WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.960 --> 00:00:31.039 If you take a state of the art supercomputer today 8 00:00:31.359 --> 00:00:34.039 and you feed it the mathematical equations for two black 9 00:00:34.079 --> 00:00:38.920 holes colliding, it will take weeks of just NonStop processor 10 00:00:38.960 --> 00:00:40.600 melting grinding to give you the answer. 11 00:00:40.759 --> 00:00:43.280 Yeah, and that's if the simulation doesn't crash halfway through, 12 00:00:43.320 --> 00:00:44.960 which it often used to. 13 00:00:45.240 --> 00:00:47.640 Right. I mean, we are talking about tracking the absolute 14 00:00:47.640 --> 00:00:51.000 most extreme violence in the cosmos. It's a collision so 15 00:00:51.200 --> 00:00:56.359 powerful that it physically bends the geometry of reality itself, which. 16 00:00:56.159 --> 00:01:00.000 Is incredibly hard to calculate. The numbers get unimaginably huge. 17 00:01:00.119 --> 00:01:03.119 Exactly. Yeah, but there's this team of physicists of recently 18 00:01:03.119 --> 00:01:05.560 published some research suggesting that you might be able to 19 00:01:05.599 --> 00:01:09.519 get the exact same answer using basically the mathematics that 20 00:01:09.599 --> 00:01:11.920 explains why your morning coffee gets cold. 21 00:01:12.280 --> 00:01:14.599 It is I mean, it's one of the most counterintuitive 22 00:01:14.599 --> 00:01:17.000 proposals in modern astrophysics right now. 23 00:01:17.159 --> 00:01:19.599 It really is. And if you follow astrophysics at all, 24 00:01:19.640 --> 00:01:23.040 you know about this enduring frustration. Right. But the two 25 00:01:23.079 --> 00:01:26.079 great paradigms of physics. You've got quantum mechounics and thermodynamaz 26 00:01:26.200 --> 00:01:28.680 on one side, and then general relativity on the other. 27 00:01:28.840 --> 00:01:32.359 And they notoriously refuse to speak the same language. It's 28 00:01:32.359 --> 00:01:35.120 like they're operating in two completely different universes. 29 00:01:34.680 --> 00:01:36.959 Right, So what we're looking at today is a tangible 30 00:01:37.480 --> 00:01:40.680 mathematical bridge between them. We are talking about how the 31 00:01:40.760 --> 00:01:46.040 ultimate agents of cosmic chaos are well secretly governed by 32 00:01:46.079 --> 00:01:48.239 the mundane physics of your kitchen. 33 00:01:48.400 --> 00:01:50.920 Yeah, the historical divide you just mentioned, that's really the 34 00:01:50.959 --> 00:01:54.920 core of the whole problem. General relativity, you know, Einstein's masterpiece. 35 00:01:55.040 --> 00:01:56.560 It's the ultimate theory of the. 36 00:01:56.439 --> 00:02:00.040 Macroscopic, the big stuff, planets, galaxies. 37 00:01:59.519 --> 00:02:03.519 Gravity exactly, and it is entirely deterministic. So if you 38 00:02:03.640 --> 00:02:07.239 know the precise state of space time right now, Einstein's 39 00:02:07.239 --> 00:02:11.159 equations should theoretically at least tell you exactly what space 40 00:02:11.199 --> 00:02:12.800 time will do a second from now. 41 00:02:12.919 --> 00:02:15.400 A cause is b every single time right. 42 00:02:15.439 --> 00:02:18.439 But thermodynamics, on the other hand, is a statistical science. 43 00:02:18.479 --> 00:02:22.039 It does not care about the deterministic path of individual atoms. 44 00:02:22.280 --> 00:02:26.840 It relies entirely on probability and macro averages. 45 00:02:27.000 --> 00:02:29.199 Like you don't track every single water molecule in a 46 00:02:29.240 --> 00:02:31.879 boying pot, You just measure the overall temperature precisely. 47 00:02:32.599 --> 00:02:35.919 So to suggest that you can bypass the deterministic tracking 48 00:02:35.960 --> 00:02:39.360 of a black hole merger and instead treat the collision 49 00:02:39.520 --> 00:02:42.520 like say, a mixing of two hot gases, that is 50 00:02:42.759 --> 00:02:46.520 a radical departure from how we've calculated these events for decades. 51 00:02:46.639 --> 00:02:49.520 It's nuts. But before we get into how a black 52 00:02:49.520 --> 00:02:53.520 hole could possibly behave like a mixing gas, I think 53 00:02:53.520 --> 00:02:57.400 we really have to establish what exactly is happening during 54 00:02:57.439 --> 00:02:59.439 one of these mergers, Like let's look at the actual 55 00:02:59.439 --> 00:03:00.639 physical crest. 56 00:03:00.240 --> 00:03:02.439 That idea visualizing it is key. 57 00:03:02.599 --> 00:03:05.400 So we've got two black holes locked in this decaying orbit, 58 00:03:05.960 --> 00:03:09.039 and because of this sheer mass involved, they're dragging space 59 00:03:09.080 --> 00:03:12.919 time along with them. They're spiraling inward, approaching a significant 60 00:03:12.919 --> 00:03:15.680 fraction of the speed of light, and they eventually. 61 00:03:15.240 --> 00:03:18.199 Touch, and that exact moment of contact is where the 62 00:03:18.240 --> 00:03:21.520 physics gets incredibly hostile. You have to remember that a 63 00:03:21.560 --> 00:03:24.560 black hole, it's not a solid object, right, There's no surface, 64 00:03:24.639 --> 00:03:26.800 no surface you can knock on. The black hole is 65 00:03:26.840 --> 00:03:29.360 just a region of space where gravity is so intense 66 00:03:29.439 --> 00:03:32.120 that the escape velocity exceeds the speed of light. The 67 00:03:32.159 --> 00:03:34.360 boundary of that region is the event horizon. 68 00:03:34.680 --> 00:03:37.680 So it's just pure math, essentially a mathematical line in 69 00:03:37.719 --> 00:03:38.039 the sand. 70 00:03:38.240 --> 00:03:42.599 Exactly, when two black holes merge, you are watching two 71 00:03:42.719 --> 00:03:47.080 purely mathematical boundaries in space time colliding and reshaping each other. 72 00:03:47.800 --> 00:03:51.280 The event horizons deform, they reach out toward each other, 73 00:03:51.560 --> 00:03:55.719 and they snap together into a single, highly distorted, sort 74 00:03:55.719 --> 00:03:57.159 of peanut shaped horizon. 75 00:03:57.319 --> 00:04:01.639 I've always loved that visual, a giant cosmic peanut. And 76 00:04:01.719 --> 00:04:04.800 the energy released when that snapping happens is staggering. I mean, 77 00:04:04.840 --> 00:04:07.439 a typical merger can release more energy in a fraction 78 00:04:07.479 --> 00:04:10.120 of a second than all the stars in the observable 79 00:04:10.199 --> 00:04:10.960 universe combined. 80 00:04:11.039 --> 00:04:14.120 It's an output of power that literally outshines everything else 81 00:04:14.159 --> 00:04:15.319 in the universe put together. 82 00:04:15.599 --> 00:04:18.399 But here's the mechanism I really want to understand. If 83 00:04:18.439 --> 00:04:21.480 there's no actual physical matter collidinge Like, there's no rock, 84 00:04:21.560 --> 00:04:24.920 no gas, just event horizons, what exactly is carrying that 85 00:04:25.040 --> 00:04:25.600 energy away. 86 00:04:25.680 --> 00:04:28.000 That's the wild part. The energy is carried away by 87 00:04:28.000 --> 00:04:32.360 the very fabric of reality itself. When those horizons merge, 88 00:04:32.439 --> 00:04:35.720 the surrounding space time is subjected to catastrophic stress. 89 00:04:35.759 --> 00:04:37.000 It's again stretched and pulled. 90 00:04:37.319 --> 00:04:42.959 Right. In general, relativity dictates that accelerating masses produce gravitational waves. 91 00:04:43.600 --> 00:04:47.680 So just as an accelerat and electrical charge produces electromagnetic waves, 92 00:04:48.000 --> 00:04:50.600 accelerating masses produce ripples and gravity. 93 00:04:50.720 --> 00:04:53.000 So in the final moments of that spiral, and especially 94 00:04:53.040 --> 00:04:56.519 during the actual merger, the black holes are just churning 95 00:04:56.680 --> 00:04:58.040 space time into waves. 96 00:04:58.319 --> 00:05:02.279 Yes, they are converting massive portion of their combined mass 97 00:05:02.560 --> 00:05:06.240 directly into the energy of these gravitational waves. Space time 98 00:05:06.279 --> 00:05:09.839 itself is stretching and squeezing, undulating outward at the speed 99 00:05:09.879 --> 00:05:10.160 of light. 100 00:05:10.319 --> 00:05:12.319 Wow. Okay, I want to use an analogy here to 101 00:05:12.319 --> 00:05:16.000 help visualize this. If space time is a trampoline, this 102 00:05:16.079 --> 00:05:19.160 collision isn't just dropping a bowling ball on it. It's like 103 00:05:19.199 --> 00:05:22.600 two bowling balls smashing into dust, sending these massive ripples 104 00:05:22.839 --> 00:05:24.959 across the entire surface of the trampoline. 105 00:05:24.959 --> 00:05:26.800 That's a great way to put it. The trampoline mat 106 00:05:26.800 --> 00:05:28.519 itself is what's carrying the energy away. 107 00:05:28.720 --> 00:05:33.639 Okay, so we have this wildly asymmetric, wobbling freshly merged 108 00:05:33.680 --> 00:05:37.439 black hole. It's highly unstable, and physicist Monica ring Con 109 00:05:37.519 --> 00:05:41.639 Ramirez describes this exact phase with some really striking imagery. 110 00:05:42.120 --> 00:05:45.319 She points out that immediately post merger, the remnant black 111 00:05:45.319 --> 00:05:47.000 hole is ringing like a struck bell. 112 00:05:47.120 --> 00:05:48.519 Yes, the ring down phase, right. 113 00:05:48.720 --> 00:05:51.959 It vibrates and it radiates away excess energy through those 114 00:05:51.959 --> 00:05:55.600 gravitational waves until it finally settles into a calm, stable state. 115 00:05:56.199 --> 00:05:59.240 But way a bell rings because the metal physically vibrates 116 00:05:59.240 --> 00:06:02.879 and displaces air molecules. A black hole is, as we said, 117 00:06:02.920 --> 00:06:08.480 empty space banded by a horizon. What is physically quivering 118 00:06:08.920 --> 00:06:10.160 if there is no matter there? 119 00:06:10.240 --> 00:06:13.040 That is the perfect question to exposse just how weird 120 00:06:13.199 --> 00:06:15.920 general relativity is. When we say it rings, we're talking 121 00:06:15.920 --> 00:06:18.560 about a phenomenon called quasinormal. 122 00:06:17.879 --> 00:06:18.959 Modes wisnero modes. 123 00:06:19.000 --> 00:06:21.600 Okay, yeah, think of space time as a highly taught 124 00:06:21.639 --> 00:06:25.040 elastic medium like your trampoline met the event horizon is perturbed, 125 00:06:25.040 --> 00:06:28.240 meaning its geometry is highly irregular, like that peanut ship 126 00:06:28.279 --> 00:06:28.959 we mentioned. 127 00:06:28.759 --> 00:06:30.279 Right, it's all lopsided. 128 00:06:30.160 --> 00:06:33.319 Exactly, and because a black hole naturally wants to be 129 00:06:33.399 --> 00:06:36.680 perfectly smooth and spherical, or at least a blate if 130 00:06:36.720 --> 00:06:39.920 it's spinning, the natural laws of gravity forced that irregularity 131 00:06:40.000 --> 00:06:43.399 to smooth out. The ringing is the actual metric of 132 00:06:43.519 --> 00:06:44.839 space time oscillating. 133 00:06:45.079 --> 00:06:48.680 So the horizon is violently shifting from elongated to compressed 134 00:06:49.079 --> 00:06:49.519 over and. 135 00:06:49.480 --> 00:06:53.519 Over, yes, shedding the energy of those deformations as gravitational waves. 136 00:06:53.560 --> 00:06:56.600 It's shedding its asymmetries, and as it sheds them, the 137 00:06:56.639 --> 00:07:02.000 amplitude of those oscillations decays exponentially. That decay, that fading out, 138 00:07:02.079 --> 00:07:03.199 is the ringing stopping. 139 00:07:03.800 --> 00:07:06.399 Okay, so the ringing is literally the new black hole 140 00:07:06.519 --> 00:07:09.480 ironing out its own wrinkles by throwing gravitational energy out 141 00:07:09.480 --> 00:07:10.120 into the universe. 142 00:07:10.279 --> 00:07:12.720 Ironing out its wrinkles is a brilliant way to describe it. 143 00:07:12.800 --> 00:07:14.800 And when that ringing stops, when the wrinkles are all 144 00:07:14.839 --> 00:07:18.680 ironed out, we are left with the final remnant. But 145 00:07:18.800 --> 00:07:21.680 what fascinates me here is the sheer simplicity of that 146 00:07:21.720 --> 00:07:25.199 final state. Based on the no hair theorem in astrophysics, 147 00:07:25.560 --> 00:07:28.079 Once a black hole settles down, all of the chaotic 148 00:07:28.199 --> 00:07:29.600 history of the collision. 149 00:07:29.160 --> 00:07:31.040 Is just wiped out, completely erased. 150 00:07:31.240 --> 00:07:34.680 The final object is defined by only two properties, mass 151 00:07:34.759 --> 00:07:35.279 and spin. 152 00:07:35.560 --> 00:07:38.920 Well, technically, the no hair theorem allows for three properties. 153 00:07:39.120 --> 00:07:41.839 It's mass, spin, and electric charge. 154 00:07:41.959 --> 00:07:42.959 Oh right, charge. 155 00:07:43.040 --> 00:07:47.560 But know, in a realistic astrophysical setting, black holes have 156 00:07:47.839 --> 00:07:51.399 negligible charge because they would just quickly attract opposite charges 157 00:07:51.399 --> 00:07:55.759 from the surrounding plasma and neutralize themselves anyway. So practically speaking, 158 00:07:55.800 --> 00:07:58.680 it's just two for all practical purposes. Yes, you are 159 00:07:58.800 --> 00:08:02.720 entirely correct. We only care about two parameters, mass which 160 00:08:02.759 --> 00:08:05.519 tells us the size of the event horizon, and spin 161 00:08:05.720 --> 00:08:08.680 or angular momentum, which tells us how fast the black 162 00:08:08.680 --> 00:08:09.560 hole is rotating. 163 00:08:09.920 --> 00:08:13.040 So all the intricate details, the varying masses of the 164 00:08:13.079 --> 00:08:17.120 original black holes, the specific angles they collided at, the 165 00:08:17.120 --> 00:08:20.160 complex geometry, or the merger, all of that is just gone. 166 00:08:20.319 --> 00:08:23.720 All that information is swallowed by the horizon or radiated 167 00:08:23.720 --> 00:08:24.759 away into the universe. 168 00:08:24.920 --> 00:08:27.959 Mass and spin. That is it. But if the final 169 00:08:28.000 --> 00:08:30.759 state is just two simple numbers, why on earth do 170 00:08:30.800 --> 00:08:33.919 we need supercomputers running for weeks to find them? I mean, 171 00:08:33.960 --> 00:08:36.840 if I smash a two kilogram ball of clay into 172 00:08:36.919 --> 00:08:39.159 a three kilogram ball of clay. I don't need a 173 00:08:39.200 --> 00:08:41.679 supercomputer to tell me I have a five kilogram ball. 174 00:08:41.480 --> 00:08:45.720 Of clay, because black holes do not obey simple Newtonian arithmetic. 175 00:08:46.080 --> 00:08:48.759 When you smash those two balls of clay together, they 176 00:08:48.799 --> 00:08:52.679 aren't radiating ten percent of their mass away into the 177 00:08:52.720 --> 00:08:54.039 geometry of empty space. 178 00:08:54.200 --> 00:08:57.080 Fair point. The energy loss is massive, right. 179 00:08:57.399 --> 00:08:59.840 The problem lies in the equations we have to use 180 00:08:59.879 --> 00:09:04.240 to calculate that loss. Einstein's field equations of general relativity 181 00:09:04.320 --> 00:09:09.399 are a set of ten highly complex coupled nonlinear partial 182 00:09:09.519 --> 00:09:13.200 differential equations, the keyword there being nonlinear. 183 00:09:13.559 --> 00:09:16.320 Let's drill into that nonlinearity because that seems to be 184 00:09:16.440 --> 00:09:19.279 the fundamental bottleneck here for the computers. Yeah, when we 185 00:09:19.320 --> 00:09:21.720 say an equation is nonlinear in physics, we usually mean 186 00:09:21.759 --> 00:09:23.600 the variables feedback into themselves. 187 00:09:23.639 --> 00:09:27.519 Right, Precisely, in general relativity, mass and energy tell space 188 00:09:27.559 --> 00:09:30.559 time how to curve, but that curvature dictates how mass 189 00:09:30.559 --> 00:09:31.399 and energy. 190 00:09:31.159 --> 00:09:33.519 Moves a chicken and egg situation exactly. 191 00:09:33.759 --> 00:09:37.679 And because gravitational waves carry energy, the waves themselves exert gravity. 192 00:09:37.799 --> 00:09:39.679 So you have a situation where the changing shape of 193 00:09:39.679 --> 00:09:42.679 space generates energy, which changes the shape of space, which 194 00:09:42.759 --> 00:09:46.080 generates more energy. It is just a catastrophic feedback loop. 195 00:09:46.159 --> 00:09:47.639 Wow, So how do you even calculate that? 196 00:09:47.759 --> 00:09:51.679 To solve this mathematically, physicists use something called numerical relativity. 197 00:09:52.399 --> 00:09:56.600 They break spacetime down into a massive three dimensional grid, 198 00:09:57.120 --> 00:10:02.159 stepping forward in time in tiny, tiny increments at every 199 00:10:02.200 --> 00:10:05.519 single intersection on that grid. For every fraction of a microsecond, 200 00:10:05.799 --> 00:10:10.399 the supercomputer has to recalculate the entire ten component metric tensor. 201 00:10:10.519 --> 00:10:14.039 That sounds incredibly taxing, and if the grid isn't precise enough, 202 00:10:14.080 --> 00:10:16.600 the math literally blows up, doesn't it. I know that 203 00:10:16.639 --> 00:10:19.360 for decades, physicists couldn't even get the simulations to run 204 00:10:19.399 --> 00:10:21.320 past the first few milliseconds of a merger. 205 00:10:21.399 --> 00:10:24.720 Oh, it was a nightmare for theoretical physicists. The coordinate 206 00:10:24.759 --> 00:10:28.000 systems would just fail, The values would shoot up to infinity, 207 00:10:28.039 --> 00:10:28.960 and the computer. 208 00:10:28.639 --> 00:10:31.879 Would crash right because it just couldn't handle the infinite 209 00:10:31.879 --> 00:10:35.279 feedback loop. It wasn't until two thousand and five I 210 00:10:35.279 --> 00:10:38.159 think that Transpiratory has finally figured out a mathematical trick 211 00:10:38.360 --> 00:10:41.360 to keep the simulation stable through the actual merger. So 212 00:10:41.440 --> 00:10:44.759 we're talking about an incredibly brutal, computationally exhausting method. 213 00:10:45.080 --> 00:10:48.879 It is a tour de force of human computation. You 214 00:10:48.919 --> 00:10:53.960 are tracking the microscopic evolution of spacetime geometry through sheer 215 00:10:54.240 --> 00:10:58.840 brute force determinism. You're mapping every single ripple, every distortion 216 00:10:58.960 --> 00:11:02.159 to see exactly how much mass and spin is radiated away, 217 00:11:02.440 --> 00:11:04.559 just so you can subtract that from the initial total 218 00:11:04.679 --> 00:11:05.399 to find out what. 219 00:11:05.440 --> 00:11:08.000 Is left over, which brings us to the alternate route, 220 00:11:08.399 --> 00:11:10.919 the shortcut that honestly feels like a cheat code. 221 00:11:11.039 --> 00:11:11.679 It really does. 222 00:11:11.919 --> 00:11:16.440 The researchers at Penn State, including bs Sethi, Podcash, Nathan K. 223 00:11:16.559 --> 00:11:20.159 John To McDaniel, and their colleagues, are proposing that we 224 00:11:20.279 --> 00:11:23.200 don't need to track the deterministic geometry of space time 225 00:11:23.360 --> 00:11:27.320 step by step. They argue we can bypass numerical relativity 226 00:11:27.440 --> 00:11:30.600 entirely by using thermodynamics. 227 00:11:29.799 --> 00:11:31.440 Which is a huge lead, right. 228 00:11:31.679 --> 00:11:33.519 But to make that lead, we have to look at 229 00:11:33.600 --> 00:11:36.320 why black holes and thermodynamics are even allowed in the 230 00:11:36.320 --> 00:11:38.480 same room together in the first place, because for a 231 00:11:38.519 --> 00:11:40.240 really long time they absolutely were not. 232 00:11:40.639 --> 00:11:43.840 Historically, black holes were considered thermodynamic dead ends. I mean 233 00:11:43.840 --> 00:11:46.720 that classical laws of general relativity state that nothing can 234 00:11:46.840 --> 00:11:50.080 escape an event horizon, not even light right, And if 235 00:11:50.120 --> 00:11:54.080 nothing can escape, a black hole cannot emit heat. If 236 00:11:54.120 --> 00:11:57.480 an object cannot emit heat, its temperature must be absolute zero. 237 00:11:57.960 --> 00:11:59.919 Okay, that makes sense under classical rule. 238 00:12:00.159 --> 00:12:03.120 But here's the catch. In classical thermodynamics. If you drop 239 00:12:03.159 --> 00:12:05.440 a hot cup of coffee, which has a lot of entropy, 240 00:12:05.519 --> 00:12:08.679 a lot of disordered microscopic states, into a black hole, 241 00:12:09.200 --> 00:12:12.200 that entropy vanishes from the observable universe. 242 00:12:12.279 --> 00:12:14.399 Oh I see, and that violates the second law of 243 00:12:14.440 --> 00:12:15.960 thermodynamics exactly. 244 00:12:16.320 --> 00:12:18.600 The second law states that the total entropy of the 245 00:12:18.679 --> 00:12:20.480 universe must always increase. 246 00:12:21.159 --> 00:12:23.240 Right, Because if you could just throw your entropy into 247 00:12:23.279 --> 00:12:26.279 a black hole and completely erase it, you're decreasing the 248 00:12:26.399 --> 00:12:28.879 entropy of the universe. You are cheating the most fundamental 249 00:12:28.960 --> 00:12:33.039 law of nature. And that paradox that's what led Jacob 250 00:12:33.039 --> 00:12:36.279 Bekenstein and Stephen Hawking to completely rewrite astrophysics in the 251 00:12:36.320 --> 00:12:37.919 nineteen seventies, isn't it it is? 252 00:12:38.039 --> 00:12:40.919 Bekenstein was the first to propose the heresy. Really, he 253 00:12:41.039 --> 00:12:43.600 suggested that black holes must have entropy, and that the 254 00:12:43.720 --> 00:12:46.559 entropy must be proportional to the surface area of the 255 00:12:46.600 --> 00:12:48.879 event horizon, not its volume. 256 00:12:48.679 --> 00:12:50.840 Not the volume, but the surface area yes. 257 00:12:51.200 --> 00:12:53.519 So when you throw the coffee cup in, the black 258 00:12:53.519 --> 00:12:57.559 hole gains mass, its event horizon physically grows, its area increases, 259 00:12:57.960 --> 00:13:01.440 and therefore its entropy increases, satisfying the second law. 260 00:13:01.399 --> 00:13:06.159 Boom paradox solved. But Hawking initially hated that idea, didn't 261 00:13:06.200 --> 00:13:09.480 he because if a black hole has entropy, it must 262 00:13:09.519 --> 00:13:11.279 have a temperature, and if it has a temperature, it 263 00:13:11.320 --> 00:13:14.600 must radiate heat. But we just establish nothing can escape 264 00:13:14.600 --> 00:13:17.759 a black hole. So Hawking actually set out to mathematically 265 00:13:17.840 --> 00:13:19.240 prove Beckenstein wrong. 266 00:13:19.480 --> 00:13:20.039 He did. 267 00:13:20.519 --> 00:13:23.799 Hawking applied quantum field theory to the curved space time 268 00:13:23.919 --> 00:13:27.960 near the event horizon, fully intending to disprove Beckenstein's theory, 269 00:13:28.080 --> 00:13:29.320 but instead he. 270 00:13:29.360 --> 00:13:31.919 Proved him right, which is hilarious and brilliant. 271 00:13:32.000 --> 00:13:34.600 It's now considered one of the greatest theoretical discoveries of 272 00:13:34.639 --> 00:13:37.840 the twentieth century. Hawking discovered that black holes are not 273 00:13:37.960 --> 00:13:39.559 completely black. They glow. 274 00:13:40.039 --> 00:13:42.600 Let's break down the mechanics of that glow because it 275 00:13:42.720 --> 00:13:45.960 is crucial for understanding how the Penn State team applies 276 00:13:45.960 --> 00:13:50.159 thermodynamics to a merger. The glow is Hawking radiation, But 277 00:13:50.240 --> 00:13:53.759 how does empty space near horizon suddenly radiate particles. 278 00:13:54.200 --> 00:13:56.440 We have to look at the vacuum of space through 279 00:13:56.440 --> 00:14:00.320 the lens of quantum mechanics. In quantum field theory, a 280 00:14:00.399 --> 00:14:03.759 vacuum is not truly empty. It is this boiling sea 281 00:14:03.960 --> 00:14:05.600 of quantum fluctuation. 282 00:14:05.200 --> 00:14:06.799 Just psi chaotic massive energy. 283 00:14:07.000 --> 00:14:10.679 Exactly pairs of virtual particles. A particle and its anti 284 00:14:10.720 --> 00:14:15.399 particle are constantly popping into existence, borrowing energy from the universe, 285 00:14:15.480 --> 00:14:18.480 and then instantly annihilating each other to pay the energy back. 286 00:14:19.080 --> 00:14:22.240 This happens everywhere, all the time, in your living room, 287 00:14:22.440 --> 00:14:23.840 in deep space, everywhere. 288 00:14:23.919 --> 00:14:26.559 But when this happens exactly on the razor's edge of 289 00:14:26.559 --> 00:14:29.879 an event horizon, the script changes dramatically. 290 00:14:30.159 --> 00:14:33.200 If a pair of virtual particles pops into existence right 291 00:14:33.240 --> 00:14:36.879 on that boundary, the intense gravitational gradient can pull them 292 00:14:36.879 --> 00:14:39.159 apart before they even have a chance to annihilate. 293 00:14:39.200 --> 00:14:41.440 Wow, so the gravity is stronger than their attraction to 294 00:14:41.480 --> 00:14:41.840 each other. 295 00:14:41.960 --> 00:14:45.360 Yes, one particle falls past the horizon into the black hole. 296 00:14:45.879 --> 00:14:49.080 The other particle, just outside the horizon, is violently propelled 297 00:14:49.080 --> 00:14:51.879 out into the universe. So to an outside observer it 298 00:14:51.919 --> 00:14:54.600 looks exactly as if the black hole just emitted a particle. 299 00:14:54.639 --> 00:14:56.200 It radiated heat I've. 300 00:14:56.039 --> 00:14:58.720 Always struggled with the mass accounting here, though. If the 301 00:14:58.720 --> 00:15:01.399 black hole absorbs one particle and shoots out the other, 302 00:15:01.600 --> 00:15:05.000 shouldn't its mass increase or at least just stay the same. 303 00:15:05.639 --> 00:15:08.600 Why does Hawking radiation cause the black hole to slowly 304 00:15:08.679 --> 00:15:09.799 evaporate over time? 305 00:15:10.120 --> 00:15:13.840 It comes down to energy conservation. The virtual particle pair 306 00:15:14.039 --> 00:15:17.639 was created by borrowing energy from the vacuum. When they 307 00:15:17.639 --> 00:15:21.120 are separated, the particle that escapes becomes a real particle 308 00:15:21.200 --> 00:15:22.320 with positive energy. 309 00:15:22.399 --> 00:15:24.360 Okay, so the universe gains a positive particle. 310 00:15:24.480 --> 00:15:27.840 Right, So for the Universe's energy ledger to balance, the 311 00:15:27.840 --> 00:15:30.840 particle that fell into the black hole must have negative 312 00:15:30.960 --> 00:15:34.080 energy relative to the outside universe. When the black hole 313 00:15:34.159 --> 00:15:37.399 absorbs that negative energy, its total mass decreases. 314 00:15:37.480 --> 00:15:40.600 That is such a brilliant mechanism. The universe balances as 315 00:15:40.639 --> 00:15:43.279 checkbook and the black hole shrinks. And by proving that 316 00:15:43.320 --> 00:15:47.639 black holes have a temperature and slowly evaporate, Hawking fundamentally 317 00:15:47.679 --> 00:15:52.759 linked gravity and thermodynamics. He finalized the Beekenstein Hawking formula, 318 00:15:53.000 --> 00:15:55.919 which mathematically defines the entropy of a black hole. 319 00:15:56.039 --> 00:16:00.000 And that formula is breathtaking. It incorporates the fundamental consts 320 00:16:00.320 --> 00:16:02.840 from almost every major branch of physics. 321 00:16:03.000 --> 00:16:04.639 It's like the ultimate crossover event. 322 00:16:04.759 --> 00:16:07.799 It really is. It includes Newton's constant for gravity, the 323 00:16:07.840 --> 00:16:11.879 speed of light for relativity, Plank's constant for quantum mechanics, 324 00:16:12.240 --> 00:16:16.799 and Boltzmann's constant for thermodynamics. It perfectly weaves them all 325 00:16:16.799 --> 00:16:19.080 together to state that the entropy of a black hole 326 00:16:19.399 --> 00:16:22.320 is exactly a quarter of the area of its event horizon. 327 00:16:22.679 --> 00:16:25.559 But here is the massive problem that the Penn State 328 00:16:25.600 --> 00:16:30.279 researchers had to confront. Hawking's math, as beautiful as it is, 329 00:16:30.759 --> 00:16:35.279 was formulated for static, stationary black holes, a black hole 330 00:16:35.639 --> 00:16:39.200 just sitting out there in the void, slowly glowing. It 331 00:16:39.240 --> 00:16:42.039 was not designed for the apocalyptic chaos of two black 332 00:16:42.080 --> 00:16:44.840 holes colliding at half the speed of light. Not at all. 333 00:16:44.960 --> 00:16:47.879 Taking the thermodynamics of a quiet black hole and trying 334 00:16:47.879 --> 00:16:50.399 to apply to a violent merger, it seems like trying 335 00:16:50.399 --> 00:16:53.039 to use a thermometer to measure a bomb going off. 336 00:16:53.159 --> 00:16:56.240 That's a very accurate comparison. It is a massive leap. 337 00:16:56.519 --> 00:16:59.480 The Penn State team, led by researchers like Safi Prickash 338 00:16:59.480 --> 00:17:02.559 and by Shock Prosad, they had to prove that thermodynamic 339 00:17:02.639 --> 00:17:05.039 rules don't just apply it to quiet black holes, but 340 00:17:05.119 --> 00:17:08.559 to dynamic, rapidly evolving space times. 341 00:17:08.240 --> 00:17:11.480 Space times that are literally ripping themselves apart exactly. 342 00:17:11.839 --> 00:17:14.640 They hypothesize that even in the midst of a violent merger, 343 00:17:15.079 --> 00:17:19.559 the underlying principles of thermodynamics are still driving the bus. Specifically, 344 00:17:19.599 --> 00:17:23.519 they proposed the maximum entropy conjecture for black hole mergers. 345 00:17:23.839 --> 00:17:26.680 Okay, we need to completely define what entropy means in 346 00:17:26.720 --> 00:17:29.480 the context of a black hole here, because the standard 347 00:17:29.480 --> 00:17:33.200 analogy everyone learns in high school physics is the messy room. Right. Ye, 348 00:17:33.400 --> 00:17:36.000 A tidy room has low entropy. A messy room has 349 00:17:36.079 --> 00:17:38.559 high entropy, just because there are more ways for things 350 00:17:38.640 --> 00:17:39.559 to be messy than. 351 00:17:39.440 --> 00:17:40.839 Tidy, the classic example. 352 00:17:40.960 --> 00:17:43.000 But a black hole isn't a room full of socks 353 00:17:43.039 --> 00:17:44.680 and books, it's empty space. 354 00:17:45.640 --> 00:17:49.279 How do you measure the messiness of a completely featureless void. 355 00:17:49.839 --> 00:17:52.480 Well, the messy room analogy is helpful for basic intuition, 356 00:17:52.880 --> 00:17:55.160 but to really understand this research, we have to look 357 00:17:55.200 --> 00:17:58.400 at entropy in terms of statistical mechanics. Entropy is not 358 00:17:58.440 --> 00:18:03.000 just messiness decisse measure of microstates mapping to a macrostate. 359 00:18:03.160 --> 00:18:06.400 Microstates and macrostates break that down for me, think of 360 00:18:06.400 --> 00:18:10.880 a digital photograph on your computer screen. The image you see, 361 00:18:11.160 --> 00:18:13.000 let's say it's a picture of an apple, that is 362 00:18:13.000 --> 00:18:18.160 the macrostate, the specific arrangement of millions of individual red, green, 363 00:18:18.200 --> 00:18:20.960 and blue pixels that make up that image. Those are 364 00:18:21.000 --> 00:18:21.759 the microstates. 365 00:18:21.759 --> 00:18:24.000 Okay, so if I change the color of one single 366 00:18:24.039 --> 00:18:26.799 pixel hidden in the shadow of the apple, the image 367 00:18:26.960 --> 00:18:29.440 still looks exactly like an apple. To make it's a 368 00:18:29.440 --> 00:18:32.720 different microstate, but the exact same macrostate exactly. 369 00:18:32.920 --> 00:18:36.119 Now apply that to a gas in a balloon. The 370 00:18:36.240 --> 00:18:40.319 overall temperature, pressure, and volume of the gas those make 371 00:18:40.400 --> 00:18:44.160 up the macrostate. The precise position and velocity of every 372 00:18:44.240 --> 00:18:48.279 single microscopic gas molecule bouncing around inside the balloon are 373 00:18:48.319 --> 00:18:49.000 the microstates. 374 00:18:49.039 --> 00:18:50.960 There's a near infinite number of this, right. 375 00:18:50.920 --> 00:18:53.319 There are billions of different ways those molecules could be 376 00:18:53.359 --> 00:18:55.720 bouncing around that would all result in the exact same 377 00:18:55.759 --> 00:19:00.319 temperature and pressure. Therefore, the gas has high entropy many 378 00:19:00.400 --> 00:19:02.759 micro states correspond to its single macro state. 379 00:19:02.960 --> 00:19:06.160 So how does this map onto a black hole? Because 380 00:19:06.200 --> 00:19:08.720 the no hair theorem says the macrostate of a black 381 00:19:08.720 --> 00:19:12.720 hole is completely defined by just mass and spin. But 382 00:19:12.839 --> 00:19:15.160 what are the hidden pixels? What are the micro states 383 00:19:15.200 --> 00:19:15.880 of a black hole? 384 00:19:16.119 --> 00:19:18.720 That is one of the deepest mysteries in theoretical physics 385 00:19:18.799 --> 00:19:21.799 right now. It's heavily researched in string theory and loop 386 00:19:21.920 --> 00:19:25.359 quantum gravity. We don't have a fully verified quantum theory 387 00:19:25.359 --> 00:19:27.960 of gravity yet, so we don't know exactly what the 388 00:19:28.000 --> 00:19:30.839 microscopic building blocks of a black hole actually are. 389 00:19:31.160 --> 00:19:32.880 So we're flying blind on the micro. 390 00:19:32.720 --> 00:19:36.920 Level we are, but the Beckenstein Hawking entropy formula guarantees 391 00:19:37.000 --> 00:19:39.839 that they exist. Even if we can't see the individual 392 00:19:39.880 --> 00:19:42.559 pixels of the black hole, we know they are there, 393 00:19:42.960 --> 00:19:45.640 and we know exactly how many there are based purely 394 00:19:45.680 --> 00:19:47.759 on the surface area of the event horizon. 395 00:19:47.960 --> 00:19:51.000 Wow. And this allows the Penn state researchers to treat 396 00:19:51.039 --> 00:19:56.279 the black holes exactly like interacting gases. Physicist Eugenio Bianki 397 00:19:56.359 --> 00:19:59.279 brought up this specific gas analogy. He said, if you 398 00:19:59.319 --> 00:20:01.480 take a box of hot oxygen and a box of 399 00:20:01.519 --> 00:20:04.319 cold nitrogen and you open a valve between them, the 400 00:20:04.359 --> 00:20:07.880 gases mix. To figure out the final temperature and pressure 401 00:20:08.200 --> 00:20:12.119