tag:blogger.com,1999:blog-22973357.post8108281827844701750..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: The concordance model strikes backSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger42125tag:blogger.com,1999:blog-22973357.post-54848416417463343682016-10-30T07:50:39.997-04:002016-10-30T07:50:39.997-04:00Shantanu,
No, sorry, they aren't. I know, I t...Shantanu,<br /><br />No, sorry, they aren't. I know, I too find it annoying. Last thing I heard was that the editing turned out to be more time-consuming than expected and they've outsourced it and now who knows when it'll be done. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9775743448932836382016-10-30T07:47:48.446-04:002016-10-30T07:47:48.446-04:00Sabine sorry for the OT question. But are the vide...Sabine sorry for the OT question. But are the videos of the QG symposium in Frankfurt a month ago online? <br />I couldn't find it. Am very eager to watch the talksShantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79283849462449398122016-10-28T11:10:50.212-04:002016-10-28T11:10:50.212-04:00Elegant gravitation theory is untestable, paramete...Elegant gravitation theory is untestable, parameterized untestable, or Yukawa potential always short an observed decimal place. Postulated mirror-symmetric universes suppress willful violation testing, Cox recanted vs. Yang and Lee (and Madame Wu!).<br /><br />Matter universes cannot be <i>exactly</i> mirror-symmetric (Sakharov conditions). Milgrom acceleration over time and space is Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27345373546271251672016-10-28T10:59:02.299-04:002016-10-28T10:59:02.299-04:00"I've just finished a book on MOND, by th...<i>"I've just finished a book on MOND, by the way. Not because I'm convinced that it is true, but because I am still learning."</i><br /><br />Just to be clear, I've just finished <b>READING</b> a book on MOND.* :-)<br /><br />A review will appear in due course in <a href="http://www.astro.multivax.de:8000/helbig/research/publications/publications.html#Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85668220009766599352016-10-28T09:46:49.032-04:002016-10-28T09:46:49.032-04:00Phillip,
I'm totally with you on that. There ...Phillip,<br /><br />I'm totally with you on that. There might be good reasons against it. But if so, I'd really like to see them. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-55924837844945697982016-10-28T09:17:54.088-04:002016-10-28T09:17:54.088-04:00@Phillip kindly read this part of the paper "...@Phillip kindly read this part of the paper "With this in mind, the following could be considered as a more<br />serious challenge for MOND than the mismatches for individual<br />galaxies. We showed our comparisons with the MOND predictions<br />when using the simple interpolating function, since it gives more<br />consistent results for our sample than the standard one (cf. also<br />Stuart https://www.blogger.com/profile/12767480095489975264noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20423671957525031552016-10-28T09:05:55.455-04:002016-10-28T09:05:55.455-04:00"There's a double-standard here. CDM fits...<i>"There's a double-standard here. CDM fits galaxies only after a lot of parameter twiddling and tuning but then it somehow counts against a much simpler model if one of its approximations (please keep in mind everyone agrees that MOND needs a relativistic completion) doesn't immediately work out for all and everything. I find this very bizarre."</i><br /><br />Indeed. I am onPhillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34887284593143790562016-10-28T07:24:43.344-04:002016-10-28T07:24:43.344-04:00Stuart,
There's a double-standard here. CDM f...Stuart,<br /><br />There's a double-standard here. CDM fits galaxies only after a lot of parameter twiddling and tuning but then it somehow counts against a much simpler model if one of its approximations (please keep in mind everyone agrees that MOND needs a relativistic completion) doesn't immediately work out for all and everything. I find this very bizarre. <br /><br />Look, modified Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54971775801363864102016-10-28T07:15:14.810-04:002016-10-28T07:15:14.810-04:00piein,
Yeah, I'm pretty good at standing out,...piein,<br /><br />Yeah, I'm pretty good at standing out, though not always for the best reasons ;) In any case, I haven't spent a lot of time on this topic. I happen to know that there's a philosopher of science who wrote her thesis on MOND vs CDM (and it's really MOND, not modified gravity), which I think is very interesting, though maybe for a physicist not quantitative enough. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43657852015309353312016-10-28T06:38:31.127-04:002016-10-28T06:38:31.127-04:00Doc Hossenfelder says "Now in the above ment...Doc Hossenfelder says <b> "Now in the above mentioned paper the authors claim basically that in a numerical simulation they've done, a also reproduces some of the correlations of b. Problem is, they use a numerical model which has been produced to the end of generating galaxies that look pretty much like the ones we observe."</b><br /><br />This and the other statements you're Anonymoushttps://www.blogger.com/profile/17852247942652368610noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-44507419775164801412016-10-28T06:34:09.999-04:002016-10-28T06:34:09.999-04:00From the paper: "Also, while the slopes of th...From the paper: "Also, while the slopes of the mass density profiles inferred from galaxy dynamics show consistency with those expected from their stellar content assuming MOND, some profiles of individual galaxies show discrepancies."<br /><br />"Some show discrepancies" is not the same as "fails dismally".<br />Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-15334833988866745582016-10-28T03:36:27.532-04:002016-10-28T03:36:27.532-04:00Are you folks aware that MOND fails dismally when ...Are you folks aware that MOND fails dismally when it comes to rotation curves of early type galaxies dominated by population II stars? https://arxiv.org/abs/1606.05003Stuart https://www.blogger.com/profile/12767480095489975264noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74286854507569278412016-10-28T02:48:07.470-04:002016-10-28T02:48:07.470-04:00Thanks Sabine,
And sorry for the rather elementa...Thanks Sabine, <br /><br />And sorry for the rather elementary question. I was ultimately able to surmise that the use of the term 'dissipative' was in reference to the action of non-conservative forces. What threw me off was the use of the phrase "dissipative collapse of baryons". It just came across as so incredibly apocalyptic sounding. ☺ Nick Maiorinohttps://www.blogger.com/profile/12881730412761414391noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-42760685209281984432016-10-27T14:10:23.902-04:002016-10-27T14:10:23.902-04:00Dear Sabine,
OK, maybe I see what I want to see. ...Dear Sabine,<br /><br />OK, maybe I see what I want to see. <br /><br />With all respect, the question "which one is correct" does not imply that any is physically significant. (i.e. dark matter particles do not exist AND the current scents of modified gravity are only a trick in the equation without physical insight or enlightening principle to back it.)<br /><br />It can also be that akidbellehttps://www.blogger.com/profile/12292741599925116131noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74627483190664671372016-10-27T12:52:42.671-04:002016-10-27T12:52:42.671-04:00I guess this means that WIMPs and MACHOs are back ...I guess this means that WIMPs and MACHOs are back in play, since axions are much more amenable to the high density, strongly coupled, low temperature scenario implied by coherence in the Lambda CDM concordance model as suggested by the rotational curves.<br /><br />That should make a whole lotta people happy.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-29601006040527915272016-10-27T12:24:24.563-04:002016-10-27T12:24:24.563-04:00akidbelle,
Yes, you see what you want to see. Com...akidbelle,<br /><br />Yes, you see what you want to see. Compared to big bang/toe/gut scales these are low energy effective theories. What happens at the big bang is irrelevant for this discussion. What happens at the big bang might one day reveal a more fundamental explanation for either dark matter or modified gravity, but it doesn't remove the question which one is correct, right here, Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23861400716257575162016-10-27T11:52:28.162-04:002016-10-27T11:52:28.162-04:00Dear Sabine,
thanks for the reference; after read...Dear Sabine,<br /><br />thanks for the reference; after reading it, I understand that a) and b) are competing because no-one solves the main failure of quantum theory and GR, which is to explain the existence of a big bang. In facts, all I see (in both cases) is an attempt to minimal progress; essentially modelling without new physical understanding (- but maybe I see what I want to see). What doakidbellehttps://www.blogger.com/profile/12292741599925116131noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-48219657601767259842016-10-26T14:00:42.449-04:002016-10-26T14:00:42.449-04:00Ben: If you are reading this, do you know if your ...Ben: If you are reading this, do you know if your simulations or any other simulations can explain why the asymptotic centripetal<br />accelerations of Dark matter dominated systems is approximately constant (See Figure 3 of 1401.1146)?<br />I have asked this question to many people who do simulations and from what they told me, simulations cannot reproduce this<br />particular observation.Shantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51656885476846828672016-10-26T10:36:01.713-04:002016-10-26T10:36:01.713-04:00Gravitation? Two black hole mergers had immediate...Gravitation? Two black hole mergers had immediate equilibrium, small binding energy, no quantum or information anomalies. No frou-frou.<br /><br />Equivalence Principle (EP): The pendulum equation has no bob; Einstein's inertial elevator. Torsion pendulums have bobs. Their angular momenta are mirror-asymmetric pseudovectors. Einstein-Cartan-Kibble-Sciama gravitation: EP = true, achiralUncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-85294455493477255522016-10-26T09:59:23.185-04:002016-10-26T09:59:23.185-04:00akidbelle,
This might be a good starting point.akidbelle,<br /><br /><a href="http://relativity.livingreviews.org/Articles/lrr-2012-10/fulltext.html" rel="nofollow">This might be a good starting point.</a>Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70860299358255667912016-10-26T09:44:42.895-04:002016-10-26T09:44:42.895-04:00Many thanks Sabine for this long explanation.
Ple...Many thanks Sabine for this long explanation.<br /><br />Please could you tell me what to read for GR modifications at this scale?<br /><br />Best,<br />J. <br /><br />akidbellehttps://www.blogger.com/profile/12292741599925116131noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-84607913971964211452016-10-26T09:20:59.302-04:002016-10-26T09:20:59.302-04:00akidbelle,
Yes, lots of papers on this in a rapid...akidbelle,<br /><br />Yes, lots of papers on this in a rapid sequence. I was just reading Milgrom's one. In a nutshell, he says the same as I did in my post, but with more details and less politely ;) <br /><br />No, this doesn't mean that baryonic matter is also dark. <br /><br />It's roughly as follows: We know there's a discrepancy between the acceleration of stars in galaxies Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4658144267466406572016-10-26T09:15:46.869-04:002016-10-26T09:15:46.869-04:00Nick M,
Yes, "baryons" are basically no...Nick M,<br /><br />Yes, "baryons" are basically normal matter - stars and gas. Dissipative just means they take into account friction/heat transfer. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67258768752025912042016-10-26T08:34:28.109-04:002016-10-26T08:34:28.109-04:00Ah, there we go: similar analysis, done with EAGLE...Ah, there we go: similar analysis, done with EAGLE. General agreement with my paper, interesting that they <i>don't</i> see a redshift dependence though! It will be fun to tease apart the differences that lead to this.Anonymoushttps://www.blogger.com/profile/06291498347766250606noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-65768880385217749402016-10-26T04:46:50.117-04:002016-10-26T04:46:50.117-04:00Hi Sabine,
despite your efforts I am not sure I u...Hi Sabine,<br /><br />despite your efforts I am not sure I understand (or maybe there is too much smoke from various papers). Could the correlation mean that baryonic matter is actually "also dark"? (the only source term in the equations).<br /><br />If so (and if I understand..) it should be the only source of gravity terms except dark energy in the Friedman equations. Would that be a akidbellehttps://www.blogger.com/profile/12292741599925116131noreply@blogger.com