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

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...)

snowwrestler 10y ago
> Evidence for atoms and protons was already there before they were "invented". Right, and there is also evidence for dark matter.
- Paul-ish 10y ago
  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.
  - legoviking 10y ago
    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.
  - snowwrestler 10y ago
    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.

snowwrestler 10y ago

> Evidence for atoms and protons was already there before they were "invented". Right, and there is also evidence for dark matter.

Paul-ish 10y ago
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.
- legoviking 10y ago
  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.
- snowwrestler 10y ago
  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.