tag:blogger.com,1999:blog-22973357.post2516272568202160293..comments2021-01-19T01:06:03.622-05:00Comments on Sabine Hossenfelder: Backreaction: Modified Gravity and the Radial Acceleration Relation, AgainSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger93125tag:blogger.com,1999:blog-22973357.post-25645772785691857832019-04-30T22:20:32.472-04:002019-04-30T22:20:32.472-04:00Curious to know how your model compares against th...Curious to know how your model compares against this new dataset of DD and LSB galaxies that doesn't obey the relation proposed by McGaugh et. al. https://arxiv.org/pdf/1810.08472.pdfPankaj Bhambhanihttps://www.blogger.com/profile/11060703897445774215noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27417553643679217112019-03-21T05:17:10.063-04:002019-03-21T05:17:10.063-04:00StrangeRep,
No, it is not. This is patently obvio...StrangeRep,<br /><br />No, it is not. This is patently obvious because I do not use the constraint in Eq (5) and in return the Zlosnik et al approach does not have the coupling that I have. They get the coupling from using Eq (5). <br /><br />The reason I don't have that is, as I have said several times, that my model is a covariant generalization of Verlinde's model, not more and not Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67072048997717947622019-03-21T04:10:56.766-04:002019-03-21T04:10:56.766-04:00Hi again Sabine,
I'm just wondering whether y...Hi again Sabine,<br /><br />I'm just wondering whether you've noticed Milgrom's update to his Scholarpedia MOND article (http://scholarpedia.org/article/The_MOND_paradigm_of_modified_dynamcs) in which he says that your MOG theory is in fact a rediscovery of the relativistic Einstein-Aether theory of Zlosnik et al (arXiv:0607411). Do you agree with Milgrom's assessment?StrangeRephttps://www.blogger.com/profile/04613522691941941832noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-56462426315170960892018-09-01T08:52:32.151-04:002018-09-01T08:52:32.151-04:00Dear B,
I would like to start with: the world hat...Dear B,<br /><br />I would like to start with: the world hates you now, but the universe supports you. Keep going! <br /><br />I was wondering, does accepting emergent gravity affect the analysis of the history of the universe, and the Big Bang? I think analysis in that direction may be valuable. I'm merely suggesting, I don't "need" the answer.Anonymoushttps://www.blogger.com/profile/07942386330463923282noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-77820665059372110682018-05-24T16:04:04.004-04:002018-05-24T16:04:04.004-04:00Hi Sabine,
It has been more than a year since it ...Hi Sabine,<br /><br />It has been more than a year since it was suggested in the paper arxiv.org/abs/1610.06183 that we could look at the redshift-dependence of the galactic rotation curves to tell apart modified gravity from dark matter. You also repeat the same suggestion in this paper. <br /><br />But I'm wondering: Why has nobody looked at it so far? It sounds like a low effort & highAnonymoushttps://www.blogger.com/profile/01386838956887216223noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-41740010096970288532018-04-11T08:21:00.430-04:002018-04-11T08:21:00.430-04:00m-artins,
I know the paper, thanks. We're loo...m-artins,<br /><br />I know the paper, thanks. We're looking into that.<br /><br />I don't see the purpose in making unnecessary statements. If an assumption isn't needed to arrive at a conclusion I prefer not to make it. The Lagrangian I'm using may or may not be a superfluid condensate of some particles. I don't know. I think it's plausible is all I am saying. But at Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88696547276468584042018-04-11T07:56:54.700-04:002018-04-11T07:56:54.700-04:00Bee, the newer paper includes dwarfs, and shows so...Bee, the <a href="https://arxiv.org/abs/1610.08981" rel="nofollow">newer</a> paper includes dwarfs, and shows some issues of them.<br /><br />Regarding the superfluid approach (that looks interesting), they state that it is about particles-based DM, and that it is just mimicking the MOND phenomena. No sociologist was successful in forcing them to hide that they deal with particles.<br />May be Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63861442042832417312018-04-10T03:33:23.874-04:002018-04-10T03:33:23.874-04:00so if the recent discovery of diffuse galaxies wit...so if the recent discovery of diffuse galaxies without or almost without DM is confirmed, how should we understand that within Verlinde and SH theories: as far as i have understood one needs at least 3 domains : the large scale regime in which the vector field is not condensed, the galactic domain in which it is condensed (to produce MOND phenomenology), and the small scale (large gravity F henry-couannierhttps://www.blogger.com/profile/13933350696243790692noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75122610338914711442018-04-04T17:23:52.566-04:002018-04-04T17:23:52.566-04:00Sabine, for whatever it is worth (probably not muc...Sabine, for whatever it is worth (probably not much to you, since you ‘Verlinde match’), assuming that the parameter L measures the (reduced) radius of the de Sitter horizon when a mass M is embedded in a de Sitter universe, the Kottler Metric (quantitatively ‘a spherical mass embedded in a de Sitter universe’), predicts a numerical parameter of 1.195 in the L-related equation you quoted in your Anonymoushttps://www.blogger.com/profile/14318195499972536515noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-91335014032993750312018-04-03T08:57:30.774-04:002018-04-03T08:57:30.774-04:00David,
The Lagrangian of this model is quite simi...David,<br /><br />The Lagrangian of this model is quite similar to what Justin Khoury and collaborators use. <a href="https://aeon.co/essays/is-dark-matter-subatomic-particles-a-superfluid-or-both" rel="nofollow">I wrote about this here</a>. They're not the same because we have a vector field and we also have a somewhat different coupling to baryons. But I believe that the estimates about Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90310536619673388162018-04-03T07:55:51.161-04:002018-04-03T07:55:51.161-04:00Sabine, your theory-model is extraordinarily compl...Sabine, your theory-model is extraordinarily complex and sophisticated, and I wouldn't even pretend to say I understand it, except in the most general sense. That said, I'm wondering if someone like Natalie Wolchover might be working on a popular exposition of it, that is more accessible and comprehensible to the lay public?<br /><br />One thing I'm curious about is whether your David Schroederhttps://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-67811101132848623932018-04-03T03:29:07.064-04:002018-04-03T03:29:07.064-04:00theonh55,
Average cluster density is too low for ...theonh55,<br /><br />Average cluster density is too low for a condensate to form. It doesn't probe the MOND regime to begin with. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5494934468115602422018-04-03T03:23:06.282-04:002018-04-03T03:23:06.282-04:00Mond, Verlinde and such stuffs have been kindly pu...Mond, Verlinde and such stuffs have been kindly put in the trash bin in the paper <br />"How Zwicky already ruled out modified gravity theories without dark matter", arXiv:1610.01543.<br />The point is that in galaxy clusters the Mond regime lies so far out, that Mond does not solve anything. <br />Without any doubt this applies also to the other McGravity models; a few are discussed inAnonymoushttps://www.blogger.com/profile/16828497721228488877noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-55650242060260252402018-04-02T11:14:13.937-04:002018-04-02T11:14:13.937-04:00milkshake,
If all you give me is a single galaxy,...milkshake,<br /><br />If all you give me is a single galaxy, I can pull parameters out of my head like a magician and fit you pretty much everything. Not that I would spend the time trying, because there's nothing to be learned from this.<br /><br />The assumption that goes into the above plot is that the system is static and spherically symmetric. Of course no galaxy is actually static and Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-19428583699576608382018-04-02T06:59:06.685-04:002018-04-02T06:59:06.685-04:00even so, my understanding is that your model does ...even so, my understanding is that your model does not have much fudge room in the form of free parameters. So lets say one takes a well-studied galaxy with "99.9% dark matter" and another one with "0% dark matter" and in between them 10% 20% etc. and then plots them onto your graph - what will the fit look like? In another words, when you are comparing how well your theory milkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74361888743882788512018-04-02T05:18:36.261-04:002018-04-02T05:18:36.261-04:00milkshake,
You have it backwards. The challenge i...milkshake,<br /><br />You have it backwards. The challenge isn't to explain individual cases. You can always do that by choosing suitable initial conditions. The challenge is to explain the regularities. Modified gravity does that, particle dark matter doesn't. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75700440263048101362018-04-02T03:13:04.525-04:002018-04-02T03:13:04.525-04:00Dear Dr. Hossenfelder, I wanted to ask you (as a n...Dear Dr. Hossenfelder, I wanted to ask you (as a non-specialist) how is your emergent gravity theory going to explain away the apparently wildly variable dark matter/regular matter ratios in the known galaxies. This is probably best exemplified by the extreme cases NGC1051-DF2 and Dragonfly 44. Do you think that gravitational lensing under your modified gravity has a chance of explaining what'milkshakehttps://www.blogger.com/profile/08188961610554710616noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83590614811489008662018-04-01T12:19:46.776-04:002018-04-01T12:19:46.776-04:00Alexey,
This has been proposed before. But it doe...Alexey,<br /><br />This has been proposed before. But it doesn't make sense if you think (like I do) that MOND is an effective theory. You shouldn't see it anywhere in the solar system. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83341818171061767952018-04-01T12:18:35.859-04:002018-04-01T12:18:35.859-04:00David,
Yes, it would be only spin 1 field that...David,<br /><br />Yes, it would be only spin 1 field that's not a gauge boson. <br /><br />Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58099843345820813222018-04-01T10:25:23.360-04:002018-04-01T10:25:23.360-04:00"The vector field is a spin 1 field, but not ..."The vector field is a spin 1 field, but not a gauge field." Assuming your model is someday demonstrated to be the correct solution to the DM/DE conundrum, or at least a close approximation, would this be the first vector field, that is not a gauge field, in the Standard Model (SM)?<br /><br />I confess I don't fully comprehend what a "gauge field" is, beyond the David Schroederhttps://www.blogger.com/profile/18048116250413347228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-64989617788846016832018-04-01T06:08:58.463-04:002018-04-01T06:08:58.463-04:00Is it possible to test MOND/MOG/CEG directly by la...Is it possible to test MOND/MOG/CEG directly by launching a satellite in the point between Earth and Sun where their gravitational forces compensate each other? It is not a stationary point due to Moon, Jupiter, Galaxy etc., but never mind. Estimates give that the (newtonian) gravitational acceleration is less than 10^-11 m/s^2 in a region with the size of several meters. Let us imagine that we Anonymoushttps://www.blogger.com/profile/11025322357461968539noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69257321771373343252018-04-01T02:25:46.904-04:002018-04-01T02:25:46.904-04:00m-artins,
I have no idea how one makes a fit for ...m-artins,<br /><br />I have no idea how one makes a fit for a random function. I would expect that a random function with probability one fits infinitely badly. If you make an assumption of it being a 2nd order polynomial with some initial and end point, you are stuffing in your assumptions into that very definition. We haven't assumed specific end points and no specifics about the function. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22453622597040602822018-03-31T14:19:28.625-04:002018-03-31T14:19:28.625-04:00In your Twitter log on the right side of the page ...In your Twitter log on the right side of the page (another one of the great things about this blog for those of us who aren't on Twitter) there is a link to an article about a "galaxy without dark matter", that is a low-density (in bright matter) galaxy which doesn't need any dark matter addition to balance its apparent rotation. No doubt this has already occurred to you, but I JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3949694898295680862018-03-31T12:40:05.574-04:002018-03-31T12:40:05.574-04:00Hi Bee, congrats to the CEG vs. RAR correspondence...Hi Bee, congrats to the CEG vs. RAR correspondence!<br />Since I am a proponent of DM (meaning dark matter, not Deutsche Mark), I am going to make dirty notices. I know it, and I apologize for it in advance (I guess it is the most you can expect from someone who considers FZ a saint).<br /><br />I would like to ask you how the fit looks when a random interpolation function is used instead of yourAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45509041391324165282018-03-31T09:00:34.169-04:002018-03-31T09:00:34.169-04:00StrangeRep,
Regarding to reply to Andrew. The vec...StrangeRep,<br /><br />Regarding to reply to Andrew. The vector field is a spin 1 field, but not a gauge field. It has a normal (minimal) coupling to the metric, so I don't know what you are referring to. What's unusual is the coupling between the field and the baryons. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.com