago, near the beginning of the universe, would now be long gone.
- 03:53: Before we get to why pop three stars were so large, let's unravel this whole lifespan thing.
- 03:59: Massive stars live fast, die young, and leave beautiful space-time warping corpses.
- 04:05: One might think that having more mass-- more hydrogen to fuse in their cores-- would allow a star to burn longer.
- 04:17: And these stars burned so very, very brightly.
- 04:20: OK, physics time-- the cores of stars are under extreme pressure due to the gravitational crush of their great mass.
- 04:34: So the cores of very massive stars are much hotter than our suns-- up to a couple hundred million Kelvin, versus the sun's 15 million K.
- 04:58: A star 10 times the mass of the sun shines around 10,000 times brighter.
- 05:15: ... the smallest population three stars would have had masses of at least several times that of the sun, while ...
- 05:26: By comparison, the most massive lighter stars are, at most, a couple of hundred solar masses.
- 05:33: With masses that high, all population three stars would have gone supernova while the universe was still in its infancy.
- 05:40: So why do we think the first stars were so massive?
- 05:44: Well, based on our understanding of how stars formed, they must have been.
- 05:52: Stars form when vast clouds of mostly molecular hydrogen collapse under their own gravity.
- 06:12: To collapse into stars, clouds have to cool.
- 07:17: At that point, the contraction is much slower, and those cloud fragments become stars.
- 07:44: The result is much larger cloud chunks that evolve into gigantic stars.
- 07:56: Even generous estimates give these gigantic population three stars only a few million years to live.
- 08:03: ... of the old universe, we expect that there were violent waves of star formation followed by cascades of supernova explosions, ripping through ...
- 08:16: Those first stars changed the face of the universe.
- 08:20: They produced the first heavy elements that would someday become dust and new stars and planets and-- well-- us.
- 08:51: These enormous stars are also thought to have left behind enormous black holes when they died.
- 08:57: In fact, it may be that stars greater than around 250 solar masses can collapse directly into a black hole without exploding.
- 09:04: ... of giant stars become clusters of giant black holes, which, in turn, would merge into ...
- 09:34: For purely theoretical objects, population three stars sure were important.
- 09:44: But we have never seen a star that has zero metal content.
- 09:47: Now, it may be that there were some smaller pop three stars that still live.
- 10:07: But the smart money seems to be on pop three stars being long gone.
- 10:26: It's hard to make sense of this light, unless there are a ton of population three stars in those galaxies.
- 10:36: The hunt continues for the first stars in the universe.
2017-05-17: Martian Evolution
- 00:06: It's fun to think about humanity settling the galaxy, outposts of familiar Homo sapiens spread among the stars.
- 00:26: And it'll start with Mars.
- 03:11: Let's start with the one that's hardest to fix-- low gravity.
- 10:31: ... line of descendent species that spread their way planet to planet, then star to star across the reaches of space ...
- 11:06: Learning this information starts with just spitting into a tube.
- 13:15: ... measured the very slight offset in the positions of stars around the limb, the edge, of the sun due to the powers of their light ...
- 13:40: ... need to compare the positions of stars on either side of the sun during the eclipse and then several months ...
- 13:49: The stars should be a few arcseconds further apart during the eclipse.
2017-05-10: The Great American Eclipse
- 00:19: The stars will emerge, and you'll be declared a god.
- 02:17: The fun starts at 9:04 AM Pacific time, when the edge of the moon's shadow first reaches the West Coast.
- 03:47: You start to realize the two objects are the same size on the sky.
- 05:31: They may be an atmospheric effect, perhaps from the same turbulence that makes stars twinkle.
- 05:40: The stars, by the way, start to come out.
- 05:54: It's the one time you can stare safely straight towards the sun.
- 06:30: Right next to the black sun, you'll see the bright star Regulus and its constellation, Leo.
2017-05-03: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson
- 00:37: In fact, with its director Neil deGrasse Tyson, along with comedian Eugene Mirman, as part of Neil's "StarTalk" radio show.
- 02:09: ... in-- is more likely to be one of them-- Than the one universe that started it ...
- 03:07: You can check out more on "StarTalk" radio, link in the description.
- 07:51: This sort of existential angst about disembodied brains being more common than real ones didn't start with Bostrom.
- 08:31: We're on a typical planet around a typical star in a typical galaxy, with one exception.
- 12:20: If you want to see more of my chat with Neil deGrasse Tyson, head over to "StarTalk" radio, "Cosmic Queries," link below.
- 12:36: It gets pretty philosophical and mind bending, as is much of "StarTalk" radio, very highly recommended.
- 14:58: Particles can start out in a high density configuration, say, in the corner of a room, and then expand.
2017-04-26: Are You a Boltzmann Brain?
- 05:16: ... by that increase in entropy includes the formation of galaxies, stars, planets, Alan Tudyk-- indeed, the entire process of ...
- 11:14: Help support the series and start your free trial by clicking on the link below or going to thegreatcoursesp lus.com/spacetime.
2017-04-19: The Oh My God Particle
- 02:13: But weirdly, above a certain height, this radiation starts to increase again.
- 06:18: When a star explodes, the expanding shock wave carries a strong magnetic field.
- 09:59: Get unlimited access starting at $2.99 a month.
2017-04-05: Telescopes on the Moon
- 01:40: On the moon, the stars are visible day and night.
- 04:11: To start with, Earth's thick atmosphere is a powerful buffer against rapid changes in temperature.
- 09:45: Learning this information starts with just spitting in a tube.
2017-03-29: How Time Becomes Space Inside a Black Hole
- 00:47: Let's get started.
- 05:46: Our future light cone stares fixedly forwards, encompassing all spatial directions equally.
- 08:20: ... of this light might be from the collapsing surface of the star that first formed the black hole, emitted long before we entered the ...
- 09:15: ... though there's a sense of past events in one direction-- the collapsing star-- and future events in the other, everything that fell into the black hole ...
2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer
- 00:20: The reality of the vast scale of our universe, even with our galaxy, is inconvenient for tales of star-hopping adventure or warring galactic empires.
- 00:30: Enter the warp drive, and hyperspace, and star gates, and the infinite improbability drive.
- 05:47: And now that you've mastered faster-than-light travel, can you pilot the Paradox back to a point before the race even started?
- 06:23: ... the Annihilator, we just make sure events stay on the contours that they started ...
- 08:37: In this case, it's the start of the race.
- 08:52: These ones represent the regions inaccessible for sublight speed travelers starting at the origin.
- 09:02: In that frame, the Paradox has moved into a region that appears to be prior to the start of the race.
2017-03-15: Time Crystals!
- 10:24: Help support the series and start your one month trial by clicking on the link in the description, or going to thegreatcoursesp lus.com/spacetime.
- 10:33: ... terrestrial and potentially habitable worlds around a nearby red dwarf star, the TRAPPIST-1 ...
- 11:07: ... from much larger orbits to their current locations very close to the star. ...
- 11:27: The answer is that, yeah, it's rare, but there are a lot of stars in the galaxy.
- 11:41: That's 578 stars out of the 100,000 stars that Kepler monitors.
- 11:54: Yet it's estimated that a system with an Earth-like planet orbiting a Sun-like star has around a 1% chance of transiting from our perspective.
2017-03-08: The Race to a Habitable Exoplanet - Time Warp Challenge
- 02:54: So you start work on an Alcubierre warp drive.
- 03:35: I recommend you start from the perspective of someone waiting around back at Earth.
2017-03-01: The Treasures of Trappist-1
- 00:10: A nearby red dwarf star was discovered to have not one, but seven Earth-like planets, and any of them may be capable of supporting life.
- 00:48: Both telescopes use the transit method, watching for the dimming of the central star as the planets pass in front of it.
- 01:11: The star, TRAPPIST-1a, is an ultra cool dwarf star, about 10% the sun's diameter and less than 10% its mass.
- 01:26: The seven planets huddle extremely close to this star-- all within one fifth of Mercury's orbit.
- 02:22: It's also unlikely that enough material resources would have been available for so much planet forming so close to the star.
- 02:30: ... chemicals condense at different temperatures, planets' distance from the star during formation largely determines the planet's chemical ...
- 02:46: Maybe the TRAPPIST-1 planets started out as mixtures of rock and ice.
- 02:50: However, three of them now occupy their star's habitable zone, where planet's surface temperature would be just right for liquid water.
- 02:59: ... can estimate the location of the habitable zone for a given star based on the intensity of its photon flux and the effect of atmospheric ...
- 03:48: ... left over from formation and generated by tidal interactions with its star and the other planets could warm it to liquid water temperatures as ...
- 04:12: Wein's law tells us that the 2,500 Kelvin TRAPPIST-1 star shines brightest at infrared wavelengths.
- 04:27: See, because the planets are so close to the star, they're probably tidally locked, like our moon.
- 04:33: One side of each planet will always face the star, the other away.
- 05:04: Partial eclipses of the central star by sister planets may be common, but there would be no full eclipses.
- 05:10: ... TRAPPIST-1a star is just too close by, standing a whopping 5 and 1/2 degrees on the sky ...
- 05:29: On the inner planets' sunny side, the star will provide about as much visible light as our sun.
- 05:35: Planets further out will receive less light, but the star's infrared intensity provides the heat needed for liquid water.
- 05:48: Being so close to the central star exposes the planets to stellar activity.
- 06:19: In addition, although this star is now relatively quiet, when these M dwarfs are young, they are extremely active.
- 06:27: This planetary system probably had a traumatic youth, which may not have been ideal for starting life.
- 07:42: ... is so much more mass in the TRAPPIST-1 star planet system than the Jupiter-Io-Europa system that, while the tides ...
- 08:23: But this finding tells us that Earth sized planets are probably common around M dwarf stars.
- 08:38: ... that M dwarfs are the most numerous stars in the galaxy, we may have seeing a giant boost in the number of ...
- 11:18: But at larger masses, the gravity wins and a star forms.
- 11:23: As long as the cloud is still smaller than the gene's length, it won't fragment further and a single star will form.
2017-02-22: The Eye of Sauron Reveals a Forming Solar System!
- 00:24: The incredible Hubble Space Telescope picture of the star Fomalhaut does excite the imagination, doesn't it?
- 00:44: Fomalhaut is an A-type star about twice as massive and much hotter and brighter than the sun.
- 00:50: At only 25 light years away, it's the 18th brightest star in the sky.
- 01:01: That dot in the middle marks the location of the star.
- 01:42: In the virtual image, the star doesn't even need to be masked.
- 01:57: The whirlpool of debris left over after the star formed, and from which a planetary system may now be forming.
- 02:14: Start with a dense core in a giant molecular cloud.
- 02:46: The star is born.
- 02:51: Conservation of angular momentum has the central star spinning rapidly.
- 03:10: ... winds from the newborn star in the center disperse this extra gas and dust, revealing whatever ...
- 03:34: They grow in size until they're large enough that they can start collecting more material through collisions.
- 04:28: The star is 440 million years old.
- 05:07: Every grain of dust in the Fomalhaut system is in orbit around the star.
- 05:11: The closer an object orbits to a given star, the faster it moves through space.
- 05:43: Having lost energy, that dust spirals closer towards the star.
- 06:32: And the light that Hubble is seeing is just reflected star light from Fomalhaut.
- 08:21: It actually has two stellar companions, making it a rare trinary star system.
- 08:34: Stars typically form in groups as very large clouds of molecular hydrogen collapse and break apart into separate pieces.
- 08:41: The stars don't always stay in the same groups.
- 08:54: By the way, the third star in the system is a flare star, violently fluctuating due to magnetic storms on its surface.
- 09:17: We're going to need more observations to figure out whether Fomalhaut is typical of stars in their youth, or is actually truly unusual.
- 09:33: Only then can we start to use it to learn about our solar system's early years.
- 10:05: Get unlimited access starting at $2.99 a month.
2017-02-15: Telescopes of Tomorrow
- 01:50: So planets form around young stars.
- 01:52: And young stars lie tucked away in blankets of gas and dust.
- 02:23: This will provide another set of baby pictures, the formation of the very first stars and galaxies in our universe.
- 02:55: Webb will help us learn whether stars form galaxies or galaxies form stars and the role of dark matter in the whole process.
- 03:23: A single point, like a star, will always be a little bit blurred when it reaches our camera.
- 05:40: We can think of light from a very distant point-like object-- say a star-- as reaching us as a series of wavefronts.
- 06:02: To our eyes, this is what causes stars to twinkle.
- 06:53: ... the upper atmosphere, where their light will produce artificial guide stars. ...
- 07:05: ... mirrors will deform up to hundreds of times per second to keep the guide stars, along with everything else in the telescope's sights, in sharp ...
- 07:36: It's hoped that GMT will even find traces of the very first population of stars that formed in our universe.
- 08:44: We'll be able to track the motion of rogue high-velocity stars whizzing through our galaxy.
- 08:58: It will be easier to find new supernovae, the explosive deaths of stars which, among other things, will improve our understanding of dark energy.
- 10:43: Help support the series and start your one-month trial by clicking on the link in the description or going to thegreatcoursesp lus.com/spacetime.
- 12:35: Well, I would start a YouTube channel called "Will it Spaghettify?"
2017-02-02: The Geometry of Causality
- 01:23: ... half the speed of light, the distance I need to travel to a neighboring star shrinks dramatically from my point of ...
- 03:29: They start at the origin, where x and t equals 0.
- 14:09: Stars are so good at fusion, in part, because they're the cause of creating high densities.
- 14:13: ... unstable and collapse, in which case you might get some weird stardust-like activity and some ...
- 14:32: Bikram Sao asks how large the original star must have been to produce a supermassive black hole.
- 14:54: ... been left over by the deaths of an insanely large first generation of stars, perhaps thousands of times the mass of the ...
- 15:30: And to all my students in Astronomy 101 this semester, no, we're not learning about the star signs.
2017-01-25: Why Quasars are so Awesome
- 00:16: Let's talk about what happens when the largest black holes in the universe start to feed.
- 00:29: Take stars-- 100 billion megaton per second thermonuclear explosions that just don't stop exploding.
- 00:42: Giant molecular clouds-- beautiful and tranquil, but also screaming vortices spitting stars into the cosmos.
- 01:47: Let me start with a bit of history.
- 02:38: That timing allowed astronomers to identify a tiny star-like point of bluish light as the source of the radio emission.
- 02:46: Astronomers turned their optical telescopes on this strange star, and split the light into a spectrum.
- 02:53: It looked nothing like the spectrum of any star ever seen.
- 03:37: ... hysterical flurry of hypothesizing followed-- swarms of neutron stars, an alien civilization harnessing their entire galaxy's power, bright, ...
- 07:29: As the first galaxies coalesced from this gas, the universe entered a long period of violent star formation.
- 07:36: As galaxies coalesced, they went through starburst phases, producing new stars at insane rates.
- 07:43: The birth of large numbers of new stars is always quickly followed by the explosive deaths of the most massive, shortest lived of those stars.
- 07:54: Waves of star formation, followed by waves of supernovae.
- 08:12: However, the same rich gas supplies that fueled those starbursts also gave rise to the epoch of quasars.
- 08:46: Hot gas doesn't collapse into stars, and so the extreme starburst activity was shut down.
- 08:52: A few billion years after the Big Bang, when the universe was around a quarter of its current age, both starbursts and quasars started to dwindle.
- 10:54: Help support the series and start your one month trial by clicking on the link in the description, or going to thegreatcoursesp lus.com/spacetime.
2017-01-19: The Phantom Singularity
- 04:16: ... the gravitational field is too strong-- say, near a star or a black hole-- Newton's law gives the wrong answers, and we need ...
- 07:40: At that point, the entire equation starts behaving very badly.
- 09:54: The act of crossing the event horizon is where this singularity really starts to behave badly.
- 17:45: You are starstuff.
2017-01-11: The EM Drive: Fact or Fantasy?
- 12:01: At some level, we start to have a pretty thorough grasp of what is possible in this universe.
- 12:46: There are even plans to use lasers to communicate between the hopefully upcoming Starshot Shot light sail mission to Alpha Centauri.
2017-01-04: How to See Black Holes + Kugelblitz Challenge Answer
- 01:18: ... the motion of a visible star reveals it to be in orbit around a companion that is dark invisible ...
- 01:29: This happens when the substance of a visible star is accreting onto a companion neutron star or black hole.
- 02:03: We call our supermassive black hole Sagittarius A star.
- 02:09: Sag A star is visible in X-rays, which occasionally flash brighter as it gobbles up a wisp of gas.
- 02:14: But more compellingly, we've tracked the motion of stars near the galactic core for many years.
- 02:49: The Event Horizon Telescope is right now in the process of mapping space around the Milky Way's Sag A star black hole.
- 03:29: This has enabled EHT to map the strange magnetic field structures around the Sag A star black hole.
- 03:43: ... online, it will actually see the dark circular shadow of the Sag A star event ...
- 03:55: Interferometry is going to be used to study much smaller black holes in our galaxy, the remnants of dead stars.
- 04:02: These black holes occasionally pass in front of more distant background stars, gravitationally lensing the star's light.
- 04:09: At visible wavelengths, this should look like a brightening of the star, an effect called microlensing.
- 04:15: ... interferometry will enable incredibly high-res mapping, and the distant star should appear to split into two or four images as its light passes ...
- 05:59: And that's exactly where we should start.
- 06:02: In the challenge question, I showed you the Penrose diagram for a star collapsing into a black hole.
- 06:27: The surface of our star is represented by its starting radius at t equals zero, but as time moves forward, the radius shrinks as the star collapses.
- 06:59: ... only part of this doomed triangle above the collapsing star's surface actually has the crazy spacetime behavior of the interior of a ...
- 07:12: Now, the collapsing star is replaced with a collapsing shell of light.
2016-12-21: Have They Seen Us?
- 00:00: ... of Earth's radio transmissions has now washed over thousands of other star systems, carrying with it some of our greatest broadcast masterpieces, ...
- 00:31: ... alien race monitoring our planet, even from the nearest neighboring star, would have seen nothing, radio quietness until only around a century ...
- 01:18: ... of "War of the Worlds." That shell has washed over several thousand star ...
- 02:31: ... SETI, in earnest since the '60s, when Frank Drake first peeked at the stars Tau Ceti and Epsilon ...
- 04:11: Our best-targeted search so far, the SETI Institute's Project Phoenix, scanned 800 stars within 200 light years.
- 04:37: In that range, there is exactly one star, ours.
- 08:42: Loeb and Zaldarriga's numbers assume pointing SKA at a target star system for an entire month and adding up all of the radio emission over that time.
- 09:02: These emission spikes may also shift back and forth in frequency due to Doppler shift, as the distant technologically advanced planet orbits its star.
- 09:38: What would be needed to, say, tune in to the first season of the original "Star Trek" series?
- 12:11: However, our steady broadcasts have only washed over a few hundred solar-type star systems and only a few thousand stars total.
2016-12-14: Escape The Kugelblitz Challenge
- 01:35: A black hole forms when the core of a very massive star collapses under its own gravity at the end of a star's life.
- 01:45: Let's start with a nice, empty universe.
- 01:48: Empty, except for a single, giant star.
- 01:52: When the core of this star has fused all of its elements into iron, it will start to collapse under its own weight.
- 02:11: If the star's core collapses to a size smaller than its own Schwarchild radius, then the event horizon forms, engulfing what's left of the star.
- 02:21: Below that horizon, but above the still-shrinking surface of the star, space-time takes on the mad properties of the black hole interior.
- 03:34: This invisible horizon of doom grows as the star shrinks and finally merges with the true event horizon.
- 03:51: OK, in the case of the collapsing start, that's still a core, is going to be an insanely hot, dense place and not great for observers.
- 04:20: Maybe they just saw the first Star Wars prequel.
2016-12-08: What Happens at the Event Horizon?
- 05:24: ... a light ray starting from really, really far away and coming towards us hugs the edge of the ...
- 07:41: With this picture, we can start to answer some very serious questions.
- 12:14: Help support the series and start your one-month trial by clicking the link in the description or going to thegreatcoursesp lus.com/spacetime.
- 14:50: ... different particle trajectories, given that the particles supposedly all start at exactly the same ...
- 15:02: Well, the simple answer is that the particles don't start at exactly the same points.
2016-11-30: Pilot Wave Theory and Quantum Realism
- 11:33: Now let's not even start talking about gravity-- no version of quantum mechanics has that sorted out.
- 12:49: In our last episode, we talked about the strangest of stars, the strange star-- aptly named.
- 14:25: Sebastian Lopez asks how are the magnetic fields of neutron stars created.
- 14:37: That might seem a problem for an object made up of neutral particles like a neutron star.
- 14:41: However, a neutron star isn't only made up of neutrons.
- 14:51: ... the neutrons, perhaps up to 10% electrons and protons by mass of the star. ...
- 15:06: With their extreme rotation rates, neutron stars support electric currents sufficient for magnetic fields of up to 100 million tesla.
- 15:49: In a neutron star, it's a superfluid, so not ideal there.
2016-11-16: Strange Stars
- 00:00: ... PLAYING] As if black holes and neutron stars aren't weird enough, physicists have very good reason to believe that ...
- 00:44: The most wonderfully monstrous of these are the remnant corpses of the most massive stars, stellar zombies like neutron stars and black holes.
- 00:55: Einstein's general theory of relativity tells us that the core of a dead star must collapse under its own incredible weight.
- 01:08: ... already talked about how quantum processes save a neutron star from collapse, but ultimately also doom the most massive to collapse ...
- 01:18: But just shy of that final transition, and on the fringe of our understanding of the quantum universe, a star may become very strange indeed.
- 01:29: Literally, I'm talking about strange stars.
- 01:32: Before we can understand strange stars, we need to start with a stellar remnant that we know for sure exists, the neutron star.
- 02:07: The rest of the in-falling star collides with the new neutron star and ricochets outwards in the most powerful explosion in the universe, a supernova.
- 02:16: The remaining neutron star is millions of Kelvin in temperature, and may be spinning thousands of times per second.
- 02:28: These jets may sweep across the Earth due to the spinning-top-like procession of the neutron star.
- 02:36: Our understanding of neutron stars seems to fit the behavior of pulsars very well, at least for most of them.
- 02:43: But for some, we see hints of weird things happening deep beneath the star's surface, which we'll get to.
- 02:49: ... ordinary neutron stars, that surface is a thin crust of iron, which quickly gives way to a fluid ...
- 03:42: And we certainly can't test what happens to it when subjected to the insane pressures at a neutron star's core.
- 04:38: ... the quark matter in a neutron star is forged by insane pressures, not by the greater-than-a-trillion-Kelvin ...
- 04:59: We sometimes call a neutron star with such a quark matter core a quark star.
- 05:19: So that probably rules out having an entire star made of this stuff, unless the quark matter is also strange.
- 06:10: A star made entirely of this stuff should be completely stable.
- 06:18: We call these strange stars.
- 06:21: Not content even with this level of weirdness, physicists have proposed even more mad ideas for neutron star cores.
- 06:51: It could be that neutron stars have an electroweak core, an apple-sized ball with the mass of two Earths in which quarks themselves burn.
- 07:08: And those may provide the final pressure that halts the collapse of some stars into a black hole, at least for another million years or so.
- 07:32: In the year 1181, Chinese and Japanese astronomers recorded a new star in the constellation of Cassiopeia.
- 07:40: ... to that spot and found a young pulsar, a rapidly rotating neutron star 10,000 light years ...
- 08:13: The x-ray data revealed a surface temperature of a more million Kelvin, much cooler than expected for a neutron star of its age.
- 08:23: A possible explanation is that a quark matter core formed at the heart of this neutron star and is slowly transforming into strange matter.
- 08:41: That energy would be the heat energy of the neutron star.
- 08:44: There are other candidates that could be quark and/or strange stars.
- 08:59: And it's been hypothesized that these may be due to a second explosion as the neutron star collapses further into a quark star.
- 09:08: Even the famous supernova that exploded in the Large Magellanic Cloud in 1987 has been hypothesized to have left behind a quark star.
- 09:17: ... dying star shouldn't have been massive enough to leave a black hole, yet ...
- 09:28: Nothing is confirmed yet, but there are tantalizing hints that these exotic stars, these monsters in the math, may be very real.
2016-11-09: Did Dark Energy Just Disappear?
- 00:37: These exploding white dwarf stars have predictable brightnesses that allow astronomers to figure out how far away they are.
- 06:35: ... effect of regular energy, and that's mostly dark matter, but also stars, planets, gas, radiation, et ...
- 12:44: So Keivan Stassun's course, "The Life and Death of Stars," gave me some great insights into the nature of the weird corpses left after stars die.
- 13:02: Help support the series and start your one month trial by clicking the link in the description or going to thegreatcoursesplus.com/spacetime.
- 14:13: ... when the rebellion starts, the centrifuge cities will be an important touchstone in the conflict ...
2016-11-02: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers
- 04:42: It tells us the number of stars of each given type within a certain distance.
- 04:46: For 100 light years, we have 512 G-Type stars: that's the same type as our sun.
- 04:54: The Frank and Woodruff (Sullivan) paper estimates that around 1 in 5 stars has a terrestrial planet in the habitable zone.
- 05:01: So, in the distance from the star where water can exist as a liquid.
- 05:05: So that means there are around 100 such planets orbiting stars like the sun within 100 light years.
- 05:52: If you allow that more star types can produce planets with life, then this number just gets smaller.
- 06:47: ... should be, under the assumption that the weird dimming seen in Tabby's Star is due to a Dyson Swarm and that it hosts the only such Type II ...
- 07:10: There are 100,000 stars in the Kepler Sample.
- 07:13: The Kepler Observatory points only in one direction, so those stars are spread along a column a few thousand light years long.
- 07:21: ... ask, "How large a sphere centered on the sun would also contain 100,000 stars?" There should be, on average, around one Dyson Swarm in those 100,000 ...
- 07:36: Again, using the "solstation" website, we get that there are around 5,000 stars total per 100 light year radius sphere.
- 07:46: So you'd get 100,000 stars in a 270 light year sphere.
- 07:52: That's a ballpark guess at how close the nearest Type II civilization would be if Tabby's Star is also a Type II civilization.
- 08:01: Now we've studied all the non-red dwarf stars in that volume pretty thoroughly, and none of them show any signs of having Dyson Swarms.
- 08:23: Ergo, Tabby's Star probably isn't aliens. Sorry!
2016-10-26: The Many Worlds of the Quantum Multiverse
- 11:46: You've got a year, starting now.
2016-10-19: The First Humans on Mars
- 09:13: Several of you asked how to tell the difference between a primordial black hole and a black hole formed when a very massive star ends its life.
- 09:52: A star's core needs to be more massive than around three times the mass of the sun in order to collapse into a black hole.
- 09:59: Otherwise, it becomes a neutron star.
- 10:01: However primordial black holes don't form from stars and so aren't subject to this restriction.
- 10:09: ... tell us that it was impossible for them to have been produced by massive stars, which are rare, as far as stars ...
- 10:37: Those supermassive black holes started as much smaller seed black holes.
2016-10-12: Black Holes from the Dawn of Time
- 00:49: That's in the core of the most massive stars when they die.
- 05:27: In stars in our galaxy, in distant quasars, even in gamma ray bursts.
- 05:44: As the heavier ones buzz around the galaxy, they should pull apart loosely bound binary systems and have an effect on the structure of star clusters.
- 05:53: The smallest should fall into neutron stars, causing them to either explode or become black holes themselves.
- 06:01: But we see loosely bound binaries, and normal star clusters, and plenty of neutron stars.
- 10:47: Help support the series and start your one-month trial by clicking the link in the description, or going to thegreatcourses.com/spacetime.
2016-10-05: Are We Alone? Galactic Civilization Challenge
- 00:19: ... biological, and sociological factors, each of which narrows the range of stars in our galaxy that may have produced a surviving ...
- 00:33: ... factors include the rate of star formation in the Milky Way, the number of planets per star that could ...
- 02:20: ... 14 billion terrestrial planets in the Goldilocks zone of their parent star. ...
- 02:43: Around 11 billion of those are Earth-like planets around Sun-like stars.
- 05:08: ... the above but also the following-- consider Tabby's Star, an otherwise normal-looking F-type star, 1,500 light years away, which ...
- 05:22: Some people like to think this is evidence of some sort of alien mega structure eclipsing the star.
- 05:48: What does your answer say about the likelihood of Tabby's Star hosting such a civilization?
2016-09-29: Life on Europa?
- 03:09: In fact, it may be that life on Earth started around its own hydrothermal vents.
- 06:00: But if life started at those vents, who's to say it stayed there?
2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate
- 00:12: The weird phenomenon of quantum entanglement gives us quite startling clues to the answer.
2016-09-14: Self-Replicating Robots and Galactic Domination
- 00:33: Stars for the most part act very star-like, their brightnesses and colors slavishly following the equations of stellar physics.
- 01:24: ... before building the great generation ships needed to seed new star ...
- 02:06: ... completely unmanned or unkerbled vessels capable of traveling between star systems, and capable of extracting resources at their destinations to ...
- 05:25: After several decades, it decelerates into a neighboring star system, and parks in orbit, or lands on a nice, big asteroid or gas giant moon.
- 06:09: At some point, the assembler starts building new Von Neumann probes which, one by one, launch to new, more distant star systems.
- 10:35: Help support the series and start your one-month trial by clicking the link in the description, or going to thegreatcoursesp lus.com/spacetime.
- 12:23: Shawn Tripp imagines how cool would be if we started exploring the Kuiper Belt, only to find out that it is the remnants of an ancient Dyson sphere.
2016-08-24: Should We Build a Dyson Sphere?
- 00:11: ... mega structures, capable of harvesting the power output of entire stars, the as yet inexplicable Kepler Space Telescope observation of swarms of ...
- 00:37: ... artificial habitats in the form of vast shells surrounding their parent star. ...
- 01:16: On the other hand, securing access to an entire star's energy output officially elevates a civilization to type 2 on the Kardashev scale.
- 02:26: But in the end, it's just not an efficient way to start your galactic empire.
- 02:39: But collecting the entire output of our home star may still be the smart choice.
- 03:10: The crazy thing about the Dyson swarm is that we could probably start building one in the not too distant future.
- 03:17: In fact, we could get started on the first collector pretty much right away.
- 04:33: We start with limited mining, space launch, and orbital construction facilities, all of it autonomous.
- 04:40: Energy supply is the big limiting factor at the start, so it takes about 10 years to build the first collector.
- 06:23: Would other civilizations have gone that route, casting very conspicuous shadows on their home stars for us to detect?
- 07:33: We talked about one example, the Kugelblitz, in our previous episode on possible starship engines.
- 09:43: Admittedly, the fading that the Kepler Space Telescope observed in Tabby's star is sort of consistent with a partial swarm.
- 10:47: Help support the series and start your one month trial, by clicking the link below or going to thegreatcoursesp lus.com/spacetime.
2016-08-17: Quantum Eraser Lottery Challenge
- 00:42: We start with a standard double-slit apparatus.
- 04:35: Photons start hitting the screen, building up some pattern.
2016-08-10: How the Quantum Eraser Rewrites the Past
- 00:25: They imply some startling things about the nature of reality.
- 11:37: These may have masses similar to planets rather than stars, if they exist.
2016-08-03: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
- 01:30: ... overturning the biosphere's equilibrium, or even nearby exploding stars. ...
- 03:57: How much lead time would we really need to build this thing, assuming we started right now?
- 08:14: But there is one threat that no settlement on any planetary surface or space hotel in the solar system can protect us from-- that's an exploding star.
- 08:47: Fortunately, we know for sure that there are no stars ready to go supernova within any dangerous distance.
- 08:58: ... a very massive star goes supernova, the resulting collapse of the core into a neutron star, ...
- 09:34: There's currently at least one star within the danger zone that could produce a gamma ray burst.
- 10:09: ... two, get the hell out of the solar system and start colonizing the galaxy beyond the 30-light-year range of a supernova and ...
2016-07-27: The Quantum Experiment that Broke Reality
- 00:30: [THEME MUSIC] Let's start with the familiar.
- 00:38: In fact, let's start with a rubber duckie.
- 00:55: When the new ripples start to overlap each other, they produce this really cool pattern.
- 03:37: If you keep firing those single photons, you start to see our interference pattern emerge once again.
- 06:17: Let's start with what we do know about the double-slit result.
- 06:24: ... starts its journey wherever we put the laser or electron gun or buckyball ...
- 07:02: ... have this family of could-be trajectories from start to finish and for some reason, when the wave reaches the screen, it ...
- 11:04: Help support the show and start your one-month trial by going to thegreatcoursesp lus.com/spacetime.
- 11:18: ... Blank asks, "Wasn't Jupiter almost a star?" Well, the lowest mass stars are around 7.5% the mass of the Sun, while ...
- 11:45: Well, the Sun and other stars don't need rocky cores because they are massive enough for all of that gas to collapse by itself.
- 12:14: For Jupiter to form its giant ball of gas, it needed a rocky core to start the process.
2016-07-20: The Future of Gravitational Waves
- 04:33: As we do so, we'll start to nail down the astrophysics of black hole formation and growth.
- 04:54: We should eventually see mergers between two neutron stars or a neutron star and a black hole, as well as supernova explosions.
- 07:23: Well, it started tunneling at the edge of the nucleus, around seven femtometers, and tunneled to 27.
2016-07-06: Juno to Reveal Jupiter's Violent Past
- 01:08: Jupiter was probably the first planet to start forming in our system.
- 01:22: ... over 40 times the mass of the Earth before it had enough gravity to start holding on to the 300-ish Earth masses of hydrogen and helium that make ...
- 04:39: There's more than one possibility, because we don't know exactly how the formation of planets started.
- 06:03: Well, computer simulations show that something like this may be expected given the right starting position for Jupiter.
- 07:32: ... events it describes starts after the protoplanetary disk had evaporated, so chronologically, after ...
- 12:54: ... actually a turtle, and not just any turtle, but Great A'Tuin, the Giant Star Turtle, bearer of ...
2016-06-22: Planck's Constant and The Origin of Quantum Mechanics
- 03:53: The blue super giant star Rigel is 12,000 Kelvin, and so it pumps out lots of high frequency blue light and even more ultraviolets.
- 10:38: ... the Planck constant can be read in the color of the sun and the stars, in the brightness of the different colors of the ...
- 11:30: Help support "Space Time" and start your one-month trial by going to thegreatcoursesp lus.com/spacetime.
2016-06-15: The Strange Universe of Gravitational Lensing
- 02:11: ... of the sun and to measure the tiny change in the position of nearby stars due to the deflection of their light by the sun's gravitational ...
- 02:26: The stars had shifted.
- 03:03: For stars, this effect is typically small.
- 06:13: ... passing through the starry lens galaxy brightens and dims due to the gravitational fields of ...
- 06:25: As those stars sweep in front of the quasars in a vortex, its different parts change in magnification to different degrees and at different times.
- 07:20: ... stellar bodies-- black holes, neutron stars, and brown dwarves-- occasionally pass in front of other starts and lens ...
- 09:19: The stars are mostly where you see them-- mostly.
- 09:51: We recently started talking about quantum physics by looking at the bizarre phenomena of quantum tunneling.
- 10:05: ... in your wave function that has an equal or lower energy state than your starting ...
2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners!
- 04:20: The LHC is currently offline for upgrades, and starts up again in June, following a two-week delay due to a weasel chewing through a power cable.
- 07:25: So the feedback cycle can start at either end.
- 09:03: For the main question, I asked you to figure out how many times the universe doubled in size after dark energy first started to show its influence.
- 09:37: To start with, let's ask how large this volume was when dark energy only comprised 10% of its total energy.
2016-06-01: Is Quantum Tunneling Faster than Light?
- 05:01: In fact, without quantum tunneling, stars could not fuse hydrogen into heavy nuclei.
2016-05-25: Is an Ice Age Coming?
- 08:05: As ice cover increases, Earth starts to reflect more incoming sunlight.
- 08:42: First, low obliquity means less overall sun at high latitudes where the glaciers start.
2016-05-18: Anti-gravity and the True Nature of Dark Energy
- 11:55: In a recent episode, we talked about the Breakthrough Starshot program, LightSail to the stars.
- 12:36: Patrick Romo and others asked whether we could decelerate the LightSail in the wind from the destination star.
- 12:48: The impulse generated by the laser is many orders of magnitude greater than that of the star at the other end.
- 13:43: Aging Reversed would like to spend the entire Starshot budget to cure cancer, rather than sending a speck of dust into nothing.
- 13:51: Well, the final cost of Starshot is expected to be several billion.
- 14:12: ... to underestimate the benefits of inspiring forward-looking projects like Starshot. ...
2016-05-11: The Cosmic Conspiracy of Dark Energy Challenge Question
- 05:43: ... I just asked, but also tell me how many billion years ago dark energy started to have a significant effect and how many billion years in the future ...
2016-05-04: Will Starshot's Insterstellar Journey Succeed?
- 00:02: Breakthrough Starshot plans to send spacecraft to the nearest star within your lifetime.
- 00:32: We've been waiting so long now that this surety of a space-faring future has started to slip into the realm of science fiction.
- 00:42: Billionaire physicist Yuri Milner recently announced the Breakthrough Starshot program.
- 01:18: Looks like light sails will be the first propulsion tick to get an unmanned probe to the stars.
- 02:56: The first serious proposal along these lines was the Starwisp, proposed by scientist and author, Robert Forward, and updated by Geoffrey Landis.
- 03:21: The Starwisp would accelerate to 10% or so of the speed of light, getting it to alpha [INAUDIBLE] barely within the science team's working life.
- 03:29: In a way, Starshot is an update to the Starwisp.
- 03:38: The main innovation of the Starshot is that it's not just low mass, it is ultra low mass, weighing in at grams rather than Starwisp's kilograms.
- 03:51: ... Starshot will be comprised of a sail around a meter in diameter that's made of an ...
- 04:24: Another big difference compared to Starwisp is that Starshot will be powered by a visible light laser, not a maser.
- 05:06: This thing could burn Yuri Milner's tag on the surface of the moon and also accelerate a Starshot craft to 20% of the speed of light in a few minutes.
- 05:45: What can a Starshot probe expect to do in those few minutes?
- 06:40: ... at the other end, Starshot probes need to know where to point the cameras and then beam that info ...
- 07:30: Well to start, it has money.
- 07:32: Milner has shelled out $100 million to get started.
- 08:26: And what will the Starshot probe find when it reaches Alpha Cen?
- 10:06: The universe expands exponentially forever and eventually the stars die out, the black holes evaporate, and the universe undergoes heat death.
- 11:03: ... that we must need some sort of luminosity reference point before we can start using white dwarf supernovae or Type 1a supernovae, the standard ...
- 11:17: We need to figure out the luminosities for a good number of these supernovae independently, before we can start using them as standard candles.
- 11:33: ... example, we can use cepheid variable stars, another type of standard candle, to get an independent distance to the ...
2016-04-27: What Does Dark Energy Really Do?
- 03:55: Take a white dwarf, the leftover core of a dead, low-mass star like our sun, and let it cannibalize some of the material from a binary companion.
- 04:04: When the star reaches a critical mass, a runaway fusion reaction obliterates the star as a supernova.
- 04:18: OK, so here's the experiment-- watch stars explode across the cosmos.
2016-04-20: Why the Universe Needs Dark Energy
- 11:35: ... and Employers found that new graduates from physics-major programs have starting salaries higher than any other science ...
- 12:23: Now, before we do any general relativity-- MAN: Start again-- had some eyebrow stuff doing on.
2016-04-13: Will the Universe Expand Forever?
- 01:17: For today's episode, we're going to start by describing the universe without dark energy.
- 10:06: ... this main sequence of elements produced in the cause of dying high-mass stars and asks how elements out of this sequence get ...
- 10:20: In fact, there are many different fusion reactions occurring in the cores of those dying high-mass stars.
- 10:36: ... if you start with an even-atomic-number element-- like carbon, with its six protons-- ...
- 11:06: As for fluorine, that's actually one of the more confusing ones, because it's not produced efficiently in any known reaction in high-mass stars.
- 11:15: But recent work has suggested that it might actually be formed in lower-mass stars like our sun after they enter the red giant phase.
- 11:54: However, stars don't all orbit at exactly the same rate.
- 11:58: Orbits aren't perfectly circular, and stars drift apart as they move in and out of the spiral arms and above and below the galactic disc.
- 12:21: It collapsed into the Sun's sibling stars, which are also scattered across the galaxy by now.
- 12:28: And it was blasted away by supernovae from the most massive stars it produced.
- 12:35: ... be from those supernovae, but more will be from previous generations of stars that enriched that giant cloud before it formed stars of its ...
- 12:57: Be noble, for you are made of stars." [THEME MUSIC]
2016-04-06: We Are Star Stuff
- 00:00: ... PLAYING] Carl Sagan said that we are "starstuff." Most of the atoms in our body were forged in violent stellar alchemy and ...
- 00:55: Perhaps not fully comprehend, but at least deduce and manipulate with startling precision and predictive power.
- 01:04: ... when those elementary particles start interacting to form nuclei, atoms, and molecules-- chemistry-- they ...
- 02:37: ... start with the simplest, hydrogen. Your body is up to 60% water, H2O, which ...
- 03:21: A few seconds after it became possible for protons to exist, new heavier elements started to form.
- 04:31: And all of that hydrogen and helium would later become the fuel for the later formation of stars.
- 04:37: And stars are important.
- 04:40: As well as providing us with all of their glorious entropy-resisting energy, stars are element factories, stellar alchemists.
- 04:48: While the early universe had around 20 minutes to forge its nuclei, stars have millions to billions of years.
- 04:55: Our sun, and in fact every star in the prime of its life on what we call the main sequence, shines by forging hydrogen into helium.
- 05:30: In order to liberate the products of stellar nucleosynthesis, we need to explode that star.
- 05:36: ... the largest stars, any bigger than around eight times the sun's mass, reach the ends of ...
- 06:08: ... the star took millions of years to burn through its original hydrogen core, when ...
- 06:57: That means that as soon as iron starts to fuse, it sucks energy out of the star rather than adding to it.
- 07:20: And the process makes it a neutron star.
- 07:24: ... collapse also, but they hit the brick wall of the newly born neutron star and ricochet back in the largest explosion in the universe, a ...
- 07:38: In this explosion, all those elements are spread into interstellar space, providing fuel for later stars to form.
- 08:27: ... in fact, a lot of the iron in your blood, was forged at the instant a star exploded, or are decay products from unstable elements formed in the ...
- 08:47: ... a white dwarf, a remnant of a low mass star like the sun, has a binary partner star and manages to accrete, to steal ...
- 09:16: ... were formed not in a supernova, but in the collision of two neutron stars. ...
- 09:27: ... two very massive stars in binary orbit leave behind neutron star corpses, those remnants will ...
- 10:13: We are "starstuff." But more, we our universe stuff, the most complex component that has risen from a beautiful and chaotic spacetime.
2016-03-30: Pulsar Starquakes Make Fast Radio Bursts? + Challenge Winners!
- 01:11: ... cataclysmic events, like colliding stellar remnants, supernovae, neutron stars collapsing into black holes, crazy stuff like ...
- 01:56: ... the best contenders involve young neutron stars, which rotate at insane rates and occasionally give off extremely intense ...
2016-03-23: How Cosmic Inflation Flattened the Universe
- 03:12: An expanding universe doesn't tend to stay flat, even if it starts that way.
- 03:44: If the universe starts out even a little bit not flat, then that not-flatness will amplify quickly.
- 04:49: It goes like this-- start with a universe so crunched down that the entire currently observable part of it was all causally connected.
- 08:52: It may have, and there are some ideas about what got it started.
- 09:17: When first conceived, the inflationary period was thought to have started at a particular point after the instant of the Big Bang.
- 11:04: This is also true of the stars in a eliptical galaxies.
- 11:08: Stars a small enough, compared to the distances between them, that they can be in these random orbits.
- 11:14: The reason spiral galaxies are discy is that those discs formed before the stars actually formed, back when the material was mostly gas.
2016-03-16: Why is the Earth Round and the Milky Way Flat?
- 00:23: It loves building spheres like stars, planets, and moons, and disks like spiral galaxies, solar systems, and some crazy stuff like quasars.
- 00:49: Let's start with equilibrium.
- 01:43: ... terms of shape, things like planets and stars have spherical symmetry, meaning you can rotate them in three dimensions ...
- 02:14: So let's start with that.
- 02:53: And this type of dimensional egalitarianism is also shared by another effect, ultimately leading to the ball shapes of stars, planets, and moons.
- 07:08: A very similar balance applies to stars.
- 07:18: And this hydrostatic equilibrium keeps stars like our sun extremely spherical and happily burning away for billions of years.
- 08:29: These things are even more massive than single planets or stars.
- 08:42: Let's think about what happens when a vast interstellar cloud of gas and dust collapses to form a star.
- 08:56: They also start out spinning very slowly, but that spin speeds up as they collapse, just like a spinning ice skater.
- 09:37: ... these giant disks of stuff will clump off and form the star in the center and the planets further out, but the disk structure ...
2016-03-02: What’s Wrong With the Big Bang Theory?
- 07:52: ... idea is the universe started subatomic, small enough that it was able to even out its temperature and ...
2016-02-24: Why the Big Bang Definitely Happened
- 00:00: Our universe started with the Big Bang, or did it?
- 01:36: Let's start with the irrefutable.
- 03:34: One such prediction is that the entire universe was once as hot and dense and opaque as the inside of a star.
- 05:46: ... colliding and merging with each other, rich in the raw materials of star formation but poor in the heavy elements released by generations of ...
- 06:54: At an age of a few seconds, we predict that all of the universe was much hotter than the very center of a star and remained so for around 20 minutes.
- 07:27: It's in startling agreement with what we see when we look out there.
- 12:11: I'll still appreciate the impractical beauty after those insights allow me to ride my inflaton-powered anti-gravity warp ship to the stars.
2016-02-11: LIGO's First Detection of Gravitational Waves!
- 02:06: Now, LIGO is sensitive to pairs of stellar mass black holes and/or neutron stars.
- 02:12: In both cases, these are the collapsed core of a dead star, stellar remnants.
- 02:18: Now these stellar remnants are sometimes found in pairs, typically when the original stars were also a binary pair in orbit around each other.
- 02:40: Now we've seen this slow orbital decay in binary neutron stars.
- 03:22: ... those few minutes, the merging black holes or neutron stars produce such strong ripples in the fabric of spacetime that LIGO can see ...
- 04:07: In the case of merging neutron stars, it's a much smaller distance, and so none have been seen yet, although it will happen eventually.
- 04:14: We'll also spot supernova explosions that produce neutron stars.
- 06:13: ... waves at frequencies produced by merging black holes and neutron stars, as well as the formation of neutron stars and supernova ...
- 06:24: And potentially, even the actual spin of neutron stars.
- 06:48: ... see the slow ringing of binary white dwarf stars in our own galaxy, as well as the final dance of pairs of truly ...
2016-02-03: Will Mars or Venus Kill You First?
- 00:00: [MUSIC PLAYING] If we want to get to the stars, we don't have to learn how to live on other planets.
- 01:04: We'll start with Mars, because it sits in popular consciousness as our go-to Earth 2.0.
- 03:13: But it does start to form bubbles of nitrogen and oxygen, and this is what will actually kill you.
- 03:21: ... soon after exposure to a vacuum, your blood will be leached of oxygen, starving your brain, and at some point blocking blood flow all ...
- 06:53: To start with, things seem lovely.
- 07:26: Your skin will start to blister and dissolve at the same time.
2016-01-27: The Origin of Matter and Time
- 00:10: In recent episodes, we started breaking apart our preconceived notions of these ideas.
- 12:17: The start of the song time should sync with the appearance of the photon clock.
2016-01-13: When Time Breaks Down
- 00:27: While weekends and summer break seem to finish even before they start.
- 01:50: This is where our conception of time starts to break down.
- 03:26: The rate of ticks is consistent, time flows smoothly, until the clock starts moving relative to me.
2016-01-06: The True Nature of Matter and Mass
- 01:33: A good place to start is with a thought experiment that we'll call a photon box.
- 03:58: Push the spring, and it doesn't all start moving instantly.
2015-12-16: The Higgs Mechanism Explained
- 08:49: Gareth Dean asks about this whole thing about using gravitational waves to turn up the core temperature of a star.
- 08:55: ... waves carry a lot of energy, and some of it can get dumped into a star by squeezing and stretching as the gravitational wave passes ...
- 09:05: ... stars near the core of a galaxy with merging super massive black holes should ...
2015-12-09: How to Build a Black Hole
- 01:09: First step-- find a very massive star, and wait.
- 01:27: The details of the deaths of massive stars are pretty awesome.
- 01:33: ... the last throes of a very massive star's life, increasingly frantic fusion in the interior produces one periodic ...
- 01:58: So starved of an energy source, the stellar core collapses on itself.
- 02:03: Electrons are slammed into protons in the ion nuclei, forging a neutron star.
- 02:17: ... leftover core, the neutron star, is a very weird beast-- a bowl of neutrons the size of a city, with a ...
- 02:33: Now, beneath the thin atmosphere of ion plasma, a neutron star is a quantum mechanical entity.
- 03:04: For a neutron star, this is the space of both 3D position and 3D momentum.
- 03:09: And it defines the volume that can be occupied by the strange matter in a neutron star.
- 03:15: ... the exact way that the matter of a neutron star fills this 6D quantum phase space depends on two important principles of ...
- 04:09: In the case of a neutron star, position momentum phase space is completely full of neutrons.
- 04:32: ... enough to initially resist the insane gravitational crush of a neutron star. ...
- 04:58: So the neutron star is safe.
- 06:23: So a neutron star is comprised of the densest matter in the universe.
- 06:55: And here's the thing-- the denser the neutron star becomes, the more momentum space you get.
- 07:06: If we can somehow add more matter to a neutron star-- throw another star at it, maybe-- it won't get spatially larger.
- 07:17: The star must expand.
- 07:22: The star expands in momentum space.
- 07:27: The more matter of the neutron star, the smaller its radius.
- 07:31: This is a quantum effect, even though it's happening on the scale of a star.
- 07:36: Until now, the neutron star has hovered above a critical size.
- 07:41: The space time curvature at the neutron star's surface is pretty extreme.
- 07:47: And the densities inside the star produce some very strange states of matter.
- 07:52: However, despite this, the star is still very much a thing in this universe.
- 07:58: And yet, below the star's surface, their lurks the potential event horizon, the surface of infinite time dilation.
- 08:05: Now, the event horizon doesn't actually exist as long as the neutron star stays larger than the would be horizon.
- 08:12: However, if we can increase the mass of the neutron star, the actual star shrinks, and the event horizon expands.
- 08:22: There's a mass where the radius of the neutron star and the event horizon overlap.
- 08:32: And the neutron star submerges beneath it.
- 08:38: But what happens to the star when it slips below its event horizon?
- 08:45: Space time is radically altered inside the star with all geodesics, space time paths, turning inward, towards the center.
- 08:54: When the black hole first forms, the material inside must resemble the stuff of the original neutron star.
- 09:09: From the point of view of the star, itself, the inward cascade happens.
- 09:29: But what happens to these as the star approaches an infinitesimal point, the Planck scale?
- 09:58: The material of the star and all of events that happened to it are no longer part of the timeline of the external universe.
2015-11-25: 100 Years of Relativity + Challenge Winners!
- 01:24: On December 9, we'll delve deeper than ever into the weirdness of black holes, after which we'll start exploring the nature of matter and time.
- 02:39: In the asteroid's frame, its starting velocity is zero.
- 03:41: ... one relating change in position, average acceleration, and time, with a starting velocity of zero in the frame of Apophis in ...
2015-11-18: 5 Ways to Stop a Killer Asteroid
- 01:38: These are the shooting stars that you see on a dark night.
- 06:20: In fact, I don't want to attempt more than one, because once the first one fails, it may be too late to start again.
- 10:47: Stars are very far apart.
2015-11-05: Why Haven't We Found Alien Life?
- 00:26: ... and probably billions of them are Earth-sized planets around sun-like stars. ...
- 00:43: ... why is the Milky Way so un "Star Warsy?" This genuine oddity is referred to as the Fermi paradox and the ...
- 01:13: As we saw in a previous episode, we're not so far from building starships ourselves.
- 01:17: Surely, some civilizations must make it through these growing pains and manage to reach the stars.
- 05:33: ... life was abundant on Earth remarkably soon after it first coalesced from stardust and that life either survived the late heavy bombardment or formed again ...
- 09:19: ... planets in the galaxy, only a tiny fraction needed to have a small head start on us in order to have produced the Federation of Planets and Stargates ...
- 09:31: So what if humanity started early?
- 09:33: ... all of the sun-like stars and Earth-like planets that will ever form over the full past and future ...
- 09:48: ... resources of past supernova explosions, but after the violence of the starburst and quasar ...
- 11:31: ... point of this philosophy is that the alien hypothesis is a bad place to start because you can explains almost any weird natural phenomenon as having ...
2015-10-28: Is The Alcubierre Warp Drive Possible?
- 00:07: So when do we get our first starship?
- 00:17: Star Trek warp drives zip around the galaxy at hundreds of times the speed of light.
- 00:33: ... and sci-fi fans was so inspired by the idea that he decided that the Star Trek warp drive should become a ...
- 02:16: But if you're cheeky, you can actually just make up a solution to the equations of GR without starting with a real mass/energy distribution.
- 02:49: A starship inside the bubble is carried along for the ride while feeling no acceleration at all.
- 06:44: As I've argued before, we'll reach the stars by sub light speed starships long before that.
- 07:38: And this should actually allow it to detect binary star systems in our galaxy.
- 08:49: ... media is hyping that there's an alien megastructure eclipsing a distance star. ...
- 09:06: Those dips are the drops in the star's brightness from some stuff moving in front of the star.
2015-10-22: Have Gravitational Waves Been Discovered?!?
- 03:16: ... most insane gravitational phenomena in the universe-- neutron stars or black holes in-spiraling just before merger, or gravitational ...
- 04:34: This has been seen in binary neutron stars.
- 04:42: ... could actually see g-waves, we'd be able to study black holes, neutron stars, even the extremely early universe in ways never before ...
- 06:51: LIGO really just scratched the minimum sensitivity needed to spot merging neutron stars and black holes in relatively nearby galaxies.
- 07:42: ... even though advanced LIGO only started running a few weeks ago on September 18, some predictions tell us that ...
- 09:24: ... week, we talked about real spaceship options for getting to the nearest star. ...
2015-10-15: 5 REAL Possibilities for Interstellar Travel
- 00:03: The future of humanity is in the stars.
- 00:10: So what would it take to build a starship?
- 00:27: Is it really so difficult to colonize other star systems?
- 00:48: Humanity's first adventure to the stars won't and shouldn't wait for far-off fantastical technologies.
- 00:54: Our first starship would use technologies achievable in our lifetimes.
- 01:01: Now building a starship is going to take a huge amount of political cooperation, money, and single-minded focus.
- 01:31: The key is finding the right balance between speed of the starship and the amount of time it would take us to develop the tech to build it.
- 02:57: The sun does this pretty well, so let's build an engine that works like a mini star.
- 03:04: In fact why not choose the most middle option and just explode nukes behind our starship and surf the blasts.
- 03:16: ... assume modern thermonuclear devices and launch with roughly 3/4 of our starship's mass being taken up by 300,000 1 megaton hydrogen bombs, blast them ...
- 05:13: We've only been able to do this with small numbers of antiprotons at a time, not the kilograms we'd need to get to the stars.
- 06:07: What if we could sail to the stars on a wind made of light, the light sail?
- 06:39: This is an update to Robert Forward's Star Wisp spacecraft, but it should be scalable.
- 07:29: There are possibilities for breaking in the stellar wind of our destination star, although that is tricky.
- 08:11: The smaller the black hole, the more radiation, and this radiation could drive our starship.
- 09:14: OK, so lots of ways to get to the stars.
- 09:44: They land us on Alpha Cen in the latter half of the 2100s, assuming we start now.
- 09:50: Pure antimatter and the Kugelblitz drives, they're the starships of the far future.
- 10:21: Maybe we could launch a Star Wisp in less than 30 years.
- 10:34: Humanity's first attempts to land on other worlds might well have us sailing to the stars.
2015-10-07: The Speed of Light is NOT About Light
- 11:17: RedomaxRedomax asks what you would see if you traveled 18 times the distance to the particle horizon to come back to where you started.
- 11:39: ... froze in its expansion, which it won't-- then you'd get back to your starting point a long, long, long time ...
- 12:00: And all stars besides red dwarves would be long dead.
2015-09-30: What Happens At The Edge Of The Universe?
- 01:22: Let's start with that 46 billion light year number.
- 04:22: But for now, let's just assume we have a nice Alcubierre-class warp-ship and we burn the mass energy of entire stars to chase the particle horizon.
- 05:12: It's lumpy on small scales due to stars and galaxies, but smooth on large, sort of like ripples on the ocean.
- 06:36: In that case, our warp-ship would eventually travel all the way around this curved hypersphere and get back to where it started.
- 06:46: ... 18 times the distance to the particle horizon to get back to where you started, assuming expansion froze for the whole ...
- 08:25: Shadowmax889 asks why stars and planets aren't filled with dark matter?
- 08:42: To collapse completely into a star-sized object, it would have to lose a lot more energy.
- 08:57: But then these clouds radiate light in different ways, allowing the gas to cool even more and collapse into stars.
2015-09-23: Does Dark Matter BREAK Physics?
- 00:18: The Milky Way galaxy is spinning so fast that it should be scattering its stars into the void.
- 00:24: ... we can see, we can only account for 10% of the mass needed to hold its stars in ...
- 01:22: But again, we find the clusters appear to have way more mass than we see in the stars alone, that is if we understand gravity.
- 02:00: OK, let's start with the first possibility.
- 02:19: ... the galaxy would need to be swarming with baryonic things as massive as stars, but that are so compacted that they're basically ...
- 02:37: And they're basically crunched down, compact, dead or failed stars, black holes, neutron stars, brown dwarfs, Macaulay Culkin, et cetera.
- 02:53: But when, say, a black hole passes between us and a more distant star, we sometimes see a brightening of that star.
- 03:23: Well, the problem is that the stars on the edge of the galaxy are moving just as fast as the stars near the center.
- 04:03: The stars alone give you plenty of gravity.
- 04:17: But you can't just break general relativity and start over.
- 04:54: The gas was ripped away from the stars and now lives between the clusters.
- 05:08: ... be, then that dark matter should pass right on through, just like the stars. ...
- 05:25: And we see that in the Bullet Cluster, the dark matter is with the stars.
2015-08-27: Watch THIS! (New Host + Challenge Winners)
- 00:13: Let's start with the answer to the Newtonian version.
- 04:04: You start with the general spherical symmetric metric.
- 04:57: And you pretty much have to start from scratch.
2015-08-19: Do Events Inside Black Holes Happen?
- 06:59: That's not the reason, but here's my guess about how this unfortunate metaphor started.
- 07:03: ... Newtonian gravity, a projectile on the surface of a planet or a star needs a minimum speed called the escape velocity in order to get really ...
- 09:33: ... hole can form when a sufficiently massive object, typically a very heavy star, collapses and becomes more compact than its own Schwarzschild ...
- 09:42: In this situation, the mass of the precursor star and the associated mass of the black hole will indeed be the same.
- 09:48: However, the horizon forms first in the interior of the star and then expands.
2015-08-12: Challenge: Which Particle Wins This Race?
2015-08-05: What Physics Teachers Get Wrong About Tides!
- 05:46: So I think you can start to see what's happening here.
- 05:59: ... same way that a blister or a pimple will bulge up in the center if you start to squeeze it from the ...
- 10:53: ... when you start looking at very small scales, like what the quantum version of gravity ...
- 15:07: This stuff takes years to grasp and you're getting a head start Glad you're watching the show.
2015-07-29: General Relativity & Curved Spacetime Explained!
- 01:51: Let's start with Newton.
2015-07-22: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments
- 00:24: ... down as the writer and host of "PBS Space Time." This fall, I'll be starting full-time work at the US National Science ...
- 02:03: But as John Buluba and [INAUDIBLE] pointed out, after you view it a second time, it starts to make more sense.
- 04:57: But here's a preview of something that we're going to do next week that I want you to start chewing over.
2015-07-15: Can You Trust Your Eyes in Spacetime?
- 01:21: Let's get started.
- 06:07: For starters, this spacetime really is flat.
2015-07-08: Curvature Demonstrated + Comments
- 03:33: Starts here.
- 04:51: ... the vector you get back in New York isn't parallel to the one that you started ...
- 05:27: ... vector around the circle and see if you end up with the same vector you started ...
2015-07-02: Can a Circle Be a Straight Line?
- 00:45: We actually started this campaign in our "Is Gravity an Illustion?" episode.
- 02:22: Let's start with this picture of the flat Euclidean 2D plane from high school math class.
- 05:55: Parallel transport a vector around a closed curve starting at A and going all the way back to A.
- 06:00: If you end up with the same vector you started with, your space is flat.
- 06:14: But if those geodesics start converging or diverging at any point, then the space is curved.
- 07:03: If you end up with the same vector you started with space is flat, if not, it's curved.
2015-06-24: The Calendar, Australia & White Christmas
- 01:47: Now, eventually, the cycle of seasons will backtrack a full 360 degrees, returning to its starting point.
- 05:17: ... we'll just reckon time in atomic clock seconds or something like the Stargate system on "Star Trek," which, yes, I know was really just a way for the ...
- 06:52: He also points out that if we put enough of them around the sun that we could cover viewing angles from most star systems.
2015-06-17: How to Signal Aliens
- 00:49: Let's start with the radio.
- 02:53: So you could target the pulse to individual star systems and avoid wasteful transmission into empty space.
- 02:58: With a lot of lasers, you could even flash several star systems per second, re-aim, and repeat over and over.
- 03:28: ... something like NASA's Kepler satellite, astronomers stare at 150,000 or so stars at once continually for a few years, looking for ...
- 04:00: With a few Kerbal Keplers, the Kerbal astronomers could look at hundreds of thousands or millions of stars at once.
- 04:07: What if, instead of a planet, the object that's transiting in front of its star looks like this?
- 05:55: ... SETI also be looking for geometric alien billboards orbiting nearby stars. ...
- 10:33: ... to you now that we've given the answer, I encourage you guys to start talking amongst ourselves in the ...
2015-06-03: Is Gravity An Illusion?
- 02:05: For example, suppose that you're in a train car that starts accelerating uniformly forward along a flat track.
- 10:42: Earth analogs in Earth-like orbits around Sun-like stars are not going to be visible.
- 11:08: ... of how planetary systems form, of how proximity to different kinds of stars affects the atmospheres of planets, and so forth-- the prospect for ...
- 11:16: We can't reposition the planets here, so other star systems are the laboratories for these kinds of investigations.
2015-05-27: Habitable Exoplanets Debunked!
- 00:25: ... are accompanied by pictures that look a lot like M-class planets from Star Trek, with a solid surface, liquid water, and a surface gravity that ...
- 00:57: To astronomers, the phrase "habitable exoplanet" just means exoplanet that lies in the habitable zone of its host star.
- 01:04: ... in turn, is defined as the sweet spot of orbital distances from that star at which the energy from starlight would produce the right temperature ...
- 01:45: Basically the habitable zone is more of a guideline, a starting point to narrow down targets of interest.
- 01:50: Those estimates you hear of an average of one habitable planet per star in the Milky Way are really just statements about this starting point.
- 02:18: In April 2014, this planet got a lot of press as the first confirmed Earth-sized exoplanet in the habitable zone of its host star.
- 02:32: It shows the microscopic dip in starlight measured by the Kepler Telescope when the planet moved in front of its star.
- 02:39: ... knowing some properties of that star, then based on how much light gets blocked and for how long, astronomers ...
- 02:49: Turns out Kepler 186F is about 10% larger in radius than Earth in an orbit around the size of Mercury around a fairly dim red dwarf star.
- 03:46: You can measure the atmosphere of an exoplanet, but not if that exoplanet is an Earth-sized rocky body in a star's habitable zone.
- 03:54: ... atmosphere, you need to isolate the planet's light from that of its star and see how bright that light is at different ...
- 04:12: ... that information with the planet's mass, radius, and distance from its star, you can use models to get a rough picture of what the atmosphere is ...
- 04:23: ... directly image the planet, improving the contrast by blocking out the star's light, kind of like putting your hand over your eyes on a sunny day to ...
- 04:39: The planet just gets washed out by the star's light.
- 04:47: You take a spectrum of the star when the planet is in front of it.
- 04:50: This will be the combined spectrum of the planet and star.
- 04:53: And then you take another spectrum when the plan is behind the star.
- 04:55: That gives you the spectrum of the star alone.
- 05:01: ... this method only works for planets that are really close to their stars, because only planets that are close in will get hot enough to glow ...
- 05:18: And it can't be either too close or too far from its star, or it won't have liquid water.
- 05:34: ... of Earth-sized planets in Earth-like orbits around Sun-like like stars. ...
2015-05-20: The Real Meaning of E=mc²
- 00:51: ... we can get a better sense of what m equals E over c squared means if we start with some things that it implies that seem at odds with our everyday ...
- 01:42: ... of that watch that heats them up ever so slightly so that its atoms start jiggling a little ...
- 03:32: Whenever you turn on a flashlight, its math starts to drop immediately.
2015-05-13: 9 NASA Technologies Shaping YOUR Future
- 00:27: What do you do with your hand inevitably gets tired and you start losing grip strength?
- 09:11: Agreed, but Venus missions are shorter, so the relative cost savings of all female crews start to become less significant.
2015-05-06: Should the First Mars Mission Be All Women?
- 00:47: Let's start with the physiological arguments for all-female missions beyond Earth's moon.
2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi?
- 00:10: [MUSIC PLAYING] Whether you realize it or not, artificial gravity is essential to most sci-fi stars.
- 00:35: ... or fictitious "gravity plating" seems to conflict with known physics. "Star Wars," "Battlestar Galactica," "Star Trek," "Andromeda," the Ridley ...
- 00:49: But with the exception of "Star Trek," none of them even bother with a detailed explanation.
- 01:06: You'd need either enormous amounts of mass, so much that you'd basically have a planet and not a starship.
- 01:32: I'm thinking of something called the Gravitron, maybe the Starship 3,000.
- 01:39: And in the process, the wall starts pushing hard against your back.
- 03:05: Let's start with the iconic scene of Frank Poole jogging around the rotating command module in "2001: A Space Odyssey." Poole's height is 1.8 meters.
- 07:46: ... about rotation-induced gravity, like the way that its fighter ships, the Starfurys, launch just by dropping outward or the fact that objects or people that ...
- 08:45: But first, an announcement-- a viewer, not us, started a sub-Reddit dedicated to our program as an alternate form for episode discussion.
- 10:40: ... for starters, do some background reading on something called "decoherence." On a ...
2015-04-22: Are Space and Time An Illusion?
- 02:35: A good starting point for objective reality is universal agreement.
- 07:10: Last week, we asked whether NASA could start a zombie apocalypse.
2015-04-15: Could NASA Start the Zombie Apocalypse?
- 00:13: Could a zombie apocalypse start with a routine trip to space?
- 00:31: And the zombie phenomenon starts unexpectedly and spreads quickly, which is why it wreaks so much havoc.
- 01:08: But maybe they should because one scenario that's more plausible than you might think is that a zombie apocalypse could start in space.
- 01:20: Let's start with bacteria.
- 04:16: Will the zombie apocalypse start in space.
2015-04-08: Could You Fart Your Way to the Moon?
- 00:42: Let's start with rockets, actually, because there's a common misconception I want to clear up from the start.
- 02:48: In truth, even starting out from low Earth order, you'd be short of Earth's escape velocity by a factor of about a billion.
- 03:11: Let's start with the exhaust velocity of a fart.
2015-04-01: Is the Moon in Majora’s Mask a Black Hole?
- 01:44: So let's get started.
- 02:15: The key evidence appears in the scenes just before the moon hits, when loose rocks start flying upward off the surface of the planet.
- 04:57: The only solid macroscopic objects in nature that are that dense are neutron stars.
- 05:08: ... if you imagine some esoteric, unnatural way to synthesize a neutron star, theoretical estimates say that you'd still need at least 1/10 of the ...
- 05:23: ... still millions of times less than what you'd need to make a pure neutron star. ...
- 05:32: So if it's not a neutron star, how can Majora's moon be so dense?
- 05:35: Well, maybe it's neutron star material, but only in the outer layers.
- 05:39: ... enough of a gravitational scaffolding, so to speak, to achieve neutron star densities with less mass than would normally be ...
- 05:50: So to serve as a gravitational seed, we need something incredibly small and incredibly dense, even denser than a neutron star.
- 06:13: You could start with a more massive and larger black hole and just let it evaporate slowly.
- 07:43: ... Smart" where Joe Hanson explained that the average color of all visible stars in the universe comes out to an off-white called Cosmic ...
- 08:01: Oxygen gets fused in the cores of stars.
- 08:03: And as far as I know, the first stars didn't start forming until a couple hundred million years or so after the sky went dark.
2015-03-25: Cosmic Microwave Background Explained
- 00:12: Stars and galaxies notwithstanding, space is pitch black.
- 03:06: At this temperature, it's too hot for electrons and protons to even coalesce into atoms, let alone stars, planets or galaxies.
- 05:03: Well, they managed to clump, become stars, galaxies, and through a complicated process of cosmic recycling, us.
- 05:24: I'll tackle as many as I can on the next episode of "Space Time." Last week, I challenged you to stabilize a gyro-driven Star Fox barrel roll.
2015-03-18: Can A Starfox Barrel Roll Work In Space?
- 00:00: Few things exhibit as much as disdain for basic physics as the space levels in Nintendo's "Star Fox," except the barrel roll.
- 00:31: I'll leave that to him, though, because I want to focus on one thing that the gaming world may have gotten right-- the "Star Fox" barrel roll.
- 00:38: In general, "Star Fox" flushes physics down the toilet during the space levels.
- 02:41: ... small thrusters on the top and bottom of each wing, one quick burst to start to ship rotating and then another opposing burst to stop ...
- 03:23: By rotating the flywheel quickly, I end up transferring its angular momentum to myself, so I start spinning.
- 04:04: When I flip the flywheel 180 degrees, its individual angular momentum starts pointing toward the rear of the ship, i.e.
- 05:10: But similar to our "Star Fox" setup, the ISS does rotate pre-spun flywheels to control its orientation.
- 05:29: I don't have any numbers on the mass and rotational inertia of a "Star Fox" Arwing.
- 05:42: ... meter is, which is apparently the official unit of measurement in the "Star Fox" ...
- 07:41: ... are unstable, and in quadrillions of years, individual nuclei will start falling ...
- 08:28: ... so much empty space between star systems and galaxies that the probability of any two of them colliding ...
2015-03-11: What Will Destroy Planet Earth?
- 00:50: Let's review some possibilities, starting with one that has probably crossed your mind at some point-- nukes.
- 03:19: But in 1%, the inner planet orbits stretch out after about three billion years and Earth starts doing drive-bys of Venus and Mars.
- 05:43: ... between 100 billion and a few trillion years from now, space could start to stretch-- not just at faster rates, but on smaller and smaller ...
- 06:35: ... for Earth destruction that I might have overlooked-- and no, the Death Star is not a viable ...
2015-03-04: Should We Colonize Venus Instead of Mars?
- 01:11: For starters, Venus is closer to Earth.
- 01:36: If we ever start a colony, we'll need to bring along almost everything.
- 04:54: ... in the favorable gravity, and it starts to look like the upper atmosphere of Venus might be the closest thing in ...
- 06:07: If we start a grassroots movement, I'll let you know on the next episode of "Space Time".
2015-02-25: How Do You Measure the Size of the Universe?
- 01:18: In a nutshell, you start with the age of the universe.
- 05:28: If you're inclined, go ahead and get the discussion about that started in the comments below.
2015-02-18: Is It Irrational to Believe in Aliens?
- 00:39: So where do we start?
- 00:40: Well, the Milky Way galaxy has about 200 billion stars.
- 00:50: It looks like it's around one habitable planet per star, on average.
- 00:54: So 200 billion stars, 200 billion habitable planets.
- 02:07: Let's start with a pro aliens argument, that intelligent life should exist.
- 02:53: ... compensate with billions or trillions of habitable worlds, it would start to look like a cosmic conspiracy, like Earth and humanity are absurdly ...
2015-02-11: What Planet Is Super Mario World?
- 00:21: Let's start with how gravity affects motion, because that a huge effect on jumping.
- 05:08: In fact, g values this large would more likely occur on stars.
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