Dark matter might not exist

originally posted by: Bluntone22
Actual headline.

"Maybe 'dark matter' doesn't exist after all, new research suggests"

That's the MOND or Modified Newtonian Dynamics idea which has been around since the 1980s, so it's not a new idea. Someone is claiming new evidence to support it but it's kind of sketchy.

The biggest problem with MOND is that it's not capable of explaining gravitational lensing, nor the large scale structure of the universe. So, the reason dark matter has been preferred over MOND are many, but the most significant factors are that it makes the most puzzle pieces fit together, like not only galaxy rotation curves but also gravitational lensing and large scale structure in the universe. That and the MOND theory seems to need too many contrived adjustments to fit the various galaxy rotation curves.

Only Dark Matter (And Not Modified Gravity) Can Explain The Universe

There have been a lot of public advocates from the “no dark matter” camp, getting lots of popular attention. But the Universe still needs dark matter. Here’s why...

Modified gravity cannot successfully predict the large-scale structure of the Universe the way that a Universe full of dark matter can. Period. And until it can, it’s not worth paying any mind to as a serious competitor. You cannot ignore physical cosmology in your attempts to decipher the cosmos, and the predictions of large-scale structure, the microwave background, the light elements, and the bending of starlight are some of the most basic and important predictions that come out of physical cosmology. MOND does have a big victory over dark matter: it explains the rotation curves of galaxies better than dark matter ever has, including all the way up to the present day. But it is not yet a physical theory, and it is not consistent with the full suite of observations we have at our disposal. Until that day comes, dark matter will deservedly be the leading theory of what makes up the mass in our Universe.

There are even some galaxies where it appears MOND doesn't have any explanatory power because those certain galaxies don't seem to have significant amounts of dark matter. The absence of dark matter could explain them, but scientists claim that the observations rule out alternatives like MOND. I made a thread about that topic:

Does the Failure to Find Dark Matter Prove the Existence of Dark Matter?

originally posted by: Tempter
I would think it'd be interesting to try to prove a non-correlative relationship between gravity as a whole vs gravity as separate at the sub-atomic level.

Whatever you theorize about gravity at the subatomic level, I don't see how you test the idea with observation or experiment. We have a hard enough time getting accurate measurements of the gravitational constant using much larger apparatus. Anyway gravity at the subatomic level seems irrelevant and doesn't pose any problems with observation that I know of. Gravity at the solar system level is also not a problem, we confirm our theories with observation all the time. It's only on larger scales like galaxy rotation curves that we invoke dark matter as a hypothesized solution to the problem of observations not matching our models without it.

originally posted by: ChaoticOrder
Makes one really wonder how WIMPs are still the most popular theory doesn't it? The reason I bring this up is because despite how weak the WIMP theory is, I still think MOND theories are weaker and have more flaws. That's ultimately why I lean more towards the bimetric relativity models I've been posting about over the last few years, it explains more without all the holes.

We agree that MOND is a weaker model. However your statement implies a false choice between WIMPs or MOND, then you suggest your model. While WIMPs may have been a popular dark matter candidate, they are certainly not the only one. This chart shows many candidates other than WIMPs, one example being axions (see lower left of this chart):



We don't know if the hypothesized axions exist but I know of only one experiment searching for axions, the The ADMX G2 Experiment, shown here:


I think the experiment has already ruled out some parameter space (from from 1.9 μeV to 3.53 μeV) but they have more parameter space to search which will take 10 years and maybe some equipment upgrades.

Here's a video discussing whether or not axions could be dark matter (and see the graphic above for many other options besides WIMPs, or axions, like sterile neutrinos, even PBH (primordial black holes) are not completely ruled out as a possibility:

Are Axions Dark Matter?

The story of the axion is a classic physics tale: intrepid scientists delve deep into trackless mathematics in search of answers to a mystery. And there, against all expectations, they find the hint of a completely new and unexpected denizen of the natural world. In this case the mystery was a subtle inconsistency in the behavior of the fundamental forces. And the unexpected discovery? A brand new particle - the axion - which, while not proven to exist, may explain a much more famous conundrum. The axion may explain dark matter.

a reply to: Arbitrageur

We agree that MOND is a weaker model. However your statement implies a false choice between WIMPs or MOND, then you suggest your model. While WIMPs may have been a popular dark matter candidate, they are certainly not the only one. This chart shows many candidates other than WIMPs, one example being axions (see lower left of this chart):

There is a lot of research which rules out more than just WIMPs, and there are many theoretical reasons which make the other candidates less promising, which is why WIMPs still remain the preferred explanation despite the overwhelming evidence against them. Put it this way, I'm confident enough to bet a substantial amount of money on the assumption we will not detect any dark matter particle because it doesn't exist. The solution involves a more complex and complete understanding of gravity and relativity, so MOND is sort of on the right path. Whether my proposed solution is correct or not, the solution will involve something more than a new particle.