How was Poirot?

I did mean KK monopoles, I guess. What is a typical mass scale for them – inverse radius of compactification? If they are heavy, then the EOS is as you say – and I wonder whether it is possible for them to play a role of dark matter, if they are present in the bulk.

I guess the next question would clarify whether it is possible – what group are they charged with respect to? Is it just ordinary EM U(1) or some “hidden symmetry” U(1)?

Cheers,
Dmitry.

sorry, I realize that I did not cover Dejan’s talk well – just lost momentum closer to the end of the post. Would you be interested to write a guest post about this work?

Cheers,
Dmitry.

No need to apologize, really . And you are right, it was 5-6 years ago. But the talk was much more than just properties of 5D black holes.

About your last sentence, the existence of the hidden symmetry of the rotating 5D black hole characterized by the Killing tensor, separability of the equations of motion, non-existence of the stable circular orbits, properties of the principal null congruences, the existence of superradiance, classification to the Petrov type D class and many other things were actually shown by Frolov and Stojkovic.

Concerning the microstates, first, I guess that you wanted to use the term “KK monopole” rather than “KK instanton”. Second, the microstates are not “just” KK monopoles. A KK monopole is a terribly simple, featureless object. The KK monopoles can appear as geometric parts – or fibers – in a microstate, but they must still be multiplied by (or fibered over) a nontrivial manifold, at least a circle, that stores the information about the microstate.

Well, obviously, if the dS/BH analogy is good for the fuzzball intuition, the fuzzballs are outside your horizon volume or patch. They may be forced to converge to something even further, so that the counting gives you a finite entropy. It should be so because the entropy should be determined by the area of the emergent horizon only, and it is finite both for dS and BH.

Concerning the KK instanton cosmological question, let me assume that you mean KK monopoles. Well, I won’t say anything terribly interesting. KK monopoles are dual – and thus qualitatively equivalent – to ordinary electrically charged objects. They are just magnetically charged but the difference between electricity and magnetism is just a matter of S-duality, which can become very rigorous in N=2 or N=4 theories.

So for large enough observers who don’t care about the internal structure of the particle, KK monopoles are just like charged objects. Charged objects have a bizarre equation of state because you can’t really squeeze too many into a volume – they repel. You want to neutralize them. If you do so sensibly enough, you get the same dust as you do for normal electrons and protons. Not sure whether you can get something else.

It seems that my answer will be disappointing for you – but you tried to combine cosmology with KK monopoles which is a particle physics question, and I attempted to separate these two different disciplines again because they have almost nothing to do with each other in this case.

Sorry, going to watch Hercule Poirot.

Everything is corrected (apart of SM), love your language corrections (and even more – physics discussion). Thanks for your explanations of locality vs. non-locality in BHs, it is so much more clearer to me now after you presented it that way.

The pinhole explanation of the thermal spectrum in a gravity well is amusing but one must be careful not to confuse the full-fledged thermal curve with the grey body factors which have a similar ?gravitational well? origin. Quite generally, I believe it must be possible to intuitively explain why the BH radiation is thermal by an analogy with the pinholes, too.

Yes, and now I wonder how would one be able to estimate gray body factors using this analogy and whether there should also be gray body factors for the situation Loeb discusses (that is, strongly gravitating body but not quite yet a BH).

I have always agreed with the de Sitter – black hole analogy, where the interior and exterior are flipped. If we live inside, the Hawking (now dS thermal) radiation always gets reabsorbed by the horizon, making the dS space effectively constant in size, unlike an unstable BH, but otherwise most other things are analogous.

As I understood, his microstates are KK instantons, so if the analogy between dS and BH works literally (it does not have to, I guess, since dS horizon is observer dependent), the question is where are they in dS case?

I also have a related cosmology question to you. How do KK instantons look like for a 4-dim observer, is it just a gravitating matter with some equation of state? If yes, what is the equation of state?

Cheers,
Dmitry.

The victory of string theory is not going to be “finally” but rather “final”. What you learned were tons of “stuff”, not tons of “staff” which would be gravitationally equivalent to dozens of employees.

The accuracy of “56 microns” in the upper bound on the distance scale where new gravity-like effects appear looks more accurate than what one would rationally expect, and it is thus probably convention-dependent.

The pinhole explanation of the thermal spectrum in a gravity well is amusing but one must be careful not to confuse the full-fledged thermal curve with the grey body factors which have a similar “gravitational well” origin.

Quite generally, I believe it must be possible to intuitively explain why the BH radiation is thermal by an analogy with the pinholes, too.

The animations are cool. Equally cool are “ad hoc panels of tools” that I accidentally discovered in Windows by moving a zipped directory to the boundary of the screen.

Sumir (rather than Samir haha) and you: There are surely features of the phases in various BH-related events that became calculable in string theory – but you would have to define your agenda more precisely. Everything is quantum: what else could a sane physicist say.

I am not sure whether I understand your query about the relationship between coherence and decoherence (they are the opposites of each other), so let me try to say what I think you may have wanted to ask, and what the answer is, and why it’s still important that the world is quantum.

Whenever we legitimately use classical physics in the real world, it’s because the classical limit is applicable. Fundamentally, the world is always fully quantum but the (usually) simpler classical description becomes OK under certain conditions.

The classical intuition – with “classical probabilities” only – is valid whenever decoherence is fast enough, which occurs for sufficiently large, sufficiently strongly interacting (with the environment) physical systems after sufficiently long times (usually supershort are already enough). This interaction with the environment destroys the purity of states of the studied quantum subsystem, destroys the quantum coherence, and is therefore called decoherence. It’s the only mechanism by which classical physics becomes legitimate.

You may have wanted to ask whether decoherence doesn’t imply that QM may always be ignored for all questions about large objects such as large black holes. The answer is No.

Why? Because on the other hand, when we study the systems exactly, like with the microstates of black holes, we never encounter any decoherence because there is no separation to the system and the environment. The fate of microstates is exactly localized, coherence and interference is always possible, even with large objects, and information can get out of a black hole because all the classical intuition (including exact causality that would follow from classical or even semiclassical GR) fails in this precise description.

So yes, I kind of agree with your following answer. The decoherence results from an approximate description, analogous to coarse-graining – the separation to the environment and the main system is not the same thing as coarse-graining but both are approximate descriptions of a system.

Whether you’re entangled with a star depends on the state of both of you, and historically such an entanglement is likely if you share a common origin.

Sumir’s fuzzball philosophy really brings the unusual conclusion that one can’t really coarse-grain over Planckian distances only, in the presence of black holes. In reality, one doesn’t really need fuzzballs for this conclusion. The latter holds because the degrees of freedom get rapidly thermalized – and smeared over the event horizon. You can’t really “localize” qubits to small – or even Planckian – regions because the qubits quickly encode themselves to properties of the whole horizon. This inability to localize qubits is pretty much equivalent to the detailed microscopic nonlocality of the black hole microstate dynamics that is needed – and true – to remove the black hole information loss.

Even the membrane paradigm prevents you from localizing things – like charge – on the horizon. The localization and locality of dynamics reappears in the classical limit only, and you are not allowed to follow individual microstates if you want to be satisfied with this classical description.

I have always agreed with the de Sitter – black hole analogy, where the interior and exterior are flipped. If we live inside, the Hawking (now dS thermal) radiation always gets reabsorbed by the horizon, making the dS space effectively constant in size, unlike an unstable BH, but otherwise most other things are analogous.

I thought that the 5D BH classification had been completed by people like Reall, Elvang, Emparan, and others years ago. Maybe not.