How about matter in a different space than ours?

This market focuses on mundane explanations: https://manifold.markets/mariopasquato/if-a-mundane-explanation-for-the-ph?r=bWFyaW9wYXNxdWF0bw

@mariopasquato other is the top response in both, I guess we really don't know.

QI should be added to one of these lists.

@robm Yeah we really don't know.

The case of Khoury's superfluid dark matter (https://arxiv.org/abs/2109.10928), (i.e. dark matter has multiple phases, in one of these phases it give rise to an additional MOND-like long range interaction) would count as MOND or not?

A recent paper proposed that GR effect leads to MOND-like behavior: https://arxiv.org/abs/2402.19459. How does it resolve in such cases? @PlasmaBallin

From recent confirmation of MOND from wide binaries, it is likely dark matter does not exist and effects attributed to dark matter are better explained by MOND.

For details, see https://manifold.markets/TomBouley/will-studies-of-wide-binaries-using

@SanghyeonSeo there are many more "effects attributed to dark matter" than Galactic dynamics <https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence>, and I'm pretty skeptical that MOND can explain them all at once.

Recent developments show that PBHs are not ruled out as DM if they are asteroid sized: https://arxiv.org/pdf/2006.02838.pdf (fig. 1)

Somewhat relevant (to the ability to find the answer to this question): https://x.com/getjonwithit/status/1706408056404238640?s=46

Sterile neutrinos at 23% is wild

@BenjaminShindel fixed it

How narrowly are we defining WIMPs?

@ArmandodiMatteo I guess it's at least partially based on, "What do most physicists refer to it as when it's discovered?", since the term WIMP is ambiguous. I can make the following clarifications, though:

• Weakly interacting means that it interacts with the weak force, specifically, and not through any other currently known force except gravity. It would be acceptable if it also interacted through some unknown force weaker than the weaker force (although it still has to interact via the weak force to count).

• I won't count a sterile neutrino as a WIMP, even though it could be argued that the fourth neutrino mass state is technically a WIMP since it contains electron, muon, and tau neutrino components, and those all interact with the weak force.

• I think a weakly interacting supersymmetric particle probably would count as a WIMP, but since I already included that as a separate category, and have from the beginning, I would probably count any WIMP that is believed to be a supersymmetric particle as part of that category. If there's a lot of doubt over whether its really a supersymmetric particle or something else, then I might hold off on resolving it until the situation is clear.

• Any amount of mass is sufficient to count as a WIMP - I take "massive" to mean "has mass", not "has a large mass".

• If any of the effects of dark matter are the result of SM particles, I won't count those as WIMPs - I take the word WIMP to refer specifically to BSM particles.

In general, I think I would probably count any fermion that follows those clarifications as a WIMP, but I'm not sure if I would count any bosons as WIMPs.

This video shows some interesting effects: https://youtu.be/aXRTczANuIs?feature=shared

I then looked up "Maxwell's equations applied to gravity" and found this: https://en.m.wikipedia.org/wiki/Gravitoelectromagnetism

And then searched for "gravitoelectromagnetism and galaxies" and found this: https://link.springer.com/article/10.1140/epjc/s10052-021-08967-3

Modelling this complex behaviour as a curved spacetime problem has yet to be done and is believed to be very difficult.[citation needed]

I think GEM seems plausible to me.

@JosephNoonan Does GEM count as an option, or am I misunderstanding something again?

@cloudprism I've added a new option, "GR effects that current theoretical models don't accurately account for - no new physics required" that would cover this idea. I'm very surprised to learn that current calculations of theoretical galactic rotation curves don't take into account GEM. I'll have to look into whether it's a plausible explanation for dark matter or not.

@JosephNoonan "timescape cosmology" (which I just found out about today -- AIUI, the hypothesis that the Copernical principle is false and our Galaxy happens to be right in the middle of a huge region of space with much lower average density than the rest of the universe) would also qualify

@ArmandodiMatteo That would be an explanation for dark energy, not dark matter.

@JosephNoonan Yeah, I had a brain fart.
You'd expect the person with the most shares of "Different sources" in https://manifold.markets/JoeCharlier/which-is-true-of-the-dark-matter-ef to be more careful about that... :-)

@PlasmaBallin https://arxiv.org/abs/2304.06151

Everyone betting here should read this IMO:

Required dark matter properties

I was on vacation last week. As soon as I got back, the first thing I did was fall off my bike onto a tree stump, breaking my wrist. I'll be okay, but I won't be typing a lot. This post is being dictated to software; I hope I don't have to do too much…

@AdamTreat I think it best to read through the whole thing, but for anyone just looking for the summary here it is:

"So in summary, we have two very different requirements on the dark matter. From a cosmological perspective, we need it to be dynamically cold. Something non baryonic that does not interact with photons or easily with baryons.

From a galactic perspective, we need something that knows intimately about what the baryons are doing. And when one does one thing, the other does a corresponding thing that always adds up to looking like MOND. If it doesn’t add up to looking like MOND, then it’s wrong.

So that’s where we’re at right now. These two requirements are both imperative – and contradictory."

@AdamTreat this McGaugh guy seems pretty smart