tag:blogger.com,1999:blog-8666091.post7666056264610248381..comments2021-05-03T21:54:48.969+02:00Comments on The Reference Frame: Insiders and outsiders debate: fuzz or fire?Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger38125tag:blogger.com,1999:blog-8666091.post-20119157487677152722013-09-20T16:33:09.068+02:002013-09-20T16:33:09.068+02:00Thanks, it's mine, at least I am not aware of ...Thanks, it's mine, at least I am not aware of anything similar sketched by someone else.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65640141750479852192013-09-20T16:17:00.693+02:002013-09-20T16:17:00.693+02:00I know nothing about anything relevant to this deb...I know nothing about anything relevant to this debate, but I really like the Mona Lisa analogy - in fact it's so good I have to ask if you took it from somewhere or is it originally yours?Łukasz Grabowskinoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-81394941829465372332013-08-31T16:49:08.486+02:002013-08-31T16:49:08.486+02:00I see, Lubos. Quite surprised to hear. I assume th...I see, Lubos. Quite surprised to hear. I assume then though that these time slices are not very well behaved, eg. they are no Cauchy surfaces.Mikaelnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-62980614393716285382013-08-31T15:47:00.238+02:002013-08-31T15:47:00.238+02:00Dear Mikael, no, for the Schwarzschild black hole ...Dear Mikael, no, for the Schwarzschild black hole in 4D (non-evaporating), for example, such slices do exist. It's not really *the* problem, you just were guessing and the guess wasn't right.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-71031254845249186372013-08-31T13:45:22.983+02:002013-08-31T13:45:22.983+02:00Dear Lubos,
I think the main problem with black ho...Dear Lubos,<br />I think the main problem with black hole interiors and quantum mechanics is that there exits no time variable which can provide global time slices which are valid both inside and outside the black hole.Mikaelnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-33301332939931973502013-08-29T09:35:55.770+02:002013-08-29T09:35:55.770+02:00One of the elements used by AMPS in their firewall...One of the elements used by AMPS in their firewall paradox argument, to convert the paradox from one excited quantum to an entire firewall, is mining black hole Hawking quanta via lowering a box on a string. In http://arxiv.org/pdf/1207.3342v1.pdf Adam R. Brown has shown some new limits on the rate at which this can be done, derived from the averaged null energy condition applied to the box and string (and if your equipment can violate the averaged null energy condition, you can trivially violate causality and clone quanta the Alcubiere way), which drastically reduce the rate at which quanta can be mined out of the black hole to one per black-hole light crossing time per string supporting your quantum mining apparatus. I'm uncertain what this does to AMPSs' proposed firewall, but I strongly suspect it will drastically reduce its intensity, possibly to down to one qbit per qbit of correlation that Alice carries in.Rogernoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-15513241822229279012013-08-28T13:34:53.912+02:002013-08-28T13:34:53.912+02:00Hi, this is not a subject that has been fully sett...Hi, this is not a subject that has been fully settled so there are no authoritative reviews with the final indisputable answers to everything. <br /><br /><br />Instead, there are research papers that contain work in progress and I have indicated over the years which of them are good, crisp, and important papers. They include Raju-Papadodimas, Maldacena-Susskind, and others that have been linked to. There exist no other, miraculously "more authoritative" papers or reviews of a sort. <br /><br /><br />Well, there exist older reviews in which some of the newest objections are ignored because they hadn't been raised yet. Those older reviews are sometimes more sensible than many papers written in the recent year - but despite this overall advantage, these reviews are still insufficient to address any of the last-year questions in any detail.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-6400510156130724222013-08-28T13:21:45.078+02:002013-08-28T13:21:45.078+02:00I am not completely ignorant in more abstract symb...I am not completely ignorant in more abstract symbolic constructions. I would enjoy reading some articles about that if you could recommend me a few. <br />Thanks a lot<br />Aandnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-41601430265534878242013-08-28T12:42:11.724+02:002013-08-28T12:42:11.724+02:00Dear and, your contributions are totally fine.
N...Dear and, your contributions are totally fine.<br /><br /><br />Non-relativistic QM with its action-at-a-distance potentials is an approximation to a local theory, quantum field theory, indeed. But quantum field theory is just an approximation to a more complete theory of the real Universe, quantum gravity or string theory, which is surely non-local again, at least in some sense and at least in principle (the effects on these non-localities for practically measurable physics are probably exponentially small), and to clarify what the sense is and what it's not is subtle and requires more than just words.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-71785239316545226612013-08-28T12:31:18.660+02:002013-08-28T12:31:18.660+02:00sorry, I hope you do not consider I over-write on ...sorry, I hope you do not consider I over-write on your blog, but I think I can say it clearer: quantum mechanics takes into account topological information which is generally not "local" so, considering this yes, quantum mechanics doesn't "demand" locality when doing calculations before calculating any observable results. Nevertheless, after calculating probabilities we do get local observable results. Allowing for the geometry to be incorporated in the quantization procedure does by all means make perfect sense to me but this will also be "before" one starts deriving results of actual measurements. Why should the procedure for obtaining predictions of observable phenomena be non-local in the generalized relativity sense and through what technique does one arrive at this?andnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-64082390955345743002013-08-28T11:45:34.669+02:002013-08-28T11:45:34.669+02:00I must admit I invest much passion in this discuss...I must admit I invest much passion in this discussion as I am willing to learn more about the subject. I nevertheless feel that the example on undergrad quantum mechanics and non-local potentials is rather unfortunate simply because nobody expects that kind of potentials to be anything else than approximations. Of course quantum mechanics can work with non-local potentials and you can construct some effective theories that are very nonlocal and some people do that in order to construct an "image" about some deeper purely quantum effects they ignored while going at lower energies. Is that the correct description of reality? Certainly, up to a given level, but beyond that you should work with "proper" quantum mechanics and the apparently non-local effects become local in the quantum interpretation. Let me try again to be clear: after one single measurement of one single photon going through a double slit aparatus you obtain one single outcome. This one is very local. After measuring many photons you obtain a staristics and some answers that are also very local although you need to "bend" some notions about locality to arrive at them... non-locality in the entanglement is actually no non-locality at all (sorry, I try to follow the official terms but sometimes they get mixed up). I tend to see it as the effect of the inclusion of the global "situation" in the calculation of probabilities. This kind of "fake" non-locality in the case of black holes is not really surprizing for me. What comes as a "surprise" is the statement that the same topological properties encoded in the quantum mechanics close to a black hole generate some "real" non-localities like those obtained in undergrad quantum mechanics or effective theories. How can you say these are "real"? Could they just be a result of our lack of information about an underlying local theory? I think it is hard to go beyond a naive combination of general relativity and quantum mechanics and indeed most of the discussions about this subject are speculations... Please, whenever you find some time, tell me all aspects that you consider wrong in what I say. I would appreciate that and try to improve.<br />Thanks a lot! <br />Aandnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-70746873652005665052013-08-28T11:18:46.318+02:002013-08-28T11:18:46.318+02:00Dear and, I am partly happy, partly unhappy. There...Dear and, I am partly happy, partly unhappy. There are statements in your comment I agree with, statements I disagree with, and the purpose of this mixture isn't quite crystalized in my eyes. What do you want to say?<br /><br /><br />Wave functions aren't observable waves, indeed. <br /><br /><br />Quantum mechanics is compatible with locality but it's not true that quantum mechanics is inevitably local. There are local quantum theories, like QFT; there are non-local quantum theories, like undergraduate textbook non-relativistic quantum mechanics that is non-local because its potentials act at a distance. This non-locality has nothing to do with the explanation of the entanglement because the interactions are pretty much turned off once the subsystems are entangled. But it's still true that the interactions make this theory (non-relativistic QM) non-local.<br /><br /><br />It's wrong to mix locality with QM which are two independent classes of constraints. In particular, the locality in black hole backgrounds is subtle and subtly violate. This does *not* contradict quantum mechanics in any way. It only contradicts special relativity - and its naive application within general relativity (that may be accurate classically but is not accurate quantum mechanically).Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-7890594925684098562013-08-28T09:31:21.296+02:002013-08-28T09:31:21.296+02:00Dear Lubos,
I am happy we don't "really&...Dear Lubos,<br /><br />I am happy we don't "really" have any subject we could disagree upon: as far as I see the quantum nature manifests itself in the way we calculate probabilities. This being said, quantum mechanics implies the calculation of probabilities while considering all the amplitudes that are possible to happen. But please note that the wavefunction (or the amplitudes) are not physically "real". Many people do make this mistake and I hope you don't do it as well... Now, my statements (which may be as well wrong): when performing a set of experiments and obtaining a statistics one obtains a glimpse on the "global" structure of the experiment, namely on its topological structure (see the Bohm Aharonov effect but also the EPR effect etc.). These effects do not violate "locality" or "causality"... they just redefine our understanding about locality in other terms, beyond simply Lorentz symmetry (although Lorentz symmetry is perfectly valid in these cases when space-time is flat ;) ). Note that topological effects are not restricted by distance... actually you do not need a metric space to define a topological space, but this is just a parenthesis... Gravitational fields redefine again what we understand under "locality" and we gain new ideas about how to understand it. It is, as far as I see, a main idea of the EPR=ER duality that one cannot gain "in reality" any information in a non-local way. I definitely agree that in order to do some computations you have to take into account some sort of "topological" or "global" results about space-time but that means you are violating locality only at the level of your calculations, in a "non-observable" way. What I want to say is that one can extend the concept of locality such that one incorporates these "non-observable" effects. Quantum mechanics *is* a local theory (how much I like to underline words with stars ;) ). The "non-local" effects are simply extensions that allow us to do some calculations taking in some way or another into account global effects when obtaining observables. They do not appear in physical measurements at all. I have no problem in allowing specific paths in a path integral do strange things close to a black hole etc. as long as these effects add up into something that corresponds with the observable reality and observable quantities. Note, that I do *NOT* refer myself to "classical" physics. Classical physics is not correct physics. It is just considering one single path, which obviously is wrong. I refer myself to measurability. Measurability does *NOT* imply classicality and this is, I hope, clear from arguments about the double slit experiment and so many others. Fact is, we do not measure one path in the path integral. We measure one outcome. Global effects do seem sometimes "non-local" but they appear only after calculating the probabilities and obtaining a statistics. They in fact are *not* non-local simply because we do not measure anything that is non-local (this is of course no good argument). Whatever *seems* non-local is, after a better understanding, incapable to produce any measurable non-local effect. What happens if one "jumps" into a black hole and tries in this way to violate locality is for me unclear, although I tend to agree with the EP=EPR conjecture. This being said I think the black hole problems will re-formulate our intuition about locality rather than abolish it at all... but this opinion has only a historical justification. <br /><br />Aandnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-81300629105418670432013-08-27T18:55:07.253+02:002013-08-27T18:55:07.253+02:00After having read your comment twice, I still don&...After having read your comment twice, I still don't understand what you find paradoxical about it.<br /><br /><br />In the ER-EPR correspondence, the reason is obvious: the Hawking radiation isn't quite "faraway" from the black hole interior - they are actually very close to each other if you go through the Einstein-Rosen bridges. So if you assume the right topology and geometry of the spacetime, this action not only refuses to violate locality badly: it doesn't violate it at all. It only violates the locality that one would deduce from a different, wrong spacetime topology.<br /><br /><br />The unitary transformation performed on the early Hawking radiation has to be extremely convoluted to achieve their "clear and readable" for the black hole interior. But if it's done, it's done.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-51712383005013685912013-08-27T18:43:59.500+02:002013-08-27T18:43:59.500+02:00Dear and,
quantizing a "classical law forbi...Dear and,<br /><br /><br />quantizing a "classical law forbidding some process" *does* mean to say that the process is quantum mechanically allowed, it's just unlikely. This *is* how quantum mechanics always works.<br /><br /><br />Some classical "forbidding laws", like the conservation laws, have to remain exact in the quantum theory. Others, like the impenetrability of a classically inaccessible potential wall - and similarly the wall separating the black hole exterior from the interior "causally" - are deformed so that they approximately (and practically) work but strictly speaking, they don't.<br /><br /><br />Such classical assertions are "broken" by quantum mechanics because there's no fundamental principle that would imply that they should remain perfectly valid. That's what quantum mechanics routinely does: certain conclusions derived from classical physics are just wrong in general!<br /><br /><br />LMLuboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-24601465953958603882013-08-27T15:55:13.591+02:002013-08-27T15:55:13.591+02:00Hi Lubos, in your argument for why (4) is not para...Hi Lubos, in your argument for why (4) is not paradoxical, you seem to overlook one point. Namely, it doesn't have to be Alice herself who applies the unitary to the Hawking radiation. Indeed, if we imagine a sphere of photodetectors surrounding the black hole and routing the Hawking radiation to a quantum computer, and Alice well in the interior of the sphere, then the decision about what Alice should experience when she falls through could be made in a region distant from Alice (unless you want to argue that Alice's backreaction would always screw things up, but I guess that argument would need to be made separately). So in particular, Alice could experience a "firewall" (or not) when she falls through, depending on decisions far away from her. So, this could be considered "superluminal signalling," except that you have to want the superluminal message *really* badly -- badly enough to jump into the black hole to get it, and then not be able to tell anyone outside the hole! (This implication is made explicit by Maldacena and Susskind, in the ER=EPR paper that you've said so many positive things about.)Scott Aaronsonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-72495824333024187332013-08-27T15:30:44.837+02:002013-08-27T15:30:44.837+02:00ok, maybe I am not so clear so here, maybe a bette...ok, maybe I am not so clear so here, maybe a better idea about what I try to say: consider you want to "glue" together the local solutions of the quantization problem and obtain a sort of geniune deformation of the algebra of the observables in such a way that you consider the non-classicality of the geometry implicitly and obtain a complete formulation with a modified (deformed) expression that keeps being local and causal but in a "deformed" way. I am mainly trying to bring to your attention that deformation quantization and sheaf cohomology may be of some use in this problem... but I admit I am pretty vague here and now...andnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-38848731365865390992013-08-27T14:53:18.081+02:002013-08-27T14:53:18.081+02:00I certainly agree but even when the spacetime geom...I certainly agree but even when the spacetime geometry is a dynamical variable and one has to incorporate it as well when "quantizing" the theory, microcausality just changes its form (deforms somehow becoming more general). Why should we assume, in the place of a modified (quantum) form of the causality a "breaking" of it? The combination of extremely curved and dynamical (quantum) spacetime geometry may result in a modified expression for locality that looks to us as "nonlocal" but, in fact, may be very local and causal nevertheless, but maybe following another interpretation... just speculating, of course...andnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-62139756251527942242013-08-27T12:29:11.552+02:002013-08-27T12:29:11.552+02:00Very interesting as always – I appreciate theses a...Very interesting as always – I appreciate theses are thought experiments to understand the interior of the event horizon, however if we use persons as observers surely the model should still remain realistic. If no particles can escape from within the event horizon because nothing can move agains the strength of gravity and therfore no blood can move from Alice’s heart to her brain and she’ll be long dead before she gets spagetifiedzbyneknoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65883708044025744292013-08-27T12:28:13.284+02:002013-08-27T12:28:13.284+02:00Dear and, right but one must be very careful what ...Dear and, right but one must be very careful what "microcausality" may mean quantum mechanically, especially in quantum gravity where the spacetime is dynamical.<br /><br /><br />Classically, things are easy: you only influence things along null or timelike geodesics in the future. Quantum mechanically, particles are inevitably delocalized by the uncertainty principle. Low enough energy particles may be forced to have wave functions spread over the curvature radius. Too high energy particles are modifying the position of the horizon so you can't assume that they respect the "pre-existing" causal structure derived from the geometry, because of the backreaction. So only some intermediate energy scales respect causality and only microscopically. The energy quanta comparable to the Hawking temperature in energy may be expected to maximally violate the naive causality.<br /><br /><br />The issue that you implicitly overlook in between the lines is that the geometry is a dynamical quantum mechanical variable, too. So to say that "two points" in the spacetime are spacelike separated may be a very subtle thing and with usual definitions, quantum mechanics doesn't guarantee that this may be satisfied with 100% probability. There's always some probability amplitude that the horizon is actually much further from the expected location etc. Consequently, there's always some probability that the points may exchange information.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-34127354382927699292013-08-27T12:24:26.343+02:002013-08-27T12:24:26.343+02:00I know I am wrong but I would want to understand h...I know I am wrong but I would want to understand how... any papers?andnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-27618511601493161332013-08-27T12:22:35.600+02:002013-08-27T12:22:35.600+02:00I may be a bit confused but maybe it's just me...I may be a bit confused but maybe it's just me: microcausality, as far as I know, but correct me if I am wrong, should be valid even when Lorentz symmetry is "broken" by the curved spacetime. Now, as I think, causality and locality are related. What do you mean by weak non-locality on strongly curved space-times? How comes to even a "weak" violation of locality? I probably am confused right now...andnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-20996274395395522182013-08-27T06:00:55.002+02:002013-08-27T06:00:55.002+02:00It's slightly more complicated than that. Alon...It's slightly more complicated than that. Along the radial timelike direction in a black hole, causal information flows (from a Cauchy surface in the past of the external spacetime before the collapse of the black hole) go radially inwards for infalling observers/matter, have a very complex interaction with the singularity that apparently thermalizes them and diffuses them along the entire (locally spacelike) extent of the singularity, and then propagte/tunnel radially *outwards* again to the event horizon where they participate in Hawking radiation production to produce the observed Harking radiation. So in the interior of the black hole, there are causal contraflows radially both inwards and outwards. All the q-bits that ever fell into the black hole get mixed together (mostly at the singularity), and they all come out gain in the black hole evaporation. This isn't quantum cloning, it's just reflection -- you can measure the same q-buts twice, if you measure them (or anything entangled with them) before they fall in, you fully centangle your self with the corresponding data about what has/will Hawking radiate out. This doesn't allow you to construct semiclassical paradoxes because the singularity scrambles everything so thoroughly, and of course at the quantum level there are no paradoxes because the sum-over-histories only includes self-consistent histories.Rogernoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-43272207627491167402013-08-26T16:47:26.216+02:002013-08-26T16:47:26.216+02:00From an essentially primal theory based position o...From an essentially primal theory based position of overview/outlook&opinion on this phenomenon (i.e. of strangely 'straying' physicists): <br />These people are likely to be responding in a roundabout way to some sufficiently similar predicaments early in their lives. Am not sure if it is a long and drawn-out birth or a dearth of touch thereafter, or both, but I think that for some such people (they are at least formerly formidable theoretical physicists) being faced with scientifically solidifying (growing increasingly theoretically tight and immutable) logic about these aspects of fundamental physical reality can cause their still present in relevant "conditioned-in" neural form predicaments to have a subliminal misconception-forming effect on how they think about these things - an effect that may very well be impossible to avoid or remedy by the use of theoretical physics type logic.Peter F.noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-61851290476675444622013-08-26T14:19:56.765+02:002013-08-26T14:19:56.765+02:00I actually meant a review paper.Some of us are too...I actually meant a review paper.Some of us are too old and too lazy to make a major effort to try to understand the original papers!!! But we would like to understand the controversy little bit more analytically. Is there a review or summary paper written by someone else? Or a detailed blog?Thanks.kashyap vasavadanoreply@blogger.com