The black hole information paradox has been receiving some attention lately. You may be able to find the same content in another format, or you may be able to find more information, at their web site. The Black Hole Information Paradox Is Unsolvable . So far the calculations presumed the AdS/CFT duality — the snow globe world — which is an important test case but ultimately somewhat contrived. Two of our best theories give us two different—and seemingly contradictory—pictures of how … The story goes like this, according to Quanta Magazine article “Stephen Hawking’s Black Hole Paradox Keeps Physicists Puzzled“: In 1991, Hawking and Kip Thorne bet John Preskill that information that falls into a black hole gets destroyed and can never be retrieved. So must the black hole. The known laws of physics should still apply. He has suggested that there’s a way that new Hawking radiation could be imprinted by … Let's nerd out together. We don't have a resolution to the black hole information paradox, but that hasn't stopped starry-eyed theorists from dreaming up a host of potential solutions over the decades. Somehow, by measuring it, you should be able to learn what fell into the black hole. But assuming that the new calculations stand up to scrutiny, do they in fact close the door on the black hole information paradox? Amongst the conundrums which arise when quantum mechanics and general relativity come to combine in an area where spacetime slowly comes to break down is a problem known as the black hole information paradox. By showing that the entanglement entropy tracked the Page curve, the team was able to confirm that black holes release information. If the weights change, the particle can abruptly lurch from one path to another, undergoing a transition that would be impossible in old-fashioned physics. The “Black Hole Information Paradox” The paradox arose after Hawking showed, in 1974-1975, that black holes surrounded by quantum fields actually will radiate particles (“Hawking radiation”) and shrink in size (Figure 4), eventually evaporating completely. “Information, they now say with confidence, does escape a black hole. Known as the path integral, it is the mathematical expression of a core quantum mechanical principle: Anything that can happen does happen. “In some way or other, space-time itself seems to fall apart at a black hole, implying that space-time is not the root level of reality, but an emergent structure from something deeper,” George Musser explains at Quanta. That would produce the downward slope that Page predicted — the first time any calculation had done that. They found that the symmetries of relativity have even more extensive effects than commonly supposed, which may give space-time the hall-of-mirrors quality seen in the black hole analyses. The authors dubbed the inner core of radiation the “island” and called its existence “surprising.” What does it mean for particles to be in the black hole, but not of the black hole? But almost everyone appears to agree on one thing. Scientists say they’re close to proving a mindboggling problem related to black holes—one that dates back to Stephen Hawking’s theories from 50 years … She has argued that wormholes need to be expressly forbidden if the integral is to give sensible results. But suppose for some reason you can’t do that. The outgoing particle escapes and is emitted as a quantum of Hawking radiation; the infalling particle is swallowed by the black hole. But eventually it became the deciding factor for entropy, leading to a drop. So do we. The Information Paradox. But when researchers used these quantum extremal surfaces to study an evaporating black hole, a strange thing happened. Theorists have been intensely debating how literally to take all these wormholes. This radiation allows black holes to lose mass and, eventually, to entirely evaporate. Gravity does not reach out across space instantly. A quantum extremal surface abruptly materialized just inside the horizon of the black hole. In doing so, he transformed a debate into a calculation. Sabine Hossenfelder Backreaction November 19, 2020 Columbia University via AP. Consider a universe encased in a boundary like a snow globe. “Hats off to them, since those calculations are highly nontrivial,” said Daniele Oriti of the Ludwig Maximilian University of Munich. When researchers set out to analyze how black holes evaporate in AdS/CFT, they first had to overcome a slight problem: In AdS/CFT, black holes do not, in fact, evaporate. Page, a physicist at the University of Alberta in Canada, also used the break to think about how paradoxical black holes really are. The research, posted in May 2019, showed all this using new theoretical tools that quantify entanglement in a geometric way. Then, in papers published last fall, researchers cut the tether to string theory altogether. But even their considerable genius struggled with how to execute the gravitational path integral, and physicists set it aside in favor of other approaches to quantum gravity. Now, scientists have found a special case of black hole that casts the rest into question. To understand this arguably groundbreaking news about black holes, you must first understand what is known as the “black hole information paradox.” This paradox stems from calculations suggesting that any physical information that falls into a black hole permanently disappears, which in itself violates a core concept … In August 2019 Almheiri and another set of colleagues took the next step and turned their attention to the radiation. They did the analysis in stages. Called the black hole information paradox, this prospect follows from Hawking’s landmark 1974 discovery about black holes — regions of inescapable gravity, where space-time curves steeply toward a central point known as the singularity. It would be impossible to recover whatever fell in. For Hawking, that meant all topologies. “We now can compute the Page curve, and I don’t know why,” said Raphael Bousso at Berkeley. The shift from one geometry to the other is impossible in classical general relativity — it is an inherently quantum process. The black hole information loss paradox is a mystery along similarly bizarre lines. It has to propagate from one place to another at finite speed, like any other interaction in nature. Nothing about the radiation reveals whether it came from an astronaut or a lump of lead. The wormholes are so deeply buried in the equations that their connection to reality seems tenuous, yet they do have tangible consequences. Any further progress would have to treat gravity, too, as quantum. If very old black holes end up slackening in a way, that tells scientists something about the way they work in the first place. Trick though it is, it has real physics in it. It competes for influence with the regular geometry of a single black hole surrounded by a mist of Hawking radiation. The path integral works so well for particle motion that theorists in the ’50s proposed it as a quantum theory of gravity. In the black hole calculations, the island and radiation are one system seen in two places, which amounts to a failure of the concept of “place.” “We’ve always known that some kind of nonlocal effects have to be involved in gravity, and this is one of them,” Mahajan said. Still, as sophisticated as the analysis is, it doesn’t yet say how the information makes its getaway. Suddenly that changed. The black hole was not a big black ball but a short line segment. If you jump into one, you will not be gone for good. But how? How we test gear. The work began in earnest in October 2018, when Ahmed Almheiri of the Institute for Advanced Study laid out a procedure for studying how black holes evaporate. The data without the password is gibberish. With that, the problem got much more acute. Second, the extremal surface split the universe in two. The black hole information paradox has been receiving some attention lately. “The hole transforms from a hermit kingdom to a vigorously open system,” Musser explains, in a sentence that no one can ever match. This is analogous to not knowing the full matrix for the black hole, yet still evaluating its entropy. But some feel uneasy about the tottering pile of idealizations used in the analysis, such as the restriction of the universe to less than three spatial dimensions. Good news: If you fall into a black hole, you'll (probably) come back out. At the start of the whole process, the entanglement entropy is zero, since the black hole has not yet emitted any radiation to be entangled with. The result is a new saddle point containing multiple black holes linked by space-time wormholes. The work appears to resolve a paradox that Stephen Hawking first described five decades ago. Radiation fills the confined volume like steam in a pressure cooker, and whatever the hole emits it eventually reabsorbs. “The system will reach a steady state,” said Jorge Varelas da Rocha, a theoretical physicist at the University Institute of Lisbon. “Most general relativists I talked to agreed with Hawking,” said Page. The bubble naturally assumes a shape that minimizes its surface area. Scientists say they’re close to proving a mindboggling problem related to black holes—one that dates back to Stephen Hawking’s theories from 50 years ago. This is a peculiar role reversal for gravity. ), Get Quanta Magazine delivered to your inbox, Ahmed Almheiri gives a lecture on black holes and quantum information at the Institute for Advanced Study in 2018.Â, Andrea Kane, Institute for Advanced Study. Are today’s physicists falling into the same trap? The Black Hole Information Paradox Is Just About Solved. Yet even though Page spelled out what physicists had to do, it took theorists nearly three decades to figure out how. But in terms of making sense of black holes, this is at most the end of the beginning. In supposing that replicas can be connected gravitationally, the authors go beyond past invocations of the maneuver. Particle by particle, the information needed to reconstitute your body will reemerge. Skepticism is warranted if for no other reason than because the recent work is complicated and raw. To suss that out, we can make analogies to a variety of other things. Video: David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics. The theory of black holes no longer contains a logical contradiction that makes it paradoxical. As the hole shrank, so did the quantum extremal surface and, with it, the entanglement entropy. Filming by Petr Stepanek. Early in the evaporation process, they found, as expected, that the entanglement entropy of the boundary rose. The puzzle wasn’t just what happens at the end of the black hole’s life, but also what leads up to it. This activates some of the latent topologies that the gravitational path integral includes. “I got curious how the radiation entropy would change in between,” Page said. Given the uncertainties of the calculation, some are unconvinced that a solution is available within semiclassical theory. They noticed that entropy doesn’t require knowledge of the full matrix. “We never really knew how to define exactly what it is — and guess what, we still don’t,” said John Preskill of the California Institute of Technology. Does the entanglement entropy follow an inverted V or not? Physicists have spent the best part of four decades grappling with the “information paradox”, but now a group of researchers from the UK thinks it … This is much earlier than physicists assumed. The researchers plopped a black hole at the center of the bulk space, began bleeding off radiation, and watched what happened. But in quantum gravity, other shapes, including much curvier ones, are latent, and they can make an appearance under the right circumstances. Put simply, a black hole rots from the outside in. So it would seem as though the information paradox has been overcome. Particle by particle, the information needed to reconstitute your body will … At first glance, this is very surprising. Third, the position of the quantum extremal surface was highly significant. And because of that, the debate over what it all means rages on, with this incredible finding as just one more data point. Physicists are now able to pinpoint which part of the bulk corresponds to which part of the boundary, and which properties of the bulk correspond to which properties of the boundary. To astronauts who ask whether they can get out of a black hole, physicists can answer, “Sure!” But if the astronauts ask how to do it, the disquieting reply will be: “No clue.”, Get highlights of the most important news delivered to your email inbox, Quanta Magazine moderates comments to facilitate an informed, substantive, civil conversation. According to Einstein’s general theory of relativity, the gravity of a black hole is so intense that nothing can escape it. As part of the work, they discovered that the universe undergoes a baffling rearrangement. But it makes up for that with vibrant quantum physics, and all in all it’s exactly as complex as the interior. Had the calculation involved deep features of quantum gravity rather than a light dusting, it might have been even harder to pull off, but once that was accomplished, it would have illuminated those depths. Even though you still don’t know the individual probabilities, you can make a basic judgment about randomness. Not only does information spill out, anything new that falls in is regurgitated almost immediately. It turns out stuff we throw into certain black holes, improbably, seems to come back out. Now physicists just had to calculate the entanglement entropy. Muted at first, these effects come to dominate when the black hole gets to be extremely old. Maybe, thought Page, information can come out of the black hole in a similarly encrypted form. That’s a problem because, at some point, the black hole emits its last ounce and ceases to be. By Caroline Delbert. “Physicists are not always so good at words,” said Andrew Strominger of Harvard University. quantum entanglement can be thought of as a wormhole, stringy effects prevent black holes from forming in the first place. The black hole information paradox has puzzled scientists for centuries and it has triggered endless debates on what actually happens once you enter a black hole. (In April 2020, Koji Hashimoto, Norihiro Iizuka and Yoshinori Matsuo of Osaka University analyzed black holes in a more realistic flat geometry and confirmed that the findings still hold.). Two of our best theories give us two different—and seemingly contradictory—pictures of how these objects work. Space-time might knot itself into doughnut- or pretzel-like shapes. These black holes are “extremely old,” and whatever mechanism has previously confined mass inside them has not just stopped working but even reversed. Over time, the entanglement entropy should follow a curve shaped like an inverted V. Page calculated that this reversal would have to occur roughly halfway through the process, at a moment now known as the Page time. Hawking recently proposed a new idea to resolve the black hole information paradox. But together they unlock the information. But they also might reveal the true nature of the universe to us. Though they can be hard to imagine, black holes are not a simple matter. This is essentially the 40-year-old unsolved puzzle called the black hole information paradox. Now when it comes to the information paradox, when the black hole evaporates it looses energy, so basically information from the black hole is not lost, it just turns into energy which then is released to space, so there is no information lost. Indeed, they thought the paradox was their fulcrum for prying out that more detailed theory. To many, that was the main lesson of the AdS/CFT duality. But they also might reveal the true nature of the universe to us. The boundary, too, is a kind of universe. The bulk in this AdS/CFT universe had just a single dimension of space, for example. The previous wave of excitement over the path integral in the ’80s, driven by Hawking’s work, fizzled out in part because theorists were unnerved by the accumulation of approximations. So they worry they may have solved this one problem without achieving the broader closure they sought. The “Black Hole Information Paradox” The paradox arose after Hawking showed, in 1974-1975, that black holes surrounded by quantum fields actually will radiate particles (“Hawking radiation”) and shrink in size (Figure 4), eventually evaporating completely. Stephen Hawking’s Black Hole Information Paradox: An Animated Explanation of the Greatest Unsolved Challenge to Our Understanding of Reality Reconciling the science of the very large with the science of the very small, with a sidewise possibility that everything we experience as reality is a holographic … A very fundamental law of physics says that quantum information can never disappear. Called the black hole information paradox, this prospect follows from Hawking’s landmark 1974 discovery about black holes … So-called space-time wormholes are little universes that bud off our own and reunite with it sometime later. They have not flown outward, but simply been reassigned. The extra connectivity creates tunnels, or “wormholes,” between otherwise far-flung places and moments. Hawking had shown that black holes are not truly black. Abstractions blog black hole information paradox black holes physics theoretical physics All topics Like cosmic hard drives, black holes pack troves of data into compact spaces. The wormholes and the single black hole are inversely weighted by, basically, how much entanglement entropy they have. The extra geometric configuration and the transition process that accesses it are the two main discoveries of the analysis. The new calculations say much the same thing, but without committing to the duality or to string theory. To us, space-time appears to have a single well-defined shape — near Earth, it is curved just enough that objects tend to orbit the center of our planet, for example. And that led to a remarkable twist in the story. I put in a Wednesday video because last week I came across a particularly bombastically … I put in a Wednesday video because last week I came across a particularly bombastically nonsensical claim that I want to debunk for you. Within the simulation, the entanglement translates into a geometric link between the simulated black hole and the original. … And black holes were holes that were black. Put simply, the two are connected by a wormhole. But to understand how and why has come down to a group of extraordinary experts trading complex mathematical arguments. In November 2019, two teams of physicists — known as the West Coast and East Coast groups for their geographical affiliations — posted their work showing that this trick allows them to reproduce the Page curve. By that I mean black holes would compress matter and energy into an infinitely dense singularity, and didn’t create a seemingly insurmountable information paradox. They found that the black hole and its emitted radiation both follow the same Page curve, so that information must be transferred from one to the other. That’s why the black hole information paradox is such a puzzle. The next step, after applying the path integral to the black hole and its radiation, was to calculate the entanglement entropy. For starters, what are “all” possible shapes? First, the sudden shift signaled the onset of new physics not covered by Hawking’s calculation. Tom Hartman (right) discusses replica wormholes with his co-author Amirhossein Tajdini, who is now at U.C. Every object in the universe is composed of particles with unique quantum properties and even if an object is destroyed, its quantum information is never permanently … But over the decades it has dawned on physicists that the symmetries on which relativity is based create a new breed of nonlocal effects. By calculating where the quantum extremal surface lies, researchers obtain two important pieces of information. Second, the area of the surface is proportional to part of the entanglement entropy between those two portions of the boundary. The Black Hole Information Paradox Is Just About Solved. But in the 1990’s it was shown that the particle which enters the black hole actually becomes entangled with the EH, so information is preserved (for by knowing state of EH, I can determine the state of the trapped particle) (Ouellette, Polchinski 41, Hossenfelder "Head"). But the new calculations, though inspired by string theory, stand on their own, with nary a string in sight. Paradoxical scenario. Wormholes, the holographic principle, emergent space-time, quantum entanglement, quantum computers: Nearly every concept in fundamental physics these days makes an appearance, making the subject both captivating and confounding. The more sophisticated understanding of black holes developed by Stephen Hawking and his colleagues in the 1970s did not question this principle. A paradox about two travelers, one of which crosses the event horizon of a black hole, while the other watches him and waits until the black hole completely evaporates. If it doesn’t, the black hole destroys or bottles up information, and general relativists can help themselves to the first doughnut at faculty meetings.