From Hawking’s second Reith lecture: The tranny
It was therefore very important to determine whether information really was lost in black holes, or whether in principle, it could be recovered.
Many scientists felt that information should not be lost, but no one could suggest a mechanism by which it could be preserved. The arguments went on for years. Finally, I found what I think is the answer.
It depends on the idea of Richard Feynman, that there isn’t a single history, but many different possible histories, each with their own probability.
In this case, there are two kinds of history. In one, there is a black hole, into which particles can fall, but in the other kind there is no black hole.
The point is that from the outside, one can’t be certain whether there is a black hole or not. So there is always a chance that there isn’t a black hole.
This possibility is enough to preserve the information, but the information is not returned in a very useful form. It is like burning an encyclopaedia. Information is not lost if you keep all the smoke and ashes, but it is difficult to read.
The scientist Kip Thorne and I had a bet with another physicist, John Preskill, that information would be lost in black holes. When I discovered how information could be preserved, I conceded the bet. I gave John Preskill an encyclopaedia. Maybe I should have just given him the ashes.
DS: In theory, and with a purely deterministic view of the universe, you could burn an encyclopaedia and then reconstitute it if you knew the characteristics and position of every atom making up every molecule of ink in every letter and kept track of them all at all times.
Information is there, but not useful ‘like burning an encyclopaedia’
Currently I’m working with my Cambridge colleague Malcolm Perry and Andrew Strominger from Harvard on a new theory based on a mathematical idea called supertranslations to explain the mechanism by which information is returned out of the black hole.
The information is encoded on the horizon of the black hole. Watch this space.
The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought. Things can get out of a black hole, both to the outside, and possibly to another universe.
So if you feel you are in a black hole, don’t give up. There’s a way out. More.
[altar call lineup forms to right]
See also: Hawking uses black hole to split physicists
Follow UD News at Twitter!
Here’s the first lecture: