Evidence for atoms and protons was already there before they were "invented". I think neutrinos and the Higgs boson were theorized before their discovery.

Physics also has an unfruitful history of invisible stuff: ether, strings (string theory), etc.

Personally I'm glad something other than dark matter is being considered. I was only told that the rotational velocities of galaxies did not match the predictions. IME simple explanations tend to work better for mechanics in physics (until quantum mechanics...)

> Evidence for atoms and protons was already there before they were "invented".

Right, and there is also evidence for dark matter.

I think arenaninja is saying that the theoretical models predicted those things, then empirical experiments later confirmed them. (I don't know if this is actually the case) This gives the theories credibility as being predictive.

In this case we have a theoretical mode, but we later notice our empirical data doesn't match this. Both MOND and dark matter are an attempt to patch up our existing theory to explain what we have seen. This is less compelling, because it is post-hoc and these theories might just work because we force it to work by over fitting. To use an analogy to machine learning, it is like training on your test set; no on is impressed when you then have good performance on your test set.

With that said, I think that point of view would apply to both theories equally.

That is an inaccurate description of dark matter. It was originally theorized to explain why the rotation curves of galaxies did not match the mass distribution of the observable mass in those galaxies. There were several ideas for what form that mass could take, but many of them have been eliminated as possibilities (black holes, stellar objects that are too dim to observe, etc.).

There have been several independent observations that are explained by dark matter, and it's not like the theory for dark matter was specifically changed to accommodate those observations. The most well-known is around gravitational lensing, as the amount of observable mass in clusters of galaxies does not match the amount of distortion that we observe. There are however several others. This kind of independent validation of a theory from other angles is a textbook case of how theories are validated - they are proposed to explain one thing, but turn out to also explain other things.

MOND meanwhile has a much tougher time explaining the other observational evidence. It has had to be extensively patched to fit the other cases. Additionally, as noted elsewhere in the comments, neutrinos are not dissimilar to dark matter. Both are forms of matter that it do not interact electromagnetically, making them all but impossible to detect directly. Theorizing that there is more than one such type of particle is not very much of a stretch. Taking that into account, MOND seems to be a much more complex solution than just having another type of matter with properties similar to those we have already seen.

Almost all of the skepticism around dark matter comes from outside of the scientific community, and I think both the name and it being lumped in with dark energy (which is just a placeholder, not an actual validated theory) are part of what contributes to this. While obviously the consequences of this skepticism are significantly less dire, the reasons for it seem pretty similar to those of climate change skeptics - primarily tied to human intuition.

It's not the case--protons were observed first, and then theory was developed to explain them, among other things.

General relativity might be wrong, but it's probably not over-fitted because it's quite simple as far as theoretical constructs go.

And it has a pretty good track record. Both black holes and gravity waves were "invented" because the theory seemed to indicate that they should exist, even though there was no evidence yet. Both were spectacularly confirmed last year.

That said, we know there is some shortcoming in either GR or quantum mechanics (or both), because they don't agree under certain conditions. Dark matter, being a gravitational phenomena that seems like it might be a new kind of particle, is potentially in that same area.

It's also worth pointing out that several similar 'holes' in theories have turned out to be correct. Things like missing elements in the periodic table, and fundamental particles like the Ω− baryon or the Higgs boson, where all things that seemed like holes in a theory, but were later discovered to exist.

And how many "holes" proved to be incorrect? I think that using the history of past true positives is a weak argument for dark matter.

I'm not sure it's as much an argument for dark matter and more an argument against the idea that if you must create a force or type of matter (or matter itself) in order to make a model work, then the flaw is in the model. By showing examples of this being a useful method in the past, it helps discredit the idea that the model has to be wrong, as opposed to proving idea that the model has to be right which are two different arguments entirely.

Obviously it's not sufficient evidence for dark matter. But I'm pretty sure that more often than not predictions of unobserved phenomena based on theories with great predictive power and mathematical elegance, turned out to be correct. Although sometimes, like with the neutrino, things turn out to be slightly different than expected.

In my opinion Verlinde's theory is a better candidate as a replacement of dark matter, since it doesn't require changing the theory of gravity as drastically as MOND does. That said, his theory does require a combination of general relativity with quantum physics, which is tricky. Compared to both just adding a bit of dark (not necessarily invisible) matter is a lot simpler.

Black holes were discovered in theory before any there was any evidence too.

Although interestingly we're not necessarily sure they're exactly what we think they are - you can come up with objects which would give the same observations we have but be quite different : https://en.m.wikipedia.org/wiki/Gravastar

> Ok, but physics has had a long and fruitful history of inventing invisible stuff when theory and results disagree

Inventing and then testing, though. As you said, GR got a huge boost last year, still being tested a century after being proposed. That's how science should be!

We know the darkX behaviour and we have some ideas as to explanation, but far from being proved in the way GR has been.

Dark energy, dark matter, string theory. Lots of IQ being poured into them, with a reasonable chance they're not the answer.

We have a lot of the same type of evidence for dark matter that we have for black holes: strange movement of distant luminous bodies. We've never directly observed either. (With light, anyway. I suppose the gravity wave observatory could be said to have directly observed black holes.)

And like dark matter, black holes point out shortcomings in our theories--they are ground zero for the incompatibility between general relativity and quantum mechanics.

And yet, even though we don't fully understand them, there is not much public doubt that black holes really exist. To the contrary: they are quite popular!

I'm not arguing that just because we think black holes exist, therefore dark matter must also exist. That's bad logic. I'm just pointing out that a lot of the popular concerns with dark matter are not unique to dark matter.