Latest / The Quark Side - Quantum Physics Podcast / Hawking Radiation and the Black Hole Information Paradox

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Hawking Radiation and the Black Hole Information Paradox · The Quark Side - Quantum Physics Podcast

• 0:01
  Speaker 1: Welcome to the quart Side Quantum Physics Podcast, an exploration
• 0:05
  Speaker 1: of the fundamental structure of reality, where quantum laws govern matter, energy,
• 0:11
  Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
• 0:16
  Speaker 1: and understanding begins at the smallest scales.
• 0:27
  Speaker 2: Welcome back to the show. Today, we're looking at something, well,
• 0:31
  Speaker 2: it's not really an object or a place. We're looking
• 0:34
  Speaker 2: at a battleground.
• 0:35
  Speaker 3: That's a good way to put it.
• 0:36
  Speaker 2: And I don't just mean a metaphorical debate in a
• 0:38
  Speaker 2: university hall. I mean a literal, honest to goodness conflict
• 0:42
  Speaker 2: in the laws of physics themselves.
• 0:44
  Speaker 3: The conflict where the universe needs to be arguing with itself. Yeah,
• 0:48
  Speaker 3: and we're caught in the middle trying to figure out
• 0:50
  Speaker 3: who's right.
• 0:51
  Speaker 2: It feels incredibly dramatic because as we've been preparing for
• 0:55
  Speaker 2: this exploration, it's become clear this is a fifty year
• 0:57
  Speaker 2: old standoff between the two pillars of modern science.
• 1:00
  Speaker 3: It really is. And this standoff, this paradox, it doesn't
• 1:04
  Speaker 3: just bend the rules of reality, it seems to snap
• 1:06
  Speaker 3: them in half.
• 1:07
  Speaker 2: And it keeps physicists awake at night. I mean, if
• 1:10
  Speaker 2: you follow the logic all the way to its conclusion.
• 1:13
  Speaker 2: It might even mean that space and time, well, they
• 1:17
  Speaker 2: aren't what we think they are at all.
• 1:18
  Speaker 3: It truly is the ultimate mystery. We are talking, of course,
• 1:22
  Speaker 3: about the black hole information paradox.
• 1:24
  Speaker 2: I have to admit when I first heard that term,
• 1:26
  Speaker 2: I thought, okay, black holes, they're mysterious, big, dark, scary,
• 1:29
  Speaker 2: We get it. But this is so much deeper.
• 1:32
  Speaker 3: It's not just about not knowing what's inside right.
• 1:35
  Speaker 2: It's about a logical contradiction. It's like a mathematician proving
• 1:39
  Speaker 2: that two plus two equals five. It threatens to bring
• 1:41
  Speaker 2: the whole structure down.
• 1:42
  Speaker 3: The gravity of the situation, if you'll excuse the pun,
• 1:45
  Speaker 3: is immense. Since nineteen seventy four, this specific problem has
• 1:50
  Speaker 3: been the engine driving so much of theoretical.
• 1:53
  Speaker 2: Physics, because it forces general relativity.
• 1:55
  Speaker 3: Einstein's grand theory of gravity, space and.
• 1:58
  Speaker 2: Time into a case match with quantum mechanics.
• 2:02
  Speaker 3: The theory of the very small of particles and forces,
• 2:05
  Speaker 3: and the terrifying thing. The central problem is that in
• 2:09
  Speaker 3: this specific scenario they cannot both be right. One of
• 2:13
  Speaker 3: them has to give.
• 2:14
  Speaker 2: So that's our mission for this investigation. We are going
• 2:17
  Speaker 2: to try to figure out what happens to information to
• 2:20
  Speaker 2: the story of something when it falls into a black hole?
• 2:23
  Speaker 3: Does it get deleted from the universe?
• 2:25
  Speaker 2: Does it get stored somewhere? Does it I don't know,
• 2:27
  Speaker 2: sneak back out in disguise, and.
• 2:29
  Speaker 3: We're going to see why the answer to that question
• 2:31
  Speaker 3: could literally determine the ultimate fate of the entire universe.
• 2:34
  Speaker 2: To get there, we have to trace the journey of
• 2:37
  Speaker 2: the black hole itself. We'll start with the simple classical view,
• 2:42
  Speaker 2: the gravity prison.
• 2:43
  Speaker 3: Then we'll move into the quantum revolution that Stephen Hawking started,
• 2:47
  Speaker 3: and from there we'll get into the really wild proposed solutions.
• 2:50
  Speaker 2: And some of these sound like science fiction. We're talking
• 2:53
  Speaker 2: about things called fuzzballs, firewalls, and even the idea that
• 2:56
  Speaker 2: the universe is a kind of hologram.
• 2:59
  Speaker 3: It's where physics gets very, very strange. But the strangeness
• 3:04
  Speaker 3: is necessary to solve the problem.
• 3:06
  Speaker 2: I love that physics terms can sound like something from
• 3:08
  Speaker 2: a fantasy novel. I cast fuzzball. But before we get
• 3:12
  Speaker 2: to any of that, we have to start at the beginning,
• 3:15
  Speaker 2: the before picture classical view. Exactly before nineteen seventy four,
• 3:19
  Speaker 2: before Hawking shook the world, what did we think a
• 3:22
  Speaker 2: black hole was?
• 3:23
  Speaker 3: You have to go back to Einstein pure general relativity,
• 3:27
  Speaker 3: and in that picture, a black hole is well. It's
• 3:31
  Speaker 3: elegantly simple and absolutely terrifying.
• 3:33
  Speaker 2: It's a region of space time.
• 3:34
  Speaker 3: Where gravity is so powerful, so unbelievably intense, that nothing
• 3:38
  Speaker 3: can escape.
• 3:39
  Speaker 2: And when you say nothing, you mean nothing, not even light.
• 3:42
  Speaker 3: And since light is the cosmic speed limit, the absolute
• 3:45
  Speaker 3: fastest anything can travel.
• 3:46
  Speaker 2: If late can't get out, then forget it.
• 3:48
  Speaker 3: Nothing else has a chance, exactly. And the key feature here,
• 3:52
  Speaker 3: the thing everyone's heard of, is the event.
• 3:54
  Speaker 2: Horizon, the point of no return.
• 3:57
  Speaker 3: It is the ultimate point of no return. Think of
• 3:59
  Speaker 3: it like one way door in space time. You can
• 4:02
  Speaker 3: pass through it going in, no problem.
• 4:04
  Speaker 2: But you can't come back out.
• 4:05
  Speaker 3: You can't even try to come back out. Inside the horizon.
• 4:09
  Speaker 3: The curvature of space time is so extreme that every
• 4:12
  Speaker 3: possible path you could take, every direction, every single direction,
• 4:15
  Speaker 3: whether you fire your rockets or just float, leads to
• 4:18
  Speaker 3: one place. Yeah, the center, the singularity. The direction out
• 4:22
  Speaker 3: literally ceases to exist. It's like trying to go south
• 4:25
  Speaker 3: from the south pole.
• 4:26
  Speaker 2: So it's the ultimate root motel. You check in, but you.
• 4:29
  Speaker 3: Never check out. And this idea comes from the schwartz
• 4:32
  Speaker 3: Child metric. Carl Schwarzschild solved Einstein's equations just months after
• 4:37
  Speaker 3: they were published back in nineteen fifteen.
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  Speaker 2: An incredible achievement.
• 4:40
  Speaker 3: It really was. And he showed that for any amount
• 4:43
  Speaker 3: of mass, there's a critical size a radius where if
• 4:46
  Speaker 3: you crush that mass down into that volume, gravity just wins.
• 4:50
  Speaker 3: It overwhelms everything and collapses.
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  Speaker 2: I always have trouble getting my head around the densities
• 4:54
  Speaker 2: we're talking about here. Can you give us a sense
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  Speaker 2: of scale?
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  Speaker 3: Sure, Let's take the Sun, a gigantic ball of fusing plasma.
• 5:02
  Speaker 3: To turn it into a black hole, you'd have to
• 5:04
  Speaker 3: crush all of its mass down into a sphere with
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  Speaker 3: the radius of just three kilometers.
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  Speaker 2: It's the entire Sun into the size of a small town.
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  Speaker 3: Or even more dramatically, take the Earth, our whole planet,
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  Speaker 3: every mountain, every ocean, all of it. To make the
• 5:18
  Speaker 3: Earth a black hole, you'd have to crush it down
• 5:20
  Speaker 3: to the size of a sugar cube.
• 5:21
  Speaker 2: Sugar cube, that's that's just unimaginable.
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  Speaker 3: It's a density that defies intuition. And the main takeaway
• 5:27
  Speaker 3: for our story in this classical view is that black
• 5:31
  Speaker 3: holes are these stable eternal prisons. They are endpoints. They
• 5:35
  Speaker 3: eat matter, they grow, and then they just sit there forever, so.
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  Speaker 2: A one way street. They only get bigger, they never
• 5:40
  Speaker 2: get smaller. That seems, I don't know, a little too
• 5:43
  Speaker 2: neat and tidy, and physics usually hates things that are
• 5:45
  Speaker 2: too neat.
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  Speaker 3: It absolutely does, because when you find a rule that
• 5:49
  Speaker 3: seems that absolute, it often means you're not looking at
• 5:51
  Speaker 3: the whole picture.
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  Speaker 2: And that's where the first crack in the armor appeared.
• 5:54
  Speaker 2: It didn't come from quantum mechanics initially, it came from thermodynamics.
• 5:58
  Speaker 3: That's right, the physics of deam engines, of all things.
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  Speaker 2: It feels like such a clash of eras nineteenth century
• 6:04
  Speaker 2: industrial physics meaning twentieth century cosmic horror.
• 6:07
  Speaker 3: It is. Specifically, we're talking about one of the most
• 6:10
  Speaker 3: sacred laws in all of science, the second law thermo dynamics.
• 6:14
  Speaker 2: Okay, remind us what that is.
• 6:15
  Speaker 3: In simple terms, it says that the total entropy of
• 6:18
  Speaker 3: a closed system can never decrease.
• 6:21
  Speaker 2: And entropy is basically a measure of disorder.
• 6:24
  Speaker 3: Yeah, messiness, messiness, disorder, or even hidden information. That's why
• 6:29
  Speaker 3: a broken egg doesn't spontaneously reassemble itself. The universe tends
• 6:33
  Speaker 3: toward more disorder, not less.
• 6:35
  Speaker 2: Okay, so things get messier over time.
• 6:38
  Speaker 3: Got it?
• 6:39
  Speaker 2: How does that connect to black holes?
• 6:40
  Speaker 3: Well, here's the problem. Imagine you have something with very
• 6:44
  Speaker 3: high entropy, like a burning library. All the ordered information
• 6:49
  Speaker 3: in the books is being turned into disordered smoke.
• 6:51
  Speaker 2: And ash, maximum messiness exactly.
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  Speaker 3: Now, what if you take that entire burning library and
• 6:56
  Speaker 3: you just dump it into a black hole? Okay, according
• 6:59
  Speaker 3: to classical general relativity, that mess is just gone. It's
• 7:03
  Speaker 3: been removed from our observable universe. The black hole itself,
• 7:07
  Speaker 3: in this classical picture is perfectly smooth and simple, has
• 7:11
  Speaker 3: no hair, as they say, it only has mass, spin,
• 7:14
  Speaker 3: and charge, no other features.
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  Speaker 2: So if the mass disappears from the universe and the
• 7:20
  Speaker 2: black hole doesn't get any mess here on the outside,
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  Speaker 2: did I just violate the second law? Did I just
• 7:25
  Speaker 2: clean up the universe's room?
• 7:27
  Speaker 3: That was the terrifying question. It looked like a perfect
• 7:29
  Speaker 3: cosmic crime, a way to delete entropy and break one
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  Speaker 3: of the most fundamental rules of nature.
• 7:35
  Speaker 2: And nature does not like its rules being broken, not.
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  Speaker 3: At all, And for a long time, physicists kind of
• 7:41
  Speaker 3: swept this under the rug they figured, well, gravity a
• 7:43
  Speaker 3: special maybe the rules just don't apply here.
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  Speaker 2: They just ignored it pretty.
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  Speaker 3: Much until the early nineteen seventies, when a graduate student
• 7:50
  Speaker 3: named Jacob Beckenstein started pushing the issue. He argued that
• 7:53
  Speaker 3: black holes must have entropy, and if they.
• 7:56
  Speaker 2: Have entropy, then they must have a temperature, right.
• 7:58
  Speaker 3: And if they have a temperature, they have to radiate heat.
• 8:01
  Speaker 2: Which totally contradicts the whole nothing can escape idea.
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  Speaker 3: Precisely Beaekenstein was on the right path, but he didn't
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  Speaker 3: have the mechanism. The person who found the mechanism improved
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  Speaker 3: it with math was Stephen Hawking, and in nineteen seventy
• 8:15
  Speaker 3: four he dropped a bombshell that changed everything.
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  Speaker 2: This is it the moment that kicks off the whole paradox?
• 8:20
  Speaker 2: What did Hawking find? What did you do differently?
• 8:23
  Speaker 3: He did something no one had successfully done before. He
• 8:26
  Speaker 3: brought the two great theories together. He applied quantum field
• 8:30
  Speaker 3: theory to the curved space time right at the edge
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  Speaker 3: of the event horizon.
• 8:34
  Speaker 2: He looked at the quantum world in the most extreme
• 8:37
  Speaker 2: gravitational field possible, and.
• 8:39
  Speaker 3: He discovered that black holes are not completely black.
• 8:42
  Speaker 2: They glow in a.
• 8:43
  Speaker 3: Very particular, very subtle way. Yes, they emit what we
• 8:46
  Speaker 3: now call Hawking radiation.
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  Speaker 2: Okay, let's unpack this slowly, because this is the absolute
• 8:50
  Speaker 2: core of the problem. How does a prison that nothing
• 8:54
  Speaker 2: can escape from suddenly start spitting things out? Is it leaking?
• 8:58
  Speaker 3: That's the crucial point. Not leaking from the inside. The
• 9:02
  Speaker 3: radiation is generated outside the event horizon, right at the edge.
• 9:06
  Speaker 3: How to understand that, you have to understand the quantum vacuum.
• 9:09
  Speaker 3: In quantum mechanics, empty space isn't empty at all. It's
• 9:13
  Speaker 3: a roiling, fizzing sea of energy.
• 9:16
  Speaker 2: The virtual particles.
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  Speaker 3: Exactly thanks to the uncertainty principle, pairs of particles and
• 9:21
  Speaker 3: antiparticles are constantly popping into existence out of borrowed energy.
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  Speaker 3: They exist for an infinitesimally small moment.
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  Speaker 2: And then they find each other and annihilate, paying back
• 9:32
  Speaker 2: the energy loan. Poof.
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  Speaker 3: Right, It's happening everywhere all the time, in this room,
• 9:36
  Speaker 3: in deep space, everywhere. But normally it's just a background hum.
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  Speaker 2: So what's different At the edge of a black hole?
• 9:43
  Speaker 3: The gravity is so extreme, the space time is so
• 9:45
  Speaker 3: warped that something dramatic can happen. Imagine a pair of
• 9:48
  Speaker 3: these virtual particles pops into existence right on the razor's
• 9:51
  Speaker 3: edge of the event horizon.
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  Speaker 2: Okay, one is just inside, one is just.
• 9:54
  Speaker 3: Outside, precisely, and the intense gravity can physically rip them
• 9:58
  Speaker 3: apart before they have a chance to annihilate.
• 10:00
  Speaker 2: It separates them permanently, exactly.
• 10:03
  Speaker 3: The particle that popped into existence inside the horizon is doomed.
• 10:07
  Speaker 3: It falls for the singularity. But the one on the
• 10:09
  Speaker 3: outside it's now an orphan. Its partner is gone forever.
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  Speaker 3: It can't annihilate, so it's stuck. It's stuck, and it's real.
• 10:18
  Speaker 3: It escapes out into the universe, and to a distant
• 10:21
  Speaker 3: observer like us with a telescope, it looks for all
• 10:24
  Speaker 3: the world like the black hole just spat out a.
• 10:27
  Speaker 2: Particle that is just mind bending. The black hole is
• 10:30
  Speaker 2: conjuring particles out of the vacuum at its edge. Ye.
• 10:33
  Speaker 2: But physics is all about balance sheets. Nothing comes from nothing.
• 10:37
  Speaker 2: There's always a cost.
• 10:39
  Speaker 3: You're absolutely right. Conservation of energy is king. If that
• 10:42
  Speaker 3: escaping particle carries positive energy away into the universe, which
• 10:45
  Speaker 3: it must, then that energy has to be paid for,
• 10:47
  Speaker 3: and it's paid for by the black hole itself.
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  Speaker 2: So the black hole loses mass.
• 10:52
  Speaker 3: It loses mass. You can think of the particle that
• 10:55
  Speaker 3: fell in as having a kind of negative energy from
• 10:57
  Speaker 3: the perspective of the outside universe. When it gets eaten,
• 11:00
  Speaker 3: its subtracts from the black hole's total mass. Energy. The
• 11:03
  Speaker 3: books have to balance.
• 11:04
  Speaker 2: And this was the revolutionary discovery.
• 11:06
  Speaker 3: This was it. Black holes aren't eternal, they have a lifespan,
• 11:11
  Speaker 3: they shrink, they evaporate.
• 11:13
  Speaker 2: That just completely upends the classical picture. And there's a
• 11:16
  Speaker 2: formula for this, right, the Hawking temperature. It's famous for
• 11:18
  Speaker 2: being this beautiful mess of letters.
• 11:21
  Speaker 3: It is. The formula itself is T T A C
• 11:25
  Speaker 3: three E g KPM.
• 11:28
  Speaker 2: Okay, don't worry about the numbers, but let's talk about
• 11:29
  Speaker 2: the letters, because it's like a guest list for the
• 11:32
  Speaker 2: Party of the century.
• 11:33
  Speaker 3: In physics, it really is a profound equation. You've got
• 11:36
  Speaker 3: daybar h bar, which is the symbol of quantum mechanics.
• 11:39
  Speaker 2: World of the small.
• 11:40
  Speaker 3: You've got Davoter Newton's constant, which represents gravity. You've got
• 11:45
  Speaker 3: t bowl order the speed of light from Einstein's relativity
• 11:48
  Speaker 3: the world, and you've got Keeler ball Er Bill Boltzmann's constant,
• 11:52
  Speaker 3: which is the cornerstone of thermodynamics.
• 11:54
  Speaker 2: The world of heat and disorder. It's like the avengers
• 11:56
  Speaker 2: of physics, all assembled in one equation to describe one
• 12:00
  Speaker 2: an object.
• 12:01
  Speaker 3: It's the first real signpost on the road to a
• 12:03
  Speaker 3: theory of quantum gravity. It proves black holes are where
• 12:06
  Speaker 3: all these theories are forced to talk to each other.
• 12:09
  Speaker 2: But there's a weird twist in there. The m for
• 12:12
  Speaker 2: mass is on the bottom of the fraction.
• 12:15
  Speaker 3: Yes, it's in the denominator, which means.
• 12:17
  Speaker 2: The bigger the black hole, the lower the temperature.
• 12:19
  Speaker 3: Exactly. It's completely counterintuitive. A supermassive black hole at the
• 12:23
  Speaker 3: center of a galaxy is incredibly frigidly cold, colder than
• 12:28
  Speaker 3: the background temperature of space. It's barely radiating at all.
• 12:32
  Speaker 2: But a small one.
• 12:32
  Speaker 3: A small black hole is scorching hot, and as it radiates,
• 12:36
  Speaker 3: it loses mass, which makes it even.
• 12:38
  Speaker 2: Smaller, which makes it even hotter, and.
• 12:40
  Speaker 3: It radiates even faster. It's a runaway process, so in
• 12:43
  Speaker 3: its very final moments, a tiny microscopic black hole would
• 12:47
  Speaker 3: evaporate in a final brilliant flash of high energy radiation. Wow.
• 12:52
  Speaker 2: So biggers are cold and quiet, small ones are hot
• 12:55
  Speaker 2: and explosive. That's the opposite of what you'd think it is.
• 12:58
  Speaker 3: In this discovery, this whole thermoe dynamic picture, it actually
• 13:01
  Speaker 3: solved that old entropy.
• 13:02
  Speaker 2: Problem, right the burning library.
• 13:04
  Speaker 3: Hawking and Beeckenstein show that, yes, black holes have entropy,
• 13:08
  Speaker 3: and the amount of entropy they have is enormous. So
• 13:11
  Speaker 3: when you throw your messy library in, the black hole's
• 13:13
  Speaker 3: own entropy increases by more than enough to account for
• 13:16
  Speaker 3: what you threw in. The second law is saved.
• 13:19
  Speaker 2: Okay, phew, so the laws of physics are safe. But
• 13:23
  Speaker 2: wait a minute. The title of this investigation has the
• 13:25
  Speaker 2: word paradox in it, So fixing one problem must have
• 13:29
  Speaker 2: created a much, much worse one.
• 13:30
  Speaker 3: And that's exactly what happened. In patching the hole in
• 13:33
  Speaker 3: the wall of thermodynamics, Hawking tore out the entire foundation
• 13:37
  Speaker 3: of quantum mechanics.
• 13:38
  Speaker 2: Okay, before we get to that crack in the foundation, though,
• 13:41
  Speaker 2: you mentioned something important the way the entropy is stored.
• 13:43
  Speaker 2: You called it the area law.
• 13:45
  Speaker 3: Yes, this is a massive clue and it's going to
• 13:48
  Speaker 3: become very important later.
• 13:49
  Speaker 2: So explain this. Why is it so strange?
• 13:51
  Speaker 3: Well, think about any normal object, a hard drive of
• 13:54
  Speaker 3: book your brain. The amount of information you can store
• 13:58
  Speaker 3: is proportional to its volume.
• 13:59
  Speaker 2: Right, more space, more stuff. If I buy a bigger
• 14:02
  Speaker 2: hard drive, I could store more data.
• 14:04
  Speaker 3: It's a three D storage system, but for a black hole.
• 14:07
  Speaker 3: Beieckenstein and Hawking found that the entropy the information it's
• 14:11
  Speaker 3: hiding is not proportional to its three D volume. It's
• 14:14
  Speaker 3: proportional to the two D surface area of its event horizon.
• 14:19
  Speaker 2: That's really weird. That's like saying the amount of data
• 14:21
  Speaker 2: on my hard drive depends on the size of the
• 14:22
  Speaker 2: sticker on the outside, not how many platters are inside.
• 14:25
  Speaker 3: That is a perfect analogy. It's as if all the
• 14:28
  Speaker 3: information of everything that ever fell in stars, planets libraries
• 14:33
  Speaker 3: isn't stored inside the black hole, but is somehow smeared
• 14:37
  Speaker 3: out and encoded on its surface, so it's plastered on
• 14:40
  Speaker 3: the walls precisely. And this was the very first hint
• 14:43
  Speaker 3: of something called the holographic principle, the idea that a
• 14:46
  Speaker 3: description of a three D volume of space can be
• 14:49
  Speaker 3: encoded on a two D boundary.
• 14:50
  Speaker 2: Okay, let's put a pin in that holography. I feel
• 14:52
  Speaker 2: like we're definitely coming back to that, but for now,
• 14:54
  Speaker 2: let's face the crisis. We have evaporation, we have entropy.
• 14:57
  Speaker 2: Why do we have a paradox?
• 14:58
  Speaker 3: Okay, this is the heart of it. All boils down
• 15:01
  Speaker 3: to the fate of the information itself. Yea. And it's
• 15:04
  Speaker 3: a direct conflict between two concepts unitarity versus.
• 15:07
  Speaker 2: Thermal radiation unitarity. Okay, that's a big physics word. Break
• 15:11
  Speaker 2: it down for us. It's basically a core belief in
• 15:13
  Speaker 2: quantum mechanics, right.
• 15:14
  Speaker 3: It is the absolute bedrock of the theory. Unitarity means
• 15:18
  Speaker 3: that information is never ever destroyed in the universe. Never never.
• 15:23
  Speaker 3: The theory is reversible. If you know the precise state
• 15:26
  Speaker 3: of a system, now you can run the clock forward
• 15:29
  Speaker 3: and predict its future, and you can run the clock
• 15:31
  Speaker 3: backward to perfectly reconstruct its past.
• 15:34
  Speaker 2: So if I burn a book, in practice, it's gone.
• 15:39
  Speaker 3: But in principle, in principle, if you could capture every
• 15:42
  Speaker 3: single particle of ash, every molecule of smoke, every photonic
• 15:46
  Speaker 3: heat and light, the laws of quantum mechanics, that you
• 15:49
  Speaker 3: could reverse the process and get the exact book back.
• 15:51
  Speaker 3: The information isn't deleted, it's just scrambled.
• 15:54
  Speaker 2: So quantum mechanics has a perfect memory it never forgets exactly.
• 15:58
  Speaker 3: Now, compare that to Hawking radiation. Hawking's original calculations show
• 16:02
  Speaker 3: that the radiation coming out is thermal, meaning it's just heat.
• 16:05
  Speaker 3: It's random, it's a perfect black body spectrum. Its properties
• 16:08
  Speaker 3: depend only on the mass, charge and spin of the
• 16:11
  Speaker 3: black hole. It does not depend on what fell in
• 16:13
  Speaker 3: to create it.
• 16:14
  Speaker 2: Wait, so you're telling me that if I make a
• 16:16
  Speaker 2: black hole out of a collapsing star, or I make
• 16:19
  Speaker 2: an identical black hole out of a giant pile of
• 16:22
  Speaker 2: encyclopedias or giant ball of rubber ducts, oh in, radiation
• 16:25
  Speaker 2: that comes out at the end is exactly the same
• 16:27
  Speaker 2: in all three.
• 16:27
  Speaker 3: Cases, according to the original calculation. Yes, yes, the radiation
• 16:31
  Speaker 3: has no memory of what it used to be. It's generic,
• 16:34
  Speaker 3: featureless heat.
• 16:35
  Speaker 2: I see the problem, I think I see the collision
• 16:37
  Speaker 2: course here. Let's make it super concrete with a thought experiment. Okay,
• 16:40
  Speaker 2: I build a quantum computer. It contains the most complex
• 16:44
  Speaker 2: information imaginable, the cure for all diseases, the works of Shakespeare,
• 16:48
  Speaker 2: my personal diary. It's a unique, highly ordered state. I
• 16:53
  Speaker 2: take this quantum computer and I throw it into a
• 16:56
  Speaker 2: black hole.
• 16:56
  Speaker 3: Okay, the black hole gets a tiny bit bigger. Then
• 17:00
  Speaker 3: over googles of years, it slowly radiates away, gets smaller
• 17:04
  Speaker 3: and smaller, and then poof.
• 17:06
  Speaker 2: It's gone, completely gone, and was left behind just.
• 17:09
  Speaker 3: A uniform, expanding cloud of warm, random Hawking radiation.
• 17:13
  Speaker 2: And if that radiation is truly random, truly thermal, there
• 17:17
  Speaker 2: is no way to look at that cloud of heat
• 17:19
  Speaker 2: and reconstruct my quantum computer.
• 17:21
  Speaker 3: No way at all. The information, Shakespeare, the cures your
• 17:26
  Speaker 3: diary has been utterly and completely erased from the universe.
• 17:30
  Speaker 2: So let's recap the conflict. General relativity says the information
• 17:33
  Speaker 2: fell past the point of no return. It's inside.
• 17:36
  Speaker 3: Quantum mechanics says the information must be conserved, it can't
• 17:39
  Speaker 3: be deleted. That's illegal.
• 17:41
  Speaker 2: But Hawking radiation says the information was converted into random heat,
• 17:44
  Speaker 2: and then the black hole disappeared, erasing it forever.
• 17:48
  Speaker 3: You've just stated the paradox perfectly. We start with what's
• 17:51
  Speaker 3: called a pure state, the ordered quantum computer, and we
• 17:54
  Speaker 3: end up with a mixed state, the disordered heat. According
• 17:57
  Speaker 3: to the rules of quantum mechanics, that transforms is forbidden.
• 18:01
  Speaker 2: So physics itself is breaking its own laws. And if
• 18:03
  Speaker 2: information can be destroyed, then then what.
• 18:06
  Speaker 3: The quantum mechanics, the theory that describes everything from transistors
• 18:10
  Speaker 3: to stars, is fundamentally wrong. We lose predictability, we lose
• 18:15
  Speaker 3: the connection between past and future. It's chaos.
• 18:18
  Speaker 2: Okay, so we have a crisis. The laws of reality
• 18:21
  Speaker 2: are on trial. Now let's talk about the proposed solutions.
• 18:24
  Speaker 2: Physicists have spent fifty years trying to find a way
• 18:27
  Speaker 2: out of this box, and.
• 18:28
  Speaker 3: There are really only a few possible escape routes. You
• 18:32
  Speaker 3: either have to modify quantum mechanics or modify general relativity,
• 18:36
  Speaker 3: or find some clever loophole that lets them both be right.
• 18:40
  Speaker 2: Let's start with solution A, the original position. What did
• 18:43
  Speaker 2: Hawking himself think? At first?
• 18:46
  Speaker 3: Hawking was nothing if not bold. He looked at his
• 18:49
  Speaker 3: own calculation and took it at face value. He said, yep,
• 18:51
  Speaker 3: the information is just lost.
• 18:53
  Speaker 2: He accepted defeat for quantum mechanics.
• 18:56
  Speaker 3: He did. He argued that gravity is special and that
• 18:59
  Speaker 3: in the presence of bla black holes, the sacred rule
• 19:01
  Speaker 3: of unitarity is violated. He famously made a bet with
• 19:05
  Speaker 3: physicists Kip Thorn and John Preskill. Hawking and Thorn bet
• 19:09
  Speaker 3: that information was destroyed, that.
• 19:11
  Speaker 2: Seems almost nihilistic, just saying, oh, well, the universe has
• 19:14
  Speaker 2: a delete button.
• 19:15
  Speaker 3: It was a radical stance, but it was consistent with
• 19:17
  Speaker 3: his math. But over the years this position became extremely
• 19:20
  Speaker 3: unpopular because if you allow information loss, it creates all
• 19:23
  Speaker 3: sorts of other paradoxes and problems. You get violations of
• 19:26
  Speaker 3: energy conservation. Things get very messy.
• 19:28
  Speaker 2: So physicists didn't like it.
• 19:30
  Speaker 3: They really didn't, and eventually needed it Hawking in two
• 19:34
  Speaker 3: thousand and four he publicly announced that he'd been wrong.
• 19:36
  Speaker 3: He conceded the bet to Priskill and gave him an
• 19:39
  Speaker 3: encyclopedia of his choice.
• 19:40
  Speaker 2: And encyclopedia yeah for the preservation of information.
• 19:44
  Speaker 3: That's clever. Okay. So solution A, information is lost is
• 19:48
  Speaker 3: off the table. What's solution B.
• 19:50
  Speaker 2: Solution B is the idea of black hole.
• 19:53
  Speaker 3: Remnants, remnants like leftovers exactly.
• 19:57
  Speaker 2: The idea is, maybe the evaporation process, it doesn't go
• 20:00
  Speaker 2: all the way to zero. Maybe it stops when the
• 20:02
  Speaker 2: black hole shrinks down to the smallest possible size, the
• 20:05
  Speaker 2: plank length, which is incredibly tiny.
• 20:07
  Speaker 3: So it leaves behind this little nugget.
• 20:09
  Speaker 2: A tiny stable nugget, and this remnant, this microscopic speck
• 20:13
  Speaker 2: would act as a kind of cosmic vault, holding all
• 20:16
  Speaker 2: the information of everything that ever fell into the original
• 20:18
  Speaker 2: black hole.
• 20:19
  Speaker 3: Wait, hold on. If I threw an entire star with
• 20:21
  Speaker 3: all of its quadrillions of particles into a black hole
• 20:25
  Speaker 3: and it evaporates down to a speck smaller than an atom,
• 20:28
  Speaker 3: how does that tiny speck store the information of an
• 20:31
  Speaker 3: entire star? That is the big glaring problem. It's sometimes
• 20:35
  Speaker 3: called the clown car problem. For this to work, this
• 20:38
  Speaker 3: tiny object would need to have a nearly infinite number
• 20:42
  Speaker 3: of possible internal states to store all that.
• 20:45
  Speaker 2: Information, and that causes problems.
• 20:47
  Speaker 3: It causes huge problems for quantum field theory. Also, if
• 20:50
  Speaker 3: these remnants are stable and can never disappear, then the
• 20:54
  Speaker 3: universe should be absolutely filled with them from all the
• 20:56
  Speaker 3: black holes that have ever evaporated. We've never seen any
• 20:59
  Speaker 3: sign of them.
• 21:00
  Speaker 2: So remnants are probably not the answer. Too much information
• 21:03
  Speaker 2: and too small a package. Okay, what's next on the menu?
• 21:06
  Speaker 2: Solution C sounds cute. The fuzzball.
• 21:09
  Speaker 3: The fuzzball paradigm. This one comes out of string theory, of.
• 21:12
  Speaker 2: Course it does. String theory is answer to everything seems
• 21:15
  Speaker 2: to be more strings.
• 21:16
  Speaker 3: Well, in a way. Yes. The fuzzball idea, championed by
• 21:19
  Speaker 3: physicists Samir Mathur and others, argues that our classical picture
• 21:23
  Speaker 3: of a black hole is just wrong. They say, when
• 21:26
  Speaker 3: matter collapses, it doesn't form a singularity and a smooth
• 21:29
  Speaker 3: empty event horizon.
• 21:30
  Speaker 2: Wait, no event horizon. That's like the defining feature of
• 21:33
  Speaker 2: a black.
• 21:34
  Speaker 3: Hole, not a sharp empty one.
• 21:35
  Speaker 2: No.
• 21:36
  Speaker 3: Instead, they propose that the fundamental strings that make up
• 21:39
  Speaker 3: matter get all tangled up into a giant, messy, vibrating ball,
• 21:44
  Speaker 3: a fuzzball.
• 21:45
  Speaker 2: So there's no empty space inside. It's filled with a
• 21:48
  Speaker 2: ball of cosmic yarn.
• 21:50
  Speaker 3: Pretty much. The surface of the black hole isn't an
• 21:52
  Speaker 3: abstract point of no return in empty space. It's a
• 21:55
  Speaker 3: physical object like the surface of the sun, but made
• 21:58
  Speaker 3: of tangled strings.
• 22:00
  Speaker 2: Okay, how does that solve the information paradox?
• 22:03
  Speaker 3: Well, it solves it beautifully. If you throw your quantum
• 22:05
  Speaker 3: computer into a fuzzball, it's information doesn't disappear into a singularity.
• 22:10
  Speaker 3: It gets absorbed into the structure of the fuzzball. The
• 22:13
  Speaker 3: vibrations of the strings change to encode the new information, so.
• 22:16
  Speaker 2: The data gets stuck in the fuzz exactly.
• 22:19
  Speaker 3: Then, when the fuzzball radiates. It's not random thermal radiation
• 22:22
  Speaker 3: from an empty horizon. It's radiation coming off a complex
• 22:26
  Speaker 3: vibrating object. The vibrations carry the information away like sound
• 22:30
  Speaker 3: waves echoing off a drum.
• 22:31
  Speaker 2: So the radiation is a detailed message from the start.
• 22:34
  Speaker 3: That's the idea. No horizon, no singularity, no information loss,
• 22:38
  Speaker 3: no paradox.
• 22:39
  Speaker 2: That actually sounds surprisingly elegant. What's the catch.
• 22:43
  Speaker 3: The main catch is that it requires string theory to
• 22:46
  Speaker 3: be the correct description of reality, and we don't know
• 22:49
  Speaker 3: if that's true, and it completely rewrites Einstein's picture. It says,
• 22:53
  Speaker 3: if you were to fall into a black hole, you
• 22:55
  Speaker 3: wouldn't just peacefully float across an invisible line. You would
• 22:58
  Speaker 3: hit a physical surface, splat against a wall of strings.
• 23:01
  Speaker 2: Okay, a very different experience for the astronaut, but it
• 23:05
  Speaker 2: saves the information. Now, let's move on to the really
• 23:08
  Speaker 2: scary standing one solution D the firewall.
• 23:12
  Speaker 3: The firewall. This is a much more recent idea, from
• 23:16
  Speaker 3: twenty twelve. It's often called the Amps paradox after the
• 23:19
  Speaker 3: four physicists superposed it. Alm Harry, MAROLV. Pulcinski and Sully.
• 23:24
  Speaker 2: Sounds like a powerful law firm it was.
• 23:26
  Speaker 3: A powerful paper. They took a very close look at
• 23:29
  Speaker 3: quantum entanglement. Remember our particle pair at the horizon, one
• 23:32
  Speaker 3: falls in, one.
• 23:33
  Speaker 2: Escapes, and they're entangled linked spooky action at a distance.
• 23:37
  Speaker 3: Exactly Now, for information to eventually get out of the
• 23:40
  Speaker 3: black hole, that escaping particle, let's call it particle B,
• 23:44
  Speaker 3: needs to be entangled with all the other hawking radiation
• 23:47
  Speaker 3: that came out before it. It needs to join the
• 23:49
  Speaker 3: collective to reconstruct the message.
• 23:51
  Speaker 2: Okay, so B needs to be linked to the cloud
• 23:53
  Speaker 2: of earlier radiation.
• 23:55
  Speaker 3: But here's the problem. Particle B is already maximally entangled
• 23:59
  Speaker 3: with its original partner, particle A, the one that fell
• 24:02
  Speaker 3: inside the black hole.
• 24:04
  Speaker 2: Can it be entangled with both?
• 24:06
  Speaker 3: Quantum mechanics says no. There's a fundamental rule called the
• 24:09
  Speaker 3: monogamy of entanglement. A quantum system can only be fully
• 24:13
  Speaker 3: maximally entangled with one other system at a time. It
• 24:16
  Speaker 3: can't have two perfect partners.
• 24:18
  Speaker 2: Quantum mechanics believes in monogamy.
• 24:19
  Speaker 3: Good to know, so amps argue that something has to
• 24:22
  Speaker 3: give if the information is going to be saved. If
• 24:26
  Speaker 3: Particle B is going to join the outside radiation cloud,
• 24:29
  Speaker 3: then it's entanglement with particle a inside must be violently
• 24:33
  Speaker 3: broken the moment it's created.
• 24:34
  Speaker 2: And breaking entanglement that's not a gentle process.
• 24:37
  Speaker 3: No, breaking that quantum link requires a huge amount of energy,
• 24:41
  Speaker 3: and they calculated that if this happens for every single
• 24:43
  Speaker 3: particle pair at the horizon, it would create an intensely
• 24:47
  Speaker 3: energetic barrier right at that spot, a literal wall of fire.
• 24:50
  Speaker 2: So if I'm the astronaut falling in instead of a
• 24:53
  Speaker 2: gentle crossing into darkness, you would.
• 24:55
  Speaker 3: Hit this wall of high energy quanta and be instantly vaporized,
• 25:00
  Speaker 3: annihilated to the horizon.
• 25:02
  Speaker 2: That seems unpleasant for me, But why is it a
• 25:04
  Speaker 2: problem for physics?
• 25:06
  Speaker 3: It's a huge problem for Albert Einstein. The absolute cornerstone
• 25:09
  Speaker 3: of general relativity is the equivalence principle. It was what
• 25:13
  Speaker 3: Einstein called his happiest thought, which says it says that
• 25:16
  Speaker 3: the experience of being in free fall in a gravitational
• 25:19
  Speaker 3: field is indistinguishable from floating in empty space. For an
• 25:25
  Speaker 3: astronaut falling into a black hole, crossing the event horizon
• 25:28
  Speaker 3: should be completely uneventful. It's not a special place in space.
• 25:31
  Speaker 3: You shouldn't even notice when you cross it.
• 25:33
  Speaker 2: Right, It's just a line on a map, not a
• 25:34
  Speaker 2: brick wall.
• 25:35
  Speaker 3: But the firewall says no, it is a brick wall,
• 25:38
  Speaker 3: a wall of death.
• 25:40
  Speaker 2: So to save quantum mechanics and its rule of monogamy,
• 25:43
  Speaker 2: the firewall has to completely shatter Einstein's equivalence principle.
• 25:47
  Speaker 3: It really feels like every solution breaks something else. One
• 25:50
  Speaker 3: breaks quantum mechanics, another breaks the structure of the black hole.
• 25:53
  Speaker 3: This one breaks general relativity. It's like trying to solve
• 25:56
  Speaker 3: a Rubik's cube, where fixing one side messes up all
• 25:59
  Speaker 3: the others. That's a perfect description of why this has
• 26:01
  Speaker 3: been such a persistent problem for fifty years. But in
• 26:05
  Speaker 3: the last couple of decades, a new heavyweight contender has
• 26:07
  Speaker 3: entered the ring. It's not so much a specific physical picture,
• 26:11
  Speaker 3: but a powerful mathematical argument.
• 26:13
  Speaker 2: And this is where we get back to holography. The
• 26:15
  Speaker 2: idea called ad SCFT, Yes, the.
• 26:19
  Speaker 3: Ad s CFT correspondence, proposed by one Meldadicina in nineteen
• 26:23
  Speaker 3: ninety seven. It's one of the most influential and cited
• 26:26
  Speaker 3: papers in the history of theoretical physics.
• 26:28
  Speaker 2: Okay, ad SCFT is a lot of letters. I need
• 26:32
  Speaker 2: you to give me the soup can analogy.
• 26:33
  Speaker 3: I read about the soup can analogy is perfect. This
• 26:36
  Speaker 3: was called a duality. Meldocinas showed a mathematical equivalence between
• 26:40
  Speaker 3: two theories that look completely different.
• 26:42
  Speaker 2: Okay, what are the two theories.
• 26:43
  Speaker 3: First, you have the physics inside a specific kind of
• 26:46
  Speaker 3: toy universe called anti de Sitter space or ADS. This
• 26:50
  Speaker 3: is the soup inside the can. It's a universe with gravity,
• 26:52
  Speaker 3: it has black holes. It's a three D bulk space.
• 26:55
  Speaker 3: Got it.
• 26:55
  Speaker 2: The soup gravity lives there.
• 26:57
  Speaker 3: Then you have a totally different theory, a normal field
• 27:00
  Speaker 3: theory or CFT. This is a quantum theory of particles
• 27:04
  Speaker 3: and fields with no gravity, and it lives only on
• 27:07
  Speaker 3: the boundary of that universe. It's the two D label
• 27:10
  Speaker 3: on the outside of the soup can.
• 27:11
  Speaker 2: So a three D universe with gravity inside and a
• 27:15
  Speaker 2: two D quantum universe without gravity on the label.
• 27:18
  Speaker 3: And here is Meldosine is incredible discovery. He proved that
• 27:21
  Speaker 3: the physics of the soup is mathematically identical to the
• 27:24
  Speaker 3: physics on the label. There are two different descriptions of
• 27:27
  Speaker 3: the exact same system, a dictionary between them, a perfect dictionary.
• 27:31
  Speaker 3: Every event that happens in the three D gravitational world
• 27:34
  Speaker 3: of the soup corresponds exactly to some event happening among
• 27:37
  Speaker 3: the two D quantum particles on the label.
• 27:39
  Speaker 2: So if a black hole forms inside the soup, can.
• 27:42
  Speaker 3: That corresponds to something like a hot, swirling fluid of
• 27:45
  Speaker 3: particles interacting on the two D label. And here's the
• 27:47
  Speaker 3: genius move go on. The theory on the label, the
• 27:50
  Speaker 3: CFT is a standard quantum field theory. We know for
• 27:53
  Speaker 3: a fact that it obeys the rules. It is unitary.
• 27:56
  Speaker 3: Information is never lost in that theory.
• 27:58
  Speaker 2: Oh, I see where this is going. If the theory
• 28:00
  Speaker 2: on the label is unitary and never loses information.
• 28:03
  Speaker 3: And the label is just a different description of the soup.
• 28:06
  Speaker 2: Then the soup must be unitary too.
• 28:08
  Speaker 3: Exactly. It proves mathematically that a theory of quantum gravity
• 28:12
  Speaker 3: must preserve information even if we don't know the exact
• 28:16
  Speaker 3: physical mechanism of how the black hole gives the information back.
• 28:19
  Speaker 3: The duality guarantees that it does.
• 28:21
  Speaker 2: That feels like I don't know a brilliant cheak code.
• 28:25
  Speaker 2: It's like saying I don't know how to solve this
• 28:27
  Speaker 2: impossible three D puzzle, but I found the two D
• 28:30
  Speaker 2: instruction Manual and it says on the last page, this
• 28:33
  Speaker 2: puzzle is solvable.
• 28:34
  Speaker 3: That's a great way to put it. It gave physicists
• 28:37
  Speaker 3: enormous confidence that information is ultimately safe. Now there's a
• 28:41
  Speaker 3: big caveat which is our real universe is not an
• 28:44
  Speaker 3: anti de Sitter space. It's a different shape. So this
• 28:48
  Speaker 3: is a proof of principle in a toy universe, not
• 28:51
  Speaker 3: a direct map of our reality. But the principle is
• 28:54
  Speaker 3: believed to be general.
• 28:55
  Speaker 2: And this idea has led to real progress.
• 28:58
  Speaker 1: Right.
• 28:58
  Speaker 2: It led to the calculation of something called Page curve.
• 29:00
  Speaker 2: This feels like the most recent breakthrough it is.
• 29:03
  Speaker 3: This is based on work by Don Page back in
• 29:05
  Speaker 3: the nineties. He thought about the entanglement entropy of the
• 29:08
  Speaker 3: Hawking radiation as the black hole evaporates.
• 29:11
  Speaker 2: Okay, so he's basically tracking how messy or how entangled
• 29:15
  Speaker 2: the radiation is over time.
• 29:17
  Speaker 3: Right, And he made a prediction. If information is truly lost,
• 29:21
  Speaker 3: as Hawking first thought, then the entropy of the radiation
• 29:25
  Speaker 3: just keeps going up and up and up as more
• 29:28
  Speaker 3: random particles are emitted, until the black hole is.
• 29:31
  Speaker 2: Gone, a straight line going up more or less.
• 29:34
  Speaker 3: But age argued, if information is conserved, something different has
• 29:38
  Speaker 3: to happen. The entropy should go up for the first
• 29:41
  Speaker 3: half of black hole's life, but then it has to
• 29:43
  Speaker 3: hit a peak the page time and start coming back down.
• 29:46
  Speaker 3: Why would it come down, Because in the second half
• 29:49
  Speaker 3: of the evaporation, the radiation that's coming out is now
• 29:52
  Speaker 3: deeply entangled with the radiation that came out in the
• 29:54
  Speaker 3: first half. It starts to purify the system. It's releasing
• 29:57
  Speaker 3: the key to the scrambled message. By the time the
• 30:00
  Speaker 3: black hole is completely gone, the total entropy of all
• 30:02
  Speaker 3: the radiation has to drop back down to zero because
• 30:05
  Speaker 3: it has reformed a pure state.
• 30:07
  Speaker 2: The original information is all there, just unscrambled. And recently
• 30:11
  Speaker 2: physicists actually managed to calculate this curve.
• 30:14
  Speaker 3: Yes, this was the huge breakthrough. In twenty nineteen, using
• 30:18
  Speaker 3: tools from the holographic principle, two different groups of physicists
• 30:22
  Speaker 3: finally figured out how to do the calculation for an
• 30:24
  Speaker 3: evaporating black hole, and they reproduce the page curve exactly.
• 30:28
  Speaker 3: They saw the entropy go up and then come back down.
• 30:31
  Speaker 2: That feels like the smoking gun. It feels like we
• 30:33
  Speaker 2: finally have concrete mathematical proof that information gets out.
• 30:37
  Speaker 3: It's the strongest evidence we have to date. It suggests
• 30:40
  Speaker 3: that somehow, through subtle correlations and entanglement, the information does escape.
• 30:45
  Speaker 3: But it still leads us with a nagging question, which
• 30:48
  Speaker 3: is how and why does the radiation look so random
• 30:51
  Speaker 3: and thermal? If it's secretly carrying this complex message.
• 30:54
  Speaker 2: Right, if it contains Shakespeare, why can't we just read it?
• 30:57
  Speaker 3: And the answer seems to be the difference between something
• 30:59
  Speaker 3: that is truely random and something that is pseudorandom.
• 31:02
  Speaker 2: Like a secret code.
• 31:03
  Speaker 3: Precisely, if I take a long novel and I encrypt
• 31:06
  Speaker 3: it with a powerful modern encryption key, what I get
• 31:10
  Speaker 3: out looks like total.
• 31:11
  Speaker 2: Gibberish, just random noise.
• 31:13
  Speaker 3: You could run every statistical test you want on it
• 31:15
  Speaker 3: and it would look perfectly random. But it's not. It
• 31:19
  Speaker 3: contains all the information of the original novel in a hidden,
• 31:22
  Speaker 3: correlated form.
• 31:23
  Speaker 2: And if you have the key.
• 31:24
  Speaker 3: If you have the key, you could decrypt it and
• 31:26
  Speaker 3: get the novel back perfectly. The modern consensus is that
• 31:30
  Speaker 3: Hawking radiation is like that. It's not random heat. It's
• 31:34
  Speaker 3: the most complexly encrypted message in the universe.
• 31:37
  Speaker 2: So the black hole is not a shredder it's an
• 31:39
  Speaker 2: ultimate scrambler.
• 31:41
  Speaker 3: That is the picture that's emerging. It scrambles the information
• 31:44
  Speaker 3: so completely that for any practical purpose it's gone. But
• 31:47
  Speaker 3: in principle, the universe holds onto the key.
• 31:50
  Speaker 2: What an incredible journey. We've gone from a simple eternal prison,
• 31:54
  Speaker 2: to a leaky radiator, to a fretter, to a hard drive,
• 31:58
  Speaker 2: to a ball of fuzz, to a wall of fu
• 32:00
  Speaker 2: and now to a holographic scrambler.
• 32:02
  Speaker 3: It's a perfect example of how science pushes at the
• 32:05
  Speaker 3: boundaries of what we know, and how each new idea
• 32:08
  Speaker 3: reveals a deeper level of reality.
• 32:10
  Speaker 2: So let's bring it all home. Let's talk about the
• 32:12
  Speaker 2: big picture. Why should someone listening right now care about
• 32:16
  Speaker 2: burning encyclopedias in space? What are the real stakes here?
• 32:20
  Speaker 3: The stakes are everything. This paradox isn't really about black holes.
• 32:25
  Speaker 3: Black holes are just the laboratory the universe has given us.
• 32:29
  Speaker 3: This is the crucible where we are trying to forge
• 32:31
  Speaker 3: a theory of quantum gravity.
• 32:33
  Speaker 2: The holy grail of physics, the theory that unites the
• 32:36
  Speaker 2: very big and the very small.
• 32:38
  Speaker 3: The theory of everything. Solving this paradox will tell us
• 32:41
  Speaker 3: something profound about the fundamental nature of space and time themselves.
• 32:45
  Speaker 2: What do you mean by that? How could it change
• 32:47
  Speaker 2: our idea of space and time?
• 32:49
  Speaker 3: Well, this holographic principle we've been talking about, it's a
• 32:52
  Speaker 3: radical idea and suggests that space time might not be
• 32:55
  Speaker 3: the fundamental bedrock of reality. It might be.
• 32:58
  Speaker 2: Emergent, emergent like it's made of something else exactly.
• 33:02
  Speaker 3: Think about temperature. A single atom doesn't have a temperature.
• 33:05
  Speaker 3: Temperature is an emergent property of a large collection of
• 33:07
  Speaker 3: atoms moving around. The idea gaining ground is that space
• 33:12
  Speaker 3: time itself might be like that. It might emerge from
• 33:14
  Speaker 3: a deeper network of quantum entanglement.
• 33:16
  Speaker 2: So space is built out of quantum connections between things.
• 33:20
  Speaker 3: That's the frontier. The slogan some physicists use is it
• 33:24
  Speaker 3: from quibit, the idea that the geometry of space time
• 33:28
  Speaker 3: is determined by the entanglement structure of quantum information. If
• 33:32
  Speaker 3: you bring the entanglement, the space itself falls apart.
• 33:35
  Speaker 2: That's a lot to wrap your head around. It makes
• 33:38
  Speaker 2: reality sound like a giant quantum computer.
• 33:40
  Speaker 3: In some sense, it might be. And the amazing thing
• 33:43
  Speaker 3: is this isn't just philosophy anymore. We have observational tools
• 33:46
  Speaker 3: coming online that could actually test some.
• 33:48
  Speaker 2: Of this, like the event horizon telescope exactly, which gave
• 33:52
  Speaker 2: us that first incredible image.
• 33:54
  Speaker 3: We have gravitational wave detectors that can listen to black
• 33:57
  Speaker 3: holes merging. And there's even the possibility of finding primordial
• 34:01
  Speaker 3: black holes.
• 34:01
  Speaker 2: Tiny ones left over from the big bag.
• 34:03
  Speaker 3: Yes, and if they exist, some of them should be
• 34:07
  Speaker 3: finishing their evaporation and exploding right now. If we could
• 34:10
  Speaker 3: detect one of those final flashes.
• 34:12
  Speaker 2: You could analyze the radiation directly, we could actually see
• 34:14
  Speaker 2: if it follows the page curve.
• 34:16
  Speaker 3: It would be the most profound discovery, imaginable, definitive proof
• 34:19
  Speaker 3: one way or the other.
• 34:20
  Speaker 2: It's just a stunning reminder that even with all our knowledge,
• 34:23
  Speaker 2: we're still just scratching the surface. The universe is so
• 34:27
  Speaker 2: much stranger than we can imagine.
• 34:29
  Speaker 3: Absolutely, the paradox isn't a failure of physics. It's a
• 34:33
  Speaker 3: signpost pointing us toward a deeper, more interconnected reality.
• 34:38
  Speaker 2: So as we close, here is a final provocative thought
• 34:40
  Speaker 2: for you to take with you. We talked about holograms.
• 34:43
  Speaker 2: We talked about how all the information of a three
• 34:45
  Speaker 2: D black hole might just be stored on its two
• 34:48
  Speaker 2: D surface. Yes, and you mentioned that some theories, like
• 34:51
  Speaker 2: at SCFT, suggests that the entire universe might work that way,
• 34:55
  Speaker 2: a three D soup with a two D label that
• 34:57
  Speaker 2: describes it all.
• 34:58
  Speaker 3: It's a leading theoretical possibility. Yes.
• 35:00
  Speaker 2: So if a black hole is just scrambled information painted
• 35:04
  Speaker 2: on a horizon, and if the whole universe is a hologram,
• 35:08
  Speaker 2: then what are we? Are we really three D beings
• 35:10
  Speaker 2: living in a three D space or are we just
• 35:13
  Speaker 2: part of the two D information painted on the distant
• 35:15
  Speaker 2: edge of the cosmos having a very convincing hallucination that
• 35:19
  Speaker 2: we have depth.
• 35:20
  Speaker 3: That is a question that pushes right up against the
• 35:22
  Speaker 3: limits of physics and into philosophy. But the math doesn't
• 35:25
  Speaker 3: say no, we might just be a.
• 35:26
  Speaker 2: Projection on that slightly unsettling thought. Thank you for joining
• 35:30
  Speaker 2: us on this exploration of the impossible, Stay curious, and.
• 35:34
  Speaker 3: Never stop questioning the nature of your reality.
• 35:36
  Speaker 2: We'll see you next time.