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View Full Version : What happens to information in a black hole?

cjackson
2013-Dec-17, 06:31 AM
According to some physicists information isn't lost in black holes. How is that possible? If it isn't lost where does it go? Is it possible to know exactly what went in based on the information? How would it be possible to observe the information?

Noclevername
2013-Dec-17, 07:53 AM
What physicists have you seen that state this hypothesis?

JohnD
2013-Dec-17, 09:00 AM
Hawking and Kip Thorne bet John Preskill that infromation would be lost going into a BH.
Then Hawking proposed a solution that it was not, conceded and gave Preskill an encylopedia.
Because he compared his theory to burning an encylopedia - you keep all the smoke and ashes, so you do not lose the information in the book.
No, I don't buy it either! I fear the analogy oversimplifies it.
See: http://www.hawking.org.uk/into-a-black-hole.html

JOhn

Noclevername
2013-Dec-17, 09:33 AM
AFAIK once information passes the event horizon of a BH (assuming it survives spaghettification (http://en.wikipedia.org/wiki/Spaghettification) as information) it cannot come out. It would have to exceed the lightspeed-plus escape velocity.

Cougar
2013-Dec-19, 08:30 PM
AFAIK once information passes the event horizon of a BH (assuming it survives spaghettification (http://en.wikipedia.org/wiki/Spaghettification) as information) it cannot come out. It would have to exceed the lightspeed-plus escape velocity.

Baez explains this problem well. (http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/info_loss.html)

In order to understand why the information loss problem is a problem, we need first to understand what it is. Take a quantum system in a pure state and throw it into a black hole. Wait for some amount of time until the hole has evaporated enough to return to its mass previous to throwing anything in. What we start with is a pure state and a black hole of mass M. What we end up with is a thermal state [the Hawking radiation] and a black hole of mass M. We have found a process (apparently) that converts a pure state into a thermal state. But, and here's the kicker, a thermal state is a MIXED state (described quantum mechanically by a density matrix rather than a wave function). In transforming between a mixed state and a pure state, one must throw away information. For instance, in our example we took a state described by a set of eigenvalues and coefficients, a large set of numbers, and transformed it into a state described by temperature, one number. All the other structure of the state was lost in the transformation.