## A Conversation for Black Holes

### Entropy?

Joe Otten Started conversation Aug 24, 2003

The thing that has always puzzled me about black holes is what happens to the entropy of objects that fall into them?

By its description, a single infinitely dense point seems to have a very low entropy. But if we then let a high entropy object fall into a black hole, we appear to have a contradiction to the second law of thermodynamics.

### Entropy?

albarn Posted Dec 1, 2003

This topic is an active one in the field of astrophysics and quantum gravitation. In general, however, it is required of a black hole that its event horizon always increase, much like the total entropy of a closed system (i.e. - the universe). This thought lead to the hypothesis that a black hole's entropy is proportional to its event horizon's surface area. This came to be the Bekenstein-Hawking Formula:

http://scienceworld.wolfram.com/physics/Bekenstein-HawkingFormula.html

If a black hole has an entropy, then it follows all the other laws of thermodynamics and has a temperature, also. So the black hole will radiate energy. This is where things start getting fuzzy. How can something that is impossible to escape radiate anything? I'm afraid I don't know much about what's new in that field of thought.

### Entropy?

Joe Otten Posted Dec 2, 2003

Thanks for that.

There is Hawking radiation, but I guess that is not what you are talking about. Could it be a mistake to consider a black hole demarcated by its event horizon to be an object, and thus to apply thermodynamic principles to that object.

After all the event horizon is not a physical structure and need not be in the same place from one moment to the next. (That episode of Voyager where the ship was stuck inside the event horizon of a black hole, looking for a crack to get out would have been hilarious if it had been slightly less obtuse.)

### Entropy?

EnergeticRobb978 Posted Aug 21, 2010

The natural answer is that the laws of physics break down in a black hole. The entropy just vanishes. Entropy is a property of the universe, and all properties of the universe break down at the event horizo of a black hole.

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