John Preskill

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seen Aug 28 '12 at 15:59

comment Reversing gravitational decoherence
Yes, I think that is correct. Penrose's proposal is very speculative. His estimate of the decoherence rate is far higher than standard gravitational theory would indicate.
comment Reversing gravitational decoherence
I'm sorry I was unclear. I meant to consider an interference experiment in which a particle can travel along either path 1 or path 2 between spacetime points A and B, where neither path is a geodesic. Then the particle emits radiation, but my point is that if the radiation is very soft we won't be able to learn whether the particle followed path 1 or path 2 by measuring the radiation field. Therefore, the two paths can interfere.