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elfmotat
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So, does anyone have any thoughts on the papers recently published by Almheiri/Marolf/Polchinski/Sully (http://arxiv.org/pdf/1207.3123.pdf) and Susskind (http://arxiv.org/pdf/1207.4090.pdf)?
Demystifier said:In quantum mechanics, complementarity can be expressed in a clear and simple mathematical way, as the fact that the same state can be expanded in different bases, corresponding to eigenstates of different observables. The nice thing about this is that the state itself, viewed as an object which does not depend on the choice of basis, does NOT DEPEND ON THE OBSERVER.
However, as far as I know, nothing similar exists for black hole complementarity. As far as this is the case, I cannot take black hole complementarity seriously.
tom.stoer said:. I mean a Bogoljubov transformation between vacuum states of QFT on curved background is more complicated that just x' = x-vt, but conceptionally is identical.
with x' = x-vt I didn't want to say that the Bogoljubav trf. applies to inertial frames. I only wanted to claim that observations are frame dependent and that the Unruh effect is nothing else but an effect due to this frame-dependence. The big difference is that it acts on the Fock space and "creates particle states from the vacuum".Finbar said:Isn't a Bogoljubov transformation conceptually the same as a transformation between non-inertial observers rather than intertial ones?
tom.stoer said:with x' = x-vt I didn't want to say that the Bogoljubav trf. applies to inertial frames. I only wanted to claim that observations are frame dependent and that the Unruh effect is nothing else but an effect due to this frame-dependence. The big difference is that it acts on the Fock space and "creates particle states from the vacuum".
But as said it's slightly more complicated than that: there is an interpretation problem regarding the "reality" of the observed particles i.e. regarding a real event"; and there seems to be a lack of "global definition" of states or d.o.f.
In the case of Unruh effect, all observers agree that the state is |0_Minkowski>. In Susskind black hole complementarity there is no such a universal object on which all observers agree.jarod765 said:Furthermore, one should not be so hesitant in discussing observer dependent theories. For example, in quantum gravity it is impossible to define a preferred vacuum state and therefore different observers will see drastically different physics (see Unruh radiation).
Demystifier said:In the case of Unruh effect, all observers agree that the state is |0_Minkowski>. In Susskind black hole complementarity there is no such a universal object on which all observers agree.
That is not true. In QM it is not possible to measure simultaneously two different (mutually non-commuting) observables, not even if the measurements are performed by different observers. For example, if one observer measures momentum at time t and obtains the value p, there is no way that another observer could get a measurement result which is not compatible with the fact that momentum at time t is equal to p.Finbar said:Anyway in QM all observers don't have to agree on what the state is. If one observer preforms a measurement of one observable then the state will be an eigenstate of the observable. But if the other observer makes a measures a different observable then for her it will be in an eigenstate of a different observable.
Currently it is quite popular to withdraw papers on that issue. Harlow also withdrew it:MTd2 said:
Demystifier said:That is not true. In QM it is not possible to measure simultaneously two different (mutually non-commuting) observables, not even if the measurements are performed by different observers. For example, if one observer measures momentum at time t and obtains the value p, there is no way that another observer could get a measurement result which is not compatible with the fact that momentum at time t is equal to p.
This fact is what makes complementarity in ordinary QM consistent. Unfortunately, it seems that nothing similar exists for black hole complementarity.
I would accept it if one could translate it into an observer-free language. For example, one can introduce Tomonaga-Schwinger formalism, in which time evolution Psi(t) (with this or that time t) is generalized to Psi[Sigma], which is a functional of an arbitrary spacelike hypersurface Sigma. If one could find SINGLE functional Psi[Sigma] that contains both complementary views of a black hole just by taking different Sigma in the same Psi[Sigma], then I would accept it.Finbar said:You're right, but I didn't say that they had to measure the observables simultaneously.
(However I concede I was far from clear.)
In relativity there is no observer independent notion of simultaneous events.
I think this an important point. For some observer (i.e. some world line) we have to pick a time slicing over which states evolve. If for the observer outside the black hole we pick a time slicing which remains within her causal diamond then ordinary QM applies without any contradictions. If we take the in-falling observer then for her she can choose a time slicing within her causal diamond and again we have consistent QM. Only if we try to do QM on a time-slicing which is not within a causal diamond does it breakdown. But since such a time slicing would lead to states that no observer could attempt to measure it is meaningless.
A quantum state should always correspond to some observers knowledge of the physical system. As long as we stick to this horizon complementarity says that consistent unitary QM applies. Could be wrong, could be right. But I think the idea is a compelling one.
Demystifier said:I would accept it if one could translate it into an observer-free language. For example, one can introduce Tomonaga-Schwinger formalism, in which time evolution Psi(t) (with this or that time t) is generalized to Psi[Sigma], which is a functional of an arbitrary spacelike hypersurface Sigma. If one could find SINGLE functional Psi[Sigma] that contains both complementary views of a black hole just by taking different Sigma in the same Psi[Sigma], then I would accept it.
valentin mano said:the event horizon is where the time stops and nothing goes further.if a singularity existed,it could not be detected,because no gravitation could be emitted by the black hole.That is what Susskind and Howking forgot.
sjweinberg said:Why don't you try jumping into a black hole and find out for yourself if you can detect the singularity.
MTd2 said:Because the result would not be reproducible since you cannot even compare results. It wouldn't be science.