tag:blogger.com,1999:blog-8666091.post2760976061987039437..comments2021-05-03T21:54:48.969+02:00Comments on The Reference Frame: Are black holes surrounded by firewalls?Luboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger28125tag:blogger.com,1999:blog-8666091.post-17892947433521212822012-09-28T21:44:25.428+02:002012-09-28T21:44:25.428+02:00Just read the guest blog of Polchinski. Really exc...Just read the guest blog of Polchinski. Really exciting stuff going on,Mikaelnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-14897913971680707502012-09-28T21:05:56.607+02:002012-09-28T21:05:56.607+02:00Dear Lubos,
the lifetime may be finite but with a...Dear Lubos, <br />the lifetime may be finite but with a big enough black hole you can make it as big as you want. Physics suddenly breaking down in a binary way is just not plausible for me. The answers should become less sharp in a continuous way when making the horizon smaller. Also all the paradoxes of the falling observer appearing frozen at the horizon and the horizon appearing hot for the distant observer already exist for the Rinder horizon of an accelerated observer in Minkowski space.Mikaelnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-43854272095246199472012-09-24T21:24:09.970+02:002012-09-24T21:24:09.970+02:00thanksthanksGeorge Christodoulideshttp://www.facebook.com/george.christodoulides.71noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-29810784051909577022012-09-24T07:50:29.311+02:002012-09-24T07:50:29.311+02:00Dear Mikael, their quantum-information argument is...Dear Mikael, their quantum-information argument is highly nontrivial, even if it is ultimately wrong. It may look like a crackpot paper but it's not.<br /><br /><br />I think that string theory doesn't allow us to calculate observations by an observer inside even in principle. Because of the finite lifetime in front of her, there are no really exact observables known that could be computed and verified. As I said, I suspect that string theory has a good reason why it keeps silence about these matters.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-78378536980601654102012-09-24T07:28:39.490+02:002012-09-24T07:28:39.490+02:00Dear Rezso, I am confident that such solutions are...Dear Rezso, I am confident that such solutions are impossible in the real world, while the technical reason is probably that they violate an energy (positivity) condition. Alternatively, one may say that the warp bubble before and behind the spaceship is a gravitational wave and it is not allowed to move superluminally, another constraint you violate.<br /><br /><br />The local speed limit at "c" isn't really the only constraint that may be derived from a special relativity limit of GR. There's another ramification. If the spacetime is asymptotically Minkowski flat, then impulses in it can't propagate superluminally, either, whether or not you find an excuse in the form of modified local geometry.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-6182211571769840342012-09-23T23:17:38.462+02:002012-09-23T23:17:38.462+02:00Wow, Lubos. If it was not for Joseph Polchinski...Wow, Lubos. If it was not for Joseph Polchinski's name on the paper (and the names of several other serious physicists discussing it) I would think this is just a crackpot paper which does not deserve a minute of attention. We may just be falling through the Rindler horizon of some aliens with their space ship so we might all be burned to death soon. :-)<br />Does nobody have an idea how to calculate the experience of an infalling observer of a black hole within string theory or is the calculation to hard?Mikaelnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-76678679200249063822012-09-23T22:15:25.329+02:002012-09-23T22:15:25.329+02:00Dear George,
the Alcubierre warp drive is a solut...Dear George,<br /><br />the Alcubierre warp drive is a solution of General Relativity and it was proposed by the mexican physicist Miguel Alcubierre.<br /><br />The basic idea is that if you can create a special spacetime geometry (warp-bubble), where space expands behind a spaceship, and contracts in front of it, than it can lead to faster than light travel. Note that this solution doesn't contradict the basic principle of Einstein's theory, because the speed of light is never exceeded in the LOCAL reference frame. This means that a light beam within the warp-bubble would still always move faster than the ship.<br /><br />However, it is very very very hard ( if not completely impossible ) to create spacetimes like this, because it requires negative energy density to be present at various locations. But there is an experimentally verified quantum phenomena, the Casimir effect, where negative energy density exists in Nature, so the solution is not completely excluded.<br /><br />Cheers,<br />RezsoRezsonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-57106188065732628972012-09-23T20:57:02.129+02:002012-09-23T20:57:02.129+02:00an expert's opinion would be good.
http://mash...an expert's opinion would be good.<br />http://mashable.com/2012/09/17/warp-drive-may-be-more-feasible-than-we-thought/George Christodoulideshttp://www.facebook.com/george.christodoulides.71noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-50294371732320287262012-09-23T18:59:59.780+02:002012-09-23T18:59:59.780+02:00Dear Lubos,
thank you for the answer. However, I&...Dear Lubos,<br /><br />thank you for the answer. However, I'm still sceptical about the claim, that the evaporation of non extremal black holes is fully understood in string theory.<br /><br />1. I found the following Strominger paper from 1996 about "Nonextremal Black Hole Microstates":<br /><br />http://arxiv.org/abs/hep-th/9603109<br /><br />Below equation (1.1):<br />"We have not been able to obtain a stringy<br />derivation of the full expression."<br /><br />Below equation (3.7):<br />"We do not know of a systematic derivation of this formula using D-brane technology.<br />However miraculously it agrees with the Bekenstein-Hawking entropy calculated in the previous section from the area of the event horizon."<br /><br />As it seems, my view was not outdated in 1996. :)<br /><br />2. I looked at a recent CMS collaboration paper which is based on the ADD model (TeV scale quantum gravity).<br /><br /><br />"Search for Microscopic Black Hole Signatures at the Large Hadron Collider"<br />http://arxiv.org/abs/1012.3375<br /><br />It sais:<br />"The parton-level cross section of black hole production is derived from geometrical considerations ...... The exact cross section cannot be calculated without knowledge of the underlying theory of quantum gravity and is subject to significant uncertainty."<br /><br />It seems to me that black hole evaporation is only understood in the semiclassical approximation.Rezsonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-48973965489994732602012-09-23T17:53:31.146+02:002012-09-23T17:53:31.146+02:00Ah, I see---you took the word "quagmire"...Ah, I see---you took the word "quagmire" and conflated it into an all out attack by me on quantum mechanics and modern science.<br />Also, my reference to Galileo, if you actually read it for the sense, was to say that Galileo and Newton were instrumental in tying physics to actual experiments and hard data--ie, the scientific method. This is not a speculation by me, and is not either promoting Galileo or wanting to return to him (or Dirac, whom I do admire).<br />What you have done is to focus on one or two words and look for negative connotations.<br />Yes, when there is experimental evidence, direct or indirect, theory needs to conform to it. I was simply TRYING to point out that these wars over a firewall remind me of the old Greek philosophers throwing up speculative theories---that in modern astrophysics, like in high energy particle physics, more theories will be inaccessible to many direct or maybe indirect--this does not mean that I attack these theories at all if they have explanatory power like string theory does (and also I am not saying that string theory is inaccessible to confirmation either, like Woit, whose attitudes are deplorable.)<br /><br />I do apologize for flaming you, and admit that the way I wrote the initial post made it seem like QM just recently entered into black hole theory. But my post wasn't meant to be critical, certainly of Hawking, whom I admire extremely and with whom my supervisor co-edited two books and spent a sabbatical year with. Also, I in no way challenge your authority in scientific matters---I have, as I indicated, been out of any active physics activity since 1972. So please lighten up. Calling me Smolian or whatever is a total insult and will simply result in my packing it in. <br />Of course I haven't read any of the firewall papers---I would be incapable of following them at this point. I assume that you don't want to limit your audience to only active theoretical physicists.<br />As for being off topic, I don't think so. Just like me saying I am misunderstood, your saying "off topic" doesn't make it so...maybe a bit tangential.<br />Anyway, thats it for at least this post. I just got back from two weeks at Cambridge and am horribly jet lagged from delays, and the initial post was quickly written after scanning your blog post (no, I didn't pay enough attention to it) but I would suggest you assume I am an ally, and if what I say sounds stupid, see if you may be over-analyzing something or taking a word literally and missing nuance or irony or maybe misuse of a word due to fatigue.Gordon Wilsonhttp://www.facebook.com/gordon.wilson.54738noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-77990957708324430462012-09-23T16:47:42.504+02:002012-09-23T16:47:42.504+02:00Dear Rezso, the view is hugely outdated. It was al...Dear Rezso, the view is hugely outdated. It was already outdated in 1996. Only the first paper by Strominger and Vafa focused on a particular extremal, supersymmetric black hole. It has over 2,000 followups at this moment, many of which are computing thermodynamic properties (the right values) of near-extremal or completely non-extremal black holes, including rotating non-supersymmetric Kerr, and 7-parameter families, and infinitely many higher-order corrections to various black holes. Many things can't be calculated analytically. However, it's still possible to prove that AdS/CFT and Matrix theory contain non-extremal black holes as they should, and so on, and so on. There's no reasonable doubt that string theory describes thermodynamics of all black holes correctly (and all of their behavior outside the event horizon, to make the possible gap very explicit).<br /><br /><br />Yes, the mixed/thermal state of the Hawking radiation is just an approximation, and in any exact theory of quantum gravity, which realistically means in any implementation or vacuum of string theory we know today, it may be seen that a pure state always evolves into a pure state, whether there is a black hole or not. The detailed information about the initial state is imprinted into subtle correlations and entanglement between all the degrees of freedom.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-91282553472951584282012-09-23T15:41:09.520+02:002012-09-23T15:41:09.520+02:00There is no doubt we are all still blind individua...There is no doubt we are all still blind individuals when it comes to the subject here. Us layman more so then others. :)<br /><br />The real issue here is a progressive approach to the questions revealed by any theoretical approach and open discussions. This provides for framework and basis for that discussion.<br /><br />This has been historically verify by information <a href="http://www.eskesthai.com/2012/09/black-holescomplementarity-vs-firewall.html" rel="nofollow">already processed</a> so by laying out Susskinds thought experiment as Gedanken Experiments Involving Black Holes I have provided for similarity of discussions on that basis alone. Adding Seth Lloyd to the question of entanglement shows this progressive connection.PlatoHagelhttp://www.eskesthai.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-49650163990127740132012-09-23T12:10:29.165+02:002012-09-23T12:10:29.165+02:00Dear Lubos,
can I ask some questions about the st...Dear Lubos,<br /><br />can I ask some questions about the standard view on quantum black holes? <br /><br />You wrote:<br />"The black holes evaporate and, as seen in AdS/CFT and Matrix Theory, <br />it's still possible without any violation of the principles of quantum <br />mechanics."<br /><br />I thought that presently, string theory can only describe the thermodynamics of extremal black holes. But the temperature of extremal black holes is zero, so they don't evaporate. Or is this an outdated view? <br /><br />"So pure states evolve into pure states."<br /><br />If I describe the black hole evaporation in the "QFT in classical curved spacetime" framework, I think that the result should be a mixed state, because it is a finite temperature state. So am I right, that in quantum gravity, this low energy effective mixed state is produced by entanglement between low and high energy degrees of freedom? <br /><br />Thank you,<br />RezsoRezsonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-2359814696510768072012-09-23T11:56:49.982+02:002012-09-23T11:56:49.982+02:00Oh Lumo,
I'm so sorry that the discussion bel...Oh Lumo,<br /><br />I'm so sorry that the discussion below your very nice answer to my question has gone bad and I hope I did not make it worse :-/<br /><br />Since I'm here on TRF I always thought that Gordon likes and appreciates modern fundamental physics a lot too. And I still dont think that he is aligned with the sourballs who want the physics wisdom we have today to be thrown out of the window by a next Newton, Einstein, etc ... Maybe Gorden was just a bit clumsy in choosing his formulations (which I agree look partly some kind of similar to what Sabine Hossenfelder could say for example ...) to explain what he wanted to say. Maybe the dust between you and Gordon has to settle too a little bit too... ;-) ?<br /><br />Anyway, I think the discussion by papers in the Arxiv among your colleagues about the firewalls is interesting and I'm curious about if some deeper insights (about the microscopic degrees of freedom of a black hole or how the information can come out again for example) will result from this when the dust has settled :-)<br /><br />CheersDilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-17006694312996956542012-09-23T11:40:44.607+02:002012-09-23T11:40:44.607+02:00Any reaction of S. Hawking regarding this matter y...Any reaction of S. Hawking regarding this matter yet?Vladnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-89621099385900298302012-09-23T08:30:20.130+02:002012-09-23T08:30:20.130+02:00You were denigrating Hawking's – and many othe...You were denigrating Hawking's – and many others' – contribution in your comment containing the sentence:<br /><br />Now, with what Lubos has reviewed, we seem to be getting into a quantum (gravity) quagmire applied to black holes.<br /><br /><br />First, this uses a negatively sounding word "quagmire" for an exciting – and largely understood as of today – science about the quantum properties of black holes. Second, this sentence is saying that quantum properties of black holes are only starting to be studied "now" (your word) which implies that you think that what Hawking realized and people started to study in 1975 is either not a research of quantum properties of black holes or it should be ignored. You did ignore it in all your comments, which is why you're denigrating this pillar of the field. You did the same to string theory.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-80304772895938592672012-09-23T07:56:01.013+02:002012-09-23T07:56:01.013+02:00Dear Gordon, you always complain that you were mis...Dear Gordon, you always complain that you were misunderstood. How can it be misunderstood? You just repeated the same thing.<br /><br /><br />What does "playing with beautiful equations" have to do with answering what the infalling observer observes when he crosses the event horizon? Try to play with the Dirac equation or equations of string theory and answer the question. Others have tried. It hasn't been possible. The Dirac equation clearly has nothing to say about it and it seems that string theory doesn't allow one to calculate "exact values" of any observables for an infalling observer, either. One has to use different methods than just "playing with beautiful equations" to find out what happens when the horizon is crossed. For the required answer, something conceptual – and perhaps some equations – are missing so the equations would first have to be found if the answer boiled down to equations.<br /><br /><br />So why are you pumping this completely irrelevant junk about playing with beautiful equation etc. if you must know that this has nothing whatsoever to do with the essence of the question here? Why are you introducing Dirac or Galileo into these debates who have *absolutely* nothing to do with these matters and who wouldn't really understand any of the papers? And what about the ancient Greeks? WTF?<br /><br /><br />If a theory is "forced on us", it is no longer speculative, so this part of your comment is internally inconsistent, too. Ancient Greeks were never properly forced to accept any theory – their arguments have never really worked. Why are you comparing their situation with the situation in science, especially modern science? They have nothing to do with each other. The ancient Greeks weren't really doing science, except for some very elementary branches of it.<br /><br /><br />String theory is not only the "canonical" theory of quantum gravity but it's also the only mathematically possible consistent one. Never heard of us, huh!!?Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-32107202786469580722012-09-23T07:51:40.862+02:002012-09-23T07:51:40.862+02:00Where, oh where am I denigrating Hawking's con...Where, oh where am I denigrating Hawking's contributions? We referenced chats with him in our paper.<br />About slinging mud on modern science---total bullshit. I was trying to praise it, not bury it. And I am not suggesting we go back to Galileo or Dirac. I am beginning to understand how people get into frustrating disagreements with you.Gordon Wilsonhttp://www.facebook.com/gordon.wilson.54738noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-70706914245199265532012-09-23T07:45:59.041+02:002012-09-23T07:45:59.041+02:00I have never seen a more COMPLETE misunderstanding...I have never seen a more COMPLETE misunderstanding of what I have said ever, anywhere. Geez, Lubos. Get someone else to scan stuff before you rant. I was certainly not calling for a modification of the Dirac equation---I was suggesting the method he used---playing with beautiful equations and following the consequences, could prove a fruitful strategy. So it goes with ALL the rest.<br />Certainly I dont think that nothing quantum was done before the present and I didnt say that. I have never come across anyone so black and white as you, or someone who seems incapable of getting the sense of a post---I am not suggesting we go back to the Greeks---just suggesting that speculative theory not tied to experiment may be forced on us by inability to experiment. And the ancient Greeks were virtuosos at that.<br />For a smart person, you are pretty dumb.<br />Yes, string theory is the best candidate quantum gravity theory, but is it presently a canonical qgt? Gordon Wilsonhttp://www.facebook.com/gordon.wilson.54738noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-10557981637605906122012-09-23T07:02:19.148+02:002012-09-23T07:02:19.148+02:00Dear Gordon, physics switched into the research of...Dear Gordon, physics switched into the research of quantum physics of black holes in 1974, due to Hawking's groundbreaking discovery, so it's clearly invalid to suggest that "today" we are making the transition. <br /><br /><br />Also, many people today are working on analytic solutions to GR. One could even say that not much has changed about the composition of the research. So your suggestion that the 1970s were about the exact solutions and "today" is about the quantum properties is just bullshit. You may have only worked on the less revolutionary part of these GR-related insights but you were not all of GR research, sorry to say.<br />If you would dismiss even Hawking's discovery and similar theoretical ones just because they're theoretical ones, I couldn't disagree more because it's one of the greatest discoveries of the 20th century science.<br /><br /><br />I think it's complete nonsense, a Smolin-style nonsense, and a kind of insulting nonsense, that we have moved "back to the Greeks". Greeks were asking and (usually incorrectly) answering ambitious questions because they're the most attractive ones and they couldn't answer any questions really correctly, so among the possible questions to work on, they chose according to the audacity.<br /><br /><br />We are solving ambitious questions because the less ambitious ones have been genuinely solved and our knowledge and tools are marginally enough to attack the ambitious ones. This boundary moving towards the previously "hopelessly detached" questions is what defines the progress in science and it's been moving largely uniformly in the positive direction, so your suggestion that 2,000 years have been undone is just shit.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-68222140355021633902012-09-23T06:01:08.910+02:002012-09-23T06:01:08.910+02:00Yes, my rather long blather above does sort of boi...Yes, my rather long blather above does sort of boil down to "play with beautiful equations, and shut up and calculate". Einstein and Dirac and Heisenberg all did this, and the genesis of their insight often seemed like magic and not reason from experiment.Gordon Wilsonhttp://www.facebook.com/gordon.wilson.54738noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-37634057455918918872012-09-23T05:57:13.490+02:002012-09-23T05:57:13.490+02:00The study of black holes has had an interesting tr...The study of black holes has had an interesting trajectory. Back when I was working on them around 1971, people were looking for exact solutions to Einstein's equations for various matter and charge distributions, stationary or in motion...an example would be the Kerr solution for an uncharged rotating black hole. Another would be the eponymous solution :).<br />The next phase has been a transition to numerical relativity (Matt Choptuik, Franz Praetorius etc), still<br />focusing on classical GR, but with the evolution of computing power, various simulations are now possible.<br />Now, with what Lubos has reviewed, we seem to be getting into a quantum (gravity) quagmire applied to black holes. The situation is reminding me of ancient Greek philosophers who had untrammeled speculation not constrained by experiment...eg Parmenides,Zeno-- nothing changes, block time vs Heraclitus---everything changes...I am not criticizing this, just a comment. <br />An (admittedly uninformed) suggestion from me would be to emulate Dirac's invention of his equation and come up with models for quantum gravity and simply see where the math leads. If the equations lead to a contradiction or inconsistency, that would still be useful. If they don't seem to, explore what the results mean. We seem to have moved beyond the Descartes/Galileo/Newton model of experimental theoretical physics and back to the Greeks armed with much more powerful tools (math).Gordon Wilsonhttp://www.facebook.com/gordon.wilson.54738noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-15790058530407533612012-09-23T04:54:07.855+02:002012-09-23T04:54:07.855+02:00As an ignoramus (in respect of relevant details) b...As an ignoramus (in respect of relevant details) but nevertheless interested bystander, I enjoyed and felt satisfied reading this overview/analysis and its concluding comment [one that _I interpret_ to mean that the 'Firewall idea' is an anomalous hypothesis that ought to have self-incinerated before it was hatched ;>].Peter F.noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-74352224037370793412012-09-23T00:59:37.634+02:002012-09-23T00:59:37.634+02:00Seth Lloyd is a joke...Seth Lloyd is a joke...lemonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-76049025946603256042012-09-22T22:54:20.968+02:002012-09-22T22:54:20.968+02:00Holy crap I didn't know so many papers had bee...Holy crap I didn't know so many papers had been published on this. It will be interesting to look at it when the dust settles.twistor59noreply@blogger.com