Why Black Holes Break The Universe

- Tonight, my friends, we stand on the brink of an unprecedented feat in space exploration. I will travel where no man has dared to go. - In the

black

hole? - Wow, that's crazy! (moans) (soft, dramatic music) - Black

holes

are the abysses of the

universe

. They are not actually a thing, but rather a region of space-time wrapped in an embrace so tight that even light is trapped forever. And it is this nihilism that poses a major problem for theoretical physics, one that could unravel our very understanding of the

universe

. How does a

black

hole trap light?

If I throw a ball into the air, it falls back to Earth due to gravity following a curve, or at least it looks like a curve to me. But in reality the ball follows the shortest line, also called the geodesic, and it is space-time that is really curved. It is the mass of the Earth that curves spacetime, and if we made it heavier, we would increase that curvature and therefore the ball would appear to follow a tighter curve back to the ground. Interestingly, although we often talk about gravity as a force, in this picture Einstein painted for us there is no force, only curved space-time.

Now, if I throw the ball hard enough, it will travel higher and therefore take longer to come back down. And if he threw it really hard, he could give it enough speed to completely escape Earth's gravity and fly into deep space. The minimum velocity needed to achieve this is known as the escape velocity and can classically be solved by equating the ball's kinetic energy to its gravitational potential energy. In 1783, John Mitchell did exactly that with a ray of light. He predicted that there should exist a certain mass, which is so large that the escape velocity is equal to the speed of light.

Mitchell called these dark stars, but no one took them very seriously until GR came along. That is Einstein's theory of general relativity. While serving for Germany during World War I, Karl Schwarzschild found a solution to GR, something Einstein did not expect to be achieved so easily, but his solution investigated the possibility that these dark stars existed, something considered implausible by Einstein and much others. . In 1971, the astronomical discovery of Cygnus Of course, since then we have amassed a wealth of observational support for their existence, from binary X-ray systems to tidal perturbation events, from gravitational wave astronomy to direct imaging.

These enigmas that Einstein so disliked are now understood as a critical component of the universe, for example, with a supermassive black hole that appears to be located at the center of every galaxy. Before we explore further, let's take a quick look at our sponsor. Finding good safety videos for esoteric topics like black

holes

and quantum theory and all the other things we're getting into here, isn't easy. If you're a creator like me, then today's video sponsor, Storyblocks, is an invaluable tool in the editing room. Storyblocks offers unlimited downloads of diverse, high-quality media for a single subscription cost, with no additional charges for individual clips.

We create B-roll clips from many places, such as NASA, ESO and sci-fi movies, but there are often missing pieces. And believe me, this is the most time-consuming and painful part of editing: finding the perfect clip. Storyblocks not only makes this much easier, but it also has templates for After Effects, Premiere Pro, and DaVinci, as well as royalty-free music, sound effects, and more. To get started with unlimited stock media downloads at one flat price, visit storyblocks.com/coolworlds. That small action also helps us. Again, that's storyblocks.com/coolworlds. Now let's go back to the video. Black holes are intoxicating because of their purpose, an absolute purpose.

Everything that falls can never come out, but that also poses a problem. Apparently they destroy information for

break

fast. In quantum theory, a basic precept is so-called unitarity, which essentially states that all processes are, in principle, reversible. For example, if I throw a book into a fire, it will quickly burn, smolder, and dissipate into fine particles of smoke and ash. In principle, unitarity dictates that we should be able to gather all those particles, reconstruct them, and reconstruct every word on every page. Of course, in practice it would never be possible to achieve this, but in theory it is possible.

This unitarity principle is often presented as a law of conservation of information similar to the conservation laws we have for energy and momentum. But it's actually better to think of it as a statement of reversibility. From some initial state, we should be able to calculate the final state and vice versa; From the final state, we can go back and calculate the initial state, therefore reversible. Black holes are the cosmic wrecking ball of the unitarity principle. If I throw a book into the black hole, those words, that information, become trapped within a region of space-time from which nothing can escape.

It's true that the mass of the book will cause a slight ripple in space-time as it falls, like the black hole merger events recently observed by LIGO. But it turns out that those gravitational waves don't take away enough information to reconstruct the words on the page. Now, as that book falls further into that dark abyss far beyond the event horizon, it will eventually reach the singularity. We generally think of the singularity as a location in space, the center of a black hole. But in reality, the warping of space-time is so severe here that space and time exchange roles.

And really, the singularity is best described as a future moment in time, a point in our future from which we can't help but reach more than we can stop tomorrow from happening. What happens when the singularity is reached is anyone's guess, general relativity explodes to infinity at this point. This uncertainty gave us hope that the apparent destruction of information was not real. Maybe the information just gets trapped down there, near the singularity or something. At the end of the day, it didn't really matter because black holes seemed to live forever and therefore we never had to deal with this loss of information.

This convenient excuse fell apart when Stephen Hawking came along and showed that black holes do not live forever as initially assumed. Quantum theory requires that they evaporate slowly. The event horizon is just a region of empty space, and like all empty space, the Heisenberg Uncertainty Principle allows for the spontaneous creation of pairs of particles that come in and out of existence. Typically, these particles form and merge at very short intervals, appearing and disappearing, so quickly that the universe doesn't have a chance to notice and complain. But if this pair of particles appears on both sides of the event horizon, one can fall and the other escape.

From the outside, the black hole appears to radiate energy, meaning that if e equals mc squared, it is losing mass. This Hawking radiation means that black holes are losing mass gradually, very, very gradually, and therefore will eventually die. It is a disturbing thought. Not only do stars end up dying, but even black holes someday die. So the fact that black holes die means we can't ignore the information they devoured. According to the principle of unitarity, we expect reversibility, so you should be able to collect all that Hawking radiation like smoke and ashes from the fire and reconstruct the book.

But Hawking radiation does not comply, which can be understood in two ways. First, according to general relativity, a black hole can be completely described with just three numbers: its mass, its spin, and its charge. It has no surface features or texture, and we call this the hairless theorem. As a result, the Hawking radiation they emit can be thought of as purely thermal radiation, heat, and in fact the temperature of that heat is completely governed by the mass of the black hole. So if we collected all the Hawking radiation, we could reconstruct the mass of everything that fell into the black hole over time, but we couldn't reconstruct the arrangement of the particles entering that mass.

We couldn't reconstruct the book. The second way to understand this is through quantum entanglement. When a pair of particles appear on the horizon, they are always entangled. This means that they are not described by bidirectional functions, but by a single joint function, which describes the superposition of their states. So, for example, this wave function might say that the sum of the spins of these two particles is zero, but it doesn't tell us which one is up or which one is down. When we measure one of these two particles, the entanglement is broken and this measured particle is forced to choose one of those two states, which instantly causes the other particle to choose the opposite state.

In this way, the ledger remains a balance. We didn't accidentally end up with two positive spins by mistake. By the way, if you're wondering, no, you can't use this for faster than light communication, check out our video above to explain why. Now, for Hawking radiation, this entanglement poses a barrier to getting information out of the black hole. Let's say I threw the XY information into a black hole. For this information to escape, we can imagine that a Hawking radiation particle escapes at some later time and takes the second particle emitted. carry Y and not X? That implies that it somehow knows that X has already been broadcast.

So to keep track of the entire book of emitted information, we need these emitted particles to be entangled with each other. Well, but therein lies the problem, because let's remember that those Hawking radiation particles are already entangled with their negative energy companion that fell into the black hole. And tangles, like lobsters, are strictly monogamous. There are no lovers or swinger parties here. They can't get involved polygamous. So this means we have a paradox. Now, whenever we have a paradox, we can usually solve it by eliminating one of the assumptions on which the paradox is based. So, for example, with the famous Fermi paradox, which is where are all the aliens, we can solve that by trivially eliminating the assumption that aliens exist.

Paradox resolved. - No! No! (broken glass) - So what are the assumptions here? Well, there are three basic ingredients, the principle of unitarity, which we already know, and in addition to that, we have the principle of equivalence and locality. The equivalence principle is Einstein's happiest thought that if someone fell from a roof he would not feel his own weight as if gravity did not exist. A consequence of this is that when someone passes the event horizon of a black hole, they wouldn't actually experience anything different. They would not notice any demarcation. That means that outside the black hole we only have empty space.

And similarly, on the horizon we also have empty space, hence Hawking radiation can occur there. The third preset is locality, which is the most complicated to explain, but essentially says that if you drop a stone in a pond, the sound, splash, and resulting wave do not occur everywhere at once, but rather located in a specific place. spot. It is quite difficult to imagine classical physics without locality. And so you can see that these three precepts are fundamental to modern physics, and it would be painful to give up any of them. Then what is? Well, we don't know, but certainly many physicists have come up with many different ideas.

For example, in a famous bet by Hawking and Kip Thorne against John Preskill, they claimed that information that falls into the black hole is irretrievably lost to the universe, although it must be said that Hawking later changed his mind on the matter and admitted the bet. Roger Penrose is also in this camp. And in fact, his conformal cyclic cosmology model, which is a kind of cyclic universe scenario, depends critically on the condition that information is actually lost inside black holes. But today, most of the community believes that unitarity is conserved and that information somehow leaves the black hole, which means we have to update our theories about how black holes work.

There are many ideas out there. There are several variations of information being simply dumped somewhere else, and this could be a baby universe inside the black hole, episodes where the black hole is reversed into a white hole that spits out information, or the black hole is actually a wormhole stops somewhere else. Recently, the idea has been suggested thatThere are many micro wormholes. Perhaps the falling particle enters a small wormhole within the event horizon that drags it back, and that is why we see Hawking radiation. Zooming out, it has also been suggested that information is lost in our universe, but at the multiverse level, information is still preserved.

Personally, anything involving multiverses feels like any media, it's like saying aliens did it. And anything involving wormholes runs the risk of violating causality, which Hawking said was sacred, but Hawking accepted the bet, remember. So what convinced him that unity could be preserved? Oddly enough, one path to resolution could come from holograms. - What about the droid attack on the Wookiees? - In 1993, Leonard Susskind suggested the notion of black hole complementarity. Someone who falls into the black hole appears to carry their information beyond the horizon and eventually reach the singularity itself. But someone observing from the outside of the black hole would not see this because of the extreme time dilation down here, they would see that the astronaut actually appears to slow down in time as he approaches the horizon and eventually even appears to freeze there.

They wouldn't actually cross the threshold. Furthermore, the light from it is redshifted and warped around the black hole. From the outside, the falling person appears to be spread on the horizon, forming a thin quantum layer. Over time, its information is re-radiated from this thin layer into space as Hawking radiation, and thus the information is preserved. But this image seems to violate and contradict the astronaut's own experience. Susskind suggested that both perspectives are correct and although they contradict each other, they can never come together to notice the discrepancy and therefore the universe is really okay with us.

This creates the strange idea that information is trapped there, floating in this incredibly thin layer just above the surface of the event horizon. But a surface is a 2D geometry and we normally think of black holes as 3D phenomena. Surely a 3D object contains much more information than a 2D surface. Turns out not. In fact, it has now been mathematically proven that the information content of a black hole can always be completely described by its 2D surface alone. In fact, this has now been generalized to basically everything. All 3D volumes must follow this rule. They can never contain more information than their 2D surfaces can contain.

What's more, if you try, you will end up creating a black hole, which, of course, also fulfills this rule. This is a holographic principle according to which all 3D phenomena can be reduced to a 2D representation. We are all holograms, empty projections, just ghostly shells, nothing more. This equivalence, formally known as anti-de Sitter correspondence/conformal field theory, is a surprising result, but it doesn't actually prove that we are all true holograms, just that it is an explanation that is fully compatible with everything we know about holograms. universe. However, it was enough to convince Hawking to accept the bet.

The principle of unitarity seems to survive. But instead we sacrificed one of those other three key precepts, locality, because now what originally appeared to be distinct 3D events have, in fact, all collapsed onto a 2D surface. But perhaps Hawking was premature in giving up the bet, as Kip Thorne, who refused to give in, thought, because despite the progress made, questions remain here. Recall that Hawking radiation comes from pairs of particles produced in the vacuum near the horizon and are therefore monogamously entangled. And remember also that information leakage requires Hawing radiation particles to become entangled with each other at different times.

So we still have an apparent contradiction that requires solution, and as always, the best way to resolve any paradox is to let go of one of its assumptions. What if Hawking radiation particles did not arise from an empty void, but from something? In that case, the sum of two entangled states does not have to be zero, like spin up, spin down. Instead, they could add up to something because they didn't come from nothing, they came from something. In this way, information can leave the black hole while preserving the entanglement rules. The implication is disturbing, however, that at the event horizon there must exist a thin burning layer known as a firewall, which incinerates anything that tries to fall into the black hole.

If this idea bothers you, it should. Many physicists don't like it. After all, this violates the equivalence principle: being incinerated in the event horizon is not Einstein's happiest thought, and that is why many physicists are still looking for some other explanation. Those baby universes don't sound so unappealing anymore, do they? A deeper question in all of this is that yes, we can find many possible explanations to resolve the information paradox, but how do we prove them? Obviously, flying into a black hole would help, but you would discover the answer and never be able to share it.

You know, it would be incredibly cruel if the universe insisted that this was the only way it would allow us to discover its secrets. The definitive deal with the devil. - The equation could not reconcile relativity with quantum mechanics, more, more is needed. - More than? - More data, you need to see the inside of a black hole. - In principle, studying Hawking radiation would help, since we can measure its entropy, for example, but Hawing radiation is so pitiful that there is really no hope of measuring it by observation. To do this we would have to build a micro black hole in the laboratory, and those energy scales are still far beyond our capabilities, so it is very possible that this puzzle will be with us for a long time, a puzzle about which we still know nothing.

We can imagine many permissible mathematical solutions, but, frustratingly, we cannot prove any of them. But working on this is still valuable in size, as the holographic principle is changing the way we approach fundamental physics and providing new mathematical tools to continue moving forward. Indeed, studying black holes may be our best hope for a unified theory of quantum gravity, the secret sauce for the ultimate theory of everything. Who would have thought that studying something so dark could reveal so much? So until next time, stay thoughtful and curious. (upbeat electronic music) Hello, thank you all very much for watching this video.

I hope you enjoyed it. Be sure to hit the like and subscribe buttons. If you want to support my research team, Cools Worlds Lab, you can use the link above and below, I sincerely appreciate it, and if you haven't seen it yet, we have a podcast, just go to Cools World Podcast on YouTube. Again, the link is below and check it out too. Thanks again for watching.