
20221123: How To See Black Holes By Catching Neutrinos
 00:30: There’s the James Webb Space Telescope and its infrared supervision and of course LIGO with its ability to see gravitational waves.


20221026: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
 15:49: There was the one about using the Sun’s gravitational field as a lens to take pictures of distant planets.
 16:01: Let’s start with the solar gravitational lens.
 16:12: ... having a hard time keeping track of the Voyager’s faint signals, and the gravitational lens focal range is at least 4 times further than ...
 17:03: Well there’s no real range limit in terms of what planets will be brought to a focus in the sun’s gravitational focal range.


20221012: The REAL Possibility of Mapping Alien Planets!
 01:25: ... rays from the exoplanet are bent inwards by the Sun’s gravitational field to all come together. Forget about a New York sized telescope ...
 04:12: ... first let’s review gravitational lensing. Einstein’s general theory of relativity tells us ...
 04:36: ... to a single focus point, allowing an image to be formed. Gravitational lenses produce highly distorted images, like these stretched out ...
 06:05: ... straightforward to do it with the very clean, wellunderstood gravitational field of our Sun. All we need to do is get our telescope ...
 10:07: ... incredible astronavigation and maneuvering. The solar gravitational lens focal range is indeed a range. While a regular lens creates a ...
 15:45: ... cool after you. Well, assuming that the whole solar gravitational lens thing pans out, we’re going to have countless ...


20220928: 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.
 09:57: Try the gravitational or Planck’s constant and you also have to define the kilogram.
 11:33: ... gravitational constant is the relationship between mass, distance, and ...


20220921: Science of the James Webb Telescope Explained!
 09:36: These arcs are much more distant galaxies whose light is warped by the gravitational field of the cluster.


20220817: What If Dark Energy is a New Quantum Field?
 03:33: ... universe gets bigger and galaxies get further and further apart, their gravitational connection dilutes away, while dark energy just keeps pushing and ...


20220727: How Many States Of Matter Are There?
 10:57: Astrophysicists routinely model the galaxies as a sort of fluid of stars, where the interactions are not electromagnetic, but gravitational.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 07:24: ... going to focus on the one main concept behind this innovation  the gravitational path integral. This is the general relativistic analog of the ...
 08:14: ... gravitational path integral you analyze some patch of spacetime changing from one ...
 10:42: ... Renyi entropy is found using the gravitational path integral. For a spacetime geometry where none of the black ...
 11:25: ... theory to derive the island rule: all you need is the gravitational path ...
 12:09: ... paradox? Well, it sort of looks like they might of. Using the gravitational path integrals and the island rule, the physicists found ...


20220601: What If Physics IS NOT Describing Reality?
 13:41: ... that black hole will end up in some orbit within our galaxy’s gravitational well. It’ll interact with stars, kicking them up to ...


20220525: The Evolution of the Modern Milky Way Galaxy
 09:11: ... the stars of Gaia Enceladus got mixed into the halo, the crazy gravitational pulls of the two galaxies slamming into each other ...
 17:21: ... asks “If space doesn't expand inside a gravitational field, then what happens at the boundary between this and ...
 18:41: ... Marsh asks if space inside gravitationally bound systems actually contracts, rather than simply ...


20220518: What If the Galactic Habitable Zone LIMITS Intelligent Life?
 03:40: ... flow of fusiongenerated energy supports the Sun against gravitational collapse. It’s been resisting its own inward crush for 5 ...
 10:04: ... gas continued to pour into the Galaxy’s growing gravitational field. It was swept up into a widening whirlpool where it ...


20220504: Space DOES NOT Expand Everywhere
 01:24: ... in space tend to move around due to nearby gravitational influences  planets orbit stars, stars orbit in the mutual gravity of ...
 05:19: ... gravity? Is the space inside, say, a galaxy growing but overcome by the gravitational attraction between the ...
 06:04: ... answer is no. Space within any gravitationally bound system is unaffected by the surrounding expansion. In the balloon ...
 07:58: ... cone, we see distant gridlines diverging, but nearby lines in a gravitational field remain ...
 08:21: ... there is no constant tug of war between the expanding universe and the gravitationally bound systems it contains. That tug of war did happen, but it happened a ...
 10:52: ... Planck length stays the same  it’s just defined as a combination of the Gravitational constant, the Planck constant, and the speed of light  so if those ...
 11:59: ... expands. But again, this will never have any effect inside bound gravitational systems. Its effect only manifests when there’s an enormous amount of ...


20220323: Where Is The Center of The Universe?
 03:04: General relativity can be used to calculate the spacetime curvature produced by the Earth or the Sun to determine their gravitational effects.
 03:11: It can also give us the gravitational field of the entire universe, which tells us the shape of all of spacetime.
 03:22: ... first to solve this was Alexander Friedman  he ignored all those little gravitational bumps  doing the mathematical equivalent of grinding up everything into ...


20220308: Is the Proxima System Our Best Hope For Another Earth?
 18:33: When those cosmic strings radiate gravitational waves, how is the Higgs field supposed to smooth itself out?


20220223: Are Cosmic Strings Cracks in the Universe?
 10:09: ... the incredible mass in the kinks causes them to radiate gravitational waves. In this way cosmic strings shed energy, and so they slowly ...
 12:19: ... like “regular” cosmic strings in many ways  like the gravitational waves and the lensing. But there are differences. While cosmic ...


20220216: Is The Wave Function The Building Block of Reality?
 08:55: ... Gravitational decoherence would simultaneously explain two mysteries of physics. 1. ...
 14:52: ... BuzzBen asks what happens when gravitational waves pass through black holes. Is there gravitational lensing? Well ...


20220210: The Nature of Space and Time AMA
 00:03: ... on depending on how fast you're moving on whether you're in a gravitational field um but this depiction of space and time has both of these ...


20220127: How Does Gravity Escape A Black Hole?
 00:20: So how does a black hole manage to communicate its gravitational force to the outside universe?
 00:48: Einstein’s theory predicted the existence of the ultimate gravitational object: the black hole.
 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.
 02:02: For example we have gravitational waves  ripples in spacetime caused by certain types of motion.
 02:08: ... travel at the speed of light, and that’s been confirmed when gravitational waves from colliding neutron stars reach us at about the same time the ...
 02:22: But this “speed of gravity” also tells us how quickly a regular gravitational field changes.
 02:46: It would take 8 minutes for the Sun’s deep indentation in the fabric of space to smooth itself  in the wake of some pretty crazy gravitational waves.
 03:34: In GR, the gravitational field  the curvature of spacetime  has an independent existence to the mass that causes it.
 03:42: ... with the Sun itself, it’s interacting only with the local part of the gravitational ...
 05:47: It breaks down at very small distances and in very high gravitational fields.
 06:28: In theories of quantum gravity, the gravitational force should probably also have a mediating particle  usually called the graviton.
 07:44: The gravitational field around the black hole is already abuzz with virtual gravitons.
 08:25: But if we’re describing the gravitational field as being built up by virtual gravitons then the event horizon is no barrier at all.
 08:54: To experience the gravitational effect of a massive object, the information about the presence of that mass does have to be able to reach you.
 09:12: ... below the event horizon, but we can see its past mass, and it’s the gravitational effect of the past mass that we actually ...
 10:06: ... we maintain a causal connection to the mass that generated that gravitational ...
 10:19: ... you who love their Penrose diagrams, just think about the source of the gravitational field as always being in your past lightcone  and that has to be ...
 11:27: ... idea of mass is poorly defined in general relativity in part because the gravitational field itself has energy, and so is a source of ...
 12:00: ... you can rest assured that your own mass will continue to exert its gravitational influence on exterior regions of space ...
 16:08: But on small scales, local gravitational influences dominate.


20220119: How To Build The Universe in a Computer
 00:47: ... know this because we’ve calculated the chaotic gravitational and hydrodynamic interactions of countless stars and gas and dark ...
 02:15: He would then measure light at each bulb, which told him the summed “gravitational” pull on that group of stars.
 02:56: ... the trajectories of a pair of massive bodies moving in each other’s gravitational ...
 03:59: ... step is short enough that we can assume that the global gravitational field is constant  it only changes in the next step, after all the ...
 06:00: ... to clump particles together and consider only their summed gravitational ...
 06:36: Next, you run an Nbody simulation by calculating the summed gravitational pull on each given particle.
 07:08: ... in which particles are converted into a density distribution and a gravitational potential across the ...
 09:34: ... including magnetic fields, or of Einstein’s general relativity when the gravitational field becomes very ...


20211220: What Happens If A Black Hole Hits Earth?
 02:50: ... pass in front of more distant stars, magnifying those stars’ light with gravitational ...
 09:24: ... really tell us much. It might also be possible to detect the tiny gravitational influence of a PBH passing close to the Earth on a near miss  but even ...
 16:33: ...  the founding idea of general relativity that says that freefall in a gravitational field is fundamentally the same as inertial motion in free space. That ...
 17:55: ... prediction of string theory. There are simulations that suggest that the gravitational waves created when fuzzball merge should look almost exactly the same as ...
 18:16: ... quantum fluctuations near the event horizon that might be amplified by gravitational lensing. None of this has been seen yet, but upgrades to the current ...


20211210: 2021 End of Year AMA!
 00:02: ... which makes me think maybe there's something wrong with the earth's gravitational field time seems to be passing more quickly actually it's been quite ...


20211117: Are Black Holes Actually Fuzzballs?
 00:20: ... us that if the density of matter is sufficiently ridiculous, ultimate gravitational collapse is ...
 09:25: ... as the neutron star’s gravitational field is so intense that atomic nuclei are crushed into a soup of ...
 10:50: Light trying to escape would still be massively redshifted  sapped of energy by the gravitational field  rendering the object effectively black.
 10:58: It would still cause massive gravitational lensing, time dilation, etc.
 12:50: As a side benefit, this eliminates the problem of the gravitational singularity at the center of a black hole.


20211110: What If Our Understanding of Gravity Is Wrong?
 00:42: ... clusters together, or to bend the path of light to the degree seen in gravitational lenses  when more distant light sources are warped by an intervening ...
 02:02: ... to Isaac Newton’s Law of Universal Gravitation, the gravitational field drops off with the square of distance from the mass ...
 02:32: ... mass that’s more evenly distributed through galaxies, strengthening the gravitational field in the outskirts to explain the high rotation ...
 02:52: ... Einstein found that Newtonian gravity breaks down when the gravitational field gets too strong  there you need his general theory of ...
 03:08: But Einsteinian gravity looks exactly like Newtonian gravity when gravitational fields get weak.
 03:35: The idea is straightforward enough  what if there exists a minimum possible acceleration that can be produced by the gravitational force?
 08:35: ... Einstein’s description, the gravitational field is what we call a tensor field  a multicomponent object ...
 09:45: The introduction of the new field fixed the problem with gravitational lensing and also tamed the awkward causalitybreaking nature of AQuaL.
 09:53: ... MOND on galactic scales, and like regular general relativity for gravitational ...
 10:58: ... clutch of light, it could have followed the dark matter into its deep gravitational wells and get to the business of forming ...
 14:01: ... by dark matter particles, or beyond general relativity by hidden gravitational modes of space ...
 16:40: Jackie Johnson asks  in the case of gravitational lensing, isn't the light still traveling in a straight line?
 17:33: In fact, in general relativity objects in gravitational fields tend to maximize, not minimize their proper time.


20211102: Is ACTION The Most Fundamental Property in Physics?
 00:02: ... straight line  like when it’s refracted by glass or traveling through a gravitational field. It took a millennium and a half following Heron for Pierre de ...
 06:47: ... rates depending on things like relative speed and position in a gravitational field. Proper time is the time that an object will perceive in its own ...


20211005: Why Magnetic Monopoles SHOULD Exist
 17:05: So the loss of electrons reduces the degeneracy pressure, allowing gravitational collapse to continue.


20210915: Neutron Stars: The Most Extreme Objects in the Universe
 01:02: ... and an antigravitational field to resist the ridiculous gravitational ...
 03:27: ... many million times greater then anything on Earth. And the gravitational pull is something like a 100 billion ...
 10:06: ... enormous strength of nuclear pasta allows it to resist the insane gravitational forces and so support a sort of jumbled texture  sort ...


20210907: First Detection of Light from Behind a Black Hole
 04:37: ... gas is accelerated by a combination of the incredible gravitational field of the black hole and the continuous blaze of high energy ...
 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.
 10:58: It was as we say, gravitationally lensed.


20210803: How An Extreme New Star Could Change All Cosmology
 02:13: ... spin should also increase as the core slowly collapses under its own gravitational crush due to conservation of angular momentum. But typical white dwarfs ...
 06:21: ... white dwarfs, matter is crushed so close together that the inward gravitational pull is insane. The only thing holding the star up from absolute ...
 09:18: ... each other, we expect them to slowly spiral together because they emit gravitational radiation that saps away their orbital energy. We’ve seen the result of ...


20210721: How Magnetism Shapes The Universe
 00:36: Imagine you can see gravitational fields.
 00:50: But there’s really only one gravitational field in the universe  manifest as the fabric of spacetime itself.
 03:17: As with the gravitational field, in a sense there’s only one universal magnetic field.


20210707: Electrons DO NOT Spin
 15:31: ... smooth. The compact part is where the low entropy comes from. The “gravitational degrees of freedom” were almost entirely unoccupied. On the other ...


20210616: Can Space Be Infinitely Divided?
 06:02: ... The photon is starting to produce an observable gravitational field. Even though photons are massless, if enclosed in a system a ...
 06:39: ... by a factor equal to the effective mass times the gravitational constant divided by c^2. Let’s replace the mass with the ...


20210609: Are We Running Out of Space Above Earth?
 14:43: The gravitational interaction is weak except right next to the relic  on the scale of Planck lenfths.


20210525: What If (Tiny) Black Holes Are Everywhere?
 11:17: ... on how to mess with the limits of the uncertainty principle in detecting gravitational ...
 13:36: ... principle can be gamed to improve measurements  in particular in gravitational wave ...


20210519: Breaking The Heisenberg Uncertainty Principle
 00:25: ... part in a billion And also pretty recently we have the measurement of gravitational waves by ...
 05:01: ... Laser Interferometer Gravitational Wave Observatory measures ripples in the fabric of space caused by ...
 05:19: For fainter gravitational waves we quickly run up against the Heisenberg limit.
 05:51: But if a gravitational wave passes through the interferometer, the relative lengths of the two paths change in a very particular way.
 06:39: And that noise will obscure faint gravitational wave signals.
 06:44: ... the laser beams are larger than the change in the arm lengths due to a gravitational wave, then we’ll never see those ...
 07:07: To improve our ability to detect faint gravitational waves we need to reduce the uncertainty in the phase of the laser beams.
 09:05: Less flickering due to random phase shifts means that we can see real signals due to much weaker gravitational waves.
 09:13: ... light in the next upgrade will allow them to detect up to 50% more gravitational wave events  events from further away, and involving lowermass mergers ...
 09:43: But that noise is less of a problem than the phase uncertainty, at least for the higher frequency gravitational waves.


20210511: How To Know If It's Aliens
 16:32: ... fact: Einstein, along with Nathan Rosen, tried to explain particles as gravitational singularities  wormholes between adjacent dimensions threaded by ...


20210413: What If Dark Matter Is Just Black Holes?
 00:18: 80% of the mass of our universe is completely invisible to us  its existence only revealed through its immense gravitational influence.
 01:13: As we’ve discussed many times before, black holes are regions of gravitational field so intense that not even light can escape.
 07:40: At this point, gravitational lensing becomes the goto method for dark matter hunters.


20210323: Zeno's Paradox & The Quantum Zeno Effect
 14:45: Max Graham asks how gravitational waves encode the distance that they've traveled.
 15:08: But it's different with gravitational waves from merging black holes.
 15:32: But that chirp mass also determines the power that was radiated in gravitational waves during the inspiral.


20210316: The NEW Crisis in Cosmology
 10:40: ... extremely promising method is gravitational lensing  the bending of light around massive objects ...
 17:08: ...  these poor guys have to fight in so many different gravitational fields  star destroyers, the death star, forest moons, ice ...


20210309: How Does Gravity Affect Light?
 00:38: ... clergyman John Michell proposed that a particle of light gripped by the gravitational field of a sufficiently massive star would slow down, stop, and fall ...
 02:26: Or of the sense of weightlessness in freefall in a gravitational field versus the weightlessness felt in the absence of gravity.
 03:29: ... tells us that we must experience all the same physics if at rest in a gravitational field  say, in a fake rocket ship in a Hollywood ...
 03:42: Light emerging from a gravitational field is stretched out  it experiences gravitational redshift.
 03:50: And we get exactly the same prediction if we use the fact that time runs slow in gravitational fields.
 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.
 04:37: ... the event horizon of the black hole, gravitational time dilation is so strong that clocks stop and the frequency of photons ...
 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 case of gravitational redshift, we could come up with a physical explanation for the ...
 06:10: Can this gravitational time dilation also explain the bending of a ray light traveling horizontally?
 09:09: But in a sense, light gets refracted by gravitational fields  or at least you can model it that way.
 09:27: And also that the speed of light changes in gravitational fields, which sounds counter to everything I’ve told you.
 10:19: ... because of two effects: your clock is ticking faster than clocks in the gravitational field, and space within the gravitational field is ...
 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.
 11:43: ... around the sun, due to their light rays being “refracted” in the Sun’s gravitational ...
 12:32: Light is a wave and a particle; time slows or space flows in gravitational fields.


20210224: Does Time Cause Gravity?
 00:25: Clocks run slow in gravitational fields.
 00:34: ... our recent episode, we saw why this gravitational time dilation is inevitable  it follows as surely as 1+1=2 if we accept ...
 01:56: Absent a gravitational field or any forces, if the teapot starts motionless it stays that way.
 02:33: We know that the presence of mass and energy warp spacetime  and the most intense part of that warping is in time  our gravitational time dilation.
 04:26: ... towards the shore." It’s the same with the 4velocity of an object in a gravitational ...
 04:56: And it’s always rotated in the direction of decreasing flow  which in a gravitational field is downwards.
 05:03: ... this is the motion of any object in a gravitational field  it gradually picks up velocity in the down direction  it ...
 07:39: If photons are already fully rotated into the spatial direction, how is it that they’re also affected by gravitational fields?
 07:48: But light DOES bend in a gravitational field  astronomers see it happening all the time in the effect we call gravitational lensing.
 08:39: Last time we talked about the gravitational wave background  the ambient buzz of gravitational waves from the distant and ancient universe.
 09:10: ... bang”  which I mentioned in reference to a potential component of the gravitational wave ...
 10:04: ... case the last instant of inflation IS the instant of the big bang, and gravitational Kinkusnacht asks whether gravitational waves can be used to test ideas ...
 10:21: The most well known prospect is by detecting the signatures of primordial gravitational waves  waves from the inflationary epoch.
 10:28: These could be found in the gravitational wave background, but also indirectly through their effect on the cosmic microwave background.
 10:56: ... inflation it’s believed that quantum gravitational effects would have been very important, so if we can get any type of ...


20210217: Gravitational Wave Background Discovered?
 00:00: ... was pretty impressive when we built this giant machine that spotted gravitational waves from colliding black holes well we've just taken it to the next ...


20210210: How Does Gravity Warp the Flow of Time?
 00:00: ... your feet will age approximately 1 second more than your head due to gravitational time dilation  and that’s assuming that your life is long and that ...
 00:25: ... following: “For an observer falling freely from the roof of a house, the gravitational field does not exist.” We now know this as the equivalence principle  ...
 01:00: ... the sense of weight you would feel accelerating at 1g distant from any gravitational field  at least as far as the laws of physics are ...
 02:30: There’s a deep connection between gravity and time  gravitational fields seem to slow the pace of time in what we call gravitational time dilation.
 03:07: ... to start out by me totally convincing you that time must run slow in a gravitational field  an effect we call gravitational time ...
 05:45: To get to gravitational time dilation all we need to do is add in the equivalence principle as our second axiom.
 05:52: It tells us that whatever we conclude about the passage of time in an accelerating frame must also be true in a gravitational field.
 09:00: ... someone standing in a gravitational field must experience the same sense of weight AND the same time ...
 09:16: ... the equivalence of acceleration and gravity, then time must run slow in gravitational ...
 09:25: ... reference frames, OR you can use general relativity to calculate the gravitational time dilation for the equivalent gravitational ...
 09:53: ... the case of the twin paradox, gravitational time dilation gives the right relative time flows if you consider the ...
 10:17: ... note of caution: be aware that circular orbital motion in a gravitational field is very different from our rotating space station then both ...
 10:45: We’ve reasoned our way to seeing that gravitational time dilation must be a thing if our axioms are right.
 10:58: What really is it about the gravitational field that’s causing time to tick slow?
 11:14: So that photon clocks and matter do evolve more slowly in gravitational fields.
 11:19: ... is it that if you’re inside a gravitational field, your sense of “now” is continually sweeping forward compared to ...


20210126: Is Dark Matter Made of Particles?
 03:27: ... the only thing we’ve ever actually seen dark matter do is to exert its gravitational ...
 04:34: In fact, galaxies are really just shiny dustings of stars, sprinkled deep in the gravitational wells of massive reservoirs of dark matter.
 15:25: ... can we apply the gravitational time dilation to the traveling twin, as though they were standing on the ...


20210119: Can We Break the Universe?
 00:02: Black holes, gravitational waves, he was even the first to realize that friggin lasers could be a thing.


20201215: The Supernova At The End of Time
 01:39: ... crystalline ball of quantum weirdness has supported itself against gravitational collapse by the pressure exerted by its electrons ...
 04:32: ... would be enough to stop them from collapsing under their own intense gravitational ...
 04:48: Once its nuclear fuel supply runs out, there would be no outward flow of energy to resist the gravitational crush.


20201208: Why Do You Remember The Past But Not The Future?
 12:58: ... when taken separately, but rather in the degrees of freedom of the gravitational ...


20201027: How The Penrose Singularity Theorem Predicts The End of Space Time
 01:17: ... a central point. At that socalled singularity, the gravitational field becomes infinite. But physicists tend to be dubious ...
 05:01: ... These are the paths traveled by an object in free fall in a gravitational field. The path traveled by a ray of light is called a ...


20200908: The Truth About Beauty in Physics
 09:42: ... between mirrors  but the resulting theory predicts black holes, gravitational waves, and even the big ...


20200824: Can Future Colliders Break the Standard Model?
 15:59: ... mass of the sun  it’s the maximum mass of a white dwarf before crushing gravitational pressure causes electrons to be pounded into protons to form neutrons, ...


20200817: How Stars Destroy Each Other
 01:02: A stream dull, red gas now connected the two  the outer envelope of the star falling into the intense gravitational embrace of its old companion.
 05:47: ... because the gravitational field of the compact object is so strong, falling gas reaches incredible ...
 10:43: ... back a few weeks to our episode on this strange new observation by LIGO: gravitational waves from the merger of a black hole with ... something ...
 12:44: ... at these masses, then the universe should be very faintly humming with a gravitational wave background from the countless mergers than happened in the earlier ...
 13:15: That's an easy one  in order to generate detectible gravitational waves, both objects need to be extremely compact.
 13:32: They are ripped apart before getting close enough to generate gravitational waves.


20200810: Theory of Everything Controversies: Livestream
 00:00: ... of two locations then we don't know what happens with the gravitational field and that's because we have not been able to combine properly ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... the predictions of this theory from 100 years ago was this notion of gravitational waves and these were only verified experimentally just a few years ...


20200720: The Boundary Between Black Holes & Neutron Stars
 00:00: When we detected the very first gravitational wave, a new window was opened to the mysteries of the universe.
 00:23: By now we’re becoming used to announcements that a new gravitational wave event has been detected.
 00:38: ... the LIGO and VIRGO gravitational wave observatories spot event after event, the excitement is shifting ...
 01:04: ... the shape of the gravitational waveform, and based on calculations using Einstein’s general theory of ...
 01:53: We’ve done gravitational wave astronomy before, but this event is so mysterious we had to cover it.
 02:18: ... passage of a gravitational wave causes extremely tiny changes in these arm lengths, which in turn ...
 02:30: ... August 14 2019, a gravitational wave hit the LIGO and VIRGO observatories one after the other in close ...
 11:01: With new gravitational wave events coming every week or two, we’re sure to see more of these sorts of mergers.


20200708: Does Antimatter Explain Why There's Something Rather Than Nothing?
 10:56: ... The CPT theorem states that the acceleration of an antiatom in Earth’s gravitational field should be exactly the same as for an atom, but scientists want to ...


20200630: Dissolving an Event Horizon
 01:30: ... the Cosmic Censorship Hypothesis  which basically states that every gravitational singularity must be surrounded by an event ...
 06:58: ... cosmic censorship hypothesis tells us that something will always stop a gravitational singularity being stripped of its event horizon  but it doesn’t tell us ...
 08:55: ... any rate, our observations of gravitational waves from colliding black holes and various other methods for estimate ...
 15:14: ... mentioned that in conformal cyclic cosmology, photons and gravitational waves can pass the boundary from universe end to new big bang, and so ...


20200622: Building Black Holes in a Lab
 00:16: ... of gas pouring into tiny spaces in quasars or Xray binary systems. Gravitational waves that perfectly match our theoretical prediction for black hole ...
 07:24: ... researchers think they’ve detected exactly the expected sapping of the “gravitational field” in a vortex black hole analog. In fact, both the analog of energy ...


20200615: What Happens After the Universe Ends?
 12:01: ... of the entropy at the Big Bang is due to the tiny entropy in the gravitational field at the ...
 12:20: In CCC, all of the energy  and, importantly, the gravitational field  is smoothed out over infinite time between aeons.
 14:02: It turns out that, as well as photons, gravitational waves should be able to pass between aeons.


20200608: Can Viruses Travel Between Planets?
 14:44: ... we have other evidence of dark matter  for example in gravitational lensing, in the cosmic microwave background speckles, and in things like ...
 15:01: ... in the Casimir force between them to get an accurate measurement of the gravitational ...
 15:15: So what if the Casimir force itself IS a modification of the gravitational force on tiny scales?


20200527: Does Gravity Require Extra Dimensions?
 00:00: It’s been 120 years since Henry Cavendish measured the gravitational constant with a pair of lead balls suspended by a wire.
 01:53: ... gravitation is an example of such a law  basically, the strength of the gravitational force drops off with the square of the distance between two massive ...
 02:03: If we have a massive object, we can depict the gravitational force (field) from this object as little arrows pointing towards the object.
 02:10: The density of the arrows at a given distance determines the strength of the gravitational field.
 02:29: So the density and the strength of the gravitational field drop proportional the surface area of that sphere  that’s 4 pi r^2.
 03:46: ... may explain the hierarchy problem  the relative weakness of the gravitational ...
 04:32: ... fact we saw in a previous episode how a particular gravitational wave detection from LIGO seemed to rule out the possibility of extra ...
 08:55: ... gravitational attraction between these masses and the balls would then rotate the ...
 09:08: ... that it had to be protected from the slightest breeze, or even the gravitational influence of other bodies  including ...
 09:34: The meticulous care paid off—Cavendish measured a gravitational constant that agrees with our modern value, with 1% uncertainty.


20200518: Mapping the Multiverse
 00:09: ... hole, the universe does not come to an abrupt halt at the bottom of the gravitational pit Instead, a path can be traced out again but you do not end up in the ...
 01:01: ... when enough mass is concentrated in a small enough space that the gravitational field becomes too strong for even light to ...
 05:53: ... nice way to map the gravitational field is according to the geodesics of objects in freefall that start ...
 12:23: That pressure produces its own gravitational effect on par with the black hole itself, accelerating the streams further.


20200511: How Luminiferous Aether Led to Relativity
 09:02: ... fringe pattern. And this is exactly the method that LIGO uses to detect gravitational ...
 12:25: ... afterlife. Einstein talked about the “new aether” as the medium of the gravitational field, and which we now think of the fabric of spacetime. Paul Dirac ...


20200504: How We Know The Universe is Ancient
 04:40: ... of the universe  they also have random motion as they’re tugged by the gravitational fields of nearby galaxies and clusters. We can deal with these “peculiar ...
 11:07: ...  which is mostly in dark matter  can be found by adding up the gravitational effect in galaxies and in galaxy clusters, and also by tracking the past ...
 15:09: ... amount of stretching of the fabric of spacetime  the strenght of the gravitational field, if you will. Same as with the rubber sheet analogy in which a ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... to the energy of photons that are redshifted okay and the restrict of gravitational waves what happens to their energy well so the answer is there are a ...


20200422: Will Wormholes Allow Fast Interstellar Travel?
 00:42: ... 1916 Ludwig Flamm realized that in certain coordinate systems, the gravitational hole described by the Schwarzschild solution was not a dead end. Rather ...


20200331: What’s On The Other Side Of A Black Hole?
 01:53: ... It allows us to calculate the path of an object moving in the insane gravitational field approaching a black hole. It even works inside the black hole  ...


20200324: How Black Holes Spin Space Time
 01:01: ... have since told us that black holes are very real. We’ve seen the gravitational waves caused by their mergers, we’ve witnessed the havoc they wreak on ...
 04:11: ... beneath the event horizon? In fact it sort of doesn’t actually. Both the gravitational field and its rotation can be thought of as properties of the spacetime ...
 05:14: ... “freefall” trajectory  the path taken by an object moving freely in the gravitational field  is dragged in the direction of the object’s spin. Gravity Probe ...
 06:48: ... have not been directly detected  though there is tentative evidence in gravitational lensing studies of ...


20200218: Does Consciousness Influence Quantum Mechanics?
 15:49: ... like the speed of light and the gravitational constant are just scaling factors and so varying them shouldn't lead to ...


20200127: Hacking the Nature of Reality
 14:50: Adam Wulg asks whether gas surrounding a pair of merging black holes might significantly affect the gravitational wave signature.


20200120: Solving the Three Body Problem
 00:20: ... one case  when two and only two bodies orbit each other sans any other gravitational influence in the ...
 03:18: ... apparent hopelessness, there was much profit in learning to predict the gravitational motion of many bodies. For most of the three centuries since Newton, ...
 04:29: ... a very low mass compared to the other two. We can ignore the minuscule gravitational influence of the smaller body and assume that it moves within the ...
 05:25: ... and solve them one at a time. A sufficiently small section of any gravitational trajectory can be approximated with an exact, analytical solution  ...


20200113: How To Capture Black Holes
 00:24: ... September 2015 the laser interferometer gravitational wave observatory  LIGO  detected its first gravitational wave from the ...
 00:59: ... were not so surprising. Einstein’s general relativity predicted gravitational waves and astrophysics predicted black hole mergers. When two very ...
 04:08: ... incandescent vortex  an accretion disk  as it plummets into the insane gravitational field of the central monster. In the case of the largest, most wellfed ...
 04:50: ... a streamer of gas is dragged out of the disk, tugged by the black hole’s gravitational field. Momentum is transferred from black hole to gas, slowing the black ...
 05:58: ... the surrounding gas saps their orbital energy much more quickly than by gravitational radiation alone. This means they can spiral together before being ripped ...
 06:15: ... When a massive object is embedded in a rotating disk, it will exert a gravitational tug on the surrounding particles. Depending on the local properties of ...
 08:50: ... after merger that could lead to a bright burst of light to accompany the gravitational ...
 09:21: ... they finally merge, they release a burst of gravitational radiation so powerful that it can carry away up to several percent of ...
 09:31: ... the binary suddenly finds itself moving too quickly for the reduced gravitational field of the final black hole. It creates an expanding expanding ...
 09:53: ... the release of gravitational waves delivers a kick to the final black hole  a bit like the recoil of ...
 10:18: ... resolution of the two LIGO and the VIRGO observatories locates a gravitational wave source to a pretty large blob on the sky, which will typically ...
 11:32: ... like I said: gravitational wave astronomy will reveal many cosmic mysteries and strange phenomena. ...


20191209: The Doomsday Argument
 14:57: ... most obvious example is that regular gravitational fields around stars and galaxies can be positively curved patches in a ...
 16:21: ... to a much flatter universe than implied by this new result from the CMB gravitational ...


20191202: Is The Universe Finite?
 05:52: One thing that we didn’t talk about is how gravitational lensing influences the overall shape of the power spectrum.
 06:02: ... full of galaxies and galaxy clusters  all of which have enormous gravitational fields that act as lenses, slightly deflecting the path of those rays of ...
 06:41: See, gravitational lensing is caused by mass  both dark matter and atoms.
 08:25: ... at all The researchers looked at a different indicator of the amount of gravitational lensing: the socalled fourpoint correlation ...


20191111: Does Life Need a Multiverse to Exist?
 07:37: ...  for example, the fine structure constant for electromagnetism and the gravitational constant for ...


20191104: Why We Might Be Alone in the Universe
 09:40: That planet acts like a gigantic gravitational vacuum cleaner, absorbing a lot of the debris left over from the formation of the solar system.


20191015: Loop Quantum Gravity Explained
 02:54: In string theory, a type of background independence emerges in an abstract space of moving strings and with that comes a gravitational field.
 09:29: ... these closed loops, with each loop like an elementary closed circuit of gravitational ...
 10:10: Not with chunks of spacetime but with quantum circuits of gravitational field.
 14:15: David Bennack likes the idea of gravitational lensing of gravitational waves. Well so do I, David.
 14:38: ... possibility is that it was just one black hole merger, but the gravitational wave from it was deflected by a galaxy or something on its way to us  ...
 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.
 15:22: Still, we'll probably see a lensed gravitational wave at some point.


20191007: Black Hole Harmonics
 00:14: And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself.
 01:08: ... now know that black holes also merge – and in the process produce gravitational radiation that we’ve only just managed to detect with the miraculous ...
 02:14: ... two inspiralling black holes make powerful spacetime ripples – gravitational waves – which intensify as the black holes approach merger, only ...
 04:24: For a black hole, another way to think of its quasinormal modes is as a set of gravitational waves trapped in orbit around the black hole.
 07:22: ... black holes with much greater precision than if they’d just used the gravitational wave signal from the leadup to the ...
 07:41: So this sort of frequency analysis of gravitational waves is being called gravitational wave spectroscopy.
 08:22: ... team analyzed the harmonics in the gravitational wave ringdown from this event and claim a likely detection of at least ...
 11:42: LIGO has a publicly available alert system so that astronomers can follow up gravitational wave detections with other telescopes.
 11:50: LIGO’s gravitationalwave candidate event database reveals many, many candidate detections – many of which will prove to be real.
 12:41: So, long story short – the initial promise of LIGO and the first detection of gravitational waves really seems to be panning out.
 12:49: Gravitational wave astronomy is now really a thing.
 12:59: ... with the new subfield of gravitational wave spectroscopy, we can now listen to the harmonics of ringing black ...


20190923: Is Pluto a Planet?
 15:45: ... effect of gravity for its inhabitants, but without an actual powerful gravitational field limiting our access to ...


20190916: Could We Terraform Mars?
 03:33: At 11% the mass of Earth, it has a weaker gravitational field that grips less tightly to an atmosphere.


20190806: What Caused the Big Bang?
 02:43: Mostly, the stuff in the universe pulls the universe back together; resists the expansion with a positive gravitational effect.
 02:50: But there's one type of energy that can have an anti gravitational effect.


20190725: Deciphering The Vast Scale of the Universe
 02:05: ... away from us so quickly that they would surely escape the Milky Way’s gravitational ...


20190718: Did Time Start at the Big Bang?
 09:52: ... options the first cyclic universe idea was the Big Bounce in which the Gravitational attraction of all matter in the universe was enough to cause it to ...


20190701: Thorium and the Future of Nuclear Energy
 16:59: ... Proghead777 asks, whether the central supermassive black holes gravitational Influence is extended by frame dragging Well, the answer is yes, but not ...


20190620: The Quasar from The Beginning of Time
 07:43: Look out for Physics Girl's exploration of gravitational waves at LIGO.


20190617: How Black Holes Kill Galaxies
 01:35: ... are Big they're peanuts compared to the Galaxies they live in their Gravitational influence should only extend to the stars right at the very centre of ...
 14:07: or in the detailed shape of the gravitational wave signal before collision.


20190606: The Alchemy of Neutron Star Collisions
 02:47: ... alternatives shot to prominence last year when the LIGO and Virgo gravitational wave Observatories spotted the spacetime ripples from the merger of a ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 15:04: ... going hypothesis  then black holes would definitely attract dark matter gravitationally, and occationally eat the ...


20190501: The Real Science of the EHT Black Hole
 10:17: ... cool fact is that, just like those gravitational wave signals from a couple of years ago, the black hole looks just like ...


20190424: No Dark Matter = Proof of Dark Matter?
 00:03: ... that the galaxies in the Coma Cluster were moving too quickly to remain gravitationally bound within that cluster he guessed the presence of Dunkel materia a ...


20190410: The Holographic Universe Explained
 11:46: ... fields are strongly coupled  then the corresponding higherdimensional gravitational structures in the higher dimensional space would be weak and ...
 11:58: ... strong gravitational fields in the higher dimensional space – like in black holes – look like ...


20190403: The Edge of an Infinite Universe
 14:49: Every particle, every gravitational effect in the bulk is represented by quantum fields on an infinitely distant surface.
 17:01: ... is created from the increasing negative potential energy of the cosmic gravitational field, but I think at that level this is all just different ...


20190328: Could the Universe End by Tearing Apart Every Atom?
 00:25: ... us safe and sound in nice galaxies like the Milky Way here the galaxy's gravitational field is plenty strong enough to resist the minuscule effect of dark ...
 06:20: ... that it is much crazier. As the rate of expansion increases and with no gravitational bodies left to resist the expansion, all points in space will eventually ...
 07:38: But as long as we have a nice gravitationally bound galaxy to live in, the cosmic event horizon can never shrink to a size smaller than that galaxy.
 10:03: ... last 30 minutes phantom energy is strong enough to overcome Earth's own gravitational binding energy and the planet is disrupted. Moments later at the 10^19 ...


20190320: Is Dark Energy Getting Stronger?
 02:22: Those same textbooks talk about dark matter – an invisible stuff whose gravitational influence overwhelms all types of visible matter combined.


20190306: The Impossibility of Perpetual Motion Machines
 07:17: And then of course there’s the gravitational radiation that will slowly sap the “perpetual motion” of celestial systems.


20190220: Secrets of the Cosmic Microwave Background
 02:05: ... wave had time to flow in reverberate out and then get captured by the gravitational field once more falling back to the centre and that could happen ...
 07:42: ... in the Universe Energy results in positive curvature due to its positive gravitational effect On the other hand an expanding universe with no energy would have ...


20190207: Sound Waves from the Beginning of Time
 03:21: ... baryons by a factor of five, Which means it was, by far, the dominant gravitational influence in the early universe as it still ...
 04:13: Each overdense region pulled gravitationally on its surroundings, gravitationally on its surroundings, drawing matter towards it.
 06:46: ... flowed together and consolidated the new structure. Once more in the gravitational grip of dark matter, hydrogen and helium could begin the long work of ...
 16:18: That's kind of like having parallel spacetimes, one with positive and one with negative masses, which can still interact gravitationally.


20190130: Perpetual Motion From Negative Mass?
 01:10: That episode really got me thinking about the subtleties of negative mass and how it should really behave gravitationally.
 02:04: We refer to the mass that exerts or responds to a gravitational force gravitational mass.
 02:12: ... we should split gravitational mass into active gravitational mass – that’s the mass that causes a ...
 02:30: In fact both gravitational masses should be the same quantity as inertial mass.
 02:46: ... you calculate the acceleration of an object in a gravitational field, inertial and passive gravitational mass cancel each other out  ...
 02:57: ... demonstrated the equivalence of gravitational and inertial mass when he showed that objects with very different masses ...
 03:24: We know that the gravitational force between positive mass objects is attractive.
 04:00: ... why this is the case, or what the spin of a field even means, but the gravitational field is spin 2 – even  so like masses should attract and opposite ...
 04:25: Except now we come back to the tricky relationship between inertial mass and gravitational mass.
 04:31: In particular, what if passive gravitational and inertial mass is the same thing?
 05:58: General relativity was, in part, inspired by the equivalence of gravitational and inertial mass.
 06:04: ... feeling of acceleration in empty space and the feeling of weight in a gravitational ...
 06:17: ... only works if all masses experience the same acceleration in a given gravitational field, so passive gravitational mass and inertial mass have to be ...
 06:36: ... presence of active gravitational mass, and of energy, momentum, pressure, and more, change the geometry ...
 06:48: A socalled geodesic path is the trajectory of an object in a gravitational field assuming no additional forces.
 07:05: In fact, in pure general relativity, inertial and passive gravitational masses don’t even appear in the equations.
 07:13: That should mean that a negative mass behaves the same in a gravitational field as a positive mass.
 07:40: But those trajectories only depend on the active gravitational mass of the central object, and on the velocity and starting position of the apple.
 07:50: This suggests that a positive gravitational field attracts everything, including negative masses.
 07:57: So what about negative gravitational fields?
 08:33: All of this assumes the simplistic case of what we call test particles – small objects moving in a much larger gravitational field.
 10:18: In this case, the basic nature of the positive versus negative gravitational fields – the way the fabric of spacetime gets stretched has to be right.
 10:32: We assumed that passive gravitational mass and inertial mass are the same thing – and that’s required by the equivalence principle.
 11:22: Either way, the structure of geodesics have inbuilt the assumption of the equivalence of gravitational and inertial mass.
 11:48: By comparison, negative gravitational mass is kind of ok.
 12:15: It also implies that ALL fundamental forces have their directions flipped by the action of the charge of the gravitational field.


20190124: The Crisis in Cosmology
 01:42: ...the rate of expansion of the universe, combined with the gravitational effect...
 06:28: ...of all the gravitational influences that affected that expansion since the Big Bang.
 11:08: ...or perhaps gravitational lensing alters the Planck speckles differently to how we thought.
 12:37: Independent methods, like using gravitational lensing, or gravitational waves,...
 14:03: ...the gravitational lensing measurements of dark matter...
 14:18: Gravitational lensing is the bending of light by a gravitational field.
 14:26: ...due to the gravitational fields of more nearby galaxies.
 14:40: ...that we wouldn't even see this sort of strong gravitational lensing...


20190109: Are Dark Matter And Dark Energy The Same?
 03:10: ... has competing effects – its positive energy density gives it a positive gravitational effect but its negative pressure is ...
 04:06: Forgetting that pressure stuff for a moment, positive masses and energies always have a positive gravitational effect.
 04:31: In Newtonian gravity, you multiply the two masses together along with some other stuff to get the strength of their mutual gravitational attraction.
 05:03: Mass determines the strength and direction of the gravitational field – that’s gravitational mass.
 05:18: It should be the same as gravitational mass for the equivalence principle to hold.
 05:45: So Farnes argues that the “attractive” gravitational force between two negative masses should actually drive them apart.
 08:10: That gives a positive pressure, and in general relativity positive pressure adds an attractive gravitational force, no matter what causes it.


20181206: Did Life on Earth Come from Space?
 00:37: ... could hitchhiking microbes have survived that ejection to escape Earth's gravitational field a chunk of impact debris has to be kicked to a minimum of eleven ...


20181121: 'Oumuamua Is Not Aliens
 02:56: It appears to be accelerating, or at least it's not slowing down as much as you'd expect due to the sun's gravitational pull.
 07:59: ... home system, much like the comet Shoemaker Levy, and then it may have gravitationally reassembled itself into an odd shape on that very long interstellar ...
 09:22: ... from our own Oort cloud and was socked from its orbit by impact and or gravitational interaction into a trajectory that will send it to the ...


20181114: Supersymmetric Particle Found?
 14:54: Some of you recalled a recent episode in which we talked about a study of gravitational waves that appears to refute the idea of extra dimensions.
 15:11: ... explanation for the unusual weakness of the gravitational force is that there's an extra special dimension that has the same scale ...


20181107: Why String Theory is Right
 03:40: In quantum theories of gravity, the gravitational force is communicated by the graviton particle.
 03:55: But in very strong gravitational interactions, that intersection itself becomes more and more point like.
 04:15: If you even try to describe very strong gravitational interactions, you get nonsense black holes in the math.
 09:02: ... possible to quantize the theory and gives us a very different field, the gravitational ...
 11:23: It's a projection of the 3D gravitational field.
 11:35: These are particles, and the first mode looks like the graviton, a quantum particle in the aforementioned gravitational field.
 11:44: ... you use string theory to write down the gravitational field in what we call the lowenergy limit, which just means not in ...


20181018: What are the Strings in String Theory?
 03:08: But the only hypothetical massless spin2 particle is the graviton, the conjectured quantum particle of the gravitational field.
 03:16: ... the gravitational field is made of quantum particles, which it might be we really don't ...
 09:10: ... you remember from our episode on quantum gravity, if you try to describe gravitational interactions on the smaller scales, the energies required to interact on ...
 09:23: There's no way to even think about the shape of the gravitational field on the Planck scale that doesn't produce a hopeless conflict.


20181010: Computing a Universe Simulation
 12:07: ... week, we looked at an amazing new result in which gravitational waves were used to search for and rule out the existence of an extra ...
 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.
 13:10: That led to the radio emission arriving hours after the gravitational waves.
 13:30: ... explosion from the neutron star merger started slightly after the gravitational wave ...
 13:41: The gravitational waves start to get strong before the neutron stars even make contact.


20181003: How to Detect Extra Dimensions
 00:10: Fortunately, with the discovery of gravitational waves, we're now living in a science fiction future.
 00:18: ... PLAYING] We may have mentioned once or twice that the new era of gravitational wave astronomy is going to open new windows to the universe and unlock ...
 00:59: The key to this breakthrough was the gravitational wave event observed in August of 2017, GW170817.
 01:17: And the LIGO and Virgo gravitational wave observatories detected the resulting ripples.
 01:29: The resulting kilonova is first observed in gravitational waves and then as a gamma ray burst.
 01:35: In GW170817, the flash of gamma radiation arrived 1.7 seconds after the gravitational waves.
 01:50: Among other things, this optical identification gave a completely independent measurement of the distance traveled by the gravitational waves.
 04:03: This relationship also applies to the force felt in a gravitational field.
 04:16: We do see slight deviations in very strong gravitational fields, like close to the sun.
 07:20: This can be used to explain the general weakness of the gravitational force on all but the tiniest scales.
 08:37: Well, here's where we finally get back to our gravitational waves.
 08:41: ... the gravitational field can extend into this hypothetical extra spatial dimension, then ...
 09:02: In regular 3D space, gravitational waves drop in intensity proportional to just distance, not distance squared.
 09:11: If space has four or more dimensions, then gravitational waves should drop off in intensity faster than you'd expect in three dimensions.
 09:22: Just observe a gravitational wave and figure out how much its intensity dropped off over the distance traveled.
 09:41: All you need is a billiondollar network of gravitational wave detectors and a way to independently measure the distance the wave traveled.
 09:58: ... stars allowed us to measure its distance completely independently to the gravitational wave signal, something that's impossible with black hole ...
 10:10: ... factor here in order to determine how much intensity was lost by the gravitational wave, we need to know how intense it was when it started its ...
 10:20: ... super convenient property of gravitational waves is that you can figure this out by looking at other properties of ...
 10:42: The gravitational wave lost the right amount of intensity for a 3plus1dimensional spacetime.
 11:06: ... the way, comparison of the electromagnetic and gravitational wave arrival times also allowed us to verify that gravity really does ...


20180920: Quantum Gravity and the Hardest Problem in Physics
 04:38: ... that approach completely fails when you have strong gravitational effects on the smaller scales of space and time, like the central ...
 05:08: ... start by thinking about what it means to define a location in a gravitational field with perfect precision or, in other words, what it means to talk ...
 08:28: The gravitational field doesn't lie on top of spacetime.
 08:52: In general relativity, the presence of mass or energy warps the gravitational field.
 10:46: When you have strong gravitational effects on the quantum scale, the selfenergy corrections blow up to infinity.
 13:30: When two black holes merge, a lot of energy is pumped into gravitational waves.


20180905: The Black Hole Entropy Enigma
 00:36: They are the inevitable result of extreme gravitational collapse.
 00:53: Also, we've seen them in their gravitational effects on their surrounding space and in the gravitational waves caused when they merge.
 06:22: If you merge two black holes, some of their mass gets converted to the energy radiated away in gravitational waves.
 06:40: Gravitational radiation and the Penrose process reduce blackhole mass and radius or the sum of masses and radii of emerging black holes.


20180830: Is There Life on Mars?
 07:08: ... it must have come from the surface of Mars, probably ejected from Mars's gravitational field after another space rock smashed into the ...


20180823: How Will the Universe End?
 05:13: As dark star remnants rotate through countless galactic orbits, they interact with each other gravitationally.
 09:03: And after that, just particles and light, now not even bound gravitationally.


20180801: How Close To The Sun Can Humanity Get?
 06:33: To escape Earth's orbit in the outward direction, you first, need to escape Earth's gravitational pull and then, accelerate to achieve a larger orbit.
 06:51: Parker will use the same trick as many of our outbound spacecraft, like Voyager or Pioneer gravitational assists.


20180711: Quantum Invariance & The Origin of The Standard Model
 01:24: An example would be a ball rolling down a hill under a constant gravitational acceleration.


20180704: Will A New Neutrino Change The Standard Model?
 05:55: ... neutrinos or lefthanded antineutrinos, should only interact gravitationally so would be near impossible to ...
 12:14: A few of you wonder whether adding extra mass to Earth from asteroid mining could lead to problems like with our orbit or Earth's gravitational pull.
 12:53: ... get stuff off the Moon, you have to contend with its admittedly low gravitational field compared to essentially no such field in the case of ...


20180627: How Asteroid Mining Will Save Earth
 08:26: This can be done with a gravitational tractor, which we talked about before, or with rockets fueled by the asteroid's own water supply.


20180620: The Black Hole Information Paradox
 02:57: The gravitational field of a black hole is expected to distort the surrounding quantum fields.
 09:16: ... Hooft realized that the threedimensional gravitational and quantummechanical interior of a black hole could be fully described ...
 12:07: ... has a really comprehensive series on gravitational physics that will take you from Newton's law all the way through ...
 14:58: HebaruSan noticed that, in our graphic, the Earth completed 1.75 orbits in the supposed 8 minutes it took the Sun's gravitational field to vanish.


20180613: What Survives Inside A Black Hole?
 00:16: ... established by now that black holes are weird, the result of absolute gravitational collapse of a massive body, a point of hypothetical infinite density ...
 02:58: After all, the forces involved, namely the gravitational and electromagnetic forces, are only communicated at the speed of light.
 03:13: Let's think about this in terms of fields, and we'll stop with the gravitational field.
 03:18: Gravity may be caused by mass, but a gravitational field is a very real thing all on its own.
 03:24: In Einstein's general theory of relativity, we think of the gravitational field as curvature in the fabric of spacetime.
 03:38: We can think of the gravitational field at any point as being caused by the gravitational field at surrounding points.
 03:45: Each point on the rubber sheet doesn't actually see the source of the gravitational field.
 03:54: The Earth orbits the Sun, but more directly it orbits the Sun's gravitational field.
 04:06: If the Sun were to suddenly vanish, Earth would continue to orbit the existing gravitational field for 8 minutes.
 04:20: ... see the mass inside the black hole, but that mass is remembered in the gravitational field, the curvature of spacetime above the event ...
 04:53: It's Gauss's law, which applies to both gravitational and electric fields.
 04:58: ... law of gravity states that the total gravitational field added up over an enclosed surface is proportional to the amount of ...
 05:19: The resulting sum of the gravitational field would be the same.
 06:16: If you've studied some introductory physics, you might remember that the gravitational and electric fields have something in common.
 07:34: ... so the gravitational and electromagnetic forces have infinite range, and so Gauss's law ...
 07:59: ... out, but new infalling material will adjust the black hole's external gravitational and electric fields on its way ...
 08:46: In a similar way, you can see a black hole's rotation in its gravitational field.


20180516: Noether's Theorem and The Symmetries of Reality
 03:36: It can be lost or gained to the gravitational field.
 03:39: This is because the direction of the gravitational field changes with respect to the road.
 03:47: On the other hand, the gravitational field across the whole stretch of road doesn't change from one point in time to the next.
 04:07: ... are symmetric under rotation for example, the sphericallysymmetric gravitational field experienced by a satellite orbiting the earth then, Noether's ...
 05:33: ... saves energy conservation by incorporating the entire universe's gravitational potential energy to offset the seeming gains or losses to redshift in ...
 11:05: ... will find more small solar system objects, detect the effects of weak gravitational lensing in distant galaxies, and see more distant supernovae, monitoring ...


20180509: How Gaia Changed Astronomy Forever
 08:02: Gaia even helps us with the pulsar timing array, a galactic scale gravitational wave observatory which we spoke about recently.


20180425: Black Hole Swarms
 02:26: ... to weigh in at between five and 15 solid amasses, although, the recent gravitational wave signals detected by LIGO, suggest they may be even more ...
 02:55: Those stars are accelerated towards the black hole and can gather behind it in a gravitational wake.
 04:57: If the companion star gets too close, its outer regions can fall into the gravitational influence of the black hole.
 07:48: Besides being very cool and kind of freaky, this result is especially important for the new field of gravitational wave astronomy.
 07:57: Now, we keep seeing these gravitational wave signals from black hole merges, and as I've discussed previously, they're kind of confusing.
 08:05: ... should probably know that, if we want to understand the source of these gravitational ...
 09:17: Last week, we talked about some of the incredible ways for detecting gravitational waves beyond LIGO.
 09:26: Majestic potato asked, whether a supernova can produce gravitational waves detectable from Earth?
 09:40: Gravitational waves are produced when the quadrupole moment of a mass distribution changes.
 09:52: So if the explosion of a supernova is concentrated, say, more on one side, then LIGO could potentially see the resulting gravitational waves.
 10:00: Juxtaposed stars asks whether, theoretically, you could build an engine to extract power from gravitational waves via the sticky bead method?
 10:29: A couple of you asked whether the gravitational waves interfere with each other?
 10:38: Two gravitational waves crossing paths will add together at any one point in space and time.
 10:55: You'd need a material capable of blocking gravitational waves.
 11:16: ... rogue wolf notes, that stellar gravitational wave detectors, like pulsar timing arrays, are a bit like using the ...


20180418: Using Stars to See Gravitational Waves
 00:07: Now that gravitational waves are definitely a thing, it's time to think about some of the crazy things we can figure out with them.
 00:14: In some cases, we're going to need a gravitational wave observatory the size of a galaxy.
 00:23: [MUSIC PLAYING] We are at the cusp of a golden age of gravitational wave astronomy.
 00:31: We've already talked about the Laser Interferometer GravitationalWave Observatory, LIGO, and the first discovery of gravitational waves here.
 02:00: Yet, everyone wants in on the gravitational wave game.
 02:09: Perhaps these gravitational waves signals were amplified by another phenomenon predicted by Einstein's general relativity, gravitational lensing.
 02:19: ... paths of gravitational waves should also be warped by intervening gravitational fields which ...
 02:45: For the first time, the event behind a gravitational wave signal was also seen in light.
 02:59: ... more observations like this should allow us to figure out where the gravitational wave signals are often also gravitationally ...
 03:10: ... the Italianbased gravitational wave observatory, was online for the neutron star merger, and was ...
 03:49: ... black holes that live in the centers of galaxies, we need to observe gravitational waves in the 0.1 million hertz to 0.1 hertz ...
 05:00: ... expect a faint gravitational wave background buzz from an earlier epoch of the universe in which ...
 05:23: But much of this gravitational wave background will have wavelengths as long as many light years.
 05:28: That's beyond any gravitational wave interferometer that we could ever physically construct.
 05:51: We're already using these to study the gravitational wave background at the 1 to 100 nanohertz range.
 06:17: ... within the pulsar array volume due to the passage of impossibly vast gravitational ...
 06:27: This galaxy scale observatory is already in operation and has placed valuable limits on the amplitude of the gravitational wave background.
 06:44: Some scientists are even trying to see how gravitational waves should interact with stars.
 06:50: Gravitational radiation should have physical effects as shown by the sticky bead argument first presented by Richard Feynman.
 06:58: He came up with a thought experiment of a simple gravitational wave detector, a rod with two sliding beads.
 07:05: ... a gravitational wave passes by, the beads are free to follow the expansion and ...
 07:18: That heat energy comes from the gravitational wave.
 07:21: ... isn't practical, but it demonstrates that in the right circumstances gravitational waves should be able to dump some of their energy into matter, for ...
 07:52: ... also contain binary supermassive black holes that are generating gravitational ...
 08:03: A similar effect may cause white dwarf stars in binary orbits to explode as they absorb gravitational radiation from their own orbits.
 08:19: Gravitational wave astronomy is currently in a gold rush.
 08:40: ... his general theory of relativity, which predicted the existence of gravitational waves, he had to master it precursor, Newtonian ...


20180404: The Unruh Effect
 09:58: According to Einstein's equivalence principle, remaining stationary in a gravitational field is equivalent to acceleration in free space.
 10:12: ... there's one place in the universe where the gravitational acceleration can get that high, and that's right above the event horizon ...


20180328: The AndromedaMilky Way Collision
 03:23: ... close enough that the mutual gravitational attraction between it and the Milky Way overcomes the outward expansion, ...
 05:06: They used simulations of the gravitational interactions of millions of particles representing groups of stars and dark matter.
 06:09: Gravitational interactions with stars slingshots those stars into larger orbits or even completely out of the galaxy.
 06:20: When those black holes are around a light year apart, they'll start losing orbital energy to gravitational waves.
 07:03: There's a higher chance of another star passing inside Neptune's orbit, which might cause some gravitational disruption.
 10:06: ... it's the name we give to the effect, whereby the gravitational response of the universe doesn't match the visible matter given our ...
 10:25: ... the dark matter mass measurements of galaxies and galaxy clusters from gravitational lensing versus ...


20180321: Scientists Have Detected the First Stars
 00:23: Not everything wows, like gravitational waves or spacefaring sports cars.


20180315: Hawking Radiation
 00:34: ... physicists realized that it allowed for the possibility of catastrophic gravitational ...
 06:49: Certain modes of the quantum field are scattered or deflected by the gravitational field of the forming black hole.


20180307: Should Space be Privatized?
 10:54: In fact, to support the increased gravitational crush of the smaller core, the fusion rate has to be even higher than when it started.


20180221: The Death of the Sun
 01:31: ... flow of energy from the core provides consistent support against the gravitational collapse well, relatively ...
 05:54: ... it loses mass, its gravitational hold weakens and so the Earth's orbit expands, perhaps eventually taking ...
 06:25: ... own gravitational pull creates a tidal bulge in the sun that may increase its ...


20180214: What is Energy?
 02:20: When she introduced the idea of gravitational potential energy, she put the laws of conservation of energy and momentum on equal footing.
 02:47: ... example, du Chatelet's gravitational potential energy, mass times the gravitational acceleration times ...
 03:26: ... as long as the downward gravitational acceleration doesn't change over time, the ball should lose speed on its ...
 03:40: Gravitational potential energy gets converted to kinetic energy in the fall and then back to exactly the same amount of potential energy in the rise.
 04:12: But even a complex path through a gravitational field can be broken down into little, perfectly reversible steps.
 04:19: That's true even if the gravitational acceleration changes from one point in space to the next.
 04:53: ... an object travels between two different points in a gravitational field, it will always experience the same conversion between potential ...
 06:25: ... we're actually including the entire ballEarth system when we add in gravitational potential energy, because that energy is stored in the Earth's ...


20180131: Kronos: Devourer Of Worlds
 01:02: However, if the gravitational connection between a pair of stars is strong enough, they might be ejected from the cluster as a binary pair.
 01:25: Or they might be a wide binary, separated by up to a few lightyears and just barely gravitationally bound.
 01:41: They're so loosely bound that even a small gravitational nudge can break apart the pair, for example, by interacting with other massive objects.
 02:26: They're so, well, widely separated that it's hard to tell if a given pair of stars is actually gravitationally bound.
 02:52: They identified plenty of stars that are close enough together that they could be gravitationally bound.
 09:05: It tugs on the Earth gravitationally, increasing our angular momentum.


20180124: The End of the Habitable Zone
 01:09: ... between the outer flow of energy produced by fusion in the core and the gravitational crush of its immense ...
 01:28: ... when the sun was born, it's initial gravitational collapse from a giant gas cloud was halted as soon as the core became ...
 02:06: ... increases fusion rate, once again reestablishing equilibrium between gravitational crush and energy ...
 02:17: But with the same mass packed into a smaller volume, the core is under more gravitational pressure than before.


20180110: What Do Stars Sound Like?
 00:38: ... models emerged in the early 1900s that described the balance between the gravitational crush and the outward flow of energy from the fusion reactions in the ...
 03:01: Now, these are not gravitational waves.
 03:04: Gravity waves result from the restoration of gravitational equilibrium.


20171213: The Origin of 'Oumuamua, Our First Interstellar Visitor
 03:22: Meaning the object is gravitationally bound to the sun.
 04:03: That's the velocity an object would need to have to escape a gravitational field.
 04:24: That means Oumuamua has enough speed to climb out of the sun's gravitational well and escape back to interstellar space.
 04:50: But perhaps Oumuamua got some sort of gravitational kick from an unknown planetary body.


20171129: Citizen Science + ZeroPoint Challenge Answer
 03:53: ... example, spotting supernovae or looking for gravitational wave signals in LIGO and finding planets forming in the debris disks of ...
 05:15: But there's also Einstein at Home, which searches for LIGO gravitational wave data for signals produced by rotating neutron stars.


20171108: ZeroPoint Energy Demystified
 05:32: The gravitational effect of energy depends on its absolute value.


20171102: The Vacuum Catastrophe
 05:07: Vacuum energy should produce a gravitational effect, and a huge vacuum energy should produce a huge gravitational effect.
 10:36: That energy comes from shocks that develop as the material flows in the gravitational field of surrounding clusters.


20171025: The Missing Mass Mystery
 05:20: Supercomputer simulations reveal the shape of this largescale structure that should result from this gravitational collapse.
 11:21: A nonzero vacuum energy would have a gravitational effect.
 12:37: TS1336 was expecting last week's episode to be about the discovery of gravitational waves from merging neutron stars.


20171011: Absolute Cold
 08:38: ... black hole binary to spiral together from losing angular momentum to gravitational ...
 10:09: We just know they must be in orbit because their probable masses are large enough that they must be gravitationally bound.


20171004: When Quasars Collide STJC
 07:30: Basically, the black holes slingshot stars outwards through gravitational interactions.
 07:35: Each time they do that they lose a bit of orbital energy or angular momentum, causing them to fall deeper into the gravitational well.
 07:44: You can think of it as a sort of gravitational friction dragging the black holes downwards and towards each other.
 08:32: A lot of you are probably thinking, what about gravitational waves?
 08:37: Can't gravitational radiation cause supermassive black holes to merge, just like it does with regular stellar mass black holes?
 08:52: ... this system is definitely producing gravitational waves, but it's going to take many billions of years to lose enough ...
 09:10: LIGO is sensitive to gravitational waves from 10 to 10,000 hertz.
 09:19: ... actual merger of a supermassive black hole binary with a galaxysized gravitational wave observatory called a pulsar timing ...


20170928: Are the Fundamental Constants Changing?
 03:11: The dimensions behind, say, Newton's gravitational constant or the mass of the electron all have arbitrary human definitions.
 12:50: Mike Williams asks about the possibility of using our sun as a gravitational lensing telescope.
 13:17: It would then look back at light lensed in the sun's gravitational field.


20170920: The Future of Space Telescopes
 11:00: ... about the tantalizing rumor that the LIGO Observatory had detected gravitational waves from the merger of a pair of neutron ...
 11:33: Nicholas Martino asks whether gravitational waves are redshifted by the expansion of the universe.
 12:26: As this happens, the stellar core succumbs to the gravitational crush and collapses incredibly quickly.


20170913: Neutron Stars Collide in New LIGO Signal?
 00:06: Last year, LIGO announced the detection of gravitational waves from the merger of two black holes.
 00:15: ... weeks ago, a new rumor emerged, that LIGO had for the first time spotted gravitational waves from the collision of a pair of neutron ...
 00:37: ... the Laser Interferometer Gravitational Wave Observatory, LIGO, detected gravitational waves from a pair of ...
 00:49: We now have an observatory that can explore the most extreme gravitational phenomena in the universe.
 02:32: We talk about the bizarre physics of these quantum and gravitational monsters in this video.
 02:55: In fact, the first real evidence of the existence of gravitational waves came from a pulsar.
 03:09: This binary pair stirs up spacetime in its vicinity, creating ripples that travel outwards as gravitational waves.
 03:17: And that gravitational radiation sucks energy from the orbiting system, causing the neutron stars to spiral inwards.
 03:30: The rate of loss of orbital energy exactly matches the expected rate of emission of gravitational radiation.
 03:38: Any neutron stars or black holes in close orbit with each other will eventually collide as they leave gravitational radiation.
 04:46: Smaller mass means weaker gravitational waves.
 05:37: ... in the final second before merger, while neutron stars ring at audible gravitational wave frequencies for at least several ...
 06:07: "Optical counterpart" means that there's a source of visible light associated with the gravitational wave.
 06:25: ... there's also the rumor that the Italian Gravitational Wave Observatory, VIRGO, also spotted the signal, which helps ...
 07:32: And the particular observing program that was triggered is one specifically intended for following up on gravitational wave detections.
 07:47: Someone in the know decided that this gamma ray burst was very likely associated with a gravitational wave.
 09:32: Seeing a gravitational wave signal from merging neutron stars would allow us to determine pretty exactly how much mass is lost in the merger.
 09:59: Black hole mergers are dark, so we have to infer almost everything from the gravitational waves alone.
 10:11: Comparing the EM and gravitational wave signatures will teach us a lot.
 11:42: As it happens, Curiosity Stream has a really excellent overview of LIGO and gravitational waves.
 11:49: "Gravitational Waves Rewinding Time" includes some fascinating behindthescenes footage at the observatories.
 14:38: ... can measure the tiny wobble in a star's motion caused by the planet's gravitational ...


20170830: White Holes
 00:50: ... xray binaries, even the center of our own Milky Way galaxy harbor these gravitational monstrosities, but the mathematics that predicts the existence of the ...
 03:49: Now, a real black hole forms from the gravitational collapse of a massive star's core.


20170816: Extraterrestrial Superstorms
 04:37: As they contract, gas giants convert gravitational potential energy into heat, which in turn powers the largest storms in the solar system.


20170810: The OneElectron Universe
 11:23: ... dark flow is real and assuming it's caused by a gravitational influence beyond the edge of the observable universe, then yeah, it no ...


20170802: Dark Flow
 00:08: It may be that much of the matter in the cosmos is drifting due to the ancient gravitational pull of something outside the observable universe.
 00:30: Galaxies whirl within the gravitational fields of giant clusters.
 07:26: Since 1973, we've noticed that galaxies in the local part of the universe seem to be drawn in that direction due to an unseen gravitational influence.
 07:50: ... or to two and a half billion light years at least, far beyond the gravitational reach of ...
 08:08: ... it's real, then the leading explanation is that it's a relic of a gravitational attraction towards something beyond the edge of the observable ...
 08:38: Things that are now beyond the cosmic horizon were close enough to affect us gravitationally.
 09:10: ... a region may have given our entire universe such a gravitational tug that even 13.7 billion years later, we still see a faint drift in ...


20170607: Supervoids vs Colliding Universes!
 04:05: A photon entering a matterrich galaxy cluster gets an energy boost as it falls into the cluster's gravitational well.
 04:13: But by the time the photon is on its way out, the expansion of the universe has actually stretched out the cluster, weakening its gravitational pull.


20170531: The Fate of the First Stars
 04:20: OK, physics time the cores of stars are under extreme pressure due to the gravitational crush of their great mass.


20170517: Martian Evolution
 04:17: A mother's pelvis needs to be able to withstand significant pressure that has nothing to do with the gravitational field.
 13:15: ... edge, of the sun due to the powers of their light bending in the suns gravitational ...


20170405: Telescopes on the Moon
 06:23: ... a cylindrical container of liquid is rotated into a gravitational field, the liquid assumes a smooth parabolic shape, exactly the shape ...
 10:52: You could transform the gravitational potential energy of things falling towards the event horizon into usable energy.
 11:03: Hydroelectric power plants on earth do it with the flow of space time that we experience as Earth's gravitational field.
 11:09: ... converts gravitational potential energy into kinetic energy but that kinetic energy is only ...


20170329: How Time Becomes Space Inside a Black Hole
 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.


20170301: The Treasures of Trappist1
 01:45: The planets live so close together that they all tug on each other gravitationally.
 01:52: The gravitational influence on each other allows us to figure out their masses, between 0.4 and 1.4 times Earth's mass.
 10:48: ... maximum size region of cloud can be before it fragments, because local gravitational collapse happens faster than pressure can equalize across the ...
 11:12: As you suggest, it's when inward gravitational forces and outward gas pressure are in equilibrium.


20170215: Telescopes of Tomorrow
 09:06: ... the distant universe as their brightnesses fluctuate due to the changing gravitational effect of nearby massive ...


20170202: The Geometry of Causality
 10:50: Janna Levin's "Black Hole Blues" is a wonderful take on the new window that gravitational waves are opening on our universe.
 13:46: We see that these xrays are stretched out as they climb out of the black hole's gravitational well.
 13:51: That gravitational redshift is the same thing as gravitational time dilation.
 14:13: ... said, it may be that parts of the accretion disks sometimes become gravitationally unstable and collapse, in which case you might get some weird ...


20170125: Why Quasars are so Awesome
 04:16: That gas descends into the waiting black hole's gravitational well and gains incredible speed on the way.


20170119: The Phantom Singularity
 00:39: Newton's equation gives you the gravitational force exerted between two masses, m1 and m2 that are a distance R apart.
 01:21: According to Newton's law, in order to fuel that infinite gravitational acceleration you need to get zero distance from an object's center of mass.
 03:02: But the gravitational singularity at the center of a black hole is a socalled real singularity, right?
 04:16: ... the gravitational field is too strong say, near a star or a black hole Newton's law ...
 06:30: In fact, it's 2 times the gravitational constant times the mass.
 07:00: This gives us the same infinite gravitational pull as the Newtonian singularity.
 07:05: And just as with the Newtonian case, this gravitational singularity can only exist if infinite densities are possible.


20170111: 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.
 04:14: It's the same tool that Henry Cavendish used to first measure the teensy tiny gravitational constant over 200 years ago.


20170104: How to See Black Holes + Kugelblitz Challenge Answer
 00:50: ... falling into the extreme gravitational well of a black hole will reach incredible speeds and temperatures, ...
 02:33: ... recent observations of gravitational waves from a pair of merging black holes by LIGO could be considered our ...
 04:02: These black holes occasionally pass in front of more distant background stars, gravitationally lensing the star's light.
 04:15: ... appear to split into two or four images as its light passes around the gravitational field of the black ...
 04:28: ... Horizon Telescope and microlensing studies, and of course, more LIGO gravitational waves observations, over the next few years, we'll have mapped the space ...
 10:26: Well, here, we're saved by Newton's shell theorem, which states that the gravitational force inside a perfectly symmetric shell is zero.


20161214: Escape The Kugelblitz Challenge
 04:42: Now, light has energy and so has a gravitational effect.
 05:22: ... inside of a spherically symmetric shell of mass or energy feels no gravitational force from that ...


20161208: What Happens at the Event Horizon?
 01:07: ... simplest black hole of Einstein's general theory of relativity purely gravitational, static, and eternal is a subtle and misunderstood ...


20161109: Did Dark Energy Just Disappear?
 00:52: They expected to see that this expansion rate was slowing down due to the gravitational effect of all of the matter in the universe.
 06:35: ... dark energy, and there are things that slow expansion, which is just the gravitational effect of regular energy, and that's mostly dark matter, but also stars, ...
 11:03: ... measure tells us that there has to be something out there countering the gravitational effect of matter and flattening the geometry of ...


20161019: The First Humans on Mars
 06:19: ... with a sloped, slightly curved outer wall so that the centrifugal and gravitational accelerations work together to give you the right direction of down on ...


20161012: Black Holes from the Dawn of Time
 00:25: LIGO's recent observation of gravitational waves from merging black holes is a stunning confirmation of this fact.
 01:32: Otherwise, there's no preferred direction for all that gravitational attraction.
 01:36: Also, the gravitational pull needs to be strong enough to overcome the expansion of the universe.
 05:07: For one thing, if these little knots of warped space time are everywhere, then they should produce obvious gravitational lensing.
 08:14: If it passed anywhere near the planetary system, the gravitational tug would disrupt the planet's orbits.
 08:40: If PBHs are closer to the mass of a large asteroid, then they're too low in mass and probably moving too fast to do any gravitational damage.


20160929: Life on Europa?
 02:42: We know that the tidal squeezing from Jupiter's gravitational field provides the energy that keeps Europa's ocean liquid.


20160824: Should We Build a Dyson Sphere?
 02:09: The sphere would not be habitable, having only a tiny gravitational pull at its surface, and that would be towards the sun.


20160727: The Quantum Experiment that Broke Reality
 12:25: Juno will figure that out by carefully mapping Jupiter's gravitational and magnetic fields.
 13:03: ... these bodies are closest together, they have the strongest gravitational pull on each other and that pull stops them from straying out of that ...


20160720: The Future of Gravitational Waves
 00:00: On June 15, the LIGO team announced their second detection of a gravitational wave.
 00:14: ... September 14, 2015, the Laser Interferometer Gravitational Wave Observatory, LIGO, detected the gravitational waves from the merger ...
 00:31: ... changes in the path lengths of the LIGO interferometer arms as the gravitational wave stretched and compressed the fabric of space as it passed ...
 00:54: This incredibly important observation was hailed at the time as representing the dawn of gravitational wave astronomy.
 01:02: However, that's only true if we ever detect another gravitational wave.
 03:20: ... already knew about the December signal when they announced the first gravitational wave detection back in ...
 03:38: ... actual fact, LIGO probably saw a third gravitational wave back in October but it wasn't quite strong enough to satisfy the ...
 04:07: Beyond the detection of gravitational waves, this is another awesome validation of the theory.


20160706: Juno to Reveal Jupiter's Violent Past
 02:23: In the wake of its intense gravitational field, it drags with it its own mini solar system of at least 67 moons and a faint ring system.
 02:34: That gravitational influence extends through the entire solar system.
 08:30: This amplified Jupiter's gravitational influence on Saturn, causing Saturn's eccentricity to increase.


20160622: Planck's Constant and The Origin of Quantum Mechanics
 11:37: Last week, we talked about gravitational lensing, and you guys asked all the good questions.
 13:13: ... like to know how we can really be confident measuring the mass of a gravitational lens, given we don't really know the composition of that ...
 14:06: Prasad Deshmukh and a few others asked, is the cosmic microwave background radiation gravitationally lensed?
 14:34: That's exactly the same type of swirliness that primordial gravitational waves should produce.
 14:45: Ed Eggermont wonders if gravitational waves are also subject to gravitational lensing.
 14:52: Gravitational waves are ripples in the fabric of space time, so they have to go where the space time goes.


20160615: The Strange Universe of Gravitational Lensing
 00:06: Much of the deep universe is shifted and magnified by the warping effect of gravitational lensing.
 02:11: ... of nearby stars due to the deflection of their light by the sun's gravitational ...
 02:46: ... touching that it assures us that we need not worry about the dangers of gravitational lensing, which is, of course, what we've come to call this ...
 02:57: The gravitational field of any massive object converges passing light rays, like a badly designed lens.
 03:15: When we look out there at the universe, we see gravitational lensing everywhere.
 03:30: ... their light travels through the deep gravitational wells of intervening galaxies and galaxy clusters, they are greatly ...
 04:19: Find that configuration, and we've mapped the gravitational field, the distribution of mass of the lens.
 05:07: You can see the nearby spiral galaxy, whose gravitational field bends spacetime to create these paths.
 06:13: ... passing through the starry lens galaxy brightens and dims due to the gravitational fields of individual stars in that lens in a process called ...
 06:43: Although this sort of obvious strong lensing is rare, the effects of gravitational lensing are everywhere.
 06:50: Weak gravitational lensing slightly warps the shapes of essentially all galaxies in the universe.
 07:36: Despite Einstein's pessimism, gravitational lensing has become an important staple in the astronomer's toolkit.
 07:50: Of course, the most extreme gravitational bending of light results in the most awesome of all astrophysical objects, the black hole itself.
 08:16: But just outside the event horizon, we find the most extreme gravitational lensing in the universe.
 08:58: This ultimate gravitational lensing has not yet been observed.
 09:33: I guess gravitational lensing is pretty cool.
 10:48: Same with trying to tunnel out of a gravitational field.


20160608: New Fundamental Particle Discovered?? + Challenge Winners!
 03:47: A highly speculative particle responsible for the transmission of the gravitational force.


20160601: Is Quantum Tunneling Faster than Light?
 05:38: Remember the LEGO interferometer that discovered gravitational waves?


20160525: Is an Ice Age Coming?
 02:14: ... was Serbian scientist Milutin Milankovitch who realized that the gravitational tug of Jupiter and Saturn would lead to three periodic shifts that might ...
 14:12: ... from a Newtonian perspective requires the invention of a new quantity gravitational potential energy in order to preserve energy ...


20160420: Why the Universe Needs Dark Energy
 00:52: ... of the universe and the resistance to this expansion due to the gravitational effect of everything it ...
 09:43: Within these regions, the shape of spacetime is dominated by the gravitational field of the densely packed matter.
 09:53: ... fact, you need to get millions of light years from the Milky Way for the gravitational field of the Milky Way and Andromeda to not dominate the shape of local ...
 10:28: ... of the universe does include dark matter, which we can measure by its gravitational effect in several independent ...


20160413: Will the Universe Expand Forever?
 02:45: ... by the time it almost stops moving, it will be so far away that Earth's gravitational pull will be close to ...
 03:14: As the apple rises, its kinetic energy, its energy of motion, is sapped by the gravitational field and converted into potential energy.
 03:27: There's a minimum kinetic energy that the apple needs in order to escape the energysucking gravitationalpotential well of the Earth.
 03:40: ... has an escape velocity that lets distant galaxies escape each other's gravitational ...
 05:17: It reflects the same balance between kinetic and gravitational potential energy that we saw in our rising apple.
 05:40: But that oomph is resisted by the gravitational effect of all the master and energy in the universe.
 05:53: So this second piece represents the capacity of the universe to slow itself down and is analogous to the gravitational potential energy.


20160406: We Are Star Stuff
 06:23: ... the core hot and puffed up, outflowing radiation pressure, resisting gravitational ...
 07:05: So that iron core, once formed, can do nothing to prevent its own gravitational collapse.
 09:27: ... will eventually spiral in as they radiate away their orbital energy in gravitational ...
 09:45: ... some also bursts out as gamma rays, as gravitational radiation, but also as a blast of newly formed heavy matter, including ...
 11:57: That stuff isn't necessarily true on a curved 2D surface like a ball, nor in curved 3D space, like within a gravitational field.


20160323: How Cosmic Inflation Flattened the Universe
 10:15: ... this is because dark matter doesn't really interact with itself except gravitationally. ...
 10:50: It just passes by with a tiny gravitational tug.


20160316: Why is the Earth Round and the Milky Way Flat?
 00:53: ... balance the tension, pressure, and torque resulting from the downward gravitational pull on all other parts of the ...
 02:34: ... of any shape and there's nothing else around, a surface of constant gravitational field is a ...
 03:15: It's held together by its own gravitational field, which conveniently also keeps me stuck to the surface.
 06:39: So a relatively solid, rocky planet will fracture and reshape itself into a sphere as long as its own gravitational field is strong enough.
 11:46: ... that speck had very similar densities, and so there was no net gravitational attraction towards our patch of the greater ...


20160309: Cosmic Microwave Background Challenge
 04:18: This coming Monday, March, 14th, I'll be participating in a public seminar on the new LIGO discovery of gravitational waves.
 04:29: If you're in the area and would like to attend, please RSVP to pbsspacetime@gmail.com with the subject line NYC Gravitational Waves.
 04:42: You'll learn way more about gravitational waves than on any YouTube show.


20160302: What’s Wrong With the Big Bang Theory?
 10:51: For example, the solar system is better described with the Schwarzschild metric, dominated by the sun's gravitational field.


20160224: Why the Big Bang Definitely Happened
 08:40: ... couple of weeks ago, the LIGO team announced the very first detection of gravitational ...
 09:41: ... kind of weird that Advanced LIGO was turned on just in time to catch the gravitational waves from the merger of black ...
 11:39: ... quote Lawrence Stanley, "OK, but until the discovery of gravitational waves can lower my mortgage and reduce the price of gas at the pump, it ...


20160217: Planet X Discovered?? + Challenge Winners!
 01:03: It looks like it's been dragged out of the Kuiper Belt by the gravitational attraction of something.
 01:25: They suggested the possibility of a large planet out there, dragging on these objects with its gravitational pull.


20160211: LIGO's First Detection of Gravitational Waves!
 00:05: Gravitational waves have been directly detected for the very first time.
 00:37: On September 18, the Laser Interferometer GravitationalWave Observatory switched back on after three years of upgrades.
 00:49: ... estimates predicted that it should certainly detect the passage of gravitational waves, of ripples in the fabric of spacetime caused by extreme ...
 01:19: ... soon after the detection, we put together a video explaining what gravitational waves are, how they're formed, and exactly how advanced LIGO detects ...
 01:53: Any orbiting pair of massive objects generates gravitational waves.
 01:57: ... massive objects, through orbiting extremely close together, produce gravitational waves strong enough for us to detect, at the ...
 02:25: These super dense objects produce serious gravitational radiation.
 02:30: But gravitational waves carry energy, which is sapped from the orbital energy of the system.
 02:45: The amount of energy being lost in these systems is exactly what we predict it should be if caused by gravitational radiation.
 02:51: And so this was a very convincing but indirect verification of gravitational waves.
 03:07: But as the cores get closer, the gravitational radiation becomes extremely intense.
 04:57: See, gravitational waves are inevitable if the theory is correct.
 06:13: ... LIGO is sensitive to gravitational waves at frequencies produced by merging black holes and neutron stars, ...
 07:03: This is a really, really big deal, and it marks the beginning of the era of gravitational wave astronomy.


20160113: When Time Breaks Down
 05:20: But Einstein's equivalence principle tells us that a frame suspended in a gravitational field is indistinguishable from an accelerating frame.
 05:29: And so clocks must also tick slower the deeper they are in their gravitational field.
 05:35: This is the gravitational time dilation of general relativity.


20160106: The True Nature of Matter and Mass
 01:22: Let's ignore the gravitational effect of mass for the moment, and just consider mass as the degree to which an object resists being accelerated.
 06:15: They have what we call gravitational mass.
 06:17: But how does the inertial mass of our photon box end up translating to gravitational mass?
 06:33: ... in space is fundamentally the same thing as the feeling of weight in a gravitational ...
 06:55: Same with the compressed spring it's harder to accelerate than a relaxed one, and it also feels heavier in a gravitational field.
 07:04: In fact, the equivalence principle tells us that the gravitational mass of an object and the inertial mass are the same thing.
 07:11: But mass doesn't just respond to a gravitational field.
 07:39: So confined massless particles generate a very real gravitational field.


20151216: The Higgs Mechanism Explained
 08:49: Gareth Dean asks about this whole thing about using gravitational waves to turn up the core temperature of a star.
 08:55: ... so gravitational waves carry a lot of energy, and some of it can get dumped into a star ...
 09:05: ... holes should have temperatures raised by an observable amount by the gravitational ...


20151209: How to Build a Black Hole
 01:20: If you get impatient, you can turn up the core temperature by bombarding it with gravitational waves.
 04:32: ... is incredibly strong strong enough to initially resist the insane gravitational crush of a neutron ...
 11:27: ... Sny and others wonder whether, instead of the gravitational tractor, you could just land a spacecraft on the asteroid and push it ...
 11:35: ... actually, it's going to take the same amount of fuel to pull by a gravitational tractor as it would to push an asteroid by landing a rocket on it, ...
 12:05: The gravitational tractor gets around these issues.


20151125: 100 Years of Relativity + Challenge Winners!
 01:51: You were tasked with assessing the plausibility of saving the Earth with a gravitational tractor.
 01:57: ... Apophis 25,000 kilometers ahead of its would be location using only the gravitational attraction of the ...
 02:57: ... gravitational force between the spacecraft and Apophis is providing all of the ...
 04:33: ... part of the calculation, which is a big part of the advantage of the gravitational ...


20151118: 5 Ways to Stop a Killer Asteroid
 06:07: Number four, the weirdest deflection option a gravitational tractor.
 07:38: A loose, gravitationallybound rubble pile is obliterated, while a single rock will be fragmented.


20151111: Challenge: Can you save Earth from a Killer Asteroid?
 00:51: You've been chosen to assess the possibility of deflecting Apophis with a gravitational tractor.
 01:03: ... spacecraft will hover just in front of the asteroid and act as a gravitational tractor, slowly increasing the asteroid speed by the mutual ...


20151028: Is The Alcubierre Warp Drive Possible?
 06:23: ... interferometer, like a mini version of the one being used to detect gravitational waves, To measure the tiny changes in path length created by a warp ...
 07:09: ... it so on the next episode of "Space Time." Last week, we talked about gravitational waves, and whether the advanced LIGO Observatory has maybe seen ...
 07:31: It'll be an orbiting gravitational wave observatory designed to detect much higher frequency gravitational waves than advanced LIGO.
 08:01: ... this was the much hyped gravitational wave detection based on polarization anisotropies in the cosmic ...


20151022: Have Gravitational Waves Been Discovered?!?
 00:03: Gravitational waves are the last prediction of Einstein's Theory of General Relativity.
 00:29: Instead, mass warps the fabric of 4D spacetime, leading to what we see as gravitational motion.
 00:41: There's the deflection of light that we see as gravitational lensing.
 00:45: There's the slowing of time in gravitational fields.
 01:03: However, there's one last, incredible prediction that has never been directly observed gravitational waves.
 01:19: However, the analogy can give us a sense of what a gravitational wave really is.
 01:37: Same deal with gravitational waves.
 01:39: ... a mass through space in the right way, and you produce gravitational ripples an outflowing fluctuation of expanding and contracting ...
 02:08: ... propagate at a certain speed determined by the stiffness of the rubber, gravitational waves and indeed, gravity itself propagate according to the ...
 02:49: ... waves which are all simple, updown, longitudinal waves gravitational waves are what we call quadrupole ...
 03:11: Well, let's first think about all the sorts of things that might produce detectable gravitational waves.
 03:16: ... most insane gravitational phenomena in the universe neutron stars or black holes inspiraling ...
 03:46: Now, this power depends on how far away our catastrophic gravitational event is.
 04:07: And so it's no wonder that gravitational waves remain the only major prediction of GR without a direct measurement.
 04:20: Gravitational waves carry energy.
 04:22: ... massive objects orbit each other close enough to produce a lot of this gravitational radiation, their obits will lose energy and decay, causing them to ...
 04:36: And the results agreed exactly with the rates of gravitational radiation predicted by General Relativity.
 05:33: ... signal is seen, but if a gravitational wave passes by, it will shrink one of those paths and lengthen the ...
 06:12: So how do we tell that it's a gravitational wave?
 06:40: Well, between 2002 and 2010 when it ran, it found zero no gravitational waves at all.
 07:24: ... times more volume of the universe much more chance of spotting crazy gravitational ...


20151015: 5 REAL Possibilities for Interstellar Travel
 12:26: Ed Stephan asks why we're even talking about gravitational waves when none have ever been observed.
 12:32: ... in the meantime, in pointing out the indirect detection of gravitational waves, Garreth Dean delivers the amazing quote, "So we haven't seen a ...


20151007: The Speed of Light is NOT About Light
 08:57: So lights or photons, also gravitational waves and gluons all have no mass.


20150930: What Happens At The Edge Of The Universe?
 08:09: And that mass predicts the deflection angle for light passing the Sun perfectly, that is its gravitational lensing effect.
 08:36: But it doesn't interact with itself in any other way besides gravitationally.


20150923: Does Dark Matter BREAK Physics?
 00:47: ... I want to give you completely independent evidence for its existence, gravitational ...
 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.
 02:46: But we can see these guys, at least sort of, with gravitational lensing.
 05:19: Again, gravitational lensing.
 05:45: It has to be pretty slow moving, or cold, because we know that dark matter clumps together gravitationally to build galaxies and clusters.


20150827: Watch THIS! (New Host + Challenge Winners)
 00:15: ... key to the Newtonian challenge was getting an expression for the gravitational force on the particle that's falling through the planet when it's a ...
 00:50: ... by drawing a formal algebraic analogy between the gravitational equation on the one hand, and the spring equation on the other, you can ...
 03:39: It's a gravitationallylensed protogalaxy.


20150819: Do Events Inside Black Holes Happen?
 01:23: This is called gravitational time dilation and the same thing happens around Earth, just to a lesser degree.
 06:54: Misconception two black holes are black because not even light can escape their gravitational pull.
 13:33: ... are gravitational effects from the Sun and Moon that do the same thing, but they're ...


20150812: Challenge: Which Particle Wins This Race?
 01:56: When the second particle is inside the planet, how do you calculate the gravitational force on it?
 02:15: ... any given location inside the planet, the particle will feel only the gravitational force from whatever mass is closer to the center of the planet than the ...
 02:26: ... geometry about spheres, you should be able to get a formula for the gravitational force on the particle when it's a distance little r from the center of ...
 02:40: ... expression for the gravitational force on the second particle when it's inside the planet should ...
 02:50: ... fact, drawing an algebraic analogy between the gravitational and nongravitational situations is actually the key to figuring out the ...


20150805: What Physics Teachers Get Wrong About Tides!
 01:28: They aren't actually being lifted or stretched by that gravitational differential.
 12:39: ... that basically give you Newton's laws of motion as if there were a gravitational force are just the pieces of the geodesic equation that involve "time" ...


20150729: General Relativity & Curved Spacetime Explained!
 00:27: ... frame, a freely falling apple accelerates down because it's pulled by a gravitational ...
 00:45: ... just get a false impression of a gravitational force downward for the same reason that a train car accelerating forward ...
 06:27: Thus, the very existence of gravitational time dilation, regardless of its degree, requires that spacetime be curved.
 07:50: ... or pretty much anything else that you would otherwise attribute to a gravitational ...
 08:22: So we often think in Newtonian gravitational terms, because it's easier, and because the resulting errors are usually small.


20150702: Can a Circle Be a Straight Line?
 00:16: ... general relativity, objects that fall or orbit aren't being pulled by a gravitational force, they're simply following straight line constant speed paths in a ...
 01:57: We'll end up seeing that all the supposedly gravitational effects on motion can be accounted for just by the geometry of spacetime.


20150624: The Calendar, Australia & White Christmas
 01:04: So the gravitational pull of the sun is slightly stronger on the slightly closer half, causing a net torque on the Earth like this.


20150617: How to Signal Aliens
 09:57: Yeah, but buoyancy only exists in the presence of a supposed gravitational field.
 10:02: ... get less dense as you rise in the opposite direction of a gravitational field, because the fluid that's lowered down has to hold up the weight ...


20150603: Is Gravity An Illusion?
 00:00: ... PLAYING] Isaac Newton said that an apple falls because a gravitational force accelerates it toward the ground, but what if it's really the ...
 00:18: ... to Isaac Newton, the ground can be considered at rest, Earth applies a gravitational force to the apple, and that force causes the apple to accelerate ...
 00:26: But according to Einstein, there's no such thing as a gravitational force.
 03:36: So in the train car's frame, which is accelerating forward, it's as if there's an additional gravitational field that points backward.
 03:44: So accelerated frames of reference mimic a gravitational field in the opposite direction of the frames acceleration.
 03:51: ... you combine that extra fake gravitational field with the actual gravitational field of the Earth, which points ...
 04:43: ... that with Earth's real gravitational field and it's as though the total gravity inside the car points down ...
 06:35: ... zero G because the downward acceleration acts like a fake extra upward gravitational field that, from the perspective of the box, just happens to exactly ...
 07:27: ... ground that's accelerating upward and what we've always been calling a gravitational force is an artifact of being in an accelerated frame of ...


20150527: Habitable Exoplanets Debunked!
 06:50: If everyone on Earth picked up a hammer at the same time, by how much would Earth's mass increase due to the excess gravitational potential energy?
 07:01: ... more gravitational potential energy in the hammers, but that was previously stored as ...


20150520: The Real Meaning of E=mc²
 03:17: You can think of it as an indicator of how hard it is to accelerate an object or an indicator of how much gravitational force an object will feel.
 05:37: ... potential energy will drop when they get closer together, just like your gravitational potential energy drops when you get closer to the surface of Earth, ...
 08:35: ... second configuration has more gravitational potential energy than the first because the second block is higher up, ...


20150429: What's the Most Realistic Artificial Gravity in SciFi?
 01:10: Or you need something exotic, like gravitationally repulsive negative mass, which doesn't exist.
 06:53: So gravitationally, "Halo" checks out.


20150408: Could You Fart Your Way to the Moon?
 06:23: The Cosmos asked whether gravitational forces are about the mass or density of the gravitational source.
 06:32: ... ripped apart by the tidal forces due to a first object, which is due to gravitational differentials, that turns out to depend on the density of that second ...


20150401: Is the Moon in Majora’s Mask a Black Hole?
 02:23: ... might think this implies that the gravitational pull on the rocks due to the moon exceeds the gravitational pull from ...
 05:39: ... denser mass at the center, the material around it might have enough of a gravitational scaffolding, so to speak, to achieve neutron star densities with less ...
 05:50: So to serve as a gravitational seed, we need something incredibly small and incredibly dense, even denser than a neutron star.


20150318: Can A Starfox Barrel Roll Work In Space?
 09:13: ... wanted to know how much energy it would take, not just to overcome the gravitational attraction between all the matter on Earth, but to split apart every ...


20150311: What Will Destroy Planet Earth?
 02:44: Well, Earth and Mars' field gravitational pulls not just from the sun, but also from the other plants and from big asteroids too.
 04:27: In the process, the sun will lose a lot of mass and a lot of gravitational pull, causing Earth's orbit to actually grow.


20150225: How Do You Measure the Size of the Universe?
 00:55: That's the part that we, in principle, can see with light or gravitational waves.
