String Theory and the Black Hole Information Paradox

One of the important aspects of the thermodynamics of black holes relates to the black hole information paradox. This paradox may well have a solution in string theory, either in the string theory analyses described in the previous section or in the holographic principle.

Hawking had said that if an object falls into a black hole, the only information that is retained are the quantum mechanical properties of mass, spin, and charge. All other information was stripped away.

The problem with this is that quantum mechanics is built on the idea that information can’t be lost. If information can be lost, then quantum mechanics isn’t a secure theoretical structure. Hawking, as a relativist, was more concerned with maintaining the theoretical structure of general relativity, so he was okay with the information being lost if it had to be.

The reason that this lost information is such a major issue for quantum mechanics once again ties into thermodynamics. In quantum mechanics, information is related to the thermodynamic concept of “order.” If information is lost, then order is lost — meaning that entropy (disorder) is increased. This means that the black holes would begin generating heat, rising up to billions of billions of degrees in mere moments. Though Leonard Susskind and others realized this in the mid-1980s, they couldn’t find the flaws in Hawking’s reasoning that would prove him wrong.

In 2004, after a debate that lasted more than 20 years, Hawking announced that he no longer believed this information was forever lost to the universe. In doing so, he lost a 1997 bet with physicist John Preskill. The payoff was a baseball encyclopedia, from which information could be retrieved easily. And who said physicists didn’t have a sense of humor?

One reason for Hawking’s change of mind was that he redid some of his earlier calculations and found that it was possible that, as an object fell into a black hole, it would disturb the black hole’s radiation field. The information about the object could seep out, though probably in mangled form, through the fluctuations in this field.

Another way to approach the problem of black hole information loss is through the holographic principle of Leonard Susskind and Gerard ’t Hooft, or the related AdS/CFT correspondence developed by Juan Maldacena. If these principles hold for black holes, it may be possible that all the information within the black hole is also encoded in some form on the surface area of the black hole.

The controversy over the black hole information paradox is described in detail in Susskind’s 2008 book, The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics.

Still one other approach is to look at the potential multiverse. It’s possible that the information that enters a black hole is, in some way, passed from this universe into a parallel universe.

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