The Reference Frame - Latest Commentshttp://thereferenceframe.disqus.com/The most important events in our and your superstringy Universe as seen from a conservative physicist's viewpointenThu, 20 Sep 2018 13:58:20 -0000Re: The Reference Frame: Frauchiger-Renner: QM is inconsistent with two Wigners and their friendshttp://motls.blogspot.com/2018/09/frauchiger-renner-qm-is-inconsistent.html#comment-4105713523<p>Before I read: I was just about to link this exact paper in a comment, to hear your thoughts about it.<br>This post is perfectly timed!</p>Niki Di GianoThu, 20 Sep 2018 13:58:20 -0000Re: The Reference Frame: Frauchiger-Renner: QM is inconsistent with two Wigners and their friendshttp://motls.blogspot.com/2018/09/frauchiger-renner-qm-is-inconsistent.html#comment-4105690644<p>From your description I can’t even grasp where the contradiction is supposed to arise, and I confess that I couldn’t get through the original paper because I got bored before getting to page three (btw, published in Nature Communications?! WTF?!)</p><p>I am making this comment because I am puzzled by this sentence of yours “Whether a measurement was performed is a subjective question”.</p><p>I would say that, while the *result* of a measurement is certainly subjective, *whether* a measurement was performed is an objective statement: without being too pedantic, A “knows” the value of B at some time t if psi_AB(t) is entangled in terms of orthogonal subspaces of A and a basis of eigenvectors of B.<br>Any friend of Wigner’s would agree about this, wouldn’t it?</p><p>PS: Upon re-reading, the puzzlement disappears, as you actually write essentially the same thing a few lines below... <br>Still, you may want to revise the offending statement :)</p>TylerDurdenThu, 20 Sep 2018 13:45:04 -0000Re: The Reference Frame: Why string theory is quantum mechanics on steroidshttp://motls.blogspot.com/2018/09/why-string-theory-is-quantum-mechanics.html#comment-4105380334<p>Dear David, it's a tiny variation of their previous nonsense that I discussed here (it uses exactly the same states of 2 bits):</p><p><a href="https://motls.blogspot.com/2018/04/frauchiger-renner-trivial-to-see-that.html?m=1" rel="nofollow noopener" title="https://motls.blogspot.com/2018/04/frauchiger-renner-trivial-to-see-that.html?m=1">https://motls.blogspot.com/...</a></p><p>They just rephrase it in terms of two Wigners and two Wigner's friends ;-) and as an inconsistency of QM. But I will probably write a separate blog post on it.</p>Luboš MotlThu, 20 Sep 2018 10:42:16 -0000Re: The Reference Frame: Why string theory is quantum mechanics on steroidshttp://motls.blogspot.com/2018/09/why-string-theory-is-quantum-mechanics.html#comment-4105377594<p>Thanks, Lubos. I’m trying to wade through it to spot the error(s)....</p>David ThorntonThu, 20 Sep 2018 10:40:34 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4105352691<p>I agree, good point, the explicit Lorentz symmetry - for QFT - was his motivation, too. I just don't see it too much as his personality trait.</p>Luboš MotlThu, 20 Sep 2018 10:25:45 -0000Re: The Reference Frame: Why string theory is quantum mechanics on steroidshttp://motls.blogspot.com/2018/09/why-string-theory-is-quantum-mechanics.html#comment-4105350496<p>I've read the abstract, the claim about the contradiction is clearly wrong, but I haven't read the body of the paper yet. Let me look.</p>Luboš MotlThu, 20 Sep 2018 10:24:27 -0000Re: The Reference Frame: Why string theory is quantum mechanics on steroidshttp://motls.blogspot.com/2018/09/why-string-theory-is-quantum-mechanics.html#comment-4105185402<p>Lubos, what do you think about<br><a href="https://www.nature.com/articles/s41467-018-05739-8.pdf" rel="nofollow noopener" title="https://www.nature.com/articles/s41467-018-05739-8.pdf">https://www.nature.com/arti...</a></p>David ThorntonThu, 20 Sep 2018 08:39:54 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4105072463<p>The problem is, there is no "analytical reformulation of a problem"! The product of machine learning / deep learning on a set of observed inputs/outputs is essentially an analogue/probabilistic computational system which can't be algorithmically described. <a href="https://ai.stackexchange.com/questions/1479/do-scientists-know-what-is-happening-inside-artificial-neural-networks/1530" rel="nofollow noopener" title="https://ai.stackexchange.com/questions/1479/do-scientists-know-what-is-happening-inside-artificial-neural-networks/1530">https://ai.stackexchange.co...</a><br>Quantum computing adds sheer computational power by more closely matching/physically modelling the observed phenomena, but it does nothing to uncover the underlying principle (express it mathematically). So, if we create a more compact "black box" with similar behavior to the observed system, isn't it a perfect case of "shut up and calculate"?</p>Max PotapovThu, 20 Sep 2018 06:59:36 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4104987278<p>Strange that you did not mention what was certainly the main motivation of Feynman, explicit Lorentz invariance. Up to this point, quantum fields had been defined from the canonical quantisation of classical field theory, which implied to choose a specific time direction. The first computations done, in particular for the Compton process, showed that nevertheless the result was, as it should, Lorentz invariant, but it was far from obvious. And the fact that the electromagnetic field give an infinite self-energy to the electron, albeit with a weaker divergence than in the classical case, was known before Feynman entered university. Explicit Lorentz invariance tremendously simplifies computation, since in the old ways, you had to consider all time orderings of the interactions.</p><p>Your view of mathematicians appears biased. Ramanujan did not wait for string theorists to propose that 1+2+3+...= -1/12<br>and the fact that the same result can be obtained by different methods gives strength to the result. But whenever one goes beyond the usual definitions, something has to give: not all properties of the sum or integral can be kept. In the case of Ramanujan sum, it is positivity, which is important because it implies continuity (if I make a small change to the series, the sum changes by a small amount). The infinities of quantum field theories are the base of anomalies, the fact that the quantum theory may not have all the symmetries of the corresponding classical theory. The best known ones are the chiral anomaly, a very strong constraint in model building, and the scale anomaly encoded by the renormalisation group equation, both Nobel primed discoveries. In some cases, you can follow physical intuition and use methods not yet validated by mathematics, but you must be aware that ambiguous result could be obtained and that, if no experimental confirmation is available, you are talking of possibilities, not truths.</p>Georges LombeThu, 20 Sep 2018 05:30:22 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4104964039<p>He does. Zeta regularization is a topic in the second linked lecture (05).</p>Edwin SteinerThu, 20 Sep 2018 05:03:09 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4104940850<p>I don't think so. Analytical reasoning and numeric parallel computing are mostly "orthogonal" disciplines, by which I mean that there is little overlap between their respective strengths and weaknesses. Isn't it therefore obvious that the largest progress is to be expected when <i>both</i> disciplines are pushed forward simultaneously?</p><p>The analytical reformulation of a problem can speed up numerical computations by many orders of magnitude. Vice versa, a supercomputer can get numerical results many orders of magnitude faster than a human physicist or mathematician. Why should humanity dispense with even one order of magnitude in what it can achieve, let alone with many?</p><p>Interesting shifts can occur at the boundary between these disciplines. In the end all such boundaries are imaginary lines that we draw to help our conceptual thinking. For example, computer calculations can gradually move from pure numerics to symbolic calculations, or even automated proof systems. One may have fun speculating about such developments but in my opinion it absolutely makes no sense to tell a specific discipline to "shut up and give up". If smart people still see much potential in a particular direction, let them the hell alone!</p>Edwin SteinerThu, 20 Sep 2018 04:35:45 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4104940810<p>Oh, I got it <a href="http://motls.blogspot.com/2018/08/theoretical-physics-remains-job-for.html" rel="nofollow noopener" title="motls.blogspot.com/2018/08/theoretical-physics-remains-job-for.html">motls.blogspot.com/2018/08/...</a></p>Max PotapovThu, 20 Sep 2018 04:35:43 -0000Re: The Reference Frame: Only strings, not branes, can be consistently quantized in the same wayhttp://motls.blogspot.com/2018/09/only-strings-not-branes-can-be.html#comment-4104795052<p>Dear Andy, things are still mostly green, nicely green, it's the last day of the summer. Šumava is pretty. But my pictures wouldn't differ much from those you can find:</p><p><a href="https://www.google.cz/search?q=%C5%A1umava&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708" rel="nofollow noopener" title="https://www.google.cz/search?q=%C5%A1umava&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708">https://www.google.cz/searc...</a></p><p><a href="https://www.google.cz/search?q=panc%C3%AD%C5%99&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708" rel="nofollow noopener" title="https://www.google.cz/search?q=panc%C3%AD%C5%99&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708">https://www.google.cz/searc...</a></p><p><a href="https://www.google.cz/search?q=hrad+%C5%A1vihov&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708" rel="nofollow noopener" title="https://www.google.cz/search?q=hrad+%C5%A1vihov&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&biw=1317&bih=708">https://www.google.cz/searc...</a></p><p>and billions of others.</p>Luboš MotlThu, 20 Sep 2018 01:38:48 -0000Re: The Reference Frame: Only strings, not branes, can be consistently quantized in the same wayhttp://motls.blogspot.com/2018/09/only-strings-not-branes-can-be.html#comment-4104619782<p>No need to be sorry, have a great trip. Are the leaves changing color? Pictures please.</p>Andy EverettWed, 19 Sep 2018 22:02:56 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4104262830<p>But he doesn't show zeta regularization right ?</p>guestWed, 19 Sep 2018 16:48:03 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103952956<p>Precisely! What surprises me is precisely this. Students follow very carefully the quite trivial building of the iteration without asking how came Richardson to think about such approximation. I’m not questioning the iteration</p>rafaWed, 19 Sep 2018 13:51:06 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103932712<p>I sent those (well-known) lectures in the context of divergent series. Regarding the Richardson extrapolation, Carl Bender loves it and uses whenever possible, and it is indeed impressive and memorable if you have ever successfully used it in research. Look at pp.6-7 of</p><p><a href="https://arxiv.org/abs/1703.05164" rel="nofollow noopener" title="https://arxiv.org/abs/1703.05164">https://arxiv.org/abs/1703....</a></p><p>for a very simple example in which the expansion in 1/N is obvious; there are zillions of such examples which is probably why Richardson devised his extrapolation. Once in my own research I had the decay</p><p>1/N^a (log N)^(1/2)</p><p>with a=0.086 (some transcendental number). The Richardson extrapolation would never help there, and without theory such a decay would never be guessed from numerics. The above example is a bit extreme, but more simple logarithms, terms like 1/N and 1/(N log N), and more complicated terms involving powers of logarithm, iterated logarithms [log(log N) etc.] routinely arise in asymptotic series and the Richardson extrapolation is impotent in those examples.</p>Pavel KrapivskyWed, 19 Sep 2018 13:39:40 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103898270<p>Nature won't care about our axioms. Nature is, in my limited understanding, inherently coherent (I just love this statement) and what we are doing is trying to uncover its coherence piece by piece. What this means is, even if we can't think of a way of defining the integrals Feynman could dance on, the mere fact that there *is* a result and that it is very precise is something mathematicians should think about. This isn't philosophy, this is physics: of course stuff does't make sense, if you haven't heard what Nature has to say about it.<br>Feynman had something like an intuition so profound it could actually turn playful rearranging of numbers into meaningful statements about physics. Feynman lived his entire life like he went through such things.</p><p>There's nothing I could really add to this post with a comment, for it is complete in infinite dimensions.</p>Niki Di GianoWed, 19 Sep 2018 13:18:05 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103847892<p>I have mixed feelings. Students are interested in following the formalism of the Richardson series. However, none of them asks the basic question, why did Richardson guess that a good approximation would be extrapolating as series in powers of 1 over N? :-) I wonder how do they think that idea came to Richardson's mind</p>rafaWed, 19 Sep 2018 12:50:10 -0000Re: The Reference Frame: Woit and probability in quantum mechanicshttp://motls.blogspot.com/2018/09/woit-and-probability-in-quantum.html#comment-4103662116<p>This is a bit belated, but anyway ....</p><p>Woits's later comments indicate that he really was trying to understand. But like so many he is overly tied to his own way of thinking about QM: for one thing ... fatal in this case ... he has trouble of thinking of verty large systems. And that's the KEY thing to use the brain for.</p><p>If you simply note that the "system" and "observation apparatus" are descried by a single complicated wave function, it all just works. You state with that big system in some, necessarily,</p><p>"hot" state ... you can't, in the age of the Universe, cool something respectably big to its absolute ground state. You then pick a wave function at some instant in time for that. Its a compound state vector, with "known" state coefficients, and a</p><p>(Gaussian or Lorentzian or any other smooth) distribution of coefficients around some mean energy.</p><p>That wave function then evolves via the time dependant Schrodinger equation. Note that its best to avoid thinking about photons hitting it ... (ordinary "old fashioned" perturbation theory is unwise because its so usually thought of in a multipole expansion, which does not apply to a large system .... it better to say "we better treat photons with real full field theory").</p><p>As the wave function evolves, of course "observables" of the large compund system evolve too. And then if you are stubborn you are back to the beginning. BUT .... some observables are "large". By that I mean they look at properties of macroscopic areas of the big blob that is the apparatus ... like whether a macroscopic part of it has moved, or accululated a large electric charge (e.g. LCD display).</p><p>The change to the apparatus caused by a small "system" hitting it (say a plane wave of electrons coming far enough away (kilometers) so that its later coherence size is centimeters) will depend on the exact state as the electron wave comes in (over a finite time, during which the apparatus itself evolves) and this will eventually "grow" into a macroscopic change.</p><p>Experiments and exact quantum calculations show that even large molecules will begin to show begin to show properties similar to "chaos" in classical mechanics given enough time.<br>This leads to the probabilistic appearance of macroscopic changes to the apparatus (i.e. it says "an electron hit such and such of the FET gates on the front side". )</p><p>Woit has a hard time with this explanation. Maybe you do, or don't. But its actually right. Its exactly Copenhagen. No funny business.</p>Doug McDonaldWed, 19 Sep 2018 11:07:31 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103586775<p>Feynman was a physicist with an extraordinary imagination and good mathematical abilities (maybe not as formal as Witten or Kontsevich). Certainly, his deep insights like his "joking" derivation of the Maxwell equations and his own graphical derivation of Kepler laws (seen, e.g., in The Character of the Physical Law). He was not perfect...It is known his skepticism towards string theory (Read the book edited and titled...Superstrings: a theory of everything? <a href="https://www.amazon.com/Superstrings-Everything-P-C-Davies/dp/052143775X" rel="nofollow noopener" title="https://www.amazon.com/Superstrings-Everything-P-C-Davies/dp/052143775X">https://www.amazon.com/Supe...</a> Certainly, I was surprised by his objections to string theory. Likely, not deep or anti-strings, but certainly he was old and critic with strings at the end -nobody is perfect).</p>Θ³Σx² - ∂³Σx² - ΘΣWed, 19 Sep 2018 10:25:34 -0000Re: The Reference Frame: Tim Gowers' conceptual thinking suckshttp://motls.blogspot.com/2018/09/tim-gowers-conceptual-thinking-sucks.html#comment-4103322384<p>Studies of savants actually reveal excellent working memory to be more shared than IQ. However, the evidence for genetic advantages for a skill couldn't be clearer than this: <a href="https://drive.google.com/file/d/1L_Cwi7DnsfgXHRFU7RJ5g9MbKF5GBrZx/view?usp=sharing" rel="nofollow noopener" title="https://drive.google.com/file/d/1L_Cwi7DnsfgXHRFU7RJ5g9MbKF5GBrZx/view?usp=sharing">https://drive.google.com/fi...</a></p><p>The more relevant argument is about the value of education and not eugenics.</p><p><a href="https://www.youtube.com/watch?v=FMtGvD9o0Oc" rel="nofollow noopener" title="https://www.youtube.com/watch?v=FMtGvD9o0Oc">https://www.youtube.com/wat...</a></p><p><a href="https://www.youtube.com/watch?v=xDKDuvhXNME" rel="nofollow noopener" title="https://www.youtube.com/watch?v=xDKDuvhXNME">https://www.youtube.com/wat...</a></p><p>See the references in the video description:<br><a href="https://www.youtube.com/watch?v=hhdd52DcfaQ" rel="nofollow noopener" title="https://www.youtube.com/watch?v=hhdd52DcfaQ">https://www.youtube.com/wat...</a></p>MD CoryWed, 19 Sep 2018 07:28:17 -0000Re: The Reference Frame: Team Stanford launches Operation Barbarossa against quintessencehttp://motls.blogspot.com/2018/08/team-stanford-launches-operation.html#comment-4103258322<p>Today Moritz, Retolaza, and Westphal uploaded a response to the 4th paper you listed: <a href="https://arxiv.org/abs/1809.06618" rel="nofollow noopener" title="https://arxiv.org/abs/1809.06618">https://arxiv.org/abs/1809....</a><br>Their conclusiuon reads:<br>"In this note we have attempted to succinctly review our<br>arguments in [1] which show that the most simple setup<br>exemplifying the KKLT mechanism where the K¨ahler<br>modulus is stabilized by a single gaugino condensate does<br>not evade the Maldacena-N´u˜nez theorem. As a consequence,<br>the warped anti-D3-brane fails to uplift the vacuum<br>energy to positive values. After summarizing the<br>10D argument we have reviewed the 4D parametrization<br>proposals made in [1] to meet the 10D results. Finally<br>we have expressed our disagreement with certain points<br>made in [2] (where [2] is the Kallosh+3 paper mentioned in this blog entry). Besides analyzing the 4D parametrization<br>proposals, a discussion of the validity of our 10D<br>argument is clearly necessary and must be carried out<br>elsewhere."</p>Harry WilsonWed, 19 Sep 2018 06:27:05 -0000Re: The Reference Frame: Bank of Korea is taking over Bitcoin Cashhttp://motls.blogspot.com/2017/08/bank-of-korea-is-taking-over-bitcoin.html#comment-4103254300<p>I really appreciate this post. Well described. Thank you so much...</p>Jamal MollaWed, 19 Sep 2018 06:23:03 -0000Re: The Reference Frame: How path integral mirrors Feynman's personality traitshttp://motls.blogspot.com/2018/09/how-path-integral-mirrors-feynmans.html#comment-4103209478<p>I never liked the name "principle of least action", because there are some cases where the maximum of the action is actually what occurs physically; I believe in optics this can happen. So better is "priniciple of stationary action".</p>Steven GreenWed, 19 Sep 2018 05:33:59 -0000