tag:blogger.com,1999:blog-22973357.post4181985143028118444..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Modified Gravity vs Particle Dark Matter. The Plot Thickens.Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger48125tag:blogger.com,1999:blog-22973357.post-57287099116421957972016-11-14T09:10:02.029-05:002016-11-14T09:10:02.029-05:00Xkcd chimes in
http://xkcd.com/1758/Xkcd chimes in<br /><br />http://xkcd.com/1758/Unknownhttps://www.blogger.com/profile/06147179799227843407noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-65710504212040491512016-11-06T19:16:45.071-05:002016-11-06T19:16:45.071-05:00I haven't posted your comment because it start...<i>I haven't posted your comment because it starts with a string of several hundred capital letters (mostly Ns and Zs). </i> <br /><br />You don't speak NZ? <br /><br /><i>Not sure what you did, but you might want to repost that.</i><br /><br />I don't know either. Could be fell asleep. I apologize for that. Also my appreciation of your being so relaxed about it. <br /><br /> <br /><iAnonymoushttps://www.blogger.com/profile/17852247942652368610noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5855659931621887982016-11-05T09:27:43.930-04:002016-11-05T09:27:43.930-04:00One has to be a Bohemian at heart in order to look...One has to be a Bohemian at heart in order to look at the universe in such a way? It has to be written in the CMB data in order for such theoretical discussions to be determinant?<br /><br />PlatoHagelhttps://www.blogger.com/profile/00849253658526056393noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79399294056552932242016-11-04T12:53:11.139-04:002016-11-04T12:53:11.139-04:00Thanks for the link. I see that the Moffat version...Thanks for the link. I see that the Moffat version of MOG is likely to fail because on their website the EHT folks report that they have observed a fuzzed version of the shadow which is already 30% less than that predicted by GR .<br />Avi Leob http:// www.nature.com/news/good-data-are-not-enough-1.20906 would agree with you and Moffat in exploring other interpretations of astrophysical data Stuart https://www.blogger.com/profile/12767480095489975264noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32787360147113864952016-11-04T12:15:33.860-04:002016-11-04T12:15:33.860-04:00Stuart,
Yes, I wrote about this here.Stuart,<br /><br />Yes, <a href="http://backreaction.blogspot.de/2015/05/testing-modified-gravity-with-black.html" rel="nofollow">I wrote about this here.</a>Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73304096935819698122016-11-04T12:01:43.131-04:002016-11-04T12:01:43.131-04:00The Event Horizon Telescope will help in discardi...The Event Horizon Telescope will help in discarding some MOG theories and give a strong test for GR. Any MOG theory that survives this test will not only be the right theory to solve the galaxy rotation curve problem but will certainly point the way to QG.Stuart https://www.blogger.com/profile/12767480095489975264noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-24851500080939229332016-11-03T14:13:23.399-04:002016-11-03T14:13:23.399-04:00Shantanu, thanks for that additional reference.
A...Shantanu, thanks for that additional reference.<br /><br />According to Mannheim, "solar system phenomenology is left intact", as he is describing in https://arxiv.org/abs/1610.08907.<br /><br />More problematic seems to be the quantum version of Confirmal Gravity (if standard quantum theory is applied) due to ghost states. But this should not really be an argument with respect to this Shttps://www.blogger.com/profile/01634740996945039551noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45875149449373794282016-11-03T11:14:56.935-04:002016-11-03T11:14:56.935-04:00And, yes, as Shantanu says, the Bullett cluster is...And, yes, as Shantanu says, the Bullett cluster is oversold. It's an appealingly simple explanation that goes well in the popular science media, but it's not as clear cut as it's been portrayed. My understanding is that some clusters are hard to fit both with modified gravity and LambdaCDM, and maybe that shouldn't be so surprising. What we observe today depends on the history of Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5820864386695958432016-11-03T11:10:02.384-04:002016-11-03T11:10:02.384-04:00Moffat gravity has MOND as a limit. MOND isn't...Moffat gravity has MOND as a limit. MOND isn't as universally applicable as MOG for the same reason Newtonian gravity isn't as universally applicable as general relativity. Hence, complaining that MOND doesn't fit this or that cluster is entirely pointless without asking first whether it even applies in that limit. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-91700896185972998902016-11-03T09:58:56.900-04:002016-11-03T09:58:56.900-04:00The question is, is Moffat gravity a MOND-type the...The question is, is Moffat gravity a MOND-type theory? The paper is about MOG. There might be some confusion here, in that other "modified-gravity" theories might be ruled out, perhaps including MOND, but not MOG.<br /><br />(One also has to be careful also when some paper has a discrepancy of a factor of 2 or 3 between theory and observations and this is touted as agreement while thePhillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70525603108608069772016-11-03T09:18:46.718-04:002016-11-03T09:18:46.718-04:00Michael, I think the Bullet cluster idea as THE e...Michael, I think the Bullet cluster idea as THE evidence for dark matter is very much oversold idea ( for example things like 8 sigma etc). As Sabine said, you should the paper mentioned and then decide. also there are counterexamples to Bullet Cluster such as Trainwreck cluster, which again no one talks about.<br /><br />Shantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-46331778748675171642016-11-03T08:26:38.418-04:002016-11-03T08:26:38.418-04:00Michael,
Paper's here, what more are you aski...Michael,<br /><br /><a href="https://arxiv.org/abs/astro-ph/0702146" rel="nofollow">Paper's here</a>, what more are you asking for? Don't know what you read but I doubt your statement is correct.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-31919594896558743002016-11-03T08:05:42.195-04:002016-11-03T08:05:42.195-04:00I may be missing it but I don't understand how...I may be missing it but I don't understand how MOND-type theories would explain observations of the Bullet Cluster. Maybe they would dispute the interpretation of the evidence but I thought it was claimed at 8σ significance that modification of gravity alone could not account for the measurements. <br /><br />Thanks,<br />MikeMichael Mussonhttps://www.blogger.com/profile/17360143418083381579noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78249178628032267212016-11-03T00:46:45.638-04:002016-11-03T00:46:45.638-04:00piein,
I haven't posted your comment because ...piein,<br /><br />I haven't posted your comment because it starts with a string of several hundred capital letters (mostly Ns and Zs). <br /><br />Not sure what you did, but you might want to repost that. I didn't post another one because it contains wrong statements about cosmology that I don't want to confuse other readers. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88303936670970692532016-11-02T19:36:58.897-04:002016-11-02T19:36:58.897-04:00no sign of my last three comments. One was just a ...no sign of my last three comments. One was just a question, Your comment-rules were abided, your good name was not derided, so wot gives?Anonymoushttps://www.blogger.com/profile/17852247942652368610noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70843756308626414572016-11-02T16:03:06.841-04:002016-11-02T16:03:06.841-04:00In one of Wittens less known papers, he basically ...In one of Wittens less known papers, he basically pioneered the physics of galactic halo neutrino detection. So yea, I'd say he's pretty famous in astrophysics as well.Haelfixhttps://www.blogger.com/profile/16980241518510365230noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86788262896208575642016-11-02T10:45:38.685-04:002016-11-02T10:45:38.685-04:00Phillip, I think Witten is equally well known amon...Phillip, I think Witten is equally well known among astrophysicists.<br />He proposed an explosion model for galaxy formation with Ostriker in 80s, worked<br />on strange quark stars, dark energy, proposed detection for dark matter detection, etc.Shantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74178873607137342232016-11-02T10:43:01.212-04:002016-11-02T10:43:01.212-04:00Phillip, in theoretical particle physics papers, u...Phillip, in theoretical particle physics papers, usually the author list is always alphabetical (unlike<br />astro papers)<br />Here the author list consists of 3 astrophysicists+ 1 particle physicist. So don't know what criterion was used.Shantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-55691268603929228932016-11-02T05:15:52.444-04:002016-11-02T05:15:52.444-04:00"Also, fourth author because we publish using...<i>"Also, fourth author because we publish using alphabetical order."</i><br /><br />Who is "we"? It certainly isn't the norm in astrophysics to publish in alphabetical order. Maybe Witten is fourth author because the order is alphabetical, OK. My comment was not a slur at Witten, but rather at the tendency to drop famous names. Why mention any of the authors at all? Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30027474987222988662016-11-02T05:10:11.385-04:002016-11-02T05:10:11.385-04:00"IMHO most LCDM folks are stringers and SUSY ...<i>"IMHO most LCDM folks are stringers and SUSY advocates."</i><br /><br />Whatever gave you that idea?<br />Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34760600514817472592016-11-01T12:09:01.226-04:002016-11-01T12:09:01.226-04:00"Witten, though relatively famous, is only th..."Witten, though relatively famous, is only the fourth author on the paper. The second and third are much more famous among astrophysicists." Wow, that is an objective attitude: fame as degree of importance and calling Witten "relatively famous", amuzing. Also, fourth author because we publish using alphabetical order. alfredo arandahttps://www.blogger.com/profile/08215209523133087877noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-29531637974764308902016-11-01T11:50:52.816-04:002016-11-01T11:50:52.816-04:00There is some hope that the LISA Pathfinder (LPF) ...There is some hope that the LISA Pathfinder (LPF) will be able to falsify at least some of the modified gravity theories deriving from MOND in a passage or passage through a gravitational saddle point (where the net Newtonian acceleration of gravity becomes small compared to the MOND acceleration parameter) during its extended mission. (Of course, if LISA Pathfinder actually sees a signal, that TMEubankshttps://www.blogger.com/profile/00271298679549213444noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81425623172690277252016-11-01T02:34:40.591-04:002016-11-01T02:34:40.591-04:00I have hard time understanding how mond prediction...I have hard time understanding how mond predictions are any simpler than LCDM. Baryons still exist and keep exploding in hard to simulate ways.Anonymoushttps://www.blogger.com/profile/16891286385442274818noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22727406728408216352016-11-01T02:16:50.210-04:002016-11-01T02:16:50.210-04:00Shantanu,
Yes, I looked at this many years ago an...Shantanu,<br /><br />Yes, I looked at this many years ago and didn't find it convincing. It won't harm though to see if anything changed since. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-24636701230907354712016-10-31T21:45:27.707-04:002016-10-31T21:45:27.707-04:00Sabine, S is referring to https://arxiv.org/abs/10...Sabine, S is referring to https://arxiv.org/abs/1011.3495 and other papers by Mannheim. I think the problem (as I understand)<br />is that this theory does not agree with solar system observations.Shantanuhttps://www.blogger.com/profile/16322812456382858228noreply@blogger.com