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	2022-11-23: How To See Black Holes By Catching Neutrinos 06:34: ... of observatory where you need to wait until your object sets below the horizon before you can observe ...
	2022-11-16: Are there Undiscovered Elements Beyond The Periodic Table? 15:46: ... hoping to gain new ground in humanity's journey to further and future horizons of space ...
	2022-08-24: What Makes The Strong Force Strong? 18:07: After all, Hawking radiation is sometimes portrayed as a virtual particle-antiparticle pair being separated by a black hole event horizon. 18:15: ... is that the story about separation of virtual particles by the event horizon is a meant to be an intuitive picture of what’s happening, and has only ... 18:28: Hawking’s original derived his radiation by calculating the disturbances on the quantum fields due to the appearance of an event horizon. 18:42: But the event horizon changes the balance of these modes causing imperfect canceling, which looks like particles are being radiated by the black hole.
	2022-07-20: What If We Live in a Superdeterministic Universe? 04:37: A horizontal measurement will yield a 50-50 chance of being left or right for his down-pointing electron.
	2022-06-22: Is Interstellar Travel Impossible? 19:10: Otinane Yos asks whether we can be sure that virtual particle - antiparticle pairs get separated near a Black Hole event horizon.
	2022-06-15: Can Wormholes Solve The Black Hole Information Paradox? 03:20: ... each other. If these particles get separated by a black hole event horizon   before they can annihilate, one particle escapes and becomes real, ...
	2022-06-01: What If Physics IS NOT Describing Reality? 05:53: ... left and right  until it’s measured. Run it through   our horizontally aligned Stern-Gerlach  divide and the electron has an even ...
	2022-05-25: The Evolution of the Modern Milky Way Galaxy 18:41: ... field. You may have heard me say that space  flows across the event horizon of a black hole   at the speed of light - that’s the ...
	2022-05-04: Space DOES NOT Expand Everywhere 11:22: ... seems to emerge from sub-Planck-wavelength radiation at the event horizon of a black hole. Its solution takes us to the realm of the holographic ... 13:16: ... receding galaxies - they will spend most of cosmic time far beyond the horizon, in which case we never would have even known that we live in an ...
	2022-04-27: How the Higgs Mechanism Give Things Mass 07:01: ... this,   the vertical represents potential energy and  the horizontal represents the field ...
	2022-04-20: Does the Universe Create Itself? 16:10: ... we should expect a type of Hawking radiation from the cosmic event horizon even if the universe isn’t a black hole. All event horizons will lead to ... 17:39: ... the stars, dark matter, other black holes, etc - then it’s event horizon is the same size as our cosmological even horizon. Sounds too much ... 16:10: ... has a wavelength that’s on the scale of the event horizon. So the horizon radiation from the cosmic event horizon would have wavelength roughly the size of ... 17:39: ... - then it’s event horizon is the same size as our cosmological even horizon. Sounds too much of a coincidence, right? Well actually, this is just another ... 16:10: ... cosmic event horizon even if the universe isn’t a black hole. All event horizons will lead to a disconnection in the vibrational modes of the quantum ...
	2022-03-30: Could The Universe Be Inside A Black Hole? 01:01: In general relativity, that looks like a point of infinite density surrounded by an event horizon. 01:07: We can think of the event horizon as the surface where the flow of space itself is like a river moving at the speed of light. 01:15: ... nothing that not even light can travel back out from below the event horizon. ... 01:26: The universe also has a singularity and an event horizon. 01:46: That expansion gives us our event horizon. 02:09: This is the cosmological event horizon. 02:12: ... we’re still receiving light from objects that are now beyond that horizon, because it was emitted by those objects before they crossed the ... 02:22: ... the accelerating expansion of the universe means the cosmological event horizon is closer to us than the spot where recession equals the speed of ... 02:33: But the effect is the same: no events that happen now beyond that horizon can ever be seen. 05:19: ... all-encompassing future for the spacetime that lives beneath the event horizon in the same way that the big bang is the encompassing past for the for ... 06:13: ... past, space-like singularity of the white hole is surrounded by an event horizon that is the opposite to a black hole event horizon - it can only be ... 06:24: Space flows at the speed of light across the event horizon from within. 06:28: That’s starting to look like our universe - a past, space-like singularity and an event horizon that can’t be crossed from the outside. 08:36: ... thing collapses under its own gravity and an event horizon forms around it, but within the collapsing cloud the matter remains ... 09:30: And that’s true even after the black hole’s event horizon forms. 12:11: If we’re within the event horizon of a black/white hole, what’s on the outside? 06:13: ... by an event horizon that is the opposite to a black hole event horizon - it can only be crossed from the inside to the ... 08:36: ... thing collapses under its own gravity and an event horizon forms around it, but within the collapsing cloud the matter remains ... 09:30: And that’s true even after the black hole’s event horizon forms.
	2022-03-23: Where Is The Center of The Universe? 13:33: ... being a boundary to our bubble is very likely far beyond our cosmic horizon. ...
	2022-03-08: Is the Proxima System Our Best Hope For Another Earth? 00:11: He made careful note of the position of a bright  star that hung just above the southern horizon. 00:57: By the end of the 17th century, the star had long since slipped below the horizon of Alexandria in its galactic wanderings. 14:56: But there’s another white star on the horizon,  but it’s slowly slipping away on its own orbit around the Milky Way.
	2022-02-23: Are Cosmic Strings Cracks in the Universe? 08:50: ... We actually expect  multiple nucleation events in each causal horizon,   potentially leading to dozens of cosmic  strings in a network ...
	2022-02-16: Is The Wave Function The Building Block of Reality? 14:52: ... wave whose wavelength is short compared to the black hole’s event horizon can be completely swallowed, while a larger gravitational wave will get ... 16:15: ... time dilation that we talk about approaching the black hole event horizon is not from the point of view of falling matter, but from the point of ... 16:48: ... asks if an outsider observer sees matter slow and freeze at the event horizon, what happens when the event horizon grows? Does that matter get ... 17:42: ... observe an object being frozen at the event horizon if the light emitted at the moment it crosses the horizon from its ... 18:05: And so everything that went into the black hole remains frozen on the horizon. 18:37: ... asks another related question. If we never see anything cross the event horizon, why do we say information is lost? When people talk about information ... 17:42: ... So to lose an object beneath a growing black hole means that the event horizon envelopes that final photon, not the object. By some definitions of the event ... 16:48: ... matter slow and freeze at the event horizon, what happens when the event horizon grows? Does that matter get swallowed up? This is tricky because that the ...
	2022-01-27: How Does Gravity Escape A Black Hole? 00:00: ... very center Fact: every black hole singularity is surrounded by an event horizon. ... 00:10: Nothing can escape from within the event horizon unless it can travel faster than light. 01:01: ... of infinite density surrounded by this boundary of no return - the event horizon. ... 02:56: ... light, and all of the mass of a black hole is hidden beneath the event horizon, how does its gravity get out to influence the surrounding ... 03:07: Shouldn’t a black hole’s event horizon protect the universe from its own malicious influence? 03:27: There’s no question here - a black hole’s gravity doesn’t care about the event horizon at all. 04:38: Falling from very far away, an observer and the patch of space that they occupy reach light speed at the event horizon of the black hole. 04:56: At some point it exceeds the swimming speed of any possible fish - that’s the event horizon. 05:13: The water at the “event horizon” doesn’t know about the fall. 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: ... of the singularity, and they don’t have to travel through the event horizon to do their ... 08:25: But if we’re describing the gravitational field as being built up by virtual gravitons then the event horizon is no barrier at all. 08:39: ... this idea of sending information across an event horizon brings us to our last argument, and this one works whether we’re talking ... 09:12: ... present mass of a black hole is hidden below the event horizon, but we can see its past mass, and it’s the gravitational effect of the ... 09:27: As it approaches the surface that is to become the event horizon, it approaches light speed with respect to someone watching from a distance. 09:39: It appears to freeze at the event horizon, and the light it emits becomes stretched out and sapped of energy. 10:01: So we can still “see” the mass of a black hole - it’s imprinted on the event horizon. 10:55: ... the black hole, but from your point of view it’s frozen on the event horizon, but is happily exerting its influence on the surrounding ... 11:18: You interact with the local curvature of spacetime, which is produced by the past mass, which from your point of view is on the event horizon. 11:45: By that definition the mass of a black hole is everywhere - so it’s not surprising that it can escape the horizon. 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. 08:39: ... this idea of sending information across an event horizon brings us to our last argument, and this one works whether we’re talking about ... 05:13: The water at the “event horizon” doesn’t know about the fall. 03:07: Shouldn’t a black hole’s event horizon protect the universe from its own malicious influence?
	2021-12-20: What Happens If A Black Hole Hits Earth? 04:26: ... then it’s probably already happened. This PBH would be small - its event horizon - its surface of no-return - would be around the size of an atom. And it ... 05:13: ... moon phobos - 10^16 kg like a large asteroid. That gives it an event horizon the size of a hydrogen atom. At interstellar speeds it spends around a ... 06:02: ... hole, gravity accelerates matter to incredible speeds. Near the event horizons, particles collide with each other sizable fractions of the speed of ... 07:05: ... tiny event horizon of a micro black hole is a very narrow choke-point for matter trying to ... 16:33: ... space. That means that an observer falling through a black hole event horizon shouldn’t notice anything special about that boundary - except the fact ... 18:16: ... lasts longer for fuzzballs than for regular black holes due to the event horizon being less cleanly defined. It’s also been suggested that the Event ... 04:26: ... then it’s probably already happened. This PBH would be small - its event horizon - its surface of no-return - would be around the size of an atom. And it ... 16:33: ... space. That means that an observer falling through a black hole event horizon shouldn’t notice anything special about that boundary - except the fact that they ... 18:16: ... being less cleanly defined. It’s also been suggested that the Event Horizon Telescope could potentially detect deviations from general relativity in the form ... 06:02: ... hole, gravity accelerates matter to incredible speeds. Near the event horizons, particles collide with each other sizable fractions of the speed of ...
	2021-11-17: Are Black Holes Actually Fuzzballs? 00:39: ... surrounded by a surface from which even light can’t escape - the event horizon. ... 01:10: And at the event horizon another paradox arises. 02:56: The no-hair theorem says that there’s no information beyond charge, mass and spin that’s observable above the event horizon. 03:04: The information contributing to black hole entropy could be beneath the horizon, but if we add one more fact we run into serious trouble. 04:29: But this is also the problem at the event horizon. 04:49: ... the surrounding quantum fields, which only worked if the gravity at the horizon was relatively weak, in which case quantum gravity effects shouldn’t ... 05:09: ... gravity starts to get quantum even above the event horizon, then it may be possible to actually encode information on that surface ... 06:17: It turns out that though, that string theory can make sense of the black hole event horizon also. 06:37: ... guys found a way to count the microstates on the horizon- the number of possible configurations of stringy structures - the 1-D ... 06:55: ... on the mechanism by which information could be encoded on the event horizon. ... 07:13: ... and Vafa did this for the somewhat unrealistic case of a black hole horizon with 4 spatial dimensions, but it was a decisive step and it gave us a ... 08:06: ... how they form, or how structure can actually be supported on the event horizon. ... 09:09: ... this is right, then black holes don’t have an empty event horizon at all, but rather a real surface that looks like a tangled nightmare of ... 09:39: ... important at the center of the black hole but instead may pile up to the horizon ... 10:37: The resulting fuzzball doesn’t have a local event horizon - in that there’s no single surface of no-return. 12:10: The event horizon is just the pair of equidistant points on the line inside of which escape is impossible. 12:38: For a fuzzball, spacetime closes on itself at the event horizon. 10:37: The resulting fuzzball doesn’t have a local event horizon - in that there’s no single surface of no-return. 09:39: ... important at the center of the black hole but instead may pile up to the horizon scale. ...
	2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light 15:36: ... monopole would manifest as a black hole - in that it would have an event horizon. ...
	2021-09-21: How Electron Spin Makes Matter Possible 15:48: ... so at most they can appear to be coming from the edge of the event horizon. ... 16:12: ... that’s exactly why the event horizon telescope image looks like that. Although in that case the dark area is ...
	2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe 13:06: ... is growing and at some point soon it’ll form an inescapable event horizon and we’ll be   stuck inside an actual black hole. Escape ...
	2021-09-07: First Detection of Light from Behind a Black Hole 01:08: Now you might remember the picture of the black hole captured by the event horizon telescope.
	2021-08-18: How Vacuum Decay Would Destroy The Universe 12:07: ... more comforting fact. If the vacuum does decay inside our cosmic horizon   we’ll never see it coming. Because no light  can outpace the ...
	2021-07-21: How Magnetism Shapes The Universe 11:40: Intense magnetic fields live just above the event horizon of some of thses black hole, and thread the infalling disk. 11:54: ... light surrounding the M81 supermassive black hole observed by the event horizon ...
	2021-07-07: Electrons DO NOT Spin 06:36: ... a second set of Stern-Gerlach magnets,  but now they’re oriented horizontally. Classical dipoles that are at 90 degrees to the field would experience ...
	2021-06-16: Can Space Be Infinitely Divided? 07:48: ... mass to produce a black hole with a Planck-length event   horizon - so any attempt to measure something that small swallows it in a ...
	2021-05-25: What If (Tiny) Black Holes Are Everywhere? 00:23: They’re surrounded by this surface we call the event horizon, whose defining property is that nothing that falls beneath it can ever emerge. 02:06: ... a sort of a hack - a brilliant workaround - to prove that if an event horizon forms in a vacuum, then the vacuum states of the quantum fields have to ... 02:36: In the common pop-sci description of Hawking radiation you often hear about particle-antiparticle pairs appearing at the event horizon. 02:45: This is misleading; for one thing, the radiation doesn’t appear right above the event horizon. 02:52: ... of the emitted particles are about the size of the whole event horizon, so they sort of emerge from the entire region surrounding the black ... 03:02: For the black hole left behind when a massive star dies, the event horizon is several kilometers in radius. 04:19: One big assumption is that the space near the event horizon isn’t TOO strongly curved compared to the smallest quantum scale. 06:41: Such a black hole would have an event horizon of around 10^-35 meters - the Planck length. 09:58: A way around this has been proposed - what if space inside black holes actually expands to a region larger than the event horizon? 02:06: ... a sort of a hack - a brilliant workaround - to prove that if an event horizon forms in a vacuum, then the vacuum states of the quantum fields have to be ... 04:19: One big assumption is that the space near the event horizon isn’t TOO strongly curved compared to the smallest quantum scale.
	2021-05-11: How To Know If It's Aliens 15:39: ... the bubble in a similar way to how things appear to freeze at the event horizon of a black hole. Nothing actually passes into the bubble, so the ship is ...
	2021-04-21: The NEW Warp Drive Possibilities 03:07: Or beyond the cosmic horizon, the expanding universe is carrying galaxies away from us faster than light.
	2021-04-13: What If Dark Matter Is Just Black Holes? 06:38: ... though these black holes would have microscopic event horizons, at those insane abundances, they’d be wreaking absolute havoc in various ...
	2021-03-09: How Does Gravity Affect Light? 04:37: ... the event horizon of the black hole, gravitational time dilation is so strong that clocks ... 06:10: Can this gravitational time dilation also explain the bending of a ray light traveling horizontally? 06:15: Well, tricky - because there’s no change in clock speed in the horizontal direction - only the vertical. 06:10: Can this gravitational time dilation also explain the bending of a ray light traveling horizontally?
	2021-01-19: Can We Break the Universe? 04:33: ... the set of simultaneous events for a motionless observer lie on a horizontal line - all events corresponding to your notion of a given tick on the ...
	2020-12-22: Navigating with Quantum Entanglement 04:07: And their horizontal orientation, or angle relative to lines of longitude.
	2020-12-08: Why Do You Remember The Past But Not The Future? 04:36: Time increases upwards, while the horizontal axis is separation in space.
	2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time 01:17: ... by a surface where time froze.   Beneath that “event horizon” all matter, light, space itself was doomed to fall inwards towards ... 01:58: ... matter could reach the densities  high enough to produce an event horizon - nor   even whether such dense matter would  really ... 05:55: ... black holes is that null geodesics beneath   the event horizon that are trying  to travel outwards also converge.   ... 01:58: ... matter could reach the densities  high enough to produce an event horizon - nor   even whether such dense matter would  really ... 05:55: ... tricky here - there are multiple ways to   define an event horizon depending on where you sit compared to the black hole. Penrose came up with ... 04:06: ... this deserve a Nobel prize? Penrose set out to show that an event horizon   and a singularity would form for any distribution of matter, no ...
	2020-08-24: Can Future Colliders Break the Standard Model? 14:28: ... tricky one: when two black holes merge and share a single, warped event horizon, shouldn’t there be a thin sliver of space in between that is not flowing ... 15:06: ... general relativity calculations reveal an event horizon cross-section that’s called the pair-of-pants function - it looks like ... 15:16: They start separate, and the event horizons move towards each other as they join, and at some point the event horizons touch and then merge. 15:28: ... flow of space anywhere on the event horizon has to be exactly perpendicular to the face of the event horizon - so at ... 15:06: ... general relativity calculations reveal an event horizon cross-section that’s called the pair-of-pants function - it looks like cross-sections ... 14:28: ... tricky one: when two black holes merge and share a single, warped event horizon, shouldn’t there be a thin sliver of space in between that is not flowing towards ... 15:16: They start separate, and the event horizons move towards each other as they join, and at some point the event horizons touch and then merge.
	2020-08-17: How Stars Destroy Each Other 11:04: Zack Hamburg asks how we know that a black hole isn’t just a neutron star behind an event horizon. 11:27: So what happens to the neutron star after it collapses enough to form an event horizon? 11:32: Well, below that event horizon, we can think of space flowing downwards faster than the speed of light. 13:37: Frank and Jim asked how the event horizons of merging black holes change just before they combine. 13:42: ... deform into a sort of 8 or hourglass shape - in the sense that the event horizons sort of reach out to each other, connect, before coming together into an ... 13:56: ... the shape of the stuff inside the black hole - we’re just the event horizon - the surface below which there’s a faster-than-light flow of ... 14:07: Here’s a simulation from the SXS - simulating extreme spacetimes group at ... that shows how the event horizons merge. 13:56: ... the shape of the stuff inside the black hole - we’re just the event horizon - the surface below which there’s a faster-than-light flow of ... 13:37: Frank and Jim asked how the event horizons of merging black holes change just before they combine. 13:42: ... deform into a sort of 8 or hourglass shape - in the sense that the event horizons sort of reach out to each other, connect, before coming together into an ... 14:07: Here’s a simulation from the SXS - simulating extreme spacetimes group at ... that shows how the event horizons merge. 13:42: ... deform into a sort of 8 or hourglass shape - in the sense that the event horizons sort of reach out to each other, connect, before coming together into an ...
	2020-08-10: Theory of Everything Controversies: Livestream 00:00: ... now through the core of the roll representing what i would call the horizontal tangent space which is not pointed along the tube if it was pointed ...
	2020-07-20: The Boundary Between Black Holes & Neutron Stars 05:42: ... black holes, which by definition have an escape velocity at the event horizon equal to the speed of ... 06:49: It’s like a phantom event horizon. 06:52: In the case of the earth the phantom event horizon is about a centimeter in diameter. 07:00: As you increase a neutron star’s mass, its phantom event horizon grows while its actual surface shrinks. 12:18: ... our last two episodes we talked about how to dissolve a black hole event horizon by adding rotation or charge to the black hole, and also about ... 12:34: ... trying to disolve an event horizon by throwoing more and more electric charge into it - Ultimantis points ... 13:03: ... Cimo has a good one: What if I cross the event horizon just for a plank lenght and the instant later the black hole shrinks due ... 13:34: ... watching from far away, you appear to freeze smeared out at the event horizon - and then yes, they would see your energy exit again as the black hole ... 05:42: ... black holes, which by definition have an escape velocity at the event horizon equal to the speed of ... 07:00: As you increase a neutron star’s mass, its phantom event horizon grows while its actual surface shrinks.
	2020-06-30: Dissolving an Event Horizon 00:44: ... surrounding all of this weirdness is the event horizon: the surface around the central singularity where the inward flow of ... 01:07: The event horizon sounds dire, but it’s a blessing. 01:30: ... that every gravitational singularity must be surrounded by an event horizon. ... 02:12: So let’s talk about how to dissolve an event horizon, although I would ask you to please not try this at home, for the sake of all of physics. 02:45: With nothing to counter the inward flow of space, an event horizon is inevitable. 03:25: It’s like the eye of the storm, and it’s separated from the surrounding cascade by the inner event horizon. 03:34: As the spin of a Kerr black hole increases, the spacetime waterfall is beaten back, and so the inner horizon grows. 03:40: At a certain very high rotation rate, the inner and outer horizons merge - which means they both vanish. 04:20: Reisner-Nordstrom black holes also have an inner horizon, interior to which space and time seem normal-ish. 04:28: The more electric charge you drop into a black hole, the larger its inner horizon becomes. 04:33: And just as with the rotating black hole, at some point the inner and outer horizons become one and vanish and you’re left with a naked singularity. 04:43: ... the tipping point - when the inner and outer horizons are right next to each other - you have what we call an extremal black ... 05:59: The outer event horizon will shrink until it meets the inner horizon, and again you have an extremal black hole. 06:21: Hawking radiation is a direct result of there being an event horizon. 06:58: ... will always stop a gravitational singularity being stripped of its event horizon - but it doesn’t tell us the physical ... 08:06: ... black hole - one that’s rotating nearly fast enough to lose its event horizon - the gas near the event horizon orbits entirely riding on the carousel ... 10:23: In fact the field itself will always generate enough mass to prevent the black hole from losing its event horizon. 11:16: ... two episodes - building black holes in the lab with analog event horizons, and Roger Penrose’s conformal cyclic ... 06:58: ... will always stop a gravitational singularity being stripped of its event horizon - but it doesn’t tell us the physical ... 08:06: ... black hole - one that’s rotating nearly fast enough to lose its event horizon - the gas near the event horizon orbits entirely riding on the carousel of ... 03:34: As the spin of a Kerr black hole increases, the spacetime waterfall is beaten back, and so the inner horizon grows. 04:20: Reisner-Nordstrom black holes also have an inner horizon, interior to which space and time seem normal-ish. 08:06: ... nearly fast enough to lose its event horizon - the gas near the event horizon orbits entirely riding on the carousel of frame-dragged state, and has no ... 01:07: The event horizon sounds dire, but it’s a blessing. 03:40: At a certain very high rotation rate, the inner and outer horizons merge - which means they both vanish. 04:33: And just as with the rotating black hole, at some point the inner and outer horizons become one and vanish and you’re left with a naked singularity. 04:43: ... the tipping point - when the inner and outer horizons are right next to each other - you have what we call an extremal black ... 11:16: ... two episodes - building black holes in the lab with analog event horizons, and Roger Penrose’s conformal cyclic ... 03:40: At a certain very high rotation rate, the inner and outer horizons merge - which means they both vanish.
	2020-06-22: Building Black Holes in a Lab 00:16: ... about never being able to see inside one beneath the inescapable event horizon. Then there’s the fact that real black holes are, thankfully, very far ... 03:05: ... where the waterfall of space equals the speed of light is our event horizon. No information - from fish or astronauts or anything - can reach us from ... 03:26: ... this was just an illustrative, evocative example of the power of event horizons. But by 1982 he realized the two situations had much more in common, ... 04:08: ... analogous situations and found a number of systems with event horizons Analog theoretical black holes are all very well, but their real value ... 04:55: At some point the flow is faster than the waves - and that’s your analog event horizon. 05:01: ... the speed of ripples on the tank surface you again have an analog event horizon. ... 05:25: ... these event horizons, physicists can look for black hole-like behavior. For example, Hawking ... 08:04: ... through the black hole’s ergosphere. That’s the region around the event horizon where the circular flow of space becomes irresistible. It turns out that ... 11:04: ... appear for a variety of systems—you just need some sort of apparent horizon then finding bonafide Hawking radiation for one system should tell you ... 03:26: ... this was just an illustrative, evocative example of the power of event horizons. But by 1982 he realized the two situations had much more in common, ... 04:08: ... analogous situations and found a number of systems with event horizons Analog theoretical black holes are all very well, but their real value ... 05:25: ... these event horizons, physicists can look for black hole-like behavior. For example, Hawking ... 04:08: ... analogous situations and found a number of systems with event horizons Analog theoretical black holes are all very well, but their real value is that ... 05:25: ... these event horizons, physicists can look for black hole-like behavior. For example, Hawking radiation. ...
	2020-05-27: Does Gravity Require Extra Dimensions? 13:29: ... episode we talked about the strange regions that lie beneath the event horizon of a rotating black hole - regions like the Carter time machine and the ...
	2020-05-18: Mapping the Multiverse 00:52: Back then we stopped short of dropping below the event horizon - the boundary of no return. 01:11: The inescapable surface surrounding a black hole is called the event horizon. 02:29: ... the event horizon is the ergosphere - a place where the fabric of space itself is whipped ... 02:40: The event horizon itself is distorted - wider at the equator than the poles, just like the rotating earth. 02:50: Now let’s peek below the event horizon to see how weird things really get. 04:20: This leads to a second event horizon called the inner horizon. 05:14: ... can try to turn around and go back the way you came through the inner horizon, or you can plunge through the singularity ... 07:41: Also, there are no horizons above you - there’s a straight path to the outside universe - but it is certainly not our universe. 07:50: For one thing, the lack of event horizons above you means the ring is a naked singularity, as well as being repulsive. 08:54: At this point we can follow an outgoing geodesic across the inner horizon. 09:03: That outgoing flow continues above the inner horizon, and will eventually eject you past the outer horizon. 11:10: ... fact of your utter obliteration before you ever cross the inner event horizon in the first ... 11:21: The complete Penrose diagram for the Kerr spacetime has not one, but two inner event horizons leading to two parallel wormholes. 11:38: ... correspond to the region below the event horizon but they’re causally disconnected, the difference being that time flows ... 11:50: So you have this messed up situation where the direction of the flow of time actually clashes at the inner horizon. 12:34: So if you do get to the inner horizon you are in a bath of energy on par with the Big Bang. 13:30: You have the same inner horizon and chain of wormhole-connected universes. 00:52: Back then we stopped short of dropping below the event horizon - the boundary of no return. 04:20: This leads to a second event horizon called the inner horizon. 07:41: Also, there are no horizons above you - there’s a straight path to the outside universe - but it is certainly not our universe. 07:50: For one thing, the lack of event horizons above you means the ring is a naked singularity, as well as being repulsive. 11:21: The complete Penrose diagram for the Kerr spacetime has not one, but two inner event horizons leading to two parallel wormholes.
	2020-05-11: How Luminiferous Aether Led to Relativity 16:14: ... Virgo supercluster. That's so weird to think about - the most distant horizon we can see is the same size as the local bubble of galaxies. Those poor ...
	2020-05-04: How We Know The Universe is Ancient 14:28: Devansh Rana asks Can wormholes exist without black holes ie without the event horizon. 14:36: ... the Schwarzschild wormhole definitely has an event horizon - although at its most open, entering the event horizon ejects you into ... 16:15: ... the distance has to be short. When the wormhole is fully open, the event horizons of the wormholes ... 16:44: Pass thorugh one event horizon at that instant you exit the other. 14:36: ... the Schwarzschild wormhole definitely has an event horizon - although at its most open, entering the event horizon ejects you into ... 16:15: ... the distance has to be short. When the wormhole is fully open, the event horizons of the wormholes ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... I hope you're okay Bob which is that when mass is just about the event horizon of a black hole is the event horizon slightly distorted due to the ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 03:45: ... of the wormhole is actually a sphere the size of the Schwarzschild event horizon. If we could pass through that event horizon we would not find ourselves ... 04:50: ... are blended and mutated so that time doesn’t freeze at the event horizon, which itself becomes this 45 degree path. Sub-lightspeed paths are ... 05:17: ... if you travel to the left at any possible speed you’ll find the event horizon and enter the interior of the black hole. But what if you could travel ... 05:43: ... has narrowed in width and passing through means crossing two event horizons - and the region in between is the inside of a black hole. When that ... 11:03: ... circumstances like on quantum scales or if they’re hidden by an event horizon. Combined with Roger Penrose’ cosmic censorship conjecture, which ensures ... 05:43: ... has narrowed in width and passing through means crossing two event horizons - and the region in between is the inside of a black hole. When that ...
	2020-03-31: What’s On The Other Side Of A Black Hole? 00:00: ... maps are useless inside black holes. At the event horizon - the ultimate point of no return as you approach a black hole - time ... 01:53: ... It even works inside the black hole - beneath the inescapable event horizon. Although it works in both these regions, the Schwarzschild metric canNOT ... 02:56: ... the tortoise, and a plummeting cartographer would fall through the event horizon. The event horizon is just a coordinate singularity like the earth’s ... 03:14: ... measure of distance that becomes infinitesimally compact approaching the horizon. That compactification cancels out the infinite stretching of time so ... 03:46: ... coordinates, and they revealed that the singularity of the event horizon was an illusion. Kruskal–Szekeres coordinates improved our map by ... 04:14: ... very clear what parts of the universe are accessible. Close to the event horizon, even a light-speed path has only a narrow window of escape. Once inside ... 07:32: ... - then you could take these horizontal which would dip beneath the event horizons and emerge in the mirror universe. You’ve just traversed an ... 09:00: ... if you can travel faster than light you’ll emerge from the same event horizon that swallowed you. Or you can plunge faster than light towards the ... 00:00: ... maps are useless inside black holes. At the event horizon - the ultimate point of no return as you approach a black hole - time and ... 01:53: ... that actually crosses the event horizon. That’s because at the event horizon, time appears to freeze from the point of view of a distant observer. And the ... 07:32: ... - then you could take these horizontal which would dip beneath the event horizons and emerge in the mirror universe. You’ve just traversed an ...
	2020-03-24: How Black Holes Spin Space Time 00:21: ... if that mass is sufficiently compressed, the metric predicts an event horizon - a spherical surface where the fabric of space cascades downwards at ... 01:01: ... own galaxy, and we’ve even taken an image of a black hole with the event horizon telescope. But none of these real black holes are particularly well ... 01:44: ... place, and the rotation of any latter object sucked through the vent horizon. Even non-rotating objects will affect black hole spin if they fall in at ... 03:54: ... tempting to just say that some physical thing deep beneath the event horizon is rotating. But if nothing can escape the event horizon, how can that ... 04:11: ... fact, how can any effect of gravity extend from beneath the event horizon? In fact it sort of doesn’t actually. Both the gravitational field and ... 04:26: ... are self-sustaining holes in the fabric of spacetime. Space at the event horizon cascades downwards, dragging more space behind it, sort of like how ... 05:49: ... common misconception, as long as you don’t get too close to the event horizon it’s possible to orbit a black hole in a perfectly stable way. For a ... 07:27: So yeah, you can orbit “safely” pretty close to the Kerr black hole’s event horizon. 07:33: ... above the event horizon is a particularly bizarre region called the ergosphere. There, frame ... 07:50: ... situation here is actually similar to the state below the event horizon where space moves downwards faster than light. In the math, that ... 08:34: The ergosphere extends all the way down to the event horizon. 08:37: ... the event horizon in the rotating case is not spherical - it’s squished at the poles, like ... 08:54: ... I know you would love to drop below the event horizon right now - but you’re going to have to wait. There’s still plenty to do ... 09:17: ... exactly the right point, one half will go plummeting through the event horizon while the other is ejected from the ergosphere and escapes. In fact it ... 12:11: ... And we'll encounter all of these when we drop below the event horizon into the deeper weirdness of the Kerr ... 00:21: ... if that mass is sufficiently compressed, the metric predicts an event horizon - a spherical surface where the fabric of space cascades downwards at the ... 05:49: ... a stable circular orbit as close as 3 times the radius of the event horizon - or 3 Schwarzschild radii. Any closer and no stable orbits exist - unless ... 08:37: ... has a similar shape - but also dips at the poles to touch the event horizon - it’s sort of pumpkin ... 04:26: ... are self-sustaining holes in the fabric of spacetime. Space at the event horizon cascades downwards, dragging more space behind it, sort of like how water drags ... 01:01: ... own galaxy, and we’ve even taken an image of a black hole with the event horizon telescope. But none of these real black holes are particularly well described by ...
	2020-03-16: How Do Quantum States Manifest In The Classical World? 02:56: ... have to choose what angle you want to measure it at - say, vertically or horizontally. ... 03:12: ... and you might see that the spin axis is pointing up or down, measure horizontally and it’ll be pointing left or right. Weirdly, if you measure vertically ... 04:28: ... basis, each particle starts in a state of both up AND down, while in the horizontal each is left AND right, etc. The only thing we know is there’s this ... 09:28: ... into the details here - suffice to say that it's possible to recover the horizontal spin information, even if it’s more straightforward to recover the ... 11:48: ... up the experiment - whether you align your magnetic field vertically or horizontally. But ultimately they are states that can survive contact with the ... 04:28: ... basis, each particle starts in a state of both up AND down, while in the horizontal each is left AND right, etc. The only thing we know is there’s this ... 09:28: ... into the details here - suffice to say that it's possible to recover the horizontal spin information, even if it’s more straightforward to recover the ... 02:56: ... have to choose what angle you want to measure it at - say, vertically or horizontally. ... 03:12: ... and you might see that the spin axis is pointing up or down, measure horizontally and it’ll be pointing left or right. Weirdly, if you measure vertically ... 11:48: ... up the experiment - whether you align your magnetic field vertically or horizontally. But ultimately they are states that can survive contact with the ...
	2019-12-17: Do Black Holes Create New Universes? 03:38: ... it sort of bounces - but unable to exit the event horizon of the black hole, it forms a new region of spacetime, effectively ...
	2019-10-21: Is Time Travel Impossible? 08:51: The maelstrom of spinning spacetime may generate closed timelike curves deep down below the event horizon.
	2019-10-15: Loop Quantum Gravity Explained 15:49: ... the black hole rotates more than a certain amount then the event horizon evaporates, exposing the singularity to the universe - or in the case of ...
	2019-10-07: Black Hole Harmonics 01:30: Imagine it: two event horizons – two roughly spherical black surfaces that are literal boundaries to our universe. 02:06: The event horizon seems to define the surface of the black hole, but really it’s the fabric of spacetime itself that’s vibrating. 03:46: The harmonic oscillations of 2-D surfaces – like drum skins, bells, or the event horizons of black holes – are a good bit more complex than in 1-D. 03:56: In the case of the event horizon, or any spherical-ish surface, we break down the oscillations not into sine waves but into spherical harmonics. 04:33: They leak away over time, but while present they warp the shape of the event horizon. 01:30: Imagine it: two event horizons – two roughly spherical black surfaces that are literal boundaries to our universe. 03:46: The harmonic oscillations of 2-D surfaces – like drum skins, bells, or the event horizons of black holes – are a good bit more complex than in 1-D.
	2019-09-30: How Many Universes Are There? 15:30: I'm also echoing some of the thoughts of Alan Stern, lead scientist on the new horizons mission to pluto.
	2019-09-23: Is Pluto a Planet? 11:11: Don’t think of this as a demotion - it’s more of a ... reincentivizing horizontal pivot.
	2019-08-26: How To Become an Astrophysicist + Challenge Question! 10:46: ... a rate for inflation Let's assume the minimum rate needed to explain the horizon and flatness problems That is all distance is increased by a factor of ...
	2019-07-25: Deciphering The Vast Scale of the Universe 00:49: ... has grown enormously – to include countless galaxies to the cosmic horizon and almost to the beginning of ... 08:27: ... the art modern observatories like the Gemini Observatory, and the Event Horizon Telescope, and LIGO, which we visited throughout this ... 08:55: If we continue exploring – if we keep looking deeper and further – who knows what we’ll find in the expanding horizons of space time? 08:27: ... the art modern observatories like the Gemini Observatory, and the Event Horizon Telescope, and LIGO, which we visited throughout this ... 08:55: If we continue exploring – if we keep looking deeper and further – who knows what we’ll find in the expanding horizons of space time?
	2019-07-15: The Quantum Internet 06:54: They’re entangled so that they have opposite polarization, say one is vertical the other is horizontal.
	2019-07-01: Thorium and the Future of Nuclear Energy 17:49: ... definitely doesn't extend more than 10 or so times the black hole event horizon Oppie asks why NASA isn't dedicating more resources to investigating all ...
	2019-06-06: The Alchemy of Neutron Star Collisions 02:47: ... of the newly formed black hole presumably doomed to fall into the event horizon but that same beta decay process the converted neutrons back to protons ...
	2019-05-09: Why Quantum Computing Requires Quantum Cryptography 14:46: ... episode on the galaxy without dark matter, and our coverage of the event horizon telescope's black hole ... 15:56: Tommy Barlow states that nor the event horizon, nor anything near it, was imaged. 16:02: The event horizon is invisible. 16:05: But the telescope DID resolve down to the size of the event horizon. 16:16: That's probably around 5 times larger than the event horizon, in the case of this quasar. 16:21: ... seriously, the "light from outside the event horizon because we can't actually see the event horizon telescope" doesn't have ... 14:46: ... episode on the galaxy without dark matter, and our coverage of the event horizon telescope's black hole ... 05:48: ... for example, pass a randomly-polarized photon through a horizontal polarization filter like a polarized sunglasses lens and the photon will ...
	2019-05-01: The Real Science of the EHT Black Hole 00:18: ... first ever actual bona fide photo of a black hole, made by the Event Horizon Telescope and revealed to the world in a press conference on April ... 01:00: It has an estimated mass of several billion times that of the Sun, which gives it an event horizon larger than the solar system. 03:31: ... to observe the event horizon of the M87 black hole you need to resolve one one-millionth of 1% of one ... 04:24: ... Event horizon Telescope - the EHT - consists of nine radio observatories across the ... 05:58: The event horizon itself is the point where even outward-pointing light can’t escape the black hole. 06:04: For a non-rotating black hole the size of the event horizon is called the Schwarzschild radius, and it’s proportional to the mass of the black hole. 06:13: But we’re not seeing the event horizon here – that’s somewhat smaller. 09:37: ... found that monster has a mass over 6 billion solar masses, with an event horizon that's about 1/5 the size of that ring– so that’s VERY big, even by ... 10:54: ... this actual picture given to us by the Event Horizon Telescope and its brilliant team – finally hits us with visceral reality ... 01:00: It has an estimated mass of several billion times that of the Sun, which gives it an event horizon larger than the solar system. 00:18: ... first ever actual bona fide photo of a black hole, made by the Event Horizon Telescope and revealed to the world in a press conference on April ... 04:24: ... Event horizon Telescope - the EHT - consists of nine radio observatories across the globe, from ... 10:54: ... this actual picture given to us by the Event Horizon Telescope and its brilliant team – finally hits us with visceral reality of the ... 04:24: ... Event horizon Telescope - the EHT - consists of nine radio observatories across the globe, from ...
	2019-04-24: No Dark Matter = Proof of Dark Matter? 00:03: ... is indeed a reasonable interpretation of the universe beyond our cosmic horizon as a hologram living in the light bill quite reach us trapped at the ...
	2019-04-10: The Holographic Universe Explained 02:41: And while it’s waiting to be radiated, that information should be encoded on the event horizon. 02:52: Things that fall into a black hole do actually experience crossing the event horizon and being inside the black hole.
	2019-04-03: The Edge of an Infinite Universe 00:46: It’s boundary is called the particle horizon. 01:02: ... define its horizon like we might build a little picket fence around our little patch – ... 01:17: We visited these cosmic horizons in one of the early Space Time episodes. 01:22: To review: the particle horizon defines the limit of the visible past, and there’s also cosmic event horizon defining the limit of the visible future. 04:20: ... spacetime –to the edge of an infinite universe or across the event horizon of a black ... 04:49: The first efforts were designed to allow physicists to cross the event horizon of black holes – mathematically. 05:03: ... the artificial infinity – the coordinate singularity - of the event horizon – also something we’ve discussed (the phantom singularity) It was Roger ... 05:31: We’ve used these before to understand black hole event horizons, but these were originally conceived to understand the boundaries of the universe. 15:45: ... all, if space is expanding faster than light at the event horizon, that should counter the light-speed flow of space into the event ... 16:01: ... stackexchange, in which he suggests that the shrinking cosmological horizon could merge with the event horizon to produce a global state where ... 15:45: ... that should counter the light-speed flow of space into the event horizon, causing the event horizon to shrink and the black hole to ... 01:22: To review: the particle horizon defines the limit of the visible past, and there’s also cosmic event horizon defining the limit of the visible future. 01:17: We visited these cosmic horizons in one of the early Space Time episodes. 05:31: We’ve used these before to understand black hole event horizons, but these were originally conceived to understand the boundaries of the universe. 05:49: ... horizontal-ish contours are our old time ticks - moments of constant time across the ...
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 07:02: ... to the nearest inaccessible region of space is called the 'cosmic event horizon'. Now, if the expansion is accelerating, then, over time the distance ... 07:38: But as long as we have a nice gravitationally bound galaxy to live in, the cosmic event horizon can never shrink to a size smaller than that galaxy. 07:47: ... dark energy there's no protection from the encroaching cosmic event horizon. ... 08:10: That is the big room scenario, It happens when the cosmic event horizon is smaller than the smallest possible structure. 09:26: ... this doesn't mean that the cosmic event horizon is quite inside the Milky Way just yet, just that the effect of phantom ... 09:38: In fact, at this point the cosmic event horizon is still about 200 million light years away.
	2019-03-06: The Impossibility of Perpetual Motion Machines 12:43: ... check out the Destination Pluto, which follow the timeline of the New Horizons mission from its inception to the date of its close encounter with ...
	2019-02-07: Sound Waves from the Beginning of Time 06:26: We call this the sound horizon. And at recombination, it was around five hundred thousand light years.
	2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe 13:52: ... everyone, I'm back from the event horizon, aka. Australia, which as you know is the CPT inverted version of Canada. ...
	2018-11-07: Why String Theory is Right 15:26: More accurately, the conducting plates create a horizon in what would otherwise be a perfect infinite vacuum. 15:33: In fact, you create two horizons between the plates and one horizon on the outside. 15:40: Those horizons perturb the vacuum which can lead to the creation of very real particles, as in Hawking radiation. 15:47: ... in the Casimir effect, the double horizon between the plates restricts what real particles can be produced there ... 15:33: In fact, you create two horizons between the plates and one horizon on the outside. 15:40: Those horizons perturb the vacuum which can lead to the creation of very real particles, as in Hawking radiation.
	2018-10-31: Are Virtual Particles A New Layer of Reality? 00:21: Near black holes, virtual matter and antimatter pairs are separated by the event horizon to create Hawking radiation. 11:11: ... virtual matter-antimatter pairs being separated by the black hole event horizon, allowing one of the pair to escape to beautiful freedom and ... 11:28: In his actual mathematical derivation, he instead talks about vibrational modes of the quantum vacuum being cut off by the event horizon. 11:11: ... virtual matter-antimatter pairs being separated by the black hole event horizon, allowing one of the pair to escape to beautiful freedom and ...
	2018-10-18: What are the Strings in String Theory? 13:50: ... what it would take to compute a universe simulation on the event horizon of a black ... 14:03: Roman R. asks whether computation at an event horizon would experience massive time dilation relative to an outside observer. 14:17: Really, you can't read off the result of an event horizon computation until practically ever.
	2018-10-10: Computing a Universe Simulation 04:13: ... at the Bekenstein bound, essentially, your memory device is the event horizon of a black ... 04:50: Again, the Bekenstein bound is the event horizon surface area in Planck areas with an extra factor of a quarter that Stephen Hawking figured out. 05:24: The radius I gave is the Schwarzschild radius, the radius of the event horizon of a non-rotating neutral black hole, again, like Switzerland. 11:34: It's not clear that programming and then reading out from an event horizon computer is even possible. 04:50: Again, the Bekenstein bound is the event horizon surface area in Planck areas with an extra factor of a quarter that Stephen Hawking figured out.
	2018-09-20: Quantum Gravity and the Hardest Problem in Physics 05:57: ... put into that region of space would make a tiny black hole with an event horizon one Planck length in ... 13:20: A few of you asked why it is that the surface area of a black hole's event horizon must always increase and how mass and radius can actually decrease. 13:46: Event horizon radius is proportional to mass. 14:30: In that process, the event horizon only changes shape. 15:56: Clue-- you'll need to go beyond the formula for the Bekenstein bound in terms of event horizon surface area. 13:46: Event horizon radius is proportional to mass. 15:56: Clue-- you'll need to go beyond the formula for the Bekenstein bound in terms of event horizon surface area.
	2018-09-12: How Much Information is in the Universe? 01:57: Jacob Bekenstein figured this out by realizing that the entropy of a black hole is proportional to the surface area of its event horizon. 07:25: And for black holes, that entropy is the Bekenstein bound, the number of Planck areas on its event horizon. 07:32: Because the information about the black hole's previous state is lost, to fully describe it, you need to fully describe its event horizon. 07:54: Its event horizon is around 12 billion meters, giving it a surface area of 10 to the power of 90 to 10 to the power of 91 Planck units. 09:05: ... limit, it would immediately become a black hole with an event horizon as big as the current cosmic ... 09:42: Essentially, they're computing on the surface of a black hole event horizon.
	2018-09-05: The Black Hole Entropy Enigma 02:47: He described a mechanism by which the information contained by infalling particles could be preserved on the event horizon of the black hole. 04:49: At the instant the star collapses far enough to form an event horizon, it becomes a black hole. 06:02: The surface area of a black-hole event horizon can never decrease, at least not according to general relativity. 06:53: That's the surface area of the event horizon. 08:37: ... is going to be directly proportional to the surface area of the event horizon. ...
	2018-08-23: How Will the Universe End? 03:13: ... all galaxies beyond the Virgo Supercluster outside of the cosmic event horizon. ...
	2018-07-04: Will A New Neutrino Change The Standard Model? 11:22: So, how does that work with the cosmic event horizon? 11:26: Shouldn't regions outside the event horizon be lost to our access and therefore impossible to trace backwards? 11:33: The statement about the retraceability of the universe doesn't actually care about event horizons, whether cosmic or black hole.
	2018-06-20: The Black Hole Information Paradox 00:22: [MUSIC PLAYING] Black holes are engines of destruction that remove from our universe anything that crosses their event horizon. 02:01: The inescapable event horizon shields the outside universe from any other influence within the black hole. 06:07: The motivation for this idea is the fact that, from the point of view of an outside observer, nothing ever actually crosses the event horizon. 06:14: For the outside universe, everything that ever fell into the black hole remains frozen in time and smeared flat over that horizon. 07:25: From the point of view of an observer falling into the black hole, they aren't frozen at the horizon. 08:44: He did a more careful calculation of the effect of infalling material and found that it doesn't exactly freeze above a completely static horizon. 08:52: Rather, it distorts the horizon, creating a sort of lump at the point of crossing. 10:00: ... how the information on an event horizon gets attached to Hawking radiation is still contentious, but a number of ... 10:09: ... tunneling from within the black hole could interact with the holographic horizon and carry information back out into the ... 14:49: ... with the interior or just the persistence of the field at the event horizon is a matter of ... 08:52: Rather, it distorts the horizon, creating a sort of lump at the point of crossing. 02:01: The inescapable event horizon shields the outside universe from any other influence within the black hole.
	2018-06-13: What Survives Inside A Black Hole? 00:16: ... body, a point of hypothetical infinite density surrounded by an event horizon. ... 00:34: At that horizon, time is frozen and the fabric of space itself cascades inwards at the speed of light. 00:40: Nothing can travel faster than light, and so nothing can escape from below the event horizon-- not matter, not light, not even information. 01:45: ... charge, and angular momentum should emerge from beneath the event horizon. ... 02:20: Nothing beneath the event horizon can influence the exterior universe because no signal can escape the event horizon to carry that influence. 02:44: Given the one-way nature of the event horizon, the loss of this information makes some intuitive sense. 03:06: So how does mass, electric charge, and angular momentum communicate their influence across the uncrossable horizon? 04:20: ... the case of the event horizon, the outside universe can't see the mass inside the black hole, but that ... 04:32: In fact, the space at the event horizon is already falling inwards. 05:22: In the case of a black hole, at least a nonrotating one, the event horizon is a closed spherical surface with a singularity at its center. 06:04: This means that the electric field above the event horizon of a black hole remembers all of the electric charge that fell through that surface. 06:12: Black holes act as though their charge is spread across the event horizon. 09:14: It dramatically changes the shape of the event horizon and the orbit of anything nearby. 09:19: ... it will either add or subtract from this flow of space above the event horizon. ... 00:34: At that horizon, time is frozen and the fabric of space itself cascades inwards at the speed of light.
	2018-05-02: The Star at the End of Time 10:25: ... the Event Horizon Telescope has now detected radio emission from pretty close to the event ...
	2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) 12:26: Moma the Belly Dancer asks whether this means that the expansion of the universe also causes an event horizon? 12:34: The cosmic event horizon is that service from beyond which we can never obtain new information. 12:39: We can actually see that horizon today. 12:59: ... horizon should produce a type of Hawking radiation, but its wavelength would be ... 13:09: On the other hand, during the inflationary epoch in the extremely early universe, the cosmic event horizon was very close to every point. 12:39: We can actually see that horizon today.
	2018-04-04: The Unruh Effect 00:06: Every time you accelerate, put your foot on the gas, quicken your step, get out of your chair, you generate an event horizon behind you. 00:58: It creates a type of event horizon. 01:00: As we saw in our episode on horizon radiation, the presence of horizons distorts the quantum vacuum in a way that can create particles. 04:59: In fact, the active acceleration does create a type of event horizon called a Rindler horizon. 05:06: ... physicist Wolfgang Rindler who, by the way, also invented the term event horizon. ... 05:20: The Rindler horizon flows at a fixed distance behind a constantly accelerating observer. 05:28: The distance of a Rindler horizon is inversely proportional to acceleration. 05:32: The larger the acceleration, the closer the horizon. 05:36: All parts of the universe beyond that horizon are out of causal connection with the Rindler observer as long as they continue to accelerate. 05:46: Even momentary acceleration generates a Rindler horizon. 05:54: It's like the projected future acceleration gives you a Rindler horizon in the present. 06:00: And just as with Hawking radiation, that horizon cuts off your access to certain fundamental frequency modes of the quantum vacuum. 06:53: This is because that distant point of space-time is smoothly connected to the space-time near the horizon. 07:00: The only observers who don't see Hawking radiation are those plummeting in freefall towards the event horizon. 10:12: ... acceleration can get that high, and that's right above the event horizon of a black ... 10:21: If you hover close enough to that event horizon, you would actually be bathed in Unruh radiation. 10:29: ... between the Unruh particle seen by someone hovering at the event horizon and the particles of Hawking radiation seen by a distant ... 04:59: In fact, the active acceleration does create a type of event horizon called a Rindler horizon. 06:00: And just as with Hawking radiation, that horizon cuts off your access to certain fundamental frequency modes of the quantum vacuum. 05:20: The Rindler horizon flows at a fixed distance behind a constantly accelerating observer. 01:00: As we saw in our episode on horizon radiation, the presence of horizons distorts the quantum vacuum in a way that can create particles. 04:50: This means that any events happening to the left of that diagonal line will never affect the accelerating observer, which sounds pretty horizon-like. 01:00: As we saw in our episode on horizon radiation, the presence of horizons distorts the quantum vacuum in a way that can create particles.
	2018-03-15: Hawking Radiation 00:50: ... create a hole in the universe, a boundary in spacetime called an event horizon that could be entered, but from beyond which nothing could ... 02:03: ... a black hole, sometimes, one of the pair will be swallowed by the event horizon, leaving the other free to escape and taking its stolen energy with ... 04:11: But spatial curvature can mess with the balance of the underlying quantum field modes by introducing horizons. 04:18: Horizons cut off access to certain modes of the quantum fields, disturbing the balance that defines the vacuum. 05:17: It emerges barely ahead of the forming event horizon. 06:55: They are nudged off their narrow escape path and so are lost behind the forming event horizon. 07:29: It produces particles that also have wavelengths about as large as the event horizon. 07:53: More directly, it's proportional to the surface area of the event horizon. 08:07: OK, so what about the whole picture of particle/antiparticle pairs being pulled apart by the event horizon? 08:27: And for the escaping modes, there exist a corresponding set of modes linked by quantum entanglement that are trapped behind the event horizon. 08:51: Remember that Hawking radiation has wavelengths the size of the event horizon, the size of the entire black hole. 09:09: Not from specific points on the event horizon. 09:12: In fact, an observer in freefall through the horizon sees nothing. 09:28: When you turn on your jet pack and hover a fixed distance above the horizon, then you do see particles. 10:17: ... radiation by thinking about particles escaping from beneath the event horizon through quantum ... 10:32: ... that we'll want on the same world line becoming separated by the event horizon. ... 02:03: ... a black hole, sometimes, one of the pair will be swallowed by the event horizon, leaving the other free to escape and taking its stolen energy with ... 09:12: In fact, an observer in freefall through the horizon sees nothing. 04:11: But spatial curvature can mess with the balance of the underlying quantum field modes by introducing horizons. 04:18: Horizons cut off access to certain modes of the quantum fields, disturbing the balance that defines the vacuum.
	2018-01-24: The End of the Habitable Zone 11:00: Existenceisillusion asked about the nature of the thermal particles produced in horizon radiation. 11:09: Actually, all quantum fields are affected by the presence of a space time horizon. 11:56: If the event horizon swallows one half of a virtual matter anti-matter pair, then how does the black hole lose mass? 11:00: Existenceisillusion asked about the nature of the thermal particles produced in horizon radiation. 11:56: If the event horizon swallows one half of a virtual matter anti-matter pair, then how does the black hole lose mass?
	2018-01-17: Horizon Radiation 00:54: But relativity can throw some weirder things into the mix, specifically the idea of a horizon. 01:01: ... example, the event horizon of a black hole, out of which no information can travel or the ... 01:11: And a strange type of apparent event horizon even appears when we accelerate. 01:17: Generally speaking, a horizon is a boundary in space time from beyond which no influence can pass. 01:29: As weird as the space times with horizons may be, the statement from before holds. 03:55: ... when an observer who sees a horizon tries to write down these equations, in order to preserve the laws of ... 09:46: OK, so what happens when we add a horizon to our infinite quantum field? 10:18: If we introduce an event horizon, then we lose access to some momentum modes, while other modes behave very differently. 11:04: So you can be that horizon's drum skin to produce oscillations that are consistent with the infinite, un-horizoned skin. 11:23: It appears to be bathed in thermal particles-- particles that don't exist for an observer who doesn't see that horizon. 11:53: So this year, keep your eye on the horizon-- the event horizon and the strange things it does to the quantum contents of space time. 10:26: ... to create and annihilate the same particles as we had in an infinite, horizonless ... 01:29: As weird as the space times with horizons may be, the statement from before holds. 11:04: So you can be that horizon's drum skin to produce oscillations that are consistent with the infinite, un-horizoned skin.
	2017-11-22: Suicide Space Robots 08:33: Pioneer 10 and 11, Voyager 1 and 2, and New Horizons are all on trajectories that will fling them into interstellar space.
	2017-10-25: The Missing Mass Mystery 12:21: ... control faster than the speed of light, can't they escape the event horizon of black holes via Hawking ...
	2017-10-04: When Quasars Collide STJC 01:49: The largest have event horizons that would envelop most of our solar system.
	2017-09-20: The Future of Space Telescopes 08:19: However, it would be able to see x-rays right down to the event horizons of super massive black holes in distant galaxies. 12:42: ... stars don't manage to stop before the core is smaller than its own event horizon, forming a black ... 12:56: So it's reasonable to imagine that neutron star-like conditions exist extremely briefly before the event horizon forms. 12:42: ... stars don't manage to stop before the core is smaller than its own event horizon, forming a black ... 12:56: So it's reasonable to imagine that neutron star-like conditions exist extremely briefly before the event horizon forms. 08:19: However, it would be able to see x-rays right down to the event horizons of super massive black holes in distant galaxies.
	2017-08-30: White Holes 01:31: ... of inward flowing space time with a one way boundary called the event horizon, from inside of which nothing can ever ... 01:45: It also has an event horizon, but that horizon prohibits entry, not exit. 03:03: We've talked quite a bit about the bizarre behavior of space and especially time at and below the event horizon of a black hole. 03:24: ... perspective of an outside observer, any events occurring at the event horizon, including folding into it, happen infinitely far in the ... 05:17: If we place an eternal black hole far to the left, then the future left boundary represents the black hole's event horizon. 05:26: Any movement the left brings you closer to that event horizon. 05:30: The event horizon itself is a 45 degree line. 05:39: ... at that 45 degree angle takes infinite time to escape the event horizon, and the region beyond that line represents the interior of the black ... 06:32: ... instead of flowing towards the singularity, it flows away, and the event horizon is now a barrier to entry, not to ... 06:51: Imagine that something in our past was traveling at the speed of light and trying to reach the past event horizon. 07:03: Oh, it'll reach an event horizon, but only the event horizon of our future, where it plunges into a regular old black hole. 07:13: Remember that all of this is from our perspective far from the event horizon. 07:17: We can never see anything cross the horizon. 07:30: ... the past region of the eternal black hole has an event horizon that's a barrier to entry, but also light rays within that region must ... 08:11: The past singularity and past event horizon are infinitely far in the past from our point of view. 03:24: ... perspective of an outside observer, any events occurring at the event horizon, including folding into it, happen infinitely far in the ... 01:45: It also has an event horizon, but that horizon prohibits entry, not exit.
	2017-08-16: Extraterrestrial Superstorms 08:48: This is perfect for measuring cloud heights and also to record horizontal cloud drift, which gives us wind speeds. 12:59: Now, draw some horizontal lines. 08:48: This is perfect for measuring cloud heights and also to record horizontal cloud drift, which gives us wind speeds. 12:59: Now, draw some horizontal lines. 08:48: This is perfect for measuring cloud heights and also to record horizontal cloud drift, which gives us wind speeds. 12:59: Now, draw some horizontal lines.
	2017-08-10: The One-Electron Universe 10:59: ... universe are drifting very slightly towards a point beyond the cosmic horizon. ...
	2017-08-02: Dark Flow 01:05: ... may be moving ever so slightly towards the same point beyond the cosmic horizon. ... 07:11: In fact, it's toward something beyond the cosmic horizon in the same direction as these constellations. 08:38: Things that are now beyond the cosmic horizon were close enough to affect us gravitationally. 08:58: ... if, somewhere beyond our cosmic horizon, there exists a region of much more stuff, a different bubble of ... 09:40: ... influence of a neighboring region of the greater universe, beyond the horizon of observable ...
	2017-04-05: Telescopes on the Moon 10:30: Last week on "Space Time," we talked about time space, the way time and space, which rolls, beneath the event horizon of a black hole. 10:52: You could transform the gravitational potential energy of things falling towards the event horizon into usable energy.
	2017-03-29: How Time Becomes Space Inside a Black Hole 00:06: ... and time that occurs in the mathematics when we drop below the event horizon of a black ... 03:14: That rs is the Schwarzschild radius, the radius of the event horizon. 03:20: Very far from the event horizon, the Schwarzschild interval becomes the good old Minkowski interval. 03:29: ... if an object gets close to the event horizon, so r just a little bit bigger than rs, that stuff in the two brackets ... 03:41: But as long as you are outside the event horizon, time behaves itself mostly. 03:56: Things change radically below the event horizon when r gets smaller than rs. 04:10: Below the event horizon, there is only one way to maintain the respectable causal progression expected of a well-mannered temporal entity. 06:12: As you approach the event horizon of a black hole, more and more light rays are turned towards the event horizon. 06:57: This entire diagonal line represents the event horizon. 07:06: Our entire future light cone encompasses more and more of the event horizon. 07:20: Meanwhile our past light cone now encompasses light that has been struggling to escape from just above the event horizon since the distant past. 07:30: But we still see nothing from below the horizon. 07:34: Yet as soon as we passed the horizon, everything changes. 07:49: At the moment of crossing, light rays from the event horizon itself are suddenly visible. 08:20: ... first formed the black hole, emitted long before we entered the event horizon. ... 08:48: This is light that entered the event horizon after we did and appears to reach us from above. 09:47: Below the event horizon, there's still a sense of spatial upness and downness. 10:28: In fact the Schwarzschild metric really gives two separate spacetime maps in a single equation, one for above and one for below the event horizon. 03:41: But as long as you are outside the event horizon, time behaves itself mostly.
	2017-02-02: The Geometry of Causality 00:32: Recently, we've been talking about the weirdness of spacetime in the vicinity of a black hole's event horizon. 00:38: Very soon, we'll be dropping below that horizon to peer at the interior of the black hole. 10:23: ... to some incredible predictions when we try to calculate the sub event horizon interval of ... 12:22: One idea is that the inside of an event horizon is composed of a ball of raw strings, a so-called fuzzball, and that no infinite density exists. 10:23: ... to some incredible predictions when we try to calculate the sub event horizon interval of ...
	2017-01-25: Why Quasars are so Awesome 04:43: However, a lot of it never makes it below the event horizon.
	2017-01-19: The Phantom Singularity 02:39: An example of a frame dependent singularity that might be familiar to space time viewers is the event horizon of the black hole. 07:51: If you haven't guessed, this bad behavior corresponds to the event horizon. 08:00: Imagine an object sitting at the event horizon but not moving, so its delta r would be 0. 08:12: The entire space time interval for a non-moving point at the event horizon is 0. 08:26: So does that mean time doesn't pass for an object hovering at the event horizon? 08:33: Time certainly doesn't pass at the event horizon. 08:40: ... the prohibition against objects experiencing time at the event horizon is actually a prohibition against objects spending time at the event ... 08:59: At the event horizon the only way to get a non-zero space time interval is to have a non-zero delta r. 09:08: An object at the event horizon has to change its distance from the black hole to keep its clock ticking. 09:14: That means falling below the event horizon. 09:42: ... a photon exists in a single instant, and so it can hang out at the event horizon, which also only exists at 1 infinitely stretched out ... 09:54: The act of crossing the event horizon is where this singularity really starts to behave badly. 10:13: ... and delta r, doesn't let us trace a world line smoothly across the event horizon. ... 10:27: That horizon is a coordinate singularity, just like Kelsey talked about. 10:55: Anyway the upshot is that it's really a breeze to drop through the event horizon, both physically and mathematically. 11:03: Of course, once inside the event horizon, we still have that central singularity to deal with. 11:34: ... theory, we have to go back to that coordinate shift at the event horizon. ...
	2017-01-04: How to See Black Holes + Kugelblitz Challenge Answer 02:49: The Event Horizon Telescope is right now in the process of mapping space around the Milky Way's Sag A star black hole. 03:36: Now, the actual event horizon is even smaller than this insane resolution, but EHT isn't finished yet. 03:43: ... it will actually see the dark circular shadow of the Sag A star event horizon. ... 04:28: ... the Event Horizon Telescope and microlensing studies, and of course, more LIGO ... 05:12: It has enough energy to produce a black hole with a mass of 100,000 suns and an event horizon that almost reaches the moon's orbit. 06:37: Eventually, it gets small enough for the event horizon to form. 06:41: On the Penrose diagram, that horizon extends both forwards and backwards in time. 06:46: This is because there are regions of the universe that are doomed to end up in the singularity even before the true event horizon forms. 07:25: ... in a volume smaller than its own Swarzschild radius, an event horizon forms as spacetime flows faster than the speed of light towards that ... 07:53: Even after the true event horizon forms, there remains this shrinking patch of normal flat spacetime. 08:15: We generate a perfectly reflective sphere at approximately half the radius of the eventual event horizon. 08:24: The light shell passes the moon's orbit, and a true event horizon forms. 08:51: See, once the event horizon forms, all paths below it lead to that singularity, even outgoing light paths. 09:01: ... that's seen as the future light cone of everything below the event horizon leading to the singularity, even of the reflected light ... 09:19: As long as the event horizon has not yet formed, the incoming light can be stopped. 09:39: Just above the sphere, which is only a bit larger than that event horizon that was going to form, the spacetime curvature is pretty insane. 09:53: ... of the near Kugelblitz to appreciably increase the size of the event horizon. ... 06:41: On the Penrose diagram, that horizon extends both forwards and backwards in time. 06:46: This is because there are regions of the universe that are doomed to end up in the singularity even before the true event horizon forms. 07:25: ... in a volume smaller than its own Swarzschild radius, an event horizon forms as spacetime flows faster than the speed of light towards that ... 07:53: Even after the true event horizon forms, there remains this shrinking patch of normal flat spacetime. 08:24: The light shell passes the moon's orbit, and a true event horizon forms. 08:51: See, once the event horizon forms, all paths below it lead to that singularity, even outgoing light paths. 09:01: ... that's seen as the future light cone of everything below the event horizon leading to the singularity, even of the reflected light ... 02:49: The Event Horizon Telescope is right now in the process of mapping space around the Milky Way's Sag A star black hole. 04:28: ... the Event Horizon Telescope and microlensing studies, and of course, more LIGO gravitational waves ...
	2016-12-21: Have They Seen Us? 13:18: A couple of weeks ago, we looked back into black holes and studied the nature of the event horizon. 13:27: Luca$sino asks what we would really see if we followed the monkey directly through the event horizon? 13:33: Would it appear ahead of us despite previously appearing frozen on the event horizon? 13:41: The light from the instant of the monkey's crossing of the event horizon is eternally trapped at that horizon. 14:57: ... light emitted by everything that fell into it as it crossed the event horizon. ... 15:49: The event horizon itself just wouldn't apply within your warp bubble. 16:31: ... the event horizon, you need to travel at the speed of light relative to the black hole's ... 16:49: ... happen to get exactly the right size for the event horizon if you use Newtonian gravity to calculate the distance at which the ... 17:06: But the concept of escape velocity at the event horizon is still as meaningful as it is from the surface of the Earth. 17:33: So once inside the horizon, avoiding a singularity is like avoiding next Tuesday.
	2016-12-14: Escape The Kugelblitz Challenge 00:14: ... infinitely stretched space-time in the vicinity of a black hole's event horizon. ... 02:11: If the star's core collapses to a size smaller than its own Schwarchild radius, then the event horizon forms, engulfing what's left of the star. 02:21: Below that horizon, but above the still-shrinking surface of the star, space-time takes on the mad properties of the black hole interior. 02:40: Outside the black hole, the event horizon becomes the new edge of the universe on our Penrose diagram. 02:47: The shape of space-time outside the horizon warps to make this diagonal line, a line of constant radius, the radius of the new black hole. 03:09: There's a region where all forward light cones only include the singularity, even before the true event horizon forms. 03:18: For anything in this region, there isn't enough time to clear the impending event horizon, even traveling at the speed of light. 03:27: On the Penrose diagram, we should extend our effective event horizon backwards to include that space. 03:34: This invisible horizon of doom grows as the star shrinks and finally merges with the true event horizon. 03:41: Any observers within this extended event horizon are cut off from any future causal connection with the rest of the universe. 04:59: So the kugelblitz event horizon forms just after the shell of light passes the moon. 05:33: Space inside the collapsing kugelblitz would remain comfortably flat until the collapsing shell overtakes it, even after the event horizon forms. 03:27: On the Penrose diagram, we should extend our effective event horizon backwards to include that space. 02:11: If the star's core collapses to a size smaller than its own Schwarchild radius, then the event horizon forms, engulfing what's left of the star. 03:09: There's a region where all forward light cones only include the singularity, even before the true event horizon forms. 04:59: So the kugelblitz event horizon forms just after the shell of light passes the moon. 05:33: Space inside the collapsing kugelblitz would remain comfortably flat until the collapsing shell overtakes it, even after the event horizon forms. 02:11: If the star's core collapses to a size smaller than its own Schwarchild radius, then the event horizon forms, engulfing what's left of the star. 02:47: The shape of space-time outside the horizon warps to make this diagonal line, a line of constant radius, the radius of the new black hole.
	2016-12-08: What Happens at the Event Horizon? 00:06: At the event horizon of the black hole, space and time are fundamentally changed. 00:16: But there is a powerful tool in physics that can give us real intuition into the true nature of the event horizon. 00:29: Black holes, objects with densities so high that there's this region, the event horizon, where the escape velocity reaches the speed of light. 00:38: ... that falls below the event horizon can never escape and is lost to the universe forever while we see ... 00:50: And anything that happens below the event horizon stays below the event horizon. 01:38: For example, are objects falling through the event horizon really physically frozen there from the point of view of the outside universe? 01:48: Would you see the entire future history of the universe playing fast forward at the instant that you crossed the event horizon? 02:08: It's a special type of space-time diagram designed to clarify the nature of horizons. 03:10: It has a point of infinite density, the singularity, and an event horizon a bit further out. 03:16: ... time so that light rays appear to crawl out of the vicinity of the event horizon before escaping to flat space-time, no longer following 45 degree ... 03:32: As it approaches the event horizon, its future light cone bends towards the black hole as fewer and fewer of its possible trajectories lead away. 03:42: Below the event horizon, all possible trajectories lead towards the singularity. 05:51: Its event horizon becomes the end of the line in that direction. 05:56: The future cosmic horizon on the Penrose diagram is replaced with a plunge into a black hole. 06:03: The compactified grid lines there now represent the stretched space-time near the event horizon. 06:41: Once you're beneath the horizon, your future light cone still represents all possible paths that you could take. 07:25: The progress of the monkey appears to slow to a halt very close to the event horizon, and the final signal at the moment of crossing never reaches us. 07:45: First, what would happen if the monkey remembered to fire its jet pack at the last instant before reaching the event horizon? 08:15: ... is probably doomed to a graceful reverse swan dive through the event horizon, watching the entire future history of the universe play out above it at ... 08:54: ... it could instead hover above the event horizon, then it would see the universe in fast forward, although that view would ... 09:04: Watching the monkey frozen on the event horizon is going to make us feel a bit guilty, after a while. 09:24: ... would see it suspended above the horizon as we're racing to meet it, but it will always appear to be just a ... 09:35: ... the monkey isn't actually above the horizon for infinite time, it only appears that way to us because as long as ... 09:50: In order to see that crossing, we would have to cross the event horizon ourselves. 00:50: And anything that happens below the event horizon stays below the event horizon. 08:15: ... is probably doomed to a graceful reverse swan dive through the event horizon, watching the entire future history of the universe play out above it at that last ... 02:08: It's a special type of space-time diagram designed to clarify the nature of horizons. 04:48: ... lines represent fixed locations in one dimension of space and red horizontalish lines are fixed moments in ...
	2016-11-16: Strange Stars 12:12: ... also not see the triangle curve over in the sense that there would be no horizon. ...
	2016-10-12: Black Holes from the Dawn of Time 09:28: A billion-ton black hole has an event horizon around the size of a proton, so it would pass through the planet as though the Earth were made of air.
	2016-09-29: Life on Europa? 09:45: ... a vertically-aligned measurement device and a second particle with a horizontally-aligned ...
	2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate 05:43: If we measure horizontally, it will be left or right.
	2016-06-15: The Strange Universe of Gravitational Lensing 08:00: The lightspeed flow of spacetime at the event horizon results in old light paths pointing inwards. 08:10: Light falling below the event horizon is lost forever, so we don't describe it as being lensed. 08:16: But just outside the event horizon, we find the most extreme gravitational lensing in the universe. 08:23: The photon sphere hovers at about half, again, the height of the event horizon.
	2016-04-13: Will the Universe Expand Forever? 08:14: Over billions of years, they will slip beyond our cosmic horizon, leaving only darkness beyond the local region of the Milky Way.
	2016-04-06: We Are Star Stuff 12:35: It's happening right now in regions of the universe beyond what we call the Hubble Horizon, which is 13.7 billion light years away. 12:44: It's happening below the event horizon of black holes.
	2016-03-23: How Cosmic Inflation Flattened the Universe 01:19: This smoothness of the CMB is called the horizon problem. 01:25: The horizon problem isn't the only troubling feature of the CMB. 04:16: This flatness problem is just as much of an issue as the horizon problem. 05:58: ... neatness with which this inflation solves both the horizon and flatness problems really has most cosmologists thinking that ... 13:05: However, the shape of the event horizon of the black hole itself does depend on spin. 01:19: This smoothness of the CMB is called the horizon problem. 01:25: The horizon problem isn't the only troubling feature of the CMB. 04:16: This flatness problem is just as much of an issue as the horizon problem. 01:25: The horizon problem isn't the only troubling feature of the CMB.
	2016-03-16: Why is the Earth Round and the Milky Way Flat? 12:45: It has always come from our cosmic horizon, but that cosmic horizon expands.
	2016-03-02: What’s Wrong With the Big Bang Theory? 07:05: Another way to say this is that those edges of the universe have always been beyond each other's particle horizons. 07:13: Here's a nice review episode on cosmic horizons. 07:25: This serious issue is called the horizon problem. 08:28: This whole idea fixes our horizon problem. 11:22: ... before the word "universe." Everything that we can see to our cosmic horizon, so the observable universe, was once compacted into something smaller ... 07:25: This serious issue is called the horizon problem. 08:28: This whole idea fixes our horizon problem. 07:05: Another way to say this is that those edges of the universe have always been beyond each other's particle horizons. 07:13: Here's a nice review episode on cosmic horizons.
	2016-02-11: LIGO's First Detection of Gravitational Waves! 05:49: The signals are expected to carry information about the strange warping of space in the region of the event horizon.
	2016-01-27: The Origin of Matter and Time 05:41: So what this means is that there's no single preferred vertical time axis, or indeed, horizontal space axis.
	2015-12-16: The Higgs Mechanism Explained 07:46: AFastidiousCuber wants to know how a black hole can grow if anything falling into it appears to freeze before it crosses the event horizon. 07:55: ... although an outside observer can never witness anything cross the event horizon, as something falls to the horizon, the light it emits is red shifted ... 08:06: ... infalling stuff does vanish, and the event horizon that an outside observer sees does grow because anything falling into ... 08:21: Casterverus would like to know if the potential event horizon that we talk about is the same thing as the Schwarzschild radius. 08:29: The Schwarzschild radius is the radius of the event horizon of a non-rotating black, and it depends on the mass.
	2015-12-09: How to Build a Black Hole 07:58: And yet, below the star's surface, their lurks the potential event horizon, the surface of infinite time dilation. 08:05: Now, the event horizon doesn't actually exist as long as the neutron star stays larger than the would be horizon. 08:12: However, if we can increase the mass of the neutron star, the actual star shrinks, and the event horizon expands. 08:22: There's a mass where the radius of the neutron star and the event horizon overlap. 08:28: At this point, the event horizon actually comes into being. 08:38: But what happens to the star when it slips below its event horizon? 09:46: But on our timeline, nothing ever happens beyond the event horizon again. 09:54: Beneath the event horizon, there is no corresponding now. 10:10: To us, there is only the event horizon. 08:05: Now, the event horizon doesn't actually exist as long as the neutron star stays larger than the would be horizon. 08:12: However, if we can increase the mass of the neutron star, the actual star shrinks, and the event horizon expands. 08:22: There's a mass where the radius of the neutron star and the event horizon overlap.
	2015-10-28: Is The Alcubierre Warp Drive Possible? 01:51: ... below the event horizon of a black hole, spacetime cascades towards the central singularity ...
	2015-10-07: The Speed of Light is NOT About Light 11:17: RedomaxRedomax asks what you would see if you traveled 18 times the distance to the particle horizon to come back to where you started. 11:26: ... that number, 18 times the particle horizon, only applies if the universe has positive curvature, making it a ...
	2015-09-30: What Happens At The Edge Of The Universe? 01:47: We call this the particle horizon of the universe. 01:56: Anything inside the particle horizon is referred to as the known universe. 02:33: To travel to the particle horizon, we need to move through expanding space. 02:51: Just as black holes have event horizons, so too do universes. 02:55: ... event horizon of a black hole is that point beyond which we can never receive ... 03:23: We can ever get to anything beyond the cosmic event horizon because that space will be moving away from us faster than light before we reach it. 03:33: The event horizon of the universe is actually closer to us than the particle horizon. 03:37: Given our best measurements of cosmological parameters, we think that the cosmic event horizon is around 16 billion light years away. 03:56: As our universe expands, more and more of it will cross the event horizon and eventually almost all of that will be lost to it forever. 04:22: But for now, let's just assume we have a nice Alcubierre-class warp-ship and we burn the mass energy of entire stars to chase the particle horizon. 04:36: Remember, the particle horizon is just defined by the limit of our current view. 04:43: Wait a minute, and my particle horizon expands. 04:46: Travel to the particle horizon instantaneously and you'll see the Milky Way as a cute baby CMB blob on your new particle horizon. 05:37: So if it's true, what happens if you cross the particle horizon? 06:46: ... to travel an absolute minimum of 18 times the distance to the particle horizon to get back to where you started, assuming expansion froze for the whole ... 04:43: Wait a minute, and my particle horizon expands. 04:46: Travel to the particle horizon instantaneously and you'll see the Milky Way as a cute baby CMB blob on your new particle horizon. 02:51: Just as black holes have event horizons, so too do universes.
	2015-09-23: Does Dark Matter BREAK Physics? 07:48: ... and others asked whether a monkey falling through a black hole's event horizon should see the entire future history of the universe happen in the ... 08:02: ... would approach infinity as the monkey drew extremely close to the event horizon. ... 08:59: ... that a free-falling monkey is eternally frozen on the event horizon with respect to a distant observer, shouldn't the black hole evaporate ... 09:14: ... see anything weird about space at the moment it crosses the event horizon. ... 09:30: The idea of the event horizon as this boiling hot sea of Hawking radiation isn't right. 09:43: So at the instant of crossing the event horizon, the monkey is not actually bathing in this stuff. 09:54: ... falling through the event horizon, the monkey's clock, its universe, now contains events that happen at the ... 10:03: The monkey's horizon crossing corresponds to a time when the black hole exists. 10:13: And with that radiation comes all of the remaining photons that the monkey emitted before crossing the horizon. 10:18: But the moment of horizon crossing is never seen. 10:03: The monkey's horizon crossing corresponds to a time when the black hole exists. 10:18: But the moment of horizon crossing is never seen. 10:03: The monkey's horizon crossing corresponds to a time when the black hole exists. 09:54: ... the monkey's clock, its universe, now contains events that happen at the horizon, including the horizon's ...
	2015-08-19: Do Events Inside Black Holes Happen? 04:25: OK, this final batch of events for all objects that enter that black void taken together is called the event horizon of the black hole. 04:34: The horizon is not just a spherical surface in space. 06:48: As long as he stays outside the horizon, he can use rockets to hover or move radially outward just like on Earth. 08:20: That means that to external observers, black holes are black because light that gets emitted just outside the horizon is redshifted into invisibility. 08:37: ... you know that it's the black hole mass divided by the volume inside the horizon, then ... 09:00: By the way, bigger black holes also have smaller tidal effects near their horizons. 09:48: However, the horizon forms first in the interior of the star and then expands. 09:52: So to external observers, most of the matter never crosses the horizon. 10:05: ... black hole that didn't form from anything, a spacetime that has an event horizon even though there's no stuff anywhere, including behind the ... 09:48: However, the horizon forms first in the interior of the star and then expands. 09:00: By the way, bigger black holes also have smaller tidal effects near their horizons.
	2015-07-15: Can You Trust Your Eyes in Spacetime? 04:18: ... on either diagram, I could also have drawn lines that are more horizontal than 45 degrees, but they wouldn't be world lines because to be present ...
	2015-06-03: Is Gravity An Illusion? 02:11: Relative to the car's interior, you will accelerate backward, even though you can't identify any horizontal forces on you.
	2015-04-08: Could You Fart Your Way to the Moon? 06:54: ... fact, far from their horizon, which in this case would be just centimeters since the horizon is ...
	2015-04-01: Is the Moon in Majora’s Mask a Black Hole? 03:50: And I put some lower limits on the radius of the planet, based on the fact that we don't see its horizon curving in the distance.

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