Let me Count the Ways

A slightly famous mathematician once said to me: “I think Hawking is the most overrated physicist.” This took me aback, and I spent quite a while explaining to him that Hawking had important results in addition to his appearances on Star Trek and The Simpsons.

Most important was his discovery of black hole radiance, and the revolution in black hole statistical mechanics it energized, which in turn is the most important result of quantum gravity. I suppose it would be more precise to say that black hole radiance and black hole thermodynamics is the nearest thing to a result in quantum gravity, since there are no experimentally confirmed predictions in quantum gravity.

Nonetheless, all roads in quantum gravity appear to lead to black hole thermodynamics, and it would be hard to find a yet unobserved phenomenon in which physicists believe more firmly. Steven Carlip gives an overview of those many paths leading there in his new paper Black Hole Thermodynamics and Statistical Mechanics (arXiv:0807.4520). Among them, classical thermodynamic arguments, semi-classical quantum field theoretic arguments, statistical mechanical arguments based on string theory, Maldacena’s ADS/CFT, loop quantum gravity calculations, Sakharov’s induced gravity, entanglement entropy, and derivations from causal sets.

What accounts for this universality of result from seeming very different approaches? That’s the question that interests Carlip, but he doesn’t have a definitive answer. He does have what he thinks is a tantalizing clue, but you will need to read the paper to get that.

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