Comment by jetrink | Hacker News Reader

Comment by jetrink | Hacker News Reader

I think we need a version of the New Battery Technology Checklist[1] for this type of article. (Though I understand that the research itself often just aims solve specific tensions in cosmology, and it is only the reporting that over-hypes it as a full replacement for dark matter.)

Dear alternative dark matter theory claimant,

Thank you for your submission of a proposed revolutionary theory to replace dark matter. Your new theory claims to be superior to dark matter models and will transform our understanding of the universe. Unfortunately, your theory will likely fail, because:

[ ] It cannot explain galaxy rotation curves across all galaxy types.

[ ] It fails to account for gravitational lensing observed in galaxy clusters.

[ ] It cannot explain the Bullet Cluster observations where dark matter appears separated from normal matter.

[ ] It is inconsistent with the cosmic microwave background anisotropies.

[ ] It cannot explain the large-scale structure and formation of the universe.

[ ] It introduces arbitrary parameters without physical justification.

[ ] It lacks a sound theoretical foundation or violates established physics principles.

[ ] It fails to explain the observed velocity dispersions in dwarf spheroidal galaxies.

[ ] It cannot account for empirical relations like the Tully-Fisher relation.

[ ] It cannot be tested or falsified by current or near-future experiments.

[ ] Your claims are unfounded or exaggerated.

1. https://news.ycombinator.com/item?id=26633670

Ironically, many of those are also levelled at dark matter theories.

Tully-Fisher - dark matter fails to explain the Tully-Fisher relation naturally, and requires a lot of tweaking and feedback effects (arbitrary parameters).

Rotation curves - recent empirical observations shows galactic rotation curves remain flat far beyond what dark matter can explain [1]

Falsified - we've been trying to find dark matter for a long time and failed. The window of possible candidates for dark matter is now surprisingly small.

I am not claiming that dark matter is wrong. I am claiming that the success of it is by no means proven , and it has many problems of its own (including those you list as problems for alternative theories).

[1] https://tritonstation.com/2024/06/18/rotation-curves-still-f...

I enjoy reading these kinds of physics / astro-physics debates on HN. They make the neuroscience ones I’m use to seem quaint and manageable in comparison.

One fun aspect of science for me is until it's explained, the explanation still exists, just our awareness and discovery doesn't, yet.

> Falsified - we've been trying to find dark matter for a long time and failed. The window of possible candidates for dark matter is now surprisingly small

It needs to be falsifiable not necessary to be in a direct or easy way. We still currently have a large portion of the dark sector parameter space unexplored. I would not call that surprisingly small [1].

Also there are many models of dark matter that was excluded by experiments already. I would describe falsifability as a problem fpr MOND models.

[1] https://pdgweb.lbl.gov/2024/reviews/rpp2024-rev-dark-matter....

Yes, I wasn't using the term falsifiable well at all there. It should be possible to falsify a theory, even if it's hard. And we are falsifying dark matter theories, excluding some of them in the process.

I'm not sure MOND is harder to falsify than dark matter. There have been some recent observations looking at wide binary stars. Throw as much money into falsifying MOND as we have into trying to find dark matter particles, and we can compare!

If you have a way of obtaining this money for MOND, that would be great. Until then the scientific community will focus the limited resources on the more sound ideas. And will focus less on a theory that have the potential to evade all observational contradictions by changing the fitting parameters.

And please don't compare that with dark matter because it has very well integrated framework with particle physics. It does not come merely as a way to only explain galaxy rotation curves while having problems with any larger structures.

MOND only has a single constant parameter, so I'm not sure if you are referring to something else here?

Making dark matter fit observation involves halos and cusps and getting the distribution just right so that the Tully Fisher relation (which is about the luminous matter) still holds.

As a layman, I find MOND involves considerably less fitting!

You will need to have a field theory to go beyond what MOND in original form does. It does only modify Newtonian gravity in the non-relativistic regime, and it applies well at the scale of galaxies but does not address relativistic effects like the one we actually see. One example would be gravitational lensing . To be a successful theory of gravity you would need to be consistent with General relativity. That's the reason why you would go to extend MOND to field theory. The most famous framework would be TeVeS and it does have many fitting parameters.

Thanks, that is helpful. I knew that MOND wasn't relativistic; that a relativistic version might have many more parameters had not occurred to me.

>[ ] It introduces arbitrary parameters without physical justification.

Every fundamental theory does this.

And they come along about once in a century.

Which doesn't make it wrong, but is it perhaps enough to call it an extraordinary claim?

Dark matter is one of the few things that has been studied enough for all of the ordinary explanations to have been ruled out.

Neither can dark matter, unless ad hoc distributions are added, and we have arbitrary speed ups and slow downs of inflation, and if current distance and red shift measurements are valid, which we know they are not.

The problem is that the distance measurements are wrong, and the models have a lot of simplifications due to otherwise being too computationally complex.

I'm doing a sed `s/dark matter/luminiferous ether/g` replacement here and it holds up!

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