Black Hole Firewalls

Finbar

Yes but if the observer measures anything but the Minkowski vacuum this implies that there is some force (be it gravity or any other force) acting on them right? This is rather different from an inertial transformation. Also to measure the Unruh effect each observer must detect particles. So each observer is conducting an experiment. But these experiments are different! So i am not so sure that it's simply frame dependence.

MTd2

Susskind withdrew his paper

http://arxiv.org/abs/1207.4090

Demystifier

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.

Finbar

Wouldn't Susskind argue that what is true of black hole horizons is true also of Rindler horizons in Minkowski space? So all observers do not have to agree.

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.

Now if they both measure the same observable they have to agree on the eigen state. Horizon complementarity seems to give this up provided there is no way for the two observers can comunicate.

Demystifier

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.

Demystifier

Currently it is quite popular to withdraw papers on that issue. Harlow also withdrew it:
http://xxx.lanl.gov/abs/1207.6243

Finbar

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

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

Ok so it's really about causality.

So let's say that we have a path integral representation of the theory and that it is a functional Z[Sigma_i,Sigma_f] of the initial and final space-like hyper surfaces Sigma_i and Sigma_f. One may want these to be arbitrary. The restriction that horizon complementarity puts on Sigma_i and Sigma_f is that they must lie in the intersection of the causal future of some point p and the causal past some other point q. This is what is known as the causal diamond associated to p and q.

(See this paper for a better explanation
http://arxiv.org/pdf/hep-th/0010252v2.pdf )

The point of this restriction is that it does not rule out any experiment that can be preformed by any physical(causal) experiment.

So QM is not defined if we try to define states that aren't in some causal diamond. But this is fine since no experiment could ever measure such a state.

MTd2

http://arxiv.org/abs/1208.2026

Is Alice burning or fuzzing?

Borun D. Chowdhury, Andrea Puhm
(Submitted on 9 Aug 2012)
Recently, Almheiri, Marolf, Polchinski and Sully have suggested a Gedanken experiment to test black hole complementarity. They claim that the postulates of black hole complimentarily are mutually inconsistent and choose to give up the "absence of drama" for an in-falling observer. According to them, at least after Page time, the black hole is shielded by a firewall. This has generated some controversy. In our opinion a lot of this is caused by confusions stemming from an observer-centric language. In this letter we formulate the AMPS's Gedanken experiment in the decoherence picture of quantum mechanics without invoking any sentient beings. While we find that the objections raised by advocates of observer complimentarily are irrelevant, an interesting picture emerges when we take into account objections from the advocates of fuzzballs. We find that low energy wave packets "burn up" like AMPS claim while high energy wavepackets do not. This is consistent with Mathur's recent proposal of approximate complementarity for high energy quanta. Within the fuzzball proposal AMPS's firewall fits in nicely as the thermal bath that low energy in-coming quanta perceive.

http://lanl.arxiv.org/abs/1208.2005

Comments on black holes I: The possibility of complementarity

Samir D. Mathur, David Turton
(Submitted on 9 Aug 2012)
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who argue against black hole complementarity based on the claim that an infalling observer `burns' as he approaches the horizon. We show that in fact measurements made by an infalling observer outside the horizon are statistically identical for the cases of vacuum at the horizon and radiation emerging from a stretched horizon. This forces us to follow the dynamics all the way to the horizon, where we need to know the details of Planck scale physics. We note that in string theory the fuzzball structure of microstates does not give any place to `continue through' this Planck regime. AMPS argue that interactions near the horizon preclude traditional complementarity. But the conjecture of `fuzzball complementarity' works in the opposite way: the infalling quantum is absorbed by the fuzzball surface, and it is the resulting dynamics that is conjectured to admit a complementary description.

Finbar

Lenny's back!


Singularities, Firewalls, and Complementarity

Leonard Susskind
(Submitted on 16 Aug 2012)
Almheiri, Marolf, Polchinski, and Sully, recently claimed that once a black hole has radiated more than half its initial entropy (the Page time), the horizon is replaced by a "firewall" at which infalling observers burn up, in apparent violation of the equivalence principle and the postulates of black hole complementarity. In this paper I review the arguments for firewalls, and give a slightly different interpretation of them. According to this interpretation the horizon has standard properties, but the singularity is non-standard. The growing entanglement of the black hole with Hawking radiation causes the singularity to migrate toward the horizon, and eventually intersect it at the page time. The resulting collision of the singularity with the horizon leads to the firewall. Complementarity applies to the horizon and not to the singular firewall.
Almheiri, Marolf, Polchinski, and Sully conjecture that firewalls form much earlier then the Page time; namely at the scrambling time. I argue that there is no reason to believe this generalization, and good reason to think it is wrong.
For most of this paper I will assume that the firewall argument is correct. In the last section before the conclusion I will describe reasons for having reservations.

MTd2

Here is the link!

http://arxiv.org/abs/1208.3445

valentin mano

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.

valentin mano

ask me why the galaxies we observe,are accelerating.

sjweinberg

Why don't you try jumping into a black hole and find out for yourself if you can detect the singularity.

MTd2

Because the result would not be reproducible since you cannot even compare results. It wouldn't be science.

tom.stoer

wow, that's a convincing reason not to jump into a black hole ;-)