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Comment by jimwhite42 | Hacker News Reader

Have you listened to Carroll on the subject? As someone who knows next to nothing on this subject, he seems to me to be claiming that dark matter explains a lot of things in the universe and is very established, whereas MOND is very fringe. The claims in this post, that NGC 1277 is not a particular issue for MOND, seem to ignore the general consensus on MOND vs dark matter. The post seems to be focused on a very specific thing which doesn't seem unreasonable to me, but doesn't change the wider context that dark matter is very established and mainstream, and MOND is not, and this single issue doesn't change the big picture. Is this a flawed reading?

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I don't doubt that the consensus is that MOND is whack but the fact is that MOND has made some stunning predictions that have come true.

For example, Korean scientists went looking to disprove MOND by showing there isn't something called the External Field Effect, which they found as a result of their studies.

MOND predicted that JWST would see old galaxies, which mainstream astronomers are now flipping out over.

MOND predicts that binary stars that are far apart would enter the MOND regime. Two studies confirm this observation. A third refutes it but there appears to be methodological problems in this third study.

Having been a scientist, I have little faith that the median practicing scientists have any concept of discernment in terns of following the scientific method.

You're supposed to flip your opinion on models when predictive data shows up. As far as I can tell LCDM can explain a lot of stuff but it hasn't predicted much.

Think of it this way. When you train a ML model if you have a ton of parameters you run the risk of over fitting unless you have a regularization scheme. LCDM easily has at least one parameter per galaxy, and the only regularization is "can we come up with some explanation for this?" Over fitting is a huge risk for LCDM.

By contrast, MOND has one (maybe two or three, if you believe in relativistic MOND) parameters for the whole universe.

Which is why it's making a priori predictions versus a posteriori explanations, it's very hard to make a priori predictions when your parameter for any given galaxy could be anything.

It should say something that "why don't we have a picture of it: is the center of the milky way a blob of dark matter and not a black hole" (paraphrased of ciurse) was a real publication in between the time that we "took a picture" of a black hole in one galaxy and before we had done so for Sagittarius X-1

I think something like the bullet cluster, where you have gravitational lensing consistent with a collision-less fluid, leading a baryonic colliding gas (which we know is present from X-ray emissions), was a prediction of CDM. So it hasn’t predicted nothing, but yeah, I want to see more.

I don't recall that to be the case. Bullet cluster was a post hoc explanation, not a prediction. Can you find me a citation where they say "we should see matter detached from dark matter" before the bullet observation? I'll happily change my memory on this. I do recall finding something that LCDM predicted though (can't remember off the top of my head it was)

In fact LCDM shouldn't predict the bullet cluster, a collision that fast between galaxies is extremely rare in LCDM models.

It is not controversial that dark matter is the orthodoxy and MOND is more on the fringe. That says nothing about how true either is.

Both DM and MOND have problems explaining various data and do well at others. DM in particular seems to require a lot of parameters and tuning to make it work.

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