Archive for the ‘quantum physics’ Category

Academics are challenging the foundations of quantum science with a radical new theory on parallel universes. Scientists now propose that parallel universes really exist, and that they interact. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Griffith University academics are challenging the foundations of quantum science with a radical new theory based on the existence of, and interactions between, parallel universes.

In a paper published in the journal Physical Review X, Professor Howard Wiseman and Dr Michael Hall from Griffith’s Centre for Quantum Dynamics, and Dr Dirk-Andre Deckert from the University of California, take interacting parallel worlds out of the realm of science fiction and into that of hard science.
The team proposes that parallel universes really exist, and that they interact. That is, rather than evolving independently, nearby worlds influence one another by a subtle force of repulsion. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Quantum theory is needed to explain how the universe works at the microscopic scale, and is believed to apply to all matter. But it is notoriously difficult to fathom, exhibiting weird phenomena which seem to violate the laws of cause and effect.

As the eminent American theoretical physicist Richard Feynman once noted: “I think I can safely say that nobody understands quantum mechanics.”

However, the “Many-Interacting Worlds” approach developed at Griffith University provides a new and daring perspective on this baffling field.

“The idea of parallel universes in quantum mechanics has been around since 1957,” says Professor Wiseman.

“In the well-known “Many-Worlds Interpretation,” each universe branches into a bunch of new universes every time a quantum measurement is made. All possibilities are therefore realised — in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese.

“But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our “Many Interacting Worlds” approach is completely different, as its name implies.”

Professor Wiseman and his colleagues propose that:

•The universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different;
•All of these worlds are equally real, exist continuously through time, and possess precisely defined properties;
•All quantum phenomena arise from a universal force of repulsion between ‘nearby’ (i.e. similar) worlds which tends to make them more dissimilar.
Dr Hall says the “Many-Interacting Worlds” theory may even create the extraordinary possibility of testing for the existence of other worlds.

“The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics,” he says.

“In between it predicts something new that is neither Newton’s theory nor quantum theory.

“We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena.”

The ability to approximate quantum evolution using a finite number of worlds could have significant ramifications in molecular dynamics, which is important for understanding chemical reactions and the action of drugs.

Professor Bill Poirier, Distinguished Professor of Chemistry at Texas Tech University, has observed: “These are great ideas, not only conceptually, but also with regard to the new numerical breakthroughs they are almost certain to engender.”

Journal Reference:

1.Michael J. W. Hall, Dirk-André Deckert, Howard M. Wiseman. Quantum Phenomena Modeled by Interactions between Many Classical Worlds. Physical Review X, 2014; 4 (4) DOI: 10.1103/PhysRevX.4.041013

http://www.sciencedaily.com/releases/2014/10/141030101654.htm

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Since the 1930s scientists have been searching for particles that are simultaneously matter and antimatter. Now physicists have found strong evidence for one such entity inside a superconducting material. The discovery could represent the first so-called Majorana particle, and may help researchers encode information for quantum computers.

Physicists think that every particle of matter has an antimatter counterpart with equal mass but opposite charge. When matter meets its antimatter equivalent, the two annihilate one another. But some particles might be their own antimatter partners, according to a 1937 prediction by Italian physicist Ettore Majorana. For the first time researchers say they have imaged one of these Majorana particles, and report their findings in the October 3 Science.

The new Majorana particle showed up inside a superconductor, a material in which the free movement of electrons allows electricity to flow without resistance. The research team, led by Ali Yazdani of Princeton University, placed a long chain of iron atoms, which are magnetic, on top of a superconductor made of lead. Normally, magnetism disrupts superconductors, which depend on a lack of magnetic fields for their electrons to flow unimpeded. But in this case the magnetic chain turned into a special type of superconductor in which electrons next to one another in the chain coordinated their spins to simultaneously satisfy the requirements of magnetism and superconductivity. Each of these pairs can be thought of as an electron and an antielectron, with a negative and a positive charge, respectively. That arrangement, however, leaves one electron at each end of the chain without a neighbor to pair with, causing them to take on the properties of both electrons and antielectrons—in other words, Majorana particles.

As opposed to particles found in a vacuum, unattached to other matter, these Majoranas are what’s called “emergent particles.” They emerge from the collective properties of the surrounding matter and could not exist outside the superconductor.

The new study shows a convincing signature of Majorana particles, says Leo Kouwenhoven of the Delft University of Technology in the Netherlands who was not involved in the research but previously found signs of Majorana particles in a different superconductor arrangement. “But to really speak of full proof, unambiguous evidence, I think you have to do a DNA test.” Such a test, he says, must show the particles do not obey the normal laws of the two known classes of particles in nature—fermions (protons, electrons and most other particles we are familiar with) and bosons (photons and other force-carrying particles, including the Higgs boson). “The great thing about Majoranas is that they are potentially a new class of particle,” Kouwenhoven adds. “If you find a new class of particles, that really would add a new chapter to physics.”

Physicist Jason Alicea of California Institute of Technology, who also did not participate in the research, said the study offers “compelling evidence” for Majorana particles but that “we should keep in mind possible alternative explanations—even if there are no immediately obvious candidates.” He praised the experimental setup for its apparent ability to easily produce the elusive Majoranas. “One of the great virtues of their platform relative to earlier works is that it allowed the researchers to apply a new type of microscope to probe the detailed anatomy of the physics.”

The discovery could have implications for searches for free Majorana particles outside of superconducting materials. Many physicists suspect neutrinos—very lightweight particles with the strange ability to alter their identities, or flavors—are Majorana particles, and experiments are ongoing to investigate whether this is the case. Now that we know Majorana particles can exist inside superconductors, it might not be surprising to find them in nature, Yazdani says. “Once you find the concept to be correct, it’s very likely that it shows up in another layer of physics. That’s what’s exciting.”

The finding could also be useful for constructing quantum computers that harness the laws of quantum mechanics to make calculations many times faster than conventional computers. One of the main issues in building a quantum computer is the susceptibility of quantum properties such as entanglement (a connection between two particles such that an action on one affects the other) to collapse due to outside interference. A particle chain with Majoranas capping each end would be somewhat immune to this danger, because damage would have to be done to both ends simultaneously to destroy any information encoded there. “You could build a quantum bit based on these Majoranas,” Yazdani says. ”The idea is that such a bit would be much more robust to the environment than the types of bits people have tried to make so far.”

http://www.scientificamerican.com/article/majorana-particle-matter-and-antimatter/

Stephen Hawking's black hole theory
Notion of an ‘event horizon’, from which nothing can escape, is incompatible with quantum theory, physicist claims.

by Zeeya Merali

Most physicists foolhardy enough to write a paper claiming that “there are no black holes” — at least not in the sense we usually imagine — would probably be dismissed as cranks. But when the call to redefine these cosmic crunchers comes from Stephen Hawking, it’s worth taking notice. In a paper posted online, the physicist, based at the University of Cambridge, UK, and one of the creators of modern black-hole theory, does away with the notion of an event horizon, the invisible boundary thought to shroud every black hole, beyond which nothing, not even light, can escape.

In its stead, Hawking’s radical proposal is a much more benign “apparent horizon”, which only temporarily holds matter and energy prisoner before eventually releasing them, albeit in a more garbled form.

“There is no escape from a black hole in classical theory,” Hawking told Nature. Quantum theory, however, “enables energy and information to escape from a black hole”. A full explanation of the process, the physicist admits, would require a theory that successfully merges gravity with the other fundamental forces of nature. But that is a goal that has eluded physicists for nearly a century. “The correct treatment,” Hawking says, “remains a mystery.”

Hawking posted his paper on the arXiv preprint server on 22 January1. He titled it, whimsically, ‘Information preservation and weather forecasting for black holes’, and it has yet to pass peer review. The paper was based on a talk he gave via Skype at a meeting at the Kavli Institute for Theoretical Physics in Santa Barbara, California, in August 2013.

Hawking’s new work is an attempt to solve what is known as the black-hole firewall paradox, which has been vexing physicists for almost two years, after it was discovered by theoretical physicist Joseph Polchinski of the Kavli Institute and his colleagues.

In a thought experiment, the researchers asked what would happen to an astronaut unlucky enough to fall into a black hole. Event horizons are mathematically simple consequences of Einstein’s general theory of relativity that were first pointed out by the German astronomer Karl Schwarzschild in a letter he wrote to Einstein in late 1915, less than a month after the publication of the theory. In that picture, physicists had long assumed, the astronaut would happily pass through the event horizon, unaware of his or her impending doom, before gradually being pulled inwards — stretched out along the way, like spaghetti — and eventually crushed at the ‘singularity’, the black hole’s hypothetical infinitely dense core.

But on analysing the situation in detail, Polchinski’s team came to the startling realization that the laws of quantum mechanics, which govern particles on small scales, change the situation completely. Quantum theory, they said, dictates that the event horizon must actually be transformed into a highly energetic region, or ‘firewall’, that would burn the astronaut to a crisp.

This was alarming because, although the firewall obeyed quantum rules, it flouted Einstein’s general theory of relativity. According to that theory, someone in free fall should perceive the laws of physics as being identical everywhere in the Universe — whether they are falling into a black hole or floating in empty intergalactic space. As far as Einstein is concerned, the event horizon should be an unremarkable place.

Now Hawking proposes a third, tantalizingly simple, option. Quantum mechanics and general relativity remain intact, but black holes simply do not have an event horizon to catch fire. The key to his claim is that quantum effects around the black hole cause space-time to fluctuate too wildly for a sharp boundary surface to exist.

In place of the event horizon, Hawking invokes an “apparent horizon”, a surface along which light rays attempting to rush away from the black hole’s core will be suspended. In general relativity, for an unchanging black hole, these two horizons are identical, because light trying to escape from inside a black hole can reach only as far as the event horizon and will be held there, as though stuck on a treadmill. However, the two horizons can, in principle, be distinguished. If more matter gets swallowed by the black hole, its event horizon will swell and grow larger than the apparent horizon.

Conversely, in the 1970s, Hawking also showed that black holes can slowly shrink, spewing out ‘Hawking radiation’. In that case, the event horizon would, in theory, become smaller than the apparent horizon. Hawking’s new suggestion is that the apparent horizon is the real boundary. “The absence of event horizons means that there are no black holes — in the sense of regimes from which light can’t escape to infinity,” Hawking writes.

“The picture Hawking gives sounds reasonable,” says Don Page, a physicist and expert on black holes at the University of Alberta in Edmonton, Canada, who collaborated with Hawking in the 1970s. “You could say that it is radical to propose there’s no event horizon. But these are highly quantum conditions, and there’s ambiguity about what space-time even is, let alone whether there is a definite region that can be marked as an event horizon.”

Although Page accepts Hawking’s proposal that a black hole could exist without an event horizon, he questions whether that alone is enough to get past the firewall paradox. The presence of even an ephemeral apparent horizon, he cautions, could well cause the same problems as does an event horizon.

Unlike the event horizon, the apparent horizon can eventually dissolve. Page notes that Hawking is opening the door to a scenario so extreme “that anything in principle can get out of a black hole”. Although Hawking does not specify in his paper exactly how an apparent horizon would disappear, Page speculates that when it has shrunk to a certain size, at which the effects of both quantum mechanics and gravity combine, it is plausible that it could vanish. At that point, whatever was once trapped within the black hole would be released (although not in good shape).

If Hawking is correct, there could even be no singularity at the core of the black hole. Instead, matter would be only temporarily held behind the apparent horizon, which would gradually move inward owing to the pull of the black hole, but would never quite crunch down to the centre. Information about this matter would not destroyed, but would be highly scrambled so that, as it is released through Hawking radiation, it would be in a vastly different form, making it almost impossible to work out what the swallowed objects once were.

“It would be worse than trying to reconstruct a book that you burned from its ashes,” says Page. In his paper, Hawking compares it to trying to forecast the weather ahead of time: in theory it is possible, but in practice it is too difficult to do with much accuracy.

Polchinski, however, is sceptical that black holes without an event horizon could exist in nature. The kind of violent fluctuations needed to erase it are too rare in the Universe, he says. “In Einstein’s gravity, the black-hole horizon is not so different from any other part of space,” says Polchinski. “We never see space-time fluctuate in our own neighbourhood: it is just too rare on large scales.”

Raphael Bousso, a theoretical physicist at the University of California, Berkeley, and a former student of Hawking’s, says that this latest contribution highlights how “abhorrent” physicists find the potential existence of firewalls. However, he is also cautious about Hawking’s solution. “The idea that there are no points from which you cannot escape a black hole is in some ways an even more radical and problematic suggestion than the existence of firewalls,” he says. “But the fact that we’re still discussing such questions 40 years after Hawking’s first papers on black holes and information is testament to their enormous significance.”

http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583?WT.mc-id=GPL_NatureNews

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“Our hypothesis is that the inside of a black hole — it may not be there. Probably that’s the end of space itself. There’s no inside at all.”
– Joe Polchinski, physicist

It could rightly be called the most massive debate of the year: Physicists are locked in an argument over what happens if you fall into a black hole.

On one side are those who support the traditional view from Albert Einstein. On the other, backers of a radical new theory that preserves the very core of modern physics by destroying space itself.

Regardless of who’s right, the new take on black holes could lead to a better understanding of the universe, says Leonard Susskind, a physicist at Stanford University. “This is the kind of thing where progress comes from.”

Black holes are regions of space so dense that nothing, not even light, can escape.

There’s a long-standing view about what would happen if you fell into one of these holes. At first, you’re not going to notice much of anything — but the black hole’s gravity is getting stronger and stronger. And eventually you pass a point of no return.

“It’s kind of like you’re rowing on Niagara Falls, and you pass the point [where] you can’t row fast enough to escape the current,” Susskind says. “Well, you’re doomed at that point. But passing the point of no return — you wouldn’t even notice it.”

Now you can’t get out. And gravity from the black hole is starting to pull on your feet more than your head. “The gravity wants to sort of stretch you in one direction and squeeze you in another,” says Joe Polchinski, a physicist at the University of California, Santa Barbara. He says the technical term for this stretching is spaghettification.

“It’d be kind of medieval,” says Polchinkski. “It’d be like something on Game of Thrones.”

In Einstein’s version of events, that’s the end. But Polchinski has a new version of things: “Our hypothesis is that the inside of a black hole — it may not be there,” he says.

So what’s inside the black hole? Nothing, Polchinski says. Actually even less than that. “Probably that’s the end of space itself; there’s no inside at all.”
This “no inside” idea may sound outrageous, but it’s actually a stab at solving an even bigger problem with black holes.

According to the dominant theory of physics — quantum mechanics — information can never disappear from the universe. Put another way, the atoms in your body are configured in a particular way. They can be rearranged (radically if you happen to slip inside a black hole). But it should always be possible, at least in theory, to look at all those rearranged atoms and work out that they were once part of a human of your dimensions and personality.

This rule is absolutely fundamental. “Everything is built on it,” says Susskind. “If it were violated, everything falls apart.”

For a long time, black holes stretched this rule, but they didn’t break it. People thought that if you fell into a black hole, your spaghettified remains would always be in there, trapped beyond the point of no return.

That is, until the famous physicist Stephen Hawking came along. In the 1970s, Hawking showed that, according to quantum mechanics, a black hole evaporates — very slowly, it vanishes. And that breaks the fundamental rule because all that information that was once in your spaghettified remains vanishes with it.

This didn’t seem to bother Hawking. (“I’m not a psychiatrist, and I can’t psychoanalyze him,” Susskind says.) But it has bothered a lot of other physicists since.

And in the intervening years, work by another theorist — Juan Maldacena, with Princeton’s Institute for Advanced Study — seems to show that Hawking was wrong. Information has to get out of the black hole … somehow. But nobody knows how.

So Polchinski took another look. “We took Hawking’s original argument,” he says, “and very carefully ran it backwards.”

And Polchinski and his colleagues found one way to keep things from vanishing when they fall inside a black hole — they got rid of the inside. By tearing apart the fabric of space beyond the point of no return, the group was able to preserve the information rule of quantum mechanics.

In this version, anything falling into a black hole is instantly vaporized at the point of no return, in a fiery storm of quantum particles. Particles coming from the hole collectively carry away any and all information about the object that’s falling in.

So in Polchinski’s version, when you fall into a black hole, you don’t disappear. Instead, you smack into the end of the universe.

“You just come to the end of space, and there’s nothing beyond it. Terminated,” Susskind says. All the information once contained in your atoms is re-radiated in a quantum mechanical fire.

This new version seems too radical to Susskind. “I don’t think this is true,” he says. “In fact, I think almost nobody thinks this is true — that space falls apart inside a black hole.”

Even Polchinski still feels that black holes should have insides. “My gut believes that the black hole has an interior,” he says. But, he adds, nobody’s been able to disprove his hypothesis that it doesn’t.

“Every counterargument I’ve seen is flawed,” Polchinski says.

Susskind agrees: “Nobody quite knows exactly what’s wrong with their argument — and that’s what makes this so important and interesting.”

And as crazy as it sounds, this is progress. In the year ahead, Susskind hopes someone can find the flaw in Polchinski’s argument, just the way Polchinski found a flaw in Stephen Hawking’s argument. But it will be awhile before we understand black holes inside and out.

http://www.npr.org/2013/12/27/256897343/stretch-or-splat-how-a-black-hole-kills-you-matters-a-lot

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1_14328

At a black hole, Albert Einstein’s theory of gravity apparently clashes with quantum physics, but that conflict could be solved if the Universe were a holographic projection.

A team of physicists have provided what has been described by the journal Nature as the “clearest evidence yet” that our universe is a hologram.

The new research could help reconcile one of modern physics’ most enduring problems : the apparent inconsistencies between the different models of the universe as explained by quantum physics and Einstein’s theory of gravity.

The two new scientific papers are the culmination of years’ work led by Yoshifumi Hyakutake of Ibaraki University in Japan, and deal with hypothetical calculations of the energies of black holes in different universes.

The idea of the universe existing as a ‘hologram’ doesn’t refer to a Matrix-like illusion, but the theory that the three dimensions we perceive are actually just “painted” onto the cosmological horizon – the boundary of the known universe.

If this sounds paradoxical, try to imagine a holographic picture that changes as you move it. Although the picture is two dimensional, observing it from different locations creates the illusion that it is 3D.

This model of the universe helps explain some inconsistencies between general relativity (Einstein’s theory) and quantum physics. Although Einstein’s work underpins much of modern physics, at certain extremes (such as in the middle of a black hole) the principles he outlined break down and the laws of quantum physics take over.

The traditional method of reconciling these two models has come from the 1997 work of theoretical physicist Juan Maldacena, whose ideas built upon string theory. This is one of the most well respected ‘theories of everything’ (Stephen Hawking is a fan) and it posits that one-dimensional vibrating objects known as ‘strings’ are the elementary particles of the universe.

Maldacena has welcomed the new research by Hyakutake and his team, telling the journal Nature that the findings are “an interesting way to test many ideas in quantum gravity and string theory.”

Leonard Susskind, a theoretical physicist regarded as one of the fathers of string theory, added that the work by the Japanese team “numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture.”

Here is the original press release from Nature:

A team of physicists has provided some of the clearest evidence yet that our Universe could be just one big projection.

In 1997, theoretical physicist Juan Maldacena proposed1 that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity.

Maldacena’s idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing — and because it solved apparent inconsistencies between quantum physics and Einstein’s theory of gravity. It provided physicists with a mathematical Rosetta stone, a ‘duality’, that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa. But although the validity of Maldacena’s ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive.

In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.

In one paper2, Hyakutake computes the internal energy of a black hole, the position of its event horizon (the boundary between the black hole and the rest of the Universe), its entropy and other properties based on the predictions of string theory as well as the effects of so-called virtual particles that continuously pop into and out of existence. In the other3, he and his collaborators calculate the internal energy of the corresponding lower-dimensional cosmos with no gravity. The two computer calculations match.

“It seems to be a correct computation,” says Maldacena, who is now at the Institute for Advanced Study in Princeton, New Jersey and who did not contribute to the team’s work.

The findings “are an interesting way to test many ideas in quantum gravity and string theory”, Maldacena adds. The two papers, he notes, are the culmination of a series of articles contributed by the Japanese team over the past few years. “The whole sequence of papers is very nice because it tests the dual [nature of the universes] in regimes where there are no analytic tests.”

“They have numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture — namely that the thermodynamics of certain black holes can be reproduced from a lower-dimensional universe,” says Leonard Susskind, a theoretical physicist at Stanford University in California who was among the first theoreticians to explore the idea of holographic universes.

Neither of the model universes explored by the Japanese team resembles our own, Maldacena notes. The cosmos with a black hole has ten dimensions, with eight of them forming an eight-dimensional sphere. The lower-dimensional, gravity-free one has but a single dimension, and its menagerie of quantum particles resembles a group of idealized springs, or harmonic oscillators, attached to one another.

Nevertheless, says Maldacena, the numerical proof that these two seemingly disparate worlds are actually identical gives hope that the gravitational properties of our Universe can one day be explained by a simpler cosmos purely in terms of quantum theory.

http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328#/b1