Hawking Radiation

Stephen Hawking Puts Forth New Theory On Black Holes

Notion of an ‘event horizon’, from which nothing can escape, is incompatible with quantum theory, physicist claims.

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.”

Artistic impression of a black hole via NASA GSFC

Hawking posted his paper on the arXiv preprint server on 22 January 1. 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.

Fire fighting
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.

Artist credit: Andy Potts [source]

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.

Beyond the horizon
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.

Theoretical calculations predict that the Milky Way’s central black hole, called Sagittarius A*, will look like this when imaged by the Event Horizon Telescope. The false-color image shows light radiated by gas swirling around and into a black hole. The dark region in the middle is the “black hole shadow,” caused by the black hole bending light around it. [source]

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).

What are black holes? [Wiki]

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.”

Source: Nature

Stay curious! Watch PBS NOVA’s ’Monsters of the Milky Way [51:23] || Stephen Hawking’s Universe: ’Black Holes and Beyond [53:31] || Monsters of the Cosmos’ by melodysheep/Symphony of Science [3:25] || Carl Sagan explores a black hole on 'Cosmos: A Personal Voyage’ [2:22]

Black Holes Could Turn You Into a Hologram, and You Wouldn’t Even Notice

By Tim De Chant

Few things are as mysterious as black holes. Except, of course, what would happen to you if you fell into one.

Physicists have been debating what might happen to anyone unfortunate enough to slip toward the singularity, and so far, they’ve come up with approximately 2.5 ways you might die, from being stretched like spaghetti to burnt to a crisp.

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sciencealert.com
Stephen Hawking just published a new solution to the black hole information paradox
How black holes can erase information, but also retain it.
By Bec Crew

Last year, British theoretical physicist Stephen Hawking hinted at research he and a couple of colleagues were working on that could solve the infamous black hole information paradox, which states that information about matter that gets destroyed by a black hole, according to Einstein’s general theory of relativity, is supposed to be fundamentally conserved, according to our understanding of quantum mechanics.

Now, that paper has finally been posted online, and as hinted by Hawking back in August, the solution to this paradox could be black hole ‘hairs’ that form on the event horizon, making a kind of two-dimensional holographic imprint of whatever’s been sucked in. He says the existence of these hairs is provable, and their existence could win him a Nobel Prize.

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Lab created analogue black hole experiment detects Hawking radiation - Some physicists at odds

Entangled Hawking radiation emitted by an analogue black hole has been observed by a physicist in Israel. The experiment simulates the event horizon of a black hole using sound propagation in a Bose–Einstein condensate (BEC). The measurement shows that, if Einstein’s general theory of relativity holds at the boundary of a black hole, then black holes must emit radiation.

READ MORE ON IOP | PHYSICS WORLD

Ref: Observation of quantum Hawking radiation and its entanglement in an analogue black hole. Nature Physics (15 August 2016) | DOI: 10.1038/nphys3863

ABSTRACT

We observe spontaneous Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose–Einstein condensate. Correlations are observed between the Hawking particles outside the black hole and the partner particles inside. These correlations indicate an approximately thermal distribution of Hawking radiation. We find that the high-energy pairs are entangled, while the low-energy pairs are not, within the reasonable assumption that excitations with different frequencies are not correlated. The entanglement verifies the quantum nature of the Hawking radiation. The results are consistent with a driven oscillation experiment and a numerical simulation.

Yes, they do—Stephen Hawking discovered that according to quantum mechanics, black holes should radiate energy. In the quantum world, space is filled with tiny particles that flash in and out of existence, and Hawking predicted that energy fluctuations would generate particle-antiparticles near a black hole’s event horizon. Before they can annihilate each other as would normally happen, the black hole pulls in the particle with negative energy and “emits” the particle with positive energy. For this reason, black holes aren’t completely black—they glow faintly.

This is called Hawking Radiation, and it results in the black hole losing energy and therefore mass according to E=mc^2. As a black hole radiates, it shrinks. The nature of the radiative process means that the more a black hole shrinks, the more it radiates—so eventually the black hole will disappear. This will take an incredibly long time, though. A black hole of the mass of the Sun will take a billion times a billion times a billion times a billion times a billion times a billion times the age of the universe to evaporate completely.

Proposed Resolution For the Black Hole Information Paradox

Shred a document, and you can piece it back together. Burn a book, and you could theoretically do the same. But send information into a black hole, and it’s lost forever.

That’s what some physicists have argued for years: That black holes are the ultimate vaults, entities that suck in information and then evaporate without leaving behind any clues as to what they once contained.

But new research shows that this perspective may not be correct.

“According to our work, information isn’t lost once it enters a black hole,” says Dejan Stojkovic, PhD, associate professor of physics at the University at Buffalo. “It doesn’t just disappear.”

Stojkovic’s new study, “Radiation from a Collapsing Object is Manifestly Unitary,” appeared on March 17 in Physical Review Letters, with UB PhD student Anshul Saini as co-author.

The paper outlines how interactions between particles emitted by a black hole can reveal information about what lies within, such as characteristics of the object that formed the black hole to begin with, and characteristics of the matter and energy drawn inside.

This is an important discovery, Stojkovic says, because even physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens. His new paper presents explicit calculations demonstrating how information is preserved, he says.

The research marks a significant step toward solving the “information loss paradox,” a problem that has plagued physics for almost 40 years, since Stephen Hawking first proposed that black holes could radiate energy and evaporate over time. This posed a huge problem for the field of physics because it meant that information inside a black hole could be permanently lost when the black hole disappeared – a violation of quantum mechanics, which states that information must be conserved.

Information Hidden in Particle Interactions

In the 1970s, Hawking proposed that black holes were capable of radiating particles, and that the energy lost through this process would cause the black holes to shrink and eventually disappear. Hawking further concluded that the particles emitted by a black hole would provide no clues about what lay inside, meaning that any information held within a black hole would be completely lost once the entity evaporated.

Though Hawking later said he was wrong and that information could escape from black holes, the subject of whether and how it’s possible to recover information from a black hole has remained a topic of debate.

Stojkovic and Saini’s new paper helps to clarify the story.

Instead of looking only at the particles a black hole emits, the study also takes into account the subtle interactions between the particles. By doing so, the research finds that it is possible for an observer standing outside of a black hole to recover information about what lies within.

Interactions between particles can range from gravitational attraction to the exchange of mediators like photons between particles. Such “correlations” have long been known to exist, but many scientists discounted them as unimportant in the past.

“These correlations were often ignored in related calculations since they were thought to be small and not capable of making a significant difference,” Stojkovic says. “Our explicit calculations show that though the correlations start off very small, they grow in time and become large enough to change the outcome.”

via University at Buffalo

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Could the LHC make an Earth-killing black hole?

“There are a number of theories that predict the existence of extra dimensions. Not merely the three spatial and one time dimension we know to be present in our four-dimensional spacetime, but at least one additional spatial dimension that exists in our Universe. While we can’t quite access those dimensions at the energies we’ve probed, it’s conceivable that at scales that are smaller than those we’ve examined — which corresponds to higher energies — these extra dimensions exist.

And if these extra dimensions exist, one theoretical possibility is that it might be possible to create tiny, miniature, microscopic black holes!”

One of the more exotic scenarios associated with the LHC — a scenario inspired by extra dimensions — would be the production of tiny, microscopic black holes that arise from super-energetic particle collisions. As the LHC is now operating at the highest energies ever created on Earth, 13 TeV or just a hair over, this has a better chance of coming to fruition now than ever before. But black holes have a reputation of sucking everything they encounter into them. If we created one here on Earth, would this potentially be dangerous? And if so, are the timescales of danger something that humans should worry about? Even if you’re willing to violate (or extend) the laws of physics to allow the production of these black holes and force them to be stable against decay, it would still take timescales many times that of the age of the Universe for them to devour even one kilogram of matter, much less the entire Earth.

A Black Hole Doesn’t Die – It Does Something A Lot Weirder

Black holes are basically “game over, man,” for anything that gets too close to them, but they aren’t invincible. In fact, they’re always in the process of self-destructing. We’ll look at how they fizzle out, and see if we can help them do it faster.

The Event Horizon

Realistically speaking, you are dead as soon as you get anywhere near a black hole. You’ll be snapped like a rubber band by the differences in the gravitational pull on your top and bottom half, or you’ll be fried by radiation (more on that later). No one in the foreseeable future (even if we try to foresee multiple millennia into the future) will get close to a black hole. Pass the event horizon, however, and you don’t even have an unforeseeable future. Once material gets beyond the event horizon, it’s being pulled into the black hole with such force that it doesn’t escape. Not even light gets out. Once something has gone beyond the event horizon, it no longer really “counts” as part of the universe anymore.

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“HAWKING’S PREDICTION OF HAWKING RADIATION MAY ACTUALLY BE TRUE”
A physicist at the Israel Institute of Technology named Jeff Steinhauer may have come up with definitive proof of the existence of the phenomenon of ‘Hawking Radiation’, the theory which suggests that it is possible for particles to escape black holes.
For the last seven years, Steinhauer has been perfecting his method in recreating a black hole in a lab and just a few months ago, his machine was brought to a reality. To create this experiment, Steinhauer cooled rubidum atoms to a few billionths of a degree above absolute zero to cause them to enter a quantum state of matter where they would behave like clones of each other and clump together to form a 'super particle’ also known as a Bose-Einstein condensate (BEC). By using lasers to force the atoms to move at supersonic speeds, sound waves were trapped inside the quantum fluid. After 4,600 successful trials (to be sure), Steinhauer observed pairs of phonons (packets of sound energy) appear spontaneously at the event horizon, with one ejected while the others fell back into the fluid.
Although this achievement is quite remarkable, some scientists are still quite skeptical of the results. Some doubt that Steinhauer actually produced what is known as a BEC (thereby arguing the artificial black hole wasn’t a real fake one) and require several more replications of this experiment. Others are more skeptical and believe only a direct observation of Hawking Radiation will settle the dispute once and for all.

Read more about this fascinating story on: http://futurism.com/lab-grown-black-hole-may-have-just-proven-that-hawking-radiation-exists/

thegayngerzone  asked:

Are black holes infinite, or will they eventually, I dunno how to phrase this, really, but cease to exist?

Well hypothetically, a black holes life should end. But for most black holes we have discovered and observed it doesn’t have much effect due to the large amount of mass present.

Stephen Hawking (in 1974) discovered that black holes radiate energy, as it radiates energy it is losing energy. While a black hole is infinitely dense, it does not have infinite mass, so it will eventually cease to exist, the scientific term for this is “evaporation.” For most black holes this would take a really really really long time — but it could be an explanation to why there are no really tiny black holes! They evaporate and die. I read somewhere that a black hole with the mass of a car would evaporate in a time under like a hundred billionth of a nanosecond.

If you go here, you can find an explanation on the lifetime of black holes explained way more in depth. 

New Quantum Gravity-Based Hypothesis Suggests Black Holes Become White Holes Soon After They Form

Black holes, as fascinating as they are, are still sort of a mystery to science. Well, perhaps not the black holes themselves as much as the things that happen inside of them. Namely, what happens to information once it’s consumed? Physics says that it can’t be destroyed entirely, yet the nature of black holes themselves seem to indicate otherwise.

Now, a team of researchers have proposed a new hypothesis suggesting that black holes indeed do not destroy information. Instead, all of it is sent barreling back out into space following their transition into white holes (the polar opposites of black holes). Learn all about it here: http://bit.ly/1rU5edV

Image Credit: Victor Habrick VISIONS/SPL/Getty

Physicists think they’re figured out how to retrieve information from a black hole

Wow.

By David Nield

Physicists in the US think they’ve solved one of the biggest mysteries around black holes: how to retrieve information from them.

The gravity inside a black hole is so strong that even light can’t escape, and according to theory, nor can any data about the quantum particles that end up inside. That’s a problem for scientists, as it makes it impossible to predict the exact evolution of the black hole, and what’s actually going on inside it. Plus the theory of quantum physics states that no information about the Universe can ever be totally lost, so what’s going on?

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Death of a Black Hole

You’ve probably heard that nothing can escape a black hole, so how can this amazing object end its life? To answer this question we have to go back to 1974, when the astrophysicist Stephen Hawking showed that a black hole should emit electromagnetic radiation. The discovery was quite impressive, since it’s known that nothing is able to escape the gravitational force of a black hole.

The process works roughly in this way: particle-antiparticle pairs are constantly created all over the universe, they come into existence and suddenly disappear by annihilating with each other. Now, if one of these pair is created on the edge of the event horizon of a black hole, one can fall into it while the other escapes, and this leads the black hole to lose mass. Moreover, the smaller is the mass of the black hole the faster it will lose mass because of the Hawking radiation.

At the very end the temperature of the black hole will become very high and it will disappear in an extraordinary burst of gamma-ray radiation.

This process that leads to the death of a black hole is known as black hole evaporation.

Sources:

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We’re back after a short break, and decided to start the New Year off with something light. You know, black holes, Hawking radiation, the theory of everything, the Hadron Collider. The typical post-holiday chitchat.

The topic today? Stephen Hawking and his contributions to science. Guest: science writer Kitty Ferguson. She’s worked extensively with Hawking and just published a new biography about him.

A Black Hole: You’re What’s for Dinner Tonight

Do you like spaghetti? If your answer is ‘yes,’ why not become what you love? You can…if you dive on into the belly of a black hole.

What are we talking about? Well, as it turns out, black holes are known for more than than being cosmic vacuum cleaners. They can essentially turn you into a long strand of pasta.

Learn more here: http://www.fromquarkstoquasars.com/black-hole-its-whats-for-dinner-tonight/

Image Credit: Andy Potts

Hawking radiation mimicked in the lab

Sound waves used to imitate light particles predicted to escape black holes.

Scientists have come closer than ever before to creating a laboratory-scale imitation of a black hole that emits Hawking radiation, the particles predicted to escape black holes due to quantum mechanical effects.

The black hole analogue, reported in Nature Physics1, was created by trapping sound waves using an ultra cold fluid. Such objects could one day help resolve the so-called black hole ‘information paradox’ - the question of whether information that falls into a black hole disappears forever.

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Hawking radiation   

n.

A form of radiation believed to emanate from black holes, emerging from the region just beyond the black hole’s event horizon (from which no radiation can emerge). Pairs of virtual particles and anti-particles, created naturally in the vacuum fluctuation near the black hole, are split apart, one particle falling into the black hole and the other radiating away. The energy lost to such radiated particles is believed to come from the mass of the black hole.