Comments on: Galactic Motion Challenges Dark Matter https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/ Brian Koberlein Tue, 19 Feb 2019 13:26:59 +0000 hourly 1 https://wordpress.org/?v=5.0.3 By: Julian Lawrence https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-5133 Thu, 30 Mar 2017 11:34:37 +0000 https://briankoberlein.com/?p=6273#comment-5133 is it too silly to suggest that since the universe is expanding so may the galaxies be, though not at the same rate? Simplistically, I wonder what the tangential accelerations would have to be to explain the differences between rotational acceleration and gravity?

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By: THX https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4900 Wed, 04 Jan 2017 21:45:58 +0000 https://briankoberlein.com/?p=6273#comment-4900 I’m with you, sir

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By: Jean Tate https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4719 Wed, 26 Oct 2016 20:02:33 +0000 https://briankoberlein.com/?p=6273#comment-4719 It’s only been on arXiv a few days, and already there are several newer preprints discussing (etc) it! In Bee’s Backreaction blog there’s a post on it, and some comments from at least one author of one of those. Interesting and exciting blog by Brain, on a really cool topic!

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By: Jean Tate https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4718 Wed, 26 Oct 2016 19:56:52 +0000 https://briankoberlein.com/?p=6273#comment-4718 Don’t think so; for black holes, mass is mass is mass. The only exception that I’m aware of is electric charge.

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By: Jean Tate https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4717 Wed, 26 Oct 2016 19:53:40 +0000 https://briankoberlein.com/?p=6273#comment-4717 Is there anything in (on?) arXiv which presents this idea? In a relevant, peer-reviewed journal? If not, why not?

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By: Jean Tate https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4713 Wed, 26 Oct 2016 17:53:43 +0000 https://briankoberlein.com/?p=6273#comment-4713 Depends on what you mean by “principle”, but MOND violates relativity. However there are several ideas which do not violate relativity and which ‘reduce to’ MOND in the appropriate limit. For example, TeVeS.

How? I’m not sure how to answer that, except perhaps to say that MOND is Newtonian, so whatever it is in Newtonian physics that violates relativity, MOND has the same violation(s).

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By: AlanE https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4683 Thu, 20 Oct 2016 08:45:06 +0000 https://briankoberlein.com/?p=6273#comment-4683 Dark matter only interacts with visible matter through gravity and the weak nuclear force but not the electromagnetic and strong nuclear forces. Since visible matter interacts through forces that do not interact with dark matter why is it assumed that dark matter does not posses interactive forces that visible matter does not interact with? Whilst this proposal might founder upon Occam’s razor it would give the whole thing a pleasing symmetry that is often observed in physics and mathematics. Moreover, if we are going to wield Occam’s razor why indeed not go the whole hog and prefer Modified Newtonian Mechanics which, with some extension, would eliminate the need for dark matter altogether. Further, if dark matter does posses such forces then it may well clump and as it can interact with visible matter through gravity the two might well be expected to clump in broadly similar places. Finally, to obtain halos of dark matter around galaxies its dominant interaction on that scale which does not interact with visible matter could simply be repulsive.

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By: jpatrick https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4633 Thu, 06 Oct 2016 02:34:37 +0000 https://briankoberlein.com/?p=6273#comment-4633 Just read the paper. This is a rather elegant challenge to the idea of dark matter. In light of all that, imagine a thought experiment where there is a black hole with an accretion disk consisting entirely of dark matter. What would it, ah, “look” like? Would there be anything expelled in jets perpendicular to the accretion disk? We have a bit of a problem here because the idea of black holes was derived entirely from the properties of baryonic matter.

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By: Nico https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4627 Tue, 04 Oct 2016 20:34:55 +0000 https://briankoberlein.com/?p=6273#comment-4627 I’m looking for assertions of the form “theory X violates principle Y”. E.g., the equivalence principle (which formulation? be specific), conservation of momentum, conservation of energy (though it’s difficult to speak of conservation of energy in an open/infinite universe), and so on. A bit of explanation to go with the assertion would be nice; explanation plus math wood be even better.

Statements of the form “theory X doesn’t explain phenomenon Z” are interesting, but perhaps less so than more categorical “theory X violates principle Y” statements. After all, with more study one might see that theory X does explain phenomenon Z, or that we didn’t quite understand that phenomenon, but violations of widely accepted principles require more effort to overcome and might even require modifying the violated principle in order to survive, which would be a tall order indeed (though maybe not insurmountable).

I’m NOT looking for statements of the form “theory X explains …”. We already get such statements from the theories’ proponents.

I’m also not really looking for objections like ” theory X is unscientific”, or ” theory Y requires fitting N parameters to data”, though these and generally statements about the degree of freedom in a theory are very useful indeed. Such features are easy enough to notice and not necessarily fatal early on. We must take notice of these, but I’m already aware of some of them, so they don’t help _me_.

I’m especially NOT looking for ad hominems of any kind, nor pointers to objectionable behavior of proponents.

Basically I’m looking for a filter and/or challenges that make one think things through more carefully before spending much effort on any I’ve theory. I do realize that study of DM gets a lot of funding, which might tend to skew some of the answers i might get, but that’s ok.

Statements of the form “i’ve not yet found our developed an objection to their X, but have tried” are useful. Explanations of what principles you think are not violated by theory X and why are very nuch welcomed.

Thanks!

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By: Nico https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4626 Tue, 04 Oct 2016 14:18:47 +0000 https://briankoberlein.com/?p=6273#comment-4626 I would really like to see a comprehensive analysis of each theory’s pros and cons: DM, MoND (and variants), and MiHsC, as well as any others that I’ve not heard of yet.

I would particularly like to hear all that us wrong with MiHsC. McCullough strikes me as socially awkward and quite possibly a charlatan who has math-not-physics, but that may just be because he’s very sure if a theory that imo needs much more fleshing out — but who would invest time into it when it seems off the wall to begin with? But surely some have thought of serious-enough objections to MiHsC and/or MoND, and I’d like to hear those. (I’ve heard a number of objections to DM; those should be cataloged also.)

I’ll settle for a non comprehensive listing of problems by commenters here. Even just a few to set me thinking would be nice!

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By: LocalFluff https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4625 Tue, 04 Oct 2016 11:20:28 +0000 https://briankoberlein.com/?p=6273#comment-4625 Maybe there’s more than one phenomena going on here. One inside of galaxies and another that forms those interclustular filaments and Bullet Galaxies.

If dark matter clings to ordinary matter, couldn’t it be that this kind of dark matter forms the correspondence of molecules and planets, but all dark to our electromagnetivity? Maybe there’s dark life around here, of which we can only notice the mass. Matter without properties, like a black hole.

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By: James Hamilton https://briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/#comment-4624 Tue, 04 Oct 2016 09:08:50 +0000 https://briankoberlein.com/?p=6273#comment-4624 Dark Matter and Dark Energy is Gas.

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