27 ms·

> distribution You're right. I was wrong. It doesn't have millions of subparameters. It is a single parameter, a vector with countably infinite dimension.

andrewflnr 4y ago
> vector with countably infinite dimension. This is equally true for baryonic matter. You might counter that baryonic matter is easier to observe/constrain. I would point out that LCDM also has ways to observe and constrain DM, and the universe doesn't owe us perfect legibility. What is it you think you're proving?
- naasking 4y ago
  What doesn't add up is that MOND can reproduce many of those observations using only the visible mass and a tweak to gravitation. This makes all of these tuned distributions seem very suspicious by comparison. It would be a remarkable coincidence if there wasn't something to MOND.
  - pdonis 4y ago
    > MOND can reproduce many of those observations using only the visible mass and a tweak to gravitation No, it can't. It can only reproduce a subset of galaxy rotation curve observations. It cannot reproduce other observations at all (such as the amount of structure in the universe as compared with the amount of baryonic matter that is consistent with Big Bang nucleosynthesis, which is about the same as the amount of matter we can see, but is much too small to account for the amount of structure--gravitational clumping into galaxies and galaxy clusters--that we see).
    - naasking 4y ago
      I suggest you review the following, it's not nearly as rosy for DM or dire for MOND as you imply: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm
      - pdonis 4y ago
        > it's not nearly as rosy for DM or dire for MOND as you imply According to that one paper, perhaps. There are lots of papers published in this area of research. If you want to say the jury is still out on a final resolution, yes, I'll agree with that.
  - andrewflnr 4y ago
    My guess would be something about the dynamics of dark matter in galaxy evolution pushes the distribution into a shape that produces those mathematically simple rotation curves. That seems Occam's-razor compliant to me; it would be weird if rotation curves with dark matter were really complicated and unpredictable. It's also possible that both MOND and LCDM have some truth to them. But usually people are trying to get rid of dark matter, and that's just not happening.
    - naasking 4y ago
      > My guess would be something about the dynamics of dark matter in galaxy evolution pushes the distribution into a shape that produces those mathematically simple rotation curves. That seems Occam's-razor compliant to me; It's not just rotation curves, there are numerous validated predictions MOND makes based only on the visible matter (see the paper at the bottom). These would all be a set of remarkable coincidences if the current CDM model were true. > it would be weird if rotation curves with dark matter were really complicated and unpredictable. It's also possible that both MOND and LCDM have some truth to them. Yes, this was the idea behind "superfluid dark matter", but it doesn't quite match observations either: https://arxiv.org/abs/2201.07282 https://arxiv.org/abs/2201.07282 Maybe another take on this fusion will stick. > But usually people are trying to get rid of dark matter, and that's just not happening. I'm not sure "usually" is an accurate summary. It's more like they're claiming that the standard CDM model is refuted or should be very disfavoured, which is not so unreasonable IMO: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm IIRC, some MOND proponents suggest that neutrinos can satisfy the dark matter observations that MOND itself doesn't explain. I believe that's discussed in the above paper but it's been awhile since I've read it.
      - andrewflnr 4y ago
        The bulk of the whining I see here about DM is on the lines of "but it's not directly observable, so it can't be real science! Can't you see this is just Big Physics trying to fool you?" These are the ones trying to falsify DM entirely, and having to ignore huge swathes of evidence to do so. Yes, the paper suggests sterile neutrinos at cluster scale, with MOND at galaxy scale. I'm fine with this, honestly.

andrewflnr 4y ago

> vector with countably infinite dimension. This is equally true for baryonic matter. You might counter that baryonic matter is easier to observe/constrain. I would point out that LCDM also has ways to observe and constrain DM, and the universe doesn't owe us perfect legibility. What is it you think you're proving?

naasking 4y ago
What doesn't add up is that MOND can reproduce many of those observations using only the visible mass and a tweak to gravitation. This makes all of these tuned distributions seem very suspicious by comparison. It would be a remarkable coincidence if there wasn't something to MOND.
- pdonis 4y ago
  > MOND can reproduce many of those observations using only the visible mass and a tweak to gravitation No, it can't. It can only reproduce a subset of galaxy rotation curve observations. It cannot reproduce other observations at all (such as the amount of structure in the universe as compared with the amount of baryonic matter that is consistent with Big Bang nucleosynthesis, which is about the same as the amount of matter we can see, but is much too small to account for the amount of structure--gravitational clumping into galaxies and galaxy clusters--that we see).
  - naasking 4y ago
    I suggest you review the following, it's not nearly as rosy for DM or dire for MOND as you imply: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm
    - pdonis 4y ago
      > it's not nearly as rosy for DM or dire for MOND as you imply According to that one paper, perhaps. There are lots of papers published in this area of research. If you want to say the jury is still out on a final resolution, yes, I'll agree with that.
- andrewflnr 4y ago
  My guess would be something about the dynamics of dark matter in galaxy evolution pushes the distribution into a shape that produces those mathematically simple rotation curves. That seems Occam's-razor compliant to me; it would be weird if rotation curves with dark matter were really complicated and unpredictable. It's also possible that both MOND and LCDM have some truth to them. But usually people are trying to get rid of dark matter, and that's just not happening.
  - naasking 4y ago
    > My guess would be something about the dynamics of dark matter in galaxy evolution pushes the distribution into a shape that produces those mathematically simple rotation curves. That seems Occam's-razor compliant to me; It's not just rotation curves, there are numerous validated predictions MOND makes based only on the visible matter (see the paper at the bottom). These would all be a set of remarkable coincidences if the current CDM model were true. > it would be weird if rotation curves with dark matter were really complicated and unpredictable. It's also possible that both MOND and LCDM have some truth to them. Yes, this was the idea behind "superfluid dark matter", but it doesn't quite match observations either: https://arxiv.org/abs/2201.07282 https://arxiv.org/abs/2201.07282 Maybe another take on this fusion will stick. > But usually people are trying to get rid of dark matter, and that's just not happening. I'm not sure "usually" is an accurate summary. It's more like they're claiming that the standard CDM model is refuted or should be very disfavoured, which is not so unreasonable IMO: From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm https://www.mdpi.com/2073-8994/14/7/1331/htm IIRC, some MOND proponents suggest that neutrinos can satisfy the dark matter observations that MOND itself doesn't explain. I believe that's discussed in the above paper but it's been awhile since I've read it.
    - andrewflnr 4y ago
      The bulk of the whining I see here about DM is on the lines of "but it's not directly observable, so it can't be real science! Can't you see this is just Big Physics trying to fool you?" These are the ones trying to falsify DM entirely, and having to ignore huge swathes of evidence to do so. Yes, the paper suggests sterile neutrinos at cluster scale, with MOND at galaxy scale. I'm fine with this, honestly.