
20220824: What Makes The Strong Force Strong?
 18:07: After all, Hawking radiation is sometimes portrayed as a virtual particleantiparticle pair being separated by a black hole event horizon.
 18:15: ... answer 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.


20220622: 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.


20220615: 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, ...


20220525: 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 ...


20220504: Space DOES NOT Expand Everywhere
 11:22: ... radiation seems to emerge from subPlanckwavelength radiation at the event horizon of a black hole. Its solution takes us to the realm of the holographic ...


20220420: Does the Universe Create Itself?
 16:10: ... Actually, 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: ... all 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 ...


20220330: 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: ... fact that 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.
 02:22: ... the accelerating expansion of the universe means the cosmological event horizon is closer to us than the spot where recession equals the speed of ...
 05:19: ... is the allencompassing 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, spacelike 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, spacelike 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?


20220216: 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 ...
 18:37: ... Thomas 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 ...


20220127: How Does Gravity Escape A Black Hole?
 00:00: ... the 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: ... of 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: ... location 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: ... inside 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.
 11:53: To sum up  don’t mess around near black holes hoping that the event horizon will protect you from the black hole’s gravity.


20211220: 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 noreturn  would be around the size of an atom. And it ...
 05:13: ... Martian 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: ... black 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 chokepoint for matter trying to ...
 16:33: ... in free 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 ...


20211117: Are Black Holes Actually Fuzzballs?
 00:39: ... is 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 nohair theorem says that there’s no information beyond charge, mass and spin that’s observable above the event horizon.
 04:29: But this is also the problem at the event horizon.
 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.
 06:55: ... stumbled on the mechanism by which information could be encoded on the event horizon. ...
 08:06: ... or 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 ...
 10:37: The resulting fuzzball doesn’t have a local event horizon  in that there’s no single surface of noreturn.
 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.


20211013: 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. ...


20210921: How Electron Spin Makes Matter Possible
 15:48: ... slingshot, 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 ...


20210915: Neutron Stars: The Most Extreme Objects in the Universe
 13:06: ... mass 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 ...


20210907: 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.


20210721: 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 ...


20210525: 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: ... used 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 popsci description of Hawking radiation you often hear about particleantiparticle 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: ... the wavelength 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?


20210511: How To Know If It's Aliens
 15:39: ... of 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 ...


20210413: 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 ...


20210309: How Does Gravity Affect Light?
 04:37: ... the event horizon of the black hole, gravitational time dilation is so strong that clocks ...


20201027: How The Penrose Singularity Theorem Predicts The End of Space Time
 01:17: ... be surrounded by a surface where time froze. Beneath that “event horizon” all matter, light, space itself was doomed to fall inwards towards ...
 01:58: ... of matter could reach the densities high enough to produce an event horizon  nor even whether such dense matter would really ...
 04:06: ... why did 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 ...
 05:55: ... about black holes is that null geodesics beneath the event horizon that are trying to travel outwards also converge. ...


20200824: Can Future Colliders Break the Standard Model?
 14:28: ... asks a 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 crosssection that’s called the pairofpants 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 ...


20200817: 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: ... do 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: ... about the shape of the stuff inside the black hole  we’re just the event horizon  the surface below which there’s a fasterthanlight flow of ...
 14:07: Here’s a simulation from the SXS  simulating extreme spacetimes group at ... that shows how the event horizons merge.


20200720: The Boundary Between Black Holes & Neutron Stars
 05:42: ... of being 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: ... In 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: ... someone 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 ...


20200630: 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: ... states 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.
 04:43: ... hole with the maximum amount of spin or charge while still having an event horizon. ...
 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: ... Kerr 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: ... covering two episodes  building black holes in the lab with analog event horizons, and Roger Penrose’s conformal cyclic ...


20200622: Building Black Holes in a Lab
 00:16: ... thing 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: ... point 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: ... that 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: ... mathematically 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 holelike behavior. For example, Hawking ...
 08:04: ... passes 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 ...


20200527: Does Gravity Require Extra Dimensions?
 13:29: ... week’s 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 ...


20200518: 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.
 07:50: For one thing, the lack of event horizons above you means the ring is a naked singularity, as well as being repulsive.
 11:10: ... 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 ...


20200504: 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.


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... dead 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 ...


20200422: Will Wormholes Allow Fast Interstellar Travel?
 03:45: ... ring 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: ... coordinates are blended and mutated so that time doesn’t freeze at the event horizon, which itself becomes this 45 degree path. Sublightspeed 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: ... throat 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: ... useless circumstances like on quantum scales or if they’re hidden by an event horizon. Combined with Roger Penrose’ cosmic censorship conjecture, which ensures ...


20200331: 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: ... hole. 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: ... catch 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: ... infinite stretching of time so that gridlines pass smoothly across the event horizon. ...
 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: ... makes very clear what parts of the universe are accessible. Close to the event horizon, even a lightspeed path has only a narrow window of escape. Once inside ...
 07:32: ... speed  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: ...  and 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 ...


20200324: How Black Holes Spin Space Time
 00:21: ... And 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: ... our 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 ...
 03:54: ... It’s 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: ... holes are selfsustaining holes in the fabric of spacetime. Space at the event horizon cascades downwards, dragging more space behind it, sort of like how ...
 05:49: ... to the 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: ... at 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: ... singularities. And we'll encounter all of these when we drop below the event horizon into the deeper weirdness of the Kerr ...


20191217: 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 ...


20191021: Is Time Travel Impossible?
 08:51: The maelstrom of spinning spacetime may generate closed timelike curves deep down below the event horizon.


20191015: 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 ...


20191007: 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 2D surfaces – like drum skins, bells, or the event horizons of black holes – are a good bit more complex than in 1D.
 03:56: In the case of the event horizon, or any sphericalish 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.


20190725: Deciphering The Vast Scale of the Universe
 08:27: ... of the art modern observatories like the Gemini Observatory, and the Event Horizon Telescope, and LIGO, which we visited throughout this ...


20190701: Thorium and the Future of Nuclear Energy
 17:49: ... this 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 ...


20190606: The Alchemy of Neutron Star Collisions
 02:47: ... field 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 ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 14:46: ...  our 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 ...


20190501: 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 onemillionth 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 outwardpointing light can’t escape the black hole.
 06:04: For a nonrotating 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 ...


20190410: 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.


20190403: The Edge of an Infinite Universe
 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: ... infinite 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: ... defeated 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 lightspeed flow of space into the event ...
 16:01: ... he suggests that the shrinking cosmological horizon could merge with the event horizon to produce a global state where everything just looks like an ...


20190328: Could the Universe End by Tearing Apart Every Atom?
 07:02: ... us 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: ... increasing 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.


20190116: Our Antimatter, Mirrored, TimeReversed Universe
 13:52: ... everyone, I'm back from the event horizon, aka. Australia, which as you know is the CPT inverted version of Canada. ...


20181031: 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: ... of virtual matterantimatter 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.


20181018: What are the Strings in String Theory?
 13:50: ... incidentally, 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.


20181010: 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 nonrotating 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.


20180920: Quantum Gravity and the Hardest Problem in Physics
 05:57: ... to 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.


20180912: 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: ... information 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.


20180905: 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 blackhole 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: ... which is going to be directly proportional to the surface area of the event horizon. ...


20180823: How Will the Universe End?
 03:13: ... dragged all galaxies beyond the Virgo Supercluster outside of the cosmic event horizon. ...


20180704: 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.


20180620: 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.
 10:00: ... how the information on an event horizon gets attached to Hawking radiation is still contentious, but a number of ...
 14:49: ... with the interior or just the persistence of the field at the event horizon is a matter of ...


20180613: What Survives Inside A Black Hole?
 00:16: ... massive body, a point of hypothetical infinite density surrounded by an event horizon. ...
 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: ... electric 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 oneway nature of the event horizon, the loss of this information makes some intuitive sense.
 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: ... of gas, it will either add or subtract from this flow of space above the event horizon. ...


20180502: The Star at the End of Time
 10:25: ... the Event Horizon Telescope has now detected radio emission from pretty close to the event ...


20180411: 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.
 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.


20180404: 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.
 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. ...
 07:00: The only observers who don't see Hawking radiation are those plummeting in freefall towards the event horizon.
 10:12: ... gravitational 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: ... relationship between the Unruh particle seen by someone hovering at the event horizon and the particles of Hawking radiation seen by a distant ...


20180315: Hawking Radiation
 00:50: ... to 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: ... near 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 ...
 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.
 10:17: ... Hawking radiation by thinking about particles escaping from beneath the event horizon through quantum ...
 10:32: ... modes that we'll want on the same world line becoming separated by the event horizon. ...


20180124: The End of the Habitable Zone
 11:56: If the event horizon swallows one half of a virtual matter antimatter pair, then how does the black hole lose mass?


20180117: Horizon Radiation
 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.
 10:18: If we introduce an event horizon, then we lose access to some momentum modes, while other modes behave very differently.
 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.


20171025: The Missing Mass Mystery
 12:21: ... particles control faster than the speed of light, can't they escape the event horizon of black holes via Hawking ...


20171004: When Quasars Collide STJC
 01:49: The largest have event horizons that would envelop most of our solar system.


20170920: The Future of Space Telescopes
 08:19: However, it would be able to see xrays 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 starlike conditions exist extremely briefly before the event horizon forms.


20170830: White Holes
 01:31: ... a region 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: ... the 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: ... traveling 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: ... but 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.
 07:30: ... 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.


20170405: 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.


20170329: How Time Becomes Space Inside a Black Hole
 00:06: ... of space 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 wellmannered 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.
 07:49: At the moment of crossing, light rays from the event horizon itself are suddenly visible.
 08:20: ... that 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.


20170202: 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.
 10:23: ... leads 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 socalled fuzzball, and that no infinite density exists.


20170125: Why Quasars are so Awesome
 04:43: However, a lot of it never makes it below the event horizon.


20170119: 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 nonmoving 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 nonzero space time interval is to have a nonzero 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: ... t and delta r, doesn't let us trace a world line smoothly across the event horizon. ...
 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: ... in Einstein's theory, we have to go back to that coordinate shift at the event horizon. ...


20170104: 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: ... online, 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.
 06:46: 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: ... is concentrated 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: ... diagram, 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: ... suns of the near Kugelblitz to appreciably increase the size of the event horizon. ...


20161221: 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.


20161214: Escape The Kugelblitz Challenge
 00:14: ... the infinitely stretched spacetime 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.
 02:40: Outside the black hole, the event horizon becomes the new edge of the universe on our Penrose diagram.
 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.


20161208: 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?
 03:10: It has a point of infinite density, the singularity, and an event horizon a bit further out.
 03:16: ... and time so that light rays appear to crawl out of the vicinity of the event horizon before escaping to flat spacetime, 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.
 06:03: The compactified grid lines there now represent the stretched spacetime near the event horizon.
 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: ... monkey 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.
 09:35: ... it only appears that way to us because as long as we're outside the event horizon, no times that we can witness correspond to the monkey crossing that ...
 09:50: In order to see that crossing, we would have to cross the event horizon ourselves.


20161012: Black Holes from the Dawn of Time
 09:28: A billionton 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.


20160615: 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.


20160406: We Are Star Stuff
 12:44: It's happening below the event horizon of black holes.


20160323: How Cosmic Inflation Flattened the Universe
 13:05: However, the shape of the event horizon of the black hole itself does depend on spin.


20160211: 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.


20151216: 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 nonrotating black, and it depends on the mass.


20151209: 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.


20151028: Is The Alcubierre Warp Drive Possible?
 01:51: ... below the event horizon of a black hole, spacetime cascades towards the central singularity ...


20150930: What Happens At The Edge Of The Universe?
 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.


20150923: 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: ... time would approach infinity as the monkey drew extremely close to the event horizon. ...
 08:59: ... that a freefalling monkey is eternally frozen on the event horizon with respect to a distant observer, shouldn't the black hole evaporate ...
 09:14: ... doesn't 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 ...


20150819: 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.
 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 ...
