# Black hole microstates and string theory

#### quantumfireball

Can someone give me a Pop science explanation of what do strings and Branes have got to do with black hole entropy.
The no of degrees of freedom or the no of microstates of the black hole corresponding to a given macrostate is given by exp(S),where S is entropy of black hole which is related to area of event horizon.
So how do you count microstates of black hole using these extended objects?

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#### tom.stoer

As far as I know the black holes in string theory are not "astrophysical" black holes with event horizons and so on. Instead they are so-called BPS states with interaction turned off. I would call them unphysical!
The idea is that nevertheless these BPS states they correspond in some sense to black holes (if you could turn interaction on). It is possible to "count" these BPS states and to relate the entropy to the number of BPS states.

#### Naty1

You can get some insights at Wikipedia:

http://en.wikipedia.org/wiki/String_theory
including:

...String theory is a theory of gravity, an extension of General Relativity, and the classical interpretation of the strings and branes is that they are quantum mechanical vibrating extended charged black holes.

#### Naty1

And at the same location in Wikipedia:

String theories are formulated on cold black holes, which are those which have as much charge as possible......a theory of a black hole horizon is a theory of everything. Finding even one consistent holographic description, a priori, seems like a long-shot, because it would be a disembodied nonlocal description of quantum gravity. In string theory, not only is there one such description, there are several different ones, each describing fluctuations of horizons with different charges and dimensions, and all of them logically fit together. So the same physical objects and interactions can be described by the fluctuations of one-dimensional black hole horizons, or by three-dimensional horizons, or by zero-dimensional horizons.

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