# Gravitomagnetic explanation of Dark Matter

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• DaveC426913
In summary, the paper discussed in the thread claims that standard GR cannot explain the rotation curves of galaxies, and that the preferred explanation is gravitomagnetic effects. There is some controversy about this claim, with some people believing it is correct and others not.
DaveC426913
Gold Member
TL;DR Summary
There was a long thread around here (which I can no longer find) about DM being explained by gravitomagnetic effects. Is there a 25 words or less explanation?
I was reading a thread on my phone that was reviewing a paper about DM being explainable by gravitomagnetic effects. Now I can't find it in any search. It was on its fourth page - so at least 80 posts over at least two years.

Anyway, what I wanted to ask was for a description that a layperson might be able to give another layperson about DM.

My tentative conclusion was that:

DM is (so this paper claims) essentially a faulty assumption in how gravity in a spatially-extended object such as a galaxy ought to behave in a Newtonian model. i.e. the 1/r^2 formula is a good approximation in other cases but, here, it just does not apply. When the gravity curve is calculated using GR, it does not work out so simply as 1/r^2, - it tends to level off to a plateau near the edges of such an object. That's just The Way Gravity Works in GR. I also got the impression that an exact solution using GR formulae is impractical, which may be why this solution has been elusive.

Am I close enough for horseshoes and hand grenades?

Last edited:
DaveC426913 said:
DM is (so this paper claims) essentially a faulty assumption in how gravity in a spatially-extended object such as a galaxy ought to behave in a Newtonian model. i.e. the 1/r^2 formula is a good approximation in other cases but, here, it just does not apply. When the gravity curve is calculated using GR, it does not work out so simply as 1/r^2, - it tends to level off to a plateau near the edges of such an object. That's just The Way Gravity Works in GR. I also got the impression that an exact solution using GR formulae is impractical, which may be why this solution has been elusive.
This is a reasonable quick summary of the general idea behind the paper discussed in the thread I linked to in post #3, and similar ones we have had in the past on PF. The work of Deur, in particular (which is mentioned in that thread), has been the subject of quite a bit of PF discussion. The only correction I would make is that the models used are not using straight Newtonian gravity: Newtonian gravity using the visible matter in galaxies is known and agreed by all participants in the debate to not give the right answer for galaxy rotation curves. The models used are GR models in the weak field limit, which is often referred to as the "Newtonian" limit but is known to include corrections not present in Newtonian gravity (for example, the extra precession of the perihelion of planets).

The major caveat, of course, is that claiming that the GR corrections are large enough even in the weak field limit to explain the actual galaxy rotation curves using just the visible matter in some cases (basically, cases like spiral galaxies which are very far from spherical symmetry) is one thing: actually demonstrating it is another. It is true that exact solutions are not known for such cases, so any investigation has to use approximations and numerical methods. It is also true, however, that GR has well tested approximation schemes and numerical methods that work well in, for example, the solar system, and these schemes do not appear to support the kinds of claims being made in papers like the one in the above thread.

vanhees71
anorlunda said:
I think you are asking about Modified Newton Dynamics, or MOND for short.
I don't think so, because the OP specified that just standard GR would be used, whereas MOND is a modified theory of gravity, not standard GR. (In fact there is no well accepted relativistic version of MOND at all.)

Gravitomagnetism is the preferred explanation of G.O. Ludwig. One of his papers got a lot of press last year.

I don't quite get what Deur's mechanism is, but I don't think it's gravitomagnetism.

The mainstream view (exemplified by Ciotti in post #44 in the thread) is that in general relativity, the gravitational field produced by a galaxy's baryonic matter is far too weak at the galactic edge for any such effects to be produced, so there has to be a mistake in papers like these.

vanhees71

## 1. What is the gravitomagnetic explanation of Dark Matter?

The gravitomagnetic explanation of Dark Matter is a theoretical concept that suggests that the effects of gravity can be explained by the presence of a large amount of unseen matter in the universe. This matter, known as Dark Matter, is thought to interact with regular matter only through gravity, making it difficult to detect.

## 2. How does the gravitomagnetic explanation of Dark Matter differ from other theories?

The gravitomagnetic explanation of Dark Matter differs from other theories, such as the particle theory, in that it does not propose the existence of a specific type of particle. Instead, it suggests that the effects of gravity can be explained by the presence of a large amount of unseen matter.

## 3. What evidence supports the gravitomagnetic explanation of Dark Matter?

There is currently no direct evidence that supports the gravitomagnetic explanation of Dark Matter. However, it is consistent with observations of the rotation of galaxies and the gravitational lensing of light, which cannot be explained by the presence of visible matter alone.

## 4. Are there any criticisms of the gravitomagnetic explanation of Dark Matter?

Yes, there are several criticisms of the gravitomagnetic explanation of Dark Matter. One of the main criticisms is that it does not provide a complete explanation for all observations, and there are still some discrepancies that cannot be explained by this theory alone.

## 5. How does the gravitomagnetic explanation of Dark Matter impact our understanding of the universe?

The gravitomagnetic explanation of Dark Matter is one of several theories that attempt to explain the mysterious substance that makes up a large portion of the universe. While it is not yet proven, it has the potential to greatly impact our understanding of the universe and the fundamental laws of physics if it is confirmed by future research and observations.

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