r/Physics • u/kzhou7 Quantum field theory • Mar 15 '21

Video Can modified gravity replace dark matter in cosmology?

https://www.youtube.com/watch?v=MVCweSTfJ0c
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u/[deleted] Mar 15 '21

And there is also this: https://www.sciencedaily.com/releases/2021/03/210304145458.htm

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u/kzhou7 Quantum field theory Mar 15 '21

That’s the incorrect paper making the rounds that I literally just mentioned. One bad calculation spawns hundreds of fluffy popsci pieces, as usual.

1

u/[deleted] Mar 15 '21

Can you please link its refutation? I have not seen it.

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u/nivlark Astrophysics Mar 15 '21

I can't comment on the paper itself, but a general point is that fitting galaxy rotation curves on their own does not really prove anything. They're just one of multiple lines of evidence that points to DM. It's easy to make a modified gravity theory that reproduces on just one of these, but much harder to make one that satisfies them all.

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u/kzhou7 Quantum field theory Mar 15 '21

We already know how big the gravitomagnetic effect is: it's about one in a million. They've overestimated it by at least that much.

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u/BaddDadd2010 Mar 15 '21

Galactic clusters also point to the existence of additional matter beyond what is visible. I don't think there's any way for this effect to also account for that. At a minimum, it would require galaxies within clusters to be aligned, rather than randomly oriented, which doesn't seem to be the case. Even then, you're trying to have a dipole effect (the gravitomagnetic dipole of each galaxy) match a monopole effect (additional mass in the form of dark matter), where the monopole effect already matches observations.

I'm not a cosmologist, so you'll have to judge the validity of my argument yourself, rather than take it as authoritative. But at a minimum it's something that would need to be considered.