Monday, August 28, 2006

Spacetime topology change and black hole information

I'm in Erice right now, so posting may (or may not) be interrupted depending on how exciting the talks are :-)


Spacetime topology change and black hole information

Abstract: Topology change --- the creation of a disconnected baby universe --- due to black hole collapse may resolve the information loss paradox. Evolution from an early time Cauchy surface to a final surface which includes a slice of the disconnected region can be unitary and consistent with conventional quantum mechanics. We discuss the issue of cluster decomposition, showing that any violations thereof are likely to be unobservably small. Topology change is similar to the black hole remnant scenario and only requires assumptions about the behavior of quantum gravity in planckian regimes. It does not require non-locality or any modification of low-energy physics.

I don't necessarily want to claim that topology change is plausible. But, it does suggest that we can't make progress on the black hole information problem by low-energy means alone, since there are possible solutions that have unobservable low-energy effects and depend on how quantum gravity behaves at planck densities.

I got some email already pointing me to the following interesting papers on this issue. The first two are by Ted Jacobson and the last by Easson and Brandenberger. All discuss, in one way or another, the possibility that things which fall into black holes end up "somewhere else" and the relation to the information loss paradox.


More. Early work by Mukhanov and Frolov on connecting deSitter space to the black hole interior (they assume strong planckian dynamics leads to a symmetrical equation of state with stress tensor proportional to g_mn, so deSitter is natural): (too old for arXiv).

There are also apparently many loop QG papers suggesting a repulsive equation of state at planck density, which is what is needed to have expansion instead of a singularity. I haven't tracked those papers down, but will add them here and to the revision of the paper. Also, Lee Smolin long ago proposed that black hole collapse might lead to new universe creation, although I believe that was part of a cosmological selection proposal and not to solve the information loss problem.

Interestingly, there seem to be two camps on this issue. People from a string theory background seem convinced that only the two traditional solutions are viable: locality violation and quantum xeroxing at the semiclassical horizon (possibly due to stringy effects and bh complementarity), or remnants. In the relativist community it seems people find the topology change option rather obvious and wonder why I wasn't aware of these earlier references. I'd like to put the two sides in a seminar room somewhere to mix it up! :-)

I came to this from the stringy side -- the review articles I cite are by Strominger, Banks, Giddings and Susskind, so I thought arguing the feasibility of the topology change scenario to be an uphill fight. The very first thing I do in the paper is present the two main objections to the idea. The first objection, that pure to mixed evolution (even at an effective level) must entail energy non-conservation, seems to have been discussed before by relativists (e.g., Wald). But the second objection, regarding cluster decomposition violation (multiple baby universe creation amplitudes don't factorize even when the black hole collapses are widely separated) does not seem to have been widely discussed.

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