Black Holes have Colored Hair

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In a startling reversal, the New York Times reports Stephen Hawking has revised a crucial aspect of his Black Hole theory.

About Those Fearsome Black Holes? Never Mind

By DENNIS OVERBYE

Published: July 22, 2004

r. Stephen W. Hawking threw in the towel yesterday, or at least an encyclopedia.

Dr. Hawking, the celebrated Cambridge University cosmologist and best-selling author, declared at a scientific conference in Dublin that he had been wrong in a controversial assertion he made 30 years ago about black holes, the fearsome gravitational abysses that can swallow matter and energy, even light.

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This esoteric sounding debate is of great consequence to science, because if Dr. Hawking had been right, it would have violated a basic tenet of modern physics: that it is always possible to reverse time, run the proverbial film backward and reconstruct what happened in, say, the collision of two cars or the collapse of a dead star into a black hole.

Now, on the basis of a new calculation, Dr. Hawking has concluded that physics is safe and information can escape from a black hole. "I want to report that I think that I have solved a major problem in theoretical physics," he told his colleagues, according to a transcript of his remarks.

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The work was, and remains, hailed as a breakthrough in understanding the connection between gravity and quantum mechanics, the large and the small in the universe.

But there was a hitch, as Dr. Hawking pointed out. The radiation coming out of the black hole would be random. As a result, all information about what had fallen in - whether it be elephants or donkeys - would be erased. In a riposte to Einstein's famous remark that God does not play dice, rejecting quantum uncertainty, Dr. Hawking said in 1976, "God not only plays dice with the universe, but sometimes throws them where they can't be seen."

That was a violation of quantum theory, which says that information is preserved, and quantum theory is a foundation of all modern physics.

Dr Hawking discovered the phenomenon of black hole "evaporation," which was expressed in the saying that black holes have hair. However, black hole radiation was hopelessly scrambled, so that nothing could be learned of the innards of the black hole. The radiation was entirely random, colorless, like white noise.

In recanting his original analysis, Prof Hawking is now saying that radiation leaking out of black holes is colorful; i.e., it carries some information about what happened inside the black hole. This is a stunning finding if true, because, as he said,

"I'm sorry to disappoint science fiction fans, but if information is preserved there is no possibility of using black holes to travel to other universes,'' he said yesterday. "If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form, which contains the information about what you were like, but in an unrecognizable state."

When Einstein's colleague, Karl Schwarzschild, discovered the possibility of black holes in 1915,

Schwarzschild himself was investigating what would happen if the mass of a fluid sphere - an idealized star - were squeezed into a smaller and smaller sphere. He found that as his model star shrank, there was a specific circumference at which its mass would reach a critical density . At that point, the star's gravitational field would be strong enough to bend spacetime so severely that it would close in on itself, creating sealed loop. As physicists later came to understand, when that happened, nothing, not even light, could escape from within that now-isolated island of spacetime.¹

Apparently, Einstein was disbelieving about the Schwarzschild radius and black holes, but this consequence of General Relativity stuck in toto until Hawking propounded his first thesis. Now, if something discernible can leak out of a black hole, the original shocking conclusions are (partially) aborted. Since Hawking's results are based on Quantum Theory, not Relativity theory, whatever methods he has yet to propose for information escaping black holes may have something important to say about the quantization of gravity.

1. Thomas Levenson, Einstein in Berlin, Bantam Books, New York, 2003, p 130

July 21, 2004

Last update: 11/13/2007