freyar
Extradimensional Explorer
I want to come back to this again briefly. From studying the CMB, we know that there must be some kind of non-normal dark matter in essentially the right amount to explain the speeds of galaxies in clusters, rotation of stars in galaxies, etc. Even some strong MOND advocates agree. Is it possible that MOND is necessary to explain the motions of, for example, stars in galaxies? Yes. I haven't heard anyone to argue that it's not possible (that is, another physicist make this case). However, it seems reasonable to most people that dark matter works well with what data we have, so there is no reason yet to add a new ingredient of MOND until we see something that dark matter predicts incorrectly.
I'm not sure about "a lot" of recent articles, at least not scientific research. The vast majority is really on dark matter. Think of it like a company. You might spend some of your capital on a risky but high-payoff kind of project (MOND), but you want to invest almost all of it on a less risky but also pretty high-payoff project (DM). I should also mention that there are strong motivations to believe that there is particle physics beyond the Standard Model of particle physics (for reasons independent of wanting dark matter) which themselves often include possible dark matter particles.
It's possible. There are people following up on the papers discussed in this blog post. But some of the history not mentioned in that post is that Verlinde's idea is very similar to work done a long time ago (10-20 years, I think) and has never produced much. Could it be right? Yes, but it just doesn't have a good track record yet. The logic in the papers also seems a bit circular in places, if I recall.
I'm listening to the clip. And people do respect that (listen to the woman talking to the other students at around 11:30). But I can tell you that he makes some inaccurate statements (in particular, saying that we believe in dark energy because of one experiment -- it was a number of things together that convinced people).
OK, I think maybe I wasn't entirely clear in what I was saying. They did not have direct data on the wind speeds at Neptune. What you're saying is that they had a lot of indirect information to build a model of Neptune's climate -- true -- but that model turned out to be incorrect. (By the way, solar wind is not the same as a planetary wind.)
This is very different than the case of dark matter. First off, the idea of dark matter was prompted by data (stellar motion in galaxies). It wasn't a case of thinking about something we already saw (Neptune) and trying to model something we hadn't directly observed yet (the winds). Then, people started asking about predictions or consequences of the idea of dark matter. And these predictions have been verified, in at least one case (the CMB) very very well.
You have more than one point here, and I'm going to address them out of order. Last one first: I think it's really quite unfair to the astrophysics/cosmology/particle physics community to say that it "discards" alternative theories because of "what they were taught as true science." First of all, there are definitely people working on alternatives, like MOND, and the division of labor is the result of an optimization process: each physicist deciding (1) what seems like a promising avenue based on current evidence and (2) where he or she can make a good contribution. Next, science has proven to be very good at self-correction. As you've cited, there are "contrarian" scientists, and people do listen when the give solid arguments. (Veltman's in that video were not well-articulated IMO, but maybe he has stronger reasons than what came out in the clip.)
Back to the first point. I hope I've made it clear that the most important, cleanest observation, the CMB, points strongly to the existence of matter outside the Standard Model. It's also pretty difficult for theories without dark matter to explain things like the Bullet Cluster.
And now, the grand finale
. Why haven't we discovered DM in a lab yet? After all, there are lots of experiments looking for it as it passes through earth. Well, first off, there are some experiments that claim to have detected it (though there is a lot of scepticism about those results for various reasons). But even leaving that aside, should we expect to have discovered DM in those experiments? Certainly, the models studied the most should be in range of detection, at least. But why are they the most studied? At least partly because people wanted to be ready in case they were detected! Remember, all cosmology tells us is that there's some kind of non-luminous nearly pressureless type of matter not in the Standard Model. The only way it absolutely has to interact with normal matter -- like our experiments -- is through gravity. If that's it, our experiments can't possibly detect dark matter passing through the earth. And I might add that there are some good possibilities for dark matter in well-motivated extensions of the Standard Model that would not be detectable. So this is what we'd call a model-dependent question. Yes, it would be disappointing if we can't find DM in a lab. Would it be a waste of money? Well, millions of dollars is chump change compared to some experiments, the profits of some corporations, etc. I tend to think of it as fulfilling our curiosity.
