Physicists Demonstrate How Information Can Escape From Black Holes

May 14, 2008
Physicists Demonstrate How Information Can Escape From Black Holes
An artist's depiction of the accretion of a thick ring of dust into a supermassive black hole. The accretion produces jets of gamma rays and X-rays. Credit: ESA / V. Beckmann (NASA-GSFC)

Physicists at Penn State have provided a mechanism by which information can be recovered from black holes, those regions of space where gravity is so strong that, according to Einstein's theory of general relativity, not even light can escape. The team's findings pave the way toward ending a decades-long debate sparked by renowned physicist Steven Hawking. The team's work will be published in the 20 May 2008 issue of the journal Physical Review Letters.

In the 1970s, Hawking showed that black holes evaporate by quantum processes; however, he asserted that information, such as the identity of matter that is gobbled up by black holes, is permanently lost. At the time, Hawking's assertion threatened to turn quantum mechanics--the most successful physical theory posited by humankind--on its head, since a fundamental tenet of the theory is that information cannot be lost.

Hawking's idea was generally accepted by physicists until the late 1990s, when many began to doubt the assertion. Even Hawking himself renounced the idea in 2004. Yet no one, until now, has been able to provide a plausible mechanism for how information might escape from a black hole.

A team of physicists led by Abhay Ashtekar, Holder of the Eberly Family Chair in Physics and director of the Penn State Institute for Gravitation and the Cosmos, now has discovered such a mechanism. Broadly, their findings expand space-time beyond its assumed size, thus providing room for information to reappear.

To explain the issue, Ashtekar used an analogy from Alice in Wonderland. "When the Cheshire cat disappears, his grin remains," he said. "We used to think it was the same way with black holes. Hawking's analysis suggested that at the end of a black hole's life, even after it has completely evaporated away, a singularity, or a final edge to space-time, is left behind, and this singularity serves as a sink for unrecoverable information."

But Ashtekar and his collaborators, Victor Taveras, a graduate student in the Penn State Department of Physics, and Madhavan Varadarajan, a professor at the Raman Research Institute in India, suggest that singularities do not exist in the real world. "Information only appears to be lost because we have been looking at a restricted part of the true quantum-mechanical space-time," said Ashtekar. "Once you consider quantum gravity, then space-time becomes much larger and there is room for information to reappear in the distant future on the other side of what was first thought to be the end of space-time."

According to Ashtekar, space-time is not a continuum as physicists once believed. Instead, it is made up of individual building blocks, just as a piece of fabric, though it appears to be continuous, is made up of individual threads. "Once we realized that the notion of space-time as a continuum is only an approximation of reality, it became clear to us that singularities are merely artifacts of our insistence that space-time should be described as a continuum."

To conduct their studies, the team used a two-dimensional model of black holes to investigate the quantum nature of real black holes, which exist in four dimensions. That's because two-dimensional systems are simpler to study mathematically. But because of the close similarities between two-dimensional black holes and spherical four-dimensional black holes, the team believes that this approach is a general mechanism that can be applied in four dimensions. The group now is pursuing methods for directly studying four-dimensional black holes.

Source: Penn State

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superhuman
3.3 / 5 (9) May 14, 2008
>Once you consider quantum gravity...

There is no accepted theory of quantum gravity.

> According to Ashtekar, space-time is not a continuum as physicists once believed.

Which experiment can confirm it?

Both quantum gravity and whether space-time is discreet or continuous are much bigger, older and more importent unsolved puzzles of physics.
mattytheory
2.7 / 5 (6) May 14, 2008
@superhuman: This guy is making assumptions about parts of reality which we will not be able to resolve through experimentation for many years to come. Quantum Gravity? Discontinuity of space? This is not how science is done. You cannot make assumptions about that which you cannot prove, either empirically or experimentally, and then base a conclusion on those assumptions. While it is not a logical fallacy, I would say that a conclusion is only as stable as the foundation upon which it is built. And, unprovable assumptions are, to me, very weak.

In my opinion, however, I do not see how information can be perfectly preserved because information is also dependent upon context. If the information emitted by black holes is not emitted in a manner that preserves context, then conservation of information is still violated.
NeilFarbstein
1.6 / 5 (9) May 14, 2008
There is no law of conservation of information. Disorder grows bigger all the time.
Ragtime
May 14, 2008
This comment has been removed by a moderator.
Ragtime
May 14, 2008
This comment has been removed by a moderator.
Ragtime
1.7 / 5 (7) May 14, 2008
..space-time is not a continuum as physicists once believed..
By AWT the space is formed by infinitelly tiny particles, so it appears like continuum. But it's never completelly homogeneous, which effectivelly means, inside of every sufficiently large density fluctuation the density gradient will become so large gradually, it will affect the energy spreading by total reflection phenomena, which means, it would behave like less or more "black hole".

For example the water droplets are rather transparent for light waves, but they're behaving like tiny reflecting singularities with respect of sound wave spreading. By analogous way, the black holes are behaving like singularities with respect of light waves, but they're should remain quite transparent for gravitational waves, and so on.

So that only observational perspective can define, what can be considered a singularity or not.
Ragtime
2 / 5 (7) May 14, 2008
..no one, until now, has been able to provide a plausible mechanism for how information might escape from a black hole..
The only true is, everybody's believing, his explanation is more plausible, then the explanation of others. But the robust theories of "white holes" are many already, for example the Yilmaz and Heim theory, gravastar theory, etc. You can find the AWT explanation for example here: http://tinyurl.com/6rpud3
mattytheory
2 / 5 (3) May 14, 2008
@Neil: Then why must black holes emit radiation? This was a major reason why Hawking Radiation is accepted by many scientists.

Or maybe I am wrong?
axemaster
3.3 / 5 (4) May 14, 2008
"Once we realized that the notion of space-time as a continuum is only an approximation of reality, it became clear to us that singularities are merely artifacts of our insistence that space-time should be described as a continuum."

Is it just me, or is this brutally obvious?

(assuming quantum gravity works)
axemaster
3 / 5 (5) May 14, 2008
"There is no law of conservation of information. Disorder grows bigger all the time." - Neil Farbstein

That is actually an increase in information, as more data is required to model the state of the universe at each moment. Equivalent to thermodynamics.
brant
1 / 5 (8) May 15, 2008
If my blackhole disappears, would you still know about my farts?
out7x
2.7 / 5 (3) May 15, 2008
information could be stored in other dimensions, as in string theory. Quantum mechanics does not say that information cannot be lost.
Alexa
1.5 / 5 (2) May 15, 2008
The formation of singularity belongs the realm of relativity theory, because from Schwarzschild solution of GR follows, every object of supercritical mass should collapse into singularity undeniably. The QM doesn't violate this theorem conceptually, being in similar position when claiming, a certain level of uncertainty is immanent to quantum reality and it cannot be avoided, as follows from EPR and Bell theorem - so that certain portion of information remains always hidden for us.

But here's still apparent caveat, because the singularity solution of GR is steady state solution and as such it doesn't care, when this situation will occur. As we know, the BH is formed by collapse of dense matter and the speed of energy spreading is the more slow, the more dense such matter is. From this follows, the infinitely dense matter (i.e. the singularity) should form just in infinite time. Which is apparently unrealistic assumption, if we consider the finite age of Universe.

From this insight follows, only sufficiently small BH can form the singular solution, the heavier ones cannot form a singularity, if they were formed just after Universe formation. Note, that such conclusion is consistent with the AWT explanation of information paradox, linked above ( http://tinyurl.com/6rpud3 )
Ivars
1.5 / 5 (2) May 15, 2008
Yes information can escape, no spacetime is not so simple. These black holes do not evaporate away, they emit information because they contain discrete fractional spacetime ; but even that is not enough to describe them fully. Continuous as such is a very weak definition as it only discerns one level of continuity, thus being unable to even contemplate what may go on beneath seemingly continuous spacetime.
Iztaru
3 / 5 (2) May 15, 2008
Quantum Gravity? Discontinuity of space? This is not how science is done. You cannot make assumptions about that which you cannot prove, either empirically or experimentally, and then base a conclusion on those assumptions.


In my opinion, you are right and wrong. This research still has value. If they can work out a model where a discrete space-time and quantum gravity are required to explain macroscopic phenomenas (e.g.: black holes), they will be building a stronger case for those hypothesis.
brant
2.5 / 5 (2) May 18, 2008
"In my opinion, you are right and wrong. This research still has value."

By the same token, research into why faeries do not exist, is also an excellent waste of taxpayer dollars.
thales
3 / 5 (1) May 19, 2008
It seems to me that the more fundamental our questions get regarding the structure of the universe, the more difficult it is to test them directly. It is often easier and less costly to come up with a model or hypothesis, work it out to its logical conclusion, and test the prediction. This is the case with string theory, for example. The benefits of pure research are not always immediately practical or even obvious -- but unusual approaches yield useful information often enough to be worthwhile.