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  • richardmitnick 12:22 pm on December 17, 2018 Permalink | Reply
    Tags: , Black holes expand by increasing in complexity inwardly – a feature we just don't see connected while watching from afar, Leonard Susskind, Why Don't Black Holes Swallow All of Space? This Explanation Is Blowing Our Minds   

    From Science Alert: “Why Don’t Black Holes Swallow All of Space? This Explanation Is Blowing Our Minds” 

    ScienceAlert

    From Science Alert

    16 DEC 2018
    MIKE MCRAE

    1
    (GM Stock Films/istock)

    Black holes are great at sucking up matter. So great, in fact, that not even light can escape their grasp (hence the name).

    But given their talent for consumption, why don’t black holes just keep expanding and expanding and simply swallow the Universe? Now, one of the world’s top physicists has come up with a new explanation.

    Conveniently, the idea could also unite the two biggest theories in all of physics.

    The researcher behind this latest explanation is none other than Stanford University physicist Leonard Susskind, also known as one of the fathers of string theory.

    Leonard Susskind by Linda Cicero-Stanford News Service

    He recently gave his two cents on the paradox in a series of papers, which basically suggest that black holes expand by increasing in complexity inwardly – a feature we just don’t see connected while watching from afar.

    In other words, they expand in, not out.

    Weirder still, this hypothesis might have a parallel in the expansion of our own Universe, which also seems to be growing in a counterintuitive way.

    “I think it’s a very, very interesting question whether the cosmological growth of space is connected to the growth of some kind of complexity,” Susskind was quoted in The Atlantic.

    “And whether the cosmic clock, the evolution of the universe, is connected with the evolution of complexity. There, I don’t know the answer.”

    Susskind might be speculating on the Universe’s evolution, but his thoughts on why black holes grow in more than they do out is worth unpacking.

    To be clear though, for now this work has only been published on the pre-print site arXiv.org, so it’s yet to be peer reviewed. That means we need to take it with a big grain of salt for now. On top of that, this type of research is, by its very nature, theoretical.

    But there are some pretty cool idea in here worth unpacking. To do that, we need to go back to basics for a moment. So … hang tight.

    For the uninitiated, black holes are dense masses that distort space to the extent that even light (read: information) lacks the escape velocity required to make an exit.

    The first solid theoretical underpinnings for such an object emerged naturally out of the mathematics behind Einstein’s general relativity back in 1915. Since then physical objects matching those predictions have been spotted, often hanging around the centre of galaxies.

    A common analogy is to imagine the dimensions of space plus time as a smooth rubber sheet. Much as a heavy object dimples the rubber sheet, mass distorts the geometry of spacetime.

    The properties of our Universe’s rubber sheet means it can form deep gravity funnel that stretches ‘down’ without stretching much further ‘out’.

    Most objects expand ‘out’ as you add material, not ‘in’. So how do we even begin to picture this? Rubber sheets are useful analogies, but only up to a certain point.

    To understand how matter behaves against this super stretchy backdrop, we need to look elsewhere. Luckily physics has a second rulebook on ‘How the Universe Works’ called quantum mechanics, which describes how particles and their forces interact.

    The two rule books of GR and QM don’t always agree, though. Small things interpreted through the lens of general relativity don’t make much sense. And big things like black holes produce gibberish when the rules of quantum mechanics are applied.

    This means we’re missing something important – something that would allow us to interpret general relativity’s space-bending feature in terms of finite masses and force-mediating particles.

    One contender is something called anti-de Sitter/conformal field theory correspondence, which is shortened to Ads/CFT. This is a ‘string theory meets four dimensional space’ kind of idea, aiming to bring the best of both quantum mechanics and general relativity together.

    Based on its framework, the quantum complexity of a black hole – the number of steps required to return it to a pre-black hole state – is reflected in its volume. The same thinking is what lies behind another brain-breaking idea called the holographic principle.

    The exact details aren’t for the faint hearted, but are freely available on arXiv.org if you want to get your mathematics fix for the day.

    It might sound a bit like downloading movies onto your desktop only to find it’s now ‘bigger’ on the inside. As ludicrous as it sounds, in the extreme environment of a black hole more computational power might indeed mean more internal volume. At least this is what Susskind’s Ads/CFT modelling suggests.

    String theory itself is one of those nice ideas begging for an empirical win, so we’re still a long way from marrying quantum mechanics and general relativity.

    Susskind’s suggestion that quantum complexity is ultimately responsible for the volume of a black hole has physicists thinking through the repercussions. After all, black holes aren’t like ordinary space, so we can’t expect ordinary rules to apply.

    But if anybody is worth listening to on the subject, it’s probably this guy.

    This research is available on arXiv.org.

    See the full article here .


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  • richardmitnick 3:21 pm on November 26, 2017 Permalink | Reply
    Tags: Einstein, ER - for Einstein-Rosen bridges, ER = EPR - (the EPR paradox named for its authors - Einstein Boris Podolsky and Nathan Rosen), Eventually Susskind — in a discovery that shocked even him — realized (with Gerard ’t Hooft) that all the information that fell down the hole was actually trapped on the black hole’s two-dimen, , Leonard Susskind, , , , The particles still inside the hole would be directly connected to particles that left long ago,   

    From Quanta: “Wormholes Untangle a Black Hole Paradox” 2015 but Worth It. 

    Quanta Magazine
    Quanta Magazine

    April 24, 2015
    K.C. Cole

    1
    Hannes Hummel for Quanta Magazine

    One hundred years after Albert Einstein developed his general theory of relativity, physicists are still stuck with perhaps the biggest incompatibility problem in the universe. The smoothly warped space-time landscape that Einstein described is like a painting by Salvador Dalí — seamless, unbroken, geometric. But the quantum particles that occupy this space are more like something from Georges Seurat: pointillist, discrete, described by probabilities. At their core, the two descriptions contradict each other. Yet a bold new strain of thinking suggests that quantum correlations between specks of impressionist paint actually create not just Dalí’s landscape, but the canvases that both sit on, as well as the three-dimensional space around them. And Einstein, as he so often does, sits right in the center of it all, still turning things upside-down from beyond the grave.

    Like initials carved in a tree, ER = EPR, as the new idea is known, is a shorthand that joins two ideas proposed by Einstein in 1935. One involved the paradox implied by what he called “spooky action at a distance” between quantum particles (the EPR paradox, named for its authors, Einstein, Boris Podolsky and Nathan Rosen). The other showed how two black holes could be connected through far reaches of space through “wormholes” (ER, for Einstein-Rosen bridges). At the time that Einstein put forth these ideas — and for most of the eight decades since — they were thought to be entirely unrelated.

    1
    When Einstein, Podolsky and Rosen published their seminal paper pointing out puzzling features of what we now call entanglement, The New York Times treated it as front-page news. The New York Times

    But if ER = EPR is correct, the ideas aren’t disconnected — they’re two manifestations of the same thing. And this underlying connectedness would form the foundation of all space-time. Quantum entanglement — the action at a distance that so troubled Einstein — could be creating the “spatial connectivity” that “sews space together,” according to Leonard Susskind, a physicist at Stanford University and one of the idea’s main architects. Without these connections, all of space would “atomize,” according to Juan Maldacena, a physicist at the Institute for Advanced Study in Princeton, N.J., who developed the idea together with Susskind. “In other words, the solid and reliable structure of space-time is due to the ghostly features of entanglement,” he said. What’s more, ER = EPR has the potential to address how gravity fits together with quantum mechanics.

    Not everyone’s buying it, of course (nor should they; the idea is in “its infancy,” said Susskind). Joe Polchinski, a researcher at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara, whose own stunning paradox about firewalls in the throats of black holes triggered the latest advances, is cautious, but intrigued. “I don’t know where it’s going,” he said, “but it’s a fun time right now.”

    The Black Hole Wars

    3
    Juan Maldacena at the Institute for Advanced Study in Princeton, N.J. Andrea Kane/Institute for Advanced Study

    The road that led to ER = EPR is a Möbius strip of tangled twists and turns that folds back on itself, like a drawing by M.C. Escher.

    A fair place to start might be quantum entanglement. If two quantum particles are entangled, they become, in effect, two parts of a single unit. What happens to one entangled particle happens to the other, no matter how far apart they are.

    Maldacena sometimes uses a pair of gloves as an analogy: If you come upon the right-handed glove, you instantaneously know the other is left-handed. There’s nothing spooky about that. But in the quantum version, both gloves are actually left- and right-handed (and everything in between) up until the moment you observe them. Spookier still, the left-handed glove doesn’t become left until you observe the right-handed one — at which moment both instantly gain a definite handedness.

    Entanglement played a key role in Stephen Hawking’s 1974 discovery that black holes could evaporate. This, too, involved entangled pairs of particles. Throughout space, short-lived “virtual” particles of matter and anti-matter continually pop into and out of existence. Hawking realized that if one particle fell into a black hole and the other escaped, the hole would emit radiation, glowing like a dying ember. Given enough time, the hole would evaporate into nothing, raising the question of what happened to the information content of the stuff that fell into it.

    But the rules of quantum mechanics forbid the complete destruction of information. (Hopelessly scrambling information is another story, which is why documents can be burned and hard drives smashed. There’s nothing in the laws of physics that prevents the information lost in a book’s smoke and ashes from being reconstructed, at least in principle.) So the question became: Would the information that originally went into the black hole just get scrambled? Or would it be truly lost? The arguments set off what Susskind called the “black hole wars,” which have generated enough stories to fill many books. (Susskind’s was subtitled My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics.)

    4
    Leonard Susskind at home in Palo Alto, Calif. Jeff Singer

    5
    Stephen Hawking. No image credit

    Eventually Susskind — in a discovery that shocked even him — realized (with Gerard ’t Hooft) that all the information that fell down the hole was actually trapped on the black hole’s two-dimensional event horizon, the surface that marks the point of no return. The horizon encoded everything inside, like a hologram. It was as if the bits needed to re-create your house and everything in it could fit on the walls. The information wasn’t lost — it was scrambled and stored out of reach.

    Susskind continued to work on the idea with Maldacena, whom Susskind calls “the master,” and others. Holography began to be used not just to understand black holes, but any region of space that can be described by its boundary. Over the past decade or so, the seemingly crazy idea that space is a kind of hologram has become rather humdrum, a tool of modern physics used in everything from cosmology to condensed matter. “One of the things that happen to scientific ideas is they often go from wild conjecture to reasonable conjecture to working tools,” Susskind said. “It’s gotten routine.”

    Holography was concerned with what happens on boundaries, including black hole horizons. That left open the question of what goes on in the interiors, said Susskind, and answers to that “were all over the map.” After all, since no information could ever escape from inside a black hole’s horizon, the laws of physics prevented scientists from ever directly testing what was going on inside.

    Then in 2012 Polchinski, along with Ahmed Almheiri, Donald Marolf and James Sully, all of them at the time at Santa Barbara, came up with an insight so startling it basically said to physicists: Hold everything. We know nothing.

    The so-called AMPS paper (after its authors’ initials) presented a doozy of an entanglement paradox — one so stark it implied that black holes might not, in effect, even have insides, for a “firewall” just inside the horizon would fry anyone or anything attempting to find out its secrets.

    Scaling the Firewall

    Here’s the heart of their argument: If a black hole’s event horizon is a smooth, seemingly ordinary place, as relativity predicts (the authors call this the “no drama” condition), the particles coming out of the black hole must be entangled with particles falling into the black hole. Yet for information not to be lost, the particles coming out of the black hole must also be entangled with particles that left long ago and are now scattered about in a fog of Hawking radiation. That’s one too many kinds of entanglements, the AMPS authors realized. One of them would have to go.

    The reason is that maximum entanglements have to be monogamous, existing between just two particles. Two maximum entanglements at once — quantum polygamy — simply cannot happen, which suggests that the smooth, continuous space-time inside the throats of black holes can’t exist. A break in the entanglement at the horizon would imply a discontinuity in space, a pileup of energy: the “firewall.”


    Video: David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics. Filming by Petr Stepanek. Editing and motion graphics by MK12. Music by Steven Gutheinz.

    The AMPS paper became a “real trigger,” said Stephen Shenker, a physicist at Stanford, and “cast in sharp relief” just how much was not understood. Of course, physicists love such paradoxes, because they’re fertile ground for discovery.

    Both Susskind and Maldacena got on it immediately. They’d been thinking about entanglement and wormholes, and both were inspired by the work of Mark Van Raamsdonk, a physicist at the University of British Columbia in Vancouver, who had conducted a pivotal thought experiment suggesting that entanglement and space-time are intimately related.

    “Then one day,” said Susskind, “Juan sent me a very cryptic message that contained the equation ER = EPR. I instantly saw what he was getting at, and from there we went back and forth expanding the idea.”

    Their investigations, which they presented in a 2013 paper, “Cool Horizons for Entangled Black Holes,” argued for a kind of entanglement they said the AMPS authors had overlooked — the one that “hooks space together,” according to Susskind. AMPS assumed that the parts of space inside and outside of the event horizon were independent. But Susskind and Maldacena suggest that, in fact, particles on either side of the border could be connected by a wormhole. The ER = EPR entanglement could “kind of get around the apparent paradox,” said Van Raamsdonk. The paper contained a graphic that some refer to half-jokingly as the “octopus picture” — with multiple wormholes leading from the inside of a black hole to Hawking radiation on the outside.

    4
    The ER = EPR idea posits that entangled particles inside and outside of a black hole’s event horizon are connected via wormholes. Olena Shmahalo/Quanta Magazine.

    In other words, there was no need for an entanglement that would create a kink in the smooth surface of the black hole’s throat. The particles still inside the hole would be directly connected to particles that left long ago. No need to pass through the horizon, no need to pass Go. The particles on the inside and the far-out ones could be considered one and the same, Maldacena explained — like me, myself and I. The complex “octopus” wormhole would link the interior of the black hole directly to particles in the long-departed cloud of Hawking radiation.

    Holes in the Wormhole

    No one is sure yet whether ER = EPR will solve the firewall problem. John Preskill, a physicist at the California Institute of Technology in Pasadena, reminded readers of Quantum Frontiers, the blog for Caltech’s Institute for Quantum Information and Matter, that sometimes physicists rely on their “sense of smell” to sniff out which theories have promise. “At first whiff,” he wrote, “ER = EPR may smell fresh and sweet, but it will have to ripen on the shelf for a while.”

    Whatever happens, the correspondence between entangled quantum particles and the geometry of smoothly warped space-time is a “big new insight,” said Shenker. It’s allowed him and his collaborator Douglas Stanford, a researcher at the Institute for Advanced Study, to tackle complex problems in quantum chaos through what Shenker calls “simple geometry that even I can understand.”

    To be sure, ER = EPR does not yet apply to just any kind of space, or any kind of entanglement. It takes a special type of entanglement and a special type of wormhole. “Lenny and Juan are completely aware of this,” said Marolf, who recently co-authored a paper describing wormholes with more than two ends. ER = EPR works in very specific situations, he said, but AMPS argues that the firewall presents a much broader challenge.

    Like Polchinski and others, Marolf worries that ER = EPR modifies standard quantum mechanics. “A lot of people are really interested in the ER = EPR conjecture,” said Marolf. “But there’s a sense that no one but Lenny and Juan really understand what it is.” Still, “it’s an interesting time to be in the field.”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 11:05 pm on November 24, 2015 Permalink | Reply
    Tags: , , Leonard Susskind, ,   

    From Nature: “Theoretical physics: Complexity on the horizon” 2014 

    Nature Mag
    Nature

    28 May 2014
    Amanda Gefter

    Temp 1

    When physicist Leonard Susskind gives talks these days, he often wears a black T-shirt proclaiming “I ♥ Complexity”. In place of the heart is a Mandelbrot set, a fractal pattern widely recognized as a symbol for complexity at its most beautiful.

    1
    Initial image of a Mandelbrot set zoom sequence with a continuously colored environment

    That pretty much sums up his message. The 74-year-old Susskind, a theorist at Stanford University in California, has long been a leader in efforts to unify quantum mechanics with the general theory of relativityAlbert Einstein’s framework for gravity. The quest for the elusive unified theory has led him to advocate counter-intuitive ideas, such as superstring theory or the concept that our three-dimensional Universe is actually a two-dimensional hologram. But now he is part of a small group of researchers arguing for a new and equally odd idea: that the key to this mysterious theory of everything is to be found in the branch of computer science known as computational complexity.

    This is not a subfield to which physicists have tended to look for fundamental insight. Computational complexity is grounded in practical matters, such as how many logical steps are required to execute an algorithm. But if the approach works, says Susskind, it could resolve one of the most baffling theoretical conundrums to hit his field in recent years: the black-hole firewall paradox, which seems to imply that either quantum mechanics or general relativity must be wrong. And more than that, he says, computational complexity could give theorists a whole new way to unify the two branches of their science — using ideas based fundamentally on information.

    Behind a firewall

    It all began 40 years ago, when physicist Stephen Hawking at the University of Cambridge, UK, realized that quantum effects would cause a black hole to radiate photons and other particles until it completely evaporates away.

    As other researchers were quick to point out, this revelation brings a troubling contradiction. According to the rules of quantum mechanics, the outgoing stream of radiation has to retain information about everything that ever fell into the black hole, even as the matter falling in carries exactly the same information through the black hole’s event horizon, the boundary inside which the black hole’s gravity gets so strong that not even light can escape. Yet this two-way flow could violate a key law of quantum mechanics known as the no-cloning theorem, which dictates that making a perfect copy of quantum information is impossible.

    Happily, as Susskind and his colleagues observed (1) in 1995, nature seemed to sidestep any such violation by making it impossible to see both copies at once: an observer who remains outside the horizon cannot communicate with one who has fallen in. But in 2012, four physicists at the University of California, Santa Barbara — Ahmed Almheiri, Donald Marolf, Joseph Polchinski and James Sully, known collectively as AMPS — spotted a dangerous exception to this rule (2). They found a scenario in which an observer could decode the information in the radiation, jump into the black hole and then compare that information with its forbidden duplicate on the way down.

    AMPS concluded that nature prevents this abomination by creating a blazing firewall just inside the horizon that will incinerate any observer — or indeed, any particle — trying to pass through. In effect, space would abruptly end at the horizon, even though Einstein’s gravitational theory says that space must be perfectly continuous there. If AMPS’s theory is true, says Raphael Bousso, a theoretical physicist at the University of California, Berkeley, “this is a terrible blow to general relativity”.

    Does not compute

    Fundamental physics has been in an uproar ever since, as practitioners have struggled to find a resolution to this paradox. The first people to bring computational complexity into the debate were Stanford’s Patrick Hayden, a physicist who also happens to be a computer scientist, and Daniel Harlow, a physicist at Princeton University in New Jersey. If the firewall argument hinges on an observer’s ability to decode the outgoing radiation, they wondered, just how hard is that to do?

    Impossibly hard, they discovered. A computational-complexity analysis showed that the number of steps required to decode the outgoing information would rise exponentially with the number of radiation particles that carry it. No conceivable computer could finish the calculations until long after the black hole had radiated all of its energy and vanished, along with the forbidden information clones. So the firewall has no reason to exist: the decoding scenario that demands it cannot happen, and the paradox disappears.

    “The black hole’s interior is protected by an armour of computational complexity.”

    Hayden was sceptical of the result at first. But then he and Harlow found much the same answer for many types of black hole (3). “It did seem to be a robust principle,” says Hayden: “a conspiracy of nature preventing you from performing this decoding before the black hole had disappeared on you.”

    The Harlow–Hayden argument made a big impression on Scott Aaronson, who works on computational complexity and the limits of quantum computation at the Massachusetts Institute of Technology in Cambridge. “I regard what they did as one of the more remarkable syntheses of physics and computer science that I’ve seen in my career,” he says.

    It also resonated strongly among theoretical physicists. But not everyone is convinced. Even if the calculation is correct, says Polchinski, “it is hard to see how one would build a fundamental theory on this framework”. Nevertheless, some physicists are trying to do just that. There is a widespread belief in the field that the laws of nature must somehow be based on information. And the idea that the laws might actually be upheld by computational complexity — which is defined entirely in terms of information — offers a fresh perspective.

    It certainly inspired Susskind to dig deeper into the role of complexity. For mathematical clarity, he chose to make his calculations in a theoretical realm known as anti-de Sitter space (AdS). This describes a cosmos that is like our own Universe in the sense that everything in it, including black holes, is governed by gravity. Unlike our Universe, however, it has a boundary — a domain where there is no gravity, just elementary particles and fields governed by quantum physics. Despite this difference, studying physics in AdS has led to many insights, because every object and physical process inside the space can be mathematically mapped to an equivalent object or process on its boundary. A black hole in AdS, for example, is equivalent to a hot gas of ordinary quantum particles on the boundary. Better still, calculations that are complicated in one domain often turn out to be simple in the other. And after the calculations are complete, the insights gained in AdS can generally be translated back into our own Universe.

    Increasing complexity

    Susskind decided to look at a black hole sitting at the centre of an AdS universe, and to use the boundary description to explore what happens inside a black hole’s event horizon. Others had attempted this and failed, and Susskind could see why after he viewed the problem through the lens of computational complexity. Translating from the boundary of the AdS universe to the interior of a black hole requires an enormous number of computational steps, and that number increases exponentially as one moves closer to the event horizon (4). As Aaronson puts it, “the black hole’s interior is protected by an armour of computational complexity”.

    Furthermore, Susskind noticed, the computational complexity tends to grow with time. This is not the increase of disorder, or entropy, that is familiar from everyday physics. Rather, it is a pure quantum effect arising from the way that interactions between the boundary particles cause an explosive growth in the complexity of their collective quantum state.

    If nothing else, Susskind argued, this growth means that complexity behaves much like a gravitational field. Imagine an object floating somewhere outside the black hole. Because this is AdS, he said, the object can be described by some configuration of particles and fields on the boundary. And because the complexity of that boundary description tends to increase over time, the effect is to make the object move towards regions of higher complexity in the interior of the space. But that, said Susskind, is just another way of saying that the object will be pulled down towards the black hole. He captured that idea in a slogan (4): “Things fall because there is a tendency toward complexity.”

    Another implication of increasing complexity turns out to be closely related to an argument (5) that Susskind made last year in collaboration with Juan Maldacena, a physicist at the Institute for Advanced Study in Princeton, New Jersey, and the first researcher to recognize the unique features of AdS. According to general relativity, Susskind and Maldacena noted, two black holes can be many light years apart yet still have their interiors connected by a space-time tunnel known as a wormhole. But according to quantum theory, these widely separated black holes can also be connected by having their states entangled, meaning that information about their quantum states is shared between them in a way that is independent of distance.

    After exploring the many similarities between these connections, Susskind and Maldacena concluded that they were two aspects of the same thing — that the black hole’s degree of entanglement, a purely quantum phenomenon, will determine the wormhole’s width, a matter of pure geometry.

    With his latest work, Susskind says, it turns out that the growth of complexity on the boundary of AdS shows up as an increase in the wormhole’s length. So putting it all together, it seems that entanglement is somehow related to space, and that computational complexity is somehow related to time.

    Susskind is the first to admit that such ideas by themselves are only provocative suggestions; they do not make up a fully fledged theory. But he and his allies are confident that the ideas transcend the firewall paradox.

    “I don’t know where all of this will lead,” says Susskind. “But I believe these complexity–geometry connections are the tip of an iceberg.”

    See the full article for References

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
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