2022-12-14: How Can Matter Be BOTH Liquid AND Gas?
- 19:51: ... would also have a much harder spectrum - so a lot more nasty UV light, not to mention x-rays and gamma rays, which may wreak havoc on the ozone ...
2022-12-08: How Are Quasiparticles Different From Particles?
- 06:25: ... a quantum of a sound wave, similar to how a photon is a quantum of light - of an electromagnetic ...
- 06:42: Phonons behave in many ways like light.
2022-11-23: How To See Black Holes By Catching Neutrinos
- 01:43: ... neutrinos means that they tend to travel at very close to the speed of light, just because it doesn’t take much energy to get them close to the cosmic ...
- 02:05: ... a low-energy neutrino with a wall of lead, the wall would need to be a light year thick to have even a 50-50 chance that the neutrino gets close ...
- 03:50: ... but an electron or muon will continue through the ice, emitting light as it interacts with other charged ...
- 04:01: This is seen as a cone of blue light that trails the particle.
- 04:05: It trails behind because the lepton is traveling faster than light.
- 04:10: See, the speed of light is reduced in any medium inside a vacuum.
- 04:17: ... it creates also start out with a speed faster than the reduced speed of light in the ...
- 04:53: The actual detectors are sensitive photomultipliers - basically extremely sensitive light detectors - suspended in deep boreholes.
- 08:08: It’s a beautiful spiral galaxy 47 million light years away.
- 09:05: ... is not that powerful, it's known as a Seyfert galaxy, and the light of its accretion disk is hidden from us by a wreath of dust and gas ...
- 10:17: This leads to massive amplification of the jet’s light due to Einstein stuff.
- 10:24: Relativistic boosting due to the jet particles racing towards us at near the speed of light.
- 16:33: ... 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?
- 06:13: ... that it takes sophisticated computer modeling to understand any but the lightest elements - and many mysteries still ...
2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations?
- 11:17: ... that expands in every direction through space at close to the speed of light, making visible changes wherever they go, and that they stick around for ...
- 11:45: ... going to be able to expand through the cosmos close to the speed of light any time ...
- 11:54: ... how to expand into space and another million to cross the galaxy at 10% light speed, this delay will have basically no effect on cosmological ...
- 12:58: Counterintuitively, this fact implies that grabby expansion is incredibly fast, around a third of the speed of light.
- 17:23: ... is made, in apparent violation of relativity and the speed of light limit on causal ...
2022-10-26: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
- 00:47: ... which tells us that no causal influence can travel faster than light. ...
- 01:48: Did you cause information to travel faster than light?
- 02:26: ... you really do seem to have an effect that travels faster than light, with the ball on the moon switching from a superposition state to a ...
- 06:29: They blasted a beam of calcium atoms through the intense light of an arc lamp.
- 06:33: ... light excited electrons in calcium atoms to higher energy level and they ...
- 09:11: Aspect’s setup was very similar to Clauser's, with a beam of calcium atoms excited by light - this time a laser rather than an arc lamp.
- 09:42: ... this case a chunk of quartz that bends the path of light in different ways depending on whether the quartz is vibrating, and that ...
- 12:18: Any violation of locality still means that some sort of influence travels faster than light - the sort of spookiness that Einstein hated.
- 15:33: So Alek, from all of us here at Space Time, we thank you for the light that you so clearly brought to science and to your community.
- 17:13: The real limit is the amount of light you receive, and that would be too low beyond a certain distance.
- 17:20: ... so I think the idea is that this works on the scales of hundreds of light years, but not many 1000s of light years type scales. And ...
2022-10-12: The REAL Possibility of Mapping Alien Planets!
- 00:03: ... happening. A train of spacecraft sailing the sun’s light to a magical point out there in space where the Sun’s own gravity ...
- 01:25: ... and it depends on size. Bigger is always better. When light passes into a telescope, its wave nature interacts with the edges ...
- 04:12: ... massive objects. But that curvature also bends the path of light. You know what also bends light? Lenses. So a gravitational field ...
- 04:36: ... lenses are designed to bring light from the same point to a single focus point, allowing an ...
- 06:05: ... small-sats are sent in a long train, each riding on the light of the sun with a solar sail. That second seems the preferred ...
- 07:45: ... times faster than Voyager. We’d want each craft to be very light - ideally under 100 kg. But with advanced modern ...
- 10:07: ... into a larger scope. It may even be possible to repurpose the light sail as a mirror, if we want to get really clever about ...
- 12:52: ... from their colours. And if we spot bright points of light on the planet’s night side - aka cities - that would ...
- 19:23: ... the vacuum permittivity the Planck constant times the speed of light. If the fine structure constant was different then one or ...
2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?
- 00:43: Like the speed of light, the gravitational constant, or Planck’s constant.
- 01:34: As with much of quantum mechanics, it started with us watching the light produced as electrons flicked between energy levels in atoms.
- 01:43: ... specific energies that we observe as spectral lines - sharp peaks in the light observed when we break it up into a spectrum of different ...
- 01:58: Hydrogen atoms only emit light with these specific energies.
- 02:55: ... pi, the permittivity of free space, Planck's constant and the speed of light. ...
- 03:28: ... charge of the electron is in Couloumbs, the speed of light in meters per second, vacuum permittivity and Planck's constant also ...
- 04:17: And the orbital speed of an electron in the ground state of the Bohr model of the hydrogen atom is 137 slower than the speed of light.
- 09:47: Transmit, say, the value for the speed of light - 299,792,458 m/s, and you also have to explain what a meter and a second are.
- 11:20: ... example, the speed of light is the translation factor between the dimensions of space and time ...
2022-09-21: Science of the James Webb Telescope Explained!
- 02:38: Another early decision that persisted was the focus on the infrared light - and I’ll come back to why.
- 03:43: The telescope is focused on the infrared - that light on the longer-wavelength side of visible light.
- 03:50: Hubble, on the other hand, did visible light into ultraviolet.
- 03:54: The choice of long wavelength light specializes JWST for a number of particular science goals.
- 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.
- 04:11: ... that UV light has now been traveling to us for most of cosmic history, and the ...
- 04:28: JWST is designed to catch that light and has already observed galaxies much closer to the Big Bang than ever before.
- 04:40: ... well as peer through that dust which normally blocks shorter wavelength light. ...
- 05:16: ... four separate instruments that allow it to take images as well as break light up into spectra, with sensitivities from visible red light through the ...
- 05:32: ... of many objects at once; or using a coronagraph to block the bright light of a star to better see its planets, to name just a ...
- 09:28: Those white blobby things are massive elliptical galaxies of the cluster, several billion light years away.
- 09:36: These arcs are much more distant galaxies whose light is warped by the gravitational field of the cluster.
- 09:54: Those pointy things are diffraction spikes, caused by interactions of incoming light with the hexagonal aperture of the scope.
- 10:07: ... the universe very differently, so studying the same objects in this new light really deepens our ...
2022-09-14: Could the Higgs Boson Lead Us to Dark Matter?
- 06:19: ... also exclude photons, because not interacting with light is the first defining characteristic of dark matter.We aren’t left with ...
2022-07-27: How Many States Of Matter Are There?
- 09:43: When this happens, objects that are light enough will float from the bottom to the surface, something that would never ever happen with a solid.
2022-07-20: What If We Live in a Superdeterministic Universe?
- 05:17: A foundational axiom of relativity is that no causal influence can travel faster than the speed of light.
- 08:34: ... Light travels a 45 degree angle, and so if local realism holds, only events in ...
- 09:01: ... electron’s spins were determined by a single event in both of their past light ...
- 09:36: Locality and realism would have been saved if it turned out that the states of the electrons were fixed when their past lightcones overlapped.
- 10:15: But what if statistical independence is an idealisation - trace past light cones back far enough and everything is connected.
- 11:54: And that’s … impossible because if you trace the past lightcone of any two points in the observable universe back far enough they will overlap.
- 12:08: ... a Bell test where the “deciders” and the measurement subjects have past light cones that intersect with each other as far back in the past as ...
- 12:29: Their first effort used the light from a pair of distant stars as proxies for Alice and Bob.
- 12:35: ... “random” color of individual photons of that light was used in place of a random number generator to decide the measurement ...
- 13:12: The same team followed up with a cosmic Bell test using rather more distant objects - quasars several billion light years away.
- 15:40: So thank you for bringing us a step closer to fiscal superdeterminism, so that the overlap of our past light cones can remain as recent as possible.
2022-06-30: Could We Decode Alien Physics?
- 00:00: ... particle running through the alien circuitry is the lightest lepton and has negative electric charge. Obviously the ...
- 16:39: ... an example is something like a giant laser array pushing a light sail. So this concern is very valid. Slowing down takes ...
2022-06-22: Is Interstellar Travel Impossible?
- 02:01: The nearest star, Proxima centauri, is 4.2 light years away.
- 02:19: ... traveling at relativistic speeds - sizable fractions of the speed of light. ...
- 02:35: ... of tiny craft powered by solar sails, which would be accelerated to 20% light speed by a giant array of lasers back on ...
- 02:57: But there are proposed advanced forms of propulsion that could in principle accelerate a proper spacecraft to a fair fraction of the speed of light.
- 03:07: For example, really REALLY big light sails, or compact fusion drives, or matter-antimatter engines.
- 04:47: We’ll be using a propulsion system that can accelerate us to 20% of the speed of light.
- 07:21: So both the gas and the dust are diffuse, but remember, we’re traveling 4 light years.
- 08:59: They figure that the light hydrogen and helium don’t do lasting damage - they just deposit heat.
- 09:27: ... eroded by tiny impact craters down to around a millimeter depth every 4 light ...
- 12:04: If you want to travel at speeds closer to that of light, you need up to several meters of titanium or tens of meters of water.
- 12:55: If you manage to accelerate to 80 or 90% light speed then most of the cosmic rays will hit from in front, and then your windshield protects you.
- 13:32: ... interstellar trips further than a few light years, shielding against the interstellar medium, micrometeoroids and ...
2022-06-01: What If Physics IS NOT Describing Reality?
- 15:25: ... the chance is very small - given that stars are of order a light-second across, while the distance between them is light years. I’ve ...
2022-05-25: The Evolution of the Modern Milky Way Galaxy
- 02:19: ... halo - also spheroidal, but twice the diameter of the 100-thousand light year wide disk. This thing is sprinkled with wayward stars ...
- 05:11: ... that result from specific elements sucking up or producing light at specific wavelengths. Stars with similar metallicities ...
- 07:58: ... parts - there’s the thin disk, which is a few hundred lightyears thick, and is the main star factory of the Milky way. It’s ...
- 08:29: ... guessed it - the thick disk, which extends a few thousand light years above and below its more slender counterpart. ...
- 09:42: ... 10 billion years ago, the Milky Way has only snacked lightly. But we can trace that history also. When a dwarf galaxy gets too ...
- 12:11: ... loop all across the ‘bottom’ half of the galaxy, a 600,000 lightyear long tail of gas called the ‘Magellanic Stream.’ And while the ...
- 14:38: ... needs to happen before the star turns on and blasts away all of the lighter ...
- 18:41: ... across the event horizon of a black hole at the speed of light - that’s the velocity of an inertial frame that falls from ...
2022-05-18: What If the Galactic Habitable Zone LIMITS Intelligent Life?
- 00:24: ... prone to erratic outbursts and wouldn’t produce enough ultraviolet light for photosynthesis. If the sun contained significantly less ...
- 02:20: ... ancestors, the Sun was a wondrous source of warmth, light, food, and stability. It was a powerful, never-tiring giver of ...
- 04:32: ... That’s the distance from the star where the intensity of light is in the right range to allow liquid water on the ...
- 08:01: ... of the atmosphere. For example, a supernova within 150 light years would obliterate our ozone layer. On the other hand, ...
- 10:48: ... starting out as a band between around 20 and 30 thousand light years from the center, it expanded inwards as the supernova ...
2022-05-04: Space DOES NOT Expand Everywhere
- 10:52: ... of the Gravitational constant, the Planck constant, and the speed of light - so if those aren’t changing - and there’s no evidence that they change ...
2022-03-30: Could The Universe Be Inside A Black Hole?
- 01:07: We can think of the event horizon as the surface where the flow of space itself is like a river moving at the speed of light.
- 01:15: ... particular location in space, due to the fact that nothing that not even light can travel back out from below the event ...
- 01:49: ... universe that are being propelled away from us faster than the speed of light. ...
- 02:12: ... it’s somewhat more complicated - for example, we’re still receiving light from objects that are now beyond that horizon, because it was emitted by ...
- 02:22: ... is closer to us than the spot where recession equals the speed of light. ...
- 06:24: Space flows at the speed of light across the event horizon from within.
2022-03-23: Where Is The Center of The Universe?
- 07:13: ... be the moon of the past, because you’re aligning your finger with the light that only now reached you from the moon, and that light has been ...
- 08:41: They’re the grid that defines the fabric of space time in general relativity, and correspond to the paths followed by light.
- 14:27: ... (like the ball stack bounce), and then goes into the speed of light and even time ...
- 18:05: It’s only equal to helicity for particles that you can’t overtake - aka light speed, massless particles.
2022-03-08: Is the Proxima System Our Best Hope For Another Earth?
- 01:38: That parallax revealed the system to be close - closer than any other - but still more than four light years distant.
- 04:22: ... the wavelengths of all the star’s light are stretched as the star moves away from us and compressed as it moves ...
- 11:36: During flares, Proxima B is blasted with X-rays and ultraviolet light and high energy particles.
- 12:05: At Proxima B’s location there’s enough light to keep water liquid but most of that is infrared.
- 12:12: There’s far less visible light, so to our eyes the star would appear very dim.
- 12:21: ... on alternative photosynthetic pathways that can make use of the infrared light. ...
- 13:19: ... from molecules in Proxima B’s atmosphere, if it has one, or even the light reflected from the planet’s ...
- 13:56: The plan is to use a giant laser array to accelerate a train of mylar light sails to 20% the speed of light in the direction of Proxima.
- 14:45: Four lights are visible through the thick atmosphere - the gleaming white twins Tolimar and Rigel Kentaurus, the glowering red orb of Proxima herself.
2022-02-23: Are Cosmic Strings Cracks in the Universe?
- 00:58: ... mass and they lash through space at a close to the speed of light. They could be the most bizarre undiscovered entities that probably ...
- 04:51: ... energy was nucleated, and it expanded at the speed of light. Many bubbles would have started at different places across the ...
- 08:50: ... these things are long. They started as long as light can travel between the nucleation event and the completion ...
- 10:09: ... away from each other along the string at near the speed of light. They’re whipped back and forth by the oscillating string, ...
2022-02-16: Is The Wave Function The Building Block of Reality?
- 00:03: ... or to teleport between locations, or to influence each other faster than light. But somehow, none of this strangeness makes its way to the familiar ...
- 14:52: ... is again yes. Just as it’s possible to create a black hole from pure light - a so-called kugelblitz - if you could focus enough energy from ...
- 17:28: ... reach YOU at your “infinite distance”. And it’s the surface from which light is infinitely redshifted - sapped of all energy - before it reaches that ...
- 17:42: ... observe an object being frozen at the event horizon if the light emitted at the moment it crosses the horizon from its perspective takes ...
2022-02-10: The Nature of Space and Time AMA
- 00:03: ... uh as an example uh we have cosmological redshift okay so a photon of light traveling from one galaxy to the other has to travel through an ...
2022-01-27: How Does Gravity Escape A Black Hole?
- 00:10: Nothing can escape from within the event horizon unless it can travel faster than light.
- 00:17: Fact: gravity travels at the speed of light.
- 00:54: These are objects of such extreme density that the fabric of space is dragged inwards at greater than the speed of light.
- 01:21: ... properties depend on how fast you are moving relative to the speed of light. ...
- 01:33: Special relativity enshrined the speed of light as the absolute cosmic speed limit.
- 01:38: It tells us that light speed is the maximum speed at which any causal influence can travel.
- 01:49: Naturally enough, the “c” of the speed of light made its way into the equations of general relativity.
- 01:55: When you use those equations to calculate the speed of various gravitational effects, they also turn out to be the speed of light.
- 02:08: ... travel at the speed of light, and that’s been confirmed when gravitational waves from colliding ...
- 02:56: ... gravity travels at the speed of light, and all of the mass of a black hole is hidden beneath the event horizon, ...
- 04:38: Falling from very far away, an observer and the patch of space that they occupy reach light speed at the event horizon of the black hole.
- 07:55: That’s easy - these are virtual particles, and in quantum field theory, virtual particles are not restricted by the speed of light.
- 08:06: ... virtual particle interactions, possible and Impossible, and the speed of light limit actually emerges in a sort of statistical ...
- 09:27: As it approaches the surface that is to become the event horizon, it approaches light speed with respect to someone watching from a distance.
- 09:39: It appears to freeze at the event horizon, and the light it emits becomes stretched out and sapped of energy.
- 10:19: ... about the source of the gravitational field as always being in your past lightcone - and that has to be outside the black ...
2022-01-19: How To Build The Universe in a Computer
- 01:40: He arrayed 37 light bulbs on a plane, each one representing billions of stars in a spiral galaxy disk.
- 01:49: The light from each bulb was its gravity - felt more strongly close to the bulb, and dropping away with the square of distance, just like gravity.
- 01:57: At any point on the disk, a galvanic cell could determine in which direction the intensity of light was strongest.
- 02:04: ... the simulation went like this: Holmberg started with a pair of these light-bulb-galaxies next to each other, with the motion of each bulb existing only as a note ...
- 02:15: He would then measure light at each bulb, which told him the summed “gravitational” pull on that group of stars.
- 03:28: ... equations - which is why Holmberg had to solve the problem with light ...
- 09:28: In your quasar disk you need to simulate separately how light travels through the hot plasma.
- 10:28: It simulated 13-billion light years wide cube containing over 300 billion particles, each representing a billion-Suns worth of dark matter.
- 11:46: Because we’ve come an awful long way since Erik Holmberg pushed some light bulbs around on his table.
2022-01-12: How To Simulate The Universe With DFT
- 18:10: ... Dyson sphere reprocessing a sun’s visible light into infrared, ultimately releasing exactly as much energy as it ...
- 19:27: ... can be a real gas guzzler, so perhaps Dyson spheres are made to power light sail lasers that accelerate craft to 99.9999blahblah% the speed of light ...
2021-12-29: How to Find ALIEN Dyson Spheres
- 01:00: ... the Sun with the radius of Earth’s orbit, we’d collect all of the Sun’s light - a billion times more than what we’d get just covering the planet in ...
- 02:49: It doesn’t reflect nearly as much of the Sun’s light as you’d expect for a globe of water and rock - it's as though that energy is being sucked up.
- 02:58: But if you shifted your gaze from visible light to infrared, you’d find all of the missing energy.
- 03:05: ... the Sun produces a thermal spectrum - light generated by its 6000K surface is distributed at all wavelengths, but it ...
- 03:17: And Earth’s biosphere - mostly its forests - absorb a fraction of that light and use it to power biological processes.
- 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 telescopes, it ...
- 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.
- 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.
- 07:24: But from our great distance the light from the star and the sphere would be blended into a point.
- 07:31: Two pure thermal spectra would be stitched into one weird spectrum with too little light at visible wavelengths and too much at infrared wavelengths.
- 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.
- 08:17: For something with a pure thermal spectrum, we can exactly identify its temperature from, say, the ratio of red light to blue light.
- 09:31: But if we measure its colour using an infrared wavelength along with our visible light, we’d find too much of that IR.
- 09:46: ... 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 ...
- 10:39: Then they checked whether these stars had an excess of light in the infrared.
- 12:33: ... used the WISE survey to look for galaxies that had too much infrared light compared to their visible ...
2021-12-20: What Happens If A Black Hole Hits Earth?
- 00:29: ... very far. The nearest known is - the Cygnus X-1 black hole - at 1000 light years distant. It’s currently devouring its binary companion star, which ...
- 02:50: ... frequently pass in front of more distant stars, magnifying those stars’ light with gravitational ...
- 03:25: ... don’t devour stars like Cygnus X-1, and they don’t warp the passage of light from distant stars strongly enough to easily spot them. But fortunately ...
- 06:02: ... particles collide with each other sizable fractions of the speed of light. This generates hilariously high temperatures - much hotter than the ...
- 07:40: ... in 1908 in the middle of Siberia. Witnesses described a stripe of light in the sky as bright as the sun and a thunderous sound like cannons that ...
2021-12-10: 2021 End of Year AMA!
- 00:02: ... that followed gabe although you can watch the one where we had a lightsaber fight to win control of the show [Music] long story short every ...
2021-11-17: Are Black Holes Actually Fuzzballs?
- 00:39: ... - the singularity - which is surrounded by a surface from which even light can’t escape - the event ...
- 10:30: The normally Planck-length strings can therefore pile up into fuzzballs with sizes ranging from kilometers to light years.
- 10:50: Light trying to escape would still be massively redshifted - sapped of energy by the gravitational field - rendering the object effectively black.
- 14:10: ... (like the ball stack bounce), and then goes into the speed of light and even time ...
2021-11-10: What If Our Understanding of Gravity Is Wrong?
- 00:42: ... way too weak to hold galaxy clusters together, or to bend the path of light to the degree seen in gravitational lenses - when more distant light ...
- 08:50: ... it was possible to see if it gave the right result for the bending of light by galaxies, which wasn’t even possible with the original ...
- 10:21: One of the most important pieces of evidence for dark matter as a particle is seen in the light that comes from the very early universe.
- 10:40: Back then, light and matter were locked together due to the extreme densities.
- 10:51: But dark matter doesn’t interact with light, so it would have been able to collapse just fine.
- 10:58: ... cooled enough for regular matter to be released from the clutch of light, it could have followed the dark matter into its deep gravitational wells ...
- 12:33: ... galaxy clusters collide and the dark matter gets ripped away from the light matter - it makes you doubt that dark matter is just light matter acting ...
- 16:40: Jackie Johnson asks - in the case of gravitational lensing, isn't the light still traveling in a straight line?
- 16:46: Isn’t it spacetime that bends, not light?
- 16:52: Light does travel a straight line if you look at an infinitesimally small patch of space.
- 16:58: Imagine light traveling through curved space as like an and walking across a disco ball.
2021-11-02: Is ACTION The Most Fundamental Property in Physics?
- 00:02: ... Here’s an example: around 40 AD, Heron of Alexandria noticed that when light moves between two points, out of all the possible paths between them, it ...
- 01:22: ... could be minimized to determine the trajectories of matter as well as light? There were some efforts - for example Euler considered properties ...
- 02:50: ... energy had the same minimizing property as does time for the path of light. He found that the ball will always follow the path that minimizes the ...
- 08:06: ... that Fermat figured out that light always travels the path that minimizes its travel time - the principle ...
- 13:46: ... remember, this all started with Heron of Alexandria studying light two thousand years ago. He found a very simple and beautiful pattern in ...
2021-10-20: Will Constructor Theory REWRITE Physics?
- 10:42: ... like the equivalence principle and the invariance of the speed of light. ...
- 14:00: ... In some cases its pretty quick - quicker than light would make the same journey sans ...
2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light
- 00:02: Paradoxically, the most promising prospects for moving matter around faster than light may be to put a metaphorical brick wall in its way.
- 00:40: ... they could travel if the barrier wasn’t there - and even faster than light could traverse the same ...
- 05:09: ... would take to travel that distance sans barrier - even at the speed of light. ...
- 05:27: ... his theory of special relativity explains that if you move faster than light, you can send signals into the past, and create a whole bunch of ...
- 06:55: Certain definitions seem to imply faster than light motion.
- 07:08: ... center of that wavefunction can’t travel faster than the speed of light, but upon measurement, the particle may appear to be at the leading edge ...
- 11:30: Did the particles travel faster than light?
- 12:21: Because as we’ve discussed many times before, when it comes to the speed of light, the house always wins.
- 13:06: ... (like the ball stack bounce), and then goes into the speed of light and even time ...
2021-09-21: How Electron Spin Makes Matter Possible
- 15:34: ... mapping, where we map the stuff around black holes by watching how light bounces ...
- 15:48: ... like dim stars rather than, well, black holes because they slingshot light around from behind them. So it’s true that black holes do this, but if ...
- 16:12: ... in that case the dark area is a little larger, because most of the light gets sling-shotted from a bit further out - the photosphere where light ...
- 16:27: ... a spectrum of a bright quasar and see the different components of that light vary in different ways over months or years. Not advisable for a school ...
- 18:06: ... me out for my using the expression “Up to 10% or more” of the speed of light, regarding how fast gas can be blasted away from a ...
- 18:19: ... moving away from the black hole a few perecent to 10% the speed of light, and in rare cases even faster. I will try to speak with better error ...
2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe
- 00:25: ... how they look from afar - perfect metronomes of flashing light as these rapidly spinning stars sweep us with their jets as ...
2021-09-07: First Detection of Light from Behind a Black Hole
- 00:07: Our cleverest astronomers have figured out ways to catch light that skims the very edge of black holes.
- 00:20: A few weeks ago a story made the rounds of pop-sci media proclaiming that for the first time light had been detected from behind a black hole.
- 01:13: We talked about this soon after it came out - but to remind you, here we have radio light from charged particles whirling around the black hole.
- 01:21: And the more recent version of this in polarized light shows the grain of the magnetic field right near the black hole’s edge.
- 02:08: ... technique is reverberation mapping, in which we watch as a flare of light from a violent event near the black hole radiates and reflects - ...
- 02:23: ... that light reaches us - many, many millions of light years away - it’s still ...
- 02:41: A spectrum, by the way, is what you get when you split light into its component colors or wavelengths.
- 02:48: ... basically you watch the quasar, which is just a faint point of light on the sky, and stretch it into an even fainter flickering rainbow, and ...
- 04:47: It can be driven to up to 10% or more of the speed of light.
- 05:04: ... allows the maelstrom to reprocess some of the light of the accretion disk so that it shines bright in very specific colors ...
- 05:15: In a normal spectrum we see the light from these electron transitions as sharp spikes at specific wavelengths - what we call emission lines.
- 05:22: But in a quasar, the gas is moving fast, and that motion shifts the wavelengths of the light as we see it.
- 06:19: The light from this gas is ultimately powered by the light from the accretion disk.
- 06:23: So when our expanding shell of light rips through this gas the broad lines get supercharged - but in a complicated way.
- 06:35: ... of the quasar is slower than the gas of near side because the far-side’s light has to travel further to get to ...
- 07:33: Its light is blue-shifted to shorter wavelengths.
- 07:36: That gas responds late to the flare because the light has to take this roundabout journey.
- 07:49: And it responds before the blue-shifted light.
- 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.
- 09:38: The object is I Zwicky 1 - a so-called Seyfert galaxy, which is like a mini-quasar - this one around 100 million light years away.
- 09:47: Near the black hole there are sources of light that I haven’t mentioned yet.
- 10:01: As light from the accretion disk passes through this haze it gains energy from the electrons, boosting it all the way up to X-ray energies.
- 10:39: ... light then spread in all directions - some traveled straight to us, some ...
- 10:49: A portion of that light was then grabbed by the black hole’s gravitational field and slung right back around towards us, and magnified in the process.
- 11:54: ... flickering points in the sky, and in that flickering reconstruct how light reverberates around the most extreme regions of space ...
- 12:54: ... V-A wonders whether faster than light communication methods might be detectable from great distances - as in, ...
2021-08-18: How Vacuum Decay Would Destroy The Universe
- 01:15: ... like a bubble of annihilation that expands at the speed of light, rewriting the nature of the quantum fields as it ...
- 07:01: ... bubble grows, and that growth very quickly approaches the speed of light. Once it gets going, the bubble is unstoppable, and will ...
- 11:34: ... safe. If the vacuum decay starts beyond several billion light years, the accelerating expansion of the universe will throw us ...
- 12:07: ... our cosmic horizon we’ll never see it coming. Because no light can outpace the expanding bubble to warn us of its approach. ...
2021-08-10: How to Communicate Across the Quantum Multiverse
- 03:55: ... us some pretty crazy science fiction powers - I’m talking faster than light communication, and even the ability to send messages between the worlds ...
- 16:58: ... see that field in many ways, including by watching the radio light emitted by electrons spiraling in that magnetic field - what we call ...
2021-08-03: How An Extreme New Star Could Change All Cosmology
- 00:00: ... of “huh, that’s weird”. Well, we’ve just observed a faint point of light on the sky whose weirdness could change the way we think about the ...
- 00:21: ... we thought all white dwarfs formed. This one peculiar point of faint light may change our understanding of not just white dwarfs, but of all ...
- 02:51: ... Keck was needed to do the spectroscopy - to break the white dwarf’s light up into component colours. Splitting the light this way makes it even ...
- 03:19: ... When electrons in an atom move between orbitals, they emit or absorb light with very specific wavelengths. That tells us what kind of atoms are in ...
- 03:58: ... our highest-resolution telescope cameras see them as single points of light. But astronomers have a clever trick. If you know how much light a star ...
- 05:24: ... Milky Way, and Zee was one of them. So we have its distance - around 135 lightyears ...
2021-07-21: How Magnetism Shapes The Universe
- 00:43: Threads tugged lightly towards the Earth, tightly towards the Sun, or into inescapable knots towards black holes.
- 04:21: We can see those tangled field lines in ultraviolet light as charged particles spiral along them, up and down from the Sun’s surface.
- 06:17: When light passes through the dusty interstellar medium it gets scattered by these grains - it bounces off them.
- 06:24: But the pattern of alignment of these grains imprints a pattern on the scattered light.
- 06:29: The light gets polarized - which means the direction of its electric and magnetic fields pick up a preferred direction rather than being random.
- 07:21: The presence of these electrons tends to slow light down - just as light is slowed down in air or glass - but to a much smaller degree.
- 07:29: But that slowing depends on the polarization of the light.
- 07:35: If the electric and magnetic fields of a collection of photons all tend to point in the same direction, we say the light is linearly polarized.
- 07:43: ... fields are not fixed but rather rotate in the same direction, we say the light is circularly polarized - and it can be left- or right-polarized, ...
- 08:18: This has been done for the Milky Way using the light from pulsars.
- 10:59: If you thought the 27 km ring of the large hadron collider was big, try the 300,000 light year ring around the Milky Way.
- 11:54: ... taken our first picture of the such a magnetic field - in the polarized light surrounding the M81 supermassive black hole observed by the event ...
- 12:23: ... magnetic fields out into the cosmos, and we see them through the radio light emitted by electrons that spiral slowly in these vast ...
2021-07-07: Electrons DO NOT Spin
- 03:48: ... moment they’d need to be spinning faster than the speed of light. This was first pointed out by the Austrian physicist Wolfgang ...
2021-06-16: Can Space Be Infinitely Divided?
- 01:16: ... blackbody, or thermal radiation - by requiring that the energy of light in this heat-glow was not infinitely divisible. Rather came ...
- 02:21: ... you get when you combine the gravitational constant, the speed of light, and Planck’s constant in just the right way to give units of ...
- 03:14: ... it, which reflects back to a detector that records the light travel time, which also gives you the distance because you ...
- 03:47: ... now you have a new problem. Light carries energy and momentum - and the shorter the ...
- 08:37: ... let me give you one more example that doesn’t involve light. Imagine we want to precisely define the position of an ...
2021-05-25: What If (Tiny) Black Holes Are Everywhere?
- 00:05: Happily for us, the nearest is probably many light years away.
- 00:31: ... from a black hole, then black holes must be A) black - they can’t emit light, and B) eternal - they can only grow in size, never ...
- 05:13: In that motion they produce thermal radiation that includes every possible wavelength of light.
- 05:18: But if you zoom in on a single iron atom - it can’t emit every wavelength of light.
- 11:54: The effect of such a bias is that you can tend to interpret all evidence in the light of that particular hypothesis.
- 13:57: ... might know that regular laser light is produced when an incoming photon causes an electron in a crystal to ...
- 14:24: ... useful devices - as well as being used to create squeezed states of light, they’re used in all sorts of other quantum optics applications like the ...
- 14:45: We said that LIGO is planning to begin using squeezed light in a future run.
- 14:54: ... Tse is part of the squeezed light team, and led their paper on the subject where they report up to 50% ...
- 15:23: ... a note of which words are appropriate descriptors to use for squeezed light in regards to Heisenberg, to wit: bending - good, breaking, ...
2021-05-19: Breaking The Heisenberg Uncertainty Principle
- 05:01: ... in the fabric of space caused by cataclysmic events up to billions of light years ...
- 05:36: ... light is split and sent along those paths and then later recombined in such a ...
- 05:58: the recombined laser no longer perfectly cancels, and so flashes of light are observed.
- 06:05: This measurement is incredibly sensitive to the path lengths - but that means it’s also sensitive to the phase of the light waves.
- 07:25: ... light from a laser beam obeys the Heisenberg uncertainty principle in a very ...
- 07:55: By playing quantum tricks on the light, we can squeeze the uncertainty in one direction at the cost of greater uncertainty in the other.
- 08:16: Light in which uncertainty has been manipulated in this way is called squeezed light.
- 08:22: In the case of LIGO, the phase of the light is squeezed - its precision increased - at the expense of increased uncertainty in amplitude.
- 09:13: ... expects that using squeezed light in the next upgrade will allow them to detect up to 50% more ...
- 09:56: The use of squeezed light is just one example of how quantum mechanics can be used to increase measurement precision.
2021-05-11: How To Know If It's Aliens
- 06:27: ... for Oumuamua is that it’s an alien artifact - in particular a light sail - probably a broken one. Now, we covered all of this before - both ...
- 09:21: ... that it’s best explained by an alien megastructure eclipsing the star’s light. That claim was on the strength that no known natural phenomenon easily ...
2021-04-21: The NEW Warp Drive Possibilities
- 00:05: His whole “nothing travels faster than light” rule seems to ensure that exploration of even the local part of our galaxy will be an excruciating slow.
- 00:39: You can’t travel through space at faster than the speed of light - but there’s no speed limit for the fabric of space itself.
- 00:46: This hints at a possibility for faster than light, or superluminal travel.
- 02:21: Before we get to the new work, let’s talk light speed and warp drives.
- 02:25: Einstein’s speed limit doesn’t directly say that nothing can travel faster than light.
- 02:30: His special theory of relativity just says that it takes infinite energy to accelerate anything with positive mass all the way to light speed.
- 03:01: For example inside black holes where we can think of space as flowing downwards faster than light.
- 03:07: Or beyond the cosmic horizon, the expanding universe is carrying galaxies away from us faster than light.
- 07:55: Bobrick and Martire also point out that there’s still no way to accelerate a warp bubble across the light speed limit.
- 11:57: And can a warp bubble be created at sub-luminal speeds and then accelerated past the speed of light?
- 12:10: And of course we still have the time travel issue - accelerating across the speed of light breaks causality and so probably can’t be a thing.
- 13:50: We might add more tubes and some flashing lights for example.
2021-04-13: What If Dark Matter Is Just Black Holes?
- 01:13: As we’ve discussed many times before, black holes are regions of gravitational field so intense that not even light can escape.
- 07:44: ... a compact mass like a black hole passes in front of a distant light source, the warped spacetime around the black hole acts like a lens, ...
2021-04-07: Why the Muon g-2 Results Are So Exciting!
- 07:04: The electron is the lightest and most common of the lepton family.
- 09:41: At the Fermilab experiment, physicists send muons flying at nearly the speed of light around a 50 foot diameter magnetic tube.
- 11:26: But if all that goes well, then this may be a fake glimmer of light in the current theoretical wasteland.
2021-03-23: Zeno's Paradox & The Quantum Zeno Effect
- 13:40: ... the current rate of expansion - which of course it can't be because that light comes from the beginning of the ...
- 14:51: Glad you asked! The intensity of light drops off with the square of the distance traveled.
- 15:05: Trouble is you can't get that luminosity directly from the light by itself.
2021-03-16: The NEW Crisis in Cosmology
- 01:16: ... first figured this out. Long story short - when a distant galaxy’s light travels to us through the expanding universe it gets ...
- 04:42: ... method for getting the expansion rate is to study the oldest light in the universe - the cosmic microwave background. ...
- 10:40: ... method is gravitational lensing - the bending of light around massive objects due to their warping of ...
- 11:57: ... get stretched by the expanding universe, just like light does. But unlike light, they also encode information about the ...
- 13:30: ... in which we explored the connection between gravity, light, and the flow of ...
- 13:38: ... that massive objects travel through time at the speed of light its just one way to interpret the math of special ...
- 14:47: ... why the c in the spacetime interval has to be the speed of light. It's worth a full episode to explore that one, and we'll ...
- 17:08: ... of you commented that this whole gravity bending light thing might explain why stormtroopers have such terrible ...
2021-03-09: How Does Gravity Affect Light?
- 00:00: We know that gravity exerts its pull on light, and we have an explanation for why.
- 00:13: So what is the true connection between light and gravity, or is truth, in fact, entirely relative?
- 00:25: Gravity bends the path of light.
- 00:38: ... 1783, the English clergyman John Michell proposed that a particle of light gripped by the gravitational field of a sufficiently massive star would ...
- 00:52: ... and Cavendish followed similar reasoning to predict that a particle of light would be deflected in its path as it passed near a massive ...
- 01:10: They assumed that light could be slowed down, and that light experiences a force of gravity in the same way that a massive object does.
- 01:17: ... that Isaac Newton’s theory of gravity was the full picture, and that light behaves like any other particle in response to Newtonian ...
- 01:34: We now know that both gravity and light are much weirder than Newton thought.
- 01:52: And yet general relativity demands that gravity does affect light, in ways eerily close to the predictions of Mitchell and Cavendish.
- 02:00: The really hard part is understanding the why of it - what is really happening when light interacts with gravity.
- 02:49: The spider still observes the laser traveling at the speed of light - because the speed of light is invariant to all observers.
- 02:58: See, light is a wave.
- 03:42: Light emerging from a gravitational field is stretched out - it experiences gravitational redshift.
- 03:56: ... down a radio antenna, or an atom vibrating back and forth in a glowing light filament due to its ...
- 04:18: But from a great distance away, those clocks run slow, and so the frequency of light emerging from within a gravitational field is lower.
- 04:27: ... if the density of the gravitating body is large enough, light emerging from it can be sapped of ALL energy - redshifted so the ...
- 04:47: ... this infinite redshift is exactly the same as is required to turn a light-speed particle around and have it fall back, as calculated by Michell from ...
- 05:02: ... shot Einstein to his international fame - the deflection of the path of light by ...
- 05:32: They have to see the light travel in straight line in the absence of any gravity.
- 05:36: But for that to be the case, light must travel a curved path from the point of view of the accelerating frame.
- 05:48: And the equivalence principle tells us we must see the same bending of the light ray in our stationary rocketship set in our gravitational field.
- 06:00: ... - the difference in the flow of time changes the frequency of outgoing light. ...
- 06:10: Can this gravitational time dilation also explain the bending of a ray light traveling horizontally?
- 06:47: But light is frozen in time from its point of view.
- 06:57: ... if we imagine light as a perfectly narrow ray, or even as a massless, timeless particle, ...
- 07:09: So let’s be smart and do what the smartest guy in the world did - let’s think about light in an entirely different way.
- 07:24: The Dutch physicist Christiaan Huygens disagreed with Newton on many things - including the idea that light is a particle.
- 07:31: Huygens’ wave theory of light advanced the field of optics enormously.
- 08:20: We can model light in the same way.
- 08:23: A plane wave of light is just an infinite number of new sources of light that generate the next step in the plane wave.
- 08:30: ... explains why light can turn corners around opaque objects in the phenomenon of diffraction, ...
- 08:41: Our plane wave reaches the boundary to a new medium with a slower speed of light.
- 09:00: So now if we connect the wavelets to reconstruct the overall wavefront, we see that the path of the light has bent.
- 09:09: But in a sense, light gets refracted by gravitational fields - or at least you can model it that way.
- 09:17: ... just need two completely crazy assumptions - first that light acts like a very classical, 17th-century style plane wave so you can use ...
- 09:27: And also that the speed of light changes in gravitational fields, which sounds counter to everything I’ve told you.
- 09:46: The only thing that’s not relative is the speed of light - everyone observes the same local speed of light - 300,000 km/s in a vacuum.
- 09:55: But notice that I said LOCAL speed of light - that means everyone measures the same speed of light passing through their own local patch of space.
- 10:03: But viewed from a distance, the speed of light can at least appear to change.
- 10:31: The photon has to travel further through a region of slowed time - and both conspire in the same direction to slow the apparent speed of light.
- 10:41: Of course for someone actually inside the gravitational field, the photon is still traveling at the speed of light as it whizzes past them.
- 10:54: At each location perpendicular to a gravitational field, the wavefront of light can be thought of as a vertical column of new wavelets.
- 11:02: But for you, tracking this from a distance, the effective speed of light decreases downwards, because time slows and space stretches.
- 11:21: Einstein used this approach to calculate the deflection expected when light passes a massive object.
- 11:43: ... offset in the apparent positions of stars around the sun, due to their light rays being “refracted” in the Sun’s gravitational ...
- 11:59: Light isn’t really a simple plane wave - it’s a much weirder quantum wave-particle thing.
- 12:32: Light is a wave and a particle; time slows or space flows in gravitational fields.
2021-02-24: Does Time Cause Gravity?
- 00:00: You are currently hurtling through time at the speed of light.
- 00:34: ... accept the two axioms of Einstein’s relativity theory: that the speed of light is constant for all observers, and that the weight induced by ...
- 05:15: There's a certain way of interpreting the math of relativity that says that everything travels at the speed of light.
- 05:22: ... Light travels at the speed of light through space - obviously enough - and we ...
- 05:50: On the other hand, light itself travels at the speed of light through space only, and not at all through time - a photon’s clock is frozen.
- 06:29: ... into energy via Einstein’s most famous equation, E=mc^2 - the speed of light is the exchange rate, and the speed of light is very ...
- 07:35: The other thorny question is about light itself.
- 07:48: But light DOES bend in a gravitational field - astronomers see it happening all the time in the effect we call gravitational lensing.
- 07:56: In fact, the imaginary paths of light rays were one the most important tools that helped Einstein develop both special and general relativity.
- 08:04: So we’d better understand the effect of gravity on the path of light.
- 10:35: ... in the distribution of matter, which we might now see in the way the CMB light is ...
2021-02-17: Gravitational Wave Background Discovered?
- 00:00: ... in the fabric of space-time produced by colliding black holes a billion light years away since then ligo and its partner virgo have detected 50 ...
2021-02-10: How Does Gravity Warp the Flow of Time?
- 03:57: This is a simple pair of perfectly reflective, massless mirrors between which bounces a single photon of light.
- 04:23: ... its speed - so twice separation of the mirrors divided by the speed of light. ...
- 04:48: ... the great founding axiom of special relativity - that the speed of light is always measured to be the same for all observers, no matter their ...
- 05:38: Time dilation due to motion is inevitable if we accept the axiom of the constancy of the speed of light.
- 09:16: ... both of our axioms are true - the constancy of the speed of light and the equivalence of acceleration and gravity, then time must run slow ...
- 11:03: ... the photon - or whatever light-speed quantum components make up matter - actually do have to travel further - ...
2021-01-26: Is Dark Matter Made of Particles?
- 00:23: ... the influence of dark matter in the orbits of stars and galaxies, in way light bends around galaxies and clusters, in the clumpiness of the cosmic ...
- 03:03: It doesn’t produce light - hence the “dark”.
- 03:05: ... it also doesn’t absorb light - otherwise we’d be able to detect it when it blocked light from the ...
- 03:45: ... the orbits of galaxies inside galaxy clusters, and by the way it bends light around galaxies and ...
- 05:41: ... enough mass in neutrinos to do the job, due to them being ridiculously light. ...
- 07:33: Axions, if they exist, would be incredibly light - maybe 1% or less the mass of the already-puny neutrino.
- 08:55: In some models these are the lightest supersymmetric particles possible - ”LSPs” - but they’re still incredibly heavy.
- 09:03: ... while normally heavy things tend to decay to lighter things, if these can’t decay into Standard Model particles then they’d ...
- 12:17: Because dark matter is weakly-interacting, our light sector is probably more complex - probably.
- 12:35: ... now, we’ll just have to enjoy knowing that our light-weight light sector exists in parallel to this completely invisible and vastly ...
- 13:39: Would a spaceship traveling near the speed of light cause a closed universe to contract so much that it would smash into its own ass?
- 14:18: ... ladder collides with the door at a high fraction of the speed of light and a shockwave blasts down the length of the ladder totally destroying ...
- 14:42: The shockwave can go no faster than the speed of light.
2021-01-19: Can We Break the Universe?
- 00:17: ... theory started with the simple assumption that the speed of light was the fastest speed possible, and that all observers should measure ...
- 01:04: Say we have a spaceship traveling from Earth to a nearby star at a good fraction of the speed of light.
- 02:23: Imagine our spaceship can travel very, very close to the speed of light.
- 02:41: ... the frame of a spaceship moving at near light-speed, the universe could contract to the point that the spaceship wraps all ...
- 03:24: ... twin hops in a spaceship and travels at a good fraction of the speed of light to a nearby star and then turns around and heads back to ...
- 08:36: ... the ladder through the barn at a significant fraction of the speed of light, then to someone standing still relative to the barn the ladder may be ...
- 12:41: ... we took your contributions and accelerated them to near the speed of light, causing them to wrap around the universe several times and ...
- 14:15: ... which interpretation of quantum mechanics is "true" is like asking if light is made up of particles or if light is a ...
2021-01-12: What Happens During a Quantum Jump?
- 01:22: ... success of Max Planck, who in 1901 had managed to explain the colors of light produced by a heated object - the so-called blackbody spectrum - by ...
- 01:56: ... quantum theory, and it very neatly explained the specific frequencies of light observed in emission spectra of hydrogen - although it failed for more ...
- 06:41: If the electron is in level 1, it should jump to level 2 by absorbing a photon from the laser light.
2020-12-22: Navigating with Quantum Entanglement
- 08:20: When light hits the protein, it knocks an electron off an attached molecule that goes onto an adjacent molecule.
- 13:37: ... what elements are observed as emission or absorption lines, the way the light decays over time, and other ...
2020-12-15: The Supernova At The End of Time
- 03:03: ... to his friends - was pondering the far future of the star whose warm light now bathed the ...
- 05:27: ... the world looks very different to things traveling close to the speed of light. ...
- 11:59: ... our Patreon supporters - even a couple of bucks a month helps keep the lights on, the camera rolling, and the green screen .. ...
2020-11-11: Can Free Will be Saved in a Deterministic Universe?
- 00:25: ... (light music) In recent episodes, we explored the notion of determinism in the ...
- 09:11: It's been thoroughly cast in a new light.
2020-11-04: Electroweak Theory and the Origin of the Fundamental Forces
- 08:16: The bosons of the version of SU(2) that I just described are simple light-speed oscillations in their fields, just like photons.
- 14:41: Dr Kres von Panzer asks how we know that two light rays inside a black hole converge and don’t just perpetually pass each other.
- 14:51: ... showed that at least some light rays - null geodesics - that start parallel from any trapped surface ...
2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time
- 00:34: ... of a star so massive that it would prevent even light from escaping its surface. Few people took these “dark stars” ...
- 01:17: ... where time froze. Beneath that “event horizon” all matter, light, space itself was doomed to fall inwards towards a central point. ...
- 05:01: ... fall in a gravitational field. The path traveled by a ray of light is called a null geodesic. They are the gold-standard ...
- 05:55: ... that has this property that null geodesics - and so any light - pointed outwards from the surface actually move ...
- 07:05: ... impossible contradictions arise otherwise. Imagine a pair of light rays emerging from the same point and then focused back ...
- 12:11: ... insights, and all from some bright ideas about how light rays travel and terminate at the singular dead ends of ...
- 13:38: ... 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 could ...
2020-10-20: Is The Future Predetermined By Quantum Mechanics?
- 02:00: ... is defined, past, present, and future, or everything outside our past light cone is undefined, including other observers and the room around you in ...
- 05:41: It's tempting to equate everything outside our past light cone with the unobserved wave function.
- 05:48: You can imagine that light cone sort of just plowing through the undefined universal wave function, collapsing it as it goes.
- 06:01: That leaves your future light cone undefined.
- 06:38: In fact, any part of spacetime, not in your future light cone is potentially the past for another observer in your present.
- 06:46: ... imagine a third observer on their different present for whom your future light cone is in their past light cone so it should have already been ...
- 08:08: Your light cone sweeps through the global wave function but it doesn't collapse that wave function, rather it selects from it.
- 08:39: That can happen at the speed of light so we can also think of the splitting as proceeding in advancing light cones.
- 09:35: Nonetheless, as your light cone moves forward in time you encounter these entanglement networks and you have to choose between them.
- 09:52: I should add that the light cone picture isn't ideal here because entanglement can travel faster than light.
- 09:59: However, light speed signaling is the surest way to transfer quantum correlations so this is still a useful picture.
- 13:07: Even though they have to wait until the light reaches them to do so.
2020-10-13: Do the Past and Future Exist?
- 06:13: Nothing, not even information, can travel faster than light.
- 06:22: ... the region of the block universe that we can possibly perceived with a light-cone - signals from things inside that cone have had time to reach ...
- 06:33: The boundary of the cone holds the paths of light-speed signals.
- 06:38: Whatever events live on that cone represents the universe that we see around us, carried to us by light.
- 06:44: Any event above that cone is unseeable in the present - we’d have to wait until our lightcone moves upwards to encompass it.
- 06:53: Which is the same as saying we have to wait until its light has had time to reach us.
- 07:29: Successive shells of light from more distant parts of that time-slice arrive one after the other, expanding your view.
- 09:40: The largest tilts are for things traveling at the speed of light, and these sweep out the future light-cone.
- 09:47: In front of the future light cone is the region that is in the future for everyone, no matter what their speed.
- 10:14: They have future light cones, simil to our, offset in space from ours.
- 10:19: ... space beneath their future light cones defines all possible defines all possible definitions of the past ...
- 11:09: ... own immediate experience, which can include events only from your past light ...
- 12:07: ... mechanics tells us that all this stuff outside our past lightcone - and even unobserved aspects of the world within that cone - exist in a ...
- 13:16: At any rate, may your future lightcone contain only wonderful things.
2020-10-05: Venus May Have Life!
- 02:22: ... other weird thing is that the clouds of Venus appear to absorb the Sun’s light in a weird way - more short wavelength visible and UV light is sucked up ...
- 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.
- 03:51: Another possibility is to look for the absorption of the planet’s own light as it emerges from deep within its atmosphere.
- 07:00: You might get some produced by lightning strikes in the cloud layers, or by cosmic rays hitting the upper atmosphere.
- 10:20: These spores are extremely tiny and light, and so they float in the haze below Venus’s cloud banks.
2020-09-28: Solving Quantum Cryptography
- 17:05: ... realization would not apply ... so like, yeah, "we’re creatures made of light and energy and are at the center of the universe, and we're orbited by ...
2020-09-08: The Truth About Beauty in Physics
- 09:30: And Maxwell’s equations, which parsimoniously unite electricity and magnetism but also predict the existence of electromagnetic waves - of light.
- 14:04: ... the answer is yes they absolutely do - and in some cases you see extra light at those special wavelengths - what we call emission lines, in some ...
- 14:19: It depends on what the background light looks like.
- 14:22: ... the atoms in question are between us and a source of light that's bright at all wavelengths, then we see absorption - that's ...
- 14:58: In that case you'll see all of those photons produced when absorbed light is reemitted - emission lines.
2020-09-01: How Do We Know What Stars Are Made Of?
- 00:02: Pin-pricks in the celestial sphere, through which shines the light of heaven?
- 00:10: Or lights kindled above middle earth by Varda Elbereth and brightened with the dew of the trees of Valinor?
- 02:57: The secret to understanding the stars is not exactly in the light they send to us.
- 03:02: Rather, it’s in the light that they fail to send.
- 03:06: ... is a modern spectrum of the Sun - it’s the amount of light we receive at different colors - or in other words, from photons of ...
- 03:15: Most of this light comes the photosphere - a layer around 100 km deep at the surface of the Sun.
- 03:35: But on its own, that thermal light is a very smooth curve across the spectrum.
- 03:44: Those are where photons of very specific energies have been plucked out of this thermal light.
- 04:36: At least, that’s true for most of the light.
- 07:38: ... one thing, each absorption line is formed as light deeper within the sun traverses a large distance, over which temperature ...
- 10:02: This was much more precise than the previous method of just observing the overall color of the thermal light.
2020-08-17: How Stars Destroy Each Other
- 01:31: Centuries later, on March 11, 1437, the light from that explosion swept past the Earth.
- 01:39: There, the royal astronomers of King Sejong’s court in Korea recorded a new point of light in the constellation of Wei, in what we call Scorpius.
- 02:45: But it can be found if you look a little off center for a spot of light that flares erratically from visible to X-ray wavelengths.
- 04:38: ... magnetic field lines they emit synchrotron radiation, and bright X-ray light is emitted as the gas hits the polar regions of the white dwarf - like a ...
- 05:47: ... speeds - which means incredible friction - which means heat and light. ...
- 06:16: ... the earth to produce metronome-precise pulses - most brightly in radio light, but potentially at all ...
- 07:09: ... know that when you look at our galaxy in gamma rays - the highest energy light there is - the brightest points you see are pulsars, and those gamma ray ...
- 07:38: He observed these objects using visible wavelength of light - and found one object was indeed pulsing.
- 08:35: The same gas blocks any radio light, but allows the more penetrating gamma ray light to pass through.
- 08:42: And the pulsing of visible light?
- 11:14: ... so that the escape velocity at its surface is greater than the speed of light. ...
- 11:32: Well, below that event horizon, we can think of space flowing downwards faster than the speed of light.
2020-08-10: Theory of Everything Controversies: Livestream
- 00:00: ... gravity then uh please tell me what's the gravitational field of light electron in a superposition can you do the calculation can you show ...
2020-07-28: What is a Theory of Everything: Livestream
- 00:00: ... are so distinguished joining us today are going to hopefully shed some light into the nature and the inner workings of the universe and be a ...
2020-07-20: The Boundary Between Black Holes & Neutron Stars
- 00:29: ... of spacetime due to a cataclysmic collision of black holes billions of light years ...
- 01:29: ... the limit for what was thought possible for a neutron star, and it’s lighter than what was thought possible for a black ...
- 02:30: ... with a wave traveling through the entire earth at the speed of light. ...
- 03:14: ... quickly swiveled to scan that region, hoping to spot a faint flash of light - any indication that the merger of these objects may have been ...
- 03:47: ... light carried with it an enormous amount of information about what happens ...
- 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: ... have an escape velocity at the event horizon equal to the speed of light. ...
- 08:26: We also see the results of these mergers in gamma ray bursts - frequent flashes of energetic light from the distant universe.
- 08:43: ... direct measurements of neutron star masses come from pulsars - cosmic lighthouses that result from a neutron star’s precessing jets sweeping past the ...
- 14:25: ... are actually antimatter galaxies - they should emit exactly the same light as regular ...
2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing?
- 00:22: ... everything just have annihilated again, leaving only a vacuum bathed in light? ...
- 07:21: ... Volts of kinetic energy, corresponding to over 99% of the speed of light. These high-energy protons then hit a metal target and produce a zoo of ...
2020-06-30: Dissolving an Event Horizon
- 00:44: ... central singularity where the inward flow of space reaches the speed of light, and time freezes from the perspective of the outside ...
- 03:46: There’s no longer a region where the inward flow of space exceeds light speed.
- 13:46: Inyobill asks if we’re assuming that the lightest particles are without dimension, so they have an undefined size relative to the universe.
- 14:04: It has the same relative size compared to the universe whether that universe is trillions of light years across or a millimeter across.
- 14:31: That’s like another type of size, and it makes a big difference if you’re a millimeter from an electron versus a trillion light years.
- 14:40: ... the interaction rate scales in the same way ... So a pair of photons one light-second apart have the same probability of interacting over one second as do a ...
2020-06-22: Building Black Holes in a Lab
- 00:16: ... this picture of the black hole at the heart of a galaxy over 50 million light years ...
- 03:05: ... replace sound with light and the water with spacetime itself and you have a black hole. The ...
- 08:04: ... by. This is the Penrose process, and when the particle being boosted is light then we call it superradiance. So this works when a particle passes ...
- 10:44: ... are even quantum optical analogs, in which light sees an apparent horizon—usually caused by some clever material that’s ...
2020-06-15: What Happens After the Universe Ends?
- 02:17: It makes a big difference whether every atom in the universe is right next to each other or a billion light years apart.
- 02:31: For example, consider a universe that’s one light-second across, and it exists for the span of a single second.
- 02:39: Light has time to travel across it once.
- 02:42: Scale it up by around 30 quintillion times to describe a second universe that’s a billion light years across and lasts a billion years.
- 02:51: Again, light crosses it once in that time.
- 02:54: Let’s say these universes contain no matter - only photons - light.
- 02:59: ... both contain the same number of light rays, which begin traveling in the same direction, although obviously ...
- 03:22: Light takes 30 quintillion times longer to cross one than the other.
- 03:28: Remember, the universes contain only light - no observers and no clocks.
- 03:33: And there’s the key point: light does not experience the flow of time.
- 04:15: ... and one dimension of time on the y, and we choose our axes so that light travels at a 45 degree path - the graph spans either 1 second in time ...
- 04:37: Either way, light travels a 45 degree path.
- 05:59: That would be the case of a universe that contained only light.
- 06:03: Light follows these tracks in between the time grid, and never, ever cross contours that mark even a single tick of a clock.
- 06:11: For light, or any light-speed particle, the beginning and end of every journey is the same.
- 06:36: ... you can build a clock and can tell the difference between the one light-second and the billion light-year sized ...
- 06:47: But with only light or other light-speed radiation there’s nothing internal to those universes that can tell them apart.
- 07:06: ... by Hawking radiation, and particles of matter will decay into their lightest possible ...
- 08:31: Kinetic energies were so high at the big bang that rest mass energy was completely negligible - all particles behaved like light-speed particles.
- 09:34: ... the one map, while at the same time preserving the 45 degree path of light. ...
- 11:10: Only radiation - light and other massless particles - can cross over this conformal boundary from one aeon into the next.
2020-06-08: Can Viruses Travel Between Planets?
- 04:57: Cellular life massively alters the atmosphere because it excretes gases - oxygen, methane, nitrous oxide as that light metabolizes.
- 07:26: ... light droplets can be lifted to the very edge of an atmosphere with the help ...
- 08:01: So yeah, stars sneeze, you might want to maintain 6 light years distance.
- 10:52: ... because a barrier of rock or ice will shield against ultraviolet light and cosmic ...
2020-05-18: Mapping the Multiverse
- 01:01: ... enough space that the gravitational field becomes too strong for even light to ...
- 02:29: ... fabric of space itself is whipped into a vortex so fast that not even light can resist its ...
- 03:17: Light always travels a 45 degree path, and normal objects can only travel paths steeper than that.
- 03:25: Your so-called “future light cone” encompasses the parts of the multiverse you could possibly get to at less than light speed.
- 03:33: Your past light cone shows you the parts of the multiverse that you can see, because light has had time to reach your position from those parts.
- 03:53: Down becomes the future, because falling space drags us there faster than the speed of light.
- 04:16: In fact the flow eventually slows to less than the speed of light.
- 05:00: It’s surrounded by a second ergosphere, where again the rotational flow of space exceeds light speed.
- 08:06: And as some of you probably remember - faster than light travel means the possibility of time travel.
- 09:34: You’d need to travel back in time-slash-faster than light to get back there.
- 15:08: ... at much higher velocities to get a better reading - say 10% the speed of light. ...
- 15:40: ... methods - lasers, vacuum chambers, strange quantum mechanical states of light - you name ...
- 15:51: No indication has ever been found that the speed of light depends on the speed of the device or of the observer.
2020-05-11: How Luminiferous Aether Led to Relativity
- 00:31: ... luminiferous aether - the invisible, all-pervasive medium through which light was thought to ...
- 01:34: ... the air breathed by the Gods, and was embodied as a primordial deity of light. In Aristotle’s cosmology, earth, air, fire and water are the physical ...
- 02:33: ... of the aether. But Huygens is most famous for his wave theory of light. By thinking of light as a wave, he was able to build a theory of optics, ...
- 03:25: ... reaction that propagates an energy pattern through some medium. So if light is a wave, surely it also needs a medium. For Huygens, that medium was ...
- 04:01: He called it the luminiferous - or light-bearing aether.
- 04:06: ... was in Huygen’s 1690 Treatise on Light, published only 5 years before his death. Across the channel, a much ...
- 05:08: ... versus Newton. Light as a wave versus a particle. Most accepted Newton - as most always did. ...
- 05:53: ... light experiences refraction and interference like a wave. Add to that the ...
- 06:22: ... of the luminiferous aether as a classical medium for the propagation of light. ...
- 06:42: The key was to observe a change in the speed of light depending on the direction of motion.
- 07:19: ... century physicist, I’d wanna hope Galilean relativity is right OK, so if light is a classical wave in some medium then we should see changes in the ...
- 08:02: ... device capable of traveling at a significant fraction of the speed of light, which in the 1890s I guess may have seemed challenging. But why build a ...
- 08:34: ... invented the ingenious Michelson-Morley interferometer. In it, a beam of light is split in two by a semi-reflecting mirror and sent along two paths at ...
- 09:02: ... Changes in length quite a bit smaller than a single wavelength of light would produce observable shifts in the fringe pattern. And this is ...
- 09:26: ... a shift in the interference pattern is by changing the relative speed of light along the two arms. That would cause the wave pattern in one arm to lag ...
- 10:02: ... long as the path lengths stay fixed and as long as the relative speed of light between the arms stays fixed. But if the speed depends on the direction ...
- 11:04: ... one that resembled a classical medium for wave propagation. The speed of light appeared to be independent of the motion of the ...
- 11:20: ... - an update to the Galilean transformation that now allowed the speed of light to remain constant, no matter your ...
- 11:42: ... that brings us to Einstein. The constancy of the speed of light and the Lorentz transformation are fundamental to his special theory of ...
- 12:25: ... is disproved - but let’s be clear. The aether as a classical medium for light is dead. However the general concept of the aether sort of has an ...
- 13:52: ... calculate the age of the universe, given that we don't even have light from its very beginning. There were some really smart questions - let me ...
- 16:14: ... now 93 billion light years across - so the CMB sphere is around 85 million light years ...
2020-05-04: How We Know The Universe is Ancient
- 01:35: ... were arguing about the nature of these faint, fuzzy patches of light on the sky known as spiral nebulae. Were they blobs of gas in the Milky ...
- 12:25: ... the one source - the cosmic microwave background radiation - the oldest light we can see, released when the universe was a mere 400,000 years old and ...
2020-04-28: Space Time Livestream: Ask Matt Anything
- 00:00: ... ether which is this archaic notion about the medium through which light propagates and the death of the idea in the late 1900s late 1800s ...
2020-04-22: Will Wormholes Allow Fast Interstellar Travel?
- 02:50: ... the wormhole were accelerated into a circular path at near the speed of light, its clock would freeze compared to the other end. By entering the ...
- 04:08: ... wormhole collapses on itself so fast that nothing - not even light - can make it through. To see that we need to turn back to a ...
- 05:43: ... Kruskal-Szekeres diagram shows that faster than light travel is needed to cross the wormhole, but to really understand this we ...
- 06:56: Fuller and Wheeler showed that even at the speed of light, nothing can get through such a wormhole.
2020-04-14: Was the Milky Way a Quasar?
- 03:18: ... gamma ray bubbles with sharp edges extending more than 25,000 light years in either direction above and below the plane of the Milky Way - ...
- 05:29: Extremely energetic electrons interact with lower-energy light, boosting that light to the much more energetic gamma ray regime.
- 05:36: And so that’s what we’re seeing here - light bounced off extremely high energy electrons within the vast bubbles.
- 08:25: ... the black hole, but 10% or more is converted into energy in the form of light before it hits the black hole, which is why quasars shine so ...
- 11:25: ... however, is that these particular structures only extend 1400 light years above and below the plane of the Galaxy — leading astronomers to ...
2020-04-07: How We Know The Earth Is Ancient
- 07:17: ... the Earth through radiometric dating. Unstable atomic nuclei decay into lighter nuclei by splitting or by ejecting particles. The rate of decay is ...
- 10:35: ... Kant’s Island Universes were indeed other galaxies, many millions of light years away. The world simultaneously got a lot older and the universe a ...
2020-03-31: What’s On The Other Side Of A Black Hole?
- 03:46: ... coordinates improved our map by enforcing that the trajectory of light always be at a 45 degree angle. In the resulting Kruskal–Szekeres ...
- 04:14: ... nothing can travel faster than light, this makes very clear what parts of the universe are accessible. Close ...
- 05:00: ... relativity uses null geodesics - the paths taken by light rays - to grid spacetime, and we also assume that those lines don’t just ...
- 05:49: ... say this Penrose diagram is geodesically incomplete because there are light rays with undefined origins. This is equivalent to saying that we have ...
- 06:15: ... we trace our light ray backwards from our universe we encounter a region that looks just ...
- 07:21: ... only way to pass between these universes is to travel faster than light. You can see that by the fact that the only paths shallower than 45 ...
- 08:22: ... inside the black hole what do you see? Light can reach you from the universe behind - those are photons that overtake ...
- 08:44: ... for now you overtake that light and get a glimpse of the black hole’s past. You never actually see the ...
- 09:00: ... and try go back the way you came - and if you can travel faster than light you’ll emerge from the same event horizon that swallowed you. Or you can ...
- 10:20: Confusing. And it’s okay that this doesn’t make much sense - faster than light travel always leads to silly paradoxes because it’s impossible.
- 10:30: Not only is faster than light travel impossible, but eternal black holes don’t exist either.
- 10:35: ... no white hole in their past. And within those black holes, any outgoing light ray can be traced back to the surface of the collapsing star and to its ...
2020-03-24: How Black Holes Spin Space Time
- 00:21: ... surface where the fabric of space cascades downwards at the speed of light, and where the flow of time halts from the perspective of the outside ...
- 07:33: ... dragging carries space around the black hole at faster than the speed of light. That means everything - even light - must move in the direction of the ...
- 07:50: ... state below the event horizon where space moves downwards faster than light. In the math, that faster-than-light flow of space is represented in a ...
- 10:11: ... a little messy actually, but you can do this with light. Light that is directed through the ergosphere in the direction of ...
- 10:51: ... are accelerated along those magnetic field and can radiate intense light. Ultimately, the energy of that light is extracted from the rotational ...
- 11:31: ... its brightness. We see these as gamma ray bursts from over 13 BIllion light years ...
2020-03-16: How Do Quantum States Manifest In The Classical World?
- 05:32: ... a sense that causal influence is transferred potentially faster than light. This is what Einstein called spooky action at a distance, and we now ...
2020-03-03: Does Quantum Immortality Save Schrödinger's Cat?
- 14:54: ... particles, and more minor interactions don't necessarily decohere the light - instead they introduce small phase shifts that can blur out the ...
- 15:23: Place two fingers in front of your eye with a tiny gap and look towards a light - you can see bright and dark fringes of Fraunhofer diffraction.
2020-02-24: How Decoherence Splits The Quantum Multiverse
- 03:29: Laser light is an example of a coherent wave.
- 04:04: This time we'll use particles of light - photons as our quantum particle.
- 08:27: ... a blur corresponding to overlapping patterns, instead of a clean set of light and dark bands that we saw in ...
2020-02-18: Does Consciousness Influence Quantum Mechanics?
- 00:26: ... being in multiple places at once, communicating faster than light, or simultaneously experiencing multiple entire timelines ... that then ...
- 04:17: ... that information travels via photons to light-sensitive molecules in our retinas, which initiate electrical signals to our ...
- 13:31: You get access with the lowest $2 per month tier on Patreon, which has the added bonus of helping us keep the space time lights on.
- 13:39: There were a couple of questions and comments on the discord about how axions could be dark matter - aren't they too fast moving? and too light?
- 14:19: Sure, each would be very light, but their could be enough of them to perfectly account for dark matter.
- 15:49: ... like the speed of light and the gravitational constant are just scaling factors and so varying ...
2020-02-11: Are Axions Dark Matter?
- 06:54: ... particle would have no electric charge, no quantum spin, be extreme ly light - a tiny fraction of the mass of the already tiny ...
- 08:23: ... this actually gives us an experiment. It should be possible to shine a light through a solid, opaque wall. It goes like this: a light is passed ...
- 10:36: ... given a reliable positive results, but it may be that axions are just lighter or more weakly interacting than we think and so not detectable by ...
- 11:08: ... They have all the right properties - no direction interaction with light, and only weak interactions via the other forces. And although these ...
2020-02-03: Are there Infinite Versions of You?
- 01:41: ... a space - 1 in 100 again and so on. “A tempestuous noise of thunder and lightning heard...” the chance of that is 1/100^50 or 10^-100 - and that’s 100 ...
- 09:40: For our 46-billion light year observable universe there are definitely no more than 2^10^123 possible unique configurations.
2020-01-27: Hacking the Nature of Reality
- 00:43: ... on observable quantities - in this case, the mysterious frequencies of light produced as electrons jump between ...
2020-01-13: How To Capture Black Holes
- 00:59: ... of a second are what LIGO detects - sometimes from over a billion light years ...
- 04:50: ... those black holes are mostly random, so the swarm forms a spheroid a few light years across. The accretion disk is quite a bit smaller than the full ...
- 08:50: ... things happen right after merger that could lead to a bright burst of light to accompany the gravitational ...
- 10:40: ... inside an accretion disk then we might see a temporary increase in the light from one of the active galaxies — a fading flash that is brightest at ...
2020-01-06: How To Detect a Neutrino
- 02:05: ... ♪ DR. DON (voiceover): In fact, it would take a wall of lead five light-years thick to have a 50/50 chance at stopping a single neutrino from the ...
- 02:47: ... giant electromagnets, ♪ (𝘳𝘩𝘺𝘵𝘩𝘮 𝘣𝘶𝘪𝘭𝘥𝘴) ♪ to around 99.997% the speed of light. ...
- 03:41: ♪ ♪ And, as awesome a piece of science equipment as this looks, ♪ ♪ It's definitely not five light-years of lead.
- 06:28: ♪ ♪ When we add that we know how far the neutrinos traveled at the speed of light, we know how fast they oscillate.
2019-12-17: Do Black Holes Create New Universes?
- 09:41: And the lower the mass of the strange quark, the easier it is to convert lighter particles into strange quarks.
- 12:42: ... and as your knowledge advances you'll learn how faster than light travel can break causality and you'll even solve the famous twin ...
2019-12-02: Is The Universe Finite?
- 00:22: Every time you walk out the door, light from the Big Bang strikes your face, enters your eyes.
- 00:33: We can’t see this microwave light with our eyes, but we can catch it with even a simple radio antenna.
- 00:50: And within this light, a group of scientists have just found evidence of the limits of space.
- 05:59: See, the light from the CMB doesn’t travel straight to us.
- 06:02: ... that act as lenses, slightly deflecting the path of those rays of CMB light. ...
- 08:15: Also, beyond a certain distance from us that expansion exceeds the speed of light, so there’s no lapping the universe regardless of its geometry.
- 08:39: In short - lensing by a cluster of galaxies tends to draw rays of light from different blobs together.
2019-11-18: Can You Observe a Typical Universe?
- 01:20: It allows us to understand the origin of the Earth and the Milky Way by studying the ancient light of distant galaxies.
2019-11-11: Does Life Need a Multiverse to Exist?
- 00:50: ... are things like the speed of light, the Planck constant, the masses of the elementary particles, and the ...
2019-11-04: Why We Might Be Alone in the Universe
- 13:37: ... about the experiment to test Loop Quantum Gravity So LQG predicts that light of different wavelengths travels at very slightly different ...
- 13:48: And this was NOT observed in the light from a distant gamma ray burst, which presents a challenge for the theory.
- 13:56: So why does LQG predict different speeds of light?
- 14:00: ... on tiny scales, then we expect the very shortest wavelengths of light to be slightly perturbed by these quantum cells of space - sort of like ...
2019-10-21: Is Time Travel Impossible?
- 01:15: Do a trip around the galaxy at close to the speed of light and very little time might pass from the perspective of the traveler.
- 01:45: The spaceship’s clock slows down as it speeds up, and it stops completely at the speed of light.
- 01:56: So if you could travel faster than light you could navigate a path to a point in spacetime before you departed.
- 02:08: Of course we know that the laws of physics forbid faster than light travel.
- 02:15: In order for any object with regular mass to even reach light speed it would need infinite energy – which can never be obtained.
- 02:35: An object with imaginary mass is now restricted to only traveling FASTER than light, never slower.
- 04:14: ... one end to close to the speed of light or drop it into a deep gravity well – its rate of time flow will slow ...
2019-10-15: Loop Quantum Gravity Explained
- 12:41: ... quantum gravity seems to predict that the speed of light should depend very slightly on the energy of the photon, with, for ...
- 13:02: This was tested in 2009 by looking for differences in the arrival time of light from a gamma ray burst nearly a billion light years away.
- 14:59: We do see this effect in the light from gravitationally lensed quasars and supernovae.
- 15:03: Gravitational waves should be lensed in the same way as light, so it's a plausible explanation.
2019-10-07: Black Hole Harmonics
- 07:35: In astronomy, the analysis of the different frequencies of light is called spectroscopy.
- 08:09: ... the mass of the sun, spiraling into each other one and a half billion light years ...
2019-09-30: How Many Universes Are There?
- 00:24: ... it: the observable part of our universe is 93 billion light years across, and that’s just a small fraction of the stuff created in ...
- 01:48: ... edge spreads into the surrounding inflating spacetime at the speed of light, causing inflation to stop within the growing ...
- 12:02: But the too-long-didn’t-calculate is this: remember that bubble edges expand at the speed of light.
- 12:09: If they form too far apart then the intervening inflating spacetime will throw them apart at faster than light speed before they can merge.
2019-09-23: Is Pluto a Planet?
- 05:24: ... Tombaugh, a 22 year old Kansas farm boy, spotted a moving speck of light in a series of photographic plates taken under the guidance of Vesto ...
2019-09-16: Could We Terraform Mars?
- 01:47: Light from the Sun, which is already fainter due to Mars’ distance – is radiated directly back out into space.
- 01:55: On Earth that same light first bounces around in our thick atmosphere, heating it up.
2019-09-03: Is Earth's Magnetic Field Reversing?
- 12:43: ... like to thank all Patreon supporters. You guys really help us keep the lights on, and we'd specially like to thank Morgan Hough, for joining the ranks ...
2019-08-12: Exploring Arecibo in VR 180
- 01:02: ... sky most telescopes radio or optical use parabolic dishes which bring light to a sharp focus But only light from the direction they are pointing Our ...
2019-08-06: What Caused the Big Bang?
- 09:46: This bubble would grow into the surrounding inflating regions at the speed of light.
2019-07-25: Deciphering The Vast Scale of the Universe
- 04:27: He found that Andromeda is around 2 million light years away.
- 06:04: And unlike regular spaceships, this dome can fly at many times the speed of light.
- 06:23: ... of our Milky Way galaxy at a few hundred billion times the speed of light. ...
- 06:50: As we zoom out, now at several trillion times the speed of light, our local group of galaxies comes into view.
- 07:18: ... galaxies belong Laniakea, a cluster of superclusters some 500 million light years ...
- 07:32: ... we accelerate to one hundred quadrillion times the speed of light we see the extent of our modern mapping of the universe – galaxies ...
- 08:07: That distant light comes to us from a much younger universe.
2019-07-15: The Quantum Internet
- 03:19: We can already send photons of light very long distances using lasers or fiber optics - and those photons are pretty quantum.
- 03:27: The problem is that to transmit quantum information we have to pay attention to individual photons - quanta of light.
- 03:34: ... transfer classical information using light, each bit is encoded with many photons, and many can be lost or altered ...
- 13:43: Still, it seems a lot safer than a traditional light-water reactor.
2019-07-01: Thorium and the Future of Nuclear Energy
- 02:49: ... of water I just described very very crudely. The principles behind the light water thermal reactor These are the most common because they're cheapest ...
2019-06-20: The Quasar from The Beginning of Time
- 01:50: ... were looking for a faint speck of light that had been noticed in one of our great surveys of the sky. ...
- 02:06: ... in the universe. What was strange about this one was its distance. Its light was SO red that astronomers realized that that light must have been ...
- 03:19: Let's actually talk about light for a second.
- 03:22: Light is a wave and the wavelength of that wave determines the properties of light.
- 03:27: For example, visible light – the wavelength range that our eyes are sensitive to – spans only a tiny fraction of the spectrum.
- 03:40: For example, viewed in visible light, the Andromeda galaxy shows us newborn stars.
- 03:45: ... atmosphere is transparent to visible light, so a ground-based telescope can see a visible universe, as can we. ...
- 04:01: ... infrared light also makes it through the atmosphere, though it helps to be up here on a ...
- 04:20: ... that flexes and bends to match and correct the warping of incoming light. To do this in real time, Gemini creates its own artificial guide star by ...
- 04:53: ... spectrograph takes incoming light and breaks it into its component wavelengths, similar to a prism, and it ...
- 05:05: When the light analyzed by this machine left its quasar, it was ultraviolet.
- 05:12: ... expanding universe sapped energy and stretched the wavelength of that light so that it was infrared by the time it reached the earth and this ...
- 05:43: ... was filled with hydrogen gas. It was murky, especially for ultraviolet lights. ...
- 06:15: Much of the quasars once ultraviolet light was sucked up before it escaped the early universe.
- 06:56: ... tiny speck is both a revelation and a mystery. It literally shines a light on the earliest epochs of our universe, teaching us about our most ...
2019-06-17: How Black Holes Kill Galaxies
- 06:33: ... 10% the mass of the infalling gas is converted to energy in the form of light and yet more of the gas is blasted outwards by that same light in ...
2019-06-06: The Alchemy of Neutron Star Collisions
- 02:47: ... it'll be detected by an as yet unborn civilization a hundred million light years away as will the explosion of electromagnetic radiation that ...
- 12:15: ... can find out with so little in this case from a single point of light that is that distant quasar." - Jan Pieter Cornet asks something that I ...
- 13:02: ... 3000 Kelvin temperature at that time although even by then most of the light was infrared the universe then expanded by a factor of a hundred over ...
2019-05-16: The Cosmic Dark Ages
- 00:04: ... 10 and 1000 billion trillion stars fill the observable universe with light. But there was a time before the first star ...
- 00:24: ... them from the other side of the universe. But there’s an up side. If the light from some space object took billions of years to get to us then we see ...
- 01:34: ... The universe became transparent for the first time, and we see the light freed at that moment as the cosmic microwave background. THAT is the ...
- 02:19: ... dark ages – characterized by two things: the absence of new sources of light and the fog of atomic and molecular hydrogen and helium that filled the ...
- 02:31: ... that formed from that gas would be the next source of light, and those stars would also burn away the remnants of that gas, ionizing ...
- 04:46: ... was only 400 million years old. But our best evidence isn’t from the light that reaches us, but rather it’s from the light that never makes ...
- 05:13: ... was mostly transparent, but it did block some very particular types of light. Any photon whose energy happened to exactly match an electron energy ...
- 07:19: ... see them – the faintest red dots in our most sensitive surveys. As the light of those most distant quasars traveled to us it passed through the last ...
- 08:36: ... because the quasar has itself ionized a bubble spanning several million light years. By the time the quasar’s light reaches the edge of that bubble, ...
- 09:21: ... rest of the quasar’s light continues on its way towards us, but the universe keeps expanding. ...
- 10:10: ... is the spectrum of a quasar from the epoch of reionization. All of this light comes from the material falling into the black hole, or being blasted ...
- 10:47: ... reach us. The jagged region is the Lyman-alpha forest, where the quasar light passed through individual clouds of neutral gas, each of which cut a ...
- 11:06: Oh, and right next to the Lyman-alpha cutoff we see a little light that made it through due to the ionized bubble around the quasar itself.
- 11:17: ... the universe finally became fully ionized. And the scant Lyman-alpha light that made it through due to the quasar’s ionization bubble can tell us ...
- 11:49: ... light absorbed from the cosmic background radiation tells us when the dark ...
- 12:16: ... the meantime, let’s take a moment to be grateful for our own light-filled stelliferous era; Probably the only habitable epoch in the past and ...
2019-05-09: Why Quantum Computing Requires Quantum Cryptography
- 06:19: Try it with two polarized sunglasses lenses at 90-degrees – all light gets blocked.
- 06:33: Bizarrely, now some light gets through.
- 16:09: What was imaged was light escaping from the photon sphere that was produced a the magnetically driven jet.
- 16:21: ... seriously, the "light from outside the event horizon because we can't actually see the event ...
2019-05-01: The Real Science of the EHT Black Hole
- 01:09: ... is 53 million light years away, so resolving that black hole is equivalent to resolving a ...
- 01:44: Interferometry is a way of combining the light taken by two or more telescopes separated by some distance to massively improve their resolution.
- 01:53: We can think of light from a very distant point as coming in a series or plane waves.
- 02:08: And that phase difference itself is different for light coming from different points on the sky.
- 03:50: ... resolution is around 1mm, which is around the shortest wavelength radio light. ...
- 05:46: We see that jet extending 5000 light years outside the galaxy.
- 05:51: To understand exactly where the light we're seeing comes from let’s look more closely at the regions around the black hole.
- 05:58: The event horizon itself is the point where even outward-pointing light can’t escape the black hole.
- 06:24: The photon sphere is where gravity is so strong that light itself can orbit the black hole.
- 06:29: That orbiting light will eventually leave the photon sphere– either falling into the black hole or escaping outwards.
- 06:36: We only see light that escapes directly towards us, so the photon sphere looks like a photon ring.
- 06:58: There are two main sources of light feeding the photon sphere.
- 07:19: Any closer and anything besides light will quickly spiral into the black hole.
- 07:24: But the accretion disk is not the source of light in this image.
- 07:43: Remember that the EHT observes radio light with a wavelength of around a millimeter.
- 08:03: So that synchrotron light shines from the jet vortex, it gets trapped briefly in the photon sphere, and then makes its way to us.
- 08:27: ... when the material is moving in the same direction as the emitted light. ...
- 08:38: ... this case, light from the magnetized plasma vortex is beamed on the side of the black ...
2019-04-24: No Dark Matter = Proof of Dark Matter?
- 00:03: ... possibilities if it were dust or gas we'd see it's obscuring effect on light passing through it if it were dark compact bodies like failed stars or ...
2019-04-10: The Holographic Universe Explained
- 18:01: Anyway, perhaps we need to accept that Penrose is beyond genre - like if Gandalf had a TARDIS and a lightsaber.
- 18:10: By the way, if anyone feels like drawing Roger Penrose as dressed as Gandalf with a lightsaber and a TARDIS, you would win the internet.
2019-04-03: The Edge of an Infinite Universe
- 00:37: For example we have the “observable universe” – that patch that we can see, and beyond which light has not yet had time to reach us.
- 06:35: This particular conformal compactification is designed to ensure that the path of every ray of light remains at 45 degrees across the map.
- 06:46: That means only lightspeed paths can hope to reach these boundaries ahead, and only light speed paths can originate from these boundaries behind.
- 07:16: Only lightspeed paths – or in the language of quantum field theory “massless fields” can access these diagonal boundaries.
- 15:45: ... all, if space is expanding faster than light at the event horizon, that should counter the light-speed flow of space ...
2019-03-28: Could the Universe End by Tearing Apart Every Atom?
- 00:25: ... of space between galaxy clusters over countless trillions of cubic light-years of emptiness the dark energy adds up the sum of this outward push ...
- 06:20: ... will eventually be racing apart from each other faster than the speed of light. ...
- 06:51: ... faster than light recession of space is already happening but right now four patches of ...
- 07:02: ... two patches of space are moving away from each other, faster than light, then they can never communicate with each other - the distance from us ...
- 09:38: In fact, at this point the cosmic event horizon is still about 200 million light years away.
2019-03-20: Is Dark Energy Getting Stronger?
- 02:32: We see its effect in the rotation and movement of galaxies and in the bending of light due its space-warping gravity.
- 04:40: The most distant supernova we’ve seen is so far away that its light has been traveling to us for around 75% of the age of the universe.
- 07:58: ... works like this: when photons of ultraviolet light radiate from the accretion disk, they bump into extremely energetic ...
- 08:17: ... and as you might expect, the brighter a quasar is in ultraviolet light the more in X-rays it can ...
- 08:32: If UV and X-ray light track each other perfectly, there would be no way to differentiate the effects of distance and intrinsic energy output.
- 08:41: Both effects would cause the UV and X-ray light to brighten or dim in the same way.
- 09:12: See, the ratio between the amounts of X-ray versus ultraviolet light depends on true ultraviolet energy output of the quasar.
- 10:25: ... UV-to-X-ray ratio, versus the redshift, which is how much the quasar’s light got stretched as it traveled the expanding ...
- 11:07: ... means the light from these quasars appears more stretched out – more redshifted on ...
- 11:35: ... more than we thought, that could explain the extra stretching of the light from these distant ...
2019-03-13: Will You Travel to Space?
- 14:38: ... device light enough to rotate its flywheel due to being hit by individual particles ...
2019-03-06: The Impossibility of Perpetual Motion Machines
- 02:37: Close, but no perpetual lighting cigar.
- 13:27: In which we deciphered the cryptic patterns embedded in the oldest light in the universe.
2019-02-20: Secrets of the Cosmic Microwave Background
- 02:05: ... stripped of their electrons in that extreme heat in this plasma state, light and matter were locked together As the baryons condensed into over-dense ...
- 07:42: ... of the universe over that time that size should be about half a million light years at Recombination theoretically And that gives us our ruler Now ...
- 11:14: ... us about the relative amount of dark matter compared to radiation, or light Now this is a bit too much of a rabbit hole for right now But in short ...
2019-02-07: Sound Waves from the Beginning of Time
- 00:11: ... Hidden patterns that echo the reverberations of matter and light From an epoch long before galaxies ever ...
- 01:46: ... and the lightest of nuclei forged in the first minutes after the Big Bang, and still so ...
- 02:01: There's also light, in fact, around a billion photons for every electron.
- 02:09: Unbound electrons present a huge target to scatter any wavelength of light.
- 02:26: We say that in this state, light was coupled with matter, And baryons and photons formed a single strange fluid: A Baryon-Photon plasma.
- 02:54: Second: Light was able to exert an enormous pressure on this plasma, as we'll see that it'd lead to the production of colossal sound waves.
- 03:08: ... meant that ripples in the plasma travelled at over half the speed of light. ...
- 03:31: But unlike baryons, dark matter does not interact with light at all.
- 03:35: Light exerts no pressure on dark matter.
- 04:43: And remember, sound travelled at over half the speed of light back then, so the shell expanded fast.
- 05:26: ... free electrons were able to interact with any frequency of light, electrons bound into atoms are restricted to only those specific ...
- 05:39: As a result, light and matter were no longer coupled.
- 05:49: As the wave of plasma and photons decoupled, light began to stream freely through the universe as the cosmic background radiation.
- 06:02: The speed of sound dropped from half the speed of light to only hundreds of meters per second.
- 06:26: We call this the sound horizon. And at recombination, it was around five hundred thousand light years.
- 07:09: So those rings should be 150 mega parsecs across, 500 million light years.
- 08:54: Redshift is just the amount by which a galaxy's light has been stretched as it travelled through the expanding universe.
- 09:01: The more stretching, the longer that light has travelled, and so the more distant that galaxy must be.
- 12:55: ... Journal' lets you take notes and measure scientific phenomena, such as light, sound, and motion, using your phone, tablet, or ...
2019-01-30: Perpetual Motion From Negative Mass?
- 00:41: ... the key to faster than light travel because it’s the only stuff that can curve space in the right way ...
- 00:52: And if you can travel faster than light you can also travel backwards in time.
2019-01-24: The Crisis in Cosmology
- 00:39: ...by measuring the distances to the spiral nebulae They were many millions of light years from us,...
- 01:58: ...whose light has traveled billions of years through this expanding cosmos.
- 02:35: ...with 1 megaparsec being around 3.3 million light-years.
- 03:05: This is the lengthening of the wavelength of light from that galaxy,...
- 06:07: The SHOES project measures the recession of galaxies up to around 2 billion light years away.
- 07:15: ...when the universe had finally cooled down enough to become transparent to light.
- 08:01: In the era just before the release of the CMB, matter and light were trapped together.
- 08:09: ...while light generated a powerful pressure to resist that collapse.
- 08:32: ...the release of the CMB meant that light and matter were no longer coupled together.
- 09:21: Those parameters include the starting combination of both dark and light matter, and radiation,...
- 14:18: Gravitational lensing is the bending of light by a gravitational field.
2018-12-12: Quantum Physics in a Mirror Universe
- 00:02: ... that we become aliens who originated life across the galaxy by sending lights-out probes carrying super resistant life-forms well maybe let's get our ...
2018-12-06: Did Life on Earth Come from Space?
- 00:37: ... DNA molecular machinery and cell walls are shredded by ultraviolet light tardigrades and bacterial spores are somewhat resistant the latter if ...
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.
- 00:29: ... endless orbits around the sun, and faintly glimmering with its reflected light. ...
- 01:15: ... possibility that Oumuamua is aliens, or more accurately an artificial light cell presumably attached to an alien ...
- 04:12: They just do a few calculations to show the plausibility of one particular explanation, that Oumuamua is a lightsail.
- 04:32: The sun's own light could be pushing on the object speeding it up.
- 04:58: ... pressure thing would only work if Oumuamua is incredibly thin and light, thinner and lighter than any conceivable natural space object, ergo ...
- 05:18: That sounds like a lightsail.
- 05:23: The Japanese Ikaros Lightsail flew to Venus in 2010.
- 05:27: And the breakthrough starship program is planning to use a lightsail as our first interstellar probe.
- 05:32: The lightsail hypothesis potentially explains the acceleration and the weird shape.
- 07:13: ... of dust, or perhaps it has unusually large dust grains that reflect less light than lots of smaller grains, or perhaps the surface material has been ...
- 09:45: Can we really say the same about the unnatural explanation of an alien lightsail?
- 09:51: One thing the lightsail doesn't explain is the tumbling motion.
- 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.
- 10:14: The other issue with the lightsail hypothesis is the speed.
- 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.
- 10:43: ... any aliens who sent it, especially when the technology to accelerate a Lightsail to a good fraction of the speed of light is within the grasp of even us ...
- 11:10: In their paper, they don't claim that an alien lightsail is the most likely explanation, just that it's a plausible one.
- 11:31: The lightsail hypothesis for Oumuamua was first presented by Avi Loeb in late September in a "Scientific American" article.
- 14:35: ... a process analogous to the refractive index, which changes the speed of light and ...
2018-11-14: Supersymmetric Particle Found?
- 05:53: It spots neutrinos when they're decayed or electrons, muons, or tau particles, which in turn produce visible light as they streak through the ice.
2018-10-31: Are Virtual Particles A New Layer of Reality?
- 00:58: For example, Max Planck used a quantization trick to figure out the spectrum of light emitted by hot objects.
- 05:36: And they can even travel faster than light or backwards in time.
2018-10-25: Will We Ever Find Alien Life?
- 04:52: An advance civilization may launch so many solar satellites that they substantially block the light from their own star.
- 05:10: ... of its parent star and also cause an unusual increase in infrared light due to waste heat shared by the ...
2018-10-10: Computing a Universe Simulation
- 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.
- 12:31: How then can we say that the gravitational waves and the light traveled at the same speed?
- 12:40: Those gravitational waves and that light traveled a crazy long distance, 40 megaparsecs or around 150 million light years.
- 12:49: ... the very low density of gas along that vast distance slowed down the light a little bit, effectively increasing the index of refraction of space, ...
- 13:04: Light traveling through space is slowed down from the full light speed of the perfect vacuum.
2018-10-03: How to Detect Extra Dimensions
- 02:38: But before we get all hyper-dimensional, let's think a bit more about 3 plus 1D space-time and how gravity, light, and matter behave there.
- 02:48: Imagine a pulse of light traveling from some distant source.
- 02:52: We can think of light rays spreading up evenly over an expanding spherical shell.
- 02:58: If we see that pulse, it means our eye or our telescope intercepts some of those light rays.
- 03:08: So as this shell expands, the light rays become more spread out.
- 06:55: ... three spatial dimensions-- for example, the usual inverse square law for light. ...
- 08:58: Wild light and the force of gravity appear to obey the inverse square law.
- 11:06: ... that gravity really does travel pretty much exactly at the speed of light. ...
2018-09-12: How Much Information is in the Universe?
- 03:31: Well, the radius of the universe is something like 47 billion light years, which is a few times 10 to the power of 61 Planck lengths.
2018-08-23: How Will the Universe End?
- 03:25: That's the boundary of our patch of the universe beyond which no new light can reach us.
- 07:44: They slowly leak away their mass as a cool heat [INAUDIBLE] of random particles for the most part faint radio light.
- 08:55: Occasional flashes of gamma rays will light up the darkness as black holes reach that last explosive stage of their evaporation.
- 09:03: And after that, just particles and light, now not even bound gravitationally.
- 09:54: ... remaining matter in the universe, quantum tunneling allows the elements lighter than iron to fuse together, while elements heavier than iron ...
- 14:59: That's the classical theory, which is wrong-- and also suggested that electrons should spin faster than light.
2018-08-01: How Close To The Sun Can Humanity Get?
- 01:15: But that energy doesn't only come as life-giving light.
- 02:19: Charged particles traveling at nearly 1% the speed of light bombarded the earth.
2018-07-04: Will A New Neutrino Change The Standard Model?
- 00:48: To have a 50/50 chance of stopping any given neutrino, you need a wall of lead 1 light year thick.
- 06:41: ... the flow of time, which means they can't be moving at the speed of light, which means they must have ...
- 09:25: That's heavier than regular neutrinos but way too light to be a candidate for dark matter.
2018-06-20: The Black Hole Information Paradox
- 14:23: They can have any mass, can travel faster than light, and can even travel backwards in time.
2018-06-13: What Survives Inside A Black Hole?
- 00:34: At that horizon, time is frozen and the fabric of space itself cascades inwards at the speed of light.
- 00:40: Nothing can travel faster than light, and so nothing can escape from below the event horizon-- not matter, not light, not even information.
- 02:58: After all, the forces involved, namely the gravitational and electromagnetic forces, are only communicated at the speed of light.
- 04:12: The spacetime at the location of Earth's orbit would remain curved until the elastic fabric straightened itself out at the speed of light.
2018-05-23: Why Quantum Information is Never Destroyed
- 11:49: Pepsi could extract some free energy if you could build a device that spans several million light years or, I don't know, install some solar panels.
2018-05-16: Noether's Theorem and The Symmetries of Reality
- 01:18: As the universe expands, light traveling through that expanding space is stretched out.
- 06:24: It's a generalization of Fermat's principle, which states that light will always take the path between two points that minimizes the travel time.
- 10:31: ... does have some overlap with Gaia in that it will measure light curves, so it changes in brightness over time for billions of objects ...
- 11:49: ... can 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 ...
2018-05-09: How Gaia Changed Astronomy Forever
- 08:33: Every dot of light in this picture is a star, with its past and future motion now known.
2018-05-02: The Star at the End of Time
- 04:52: This is because the light produced by stars comes from the heat glow of their surfaces.
- 05:36: To us, they appear red because they're producing more red light than yellow, blue, green, et cetera.
- 07:03: Individual points of white light will appear in the night sky, shining for up to a few billion years before winking out.
- 09:41: ... matter exists in a puffy sphere some 200,000 light years in radius surrounding the Milky Way, compared to the 100,000 light ...
2018-04-25: Black Hole Swarms
- 00:43: We know these things because we see them, from our comfortable vantage 28,000 light years out in the galactic disk.
- 00:58: ... central few light years of the Milky Way is thought to contain a vast swarm of smaller ...
- 03:33: Over a few billion years, we only expect the black holes from the central several light years to have made much progress inwards.
- 04:34: ... should lead to tens of thousands of black holes in the central few light years of the Milky Way's ...
- 06:11: They spotted 92 point-like X-ray sources within one parsec, or around three light years, of the galactic center.
- 07:25: ... to be at least hundreds of stellar-mass black holes in the central few light years in order to get these 13 X-ray ...
2018-04-18: Using Stars to See Gravitational Waves
- 02:45: For the first time, the event behind a gravitational wave signal was also seen in light.
- 05:23: But much of this gravitational wave background will have wavelengths as long as many light years.
- 06:06: It monitors dozens of the fastest rotating pulsars, millisecond pulsars, spanning many thousands of light years.
- 11:23: ... with the help of its absorbing biosphere, reprocesses a lot of that light and radiates something closer to a 300 Kelvin thermal ...
2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)
- 03:56: ... light warms the atmosphere in the oceans and it powers photosynthesis at the ...
- 08:10: A plant absorbs the concentrated ultraviolet light from the sun and reprocesses it into a much higher entropy infrared heat glow.
- 12:41: It's around 16 billion light years away.
- 12:52: Before they get to us, they'll find themselves in a patch of space that is moving away from us faster than the speed of light.
2018-04-04: The Unruh Effect
- 01:57: Einstein taught us that an object without mass, like a photon, can only travel at the speed of light and no slower.
- 02:16: ... with mass can never reach the speed of light, so the world line of a massive object, which includes any observer, has ...
- 02:26: ... light ray world lines backwards from our observer defines what we call the ...
- 02:38: ... because photons fired from anywhere in the past light cone can reach our observer either at the current point or at some point ...
- 02:47: ... observer moves forward in time, as long as they don't travel faster than light, their past light cone should eventually contain the entire ...
- 03:06: But, actually, there is a sublight speed world line that can outpace light or at least keep ahead of it.
- 03:24: Imagine my friend is traveling towards me initially at close to the speed of light.
- 03:49: They then accelerate back up to close to the speed of light and keep accelerating.
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.
- 00:38: ... a beautiful spiral structure, spanning its gently rotating disk 220,000 light years in diameter, and a central bulge that hides a giant black hole ...
- 06:20: When those black holes are around a light year apart, they'll start losing orbital energy to gravitational waves.
- 10:43: ... on it being some sort of stuff that can interact with either matter or light. ...
2018-03-21: Scientists Have Detected the First Stars
- 01:05: [MUSIC PLAYING] So the very early universe was full of hydrogen gas and light.
- 01:12: That light was the leftover heat glow from before those first hydrogen atoms formed.
- 01:21: It's the oldest light that we can see, and we explained it in detail in a previous episode.
- 01:27: We can also, try to see the light signature from that very early hydrogen gas.
- 01:42: That photon has a wavelength of 21 centimeters, which is radio light.
- 02:20: ... ultraviolet light from those stars shifted the equilibrium so that the electron spin ...
- 03:43: So the research team added together the CMB light from the entire visible sky and recorded this spectrum.
- 03:50: The dip shows the drop in CMB light due to 21 centimeter absorption.
2018-03-15: Hawking Radiation
- 04:58: He imagined a single spacetime path, a lightspeed trajectory called a null geodesic.
2018-02-21: The Death of the Sun
- 10:31: The resulting combined nucleus is lighter than the sum of the masses of the two distant protons.
2018-02-14: What is Energy?
- 12:40: These star-forming clouds can vary in metallicity across their vast widths, which are often hundreds of light years.
2018-01-31: Kronos: Devourer Of Worlds
- 01:25: Or they might be a wide binary, separated by up to a few light-years and just barely gravitationally bound.
- 03:10: ... came upon HD240430 and HD240429, Kronos and Krios, two stars nearly two light-years apart from each other, about 326 light-years from our solar ...
- 07:30: And it may also reveal other planet-eating stars, which will shed light on the whole planet formation process.
- 08:28: Andrew Milo recommends we block out some of the sun's light with orbiting solar farms.
2018-01-24: The End of the Habitable Zone
- 06:44: ... in the stratosphere will be broken into hydrogen and oxygen and the light hydrogen atoms will be lost to ...
- 09:26: Now we're not going to stop the sun from brightening but we might try to block some of the extra light.
2018-01-10: What Do Stars Sound Like?
- 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.
- 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.
- 08:43: Their harmonies are hidden in the flickering of their light and in the subtle in and out breathing of their services.
- 10:37: You are keeping the studio lights on and the camera running.
- 11:12: A GRB within a few light years would be directly devastating to life.
- 11:24: Because there are no stars that could possibly explode that way for hundreds of light years.
- 11:53: ... even if a super-focused 1-degree gamma ray burst hit us from a single light year away, that jet would have diverged to something like 10 times the ...
- 12:33: As Felix realizes, light is not electrically charged, and so it isn't affected by EM fields.
- 13:17: ... relativistic beaming massively amplifies our perceived brightness of the light emitted in the same direction as the near light speed charged particles ...
2017-12-22: Space Time VR
- 00:16: ... in which we explore the electromagnetic spectrum, the speed of light, and time ...
2017-12-20: Extinction by Gamma-Ray Burst
- 02:46: ... resulting explosion sprays high-energy light, so ultraviolet, x-rays, gamma rays, and near-light-speed particles-- so ...
- 02:58: Any planet within a few tens of light years of a supernova is in trouble.
- 04:22: And nitrogen dioxide absorbs visible light, reducing the energy received from the sun.
- 04:44: ... estimated that a typical gamma-ray burst within 10,000 light years could deplete ozone enough to cause up to a 30% increase in ...
- 05:25: ... extinct and the exposure that species would have had to ultraviolet light. ...
- 06:50: ... finds itself in the path of between one and three GRBs within 10,000 light ...
- 07:10: The nearest potential GRB in the brewing is 8,000 light years away, so within the danger zone.
- 08:46: However, for a supernova to produce the same effects, it needs to be much closer, within 20 to 30 light years.
2017-12-13: The Origin of 'Oumuamua, Our First Interstellar Visitor
- 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.
- 08:14: ... under construction in the Anacondian Andes in northern Chile, with first light planned for ...
- 09:50: [INAUDIBLE] Leonard asks whether a particle can have momentum higher than its mass times the speed of light.
- 09:56: In other words, shouldn't there be an upper limit to momentum if the speed of light is limited?
- 10:00: Well actually, momentum can be arbitrarily high, even when speed is limited to the speed of light.
- 10:05: The equation for momentum, P = M times V, only works at low speeds approaching the speed of light.
- 10:14: That factor, the square root of one minus V squared on C squared, approaches 0 as velocity approaches the speed of light.
- 10:22: That means momentum approaches infinity for any object with mass that's approaching the speed of light.
2017-12-06: Understanding the Uncertainty Principle with Quantum Fourier Series
- 13:13: ... kill time during warp journeys by scanning light curves of distant stars for the characteristic dips in brightness due to ...
- 13:53: Hanny's Voorweep is a wee blob of light right next to a spiral galaxy.
- 13:58: ... hypothesized to be the light echo from a dead quasar that was once in that galaxy, so the cloud of ...
2017-11-29: Citizen Science + Zero-Point Challenge Answer
- 01:52: These exploding stars show up as transient point of light, typically in very distant galaxies.
2017-11-22: Suicide Space Robots
- 15:07: Now sometimes the path to truth is extremely surprising, like the invariance of the speed of light the quantum nature of subatomic world.
2017-11-02: The Vacuum Catastrophe
- 09:28: Lucas Kukowski asked whether neutrinos belong to the dark sector or the light sector.
2017-10-25: The Missing Mass Mystery
- 00:33: The shining light of these stars illuminates or is conspicuously absorbed by gas and dust within those galaxies.
- 00:59: This dark sector doesn't interact with light in any way and so is invisible to us.
- 01:06: The remaining 5%, the light sector, represents all of the regular matter in the universe.
- 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?
- 02:43: Baryonic matter interacts with light, so we can search for it by scanning the electromagnetic spectrum.
- 03:44: It's the light released at the moment the first atoms formed nearly 400,000 years after the Big Bang.
- 03:50: We still see that light today traveling to us from distant parts.
- 04:43: Those large blobs are driven by dark matter, which doesn't interact with light, so it can't produce density oscillations.
- 06:15: We typically see that stuff inside galaxy clusters where the plasma is relatively dense and is energized by the light of the galaxies themselves.
- 06:33: This cool gas then absorbs signature wavelengths from light that passes through it.
- 06:39: Absorption features in the light of distant quasars reveal this gas lurking between clusters of galaxies.
- 07:56: And yet, those filaments are vast, tens of millions of light years long.
- 12:21: ... also asks, if virtual particles control faster than the speed of light, can't they escape the event horizon of black holes via Hawking ...
2017-10-19: The Nature of Nothing
- 00:24: An empty jar still contains something-- molecules of air and a bath of infrared light from its warm environment.
- 05:01: For example, in QFT, virtual particles can have any mass and any speed, including speeds faster than light, and can even travel backwards in time.
2017-10-11: Absolute Cold
- 02:15: This quantum nature is revealed when we look at the spectrum of light produced as those particles hop between energy levels.
- 06:46: To understand the universe, we need to understand how it behaves absent heat, absent light, and absent matter.
- 08:26: ... of a potential pair of binary supermassive black holes orbiting only one light year ...
- 09:53: ... Gamble points out that if this binary pair is a whole light year apart, then for us to see them orbiting each other, they need to be ...
2017-10-04: When Quasars Collide STJC
- 00:38: ... the detection of a pair of supermassive black holes orbiting only one light-year apart from each ...
- 03:32: The Seyfert galaxy in question is Markarian 533, which is around 400 million light-years away.
- 03:38: The black holes are around one light-year apart in the center of the galaxy.
- 05:15: The radio light seen here is from electrons spiraling in those magnetic fields, so-called synchrotron radiation.
- 05:27: ... frequently see separate knots of radio light in AGN jets, which can splatter as their fuel supply changes or as the ...
- 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.
- 08:04: In fact, we still don't know how supermassive black holes merge once they're within one parsec, or a few light-years, of each other.
- 09:48: And this galaxy is so dusty that it's hard to peer into the core at other wavelengths of light.
2017-09-28: Are the Fundamental Constants Changing?
- 02:01: Let's try the speed of light.
- 02:13: It's been suggested that a changing speed of light might be an alternative to inflation theory, or even to the apparent expansion of the universe.
- 02:24: For one thing, our definitions of the units used to define the speed of light are arbitrary, and themselves depend on that speed.
- 02:31: The meter is officially defined as the distance light travels in one 299,792,458th of a second.
- 02:41: And the second is defined in terms of a particular frequency of light emitted by the cesium-133 atom.
- 02:48: If the speed of light changes, the rulers we use to measure that speed change also.
- 02:54: ... speed of light defines the relationship between space and time, so is it even ...
- 04:48: We see this effect in the sharp spikes or dips in light at specific wavelengths when we observe the spectrum of a gas.
- 06:44: These things can be seen out to billions of light years.
- 06:48: When a quasar's light passes through giant clouds of gas on its way to us, elements in those clouds absorb photons to produce spectral lines.
- 13:17: It would then look back at light lensed in the sun's gravitational field.
- 13:21: That light could be magnified up to 100 million times.
- 14:02: To do something similar with visible light, you'd need a nanofabricated structure with actual concentric rings.
2017-09-20: The Future of Space Telescopes
- 01:49: So how can we find a terrestrial planet around a star light years away?
- 01:58: ... a disk inside a telescope that occludes a star, blocking its light so that any planets can be seen more ...
- 02:12: The wave nature of light causes it to bend or diffract around the edges of a coronagraph back towards the central optical axis.
- 02:21: This means it's never possible to completely block the star's light.
- 03:16: ... shape, whose cleverly calculated petal geometry is designed to diffract light away from the central axis, not towards ...
- 03:27: The number and length of pedals optimizes each starshade for a particular wavelength of light.
- 05:56: ... a revolutionary idea to use diffraction optics to focus light, instead of what we call geometric optics, so reflection or refraction ...
- 06:16: Light diffracts around the disk, coming to focus on the optical axis where the light's wavefronts line up in constructive interference.
- 06:55: It's also a giant coronagraph, blocking most of the light from the object of interest.
- 07:00: All you get is the thin ring of light diffracted around the edge.
- 07:05: Although that light comes to an incredible focus, the actual amount of light you get is the same as if you didn't have a telescope at all.
- 07:27: There are challenges to bring the light from each ring to the same focus, but fortunately humans are pretty smart and there are ways to do this.
- 07:41: ... outwards, it could spot a terrestrial planet at tens of light years distance and even map the cloud structure of a gas giant, ...
- 08:46: ... by how water droplets focus light into colorful arcs across the sky, scientists have proposed we use ...
- 09:57: It may be possible to launch multiple such telescopes that have several times the light collecting power of the Hubble Space Telescope.
- 11:40: They have to travel along the same space-time fabric as light waves, after all.
2017-09-13: Neutron Stars Collide in New LIGO Signal?
- 02:39: ... per second and have enormous magnetic fields that result in jets of near light speed particles that sweep through space like a ...
- 06:07: "Optical counterpart" means that there's a source of visible light associated with the gravitational wave.
- 06:38: ... satellite had spotted a flash of gamma radiation-- so the highest energy light-- from a galaxy 130 million light years ...
- 07:43: Astronomers don't trigger Hubble observations lightly.
- 08:16: NGC 4993 is 130 million light-years away, which is about at the limit for LIGO sensitivity to neutron star mergers.
- 08:25: Compare that to the around 1 billion light-year distance of the earlier black hole mergers.
- 08:43: Most heavy elements like gold, lead, uranium, et cetera, are produced when the nuclei of lighter elements capture fast-moving neutrons.
- 09:49: Besides their importance to nucleosynthesis, the simple fact that we can see neutron star mergers in regular light is extremely powerful.
- 11:17: ... we will have learned it from over 100 million light-years' distance by collecting only a handful of gamma rays and by sensing the ...
- 14:10: That method is to watch the effect on the parent stars' light as it passes through the planet's atmosphere.
2017-08-30: White Holes
- 01:56: Not even light can leave a black hole, hence the whole black thing, but light can only leave a white hole.
- 05:04: Also, lines of constant distance and time curve, so that light paths always travel on 45 degree paths.
- 05:39: ... Light traveling at that 45 degree angle takes infinite time to escape the ...
- 06:51: Imagine that something in our past was traveling at the speed of light and trying to reach the past event horizon.
- 06:58: There is no way it can get there unless it goes faster than light.
- 07:20: The light rays from any crossing reach us infinitely far in the future, even if the black hole plunge began far in the past.
- 07:30: ... black hole has an event horizon that's a barrier to entry, but also light rays within that region must move up on the ...
- 08:06: One, light rays exiting that past white hole can never reach us.
- 08:18: Light has to traverse infinite time to reach our location.
- 11:51: But what about light rays entering or leaving our eternal black hole from the opposite side?
2017-08-24: First Detection of Life
- 01:47: ... from molecules in Earth's atmosphere absorbing specific wavelengths of light from what would otherwise be the smooth heat glow of the ...
- 04:15: It's destroyed by solar ultraviolet light in the atmosphere with a half-life of around 50 years.
- 04:25: While there are non-biological ways of making nitrous oxide, like lightning, these aren't nearly enough to account for the amount observed.
- 06:11: Of course, these revealed strangely green land masses due to chlorophyll absorbing red light and reflecting green light.
- 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.
- 07:42: ... a tiny fraction of the star's light passes through the planet's atmosphere when this happens, but by ...
- 09:32: This is facilitated by the fact that the star itself is very dim, making subtraction of its light easier.
- 10:31: Perhaps that answer is already traveling to us in the light of a distant planet's atmosphere calling to us from across spacetime.
2017-08-16: Extraterrestrial Superstorms
- 11:44: Mars, you're hoping us keep the lights on and the convection cells powered.
2017-08-02: Dark Flow
- 05:17: ... around 700 clusters in all directions on the sky and out to billions of light ...
- 06:02: When you look at scales larger than around a billion light years, you have basically the same amount of matter everywhere.
- 07:36: ... is a vast cluster of clusters that encompasses hundreds of millions of light years and several hundred entire galaxy ...
- 07:50: ... galaxies across the observable universe, or to two and a half billion light years at least, far beyond the gravitational reach of ...
- 08:22: It's moving away from us faster than the speed of light, and is now forever beyond the reach of light or gravity or anything.
2017-07-26: The Secrets of Feynman Diagrams
- 06:44: These particles aren't even limited by the speed of light or the direction of time, which leads to all sorts of fun.
- 07:51: As well as infinite possibilities for particle momenta, we have to consider even impossible faster than light paths.
- 12:09: To all of our Patreon supporters, thanks so much for helping us keep the lights on.
2017-07-19: The Real Star Wars
- 05:12: This produces a beam of coherent lights, making it possible to deliver very large intensities in very narrow beams.
2017-07-12: Solving the Impossible in Quantum Field Theory
- 02:13: Vibrations in the EM field are called photons, what we experience as light.
- 14:04: That approximation is OK at low speeds but breaks when things get close to the speed of light.
- 15:03: Feynman didn't limit particle velocity to the speed of light.
2017-07-07: Feynman's Infinite Quantum Paths
- 04:14: There was absolutely no physics in this description so far, not even the limit of the speed of light.
- 13:12: ... proposed in the late 19th century as the medium for the propagation of light ...
- 13:40: That should cause different observers to measure a different speed of light.
2017-06-28: The First Quantum Field Theory
- 04:08: This is exactly how light behaves, as was first realized by Max Planck and proved by Einstein.
- 04:16: Light is a wave in the electromagnetic field.
- 04:51: Quantum physics may have started with Planck's discovery of the quantum nature of light.
- 04:56: However, the first full formulation of quantum mechanics was Schrodinger's equation and it couldn't account for light at all.
- 05:13: It can't describe things moving anywhere near the speed of light and it implicitly assumes that forces act instantaneously.
- 05:31: However, understanding the behavior of light and its interaction with matter required a different approach.
- 08:43: And there's another reason this second quantization is better at describing the interactions of light and matter.
2017-06-21: Anti-Matter and Quantum Relativity
- 00:50: By the late 1920s, Einstein and Planck had already shown that light is a particle, as well as a wave.
- 02:17: Subatomic particles are often moving at close to the speed of light.
- 05:55: It contains the marks of both quantum mechanics, in the Planck constant, and relativity, in the speed of light.
- 06:38: ... moving in an electromagnetic field could keep releasing energy as light infinitely, and sink lower and lower, to infinite negative energy ...
- 14:38: ... that change in the vacuum energy state would propagate at the speed of light to fill that universe, fundamentally changing the way its elementary ...
2017-06-07: Supervoids vs Colliding Universes!
- 01:37: It's the light that was released at the moment that the first atoms formed 380,000 years after the Big Bang.
- 01:52: When it formed in the early hot universe, it was mostly infrared light with a temperature of 3,000 Kelvin.
- 05:46: ... in layman's terms, they split the light from those galaxies into component wavelengths and determined the shift ...
- 12:48: ... the metallicity of a star or a galaxy, you need to be able to split the light into a spectrum and look for emission lines, light at the signature ...
- 13:00: We can't collect nearly enough light yet to do that.
- 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
- 00:39: In its light, we see telltale signs of the generations of stars that came before it.
- 00:54: When the sun's light is broken into a spectrum, it reveals traces of many of the heavier elements of the periodic table.
- 04:13: However, the light that burns twice as bright burns half as long.
- 05:26: By comparison, the most massive lighter stars are, at most, a couple of hundred solar masses.
- 06:29: Those electrons then lose that energy by emitting light at specific wavelengths-- signature photons that are different for every element or molecule.
- 10:21: They radiate intense light, with a signature ultraviolet wavelength of hydrogen.
- 10:26: It's hard to make sense of this light, unless there are a ton of population three stars in those galaxies.
2017-05-17: Martian Evolution
- 13:15: ... stars around the limb, the edge, of the sun due to the powers of their light bending in the suns gravitational ...
2017-05-10: The Great American Eclipse
- 02:44: But something about the light seems clearer, the shadows sharper.
- 02:49: Take a walk through the pine woods behind you, and you might notice the dappling of light between the shadows has changed.
- 05:05: Now there's something definitely off about the light.
- 06:18: What shows up next is the ghostly light of the corona, the sun's outermost atmosphere.
2017-04-19: The Oh My God Particle
- 00:25: ... atomic nucleus travelling at 99.99999999999999999999951% of the speed of light crashed through our atmosphere and streaked across the Utah ...
- 00:46: The nucleus quickly disintegrated into a shower of subatomic particles and lights.
- 00:51: ... light was seen by the Fly's Eye Observatory, a collection of oversized tin ...
- 02:56: You can't focus them into a camera like you can with light.
- 03:09: All cosmic rays are traveling at pretty close to the speed of light, but that's the speed of light in a vacuum.
- 03:15: Light travels slower in a medium like air.
- 03:18: So when cosmic rays enter the atmosphere, they're actually traveling faster than the new, lower speed of light.
- 04:51: ... metal plates designed to stop air shower particles and detect the light produced as they smack into nuclei within the ...
- 07:52: In Now I'm talking close by on cosmic scales, so within 1 to 200 million light years.
- 08:39: ... traveling outside Earth's magnetosphere reported strange flashes of light, which may be due to Cherenkov radiation from cosmic rays passing through ...
2017-04-05: Telescopes on the Moon
- 01:18: That means-- one, the potential for extreme image sharpness with no turbulence to blow light from above.
- 02:20: ... only does it allow the scope to collect more light, increasing sensitivity, but when you're in space or on the moon, ...
- 06:23: ... assumes a smooth parabolic shape, exactly the shape needed to bring light to a perfect ...
2017-03-29: How Time Becomes Space Inside a Black Hole
- 01:41: That just means that a lightspeed causal link may have traveled between them.
- 02:29: In our episode on superluminal time travel, we saw that in flat space, this means traveling faster than light, which is, of course, impossible.
- 03:51: And the only way to break causality is still with faster than light travel.
- 04:26: Space itself is falling inwards faster than the speed of light towards the central singularity.
- 05:25: ... past light cone encompasses all of spacetime that could have influenced us, while ...
- 05:46: Our future light cone stares fixedly forwards, encompassing all spatial directions equally.
- 06:04: Send out a burst of future defining light rays, and they won't spread out evenly because they bend towards the gravitational field.
- 06:12: As you approach the event horizon of a black hole, more and more light rays are turned towards the event horizon.
- 06:18: Your future light cone and your time axis begin to blur together with the inward radial axis of the black hole.
- 06:44: But an important thing to remember is that the lines of constant space and time are curved so that light cones remain upright.
- 06:52: And light always travels at a 45 degree angle, even inside the black hole.
- 07:06: Our entire future light cone encompasses more and more of the event horizon.
- 07:12: That last tiny sliver is a narrowing window directly above that you could escape to at close to the speed of light.
- 07:20: Meanwhile our past light cone now encompasses light that has been struggling to escape from just above the event horizon since the distant past.
- 07:38: The outside universe exits our future light cone, which now just contains the singularity.
- 07:49: At the moment of crossing, light rays from the event horizon itself are suddenly visible.
- 07:54: In fact, we plummet through a sea of light that is eternally climbing outwards but getting nowhere.
- 08:05: As we fall with the faster than light flow of space time, we overtake light that is outward pointing.
- 08:12: That light isn't actually making headway outwards.
- 08:14: It's trying to swim upstream and failing against the faster than light cascade of spacetime.
- 08:20: ... of this light might be from the collapsing surface of the star that first formed the ...
- 08:39: Also in our past light cone are light rays that are pointed inwards, some of them coming from the outside universe.
- 08:46: This light overtakes us as we fall.
- 08:48: This is light that entered the event horizon after we did and appears to reach us from above.
- 08:54: We can try to move towards either source of light, down towards light from the black hole's past or up towards light from the black hole's future.
- 09:26: But remember that future light cone actually just points towards the singularity.
- 10:03: Even if it's old light struggling outwards, the past is radially outwards.
2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer
- 00:02: Traveling faster than light and traveling backwards in time are the same thing.
- 02:59: Those axes reflect symmetrically around this 45 degree path, representing the unvarying speed of light.
- 03:37: ... have to be negative, as long as you travel at less than the speed of light. ...
- 04:20: You're in a race to claim a newly discovered exoplanet 100 light years away.
- 04:25: Your competitor immediately launches a 50% lightspeed ship, the anti-matter powered Annihilator.
- 04:39: Your ship, the Paradox, can travel at twice the speed of light.
- 04:57: The Annihilator races off towards the exoplanet, 100 light years this way.
- 05:02: At 50% lightspeed, the Annihilator would take 200 years to reach its destination, from Earth's perspective.
- 05:14: However, when you launch, you travel at twice the speed of light.
- 05:23: You overtake the Annihilator at around the 67 light year mark and finish the race 150 years after the race began.
- 06:05: Their time axis is their own world line, and their space axis is symmetrically reflected around the path of light.
- 06:34: ... stationary and sees Earth racing away in the opposite direction at half light speed, while its destination races towards it at the same ...
- 06:55: The Paradox still appears to be traveling forward in time with respect to the Annihilator, even though it's traveling faster than light.
- 07:14: The Paradox outraces its own photons as it catches up to the Annihilator, and then it continues to emit light backwards behind it after it passes.
- 08:03: Let's look at the perspective of a different space time traveler, one traveling at very near the speed of light.
- 08:58: Now we transform back to the near lightspeed reference frame.
- 09:14: ... far enough, then when we finally turn the Paradox around, it's twice lightspeed movement will take us back to the beginning of the race, long before the ...
2017-03-15: Time Crystals!
- 12:03: ... who pointed out that we basically just learned all about a solar system light years away by studying how faint shadows make other faint shadows ...
2017-03-08: The Race to a Habitable Exoplanet - Time Warp Challenge
- 00:02: If you travel faster than light, you can travel backwards in time.
- 00:58: We talked about how the constant or invariant nature of the speed of light governs that transformation.
- 01:50: To increase your spacetime interval, to cross these contours backwards uphill, you must travel faster than light.
- 02:04: A race to a newly found habitable planet 100 light years away.
- 02:22: They launched the fastest ship that exists, the Annihilator, powered by an anti-matter drive capable of reaching 50% light speed.
- 02:58: It takes you 100 years to build a ship capable of traveling at twice the speed of light.
2017-03-01: The Treasures of Trappist-1
- 01:06: The TRAPPIST-1 system lies 39 and 1/2 light years away in the constellation of Aquarius.
- 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.
- 09:53: It's design phase is a little further along, and it'll see first light a few years earlier than EELT.
2017-02-22: The Eye of Sauron Reveals a Forming Solar System!
- 00:06: ... age, the Dark Lord Sauron fled Mordor into the sky and traveled about 25 light years towards the constellation Piscis ...
- 00:50: At only 25 light years away, it's the 18th brightest star in the sky.
- 01:14: And its purpose is to block the bright light of Fomalhaut so that its fate surrounding structures can be studied.
- 06:32: And the light that Hubble is seeing is just reflected star light from Fomalhaut.
- 09:25: We'll need to figure out if this planet is real and what causes its strange mismatch in visible and infrared light.
2017-02-15: Telescopes of Tomorrow
- 01:34: These cameras see mostly at infrared wavelengths of light, unlike Hubble's, which are optimized for visible and ultraviolet light.
- 01:57: Longer wavelengths of light scatter less easily than shorter wavelengths, and so have an easier time escaping these dust-packed stellar nurseries.
- 02:11: Webb will see even longer wavelength infrared light and so will bore even deeper.
- 02:36: Light from these earliest of galaxies has been traveling through our expanding universe since near the beginning of time.
- 02:43: That light has been stretched out by that expansion deep into the infrared.
- 03:03: Using infrared light is a double-edged sword, because light has a dual nature.
- 03:19: As a result, there's an absolute limit in how sharply light can be focused.
- 03:36: This means that infrared has a disadvantage over visible or ultraviolet light.
- 03:53: Its infrared pics will be just as clear as Hubble's visible light images.
- 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.
- 06:53: ... sodium lasers 90 kilometers into the upper atmosphere, where their light will produce artificial guide ...
- 09:06: ... also catch the visible light counterparts to gamma ray bursts, the most energetic explosions in the ...
2017-02-02: The Geometry of Causality
- 01:23: ... I accelerate my rocket ship to half the speed of light, the distance I need to travel to a neighboring star shrinks dramatically ...
- 03:16: Motion at a constant velocity appears as a sloped line, and the time axis is scaled so that the speed of light is a 45 degree line.
- 03:39: They all travel at different speeds, some close to the speed of light, but never faster.
- 05:28: To observe those points, I just wait around until their light had time to reach me.
- 06:27: That comes from insisting that we all see the same speed of light, 45 degrees on the spacetime diagram.
- 09:33: There's no point anywhere downhill that I can't reach as long as I can get close enough to the speed of light.
- 09:40: In fact, the nearest downhill contour defines the forward light cone for anyone anywhere on the spacetime diagram.
- 10:08: ... looked at today was for a flat or Minkowski space, in which faster than light travel is the only way to flip your space time ...
- 13:24: We actually do see the effect of time dilation in some of the x-ray light coming from right near the black hole.
2017-01-25: Why Quasars are so Awesome
- 01:19: Sometimes they even have jets of near light speed particles filling the surrounding universe with giant radio plumes.
- 01:49: When the very first radio telescopes pointed to the heavens, they saw fat blobs of radio light, whose sources were unknown.
- 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.
- 03:05: For one thing, its spectrum was redshifted, the wavelength of its light stretched out as those photons traveled through the expanding universe.
- 03:19: Its light must have been traveling from two billion light years away to acquire the observed redshift.
- 03:24: ... distance, the weird object had to be emitting many galaxies worth of light from a seemingly impossibly small region of ...
- 04:46: Some is converted directly into energy and radiated as light.
- 04:50: And this same light drives powerful winds of gas back out into the surrounding galaxy.
- 05:28: Then, we only see hints of the central monster because it lights up gas in the surrounding galaxy.
- 05:48: Oh, and if one of these jets happens to be pointed directly at us, then we see strange effects due to the near light speed motion of the jet material.
- 05:57: In an effect called relativistic beaming, the light from the jet is vastly magnified.
- 06:45: We're talking, at most, a few light days across.
- 09:32: Although it's far away, its light comes to us from a time long after the peak of the quasar epoch.
2017-01-19: The Phantom Singularity
- 06:07: ... long as our objects world line doesn't require faster than light motion, then the square root of the space time interval is equal to the ...
- 06:34: There would have been some speed of lights through the equation, but we set them equal to 1 because we're that cool.
- 09:30: There is one thing that can have a space time interval of 0, light.
- 09:36: Actually, anything capable of traveling at light speed can only have a space time interval of 0.
- 10:13: ... the fact that even an outgoing light ray takes infinite time to move any distance, so using boring old time ...
2017-01-11: The EM Drive: Fact or Fantasy?
- 00:59: Most often, they turn out to be in error, like Opera's faster than light neutrinos and the BICEP2 primordial gravitational waves.
- 09:38: Joel, we're considering buying a lightly used EmDrive with your contribution, only 1,000 light years on the clock, apparently.
- 12:22: There's very good reason to think that aliens will use light, with a radio or otherwise.
- 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
- 00:40: Although they don't emit any light themselves, they can have a very visible effect on their surroundings.
- 01:18: ... star reveals it to be in orbit around a companion that is dark invisible light but bright in fluctuating X-ray ...
- 01:36: The most famous and the closest is the Cygnus X-1 black hole, 6,000 light years away.
- 04:02: These black holes occasionally pass in front of more distant background stars, gravitationally lensing the star's light.
- 04:15: ... the distant star should appear to split into two or four images as its light passes around the gravitational field of the black ...
- 04:59: An extremely advanced alien race has decided to destroy the Earth by enveloping it in a giant Kugelblitz, a black hole made entirely of lights.
- 05:08: They direct an intense shell of light inwards towards the Earth.
- 07:12: Now, the collapsing star is replaced with a collapsing shell of light.
- 07:17: That shell takes a 45-degree path, as do all light speed things on the Penrose diagram.
- 07:25: ... an event horizon forms as spacetime flows faster than the speed of light towards that superdense region of ...
- 08:00: In our Kugelblitz scenario, Earth won't even see the incoming shell of light until it reaches us.
- 08:24: The light shell passes the moon's orbit, and a true event horizon forms.
- 08:38: ... the light reaches our reflective barrier, it is indeed perfectly reflected, ...
- 08:51: See, once the event horizon forms, all paths below it lead to that singularity, even outgoing light paths.
- 09:01: ... on the Penrose diagram, that's seen as the future light cone of everything below the event horizon leading to the singularity, ...
- 09:19: As long as the event horizon has not yet formed, the incoming light can be stopped.
2016-12-21: Have They Seen Us?
- 00:57: ... of chatter is, as I speak, spreading out into the galaxy at the speed of light, the unmistakable signature of an emerging technological ...
- 01:09: The outer edge of this bubble is now over a hundred light years away.
- 04:11: Our best-targeted search so far, the SETI Institute's Project Phoenix, scanned 800 stars within 200 light years.
- 04:27: ... from a civilization's internal broadcasts from within a couple of light years, if those broadcasts with the same strength as our ...
- 06:38: ... with the sensitivity to potentially see an alien TV bubble to many light years and that is large enough to filter out local ...
- 08:24: ... be sensitive enough to spot our own TV bubble from a hundred or more light years ...
- 09:44: That signal is now 50 light years away.
- 12:43: Any civilization within 40 to 50 light years could have sent a return signal that will reach us any day.
- 13:41: The light from the instant of the monkey's crossing of the event horizon is eternally trapped at that horizon.
- 13:54: But you're traveling down that same escalator and so you pass this light.
- 14:05: And so light that the monkey emitted from below that point is trying to go up, but is actually going downwards.
- 14:16: So you overtake some of that light, which means you see the monkey ahead of you.
- 14:57: ... as a black hole evaporates will be accompanied by all of the remaining light emitted by everything that fell into it as it crossed the event ...
- 15:29: You can escape a black hole by traveling faster than the speed of light.
- 15:59: Some people complained about my use of the expression "escape velocity greater than the speed of light" at the beginning of the episode.
- 16:31: ... the event horizon, you need to travel at the speed of light relative to the black hole's stationary frame of reference as recorded ...
- 16:49: ... calculate the distance at which the escape velocity reaches the speed of light. ...
- 16:59: The correct way to get this number is by using general relativity to find the point where the flow of spacetime reaches the speed of light.
2016-12-14: Escape The Kugelblitz Challenge
- 00:34: ... limit is defined by where something traveling at the speed of light can get to, and the speed of light is always at a 45-degree angle on ...
- 02:30: Space and time switch places, and the singularity soon forms, with all space within the black hole flowing towards it faster than the speed of light.
- 03:09: There's a region where all forward light cones only include the singularity, even before the true event horizon forms.
- 03:18: For anything in this region, there isn't enough time to clear the impending event horizon, even traveling at the speed of light.
- 04:19: They're light years away.
- 04:23: So these guys plan to destroy the Earth with a kugelblitz, a black hole formed entirely from light.
- 04:31: Their spaceships form a sphere around the solar system and blast a pulse of light inwards.
- 04:37: This gigantic shell of light descends around the earth and will reach us in about a day.
- 04:42: Now, light has energy and so has a gravitational effect.
- 04:53: The Schwarchild radius of a black hole with this mass is about one light second.
- 04:59: So the kugelblitz event horizon forms just after the shell of light passes the moon.
- 06:32: ... shield will reflect all light outwards and uses an impossible EM Drive technology that allows it to ...
- 06:46: Maybe the outgoing light wave will destroy the alien ships.
2016-12-08: What Happens at the Event Horizon?
- 00:29: Black holes, objects with densities so high that there's this region, the event horizon, where the escape velocity reaches the speed of light.
- 02:19: ... our access to the universe due to its absolute speed limit, the speed of light. ...
- 02:30: With the right choice of space and time units, the speed of light becomes a diagonal line on the space-time diagram.
- 02:37: ... area encompassed by the so-called light-like paths defines all future events or space-time locations that we could ...
- 02:51: That's our forward light cone.
- 02:54: Our past light cone defines the region of the past universe that could potentially have influenced us.
- 03:16: ... mass of the black hole stretches space and time so that light rays appear to crawl out of the vicinity of the event horizon before ...
- 03:32: As it approaches the event horizon, its future light cone bends towards the black hole as fewer and fewer of its possible trajectories lead away.
- 03:48: The problem with the regular space-time diagram is that the path of light and the shape of the light cone changes as space-time becomes warped.
- 04:25: It also curves the lines of constant time and constant space in what we call a conformal transformation so that light always follows a 45 degree path.
- 04:34: That means light cones always have the same orientation everywhere.
- 05:16: The lines also converge together towards the corners so that light travels a 45 degree path everywhere on the diagram.
- 05:24: ... a light ray starting from really, really far away and coming towards us hugs the ...
- 06:21: Space flows at greater than the speed of light inwards, towards the central singularity.
- 06:41: Once you're beneath the horizon, your future light cone still represents all possible paths that you could take.
- 06:52: The only way to escape back to the outside universe would be to widen your light cone by traveling faster than light.
- 07:08: Our space-faring simian begins its journey and emits a regular light signal that we observe from a safe distance.
- 07:14: ... it approaches the black hole, these light rays have further and further to travel through increasingly curved ...
- 07:35: It's trying to travel at the speed of light against light speed cascade of space-time.
- 07:55: Its future light cone still includes a tiny sliver of the outside universe.
- 08:00: It had better be a good jet pack because it's going need to follow a very long near light speed path away.
- 08:32: ... monkey's last view of the outside universe is defined by its past light cone that encompasses all of the light that will catch up to it and that ...
- 09:17: Even if we do travel at the speed of light, after a certain point there's no catching the monkey.
- 10:00: All space-time within the black hole is flowing toward the singularity faster than the speed of light.
- 10:06: The two neighboring radial layers aren't traveling faster than light relative to each other.
- 10:21: But even that so-called outgoing light is still moving downwards, doomed to hit the singularity along with the monkey and our rescue mission.
2016-11-30: Pilot Wave Theory and Quantum Realism
- 13:34: In that case, any mass of strange quarks will decay into the lighter up or down quarks.
2016-11-16: Strange Stars
- 07:40: ... spot and found a young pulsar, a rapidly rotating neutron star 10,000 light years ...
- 12:25: That's because light would also have to follow the curve of that space.
- 13:24: Pipe2DevNull suggests that the finger slit light diffraction test can be used as a secret salute when the science deniers finally take over.
2016-11-09: Did Dark Energy Just Disappear?
- 14:35: Well, the cool thing about the double slit experiment is that it's really easy to do with light.
- 14:40: ... when the distance between the slits is similar to the wavelength of the light, and with slit widths significantly narrower than that ...
- 14:52: So that's 500 nanometers' separation for visible light.
- 15:20: Make a narrow gap with your fingers and put them really close to your eye and look at a light.
2016-11-02: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers
- 03:00: ... is the only technological civilization to have ever arisen within 100 light years of Earth, what would that tell us about the chance of such a ...
- 03:58: So we're being pessimistic when we say that humanity is the only such civilization to have formed within 100 light years.
- 04:33: There are a few different ways to get the number of habitable planets within 100 light years.
- 04:46: For 100 light years, we have 512 G-Type stars: that's the same type as our sun.
- 05:05: So that means there are around 100 such planets orbiting stars like the sun within 100 light years.
- 07:13: The Kepler Observatory points only in one direction, so those stars are spread along a column a few thousand light years long.
- 07:36: 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.
2016-10-19: The First Humans on Mars
- 04:57: Growing plants for food requires water and air, but also light.
- 09:29: Even a black hole made entirely from light, a kugelblitz, is the same thing as a black hole formed from regular matter.
2016-10-12: Black Holes from the Dawn of Time
- 02:01: The oldest light we can see is the cosmic microwave background radiation.
- 07:24: ... radiation definitely are not dark matter, and that rules out any PBHs lighter than about a billion ...
2016-10-05: Are We Alone? Galactic Civilization Challenge
- 01:23: And at the high end, there should be civilisations within 100 light years, which may have detected our own radio transmissions by now.
- 04:38: ... civilization to have arisen on any habitable planet within 100 light years, how low would that probability of technological emergence need to ...
- 05:08: ... consider Tabby's Star, an otherwise normal-looking F-type star, 1,500 light years away, which the Kepler mission revealed to be experiencing some ...
2016-09-29: Life on Europa?
- 00:33: Sporadic jets of something appeared to block some of Jupiter's light.
- 07:46: The original plan was a lightweight spacecraft carrying several instruments.
- 09:06: ... on Europa, it may be possible to see the absorption of Jupiter's light, due to specific molecules in those water plumes-- molecules that tell us ...
2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate
- 03:05: This is fundamental to Einstein's relativity, which tells us that the chain of cause and effect can't propagate any faster than the speed of light.
- 04:17: ... variables that could affect each other no faster than the speed of light. ...
- 08:25: The experiment was even set up so that the influence had to travel between the photons at faster than the speed of light.
- 09:50: Relativity requires that causality is preserved, so no faster than light information flow.
- 10:15: The universe seems to conspire to avoid the paradox of information traveling faster than light, or backwards in time.
2016-09-14: Self-Replicating Robots and Galactic Domination
- 05:06: So a spacecraft is launched from the home Solar System with an engine capable of taking it to 10% or 20% lightspeed.
- 06:21: Assume an average 10% light speed, 10 light year jumps for each probe, and up to 500 years for production of the first daughter probe at each jump.
2016-09-07: Is There a Fifth Fundamental Force? + Quantum Eraser Answer
- 06:17: That information can't travel backwards in time or faster than light.
2016-08-24: Should We Build a Dyson Sphere?
- 00:53: ... intelligence, appearing only as strange points of infrared lights but otherwise black at visible ...
- 04:13: It would reflect light into a small solar power plant that would then beam energy somewhere useful, perhaps with a laser or a maser.
2016-08-10: How the Quantum Eraser Rewrites the Past
- 05:14: Detector A lights up if the original photon passed through slit A. And detector B lights up for slit B.
- 05:21: If we run this for a bunch of photons, we see that whenever detectors A or B light up, we get a simple pile of photons here at the screen.
- 06:57: But this clever arrangement ensures that if C or D light up, we have no idea which slit that photon came from.
- 07:54: Part of the appeal of the Copenhagen interpretation is that it avoids any physical interaction that moves faster than light.
2016-08-03: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
- 08:25: A supernova explosion within 30 light years would destroy the ozone layer, leading to a horrible hard ultraviolet bath and the worst sunburn ever.
- 08:58: ... enough to do the same damage as a nearby supernova, but from 6,500 light years ...
2016-07-27: The Quantum Experiment that Broke Reality
- 01:34: Any type of wave should make an interference pattern like this, for example, water waves and sound waves but also light waves.
- 01:43: This double-slit interference of light was first observed by Thomas Young back in 1801.
- 01:49: ... source of light passing through two very thin slits produces bands of light and dark ...
- 02:01: Of course, we now know that light is a wave in the electromagnetic field thanks to the work of James Clerk Maxwell a century later.
- 02:13: ... wait, we also know that light comes in indivisible little bundles of electromagnetic energy called ...
- 09:54: ... we know that light is a wave in the electromagnetic field and quantum field theory tells us ...
2016-07-06: Juno to Reveal Jupiter's Violent Past
- 11:05: The sun does emit a bit more light in the yellowy green part of the electromagnetic spectrum compared to the blue and the red parts on either side.
2016-06-22: Planck's Constant and The Origin of Quantum Mechanics
- 03:03: Science fact-- everything in the universe glows with the light of its own internal heat.
- 03:14: Accelerated charges produce electromagnetic radiation-- light.
- 03:30: And so the average frequency of the resulting particles of light, of photons, increases with temperature.
- 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.
- 05:41: For low frequency, infrared light.
- 08:11: Planck's new equation described the shape of the blackbody spectrum exactly, across all frequencies of light.
- 09:31: Einstein realized that it's actually light that is quantized.
- 09:36: ... can only gain or lose energy by absorbing or emitting one particle of light at a ...
- 09:48: And that light comes in indivisible energy packets.
- 11:50: ... if your light source, your lens, and your telescope are all perfectly lined up, and ...
- 12:08: In that case, all of the paths around the lens are equally good, and so light from the source can travel all of them.
- 12:50: ... the other hand, if the light source is large, for example, an entire galaxy, then it's easy for at ...
- 13:22: ... different configurations of matter that produce the same distribution of light seen in the lens, so image positions and ...
- 13:34: ... if you know the distance to the light source, and the distance to the lens, both from redshift, then you can ...
2016-06-15: The Strange Universe of Gravitational Lensing
- 00:31: In the world of our mind's eye, light travels in straight lines.
- 00:43: This works beautifully, as long as those light paths are truly straight.
- 01:18: And the path traveled by light follows the curve.
- 01:45: Light follows this curvature, and so gravity bends the path of light.
- 01:50: The prediction of general relativity that gravity deflects the path of light rays was one of the first to be directly verified.
- 02:11: ... change in the position of nearby stars due to the deflection of their light by the sun's gravitational ...
- 02:28: Their light paths were slightly deflected, making them appear a bit further from the sun.
- 02:57: The gravitational field of any massive object converges passing light rays, like a badly designed lens.
- 03:30: ... their light travels through the deep gravitational wells of intervening galaxies and ...
- 04:09: ... in that parameter space is a configuration of lens and light source that will collapse those distorted images into the true galaxies ...
- 04:37: When the distortion of the light source is this obvious, we call it strong lensing.
- 06:13: ... Light passing through the starry lens galaxy brightens and dims due to the ...
- 07:50: Of course, the most extreme gravitational bending of light results in the most awesome of all astrophysical objects, the black hole itself.
- 08:00: The lightspeed flow of spacetime at the event horizon results in old light paths pointing inwards.
- 08:10: Light falling below the event horizon is lost forever, so we don't describe it as being lensed.
- 08:29: This is a region where light paths are so strongly curved that photons can actually orbit the black hole, forming a shell of light.
- 08:46: ... outspiraling light escapes the photon sphere, it joins with severely lensed light from any ...
2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners!
- 01:03: A ring of gigantic magnets accelerates protons to up to 0.99999999 of the speed of light before colliding them from opposite directions.
- 01:42: And some are so hopelessly unstable that they decay into high energy light-- gamma rays-- before they ever reach a detector.
2016-06-01: Is Quantum Tunneling Faster than Light?
- 05:21: That suggests a velocity faster than light, which sounds problematic.
- 07:16: It offers another tantalizing hint at faster than light influences.
- 08:00: It appears to teleport through the barrier and so travel faster than light.
- 08:59: This can look like an increase in the speed of light, but only within the uncertainty range defined by the de Broglie wavelength.
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.
2016-05-11: The Cosmic Conspiracy of Dark Energy Challenge Question
- 01:36: Say a cubic million light years, around 70% dark energy, 30% matter.
2016-05-04: Will Starshot's Insterstellar Journey Succeed?
- 00:49: To send swarms of light sail driven nanocraft to Alpha Centauri fast enough that we may have close-up images of alien worlds within our lifetimes.
- 01:18: Looks like light sails will be the first propulsion tick to get an unmanned probe to the stars.
- 01:26: Let's review the essential awesomeness of light sails.
- 01:31: A spacecraft is propelled as the light from the sun-- or from a giant laser-- accelerates a sail of reflective material.
- 01:39: The advantage of light sails lies in the fact that they don't have to carry any propellant.
- 01:57: Light sails need no onboard propellant and the power generation stays back at home, whether it's the sun or an Earth-based laser.
- 02:10: The Japan Aerospace Exploration Agency, JAXA, flew the first interplanetary light sail in 2010, Ikaros.
- 02:35: Well in that case, light from the sun just won't cut it.
- 02:38: Alpha Centauri is 4.4 light years away and so even at a good fraction of the speed of light, it's a many year mission.
- 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.
- 03:33: The basic concept is the same-- an extremely low mass laser powered light sail.
- 04:24: Another big difference compared to Starwisp is that Starshot will be powered by a visible light laser, not a maser.
- 04:31: This is important because visible light lasers can maintain a much tighter beam than a maser can.
- 04:58: It would be a ground-based phased array of mini lasers called a light beamer that will produce a combined 100 gigawatt beam.
- 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.
- 06:18: The light sail will need to be insanely thin and almost immune to heating.
2016-04-27: What Does Dark Energy Really Do?
- 01:23: That history is coded in every photon of light that reaches our telescopes from the distant universe.
- 01:29: See, as space expands, it stretches out the light that is traveling through it.
- 01:53: But how do we figure out how much time the light traveled for?
- 01:57: Well, we know the speed of light.
- 02:53: ... the universe will have expanded significantly in the time it took their light to reach us-- so billions of light years ...
- 03:12: If something else happened to that traveling light that independently kept track of the distance it travelled.
- 03:24: We just need some source of light out there whose true, intrinsic brightness is known.
- 03:36: We call such a magical source of light a standard candle, and we kind of got lucky there.
- 04:28: ... that would mean the universe expanded a lot during the corresponding light travel ...
- 06:03: ... years catching white dwarf supernovae exploding in galaxies billions of light years away to measure the past expansion history of the ...
- 06:41: That means the expansion rate of the universe has actually sped up, accelerated, while that supernova light was traveling to us.
2016-04-20: Why the Universe Needs Dark Energy
- 09:53: ... fact, you need to get millions of light years from the Milky Way for the gravitational field of the Milky Way ...
2016-04-13: Will the Universe Expand Forever?
- 04:13: ... do this and only possible because, on its largest scales, billions of light years, all of the galaxies and galaxy clusters are very evenly dusted ...
2016-04-06: We Are Star Stuff
- 04:08: ... protons that went into it, and the difference is released in the form of light and ...
- 07:24: ... the surrounding onion shells of lighter elements collapse also, but they hit the brick wall of the newly born ...
- 12:07: A few of you asked about my statement that the universe expanded faster than the speed of light.
- 12:14: Well, the speed of light is an absolute speed limit for a thing in the universe traveling through space.
- 12:25: General relativity allows that two patches of space can move apart faster than the speed of light.
- 12:35: It's happening right now in regions of the universe beyond what we call the Hubble Horizon, which is 13.7 billion light years away.
- 12:52: How much faster than the speed of light did the universe blow up during inflation?
- 13:09: So that's something like 10 to the power of 20 times faster than light.
2016-03-30: Pulsar Starquakes Make Fast Radio Bursts? + Challenge Winners!
- 00:55: It was an elliptical galaxy 6 billion light years away.
- 02:42: The light traveled 13.7 billion light years.
- 02:47: It traveled exactly at the speed of light.
- 03:25: It's those electrons that were the problem for light.
- 05:57: 46.6 billion light years in radius now, translates to 42.3 million light years then, which is a volume of 2.7 times 10 to the 71 cubic meters.
- 07:50: Plug our numbers into this equation and we get a mean free path of around 7,500 light years.
- 08:08: But 7,500 light years is still very small compared to the size of the universe, even back then.
2016-03-23: How Cosmic Inflation Flattened the Universe
- 00:55: ... so huge, 93 billion light years from one edge to the other, that those most distant points should ...
- 04:03: ... within 0.4 of a percent of the center of the alley, and the alley is a light year ...
- 05:00: ... a very short period of time, blow it up much faster than the speed of light so that most of it appears causally disconnected, at which point ...
- 06:08: For this to work, that inflationary expansion had to throw neighboring regions of space apart at many times faster than the speed of light.
2016-03-09: Cosmic Microwave Background Challenge
- 01:37: The universe was much smaller when the CMB light was emitted.
- 01:41: In fact, all of those blobs of plasma were a mere 43 million light years away from the patch of space that would later contain the Milky Way.
- 01:58: ... the light from the CMB had to travel a lot further than those 43 million light ...
- 02:10: ... times further away, giving us an observable universe that's 93 billion light years ...
- 02:28: So first question-- what physical distance did that light from the CMB travel through an expanding universe to reach us today?
2016-03-02: What’s Wrong With the Big Bang Theory?
- 05:33: We now see this light as an almost perfectly smooth microwave buzz across the entire sky.
- 06:40: And there just wasn't, not even for light, the fastest thing that there is.
- 06:59: See, although light is fast, those opposite edges of the universe were traveling apart even faster.
2016-02-24: Why the Big Bang Definitely Happened
- 01:42: Light from distant galaxies is red shifted, stretched to longer wavelengths.
- 01:47: And the further away the galaxy is, the more its light is stretched.
- 01:50: ... interpretation for this fact is that space itself is expanding and light traveling through expanding space is ...
- 04:11: In the same moment, the infrared light that had previously been trapped in this fog was free to travel the width of the cosmos.
2016-02-17: Planet X Discovered?? + Challenge Winners!
- 03:14: ... a clock, or a photon clock, traveling towards you at 50% of the speed of light, would seem to have a tick rate that was slower, faster, or the same as ...
- 03:37: The relativistic Doppler effect classically changes the wavelengths of light, blue-shifting approaching material and red-shifting receding material.
- 04:06: To determine the observed tick rate, you also have to factor in the travel time of light.
- 04:48: To understand that, you need to draw lights like photon paths between the moving clock and the stationary observer.
- 05:14: ... of chases after its own photons, condensing the distance between the light signals that carry those ...
- 06:28: Our clock is moving at 50% the speed of light.
2016-02-11: LIGO's First Detection of Gravitational Waves!
- 03:33: In the case of merging black holes, to five billion light years.
2016-02-03: Will Mars or Venus Kill You First?
- 06:06: ... and are preceded by some visible indication like a solar flare, whose light reaches you in ...
- 08:54: ... Earth without having spent a lot of time traveling close to the speed of light, with respect to ...
2016-01-27: The Origin of Matter and Time
- 02:32: Let's make it easy and use what physicists call natural units, which just means that we take the speed of light equal to 1.
- 02:40: Light travels 1 x tick for every 1 t tick.
- 02:46: For example, we could make the time divisions 1 second, and the space divisions 300,000 kilometers, because that's how far light travels each second.
- 02:55: If we do that, then light speed things will always level a 45 degree diagonal path.
- 03:13: Sub light speed things can travel them.
- 03:15: And we call them time light paths.
- 03:18: These would be impossible faster than light paths.
- 03:27: And the 45 degree path, that's a light like path.
- 03:37: Now remember, a photon clock marks time with a particle of light bouncing between two mirrors.
- 03:59: However, the internal photon still has to travel those 45 degree light like paths, because photons can only travel at the speed of light.
- 04:08: A second photon clock with a constant speed with respect to the first, travels a steeper time light path.
- 04:15: This is where that whole invariant speed of light thing gets really interesting.
- 04:40: ... besides the invariance of the speed of light, the other fundamental principle of Einstein's special relativity at play ...
- 05:24: But those 45 degree lines, and hence the speed of light, stay the same for everyone.
- 06:17: ... already covered the fact that real matter is comprised of massless light speed components confined not by mirrored walls, but by interactions ...
- 07:04: And on our space time diagram, our object becomes an impossibly complex ensemble of light speed world lines confined in equally complex ways.
- 07:15: Just as with the photon clock, it's only the ensemble that can travel slower than light, or be still.
- 07:24: They have to travel at light speed.
- 07:45: ... not just a single world line, but an evolving arrangement of many light-like paths that only taken together, give us a sense of stillness, a sense of ...
- 08:24: Those causal time-like paths can be thought of as a series of light-like segments.
- 08:30: Two infinitesimally nearby bits of the universe can affect each other at exactly the speed of light.
- 10:21: What happens when an astronaut does a round trip at a large fraction of the speed of light, and returns to compare her clock to one left on Earth?
- 12:07: ... your clock by accelerating uniformly from rest to 99% of the speed of light by the end of ...
2016-01-20: The Photon Clock Challenge
- 00:27: But you still see it traveling at the same old speed of light.
- 00:50: Imagine observing a clock moving toward you at 50% the speed of light.
- 00:55: As the light from that clock reaches you, you see the hands of the clock tick.
2016-01-13: When Time Breaks Down
- 02:04: A particle moving at the speed of light experiences no time.
- 02:34: ... to show you why time depends on motion, which in turn will show us why light speed particles are timeless, and why having mass and experiencing time ...
- 02:46: ... to the imaginary photon box, a massless mirrored box filled with light, which despite being composed only of massless things, itself does have ...
- 03:19: The tick rate depends on the speed of light and on the distance that the photon has to travel between the mirrors.
- 03:35: From my perspective, light now takes a longer, diagonal path.
- 03:40: As we saw in a previous episode, the speed of light is what we call invariant.
- 03:46: All observers, regardless of their own speed, will report seeing the same speed for any particle of light-- any photon.
- 04:35: Now what if the clock is traveling at the speed of light?
- 04:45: And that distance is infinite when the clock reaches the speed of light.
- 06:17: They're made up of things that would move at the speed of light, except that they're confined.
- 07:14: So the confinement of light speed particles gives matter mass.
- 07:24: But now it looks like this same bundling of light speed particles can also given matter time.
- 07:38: But what is it about not traveling at the speed of light that allows matter to have structure and to change?
- 07:44: What prohibits matter from reaching the speed of light?
- 08:18: In that case, the box's mass increases by the amount equal to the energy of the contained photons, divided by the speed of light squared.
2016-01-06: The True Nature of Matter and Mass
- 00:18: In a previous episode, we talked about the speed of light-- the fastest speed there is.
- 04:16: ... the confinement of interactions that themselves travel at the speed of light. ...
- 04:46: That itself is a speed of light interaction, even if the resulting density wave isn't.
- 05:31: Take away the Higgs field, and they are massless speed of light particles.
- 05:36: ... with mass is composed of a combination of intrinsically massless, light-speed particles that are prevented from streaming freely through the universe, ...
- 09:02: And importantly, it prevents them from traveling at the speed of light.
2015-12-16: The Higgs Mechanism Explained
- 02:19: As we'll see in the next couple of episodes, this masslessness means that particles should travel only at the speed of light and experience no time.
- 03:15: It travels at the speed of light, and it experiences its entire existence in an instant.
- 05:44: On its own, the electron would travel at light speed, but trapped in this Higgs field buzz, the electron feels mass.
- 07:55: ... anything cross the event horizon, as something falls to the horizon, the light it emits is red shifted such long wavelengths that it effectively ...
2015-11-18: 5 Ways to Stop a Killer Asteroid
- 05:53: The sun's light will push harder on the more reflective side, slowly pushing it just far enough off course to miss us.
- 06:00: A similar proposal fixes a giant light sale to the side of the rock.
2015-11-05: Why Haven't We Found Alien Life?
- 05:26: Any carbon that's been through living systems will have the same C13 light isotopic ratio that we see in this zircon.
- 07:42: ... we could analyze light passing through these atmospheres, we would see signatures of oxygen, ...
- 10:55: ... bubble would definitely leave some sort of light signature because light inside the bubble can traverse the walls in any ...
- 11:07: Because the bubble is superluminal, any light that we see would trail the bubble just like the sound of a supersonic jet.
2015-10-28: Is The Alcubierre Warp Drive Possible?
- 00:00: Rumor has it NASA is actually working on a real faster than light warp drive.
- 00:08: Faster than light travel is a staple of science fiction.
- 00:17: Star Trek warp drives zip around the galaxy at hundreds of times the speed of light.
- 00:21: But traveling at the real cosmic speed limit of 1 times the speed of light would make for some pretty dull sci-fi.
- 00:27: It would have taken Han Solo 40 years to make the Kessel Run in 12 parsecs, traveling at only light speed.
- 00:45: ... solution to the equations of GR that would actually allow faster than light ...
- 01:27: That limit, the speed of light, refers to things-- mass, energy, information-- traveling through space.
- 01:40: ... that very distant galaxies are moving apart from each other faster than light, even if the galaxies are relatively still in their local frames of ...
- 01:51: ... hole, spacetime cascades towards the central singularity faster than light, carrying light, matter, monkeys, and everything else with ...
- 02:58: You stand still with respect to the conveyor belt, but the belt itself moves faster than light.
- 04:55: The first trip has to be made at sub light speed.
- 06:44: As I've argued before, we'll reach the stars by sub light speed starships long before that.
2015-10-22: Have Gravitational Waves Been Discovered?!?
- 00:41: There's the deflection of light that we see as gravitational lensing.
- 02:08: ... to the stiffness of spacetime-- in other words, at the speed of light. ...
- 02:25: ... speed limit comes from the fact that the speed of light is built into Einstein's field equation, which is necessary for it to be ...
- 02:42: And all massless things, including g-waves and light, must travel at that speed.
- 03:58: Any g-wave that we're likely to spot is going to come from a distant galaxy, hundreds of millions of light-years away.
- 09:48: A 10 milligram grain would strike with the kinetic energy of around 100 kilograms of TNT if your spaceship was moving at 10% the speed of light.
- 10:11: Now actually, you can get to 10% of lightspeed by accelerating at a comfortable one g over a little less than five months.
2015-10-15: 5 REAL Possibilities for Interstellar Travel
- 01:19: It's only 4.4 light years away, but we have to get there before the Curbles and the impending K1 asteroid that's on its way.
- 02:25: If you want to get to Alpha Cen in a human lifetime, you need to get to 10% the speed of light.
- 03:16: ... about a month, and we accelerate at 1G to around 10% of the speed of light. ...
- 05:28: Annihilate a proton and an antiproton, and you get charged pions moving at near light speed.
- 06:07: What if we could sail to the stars on a wind made of light, the light sail?
- 06:25: OK, most of the interstellar thinking for light sails has been about unmanned probes.
- 06:30: 10% light speed is pretty reasonable with modern materials like a carbon web sail driven by a microwave beam running on a single nuclear power plant.
- 06:44: ... we're going to need to a bigger boat, which means a proper visible light laser and a larger sail, coated with advanced, reflective and heat ...
- 07:18: 10% light speed or higher should be doable.
- 07:35: Ultimately, though, the scalability of the light sail means that speeds even greater than .1C are possible.
- 07:52: This is a black hole made not from mass but from light.
- 07:56: ... sufficient energy density of laser light focused in a small enough region would bend the fabric of space time ...
- 08:45: ... .1C in 20 days and presumably to a significant fraction of the speed of light in the lifespan of the black ...
- 09:55: ... out, these are what we'll want to actually explore the galaxy with near light speeds dilating apparent travel time down to human ...
- 10:08: Light sails.
- 10:29: Manned light jammers are way off but totally plausible.
- 10:52: Last week we talked about why the speed of light is really the speed of causality.
- 10:59: Andrea Prapone and others asked, why does the speed of light have to be that specific number, 300,000 kilometers per second?
- 11:17: Now physicists often choose to define the speed of light as C equals 1, which we call natural units.
- 11:24: ... of nature have the values that they do compared to the speed of light. ...
- 11:33: ... that said, the relative units of the fundamental constants, the speed of light, the strength of the fundamental forces, et cetera, are important for the ...
- 12:13: However, it turns out that this can't ever be used to transmit new information faster than the speed of light, so causality is preserved.
- 12:32: ... TheColonel asks, "Does this now mean I can refer to the speed of light as total monkey speed?" The answer is ...
2015-10-07: The Speed of Light is NOT About Light
- 00:00: [MUSIC PLAYING] Does the speed of light actually have anything to do with light?
- 00:06: [MUSIC PLAYING] So what is it about the speed of light that's so special?
- 00:32: The universe doesn't arrange itself to keep the speed of light constant.
- 00:36: In fact, spacetime couldn't care less about light.
- 00:59: And why is that speed the same as the speed of light?
- 02:38: In fact, we now know that even Newton's mechanics were using assumptions that implied an infinite speed of light, which is really bad.
- 05:26: Now, you can get to this transformation the way Lorentz and Einstein did by requiring a constant speed of light.
- 05:37: But forget about the speed of light.
- 07:47: But for other reasons-- still unrelated to light-- we know that it cannot be.
- 08:20: For the laws of electricity and magnetism to work, we need a finite maximum cosmic speed, even without considering light.
- 08:29: ... define the speed of propagation of electromagnetic waves-- the speed of light. ...
- 08:38: c is the speed of light.
- 08:57: So lights or photons, also gravitational waves and gluons all have no mass.
- 11:48: If you travelled at the speed of light, it would take around 750 billion years, or 55 times the current age of the universe.
2015-09-30: What Happens At The Edge Of The Universe?
- 01:08: We even gave you a number, 93 billion light years in diameter, 46 billion in radius.
- 01:22: Let's start with that 46 billion light year number.
- 01:33: Now, it's not 46 billion light years to that actual blob.
- 01:37: ... is currently 46 billion light years to whatever galaxy or galaxy clusters that blob evolved into, ...
- 02:21: The shortest path in spacetime is defined by the geodesic, the path of light between two points.
- 02:26: Even light takes time to make any journey.
- 02:44: Bad news, you'd have to travel infinitely far, even if you were in a spaceship that could travel at the speed of light.
- 02:55: ... hole is that point beyond which we can never receive information because light from that point is redshifted into ...
- 03:13: This is because the distance that signal has to travel to get to us will be expanding faster than the speed of light before the signal reaches us.
- 03:21: The same thing applies to our light speed spaceship.
- 03:23: We can ever get to anything beyond the cosmic event horizon because that space will be moving away from us faster than light before we reach it.
- 03:37: Given our best measurements of cosmological parameters, we think that the cosmic event horizon is around 16 billion light years away.
- 08:09: And that mass predicts the deflection angle for light passing the Sun perfectly, that is its gravitational lensing effect.
- 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?
- 00:56: Thanks to general relativity, we know that light fall is the curved geodesics of a gravitational field.
- 01:01: Place a strong gravitational field on an axis between a light source and an observer and voila, you basically have a lens.
- 02:17: But they can't be interacting with light.
- 05:21: Map the mass based on the warping of light from more distant galaxies.
- 08:30: ... from the future universe will never catch up to the monkey because that light has to contend with the same crazy-curved space-time that the monkey ...
- 08:39: ... arbitrarily distance times in the future, only signals within its past light cone can catch up to ...
2015-08-19: Do Events Inside Black Holes Happen?
- 06:54: Misconception two-- black holes are black because not even light can escape their gravitational pull.
- 07:15: If a planet's radius equals the Schwarzschild radius of the equivalent-mass black hole, it turns out that the escape velocity is the speed of light.
- 08:10: ... freezes from our perspective, the time dilation is so severe that any light he emits gets redshifted to undetectably low ...
- 08:20: That means that to external observers, black holes are black because light that gets emitted just outside the horizon is redshifted into invisibility.
2015-07-29: General Relativity & Curved Spacetime Explained!
- 05:49: ... making any assumptions about how gravity effects light, that would be true even if it turned out that gravity slowed photons ...
2015-07-15: Can You Trust Your Eyes in Spacetime?
- 02:09: ... that vertical axis is showing the distance ct that light travels per tick of my clock, which is interchangeable with clock ticks ...
- 04:00: We agree about the speed of light, so its world line looks the same as in my diagram.
- 04:18: ... such a line an observer or a photon would have to be moving faster than light, which normal objects and photons cannot ...
- 08:23: And more interestingly, the length of that vector, at least in the sense of spacetime interval length, is minus the speed of light squared.
- 08:30: In fact, every observer's 4-velocity always has a length of minus the speed of light squared, even the accelerating car's 4-velocity.
2015-06-17: How to Signal Aliens
- 01:39: ... here minimum-- an array like this could be detected from a few thousand light years ...
- 02:45: You only get about 1,000 light years or so before it becomes too dim.
- 04:59: ... like the lasers, billboard transits could only be seen within a few light years of earth or maybe a couple thousand if the Kerbal Kepler ...
2015-05-27: Habitable Exoplanets Debunked!
- 02:39: ... knowing some properties of that star, then based on how much light gets blocked and for how long, astronomers were able to infer the radius ...
- 03:00: ... maybe it's nothing like Krypton, because at 500 light years from Earth, Kepler 186F is just too far away to determine its mass ...
- 03:54: ... analyze a planet's atmosphere, you need to isolate the planet's light from that of its star and see how bright that light is at different ...
- 04:05: Since different atoms and molecules emit or absorb particular wavelengths of light only, the spectrum tells you a lot about atmospheric composition.
- 04:20: So how do you isolate a planet's light?
- 04:23: ... 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 help see ...
- 04:39: The planet just gets washed out by the star's light.
- 08:02: Hansen from It's OK To Be Smart asked, if my mirrored box had a tiny hole in it so some light could escape, would its mass go down?
- 10:09: ... fundamental constants of nature, like Planck's constant and the speed of light. ...
2015-05-20: The Real Meaning of E=mc²
- 02:11: ... just add up all that energy, divide it by the speed of light squared, and that's how much extra mass the kinetic and potential and ...
- 02:20: Now since the speed of light is so huge, this extra mass is tiny, only about a billionth of a billionth of a percent of the total mass of the watch.
- 03:37: ... light carries energy, and that energy was previously stored as electrochemical ...
- 04:17: ... that light was emitted, there was simply more kinetic and potential energy ...
- 04:53: ... energy, but it's also registering an exactly equal amount of extra light energy that we're not allowing to escape this ...
- 05:03: ... right, even though light itself is massless, if you confine it in a box, its energy still ...
- 07:34: There's a way to conceptualize even this process as simple conversions of one kind of energy to another-- kinetic, potential, light, and so forth.
2015-05-13: 9 NASA Technologies Shaping YOUR Future
- 05:18: Answer, infrared laser strobe lights connected to a video camera.
- 05:22: See, fog is opaque to visible light, but somewhat transparent to infrared light.
- 05:37: Now, you know what else is also transparent to infrared light?
2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi?
- 08:10: ... to be fair, in light of some of its errors, I gotta give my vote to "Halo." Truth is I can't ...
- 09:53: ... turn out to be event pairs for which a single piece of matter or light could have been present at both events, which corresponds to a zero or ...
2015-04-22: Are Space and Time An Illusion?
2015-03-25: Cosmic Microwave Background Explained
- 01:34: That glow isn't ambient light reflecting off the toaster, it's light being emitted by the toaster itself.
- 01:39: ... eyes, you would realize that the toaster isn't just emitting pale, red light. ...
- 02:12: In fact, it's called a thermal spectrum because the light is generated by the random motions of particles in the material.
- 03:22: ... because there were no neutral atoms yet, the light the plasma emitted just couldn't travel very far before it would run ...
- 03:30: ... wouldn't be able to see very far on the viewscreen, maybe a few thousand lightyears, which sounds like a lot, but it's basically zero visibility in ...
- 03:43: So at this moment, it was as if flash bulbs were constantly going off everywhere in space, but the light was being snuffed out by a fog.
- 03:58: With no more free electrons to redirect the light, the universe became, for the very first time, transparent.
- 04:04: ... light that the plasma had emitted then just before neutralized was one last ...
- 04:16: And now, that light could free stream through the universe forever.
- 04:28: ... revisit here, expanding space stretches the wavelength of free streaming light through a process called cosmological ...
- 04:37: ... over the course of a few million years, that orangey thermal spectrum of light was redshifted to longer and longer wavelengths, becoming toaster read ...
- 04:52: ... you throw in another 13 plus billion years of space expansion, all that light has redshifted into the microwave band to become what we today perceive ...
- 06:43: ... some fictitious, really light but really strong material could be spun sufficiently fast, you could ...
2015-03-04: Should We Colonize Venus Instead of Mars?
- 06:16: awtizme asked, how can space be expanding faster than light if the speed of light is the ultimate speed limit?
- 06:23: First, the speed of light speed limit is for things moving through space, not about expansion of space itself.
- 06:36: ... they're far enough apart to begin with-- will end up more than one extra light second apart after I hit that photocopier ...
2015-02-25: How Do You Measure the Size of the Universe?
- 00:16: It's common to put astronomical distances in light years.
- 00:19: That's the distance light travels in a year or about 9 trillion kilometers.
- 00:26: The diameter of the solar system is about 8 light hours or 9 billion kilometers.
- 00:30: The Milky Way, our galaxy, that's about 100,000 light years across or close to 1 quintillion kilometers.
- 00:37: And the next closest major galaxy, Andromeda, that's 2 and 1/2 million light years away, which is just silly to talk about in kilometers.
- 00:49: Some things are so far away that light from there hasn't reached us yet.
- 00:55: That's the part that we, in principle, can see with light or gravitational waves.
- 01:01: Well, it's a sphere with a radius of about 46 billion light years, or, rounding down to keep it simple, about 90 billion light years end to end.
- 01:23: That's the maximum amount of time light has had to travel to us.
- 01:26: And then you work out how far away the emission point of that light is right now.
- 01:33: Remember, that distance is not 13.8 billion light years.
- 02:26: In fact, space itself can expand at any rate it wants to, even faster than the speed of light.
- 02:32: So over the lifetime of the universe, the birthplace of a beam of light can be carried ridiculously far away by the expanding space dough.
- 02:53: Using something called cosmological redshift, which is like a fingerprint that the expansion of space leaves on beams of light.
- 03:02: Light has a color determined by its wavelength.
- 03:04: Longer wavelength light is redder, shorter bluer.
- 03:07: ... space were not expanding, then light from a distant galaxy would be the same color when it arrived on Earth ...
- 03:14: But because space is expanding, the wavelength of light gets stretched as it travels to us, making the blue light red; hence, the term redshift.
- 03:31: The light from more distant galaxies is redshifted more than light from nearby ones.
- 03:37: You see, the light from more distant places has further to go.
- 04:47: Imagine that seconds after the Big Bang happens, every raisin emits a beam of light that can then travel without hitting any obstacles.
- 05:03: One of those beams of raisin light would be just switching as the clock hits 13.8 billion years.
- 05:10: Answer, about 46 billion light years away.
- 05:13: So that's how we know that the observable universe is about 90 billion light years in diameter.
- 05:21: Aren't there galaxies even further away, whose light hasn't reached us yet?
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