On 12/30/2011 4:13 AM, Bruno Marchal wrote:

On 29 Dec 2011, at 20:44, Charles Goodwin wrote:

Hi Bruno

What observable properties of black holes may be explained by the fact that they don't erase information?

Black hole evaporation. I am thinking about some work by Hawking.

Hawking's theory of BH radiation did entail erasing information because the radiation is purely thermal. That's why it was so controversial. Erasing information would be an exception the unitary evolution of QM. It is now widely thought that the holographic principle saves the information on the BH event horizon and Leonard Susskind has an explanation of how string-theory accomplishes this But it's far from a settled question.

But $any* true erasing of information is forbid in any theory where QM applies universally. Unitary evolution cannot erase information, although it can hide it and makes it very hard to recompose.

Is that a purely hypothetical suggestion, or is it something we may observe in the near future, or may have already observed, indirectly?

I think some cosmological observations confirm this. It makes QM necessary to justify the existence and stability of Black Hole.

There have been no observations of Hawking radiation from a BH, but there are claims of observing radiation due event horizons created experimentally:


And a Happy New Year to you too, Bruno.


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