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Comment by BenMorganIO | Hacker News Reader

It is known that certain types of galaxies can have less dark matter than others. I believe that jury is still out. I'm a little concerned by how many people "believe" there is dark matter. This adds a bias to the proposed solutions and the funding for each. It leads me to be a little skeptical when I hear that dark matter is being found and whatnot through the speed of stars. I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass.

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> I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass.

Such as?

MOND (Modified Newtonian Dynamics) is one, though it has quite a few problems, as you can read here https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

Another interesting one is Superfluid Dark Matter (first proposed, to my knowledge, here: https://arxiv.org/abs/1507.01019).

Those are just a few, there are probably more theories that I haven't heard about. Whatever the case, Sabine Hossenfelder recently posted three videos about Dark Matter/MOND/Superfluid Dark Matter that I wholeheartedly recommend:

Dark Matter: https://www.youtube.com/watch?v=FN2d2cmi_Gk

MOND: https://www.youtube.com/watch?v=2VNcDoLNJk8

Superfluid Dark Matter (note that it's the theory she supports): https://www.youtube.com/watch?v=468cyBZ_cq4

> Dark Matter

> Superfluid Dark Matter

As far as I see, from three theories you listed, two are the dark matter theories. The only "alternative" from your list is MOND and as far as I know it has more problems than it can solve:

https://medium.com/starts-with-a-bang/theres-a-debate-raging...

"The tests on the largest scales give us the best tests for dark matter. And these are the ones that dark matter not only universally passes, but that MOND has failed spectacularly for, on every account, for the past 35 years. Among cosmologists*, there is no debate, because there is no alternative to dark matter that reproduces the observed successes."

https://arxiv.org/abs/1112.1320

"The biggest challenge facing MOND today is the shape of the matter power spectrum. The shape depicted in Fig. 1 is related to the acoustic oscillations observed in the CMB. If the Universe is dominated by dark matter, these matter oscillations, dubbed Baryon Acoustic Oscillations (BAO), are highly suppressed as the baryons fall into the potential wells created by dark matter, leaving only percent level traces of the primordial oscillations. In a no-dark matter model, on the other hand, the oscillations should be just as apparent in matter as they are in the radiation. Indeed, Fig. 1 illustrates that – even if a generalization such as TeVeS fixes the amplitude problem – the shape of the predicted spectrum is in violent disagreement with the observed shape."

I'm just a layman, so I may have misunderstood Sabine's explanation, but to my knowledge Dark Matter, as a theory, is fundamentally different from Superfluid Dark Matter. In the latter, there's a new kind of force explaining why MOND, in certain cases, works. She notes at the end of the third video I listed above that Superfluid Dark Matter should be considered a combination of both Dark Matter and MOND. I would recommend taking a look at her video, it's short (about 6 mins) and I found it quite clear. Anyway, this is far from a solved problem, and no theory is sufficiently developed to be the last word on the subject.

> to my knowledge Dark Matter, as a theory, is fundamentally different from Superfluid Dark Matter.

To to be able to fit with the CMB measurements, at that scale this theory behaves exactly like a normal dark matter, so there is still 5 times more dark matter than a baryonic matter.

So it's just "more complicated" at the galaxy level than a normal dark matter, to fit with these measurements "better" too: it involves an "additional force" there. That also means, considering everything together, it's nothing that should make happy those that consider the normal dark matter "unintuitive."

Dark matter is a supersolid that fills 'empty' space, strongly interacts with ordinary matter and is displaced by ordinary matter. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the supersolid dark matter. The state of displacement of the supersolid dark matter is gravity.

The supersolid dark matter displaced by a galaxy pushes back, causing the stars in the outer arms of the galaxy to orbit the galactic center at the rate in which they do.

Displaced supersolid dark matter is curved spacetime.

In the Bullet Cluster collision the dark matter has not separated from the ordinary matter. The collision is analogous to two boats that collide, the boats slow down and their bow waves continue to propagate. The water has not separated from the boats, the bow waves have. In the Bullet Cluster collision the galaxy's associated dark matter displacement waves have separated from the colliding galaxies, causing the light to lense as it passes through the waves.

> I'd love for research to be more balanced since the phenomena can be explained through more hypothesise than just increased mass.

I'd love for climate science research to be more balanced...

Seriously, the "balance" tends to fall towards the theories that have the strongest indications of being on the right track, and that's what's happened with dark matter.

In the video on the only non-dark-matter theory that you linked, MOND, it is pointed out that MOND is known to be wrong, and is considered to at best be an approximation to an unknown theory of modified gravity. MOND itself also has no real theoretical justification, i.e. no explanation for how or why the gravitational equations should be modified.

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