tag:blogger.com,1999:blog-22973357.post296075151187741914..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Evidence for modified gravity is now evidence against it. Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger62125tag:blogger.com,1999:blog-22973357.post-41765360401539071232018-08-01T23:23:55.555-04:002018-08-01T23:23:55.555-04:00B,
Stay between the two ideas... they are both mer...B,<br />Stay between the two ideas... they are both merely wrong. <br /><br />"what the heck is going on?" The universe is cyclic in Mass and Time. That merely requires that the Temporal Curvature term be considered an imaginary quantity.. just like in every other field of physics, the representation geometry is FUNDAMENTAL. (not just a "visual aid")WRLhttps://www.blogger.com/profile/04323354407920835050noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-52362735663129037282018-07-31T22:48:36.082-04:002018-07-31T22:48:36.082-04:00Is it statistically significant to 4-sigma? McGaug...Is it statistically significant to 4-sigma? McGaugh answered my question in his blog post, The Acceleration Scale in the Data. To quote: “if these results really do indicate the action of a single universal force law, then it should be possible to fit each individual galaxy… Does it work for the entirety of SPARC?... the answer is yes… There are some inevitable goofballs; this is astronomy after Enricohttps://www.blogger.com/profile/11062542721973950650noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-22704655804991842002018-07-30T14:22:19.663-04:002018-07-30T14:22:19.663-04:00Sabine,
We have recently published a paper (MNRAS2...Sabine,<br />We have recently published a paper (MNRAS2018; Astroph-1705.02918) discussing the “acceleration discrepancy” (AD) found in the analysis of McGaugh and collaborators, in the light of what we call the “Two-Component Virial Theorem”. This is a simplified extension of the usual Virial Theorem describing the equilibrium of a system composed by a spheroidal subsystem (e.g baryonic matter)H Capelatohttps://www.blogger.com/profile/05231026708575538371noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54131735358372154382018-07-30T11:58:29.262-04:002018-07-30T11:58:29.262-04:00also in response to SpaceTime's question, stil...also in response to SpaceTime's question, still puzzling about how Sabine's logarithmic potential plays. Can anyone help with this? It's a step on the way to a scale invariant potential, but having a hard time getting an intuitive sense of thispeter cameronhttps://www.blogger.com/profile/03250964174803903885noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-56056294875107961492018-07-30T11:49:42.369-04:002018-07-30T11:49:42.369-04:00Space Time said...
"Are there any modified gr...<i>Space Time said...<br />"Are there any modified gravity proposals that are actually modified gravity, not just in name?"</i><br /><br />to first order both QED and QCD <b>and</b> both Newtonian and relativistic gravity regard the sources as monopoles with corresponding 1/r potentials. While both QED and Yang-Mills include the 2D bivector as a second component of the two component peter cameronhttps://www.blogger.com/profile/03250964174803903885noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33167582313026117132018-07-30T07:21:51.456-04:002018-07-30T07:21:51.456-04:00If read right Rodrigues et al use flat statistics ...If read right Rodrigues et al use flat statistics with hard boundaries instead of gaussian. Do this simulate the pre-selected model? I see as if they try to aim to the their most wanted conclusion... :)Eusahttps://www.blogger.com/profile/14114706429392111062noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-28573466716536832262018-07-30T06:24:53.538-04:002018-07-30T06:24:53.538-04:00Are there any modified gravity proposals that are ...Are there any modified gravity proposals that are actually modified gravity, not just in name?Anonymoushttps://www.blogger.com/profile/06098439870046873701noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-49314214796251633822018-07-30T04:06:13.373-04:002018-07-30T04:06:13.373-04:00My guess is that the universe sucks.
That's a...My guess is that the universe sucks.<br /><br />That's all we're doing here now, right? Guessing?Liralenhttps://www.blogger.com/profile/06675133437955499435noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-28063184721299477142018-07-30T01:12:57.309-04:002018-07-30T01:12:57.309-04:00@Bee
what if some researchers write a paper simul...@Bee<br /><br />what if some researchers write a paper simulate the universe using MOND + primordial black hole dark matter (and possibly neutrinos) at 6x baryonic visible matter, and are able exactly reproduce the observed universe, from gravitational lensing to CMB to large scale structure, with MOND explaining galaxy rotation curves. these results pass peer review and are reproducible <br /><neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30691232997204045172018-07-29T21:26:13.747-04:002018-07-29T21:26:13.747-04:00Sabine,
My misunderstanding is acknowledged. I th...Sabine,<br /><br />My misunderstanding is acknowledged. I thought McGaugh has a MOND hypothesis to replace the dark matter hypothesis. Thank you for clarifying that he has none. He merely observed that there is a preferred acceleration scale. Is it statistically significant to 4-sigma? If yes, theorists should formulate a MOND hypothesis from it. If not, the null hypothesis stands.Enricohttps://www.blogger.com/profile/11062542721973950650noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45254232152229622092018-07-29T16:05:09.549-04:002018-07-29T16:05:09.549-04:00Sean s.: It hasn't been detected directly, but...Sean s.: It hasn't been detected directly, but to me there's no difference between dark matter and something that acts exactly like dark matter (and not like modified gravity) in everything we measure, every model we produce, and every observation we make. It's more accurate to say we don't have a theoretical explanation for dark matter than to say we don't know if it exists.Anonymoushttps://www.blogger.com/profile/03206350270780025675noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-63389551823480976942018-07-29T09:57:00.593-04:002018-07-29T09:57:00.593-04:00Rob,
Yes, that's the idea. It's a kind of...Rob,<br /><br />Yes, that's the idea. It's a kind of particle that forms a fluid and the fluid makes a phase-transition to a superfluid phase, which causes a long-range force that reproduces the MOND-law. This means in cases when the density contrast is small and average temperatures are large (early days in cosmology) then particle dark matter is a good description, but in cases where Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-55386171342564155472018-07-29T09:53:19.821-04:002018-07-29T09:53:19.821-04:00NAP,
I think that's implausible.NAP,<br /><br />I think that's implausible. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33854033536233284982018-07-29T09:52:58.081-04:002018-07-29T09:52:58.081-04:00neo,
Yeah, maybe this, maybe that, maybe all of t...neo,<br /><br />Yeah, maybe this, maybe that, maybe all of this. But maybes aren't a good way make progress. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-7320242126018983492018-07-29T09:51:55.885-04:002018-07-29T09:51:55.885-04:00Miki,
Yes, there are various relativistic extensi...Miki,<br /><br />Yes, there are various relativistic extensions of MOND, Bekenstein's is one of them. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-74114159587836447372018-07-29T09:51:01.805-04:002018-07-29T09:51:01.805-04:00David,
Maybe dark matter is related to quantum gr...David,<br /><br />Maybe dark matter is related to quantum gravity (some physicists think it is), but there is presently no particular reason to think so. The reference to particles is actually unnecessary. We just did this to avoid having to explain what a field is. A more correct but somewhat more difficult to understand statement is that both dark matter and modified gravity require the Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-9516738325470290642018-07-29T07:57:36.488-04:002018-07-29T07:57:36.488-04:00The standard MOND model is based on a change in Ne...The standard MOND model is based on a change in Newtonian dynamics for extremely small accelerations. It may also be seen as a change in gravitation for cases where GM/r (potential) or GM/r^2 (force) are very small. Either the 1/r and 1/r^2 law is changed by some tiny amount or there is some change in the gravitational coupling μ = GM so that μ = μ(r) according to some tiny variation. This is Lawrence Crowellhttps://www.blogger.com/profile/12090839464038445335noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-17931445650542395582018-07-28T20:05:01.098-04:002018-07-28T20:05:01.098-04:00Hi! I recently read yours and Dr. McGaughs article...Hi! I recently read yours and Dr. McGaughs article on dark matter in the August issue of Scientific American and came across a puzzler which happens frequently in discussions involving gravity. In the opening paragraphs, you assert “But Einstein’s general theory of relativity taught us that gravity is not a force and is instead caused by the curvature of space and time.” And yet, later in the Anonymoushttps://www.blogger.com/profile/12706222065197742466noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90112031199290459622018-07-28T16:42:46.386-04:002018-07-28T16:42:46.386-04:00Hi,
concerning "To begin with because we alre...Hi,<br />concerning "To begin with because we already know that MOND is wrong because it's only a non-relativistic limit" - didn't Prof. Beckenstein (RIP)extended MOND to relativistic?<br />Mentioning Beckenstein - shouldn't the "Hawking radiation" termed "Beckenstein radiation"? or at least "Beckenstein-Haking", since he was the first one to Anonymoushttps://www.blogger.com/profile/12448204299298989587noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32734041738296607702018-07-28T15:35:07.367-04:002018-07-28T15:35:07.367-04:00unknown;
“... dark matter has decisively won.”
D...unknown;<br /><br />“<i>... dark matter has decisively won.</i>”<br /><br />DM is <i>fashionable</i>, but it’s not won because no one can find it. The uncertainty remains.<br /><br />sean s.sean s.https://www.blogger.com/profile/04190153587965701495noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-47914230053195968062018-07-28T15:16:07.526-04:002018-07-28T15:16:07.526-04:00Is there a reason MOND and dark matter in the form...Is there a reason MOND and dark matter in the form of (primordial) black holes, or possibly neutrinos, couldn't both be correct? so MOND explains galaxy rotation curves, and the dark matter is all black holes, (or possibly neutrinos) which also explains CMB and large scale structure? maybe there's more neutrinos than standard big bang cosmology, and more black holes. <br /><br />maybe theneohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-62666597770563557352018-07-28T14:31:59.460-04:002018-07-28T14:31:59.460-04:00It is a false choice, this MOND/dark matter dichot...It is a false choice, this MOND/dark matter dichotomy. DM is a physical conjecture in which a proposed entity has only a gravitating effect and no other observable properties. It is useful for calculational purposes because it can be sprinkled in just the necessary amounts and locations to reconcile any discrepancy between a gravitational model and observed reality. It produces a non-empirical, bud raphttps://www.blogger.com/profile/06948881286545517324noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90615410790461904712018-07-28T09:53:24.385-04:002018-07-28T09:53:24.385-04:00I read an article in Astronomy magazine, written b...I read an article in Astronomy magazine, written by Tyler, that talks about MOND and I understood that changing the Hubble constant would be the reason for the flat speed of galaxies, what do you think?NAPhttps://www.blogger.com/profile/07163092774449430219noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-4193668949746506882018-07-28T00:51:25.165-04:002018-07-28T00:51:25.165-04:00There's not really a war going on anymore; dar...There's not really a war going on anymore; dark matter has decisively won. I'm an astronomy graduate student, and in every textbook, class, colloquium, and conference I'm aware of, dark matter is taken as a given while MOND is hardly mentioned. Maybe the victory is unfair or premature, but there's no doubt that it happened.<br /><br />As for the paper, it's an interesting Anonymoushttps://www.blogger.com/profile/03206350270780025675noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18791704825299627152018-07-27T12:08:57.335-04:002018-07-27T12:08:57.335-04:00Bee
what more work needs to be done with covarian...Bee<br /><br />what more work needs to be done with covariant emergent gravity to establish that MOND does have a relativistic completion?<br /><br />do you prefer MOND as modification of gravity or inertia? and is there a way to tell?neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.com