1. Black Holes, Entropy, and Information
Gary Horowitz
UCSB
This is a 1/2 hour talk given at space telescope science meeting April 2007.

2. What happens to all the information that fell in?
In 1973, Hawking discovered that black holes are not really black. When the effects of quantum mechanics are included, they act like a hot object and emit thermal radiation.
If no matter falls in, a black hole can evaporate and completely disappear.
This started a debate which lasted thirty years.
What happens to all the information that fell in?

3. Hawking argued that this is very different from burning a book:
This may seem like it is destroying information, but
All the information in the book can in principle be recovered from the ashes and emitted radiation.

4. String theory is a promising candidate for both
a quantum theory of gravity
a unified theory of all forces and matter
Over the past ten years, string theory has shown that black hole evaporation is qualitatively similar to burning a book. This process does not destroy information.

5. String theory has also given a description of quantum states of black hole. Originally this was possible only for exotic charged black holes. In the past year, it has become possible to do this for more familiar black holes.

6. This leads to a simple picture of black hole evaporation:
string radiation
string ls
Simple picture of BH evaporation. In Hawking’s picture, the BH evaporated down
to the planck scale where the approximations being use broke down. Now
BH evaporates until it reaches the string scale, at which point it turns into a highly
excited string. The excited string continues to radiate
until it becomes an unexcited string I.e. just another elementary particle.
Hawking radiation
black hole