1. Jan 24, 2010

### atyy

In a spacetime with a black hole, where is the horizon in the CFT?

Also, if a black hole spacetime corresponds to a thermal CFT, doesn't that mean the CFT is in a box where there is still a universe outside to provide a temperature?

2. Jan 24, 2010

### atyy

Hmm, here there are two copies of the CFT and one of them is averaged over.
http://arxiv.org/abs/hep-th/0106112
Juan M. Maldacena

I wonder if this has held up?

http://arxiv.org/abs/hep-th/9903237
D.A. Lowe, L. Thorlacius

http://arxiv.org/abs/0811.0263
Black Holes as Effective Geometries
Vijay Balasubramanian, Jan de Boer, Sheer El-Showk, Ilies Messamah

http://arxiv.org/abs/0909.1038
The information paradox: A pedagogical introduction
Samir D. Mathur

Last edited: Jan 24, 2010
3. Jan 25, 2010

### Finbar

You have to assume that the black hole is coupled to a heat bath such that the temperature remains constant and it's in thermal equilibrium. Then the black hole will remain at some temperature forever.

The CFT is finite and unbounded as is the horizon of the black hole. So the CFT isn't in a box since a box has bounds. Therefore the CFT doesn't need a heat bath because there is no where for the heat to flow from/to. So the whole CFT is the horizon.

4. Jan 25, 2010

### atyy

So if the CFT is the whole universe, then the universe will be in a mixed state - but how can that be - quantum mechanically, shouldn't there be only pure states when it comes to the whole universe?

5. Jan 29, 2010

### Physics Monkey

In the case of the eternal black hole discussed by Maldecena in your first link, there are actually two copies of the CFT. The black hole geometry is an approximate description of an entangled state of the two CFTs. This entangled state has the property that it looks exactly thermal to each CFT individually. Additionally, the CFTs are unable to communicate due to the black hole horizons.