tag:blogger.com,1999:blog-8666091.post8696491775215867256..comments2021-06-11T20:12:08.082+02:00Comments on The Reference Frame: Many worlds vs positivism and symmetriesLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger37125tag:blogger.com,1999:blog-8666091.post-46241620600834950402012-12-05T22:19:00.506+01:002012-12-05T22:19:00.506+01:00Dear Pablo, chances are high that I may misunderst...Dear Pablo, chances are high that I may misunderstand your question.<br /><br /><br />If you're asking about the correlations in positions where photons from a pair etc. are detected, they're generally detected in the opposite positions pretty much by momentum conservation. Well, the momenta are opposite and they get "classically" translated to the directions of future position, at least if they interact with the environment.<br /><br /><br />On the other hand, for electron-positron pairs, the entanglement of the momenta and the entanglement of the spins are two independent entanglements, mostly. So the spins are entangled in the same way regardless where you measure them and which axes you choose - for any relative orientation of the spin axis and the momentum.<br /><br /><br />For photons, the polarization vectors used for measurements must always be orthogonal to the momentum direction.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-60188425042981530322012-12-05T22:08:26.069+01:002012-12-05T22:08:26.069+01:00Dear Lubos, thanks for clearing up, I read too qui...Dear Lubos, thanks for clearing up, I read too quick and confused your "measuring to the left or right" with the electron emerging to the left or to the right in the experiment. Now everythinig is clear and it's easy to understand and accept, except one thing. We know the correlation results are independent of the axes chosen for the measure, but, what if the photons are located in any other point of the upper and lower conus, respectively? The situation would be the same, we get the same results and correlations indpendently of the axes chosen. What difference does it make with the photons emerging at the "entangling" points? The only difference I see is that in this case, the photon to the left will belong 50% of the times to the upper conus (spin "up") and 50% of the times to the lower conus. Is entanglement so a simple idea?<br />Thanks and cheersPablonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-13688303830422301572012-12-02T18:21:06.764+01:002012-12-02T18:21:06.764+01:00Dear Pablo, right, the correlation, whenever it...Dear Pablo, right, the correlation, whenever it's perfect, always follows from the angular momentum conservation law. But in local classical physics, it would simply be impossible to produce the correlation regardless of the choice of the axes that the experimenters choose for the measurement of the two photons. I have already explained why and have no time to do so again.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-30883924068436811482012-12-02T15:16:24.651+01:002012-12-02T15:16:24.651+01:00Hi Lubos, thanks for your explanation. However if ...Hi Lubos, thanks for your explanation. However if we go back to the Wikipedia article, the fact that the two photons have to show opposite polarization is always guaranteed, because of conservation laws and as they both come from one photon that gets split in the crystal. If one gets polarized up it belongs to the upper conus, and the other must get polarized down and belongs to the lower conus (and viceversa). I don't get yet why we need of quantum explanation for this case.<br /><br />I suppose you see this reasoning is wrong at some point. Would you mind explain where?<br /><br />Cheers and thanks for your blog.<br /><br />PabloPablonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-60021192822810970912012-12-02T12:55:45.701+01:002012-12-02T12:55:45.701+01:00Hi Luboš, could we win you to post a blog entry at...Hi Luboš, could we win you to post a blog entry at our site <br />http://positivists.org/blog/ on the question: "is positivism dead?" - or<br /> the question we do not know and you would find far more interesting?Olaf Simonshttp://www.facebook.com/olaf.simonsnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-70457200305720691822012-11-29T19:38:13.053+01:002012-11-29T19:38:13.053+01:00Steven Hsu, now at Michigan St. U., believes MWI i...Steven Hsu, now at Michigan St. U., believes MWI is true and that the proof (not given) is trivial.Robert Sykesnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-28707869969764377452012-11-29T07:49:39.639+01:002012-11-29T07:49:39.639+01:00They're not recent ideas, first of all, he beg...They're not recent ideas, first of all, he began with them 15 years ago or so, when I began as a grad student, and I have already won some bets that they would remain considered wrong.<br /><br />They're wrong and the paper you mention that tries to "apply" these wrong ideas to string theory is even more wrong. It contradicts pretty much every important principle here. Superposition principle of quantum mechanics, symmetries of the theory, everything.<br /><br /><br /><br />I know that it's tempting to think that a famous author name on the title page implies a correct or valuable paper but it ain't the case.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-9319534450165253502012-11-28T23:32:24.005+01:002012-11-28T23:32:24.005+01:00what do you think of the recent 't Hooft ideas...what do you think of the recent 't Hooft ideas on cellular automata and QM?<br />http://inspirehep.net/record/1122662sadpandabearnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-74093954297317382542012-11-27T19:54:44.137+01:002012-11-27T19:54:44.137+01:00Hola Pablo, thanks for your interest and kind word...Hola Pablo, thanks for your interest and kind words. The pre-existing classical correlation - referred to as "Bertlmann's socks" by Bell because they have the opposite color "objectively" even before we look - is enough to explain one particular correlation. However, the funny thing about the quantum entanglement is that the same photon pairs may show perfect (or very high) correlation in a different quantity you decide to measure.<br /><br /><br />For example, 2 electrons may have spin "up" and "down", respectively, or vice versa. And if you measure the spin to the left or right, they will show "left" and "right" or vice versa but never left-left or right-right. This correlation in "multiple quantities" already contradicts any conceivable local classical description.<br /><br /><br />For example, if your electron 1 is objectively "up" and the other is objectively "down", then you can derive that if the left/right measurements of the spin are done with both of these electrons, you will get left-left, left-right, right-left, right-right possibilities in 25% of cases each - but quantum mechanics shows that only left-right or right-left will occur, each in 50% of cases. The correlation survives to many more pairs of observables that can be measured than classical physics could explain.<br /><br /><br />Cheers<br />LMLuboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-55489649875899664112012-11-27T19:37:47.089+01:002012-11-27T19:37:47.089+01:00Hi Lubos, I did not study Physics but read your bl...Hi Lubos, I did not study Physics but read your blog regularly. I have a question that may be interesting for laymen like me. When searching in the Wikipedia for methods of generating entanglement, I saw the following figure in the article "Spontaneous parametric down-conversion":<br />http://en.wikipedia.org/wiki/File:SPDC_figure.png<br />The figure tells us that photons in the points are entangled. If you measure for example all the time the photon emerging at the left, you will see 50% of the times the polarisation "up" and 50% of the times the polarisation "down". However, could this case in particular be explained by "classic" means? Why not consider that in this case the photon at the left may come from the up of the down conus, 50% of the times, and its state was perfectly defined before detection? The final results are the same, don't they?<br /><br /><br />If any other layman can give an explanation for this (or Lubos himself, better) it would be great for readers of this blog like me (hope not to be the only silly reader...)<br /><br /><br />CheersPablonoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-86072318849894679942012-11-27T14:59:46.287+01:002012-11-27T14:59:46.287+01:00I meant identification of the external outgoing mo...I meant identification of the external outgoing modes with infalling modes which are outside the horizon by more than the Planck length. I wasn't referring to the external side, which can be arbitrarily far away. I was referring to the infalling side.Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65096723726719837562012-11-27T14:55:10.175+01:002012-11-27T14:55:10.175+01:00Sorry, this is a deep misunderstanding of yours.
...Sorry, this is a deep misunderstanding of yours. <br /><br /><br />Black hole complementarity relates two sets of observables, internal and external ones, and the external side has always included the degrees of freedom of the Hawking radiation, pretty much all of them – degrees of freedom very far away from the black hole. <br /><br /><br />If the identification involved just some "closer than Planck length" degrees of freedom near the black hole, the whole concept of "black hole complementarity" would be pretty much vacuous.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-19408805366944533652012-11-27T14:46:36.580+01:002012-11-27T14:46:36.580+01:00No, my surprise is that I always though complement...No, my surprise is that I always though complementarity is the identification of modes inside the horizon with external modes. At best, this might include modes up to a Planck scale distance above the horizon.<br /><br /><br />You're claiming something much stronger. You're claiming the identification also applies to infalling modes above the horizon by more than the Planck scale!!!Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-80495649598897419602012-11-27T13:55:47.184+01:002012-11-27T13:55:47.184+01:00Yes, they're the same degrees of freedom. That...Yes, they're the same degrees of freedom. That's what the term "black hole complementarity" meant in the first place.<br /><br /><br />Yes, locality is violated by the black hole evaporation – that's always been known to be a necessary condition for the information to get out of the black hole, as a simple look at the Penrose diagram shows.<br /><br /><br />However, the violation of locality goes to zero when one studies ordinary low-energy modes with wavelength much longer than the Planck length but much shorter than the black hole radius.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-32487978147243422112012-11-27T13:06:04.430+01:002012-11-27T13:06:04.430+01:00Dear Lumo,
want to become a Chieftain at Physics ...Dear Lumo,<br /><br />want to become a Chieftain at Physics SE too ?<br /><br />http://physics.stackexchange.com/election<br /><br /><br />I would vote for you :-) !<br /><br /><br />(Sorry for the off topic, I'm still reading this nice text)Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-61687008490799368392012-11-27T13:00:47.925+01:002012-11-27T13:00:47.925+01:00The infalling modes and the earlier radiation are ...The infalling modes and the earlier radiation are the same degrees of freedom???<br /><br /><br />This includes the infalling modes just before crossing the horizon. When they are still a little bit outside by more than the Planck scale.<br /><br /><br />This violates locality between degrees of freedom which are both outside the horizon by more than the Planck scale!!!Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-73696159638919754552012-11-27T12:47:05.195+01:002012-11-27T12:47:05.195+01:00No, this argument is wrong because the infalling H...No, this argument is wrong because the infalling Hawking radiation and the earlier Hawking radiation are described by the *same degrees of freedom* written in different, complementary bases, so the outgoing later Hawking radiation that is entangled with "both" is actually entangled with one set of degrees of freedom only, with one wife, and the monogamy holds perfectly.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-33371708972909173072012-11-27T12:37:25.376+01:002012-11-27T12:37:25.376+01:00If Alice detects no firewalls in this region, then...If Alice detects no firewalls in this region, then according to QFT in curved spacetime, there has to be entanglement between the outgoing Hawking radiation and the infalling Hawking radiation.<br /><br /><br />By the monogamy of entanglement, the outgoing Hawking radiation can't be entangled in any way with earlier outgoing radiation. This violates the assumption of strong scrambling.Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-70524192671491588702012-11-27T12:20:47.811+01:002012-11-27T12:20:47.811+01:00Excellent, then there can't be any contradicti...Excellent, then there can't be any contradiction involving objects constrained in this way and the equivalence principle guarantees that no observations done in the region you have described will deviate from observations done elsewhere in nearly empty space.<br /><br />If you want to reconstruct the observations of Alice done in that region, you need to follow all the observables all the way up to the actual event horizon. This was shown e.g. here http://arxiv.org/abs/arXiv:1208.2005<br /><br /><br /><br />The conclusion is obvious and expected - there can't obviously be any contradiction between the two viewpoints.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-45289744462002747362012-11-27T12:12:30.592+01:002012-11-27T12:12:30.592+01:00The whole point about firewalls is that
a) they ...The whole point about firewalls is that<br /><br /><br />a) they are located outside the event horizon<br />b) they are located at scales much greater than the Planck scale above the horizon.Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-81719827207766751212012-11-27T12:01:10.863+01:002012-11-27T12:01:10.863+01:00Dear Quantum, your instructions for Bob are ill-de...Dear Quantum, your instructions for Bob are ill-defined. What does it mean for an observer outside to "detect a firewall"? Tell me exactly what he should do before he decides to raise or not to raise his hand.<br /><br /><br />Otherwise he won't know whether he should raise his hand and your thought experiment makes no sense.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-47303051868689737982012-11-27T11:52:25.554+01:002012-11-27T11:52:25.554+01:00So, it's OK if Alice observes Bob raising his ...So, it's OK if Alice observes Bob raising his hand if her consistent histories are chosen, while Bob never remembers raising his hand if his consistent histories is chosen?<br /><br /><br />Alice is freefalling. Bob is an external observer. Bob has decided beforehand to only raise his hand if no firewall is detected.Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-16744994909895731082012-11-27T11:27:35.321+01:002012-11-27T11:27:35.321+01:00Each observer chooses his or her own account and n...Each observer chooses his or her own account and none of them is "objectively better than others". Indeed, this is the whole point and meaning of complementarity, and not only black hole complementarity.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-44244286968928189432012-11-27T11:15:20.915+01:002012-11-27T11:15:20.915+01:00What about black hole complementarity? Does it mat...What about black hole complementarity? Does it matter which observers have "consciousness"? If not, which observer's account should we choose?Quantumnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-24433912323298576092012-11-27T08:31:30.373+01:002012-11-27T08:31:30.373+01:00I shall not repeat it. I apologize. I actually was...I shall not repeat it. I apologize. I actually was intending to agree with exactly your view. <br />Robert Rehbocknoreply@blogger.com