Dark Matter Real: Studies Confirm, Modifying Gravity Can't Work

[Orodruin]

I'm not convinced that this is accurate.

I do not think it is controversial to claim that neutrinos are hot dark matter. The problem is that their abundance can only account for between 0.1% and 0.3% of the energy budget as compared to the ca 1/4 of the budget that would be required to be the main dark matter component.

 

[timmdeeg]

The other problem is that neutrinos moving almost with light speed are to fast to form a “cloude” around a galaxy.

 

[Orodruin]

The other problem is that neutrinos moving almost with light speed are to fast to form a “cloude” around a galaxy.

As I said, neutrinos are hot dark matter, not cold dark matter. This does not mean that the neutrino background cannot cluster today. Whether they do that or not (and to what degree) depends on the neutrino masses.

 

[Ken G]

The originally most popular WIMP theories, those in which the lightest supersymmetric particle serves as the dark matter candidate, are virtually entirely ruled out.

Ruling out supersymmetric versions of WIMP theories is hardly the same thing as ruling out all WIMP theories.

Some of the most promising dark matter particle theories these days are those with axion-like dark matter particles, and those with self-interacting dark matter particles with this fifth dark matter force mediated by a massive carrier boson.

And the particles you are describing are weakly interacting, are they not? That's the "WI". They are nonrelativistic, are they not? That means they are massive, the "M". They are particles, are they not? That's the "P". I'm not sure what other distinction you are making, perhaps you are saying the term has fallen out of favor, but it's still WIMPs.

 

[sector99]

No. Oil and water are both liquids. DM and DE are more like fish and bicycles. They have absolutely nothing to do with each other.

The SDSS (and its supercomputer facimilies) reveal spatial voids and enveloping baryonic aggregations.

It appears that baryons/DM have more affinity for themselves than they do for whatever is filling the voids. Ergo my query.

 

[FourEyedRaven]

Two recent studies have found galaxies with little or no apparent dark matter, indicating modifying gravity can't work.
https://iopscience.iop.org/article/10.3847/2041-8213/ab0e8chttps://iopscience.iop.org/article/10.3847/2041-8213/ab0d92/meta

This PBS Space Time video gave a good explanation, at least for amateurs like me.

 

[sector99]

FYI

https://phys.org/news/2019-04-hubble-universe-faster.html

 

[Bandersnatch]

@sector99 FYI I'm pretty sure most posting here (and certainly Orodruin) are aware of the discrepancy referred to above, since it's nothing new and the thread level is 'A'. Some might even be aware of the avenues currently explored to address it.
What is objectionable is saying 'X isn't known, Y isn't known - therefore X is Y'. At least not without good reason.

 

[PeterDonis]

Thread closed for moderation.

Edit: Some off topic posts have been deleted. Thread reopened.

 

[PeterDonis]

It appears that baryons/DM have more affinity for themselves than they do for whatever is filling the voids

There isn't anything filling the voids; that's why they're called "voids". The "affinity" you refer to is called "gravity"; basically you're saying that baryons and DM are sources of gravity. This is hardly news.

 

[cube137]

WIMP theories are among the least viable of dark matter particle theories outstanding and have been ruled out over very wide areas of parameter space. The originally most popular WIMP theories, those in which the lightest supersymmetric particle serves as the dark matter candidate, are virtually entirely ruled out.

Some of the most promising dark matter particle theories these days are those with axion-like dark matter particles, and those with self-interacting dark matter particles with this fifth dark matter force mediated by a massive carrier boson.

Ohwilleke. Id like to ask you something.

https://arxiv.org/abs/1512.06471

In the paper, dark plasma (that is, NOT baryonic plasma) was suggested. I'd like to know if it is compatible with many cosmic phenomena (like bullet clusters). Can you think of one where the data (especially new ones) don't support it?

In baryonic matter. Plasma only occurs when energy is so high that the electrons separate from the nucleus.

In dark plasma theory. Is it also the dark electrons separating from the dark nucleus or can the particles just be highly energetic and independent. In baryonic matter, what kind of plasma where it is not based on separated electrons from nucleus?

 

[Deepblu]

It might be speculated that GR is only accurate for small range and is wrong on large galactic scale, which means that dark matter is just an ad hoc to rescue general relativity with no prove it actually exists.

But then we have this study that shows galaxies with no dark matter, which suddenly means that the problem is not that GR is not accurate on large scale, but rather there is actually no dark matter in those galaxies! which is amazingly an indirect proof that DM actually exists. However maybe there is something else totally unexpected for why these galaxies appear empty of dark matter, and I think it is still early to judge.

 

[PeterDonis]

It might be speculated that GR is only accurate for small range and is wrong on large galactic scale

This speculation is called MOND (which actually stands for Modified Newtonian Dynamics, but in practice it means what you say in the quote just above). It has already been discussed in this (and other) threads.

 

[Gigel]

Maybe the dark matterless galaxies are the result of a weird collision and the presence of a much larger galaxy that they orbit.

Now if a small galaxy rotating around a much larger one is collided by another galaxy as in the Bullet Cluster collision, with the second galaxy going radially (say towards the larger central one), then dark matter from the initially orbiting galaxy could be separated and effectively set into a different orbit. The result may be that the dark matter and baryonic matter end up rotating one around the other and both around the larger galaxy. Meaning that the dark matter may still be around there somewhere, only separated from the initial galaxy. Tidal effects on the small galaxy may point at its (now separated) dark matter.

Something like:

g-->...db...G

.....b...d...G....g-->?

where db is the initial small galaxy rotating around big galaxy G, and after impact with g the 2 kinds of matter b and d separate and start rotating around their common center of mass.

A bit weird and presumably rare.

One would have to think about galaxy collisions with satellite galaxies and their result.

 

[Ken G]

The hope is that by seeing how dark matter responds in these unusual dynamical contexts, it might help us understand dark matter better. It's a bit like how an animal behavioralist might want to study some animal in an unusual setting to get insight into how they behave differently in more normal situations. It's not so much a question of dark matter vs. MOND, it's a question of how this data forces you to constrain the attributes of either theory, and then at the end of the day, you sit back and just look at which theory seems to be working with the fewest kluges that you have to intentionally insert every time you see a new context for your theory.

 

[ohwilleke]

It might be speculated that GR is only accurate for small range and is wrong on large galactic scale, which means that dark matter is just an ad hoc to rescue general relativity with no prove it actually exists.

But then we have this study that shows galaxies with no dark matter, which suddenly means that the problem is not that GR is not accurate on large scale, but rather there is actually no dark matter in those galaxies! which is amazingly an indirect proof that DM actually exists. However maybe there is something else totally unexpected for why these galaxies appear empty of dark matter, and I think it is still early to judge.

It isn't really proof that DM exists because it can be explained, for example, in a theory like MOND with what is known as the external field effect which was predicted in 1983 for a system just like the one that you are referencing.

 

[ohwilleke]

Ohwilleke. Id like to ask you something.

https://arxiv.org/abs/1512.06471

In the paper, dark plasma (that is, NOT baryonic plasma) was suggested. I'd like to know if it is compatible with many cosmic phenomena (like bullet clusters). Can you think of one where the data (especially new ones) don't support it?

In baryonic matter. Plasma only occurs when energy is so high that the electrons separate from the nucleus.

In dark plasma theory. Is it also the dark electrons separating from the dark nucleus or can the particles just be highly energetic and independent. In baryonic matter, what kind of plasma where it is not based on separated electrons from nucleus?

Thanks for the heads up. I'll look into it when I have more than a few moments to glance at it.