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Comment by throwawaymaths | Hacker News Reader

Worth noting: For a very long time MOND has been predicting earlier galaxies than LCDM.

As far as I know , MOND is not compatible with some observations. So dark matter and MOND have to be tweaked to agree with what we see.

MOND is not compatible with all observations but neither is dark matter. A lot of scientists think MOND is a better explanation than a new particle that we've not yet observed. Have a look at Sabine Hossenfelder's work for some of those arguments.

Which researchers (as opposed to pop-sci pundits) think MOND is a better explanation than Dark matter?

That is a very, very fringe alt-science view that so far exists in various pop-sci blogs and informal youtube discussions, rather than in mainstream conferences, journals, and research centers.

I'm not saying it's bad to speculate or write whimsical blog articles about these topics, there's lots of room for creative speculation, but MOND does not respect Lorentz invariance which is basically a deal breaker for virtually all serious researchers. Fewer things have more robust empirical support than Lorentz invariance, so discarding it forces you to say that your violation is always just over the horizon of what is testable (and this horizon keeps getting pushed back). That's generally a discrediting feature of any theory and a huge red flag. Much better to say "you don't know" than to postulate something which requires such massive fine tuning to always be just beyond the horizon of what is testable, but close enough to that horizon to have explanatory power for observed phenomena.

https://phys.org/news/2017-11-evidence-violation-lorentz-inv...

https://asfriedman.physics.ucsd.edu/Papers/Friedman+2020a.pd...

He's passed, but jacob bekenstein?

Bekenstein wrote an interesting paper on MOND in 2010 here: https://arxiv.org/abs/1001.3876

But again, the 2017 experimental data [cited previously] in support of Lorentz invariance and the 2016 bullet cluster data in support of dark matter basically killed MOND in the eyes of most researchers.

As I said before, nothing wrong with writing papers exploring the consequences of MOND or trying to come up with alternatives, science does not work by consensus, but the bar for dropping Lorentz invariance is really high given the experimental support for it.

I don't know where you're getting this idea that MOND breaks Lorentz invariance. I've never heard of anyone claiming that that is evidence against mond. Hell, a search of mond and Lorentz invariance turns up your comment as one of the top results.

First, it might be 'a lot of scientists' in absolute terms because this is such a fertile field, but it is a tiny minority of cosmologists who believe MOND is the best explanation for these effects.

Secondly, even the proponents of MOND concede that you need to introduce some amount of dark matter in order to explain e.g. observations of the Bullet Cluster. So the competition isn't between new particle vs MOND, it is between MOND + new particle vs new particle.

Sabine says the Bullet Cluster is a problem for dark matter EVEN MORE than it's a problem for MOND!

Yeah, but is it even worth saying that when the response will inevitably be "so what?" by the entrenched anti-MOND orthodoxy?

This is not unusual. There's many predictions made by MOND ahead of the fact that are borne out by reality. But don't worry - dark matter will be "retrofitted" so that it fits the facts and everybody will suffer collective memory loss again.

Edit: see for example table 1 on page 12 here: https://arxiv.org/pdf/2110.06936.pdf from a review of prior expectations by both MOND and dark matter vs how they turned out against reality for a large variety of astrophysical scenarios.

But MOND itself is a "retrofit" to make it agree with the data, isn't it? It's in the name.

Every theory is a retrofit. A useful theory is also predictive.

MOND is not compatible with some observations. It and dark will probably be tweaked until both agree with observations. At that point they will be the same.

That's a false equivalence. MOND has made several predictions before they were observed (external field effect, linear Tully fisher relationship, early galaxies). I think LCDM's made fewer if any predictions.

MOND has its share of failed predictions. It also still requires a certain amount of DM to work.

This is fine for work in progress that all frontier science is but the issue is far from settled.

Dark matter is the umbrella term for the observed discrepancies. MOND is one possible possible explanation for DM. The paper you linked doesn't compare MOND to DM, because that doesn't make any sense. It compares MOND to ΛCDM which is a competing explanation.

Am I understanding that paper correctly that their suggested solution to explain the Bullet Cluster using MOND is too introduce an additional kind of matter which can not be detected on earth and doesn't interact with light (namely sterile neutrinos)?

Is this satire?

"dark matter but not as much" is still an improvement if you replace it with something better. If MOND predicted these observations and LCDM didn't it's reasonable to say that it is better.

Yeah that's fair. I guess it could also explain why DM has been so hard to pin down, if both MOND and DM are true then there might be DM candidates that have been unfairly ruled out.

I do think it significantly hurts the (more philosophical) argument that MOND is simpler or has fewer parameters than DM though.

So the ongoing problem with LCDM is that the parameter space for allowable particles keeps getting pushed back. We keep falsifying classes of potential particles that could be WIMPs. MOND+ some standard model-adjacent particle (like say right handed neutrinos), if we can have a phenomenological estimate of how much of them should exist, would at least be credible on account of having a constrainable set of parameters, whereas the density of WIMPs in normal LCDM has no constraint besides the same measure that we have to infer its existence (gravitation)

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