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	2022-12-14: How Can Matter Be BOTH Liquid AND Gas? 04:37: ... pulls liquids into spherical blobs in freefall or in the absence of gravity, while under gravity they take the shape of the bottom of their ...
	2022-11-23: How To See Black Holes By Catching Neutrinos 01:55: But perhaps the most characteristic property of the neutrino is that they only interact via the weak nuclear force and gravity.
	2022-10-19: The Equation That Explains (Nearly) Everything! 02:21: ... it is with the phase invariance of U(1). You may have noticed I skipped gravity. We’re still working on that one, although it may have nothing to do with ...
	2022-10-12: The REAL Possibility of Mapping Alien Planets! 00:03: ... light to a magical point out there in space  where the Sun’s own gravity turns it into a   gigantic lens. What could such a  ... 04:12: ... Einstein’s general theory of relativity   tells us that gravity is due to curvature in the fabric of spacetime due to massive ... 00:03: ... light to a magical point out there in space  where the Sun’s own gravity turns it into a   gigantic lens. What could such a  ...
	2022-09-21: Science of the James Webb Telescope Explained! 14:28: ... by about 20 orders of magnitude and developed into a theory of quantum gravity. ...
	2022-09-14: Could the Higgs Boson Lead Us to Dark Matter? 01:33: We know that there’s some source of gravity out there in the universe NOT caused by the particles of the standard model.
	2022-08-17: What If Dark Energy is a New Quantum Field? 00:00: ... what it is - just that it competes against the inward-pulling effect of gravity. And it’s winning - it looks like the universe will expand forever, at an ... 02:31: ... effect of its negative pressure, it also produces regular attractive gravity due to its positive energy density, just like regular matter and energy ... 03:33: ... So its antigravitational effect not only overcomes its own positive gravity, but also the positive gravity of all other matter. And it’s only getting ... 12:31: ... negative pressure still dominates over the inward pull of regular gravity, so expansion still accelerates - but that expansion is restricted to ...
	2022-06-22: Is Interstellar Travel Impossible? 17:43: ... force combine, but almost certainly also the strong force and perhaps gravity ... 18:03: And we even have ideas for black holes in theories of quantum gravity - for example, the fuzzball of string theory, which we did an episode on.
	2022-06-15: Can Wormholes Solve The Black Hole Information Paradox? 00:26: ... of relativity, from which followed our  modern description of gravity, space and time in   general relativity. Now, there’s an ...
	2022-05-25: The Evolution of the Modern Milky Way Galaxy 10:34: ... years or so when it punches through the   Milky Way’s disk its gravity hits like a  hammer. Actually, more like a drum ...
	2022-05-18: What If the Galactic Habitable Zone LIMITS Intelligent Life? 06:56: ... our local lump started to pull itself   together under its own gravity. Fragments broke  off to collapse into galaxies. Fragments ...
	2022-05-04: Space DOES NOT Expand Everywhere 01:24: ... influences - planets orbit stars, stars orbit in the mutual gravity of their galaxies, galaxies whirl and collide in local groups and ... 05:19: ... Does the underlying expanding sphere fight against the inward pull of gravity? Is the space inside, say, a galaxy growing but overcome by the ... 07:12: ... growth during inflation, then the expansion slows under the influence of gravity, then dark energy takes over and expansion accelerates ... 08:34: ... and the spacetime grids they trace. But in sufficiently dense regions gravity won and there the only evidence of the greater expansion comes from the ... 08:51: ... of, if anything. That’s the province of a long-sought theory of quantum gravity. ...
	2022-04-20: Does the Universe Create Itself? 15:24: ... we didn’t have dark energy. If you just consider the positive effect of gravity, then the spatial geometry dictates the final fate. But dark energy ...
	2022-03-30: Could The Universe Be Inside A Black Hole? 00:58: Collapse any chunk of matter far enough and it gets stuck in its own gravity. 08:36: ... thing collapses under its own gravity and an event horizon forms around it, but within the collapsing cloud ...
	2022-03-23: Where Is The Center of The Universe? 02:57: His general theory of relativity explains gravity as the warping of space and time due to the presence of mass and energy. 03:03: Explains gravity as the warping of space and time due to the presence of mass and energy. 10:45: Stand by for our theory of quantum gravity to resolve that one.
	2022-03-08: Is the Proxima System Our Best Hope For Another Earth? 17:27: ... yes, one field that might be able to do this is gravity, in which case the wavefunction is being “hit” by the non-linearities ... 17:38: And on the subject of gravity, Jan Wester asks why the curvature of spacetime can’t be in a superposition. 18:22: Resolving that has been the major work of all of our searches for quantum gravity and theories of everything. 17:38: And on the subject of gravity, Jan Wester asks why the curvature of spacetime can’t be in a superposition.
	2022-02-23: Are Cosmic Strings Cracks in the Universe? 10:09: ... of background light sources due to the space-time warping effect of gravity.   When a massive object sits between  us and a distant light source, ...
	2022-02-16: Is The Wave Function The Building Block of Reality? 08:32: ... already gave us a perfectly good source of wave function collapse: gravity. ... 08:55: ... What causes the transition from quantum to classical? And 2. Why can’t gravity be quantized like the other forces. All of the collapse models attempted ... 09:25: ... mechanics rules when things are small, but add enough mass, and the gravity of the system will cause it to rapidly decohere into a classical object. ... 11:09: ... a quantum wave function will be randomly tossed about and jostled by gravity or some other collapsing field. If the quantum object happens to be ... 14:42: Last time we tackled a question of utmost gravity. Literally. How does gravity itself escape the inescapable gravity of a black hole. 08:55: ... and Penrose’s model could answer 2: gravity can’t be quantized because gravity isn’t quantum. They proposed that gravity and the three quantum forces are ... 14:42: Last time we tackled a question of utmost gravity. Literally. How does gravity itself escape the inescapable gravity of a black hole.
	2022-02-10: The Nature of Space and Time AMA 00:03: ... try to figure it out the emerging generations of theories of quantum gravity theories of the theme some of them try to answer this theory doesn't ...
	2022-01-27: How Does Gravity Escape A Black Hole? 00:17: Fact: gravity travels at the speed of light. 00:27: How does gravity escape a black hole? 00:35: ... the equations behind his general theory of relativity, which describe gravity not as a traditional force, but rather in terms of the curvature of the ... 01:16: One of them is that gravity itself has a speed. 02:22: But this “speed of gravity” also tells us how quickly a regular gravitational field changes. 02:56: ... gravity travels at the speed of light, and all of the mass of a black hole is ... 03:12: To answer this we’re going to look at gravity in two completely different ways. 03:17: First we’ll see what Einstein has to say on the matter, and then we’ll go deeper, into the speculative realm of quantum gravity. 03:27: There’s no question here - a black hole’s gravity doesn’t care about the event horizon at all. 03:42: ... example, when Earth feels the pull of the Sun’s gravity - it’s not directly interacting with the Sun itself, it’s interacting ... 04:24: ... there’s another way to think about the action of gravity: instead of a stretching spacetime, we can think about space as flowing ... 04:46: A close analogy to this picture of gravity is a river flowing towards a waterfall. 05:24: Gravity works like the rubber sheet or the flowing river. 05:54: ... that general relativity needs to be replaced by a theory of quantum gravity to explain the behavior of gravity in these ... 06:03: So can gravity escape from a “real” black hole of quantum gravity? 06:28: In theories of quantum gravity, the gravitational force should probably also have a mediating particle - usually called the graviton. 06:42: If gravity is really communicated by a particle, how does that particle escape the event horizon? 06:47: Actually, even in this picture, the event horizon has no way to halt the force of gravity. 07:33: ... if gravity is really mediated by virtual gravitons, then those gravitons don’t ... 08:39: ... argument, and this one works whether we’re talking about the classical gravity of Einstein or some deeper theory of quantum ... 10:06: ... gravity is communicated by the curvature of spacetime or by virtual gravitons, ... 11:53: To sum up - don’t mess around near black holes hoping that the event horizon will protect you from the black hole’s gravity. 03:42: ... example, when Earth feels the pull of the Sun’s gravity - it’s not directly interacting with the Sun itself, it’s interacting only ... 03:27: There’s no question here - a black hole’s gravity doesn’t care about the event horizon at all. 00:27: How does gravity escape a black hole? 06:03: So can gravity escape from a “real” black hole of quantum gravity? 00:17: Fact: gravity travels at the speed of light. 02:56: ... gravity travels at the speed of light, and all of the mass of a black hole is hidden ... 05:24: Gravity works like the rubber sheet or the flowing river.
	2022-01-19: How To Build The Universe in a Computer 01:49: The light from each bulb was its gravity - felt more strongly close to the bulb, and dropping away with the square of distance, just like gravity. 03:17: For 3 or more bodies there  is no simple set of equations   describing their future evolution under gravity. 03:53: In an N-Body simulation Newton’s laws of motion and gravity are applied over a series of time steps. 05:56: Remember, the strength of gravity drops off with distance squared. 07:41: These mesh codes are useful for systems of particles interacting under gravity. 01:49: The light from each bulb was its gravity - felt more strongly close to the bulb, and dropping away with the square of distance, just like gravity. 05:56: Remember, the strength of gravity drops off with distance squared.
	2021-12-29: How to Find ALIEN Dyson Spheres 06:37: ... flow of fusion-generated energy balances the inward crush of its own gravity. ...
	2021-12-20: What Happens If A Black Hole Hits Earth? 01:23: ... was smoothly spread out with only tiny density fluctuations. And so gravity had no strongly preferred direction to collapse towards. The expanding ... 06:02: ... enters the atmosphere. In the immediate surroundings of any black hole, gravity accelerates matter to incredible speeds. Near the event horizons, ... 06:35: ... causes an outward pressure that partly counters the black hole’s intense gravity. Try to feed a black hole too fast and it starts to blast away its own ... 09:24: ... PBH passing close to the Earth on a near miss - but even after years of gravity monitoring none of these seems to have shown ... 06:02: ... enters the atmosphere. In the immediate surroundings of any black hole, gravity accelerates matter to incredible speeds. Near the event horizons, particles collide ... 09:24: ... PBH passing close to the Earth on a near miss - but even after years of gravity monitoring none of these seems to have shown ...
	2021-12-10: 2021 End of Year AMA! 00:02: ... this on slow but it's gone so fast uh does quantum does loop quantum gravity attempt to explain dark energy uh i think so i think so i think blue ...
	2021-11-17: Are Black Holes Actually Fuzzballs? 04:23: The impossibility of the central singularity is the most obvious place where we need a theory of quantum gravity. 04:32: A theory of quantum gravity would have really helped Stephen Hawking in deriving his eponymous radiation. 04:49: ... its effect on the surrounding quantum fields, which only worked if the gravity at the horizon was relatively weak, in which case quantum gravity ... 05:09: ... gravity starts to get quantum even above the event horizon, then it may be ... 05:22: And it turns out that our most advanced theory of quantum gravity can do this quite neatly. 08:26: If you were to dial up the strength of gravity, black holes would get bigger. 08:32: That’s different to pretty much everything else in the universe, which are crunched down to smaller size if you increase the power of gravity. 08:39: This property of black holes is actually quite hard to reproduce in theories of quantum gravity. 08:45: ... that formed the black hole would increase in size as the strength of gravity ... 09:39: ... amazing element of the fuzzball paradigm is the discovery that quantum gravity effects might not just be important at the center of the black hole but ... 09:52: The ability for strings to maintain structure in this extreme gravity comes down to an effect specific to string theory called fractionation. 08:26: If you were to dial up the strength of gravity, black holes would get bigger. 04:49: ... if the gravity at the horizon was relatively weak, in which case quantum gravity effects shouldn’t play a ... 09:39: ... amazing element of the fuzzball paradigm is the discovery that quantum gravity effects might not just be important at the center of the black hole but instead ... 04:49: ... if the gravity at the horizon was relatively weak, in which case quantum gravity effects shouldn’t play a ... 08:45: ... that formed the black hole would increase in size as the strength of gravity increased. ... 05:09: ... gravity starts to get quantum even above the event horizon, then it may be possible to ...
	2021-11-10: What If Our Understanding of Gravity Is Wrong? 00:03: What if there is no such thing as dark matter.   What if our understanding  of gravity is just wrong? 00:24: ... fling themselves apart - assuming  they are held together by the gravity of their visible mass ... 00:36: They would need at least 5 times as much  matter to provide the gravity needed to hold these galaxies together. 00:42: ... the gravity of visible matter is also way too weak to hold galaxy clusters together, ... 01:22: The expected rotation rates of galaxies come  from applying our laws of gravity based on the observed mass. 01:31: Or the laws of gravity could be wrong. 01:39: ... dark matter, others have been hunting for an alteration to our theory of gravity that can explain the effect of dark matter without the actual ... 02:02: ... drops off with the square of distance from  the mass producing that gravity. ... 02:11: In most galaxies, stars are somewhat concentrated  towards the centers, which means gravity should weaken towards the outskirts. 02:46: But what if gravity doesn’t obey Newton’s law of gravity? 02:52: ... - there you need his general theory  of relativity, which explains gravity as the curvature in the fabric of space and time  rather than just ... 03:08: But Einsteinian gravity looks exactly like Newtonian gravity when gravitational fields get weak. 03:18: What if Newtonian gravity breaks down  both for very strong AND very weak fields? 03:53: ... to either  Newton’s law of universal gravitation - in which case gravity has a minimum strength - or by a modification to Newton’s 3rd law of ... 05:22: You still need about 20% of the current dark matter requirement to explain all the gravity we see in clusters. 06:10: ... it does what it was designed to do - it reproduces good ol’ Newtonian gravity. ... 08:29: Bekenstein and Milgrom achieved this  by adding a second field to gravity. 09:32: ... 2005 Bekenstein introduced TeVeS, for Tensor  Vector Scalar gravity - based on the fact that it describes gravity with three fields - a ... 10:29: ... that tells us how matter pulled itself together under its  own gravity at the earliest ... 11:12: But if dark matter isn’t real, and regular matter controls gravity completely, then no structure should have been able to form at those early times. 12:25: Modified gravity theories still can’t explain the Bullet Cluster - and I don’t have time to get into that and we’ve covered it before. 12:45: ... the Bullet Cluster might be the most awkward result  for modified gravity ... 09:32: ... 2005 Bekenstein introduced TeVeS, for Tensor  Vector Scalar gravity - based on the fact that it describes gravity with three fields - a ... 01:22: The expected rotation rates of galaxies come  from applying our laws of gravity based on the observed mass. 03:18: What if Newtonian gravity breaks down  both for very strong AND very weak fields? 11:12: But if dark matter isn’t real, and regular matter controls gravity completely, then no structure should have been able to form at those early times. 02:46: But what if gravity doesn’t obey Newton’s law of gravity? 12:45: ... the Bullet Cluster might be the most awkward result  for modified gravity folks. ... 00:36: They would need at least 5 times as much  matter to provide the gravity needed to hold these galaxies together. 12:25: Modified gravity theories still can’t explain the Bullet Cluster - and I don’t have time to get into that and we’ve covered it before. 02:52: ... Einstein found that Newtonian gravity  breaks down when the gravitational field gets too strong - there you ...
	2021-11-02: Is ACTION The Most Fundamental Property in Physics? 05:52: ... of Relativity, which, as we’ve discussed before, describes the force of gravity in terms of the bending of the fabric of space and time. One of ...
	2021-10-20: Will Constructor Theory REWRITE Physics? 05:11: We use that state as the input, apply the laws of gravity and motion - and we find the output state - that the apple fell to the ground. 08:07: For example Chiara Marletto has used constructor theory to describe a scenario for testing whether gravity is quantum in nature. 08:16: And we certainly don’t have a mechanistic theory for quantum gravity. 09:35: ... if we could design an experiment that showed that gravity could induce entanglement between separated qubits, then gravity has ... 09:47: This is cool because it gives us an experimental test of quantum gravity that has absolutely no dependence on a particular theory of quantum gravity.
	2021-10-05: Why Magnetic Monopoles SHOULD Exist 18:01: Or maybe you could just use USBC - they’re spin-2 bosons like gravitons, so easily understood with a basic theory of quantum gravity.
	2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe 03:27: ... thin shell 10cm above the star’s surface. This is due to the insane gravity at that surface - which I’ll come back to. Once we’ve landed on the ...
	2021-09-07: First Detection of Light from Behind a Black Hole 06:52: One - it’s pouring in, rivers of gas dragged down by the black hole’s gravity.
	2021-08-03: How An Extreme New Star Could Change All Cosmology 06:51: ... is to escaping the atom. Electrons are bound to the white dwarf by gravity, but they still have discrete energy levels. A forming white dwarf will ... 07:24: ... closer together until there’s enough pressure to resist the extra gravity - so the original matter contains a smaller volume. But that doesn’t ... 17:08: ... on scales from stars to galaxies - they’re still much, much weaker than gravity. Some people also hopped on to imply that with this episode I’d validated ... 07:24: ... closer together until there’s enough pressure to resist the extra gravity - so the original matter contains a smaller volume. But that doesn’t ... 17:08: ... most powerful of all mutants? He should have been able to control all gravity - not just metal stuff. Personally, that’s enough evidence for me - but if ...
	2021-07-21: How Magnetism Shapes The Universe 01:03: But for all its importance, gravity is a bit boring. 01:16: Magnetism is one half of electromagnetism, one of the four fundamental forces alongside gravity. 01:22: Magnetism shares a property with gravity that none of the other forces have - it manifests on enormous scales. 12:45: In some ways they’re the curse of the astrophysicist because they’re so tricky to model - far more so than simple-old gravity.
	2021-07-07: Electrons DO NOT Spin 15:31: ... of time, because that moment lost in our ignorance about quantum gravity and inflation and whatever  other crazy theory we haven’t figure ...
	2021-06-23: How Quantum Entanglement Creates Entropy 00:27: ... paradox—a solution that may one day unite quantum physics with gravity. ... 16:39: ... The answer is yes - and various people  have tried. Loop quantum gravity is a   good example - but for that to work the  ...
	2021-06-16: Can Space Be Infinitely Divided? 10:55: ... - but we just don’t know in what way. We need a theory of quantum gravity to answer this.   We’ll come back to what the contending ...
	2021-06-09: Are We Running Out of Space Above Earth? 02:50: The movie Gravity depicted this domino-chain of destruction as unfolding over minutes to hours.
	2021-05-25: What If (Tiny) Black Holes Are Everywhere? 01:57: Now to do this properly, you really need a theory of quantum gravity, which we don’t even have now and certainly didn’t in 1974. 04:49: At that point you need a proper theory of quantum gravity to describe the process.
	2021-05-11: How To Know If It's Aliens 14:48: ... Randlepp asks whether understanding quantum gravity might be helpful for developing warp drives. Good insight. All this warp ...
	2021-04-21: The NEW Warp Drive Possibilities 11:07: Both of these papers are peer reviewed and published in the reputable journal Classical and Quantum Gravity.
	2021-04-13: What If Dark Matter Is Just Black Holes? 00:44: ... are trying to find holes in Einstein’s theory of gravity - the general theory of relativity - that might explain dark matter’s ... 04:07: ... density fluctuations in the cosmic microwave background tell us that the gravity of dark matter was pulling matter together long before the first stars ... 00:44: ... are trying to find holes in Einstein’s theory of gravity - the general theory of relativity - that might explain dark matter’s ...
	2021-04-07: Why the Muon g-2 Results Are So Exciting! 00:45: For one thing, it doesn't explain gravity. 00:47: In fact, it doesn't play nice with Einstein's entire theory of gravity, which itself is clearly right in its own way.
	2021-03-16: The NEW Crisis in Cosmology 17:08: ... of you commented that this whole  gravity bending light thing might explain   why stormtroopers have ...
	2021-03-09: How Does Gravity Affect Light? 00:00: We know that gravity exerts its pull on light, and we have an explanation for why. 00:13: So what is the true connection between light and gravity, or is truth, in fact, entirely relative? 00:25: Gravity bends the path of light. 01:10: They assumed that light could be slowed down, and that light experiences a force of gravity in the same way that a massive object does. 01:17: ... assumed that Isaac Newton’s theory of gravity was the full picture, and that light behaves like any other particle in ... 01:34: We now know that both gravity and light are much weirder than Newton thought. 01:38: ... in recent episodes, when we saw that what we experience as the force of gravity is mostly due to the way mass warps the flow of ... 01:52: And yet general relativity demands that gravity does affect light, in ways eerily close to the predictions of Mitchell and Cavendish. 02:00: The really hard part is understanding the why of it - what is really happening when light interacts with gravity. 02:14: ... due to being in an accelerating reference frame and the downward pull of gravity of the same ... 02:26: Or of the sense of weightlessness in freefall in a gravitational field versus the weightlessness felt in the absence of gravity. 05:02: ... to his international fame - the deflection of the path of light by gravity. ... 05:32: They have to see the light travel in straight line in the absence of any gravity. 06:57: ... none of our intuitive explanations say that it should be deflected by gravity. ... 11:28: The number he got was exactly twice the deflection calculated by Cavendish based on Newton’s gravity. 12:08: ... you solve Einstein’s equations in a different way, you can show that gravity is due to a free-falling waterfall of space, rather than a gradient in ... 00:25: Gravity bends the path of light. 00:00: We know that gravity exerts its pull on light, and we have an explanation for why.
	2021-02-24: Does Time Cause Gravity? 00:15: I just described the true source of gravity. 00:34: ... induced by acceleration is fundamentally the same as that induced by gravity - the so-called equivalence ... 01:05: We know that gravity must cause clocks to run slow on the basis of logical consistency. 01:11: And we know that gravity DOES cause clocks to run slow based on many brilliant experiments. 01:17: But I never explained WHY or HOW gravity causes the flow of time to slow down. 01:28: Gravity does NOT warp the flow of time. 01:30: It’s the other way around - the warping of time causes gravity. 01:45: So how is it that time causes gravity? 06:56: Do we now perfectly understand the source of gravity? 07:25: But actually general relativity doesn’t need quantum mechanics to explain gravity. 08:04: So we’d better understand the effect of gravity on the path of light. 08:18: ... with those new perspectives we’ll get a new insight into the source of gravity that seems weirdly at odds with everything I just told you - and yet is ... 10:04: ... asks whether gravitational waves can be used to test ideas in quantum gravity. ... 00:34: ... induced by acceleration is fundamentally the same as that induced by gravity - the so-called equivalence ...
	2021-02-17: Gravitational Wave Background Discovered? 00:00: ... between a lab in freefall versus a lab floating in the absence of gravity because in free fall there's a difference between the strength of the ...
	2021-02-10: How Does Gravity Warp the Flow of Time? 00:25: ... field from a frame of reference floating off in space in the absence of gravity. ... 01:22: It took him another 8 years and a lot of help to grow this simple idea into his full theory of gravity - the general theory of relativity. 01:30: General relativity, or “GR” explains the force of gravity as being due to curvature in space and time. 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. 02:43: ... of time dilation - can be thought of as the true source of the force of gravity. ... 06:11: If we set it rotating at the right speed then centripetal acceleration leads to some nice artificial gravity. 08:50: OK, so what does all this have to do with gravity? 08:54: The equivalence principle demands that there’s no experiment that can distinguish between acceleration and gravity. 09:16: ... constancy of the speed of light and the equivalence of acceleration and gravity, then time must run slow in gravitational ... 10:29: So is it some sort of cosmic coincidence that you get the same number with shifting reference frames as with artificial gravity? 11:40: But ultimately, asking “why does gravity slow time” is a bit backwards. 11:46: A better question may be “why does slowed time cause gravity”. 11:51: The curvature of space by matter isn’t nearly enough to give gravity at the strength we feel it. 12:04: And I’ll show you exactly why that’s true real soon, when we explore the tangled connections between time and gravity in a curved spacetime. 01:22: It took him another 8 years and a lot of help to grow this simple idea into his full theory of gravity - the general theory of relativity. 11:40: But ultimately, asking “why does gravity slow time” is a bit backwards.
	2021-01-26: Is Dark Matter Made of Particles? 01:20: It might even be that what we perceive as dark matter is really a glitch in the laws we use to describe gravity. 01:54: Plus gravity. 02:45: The force of gravity is a sort of lingua franca, a common language that every particle with mass can speak. 02:51: But gravity is a little different to the other forces - it’s not part of the Standard Model, and we don’t even know if it has a quantum field. 03:38: Dark matter “speaks gravity”. 03:40: And we can learn an awful lot from HOW it exerts its gravity.
	2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time 00:00: ... every black hole contains a place of   infinite gravity - a singularity. But the true  impact of Penrose’s singularity ... 00:34: ... holes have haunted our  theories of gravity since the 1700s.   When John Mitchell and Pierre-Simon ... 03:18: ... hole in Einstein’s theory. In it, the central point of infinite gravity is spun out into a   ring - but it was a singularity ... 08:49: ... tend to be associated with infinite spacetime curvature - infinite gravity. In other   words, singularities. Penrose didn’t ... 11:10: ... relativity and quantum mechanics - a   theory of quantum gravity, from which both quantum mechanics and relativity are just ... 00:00: ... every black hole contains a place of   infinite gravity - a singularity. But the true  impact of Penrose’s singularity ... 00:34: ... And then of course we figured out that not  even gravity worked as Newton had told us.   In 1915, Newtonian gravity was ...
	2020-09-08: The Truth About Beauty in Physics 02:27: Not only can Kepler’s complicated laws be derived from Newton, but Newtonian gravity makes predictions far beyond the motion of the planets. 02:35: But even Newtonian gravity proved to be a special case of a much deeper law. 02:41: Einstein’s equations of general relativity give even better precision than Newton’s law - perhaps perfect precision - in their description of gravity. 02:50: And general relativity is also more explanatory than Newton - it tells us that gravity results from the warping of space and time. 03:13: Ptolemy, Copernicus, Kepler, Newton, Einstein - each followed their own sense of mathematical beauty in this long quest to understand gravity. 09:23: Same with Newton’s gravity, derived from observations of apples and the moon, but it predicts the motions of galaxies. 10:01: ... of relativity - Weyl found a simple, elegant way to unify Einsteinian gravity with the other force of nature known at the time - ... 10:46: The first compellingly beautiful aspect of string theory is that gravity, in the form of the Einstein field equations - automatically emerged from it. 11:10: And yet it hasn’t managed to produce a testable prediction - besides the whole gravity thing of course. 11:24: Actually, Weyl’s “incorrect” attempt to integrate gravity and electromagnetism wasn’t such a failure. 09:23: Same with Newton’s gravity, derived from observations of apples and the moon, but it predicts the motions of galaxies. 02:35: But even Newtonian gravity proved to be a special case of a much deeper law. 11:10: And yet it hasn’t managed to produce a testable prediction - besides the whole gravity thing of course.
	2020-08-24: Can Future Colliders Break the Standard Model? 05:25: ... - the fact that there’s a huge difference between the strength of gravity and the other forces, and a huge difference between the measured masses ...
	2020-08-17: How Stars Destroy Each Other 01:11: There, in the extreme surface gravity of the ultradense white dwarf, a layer of hydrogen built up. 11:50: ... think a theory of quantum gravity probably prevents the singularity from really forming - but quantum ...
	2020-08-10: Theory of Everything Controversies: Livestream 00:00: ... um where she works extremely broadly uh but generally in quantum gravity research uh sabine is also a prolific writer for popular media a ...
	2020-07-28: What is a Theory of Everything: Livestream 00:00: ... broad range of interests including string theory and loop quantum gravity in principle we could do this entire conversation just with stefan ...
	2020-07-20: The Boundary Between Black Holes & Neutron Stars 04:50: Once it was the burning heart of the star - a fusion engine that allowed the star to resist the inward crush of gravity. 04:57: But when it ran out of fuel, gravity took over and the entire star collapsed. 05:20: That insane density gives the neutron star a surface gravity around 100 billion times stronger than the surface of the Earth. 06:36: So more mass in a neutron star means higher surface gravity means higher escape velocity. 11:08: Each will be rich in information on the nature of stars, and gravity, and strange quantum states of matter.
	2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing? 10:56: ... holding their breath. They’re pretty sure anti-matter interacts with gravity in the exact same way as matter, but why not test ...
	2020-06-30: Dissolving an Event Horizon 02:37: These are Schwarzschild black holes, and with only mass that means they also only have inward-pulling gravity. 04:10: ... - results in a negative pressure that again resists the inward pull of gravity. ... 05:07: More mass means more inward gravity, and so the black hole can hold more spin and charge before going extremal.
	2020-06-22: Building Black Holes in a Lab 11:04: ... radiation need not necessarily depend on a specific theory of quantum gravity. Proponents of this line of thought have triumphantly pointed to ...
	2020-06-15: What Happens After the Universe Ends? 07:16: ... and neutrinos, as well as gravitons - the quantum particles of gravity. ...
	2020-06-08: Can Viruses Travel Between Planets? 13:42: ... that the existence of hidden extra dimensions might change the law of gravity on the smallest scales, and we saw how the 120 year old Cavendish ... 13:58: ... Sokic asks how we can know the inverse square law for gravity holds on the cosmic scales if we haven’t explained dark matter yet, ... 14:22: ... theory is modified newtonian dynamics - MONDS - in which gravity doesn’t drop off as quickly as the inverse square law when you get to ... 14:44: ... the stars and therefore can’t be due to just having the wrong theory of gravity. ... 15:33: So why couldn’t it be an increase in the strength of gravity? 16:06: CastleKnight7 asserted that Gravity, as with all forces is created by consciousness. 16:43: ... eminent science journal The Onion - it’s a refutation of mainstream gravity called Intelligent ... 14:22: ... theory is modified newtonian dynamics - MONDS - in which gravity doesn’t drop off as quickly as the inverse square law when you get to very large ... 13:58: ... Sokic asks how we can know the inverse square law for gravity holds on the cosmic scales if we haven’t explained dark matter yet, which ...
	2020-05-27: Does Gravity Require Extra Dimensions? 00:08: The fundamental nature of gravity still eludes our best minds - but those secrets may be revealed by turning back to the Cavendish experiment. 00:27: Gravity is by far the most familiar of the four fundamental forces - after all, we wrestle with it every day. 00:44: But what is surprising that nearly 500 years later, gravity remains the most mysterious of the four forces. 00:54: ... big difference is that the strength of gravity is vastly weaker than the other forces - I’m talking 10^24 times weaker ... 01:06: ... is known as the hierarchy problem, and understanding the puniness of gravity may help us figure out what gravity really IS, and to unify it with the ... 01:18: ... like I said, despite the mysteries about why gravity works the way it does, our current theories still describe how gravity ... 01:28: ... of relativity has a perfect track record predicting the behavior of gravity in terms of the warping of the fabric of space and ... 02:15: So as you get further away, those arrows are more and more spread out - their density, and so the strength of gravity drops. 02:43: So gravity sort of gets diluted in strength because it’s increasingly spread out over a 2-D spherical surface within our 3-D space. 02:53: ... our universe were 2-dimensional - say, a flat plain - then gravity would be spread out over the circumference of concentric circles - ... 03:09: ... if our universe had more dimensions, say 4, then gravity would spread out over the “surface” of a 4-D hypersphere - that surface ... 03:24: In general, gravity drops off as 1/r to some power - and that power is the number of spatial dimensions minus one. 03:36: Newton’s inverse square law for gravity tells us there are 2+1 = 3 spatial dimensions. 03:46: ... for the fact that some of the most promising approaches to unifying gravity with the other forces actually propose that there are MORE than 3 ... 05:03: In that case, gravity would only deviate from the inverse square law on the tiny scales of these compactified dimensions. 06:10: ... theory - one of the first attempts to unify electromagnetism with gravity. ... 06:25: ... extra dimensions, they seem a promising potential solution to unifying gravity with the other forces - and in the process explaining gravity’s ... 06:36: There are different ways of thinking about how compactified extra dimensions can effect the strength of gravity. 06:42: One is that you can imagine the gravity trying to propagate through multiple dimensions, which would dilute it more quickly. 06:48: We can also think about it as gravity producing excitations within those extra dimensions that sap its energy. 06:55: ... large scales, gravity would still follow the inverse square law, but would be diluted due to ... 07:06: ... on small scales these extra dimensions would actually change the way gravity falls off with distance - but to see that you’d need to test the ... 07:21: So, to search for these hidden dimensions, we need a way to test gravity on very small length scales. 07:36: It’s actually the OG - the experiment first used to measure the strength of the force of gravity - or the G in Newton’s law of gravitation. 09:24: ... allowed him to measure a force of gravity between the masses which was something like 10 million times smaller ... 09:47: ... only did this contribute to our understanding of gravity, but also arguably marked the beginning of a grand tradition in physics ... 10:53: ... on other factors - most importantly depending the strength with which gravity interacts with these extra ... 07:36: It’s actually the OG - the experiment first used to measure the strength of the force of gravity - or the G in Newton’s law of gravitation. 01:18: ... gravity works the way it does, our current theories still describe how gravity behaves remarkably ... 02:15: So as you get further away, those arrows are more and more spread out - their density, and so the strength of gravity drops. 03:24: In general, gravity drops off as 1/r to some power - and that power is the number of spatial dimensions minus one. 07:06: ... on small scales these extra dimensions would actually change the way gravity falls off with distance - but to see that you’d need to test the strength of ... 10:53: ... on other factors - most importantly depending the strength with which gravity interacts with these extra ... 06:48: We can also think about it as gravity producing excitations within those extra dimensions that sap its energy. 00:44: But what is surprising that nearly 500 years later, gravity remains the most mysterious of the four forces. 02:43: So gravity sort of gets diluted in strength because it’s increasingly spread out over a 2-D spherical surface within our 3-D space. 03:36: Newton’s inverse square law for gravity tells us there are 2+1 = 3 spatial dimensions. 01:18: ... like I said, despite the mysteries about why gravity works the way it does, our current theories still describe how gravity behaves ... 06:25: ... unifying gravity with the other forces - and in the process explaining gravity’s ...
	2020-05-18: Mapping the Multiverse 02:16: Well, in a Kerr black hole that rotation results in an outward pressure that partially counteracts the inward flow due to gravity.
	2020-05-11: How Luminiferous Aether Led to Relativity 02:33: ... Huygens developed a detailed mathematical theory around this idea that gravity results from the fluid dynamics of the aether. But Huygens is most ... 04:06: ... gravitation conflicted with the predictions of Huygens’ aetheric gravity. And Newton also opposed this whole wave theory for light business. Now ... 06:22: ... so we get to the end of the 19th Century. With Newton’s mechanics and gravity, Huygen’s optics, Maxwell’s electromagnetism, physics seemed pretty much ... 11:42: ... theory of relativity that ultimately overthrew Newton’s theory of gravity, and, according to Einstein, it revealed the cracks in the foundations of ... 06:22: ... so we get to the end of the 19th Century. With Newton’s mechanics and gravity, Huygen’s optics, Maxwell’s electromagnetism, physics seemed pretty much wrapped ... 04:06: ... business. Now Newton’s case is complicated - some of his early ideas on gravity incorporated the aether, and he was also an avid alchemist, so must have studied the ...
	2020-05-04: How We Know The Universe is Ancient 06:22: ... the right units - you have the age of the universe, at least assuming no gravity. And if your Hubble constant was determined by looking at lots of ... 09:39: ... it gives an age of the universe of around 13 billion years, assuming no gravity and no dark energy. But that’s remarkably close to the currently ... 11:07: ... into account the effect of matter slowing down expansion through its gravity and also the effect of dark energy speeding it up. Those can be put into ... 12:09: ... the accelerating effect of Dark Energy counters the slowing effect of gravity to ultimately give us an age of the universe very close to the roughly ... 09:39: ... close to the currently accepted value. Sandage figured out that with gravity playing its part to slow down the expansion, the universe must have been ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... about stuff as well I was certainly dreaming about quantum with gravity and string theory when we were writing those episodes so so it varies ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 08:42: ... Something with negative mass could produce the required negative gravity. But actually “exotic matter” is a broader class of weirdness than that. ...
	2020-03-24: How Black Holes Spin Space Time 04:11: ... fact, how can any effect of gravity extend from beneath the event horizon? In fact it sort of doesn’t ... 05:14: ... gravitational field - is dragged in the direction of the object’s spin. Gravity Probe B measured the Earth’s frame dragging and it was exactly as ... 04:11: ... fact, how can any effect of gravity extend from beneath the event horizon? In fact it sort of doesn’t actually. ... 05:14: ... gravitational field - is dragged in the direction of the object’s spin. Gravity Probe B measured the Earth’s frame dragging and it was exactly as Einstein’s ...
	2020-02-11: Are Axions Dark Matter? 07:47: It would interact very weakly via the strong and weak nuclear forces, and via gravity. 11:08: ... means there could be enough of them to explain the invisible source of gravity that seems to dominate the universe - what we call dark matter. If ...
	2020-02-03: Are there Infinite Versions of You? 12:29: Ilavenya rightly points out that no nice analytical solutions to the 3-body problem exist in general relativity - Einstein's modern theory of gravity. 12:40: The solutions only exist in special cases for Newtonian gravity.
	2020-01-27: Hacking the Nature of Reality 11:35: ... quantum chromodynamics took over - but then as a theory of quantum gravity. ...
	2020-01-20: Solving the Three Body Problem 00:20: ... Newton published his Principia. Within it were equations of motion and gravity that transformed our erratic-seeming cosmos into a perfectly tuned ...
	2020-01-06: How To Detect a Neutrino 01:57: ♪ ♪ ♪ ♪ Neutrinos are among the most elusive elementary particles of nature, ♪ ♪ only interacting by the weak nuclear force and gravity. 04:16: ♪ ♪ As we mentioned: they only experience the weak nuclear force and gravity, ♪ ((𝘴𝘰𝘧𝘵)) ♪ and the latter is so weak we can ignore it altogether.
	2019-12-17: Do Black Holes Create New Universes? 03:48: The details of how this happens is presumably buried in the as-yet-unknown theory of quantum gravity. 06:13: Stars are formed when giant clouds of gas collapse under their own gravity.
	2019-12-02: Is The Universe Finite? 04:10: ... stuff in the universe - a higher energy density - means more gravity, which tends to pull a universe in on itself - it gives positive ...
	2019-11-11: Does Life Need a Multiverse to Exist? 06:36: Now, this all assumes that the universe has the same strength of gravity as our real one. 06:42: With weaker gravity, diproton-burning stars could last longer, and with stronger gravity, fusion could skip the deuterium step. 06:51: But the fine-tuning is still there - we need the right balance between between the strengths of the strong nuclear force and gravity. 07:37: ... constant for electromagnetism and the gravitational constant for gravity. ... 07:47: ... a vast range of values nearly 10^40 from the strong nuclear force to gravity, and there’s no apparent pattern in their values. As far as we know, they ... 06:42: With weaker gravity, diproton-burning stars could last longer, and with stronger gravity, fusion could skip the deuterium step.
	2019-11-04: Why We Might Be Alone in the Universe 12:21: We skipped comment responses last episode, so today we're covering two episodes - loop quantum gravity and time travel. 12:30: A few of you wondered if there's a connection between the loops of loop quantum gravity and the closed strings of string theory. 12:52: Which brings us to the most common question - what actually ARE the loops of loop quantum gravity? 13:37: ... Receiver asked about the experiment to test Loop Quantum Gravity So LQG predicts that light of different wavelengths travels at very ... 15:16: Surely as time travelers you could have reminded me in the loop quantum gravity comments the week before.
	2019-10-21: Is Time Travel Impossible? 03:16: ... which incorporates special relativity, but also explains the force of gravity as a result of curvature in the fabric of spacetime due to the presence ... 04:14: ... one end to close to the speed of light or drop it into a deep gravity well – its rate of time flow will slow relative to the other end of the ... 05:17: We need to counter gravity, and to do that we need another probably-non-existent form of mass – negative mass – also referred to as exotic matter. 11:36: ... actual fact we can’t know until we have a full theory of quantum gravity – until then we’re working with the approximate theories general ...
	2019-10-15: Loop Quantum Gravity Explained 00:00: It’s time we talked about loop quantum gravity. 00:32: ... search for a theory of quantum gravity is a century old, and we’ve talked about it quite a bit already, ... 00:47: ... of the tiny and the gigantic - another way to a theory of quantum gravity that avoids a lot of conceptual baggage like tiny wiggling strings made ... 01:03: That other way would be loop quantum gravity, and today we’re going to find out exactly what it is. 01:34: ... thing because this is what really inspired the invention of loop quantum gravity. ... 03:10: ... quantum gravity tries to quantize general relativity with no strings attached, while ... 05:13: A quantum theory of gravity needs to fix both of these issues - but we’re going to focus on background independence for now. 06:52: A contender for a theory of quantum gravity. 07:16: ... what loop quantum gravity does - it takes us down the abstraction rabbit hole - past our space of ... 08:54: Quantized gravity suddenly looked to be in reach. 08:59: And now we get to the loops of loop quantum gravity. 10:01: The result, of course, is loop quantum gravity. 10:03: It’s general relativity – our modern theory of gravity – cast in terms of very abstract building blocks. 11:01: ... big success of loop quantum gravity is that it manages to combine general relativity and quantum mechanics ... 12:41: ... quantum gravity seems to predict that the speed of light should depend very slightly on ... 13:10: If there was any difference it was barely measurable, and that doesn't look great for loop quantum gravity. 13:16: Loop quantum gravity is an intriguing alternative to the more popular string theory. 13:58: David, we already spent all of your money ... on aspirin, after loop quantum gravity broke our brains. 12:41: ... due to the way they propagate through the graininess of a loop quantum gravity spacetime. ... 08:54: Quantized gravity suddenly looked to be in reach.
	2019-09-23: Is Pluto a Planet? 02:27: Newton’s Laws of Gravity led to consistent predictability of the motion of the heavenly spheres. 15:36: Now, the argument is compelling: why would we want to go and live back down in a gravity world right after getting out of this one? 15:45: ... a rotating habitat or cylinder in space can produce the effect of gravity for its inhabitants, but without an actual powerful gravitational field ... 02:27: Newton’s Laws of Gravity led to consistent predictability of the motion of the heavenly spheres.
	2019-09-16: Could We Terraform Mars? 14:16: ... of centrifuge cities – mag-lev rotating habitats to simulate Earth gravity. Also shown rather beautifully in this more practical design by James ...
	2019-08-19: What Happened Before the Big Bang? 06:04: As well as theories which also unify gravity, like string theory. 07:19: These same fluctuations collapsed under their own gravity to become the first galaxies.
	2019-08-06: What Caused the Big Bang? 02:14: In the case of inflation part of the appeal is that it fits extremely nicely into our modern understanding of gravity and quantum mechanics. 02:31: Our modern theory of gravity can be used to predict the behavior of the universe as a whole.
	2019-06-17: How Black Holes Kill Galaxies 04:05: ... from the same material and they can't directly influence each other with gravity how do they know what size to ... 07:21: ... hot gas can't form new stars gas has to cool down before the force of gravity can cause it to collapse into the stars too hot and it stays puffed up ...
	2019-06-06: The Alchemy of Neutron Star Collisions 02:47: ... that combined core has almost certainly pushed beyond the limits of gravity and collapses into a black hole within milliseconds in the meantime the ...
	2019-05-16: The Cosmic Dark Ages 02:52: ... when tiny fluctuations in density began to collapse under their own gravity. These stars were exceptionally massive because they were unpolluted by ...
	2019-05-01: The Real Science of the EHT Black Hole 06:24: The photon sphere is where gravity is so strong that light itself can orbit the black hole.
	2019-04-24: No Dark Matter = Proof of Dark Matter? 00:03: ... not explained by modern particle physics or our understanding of gravity is completely broken the debate over which is true has raged for decades ...
	2019-04-10: The Holographic Universe Explained 08:23: ... you get the wave equation for a graviton – the quantum particle of gravity. ... 08:49: ... it was quickly rejigged to make it a theory of quantum gravity, and the scale invariance of the strings becoming a central feature of ... 11:24: The conformal field theory in the original space included no gravity, but in the higher-dimensional space it became a full quantum theory of gravity. 13:28: But those rules translate to interactions in the volume – in the bulk – and there they are a theory of gravity. 15:28: ... AdS/CFT correspondence, the volume exhibits gravity via a type of string theory, while the surface exhibits no gravity - ... 16:00: ... according to Ads/CFT correspondence, can we say there would be no gravity on the surface of the (2+1)Minkowski ... 16:20: That surface contains only a conformal field theory and no gravity. 16:27: ... strange miracle of AdS/CFT is that gravity arises naturally when you add an extra spatial dimension, which ends up ... 15:28: ... gravity via a type of string theory, while the surface exhibits no gravity - only a quantum field theory similar to the field theory behind the ... 16:27: ... strange miracle of AdS/CFT is that gravity arises naturally when you add an extra spatial dimension, which ends up looking ...
	2019-04-03: The Edge of an Infinite Universe 07:44: ... that is “asymptotically flat” – it may have some local curvature due to gravity of massive objects inside, but at its boundaries the simple rules of ... 14:20: That structure looked exactly like a string theory with gravity and everything. 14:31: Quantum mechanics in the form of a conformal field theory in one space is a theory of quantum gravity in a space with one higher dimension.
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 01:55: ... so far apart that they can't see each other let alone fill each other's gravity but as long as dark energy doesn't increase there'll be no expansion ... 03:05: ... Friedman equation it's basically the equivalent of Newton's law of gravity for the whole universe describing the acceleration or deceleration of ... 09:26: ... just yet, just that the effect of phantom energy is stronger than the gravity binding the stars ... 15:06: The amount of mass and energy it contains just doesn't provide enough gravity. 09:26: ... just yet, just that the effect of phantom energy is stronger than the gravity binding the stars ...
	2019-03-20: Is Dark Energy Getting Stronger? 02:32: We see its effect in the rotation and movement of galaxies and in the bending of light due its space-warping gravity. 15:02: ... out the course: Black Holes, Tides, and Curved Spacetime: Understanding Gravity. ... 15:12: ... is a series of twenty four thirty minute lectures on gravity, that can help you get a deeper understanding of both the history and the ...
	2019-03-06: The Impossibility of Perpetual Motion Machines 01:40: Basically the shift in the center of gravity of the spokes on one side should drive the wheel around.
	2019-02-20: Secrets of the Cosmic Microwave Background 02:05: ... by gravity Regular matter, what we call baryons was in plasma form with the simple ... 11:14: ... was in the radiation-dominated epoch Basically photons produced more gravity than matter Fluctuations that were small enough to oscillate at least ... 02:05: ... that could happen multiple times Everywhere in the universe the pull of gravity fought against the outward push of radiation pressure causing density ...
	2019-02-07: Sound Waves from the Beginning of Time 07:44: Gravity pitted against radiation pressure. 16:08: In so-called bimetric gravity, you can have positive and negative masses, but each is described by its own set of Einstein field equations. 07:44: Gravity pitted against radiation pressure.
	2019-01-30: Perpetual Motion From Negative Mass? 01:48: Mass is also the property that both causes and responds to gravity. 01:56: The more massive an object, the more strongly its gravity pulls on surrounding objects and the more strongly it gets pulled by gravity. 02:35: ... and you see that although massive objects get pulled more strongly by gravity, they also accelerate more ... 03:08: ... pretty mysterious that the same property that defines the response to gravity also defines resistance to acceleration by all forces – including ... 03:28: In fact, in Newtonian gravity, any like masses – both positive or both negative - should produce a mutually attractive force. 04:13: Electromagnetism is spin 1 - odd - so attraction and repulsion are flipped compared to gravity. 05:47: ... is really only approximation of a much more complete description of gravity: Einstein’s general theory of ... 06:31: General relativity describes gravity as the warping of the fabric of spacetime. 05:47: ... is really only approximation of a much more complete description of gravity: Einstein’s general theory of ... 01:56: The more massive an object, the more strongly its gravity pulls on surrounding objects and the more strongly it gets pulled by gravity.
	2019-01-24: The Crisis in Cosmology 08:06: Matter wanted to collapse under its own gravity,...
	2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe 16:49: ... of string theory is connected to the extreme energy scale of quantum gravity and that problem is not unique to string theory. Now we do talk about ...
	2019-01-09: Are Dark Matter And Dark Energy The Same? 01:23: Based on the gravity from visible matter alone they shouldn’t be able to hold themselves together. 02:25: According to Einstein’s general theory of relativity, any such positive energy produces an inward-pulling gravity. 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. 04:51: But with one negative and one positive mass, the final force of gravity has the opposite sign - that makes it repulsive. 06:50: This confines the galaxy from the outside so it can spin faster than if it were held together by its gravity alone. 08:18: ... second Friedmann equation, which is really the analog of Newton’s law of gravity for the whole cosmos, this negative mass fluid – as a negative ... 10:31: Those supernova results suggest a universe that started expanding rapidly and then slowed down due to the gravity of matter – mostly dark matter.
	2018-12-20: Why String Theory is Wrong 01:35: ... seemed so beautiful, the effortlessness of its inclusion of quantum gravity, its promise to unify all particles under one umbrella, and there's also ... 02:27: In 1919, not long after Einstein published his great theory of gravity, Theodor Kaluza discovered something strange. 03:08: It appeared that gravity acting in this fifth dimension looks like electromagnetism to being trapped in our 4-D space-time. 11:41: See, in parallel to the development of super string theory, other physicists have been working on super gravity. 11:49: ... we don't have time to get into, 11 is also the magic number for super gravity dimensions. Super gravity should be the low energy, large-scale limit to ... 12:14: ... convergence of the superstring theories with each other and with super gravity restored the sense of beauty to string theory. It appeared to be on the ... 03:08: It appeared that gravity acting in this fifth dimension looks like electromagnetism to being trapped in our 4-D space-time. 11:49: ... we don't have time to get into, 11 is also the magic number for super gravity dimensions. Super gravity should be the low energy, large-scale limit to super ... 12:14: ... convergence of the superstring theories with each other and with super gravity restored the sense of beauty to string theory. It appeared to be on the track to ... 02:27: In 1919, not long after Einstein published his great theory of gravity, Theodor Kaluza discovered something strange.
	2018-12-12: Quantum Physics in a Mirror Universe 00:02: ... it appeared to be the case in experiments at least for tests involving gravity electromagnetism and the strong nuclear forces it was assumed that the ...
	2018-11-21: 'Oumuamua Is Not Aliens 16:04: It appeared to say that the weak force is 1,024 times stronger than gravity.
	2018-11-14: Supersymmetric Particle Found? 01:30: ... being that the standard model can't explain the minuscule weakness of gravity compared to the other three ... 15:27: Gravity then leaks into the extra fourth dimension, causing it to weaken. 15:36: Those dimensions are tiny in extent and they're coiled on themselves so there is nowhere for gravity to escape into. 01:30: ... being that the standard model can't explain the minuscule weakness of gravity compared to the other three ...
	2018-11-07: Why String Theory is Right 00:06: ... hope for a theory of everything that will unify quantum mechanics and gravity and so unify all of physics into one great, glorious theory of ... 01:36: ... all forces and particles, and most importantly that unification includes gravity. ... 02:28: It predicts the existence of gravity, which is stupid, of course. 02:33: Everyone knows that Isaac Newton discovered gravity when he fell out of an apple tree, or something like that. 02:41: But the fact is when you start to work out the math of string theory, gravity appears like magic. 02:47: You don't need to try to fight gravity into string theory. 02:50: ... fact, it will be difficult to remove it, and the quantum gravity of string theory is immune to the main difficulty in uniting general ... 03:01: It doesn't give you tiny black holes when you try to describe gravity on the smaller scales. 03:07: ... talk about this and other problems with developing a quantum theory of gravity in a recent episode, but before we get to the nuts and bolts of how ... 03:40: In quantum theories of gravity, the gravitational force is communicated by the graviton particle. 05:06: ... illustrate why quantum gravity isn't hopelessly broken in string theory, and that's a huge point in ... 11:19: That field looks like a 2D gravity on the world sheet. 02:41: But the fact is when you start to work out the math of string theory, gravity appears like magic. 03:07: ... theory predicts gravity, it's worth taking a moment to see how stringy gravity avoids the problem of black ... 05:06: ... illustrate why quantum gravity isn't hopelessly broken in string theory, and that's a huge point in favor of ...
	2018-10-18: What are the Strings in String Theory? 00:10: There are these tiny vibrating strings, and that's where all the force's particles, including gravity, in the entire universe come from. 01:06: And then there's gravity, which doesn't fit into the standard model at all. 03:16: ... it might be-- we really don't know, but if it is-- then the quanta of gravity should have an uncanny resemblance to the type of particle produced by ... 03:45: What if the math of this theory could be used in a theory of quantum gravity? 09:06: It solves one of the main problems with quantizing gravity. 09:10: ... you remember from our episode on quantum gravity, if you try to describe gravitational interactions on the smaller scales, ...
	2018-10-03: How to Detect Extra Dimensions 01:59: This allowed us to make some really important conclusions about how gravity travels through space. 02:26: ... usual three could actually explain a lot, from the difference between gravity and the other forces of nature to the nature of dark ... 02:38: But before we get all hyper-dimensional, let's think a bit more about 3 plus 1D space-time and how gravity, light, and matter behave there. 04:07: In our universe, gravity appears to diminish according to the inverse square law, as reflected in Newton's law of universal gravitation. 04:21: But even there, Einstein's general relativity describes gravity perfectly with three spatial dimensions. 04:27: In general, general relativity in 3 plus 1 space-time does a great job at describing gravity in the large-scale universe. 04:35: But there are some things about this version of gravity that seem peculiar-- for example, its pathetic strength. 04:44: ... and weak forces are all in the same ballpark in terms of strength, gravity is vastly weaker, 10 to the power of 32 times weaker, than even the weak ... 04:56: The only reason we see so much gravity is that its range is infinite-- and unlike the nuclear forces. 05:06: This mismatch in strength might be because gravity is really fundamentally different to the other forces. 05:22: That means gravity has to look just like the other forces at very high energies. 05:44: So you drain gravity into an extra dimension. 05:56: All of that stuff will behave relatively normally, while gravity is weakened. 06:47: Most of the stuff in such a universe, including all of the fundamental forces besides gravity, would be restricted to the 3-brane. 07:05: On some spatial scales, you even get the inverse square law for gravity. 07:10: But on other spatial scales, gravity can behave very differently. 07:14: If gravity spreads out in four dimensions rather than three, then it should become much weaker. 07:48: In our hypothetical universe with four spatial dimensions, gravity is already weak on the scale of the solar system and the galaxy. 07:59: ... on how you tweak the theory, gravity can obey an inverse square law on galactic scales, where it's sort of ... 08:58: Wild light and the force of gravity appear to obey the inverse square law. 10:49: There was no observable leakage of gravity into extra spatial dimensions, pretty much ruling this out as an explanation for dark energy. 11:06: ... and gravitational wave arrival times also allowed us to verify that gravity really does travel pretty much exactly at the speed of ... 12:23: ... and quantum theory towards the development of a theory of quantum gravity. ... 12:36: Devin Faux asks whether gravity is maybe the exception to the rule that the forces arise from quantizing [INAUDIBLE] fields. 12:47: Theories of quantum gravity go in both directions. 12:50: ... theories of everything try to quantize gravity by placing it within the same framework as the other forces to show that ... 13:05: Other theories treat gravity very differently to the other forces. 13:14: An example is loop quantum gravity. 14:14: For the simplest attempts at quantum gravity, you need infinite measurements. 04:07: In our universe, gravity appears to diminish according to the inverse square law, as reflected in Newton's law of universal gravitation. 02:38: But before we get all hyper-dimensional, let's think a bit more about 3 plus 1D space-time and how gravity, light, and matter behave there. 04:21: But even there, Einstein's general relativity describes gravity perfectly with three spatial dimensions. 07:14: If gravity spreads out in four dimensions rather than three, then it should become much weaker. 01:59: This allowed us to make some really important conclusions about how gravity travels through space.
	2018-09-20: Quantum Gravity and the Hardest Problem in Physics 00:34: First, Einstein's relativity utterly changed the way we think about space, time, motion, and gravity. 01:12: ... of the great quest for this union, the quest for a theory of quantum gravity and for a theory of ... 01:41: General relativity, GR, is Einstein's great theory of gravity. 01:53: This results in the effect we perceive as gravity. 04:50: For that, you need a true quantum theory of gravity. 08:26: So what if you want to quantize gravity? 08:34: To quantize gravity, you have to quantize space-time itself. 09:08: In quantum gravity, gravity itself becomes an excitation in our quantized space-time. 09:22: In other words, gravity should produce more gravity, ad infinitum. 11:23: And so the simplest approach to quantizing gravity and space-time must be wrong. 11:54: ... leading example of this is loop quantum gravity, or you just assume that GR and, indeed, the mutable fabric of space-time ... 09:08: In quantum gravity, gravity itself becomes an excitation in our quantized space-time.
	2018-08-01: How Close To The Sun Can Humanity Get? 06:23: The sun's the biggest object in the solar system and has the strongest source of gravity.
	2018-07-11: Quantum Invariance & The Origin of The Standard Model 02:03: Newton's laws of motion and gravity, Maxwell's equations for electromagnetism, Einstein's general relativity, and of course, the standard model.
	2018-07-04: Will A New Neutrino Change The Standard Model? 00:36: They don't interact by the electromagnetic or strong nuclear forces, only by the weak nuclear force and gravity. 12:26: Even if the entire belt were brought to Earth, you wouldn't notice the difference in gravity.
	2018-06-20: The Black Hole Information Paradox 04:18: After all, without a theory of quantum gravity, Hawking had to hack both general relativity and quantum-field theory to do the calculation. 09:16: ... be fully described by interactions on a 2D surface that did not include gravity. ... 09:29: This led him to realize that the union of quantum mechanics and gravity may require that the entire 3D universe be a projection on a 2D structure. 11:41: Black holes represent the ultimate victory of gravity. 12:01: So, to continue your own mathematical journey into black holes, Newton's gravity is the place to start. 04:18: After all, without a theory of quantum gravity, Hawking had to hack both general relativity and quantum-field theory to do the calculation.
	2018-06-13: What Survives Inside A Black Hole? 03:18: Gravity may be caused by mass, but a gravitational field is a very real thing all on its own. 04:58: ... law of gravity states that the total gravitational field added up over an enclosed ... 07:08: But both Gauss's law and the inverse-square law work because of a key similarity between gravity and the electric field. 08:25: OK, so we've covered gravity and the electrostatic part of electromagnetism. 09:00: ... been detected, but it required the incredible precision and ingenuity of Gravity Probe ... 09:43: It's because these properties are conserved and are communicated by gravity and electromagnetism, which have infinite range. 09:00: ... been detected, but it required the incredible precision and ingenuity of Gravity Probe ... 04:58: ... law of gravity states that the total gravitational field added up over an enclosed surface is ...
	2018-05-23: Why Quantum Information is Never Destroyed 12:59: When she did publish it, Einstein supposedly remarked that he had no idea that anyone could think about gravity in such general ways.
	2018-05-16: Noether's Theorem and The Symmetries of Reality 03:11: For example, moving along a perfectly flat road, the downward force of gravity stays constant. 04:35: See, Einstein's description of gravity reveals the dimensions of space and time to be dynamic and changeable. 03:11: For example, moving along a perfectly flat road, the downward force of gravity stays constant.
	2018-04-25: Black Hole Swarms 11:11: Well, to answer that, I'd need a theory of quantum gravity so let me get back to you.
	2018-04-18: Using Stars to See Gravitational Waves 08:40: ... of gravitational waves, he had to master it precursor, Newtonian gravity. ... 08:51: He needed to understand Newton's theory of gravity well enough to see where it failed. 08:56: ... done some serious university-level physics, then mastering Newtonian gravity is also your next step toward understanding Einstein's view of ... 09:10: ... the basics of classical mechanics through the intricacies of Newtonian gravity. ...
	2018-03-28: The Andromeda-Milky Way Collision 10:06: ... visible matter given our understanding of that matter and/or the laws of gravity. ... 10:33: ... itself differently to regular matter but still comes together under gravity, for example, in the Bullet ...
	2018-03-21: Scientists Have Detected the First Stars 05:30: It doesn't interact with regular matter, except through gravity.
	2018-03-15: Hawking Radiation 04:35: To answer that properly, he would need a full union of general relativity and quantum mechanics, a theory of quantum gravity, a theory of everything. 06:14: In the absence of a theory of quantum gravity, Hawking needed a hack. 11:13: Without a full quantum theory of gravity, the origin of Hawking radiation will remain mysterious. 06:14: In the absence of a theory of quantum gravity, Hawking needed a hack.
	2018-02-21: The Death of the Sun 02:22: ... than 20 million K. So with no outward flow of energy to fight against gravity, that core begins to collapse, dragging the surrounding layer of hydrogen ... 03:09: That incredible outward flow energy does counteract gravity for the outer layers of the sun, and those layers expand.
	2018-01-24: The End of the Habitable Zone 01:53: But as soon as that starts to happen, the drop in energy production disrupts the delicate balance between outward pressure and gravity. 10:29: In no time at all you'll be coding gravity simulations in Python and calculating the radiation emitted by black holes.
	2018-01-10: What Do Stars Sound Like? 02:57: However, they do support two types of gravity waves. 03:04: Gravity waves result from the restoration of gravitational equilibrium. 07:11: Those modes allow us to determine fundamental properties like radius, mass, density, and surface gravity. 09:53: In no time at all, you will be coding gravity simulations in Python and calculating the radiation emitted by black holes. 02:57: However, they do support two types of gravity waves. 03:04: Gravity waves result from the restoration of gravitational equilibrium.
	2017-12-13: The Origin of 'Oumuamua, Our First Interstellar Visitor 03:49: Rather, they're deflected by the sun's gravity as they pass by.
	2017-11-29: Citizen Science + Zero-Point Challenge Answer 06:38: Multiply those together and you get that a gecko can support something like 40 newtons, or four kilograms, in Earth gravity.
	2017-11-22: Suicide Space Robots 12:34: But as you mention on the subreddit, I'm more of a gravity guy than a quantum guy.
	2017-11-02: The Vacuum Catastrophe 03:24: Until we develop a theory of quantum gravity, we can't say whether the photons above this energy are possible. 04:57: Einstein's theory tells us that any form of energy produces gravity, and what matters is the absolute amount of energy, not relative deviations.
	2017-10-25: The Missing Mass Mystery 01:45: Dark matter is believed to be an invisible stuff that interacts only through gravity. 01:59: Its gravity holds galaxies together and governed to the growth of large-scale structure in our universe throughout cosmic time. 05:08: ... the release of the cosmic background radiation, gravity continued to do its work and collapse these faint fluctuations into ... 01:59: Its gravity holds galaxies together and governed to the growth of large-scale structure in our universe throughout cosmic time.
	2017-08-24: First Detection of Life 00:33: [THEME MUSIC] In December of 1990, during its first gravity assist flyby, the Jupiter-bound Galileo spacecraft turned its eye towards the earth.
	2017-08-02: Dark Flow 08:22: It's moving away from us faster than the speed of light, and is now forever beyond the reach of light or gravity or anything.
	2017-07-19: The Real Star Wars 02:14: ICBMs follow the parabolic path dictated by gravity when they're between an initial boost phase and an optional final guided phase.
	2017-07-12: Solving the Impossible in Quantum Field Theory 09:27: The answer probably lies within a theory of quantum gravity which we don't yet have.
	2017-06-07: Supervoids vs Colliding Universes! 04:00: Gravity pulls things in while dark energy pushes things out. 05:07: ... begin accelerating, whereas previously it had been slowing down due to gravity. ... 07:42: First there's the ever recurring idea that gravity is wrong. 07:51: ... effect of the voids, is lower than expected because we don't understand gravity on large ... 08:01: However, modified gravity is on shaky ground because, well, dark matter is looking more and more like real stuff, not incorrect gravity. 08:10: Also, the control field gave roughly the right answer, which it shouldn't have if our understanding of gravity was so far off. 04:00: Gravity pulls things in while dark energy pushes things out.
	2017-05-31: The Fate of the First Stars 05:52: Stars form when vast clouds of mostly molecular hydrogen collapse under their own gravity. 05:58: Now, for that collapse to proceed, the pull of gravity needs to overcome the cloud's own internal thermal pressure. 06:05: Warm clouds have more internal energy, helping them to stay puffed up against their own gravity. 06:45: ... a metal-rich giant molecular cloud that begins to contract under its own gravity, it can shed its thermal energy quickly, and that includes the extra heat ...
	2017-05-17: Martian Evolution 03:11: Let's start with the one that's hardest to fix-- low gravity. 03:16: Mars has a surface gravity 38% that of Earth. 03:21: Low gravity requires less bone and muscle strength to function normally. 04:54: That same low gravity may also affect height. 05:35: OK, gravity isn't the only difference between Mars and Earth. 09:21: They'll find Earth's nearly three times higher gravity incredibly uncomfortable. 03:16: Mars has a surface gravity 38% that of Earth. 09:21: They'll find Earth's nearly three times higher gravity incredibly uncomfortable. 05:35: OK, gravity isn't the only difference between Mars and Earth. 03:21: Low gravity requires less bone and muscle strength to function normally.
	2017-04-05: Telescopes on the Moon 05:17: Hit by sunlight, tiny regolith particles build up electric charge, and so repel each other into dust fountains in the low lunar gravity. 07:49: Lower gravity could facilitate the formation of large liquid mirrors, maybe up to 100 meters across. 11:44: So there should be a point inside such a black hole where this anti-gravity perfectly balances regular gravity, and it's possible to float.
	2017-03-29: How Time Becomes Space Inside a Black Hole 05:52: This is no longer true if we introduce gravity.
	2017-03-01: The Treasures of Trappist-1 11:18: But at larger masses, the gravity wins and a star forms.
	2017-02-22: The Eye of Sauron Reveals a Forming Solar System! 02:17: Cold and adrift, the mostly hydrogen gas yields to gravity once it reaches the critical Jeans mass. 03:03: But gravity can still pull the debris together in the up/down direction. 03:46: Eventually, the growing rock has enough mass to attract material through its own gravity. 04:45: The leading idea is that newly formed planets carved out that ring with their gravity.
	2017-02-15: Telescopes of Tomorrow 09:24: This will allow us to map the universe using gravity itself as a lens.
	2017-02-02: The Geometry of Causality 10:58: ... Caleb Scharf's "Gravity's Engines" gets into my favorite space things of all-- quasars, and ...
	2017-01-19: The Phantom Singularity 04:16: ... general theory of relativity, which is the far more complete theory of gravity. ... 07:13: But unlike Newton's laws of gravity, the Schwarzschild metric actually tells us whether or not that infinite density is expected.
	2016-12-21: Have They Seen Us? 16:49: ... to get exactly the right size for the event horizon if you use Newtonian gravity to calculate the distance at which the escape velocity reaches the speed ...
	2016-12-14: Escape The Kugelblitz Challenge 01:35: A black hole forms when the core of a very massive star collapses under its own gravity at the end of a star's life.
	2016-11-30: Pilot Wave Theory and Quantum Realism 11:33: Now let's not even start talking about gravity-- no version of quantum mechanics has that sorted out.
	2016-11-16: Strange Stars 12:57: ... and I mean a lot, also want me to talk about Erik Verlinde's entropic gravity, and the possibility that it might explain both dark matter and dark ...
	2016-11-09: Did Dark Energy Just Disappear? 01:07: It appeared that something was acting to counter gravity. 11:03: ... to wrap up: everything we know about the way gravity works, combined with the expansion history that we measure tells us that ...
	2016-10-19: The First Humans on Mars 05:36: The one outstanding technical issue is the gravity. 05:40: Mars's gravity is 0.38 times that of Earth. 05:55: To build a sustainable multigenerational civilization, it may be necessary to simulate Earth gravity. 06:12: This has been proposed for artificial gravity on long-term space missions, but it's also possible on a planetary surface.
	2016-10-12: Black Holes from the Dawn of Time 10:31: I found some amazing insights into the nature of black holes in Benjamin Schumacher of course Understanding Gravity. 11:37: Well, Europa's surface gravity is only about 13.5% that of Earth's.
	2016-08-24: Should We Build a Dyson Sphere? 04:21: ... other nice thing about Mercury is that its gravity is low enough that launching mined raw material into space for ...
	2016-07-06: Juno to Reveal Jupiter's Violent Past 00:45: Jupiter's enormous gravity influences the orbit of all the planets in the solar system. 01:22: ... 10 and maybe over 40 times the mass of the Earth before it had enough gravity to start holding on to the 300-ish Earth masses of hydrogen and helium ... 03:03: Its powerful gravity clears up some of the most dangerous comets before they could collide with the Earth. 00:45: Jupiter's enormous gravity influences the orbit of all the planets in the solar system.
	2016-06-15: The Strange Universe of Gravitational Lensing 01:41: The curvature produced by mass gives gravity. 01:45: Light follows this curvature, and so gravity bends the path of light. 01:50: The prediction of general relativity that gravity deflects the path of light rays was one of the first to be directly verified. 01:45: Light follows this curvature, and so gravity bends the path of light. 01:50: The prediction of general relativity that gravity deflects the path of light rays was one of the first to be directly verified.
	2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners! 03:52: But it's not yet even known whether such a particle exists, or is needed to explain gravity.
	2016-05-25: Is an Ice Age Coming? 14:12: ... gravity from a Newtonian perspective requires the invention of a new quantity-- ...
	2016-05-18: Anti-gravity and the True Nature of Dark Energy 03:48: The more matter and energy in the universe, the harder gravity pulls inwards, trying to stop the expansion or speed up the collapse. 06:12: In other words, gravity is always attractive. 07:39: That means its density term also works on the side of matter to try to slow down the universe in the regular attractive gravity way. 03:48: The more matter and energy in the universe, the harder gravity pulls inwards, trying to stop the expansion or speed up the collapse.
	2016-04-27: What Does Dark Energy Really Do? 05:04: So measuring a rapidly-expanding universe in the past points to it having had its gravity brakes on between then and now.
	2016-04-13: Will the Universe Expand Forever? 02:16: ... any general relativity, let's develop intuition a bit by thinking about gravity from a Newtonian perspective-- as a force, rather than as an Einsteinian ... 02:37: If I throw an apple in the air, then gravity pulls it back down. 03:07: The mathematical step from Newton's gravity to escape velocity comes from thinking about energy. 06:39: There will be some expansion energy remaining after gravity is diluted to nothing, and the universe will expand forever, never stopping. 09:36: It'll shatter our intuitions about energy conservation and gravity on the largest scales of spacetime. 02:37: If I throw an apple in the air, then gravity pulls it back down.
	2016-03-23: How Cosmic Inflation Flattened the Universe 04:21: Both seem strange if we assume that regular gravity was always the only force affecting the rate of expansion after the initial kick of the Big Bang. 11:52: ... you have a center-pointing or centripetal force-- in this case, that's gravity-- acting on the orbiting ... 12:08: The orbiting object is subject to the full acceleration caused by gravity, which is what causes it to move in an orbit. 11:52: ... you have a center-pointing or centripetal force-- in this case, that's gravity-- acting on the orbiting ...
	2016-03-16: Why is the Earth Round and the Milky Way Flat? 00:35: All of these things obey the same laws of physics and all of them are held together by gravity. 02:06: In the case of all the really big space stuff, one of the important forces is always gravity. 02:15: Here it's fine to think about gravity Newtonianly as a force rather than as an Einsteinian warping of space time. 02:23: ... Universal Law of Gravitation tells us that the strength of gravity drops off with the distance to the center of mass squared, and it drops ... 02:34: ... gravity has spherical symmetry in the sense that, if you're some distance from a ... 02:48: Gravity exerts itself equally along the three spatial dimensions. 03:51: And the resulting pressure gradient force balances gravity in the up-down direction. 04:56: See, pressure shares that same symmetry as gravity. 07:26: But wait, gravity and pressure are not the only things at work here. 07:34: ... a centrifugal force that can counteract gravity and should actually push a spherical object towards exactly that ... 07:43: It counteracts gravity so we can build higher block towers towards the Equator while still maintaining equilibrium. 07:55: ... per second squared, compared to 9.8 meters per second squared due to gravity. ... 08:49: These things are so huge and spread out, they barely fuel their own gravity, and they collapse very, very slowly. 09:21: However, gravity is pulling both inward towards the axis and down towards the center. 09:58: Spheres happen when pressure is the dominant effect resisting gravity. 10:05: Disks happen when orbital motion dominates the resistance to gravity. 02:23: ... Universal Law of Gravitation tells us that the strength of gravity drops off with the distance to the center of mass squared, and it drops off at ... 02:48: Gravity exerts itself equally along the three spatial dimensions. 02:15: Here it's fine to think about gravity Newtonianly as a force rather than as an Einsteinian warping of space time.
	2016-03-02: What’s Wrong With the Big Bang Theory? 03:46: We do think that we can describe gravity and the shape of space time at these densities and temperatures. 04:26: And we need a theory of quantum gravity, a so-called theory of everything, to go further.
	2016-02-24: Why the Big Bang Definitely Happened 02:56: While general relativity is incredibly successful, it doesn't contain the machinery to describe the quantum scale gravity of that first speck.
	2016-02-11: LIGO's First Detection of Gravitational Waves! 05:11: Except that now we have the capacity to do detailed tests of general relativity in a regime previously unavailable, in the regime of extreme gravity. 07:32: TheRealBileth asks, wouldn't Mars' low gravity mess up bones and muscles? 08:03: Venus' surface, or even cloud city gravity, is 90% that of Earth's. 07:32: TheRealBileth asks, wouldn't Mars' low gravity mess up bones and muscles?
	2016-02-03: Will Mars or Venus Kill You First? 01:13: Mass is only 1/10 the mass of the Earth, and 40% of its surface gravity. 01:44: And this is exacerbated by point two, the atmosphere was already only weakly held by Mars' low gravity. 06:56: It's a pleasant 0.9 times Earth's gravity, and the atmospheric pressure is around that of Earth's surface. 10:11: For one thing, we don't have a theory of quantum gravity to get us into the Planck era.
	2016-01-06: The True Nature of Matter and Mass 06:08: But we can't talk about mass without talking about gravity. 06:11: Massive objects exert and respond to the force of gravity. 06:23: ... relativity, it's not so surprising that the photon box feels the pull of gravity. ... 06:44: Holding up our photon box against Earth's surface gravity has to be just as hard as trying to accelerate it at 1 g in empty space. 07:33: And when you trap them in a box, the curvature that they produce looks just like gravity.
	2015-12-09: How to Build a Black Hole 11:54: ... probe on a comet, landing on irregularly shaped bodies, with very weak gravity, is extremely ...
	2015-11-25: 100 Years of Relativity + Challenge Winners! 03:53: ... meters per second squared or around one ten billionth of Earth's surface gravity. ...
	2015-11-18: 5 Ways to Stop a Killer Asteroid 06:11: Fly a 20 ton spacecraft alongside the object for 10 years, and their mutual gravity will pull the impactor off course.
	2015-11-11: Challenge: Can you save Earth from a Killer Asteroid? 01:46: This is the weak gravity regime.
	2015-10-22: Have Gravitational Waves Been Discovered?!? 00:22: It has a lot to do with his revolutionary Theory of General Relativity, in which he showed us that the force of gravity is an illusion. 00:37: Now it turns out that General Relativity makes predictions far beyond the familiar gravity. 01:09: The idea of gravity not as a force, but as warped spacetime is often depicted in analogy as a flexible rubber sheet being depressed by a heavy ball. 01:23: Drop a ball onto a rubber sheet, and a dip forms, which then causes other objects to move differently along the sheet, analogous to gravity. 02:08: ... by the stiffness of the rubber, gravitational waves-- and indeed, gravity itself-- propagate according to the stiffness of spacetime-- in other ...
	2015-09-23: Does Dark Matter BREAK Physics? 00:24: ... on the amount of binding gravity that we calculate from everything we can see, we can only account for ... 00:34: Either we're missing and frankly don't understand at least 80% of all the matter in the universe or our current understanding of gravity is wrong. 01:22: But again, we find the clusters appear to have way more mass than we see in the stars alone, that is if we understand gravity. 01:52: Gravity just behaves differently on the vast scales of galaxies and clusters. 03:28: But they should be moving slower because the gravity out there should be weaker. 03:32: According to Newton, gravity weakens proportional to distance from its source squared. 03:43: Could it be that what we see as dark matter just comes from gravity behaving differently on truly gigantic scales? 03:50: Well, it turns out that if you make a simple change to Newton's gravity, things work out. 03:55: ... gravity a bit more staying power, make it drop off proportional to distance ... 04:03: The stars alone give you plenty of gravity. 04:05: The original modified Newtonian dynamics hypothesis, and it's a general relativity extensions, tries to give us this basic relationship for gravity. 04:46: But there's an even bigger nail in the coffin of modified gravity. 05:02: So if dark matter really comes from weirdly behaving gravity, then the cluster's gravity should stay concentrated on the gas. 05:29: This tells us that matter is a real particle, not just broken gravity. 05:59: ... universe of clusters and galaxies, something had to act with enough gravity to pull stuff ... 03:43: Could it be that what we see as dark matter just comes from gravity behaving differently on truly gigantic scales? 03:50: Well, it turns out that if you make a simple change to Newton's gravity, things work out. 03:32: According to Newton, gravity weakens proportional to distance from its source squared.
	2015-08-27: Watch THIS! (New Host + Challenge Winners) 01:09: ... for the orbital period of a particle moving under the planet's gravity in a circular orbit right at the ...
	2015-08-19: Do Events Inside Black Holes Happen? 00:37: ... treat gravity Einsteinially rather than Newtonianially from the outset, it will help a ... 07:03: ... Newtonian gravity, a projectile on the surface of a planet or a star needs a minimum speed ... 07:25: In general relativity, remember, gravity is not a force at all. 00:37: ... treat gravity Einsteinially rather than Newtonianially from the outset, it will help a lot if I can ...
	2015-08-12: Challenge: Which Particle Wins This Race? 00:17: For the purposes of this challenge, I want you to treat gravity and all physics Newtonianly. 00:22: ... at the same rate everywhere, space and time are two separate things, and gravity is an actual force that masses exert on each ... 00:59: ... Newtonian gravity, you can work out an expression for the orbital speed of this particle in ... 03:35: Use the subject line "Two-particle Newtonian gravity challenge". 04:58: You can submit your answers to that challenge by email with the subject line "Two-particle Einsteinian gravity challenge". 03:35: Use the subject line "Two-particle Newtonian gravity challenge". 04:58: You can submit your answers to that challenge by email with the subject line "Two-particle Einsteinian gravity challenge".
	2015-08-05: What Physics Teachers Get Wrong About Tides! 00:00: [MUSIC PLAYING] As we've seen before on "Space Time," gravity affects the motion of all objects identically. 00:07: So if gravity from the Moon and the Sun is really responsible for tides in the ocean and water is water, then why don't we see tides in lakes? 00:38: The moon's gravity is stronger at Point A and weaker at Point B than it is at Earth's center. 00:42: ... net effect of this differential of the Moon's gravity across the Earth is to stretch the oceans out like taffy, ergo why the ... 01:00: ... really is a gravity differential from the Moon at points A and B. And at least in this ... 02:01: Assumption one-- we're going to use Newtonian gravity. 02:24: And finally, assumption four-- we're going to pretend that we can switch Earth's gravity on and off whenever we want to. 02:31: ... take a closer look at the Moon's gravity differential and how it manifests itself from the perspective of a frame ... 02:47: Turn off Earth's gravity. 04:14: ... tidal acceleration on objects due to the Moon's differential gravity along the Earth/Moon line works out to only 1/10,000,000th of an Earth ... 04:28: Plus, even if you turned Earth's gravity off, you would never notice an outward acceleration of one micron per second per second. 05:26: Remember, the radially inward acceleration caused by Earth's own gravity on objects is 10 million times bigger. 10:18: So if gravity is not a force and it's considered spacetime curvature, then why do people talk about gravitons? 10:53: ... you start looking at very small scales, like what the quantum version of gravity tells you on very small scales or very high energies, that a lot of ... 01:00: ... really is a gravity differential from the Moon at points A and B. And at least in this simplified model, ... 02:31: ... take a closer look at the Moon's gravity differential and how it manifests itself from the perspective of a frame of reference ... 10:53: ... you start looking at very small scales, like what the quantum version of gravity tells you on very small scales or very high energies, that a lot of infinities ...
	2015-07-29: General Relativity & Curved Spacetime Explained! 00:14: [THEME MUSIC] Newton's and Einstein's dispute over gravity comes down to competing notions of what constitutes an inertial frame of reference. 00:55: Well, between our gravity illusion episode and your comments, we've seem that Einstein's position seems internally inconsistent. 01:33: But even in a world without gravity, we already know that clocks, rulers, and our eyes can all mislead us. 02:08: ... gravity would just be an additional force we introduced, like any other force, ... 04:16: It has no forces on it, so there's no need to invent gravity. 04:20: OK, but what about two apples in a falling box, like at the end of our gravity illusion episode? 05:09: But then again, so does Newton's flat spacetime picture that has gravity injected as a kicker. 05:49: ... making any assumptions about how gravity effects light, that would be true even if it turned out that gravity ... 06:36: ... most of the everyday effects on earth that Newton would attribute to gravity are due to curvature in ... 08:11: If there's no gravity and gravity is not a force, then why do we keep using that word? 08:32: ... or string theory or whatever, it's just a lot easier to say the word gravity than say curvature of four dimensional ... 05:49: ... making any assumptions about how gravity effects light, that would be true even if it turned out that gravity slowed ... 00:55: Well, between our gravity illusion episode and your comments, we've seem that Einstein's position seems internally inconsistent. 04:20: OK, but what about two apples in a falling box, like at the end of our gravity illusion episode? 00:55: Well, between our gravity illusion episode and your comments, we've seem that Einstein's position seems internally inconsistent. 04:20: OK, but what about two apples in a falling box, like at the end of our gravity illusion episode? 05:09: But then again, so does Newton's flat spacetime picture that has gravity injected as a kicker. 05:49: ... how gravity effects light, that would be true even if it turned out that gravity slowed photons down and bent their world lines, since both photons would be ... 05:04: OK, so Einstein's gravity-free curved space time sounds like it's self consistent.
	2015-07-22: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments 03:05: ... the flat space time picture-- tells you is that in a world without gravity, there's a way to discern who's really moving at constant ... 05:41: ... and, finally, an explanation of Einstein's self-consistent view of what gravity ...
	2015-07-15: Can You Trust Your Eyes in Spacetime? 01:30: Pretend the world has no gravity, Newtonian or otherwise. 01:35: In fact, there is no Earth since Earth is held together by gravity. 01:30: Pretend the world has no gravity, Newtonian or otherwise. 01:38: This gravity-free world is what flat spacetime describes.
	2015-07-08: Curvature Demonstrated + Comments 06:34: ... and vectors in that space mean, and how it helps explain away Newtonian gravity. ...
	2015-07-02: Can a Circle Be a Straight Line? 00:00: [MUSIC PLAYING] Einstein said that gravity is not a force. 00:36: ... and how they add up to the idea that there simply is no force of gravity. ... 00:45: We actually started this campaign in our "Is Gravity an Illustion?" episode. 01:21: ... account for the motion we observe even if there's no Newtonian force of gravity. ... 01:50: ... together to tie up all the loose ends that we raised at the end of our gravity illusion ... 07:24: And 3D curved space isn't what explains away gravity, it's four dimensional curved spacetime. 01:50: ... together to tie up all the loose ends that we raised at the end of our gravity illusion ...
	2015-06-17: How to Signal Aliens 06:10: Two weeks ago, we asked whether gravity was an illusion. 06:16: I'm going to answer comments from the gravity episode first, then give you the answer to the challenge question. 06:55: ... I was just trying to give the gist of Einstein's early thinking about gravity, which evolved and to give you a general flavor of the seeming tension ... 07:26: ... out that you can distinguish ordinary celebration from real Newtonian gravity, because real gravity will vary in strengths slightly at both ends of a ... 08:49: ... reasons that maybe "illusion" isn't the best word to use when describing gravity. ... 09:30: The frame of the falling van should be equivalent to a frame that's an intergalactic space away from gravity. 09:42: All directions are equivalent in the absence of some kind of real gravity in the Newtonian sense picking out some direction. 06:16: I'm going to answer comments from the gravity episode first, then give you the answer to the challenge question.
	2015-06-10: What Happens to a Helium Balloon in Freefall? 00:08: ... you with a challenge question that relates to a recent episode about gravity and also to some other episodes we've got coming up in the ... 00:19: ... our gravity episode-- that you can click over here to view-- we referenced the ...
	2015-06-03: Is Gravity An Illusion? 03:26: There's something else familiar that makes people, books, and elephants accelerate in lockstep-- the Newtonian force of gravity. 03:32: In fact, in the absence of air resistance, that's the defining feature of gravity. 04:37: You can also think that the car's forward acceleration is mimicking some extra gravity pointing backward. 04:43: ... that with Earth's real gravitational field and it's as though the total gravity inside the car points down and back at around a 30-degree ... 05:05: ... car stationary on the surface of some other planet with slightly bigger gravity than Earth and tilted upward by about 30 ... 05:35: Really, Destin's car is accelerating and this extra backwards gravity is fake. 05:39: ... Einstein asked, hold on, what if the so-called "real" downward gravity from Earth is also fake, a side effect generated because Earth's surface ... 06:19: The falling frame of the box behaves just like a stationary inertial frame that's way out in intergalactic space where there's no gravity. 07:05: But freely-falling frames here on Earth also pass that test if your so-called gravity is fictitious. 07:18: This inability to distinguish freefall from lack of gravity has a name, by the way. 07:53: Maybe gravity, just like that backward jolt on the train, is an illusion. 08:03: ... with thinking about freely-falling frames as inertial or thinking about gravity as an ... 09:19: It makes several predictions that Newton's theory of gravity does not, and so far, it has passed all its experimental tests. 09:42: You, my friend, are accelerating, giving you the impression that there's a force of gravity when, in fact, no such thing exists. 04:43: ... that with Earth's real gravitational field and it's as though the total gravity inside the car points down and back at around a 30-degree ... 04:37: You can also think that the car's forward acceleration is mimicking some extra gravity pointing backward.
	2015-05-27: Habitable Exoplanets Debunked! 00:25: ... from Star Trek, with a solid surface, liquid water, and a surface gravity that humans could at least function ...
	2015-05-13: 9 NASA Technologies Shaping YOUR Future 03:58: Now a really big problem-- astronauts in micro gravity lose bone density 10 times faster than people on earth with osteoporosis do.
	2015-05-06: Should the First Mars Mission Be All Women? 02:06: And women faint more easily from standing up too fast once they get back to Earth, which may not be as big a deal in Martian gravity-- still unclear. 07:23: ... of "Space Time." Last week we asked what the most realistic artificial gravity in sci-fi ... 08:17: Finally, some people brought up using an accelerating ship in order to get artificial gravity. 08:52: ... Conte asked why we didn't bring up gravity gradient effects, namely that in a small ring-- this is not as a big a ... 09:04: ... and you might get more bone leeching in your neck because there's less gravity there compressing your ... 09:22: ... would have two counter-rotating sections, so that there would be gravity here and gravity here but no net angular momentum, and thus no net ... 08:52: ... ring-- this is not as a big a problem in large rings-- there would be a gravity differential between what you'd feel at your feet and your ...
	2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi? 00:00: [MUSIC PLAYING] Artificial gravity, it's an essential plot element in most science fiction stories. 00:06: But do any of those stories actually get artificial gravity right? 00:10: [MUSIC PLAYING] Whether you realize it or not, artificial gravity is essential to most sci-fi stars. 00:24: ... another rationale for inventing some kind of mechanism for artificial gravity on ... 00:35: ... artificial gravity that's just there, either through some kind of gravity generators or ... 00:53: Whether you want to think of gravity in the Newtonian or the Einsteinian sense, the problem persists. 01:20: ... that use the only semi-realistic way we know of to get artificial gravity, namely rotating your ... 01:29: All right, so how exactly does rotation simulate gravity? 02:10: ... of the room, it's as though there's a radially outward directed "gravity." Now, if you were out in space, Earth's real gravity, which also pulls ... 02:24: Put your feet up against a wall, stand up straight, boom, artificial gravity. 02:27: It turns out that there's a simple formula for how big the effective surface gravity produced by this rotating structure would be. 02:38: ... ground currently on your feet and thus simulate Earth's 1 g of surface gravity. ... 02:49: ... "Halo," and "Babylon 5"-- all which use rotation-induced artificial gravity. ... 03:00: I'm just focusing on well-known sci-fi franchises that offer salient examples of artificial gravity in action. 03:17: ... produce 1 Earth g of effective gravity at its surface or 10 meters per second squared, our earlier formula says ... 04:57: ... even though "2001" gets the overall concept of artificial gravity correct, given its small radius and high rotation rate, it ends up ... 05:11: You can minimize these problems with a bigger ring, since that'll require less rotation to get the same 1 g of surface gravity. 06:04: And once you have to use some kind of fictional, super strong material, you're not gonna win a most realistic artificial gravity title. 06:43: ... was also the science adviser for "Battlestar Galactica" and the movie "Gravity," did the ... 07:46: ... gets a lot of other qualitative things right about rotation-induced gravity, like the way that its fighter ships, the Starfurys, launch just by ... 08:01: They get correct that you already have to be rotating to feel the artificial gravity. 08:05: So I really want to say that "Babylon 5" has the most realistic depiction of artificial gravity in sci-fi. 08:10: ... anything that the game gets wrong per se in its rotational artificial gravity. ... 08:20: ... along with your own votes for what the most realistic artificial gravity in sci-fi ... 04:57: ... even though "2001" gets the overall concept of artificial gravity correct, given its small radius and high rotation rate, it ends up sweeping major ... 00:35: ... artificial gravity that's just there, either through some kind of gravity generators or fictitious "gravity plating" seems to conflict with known physics. ... 02:27: It turns out that there's a simple formula for how big the effective surface gravity produced by this rotating structure would be. 06:04: And once you have to use some kind of fictional, super strong material, you're not gonna win a most realistic artificial gravity title.
	2015-04-22: Are Space and Time An Illusion? 07:42: Is it the low gravity or the radiation?
	2015-04-15: Could NASA Start the Zombie Apocalypse? 02:11: Preliminary evidence suggests that the 3D structure of viral proteins, which dictates in part how viruses enter cells may be altered in micro gravity.
	2015-04-08: Could You Fart Your Way to the Moon? 02:46: And that's only if there were no gravity.
	2015-04-01: Is the Moon in Majora’s Mask a Black Hole? 01:29: ... gives us a chance to explore some often unappreciated features of how gravity ... 02:30: What has to beat the planet's gravity, in this case, to make the rocks levitate is something called the moon's tidal force. 02:45: ... the rocks are closer to the moon, where the moon's gravity is stronger, they do accelerate towards the moon slightly more quickly ... 03:18: Ordinarily, though, that outward push is tiny, so tiny that a planet's own gravity is more than enough to hold things in place. 06:39: For example, gravity would be billions of times stronger on Termina's moon than on Earth. 01:29: ... gives us a chance to explore some often unappreciated features of how gravity works. ...
	2015-03-11: What Will Destroy Planet Earth? 00:24: Now in the case of Earth, the main glue is the collective gravity of almost six septillion kilograms of mass. 07:18: Quite Likely points out that we don't actually know how bad Martian gravity will be for humans, and we don't.
	2015-03-04: Should We Colonize Venus Instead of Mars? 02:04: But the real kicker is gravity. 02:10: And one thing we do know is that prolonged low gravity is bad for humans. 02:21: Now no one knows exactly how bad Martian gravity would be for humans, but it's definitely not going to be good. 02:33: ... a planet's surface and oxygen to its air, changing the planet's surface gravity is currently not even within the realm of ... 04:54: ... in the favorable gravity, and it starts to look like the upper atmosphere of Venus might be the ... 05:45: The gravity issue alone might make Venus the go-to option for long-term human habitation.
	2015-02-11: What Planet Is Super Mario World? 00:21: Let's start with how gravity affects motion, because that a huge effect on jumping. 00:58: ... or 10 meters per second squared, is called the acceleration due to gravity, or the surface gravity of ... 01:09: Now a planet's surface gravity has a huge effect on how high you can jump on that world. 01:14: Low gravity, for instance, is why astronauts in heavy spacesuits could jump so high on the moon. 02:51: That means "Super Mario World" has about eight times the surface gravity of Earth. 03:03: Their results show some variation, but all give surface gravities of between 5 and 10 Earth g's, which is consistent with my crude calculation. 03:10: ... detailed analyses confirm that "Super Mario World" respects the rules of gravity, meaning Mario's speed does indeed change at a steady rate whenever he ... 03:22: And the bottom line is that g is bigger on Super Mario World than on Earth, so that weaker gravity is not in fact the key to Mario's jumping prowess. 03:33: Remember, gravity is eight times stronger on Super Mario World than it is on Earth, yet Mario jumps much higher than we can on Earth. 04:00: On a planet with eight times Earth's surface gravity, your blood is eight times as heavy. 04:59: ... you can search through the ones for which we can estimate the surface gravity, and you find those with values that are many times Earth g's are thought ... 05:42: It'd actually be cool to know how strong gravity is in older versions of "Super Mario" games, or in other games altogether. 05:47: ... you find out, and especially if you find a game that mimics the gravity of any actual planet, please let me know in the comments, along with ... 03:10: ... detailed analyses confirm that "Super Mario World" respects the rules of gravity, meaning Mario's speed does indeed change at a steady rate whenever he jumps or ...

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