tag:blogger.com,1999:blog-22973357.post2390019488723825350..comments2021-04-18T18:16:05.056-04:00Comments on Sabine Hossenfelder: Backreaction: Book Review: “Quantum Space” by Jim BaggottSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger25125tag:blogger.com,1999:blog-22973357.post-35730153758415235922019-01-20T13:45:42.956-05:002019-01-20T13:45:42.956-05:00As I'm sure all are aware, I have been "n...As I'm sure all are aware, I have been "notably absent" for a couple of days due to the fact that my "internet" was hauled off with a load of hurricane debris.<br /><br />Someone in the neighborhood... likely a physicist or other wealthy person who lives across the street on the lakefront... decided it was a good idea to make a debris pile on top of our local R. Taylorhttps://www.blogger.com/profile/10621243868815039607noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43069461413105583772019-01-17T04:23:37.343-05:002019-01-17T04:23:37.343-05:00naive theorist,
I am not in a bad mood, I merely ...naive theorist,<br /><br />I am not in a bad mood, I merely tried to answer the question that you asked. Now you are asking a different question. I think the book may be suitable for students who want to get a sense of what lqg is all about and for interested non-experts who want to see how lqg holds up against string theory. Though, as I mentioned, the book requires the reader to cope with quiteSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22068993550862404312019-01-17T04:02:00.798-05:002019-01-17T04:02:00.798-05:00bee:
you seem to be in a rather bad mood "ho...bee:<br /><br />you seem to be in a rather bad mood "how am i supposed to know...". i wasn't asking what the author was intending; i was asking who you thought the book would be suitable for. that's what i thought book reviews were supposed to mention. after all why do publishers send people free review copies of a book - because they like them or in hope of promoting sales of naivetheoristhttps://www.blogger.com/profile/00425164894020381981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-41539509660355991542019-01-17T03:33:27.778-05:002019-01-17T03:33:27.778-05:00"Einstein;s book popularizing his work on rel...<i>"Einstein;s book popularizing his work on relativity was, i think, quite accessible to the public."</i><br /><br />In a pun which doesn't translate directly, Einstein once remarked that, instead of gemeinverständlich, his book was gemeinunverständlich.<br /><br />(The pun is related to the similarly related meanings (no pun intended---wait for it) of "mean" in the sensePhillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75838046635273608792019-01-17T02:27:28.619-05:002019-01-17T02:27:28.619-05:00naive theorist,
How am I supposed to know what au...naive theorist,<br /><br />How am I supposed to know what audience the author intended? Judging by the publisher, mostly academics in related disciplines. Maybe students? I think that Smolin's book "Three Roads to Quantum Gravity" is more digestible than Baggott's. (Alas, it's also quite out of date now.)<br /><br />Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3937188382614336022019-01-17T02:08:18.755-05:002019-01-17T02:08:18.755-05:00bee:
your review passes over the question as to w...bee:<br /><br />your review passes over the question as to who is its intended audience? it can't be a person who doesn't understand "braids in the spin-foam." despite the author's 'attempt' to explain it. Einstein;s book popularizing his work on relativity was, i think, quite accessible to the public. but after reading "Quantum Space" i recalled the BBC naivetheoristhttps://www.blogger.com/profile/00425164894020381981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-17097624404915240252019-01-13T16:38:17.509-05:002019-01-13T16:38:17.509-05:00Sabine said:
"Baggott is reffering specifica...Sabine said:<br /><br />"Baggott is reffering specifically to Bianchi's calculation, which I commented on here. The brief summary (for what I recall) is that he circumvents these problems by not calculating the microscopic degrees of freedom in the first place"<br /><br />If LQG is not counting the microscopic degrees of freedom then what the point? At most LQG is reproducing the Udi Fuchshttps://www.blogger.com/profile/02529460830838964526noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20932124829515231542019-01-13T09:51:06.548-05:002019-01-13T09:51:06.548-05:00Lawrence,
"The idea was that maybe there is ...Lawrence,<br /><br /><i>"The idea was that maybe there is some prospect for quantum gravity or supergravity at TeV energy."</i><br /><br />Yes, and the argument for this was naturalness. As I already told you. If you don't believe it, look up the literature. Or read <a href="http://backreaction.blogspot.com/2018/12/how-lhc-may-spell-end-of-particle.html" rel="nofollow">this</a>, or Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58833871284400382422019-01-13T09:24:07.487-05:002019-01-13T09:24:07.487-05:00SH wrote No, it does not because there's no pa...SH wrote <i>No, it does not because there's no particular reason those extra dimensions need to be large. The only reason physicist thought this would be the case is naturalness.</i><br /><br />I think the idea of large dimensions was in part a sort of desperation. The idea was that maybe there is some prospect for quantum gravity or supergravity at TeV energy. The result from LIGO that over Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27971201971314586542019-01-13T08:03:50.436-05:002019-01-13T08:03:50.436-05:00Dr. A.M. Castaldo,
Thanks for catching that, I'...Dr. A.M. Castaldo,<br />Thanks for catching that, I've fixed it. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-10413103064660313092019-01-13T07:55:14.231-05:002019-01-13T07:55:14.231-05:00This comment has been removed by the author.Dr. A.M. Castaldohttps://www.blogger.com/profile/17988116835722393503noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-82989819748807144502019-01-13T00:54:22.062-05:002019-01-13T00:54:22.062-05:00Chris,
No, the book does not mention deviations f...Chris,<br /><br />No, the book does not mention deviations from Lorentz-invariance or the predictions you mention, which largely have fallen out of favor. It briefly comes up, or so I think, in the Q&A where Smolin explains why, ten years ago, he was more optimistic about the prospects of figuring out what's the right theory of quantum gravity. But it's not expanded upon. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20523571549403798252019-01-13T00:50:26.148-05:002019-01-13T00:50:26.148-05:00Lawrence,
Fwiw, they seem to have given up the id...Lawrence,<br /><br />Fwiw, they seem to have given up the idea that LQG leads to deviations from Lorentz-invariance and hence modified dispersion relations. That it fit badly with the data probably had something to do with it. <br /><br /><i>" Further, recent LIGO data indicates there is no leaking of gravitation due to extra large dimensions, and in fact this applies to small dimensions. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22512973754822145742019-01-13T00:39:50.766-05:002019-01-13T00:39:50.766-05:00Udi,
Baggott is reffering specifically to Bianchi...Udi,<br /><br />Baggott is reffering specifically to Bianchi's calculation, which I commented on <a href="http://backreaction.blogspot.com/2012/05/note-on-black-hole-entropy-in-lqg.html" rel="nofollow">here</a>. The brief summary (for what I recall) is that he circumvents these problems by not calculating the microscopic degrees of freedom in the first place but (in essence) calculating a Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79132638809894922082019-01-12T22:50:56.878-05:002019-01-12T22:50:56.878-05:00The book sounds interesting!
Does it touch at all...The book sounds interesting!<br /><br />Does it touch at all on the idea about how, with distant light sources, photons could take different paths through the LQG mesh and show slightly different arrival times? The idea was proposed some times ago, and I've always wondered what resulted.Wyrd Smythehttps://www.blogger.com/profile/06694506351266400927noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-37673422060375386562019-01-12T16:51:28.548-05:002019-01-12T16:51:28.548-05:00I found Baggott's book Quantum Space to be sca...I found Baggott's book Quantum Space to be scattered and lacking continuity. Perhaps my opinion is extra critical because this is my first exposure to loop quantum gravity I found LQG to be greatly disappointing nonsense. Anonymoushttps://www.blogger.com/profile/06444073442376283232noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23976080643833660472019-01-12T14:17:46.037-05:002019-01-12T14:17:46.037-05:00String theory has lots of structure, and some of i...String theory has lots of structure, and some of it may end up playing a role in physics. What is remarkable is that the bosonic string is in 26 dimensions, and this is also the size of the space of the Jordan 3x3 matrix systems of three e8's. This has the automorphism of the Monster or Fischer-Griess group, where of course that takes one into some deep math. How all of this stringy structureLawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70832841016498271932019-01-12T13:55:15.609-05:002019-01-12T13:55:15.609-05:00I never understood how black hole entropy can be c...I never understood how black hole entropy can be calculated in LQG considering that the Schwarzschild metric is not even a solution of LQG.<br /><br />From what I understand they assume that they have a black hole solution. Then they assume that this solution has a horizon and that the number of degrees of freedom is related the area of this horizon. Then they go through some complicated math to Udi Fuchshttps://www.blogger.com/profile/02529460830838964526noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-39949806079490127242019-01-12T13:38:34.795-05:002019-01-12T13:38:34.795-05:00It seems to me there are several possible reasons ...It seems to me there are several possible reasons why Baggott is so kind to LQG: maybe he believes it is the correct approach, maybe "the enemy of my enemy is my friend," also the dedication "To Carlo and Lee For entrusting me with your stories," or not.robhttps://www.blogger.com/profile/02291157129190067010noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-82682676369208258922019-01-12T12:36:09.017-05:002019-01-12T12:36:09.017-05:00Two problems with `quantum gravity':
1. Extra...Two problems with `quantum gravity':<br /><br />1. Extrapolation of known physics to much smaller scales. Take Maxwell's equations in vacuum as an example. All he knew was certain relations between the electric and magnetic fields, experimentally deduced by Faraday on scales on the order of a centimeter. Extrapolating these relations to the scale describing the propagation of light, Yehonatan Knollhttps://www.blogger.com/profile/09680318989713357978noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67171087373339706832019-01-12T11:45:05.686-05:002019-01-12T11:45:05.686-05:00dear bee,
can you upload videos on youtube on pro...dear bee,<br /><br />can you upload videos on youtube on pros and cons of Loop Quantum Gravity, Loop Quantum Cosmology , spin-form, and Loop Quantum Gravity-string theory mergers?<br /><br />the only other Loop Quantum Gravity done by a physicist thus far on youtbe is by don lincoln fermilabs. neohttps://www.blogger.com/profile/16769182614452171312noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-14544698283683839362019-01-12T10:54:56.832-05:002019-01-12T10:54:56.832-05:00I love the idea of background independence and gra...I love the idea of background independence and granular, discretized spacetime that LQG espouses. But the idea is burdened by the constraints in the Hamiltonian formalism (which I can't follow) and not Lagrangian formalism (which I can), while the Ashtekar variables used in the theory are completely incomprehensible to me. <br /><br />Even so, LQG sounds a lot better than string theory.Billhttps://www.blogger.com/profile/13243006930165511059noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73031609496095997612019-01-12T10:04:15.742-05:002019-01-12T10:04:15.742-05:00"removal of the big bang singularity" P..."<i>removal of the big bang singularity</i>" Physics suffers singularities, infinities, and absence of <i>S</i>_n symmetries (geometric chirality). It denies, writes math, then parameterizes versus observation. <br /><br />https://www.youtube.com/watch?v=1sdRBX_6PGo&t=2m13s<br />… Group theory says, "Tully-Fisher is not dark matter."<br /><br />https://physicsworld.com/Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85142258170792670832019-01-12T07:35:50.900-05:002019-01-12T07:35:50.900-05:00Francesca,
I'm referring to this. Baggott wri...Francesca,<br /><br /><a href="https://arxiv.org/abs/1406.2610" rel="nofollow">I'm referring to this</a>. Baggott writes quite a lot about string theory, but only mentions its problems. Then, when it comes to phenomenology, he forgets to say anything about string theory. Now, it would have been fine with me had he said nothing about string theory to begin with and just stuck with LQG, but theSabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-60931948695646005202019-01-12T07:18:48.901-05:002019-01-12T07:18:48.901-05:00Nice review Sabine! Two comments:
- I do not under...Nice review Sabine! Two comments:<br />- I do not understand your comment about Lorentz invariance, you maybe refers to old concerns. LQG is a gauge theory whose local symmetry is the Lorentz one. See here for instance: https://arxiv.org/abs/1012.1739<br />- Why does Baggott has to talk about string cosmology in this book? Does it help to understand fundamental cosmology? Does it help to Kecahttps://www.blogger.com/profile/07634024555578567896noreply@blogger.com