3 ms·

Far from settled: https://arxiv.org/abs/1003.0939 https://arxiv.org/abs/1003.0939 But armchair physicists love to shriek 'bullet cluster' every time because th

by uoaei 3y ago

Far from settled: https://arxiv.org/abs/1003.0939 https://arxiv.org/abs/1003.0939 But armchair physicists love to shriek 'bullet cluster' every time because they aren't aware of the extent of their ignorance. Considering your HN bio I'd comfortably classify you as "knows just enough to be dangerous". Fair, given your generalization knowing nothing about me? More reading for your benefit, from a working astrophysics professor specializing in ultra-diffuse galaxies: https://tritonstation.com/2016/12/23/crater-2-the-bullet-cluster-of-lcdm/ https://tritonstation.com/2016/12/23/crater-2-the-bullet-clu... https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-and-it-is-itself/ https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-... https://tritonstation.com/2016/07/30/missing-baryons/ https://tritonstation.com/2016/07/30/missing-baryons/

deleted 3y ago
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JumpCrisscross 3y ago
Lots of ground between settled science and “no good reason is ever given.” There are strong arguments for dark matter (broadly, not just Lambda CDM). They are inconclusive. The bullet cluster is less strong evidence for dark matter than good evidence against common armchair refutations. (I agree with your author that it doesn’t rule out MOND as is commonly claimed.)
- uoaei 3y ago
  The arguments inevitably and only boil down to "look, our model converged". The point is, dark matter is not a theory, just a supposition that can always be "proven" with conveniently arbitrarily flexible models (no one can see it so it might be anywhere!). There is no positive theory that has been brought out to explain dark matter, only mere deductive hypothesis about where it would be. Deduction needs a culprit so people keep reaching for different kinds of particles. Jury's out on whether they exist but keeps the experimentalists employed, so at least it's worth that much.
  - JumpCrisscross 3y ago
    Fair enough. I think it’s qualitatively different from SUSY, where I tend towards your conclusion of jobs programme masquerading as theory. (I’m much less convinced dark matter is a novel particle.)
  - jboy55 3y ago
    There have been actually many positive theories trying to explain what particles dark matter could be, they've all been proven wrong. To me dark matter came about from this, "As we understand gravity we can postulate how galaxies rotate given an estimate on its mass, galaxies do not rotate like this" In this statement there are three elements; 1) Our understanding of gravity 2) Our estimates of the mass of galaxies 3) Our ability to determine how galaxies rotate. At one point in time this last 100 years, we had "solved" gravity with regards to our solar system, and we were finding so many new particles that #2 seemed like a great explanation. However, we are now left with no room in our understanding of particles, I think its time to look at the other elements. Put it this way, if we had never observed the galaxy, but developed the standard model in isolation. Then we looked at the stars and tried to define gravity, I'm not sure we'd be so quick to introduce a new type of matter to define gravity.
    - nyssos 3y ago
      > There have been actually many positive theories trying to explain what particles dark matter could be, they've all been proven wrong. Not at all. Ordinary neutrinos and MACHOs (black holes, rogue gas giants, extremely faint dwarf stars) are mostly ruled out. Supersymmetry is not looking promising but certainly not proven wrong. Sterile neutrinos and axions are very much live candidates. > However, we are now left with no room in our understanding of particles There's plenty of room. Quantum gravity is obviously the elephant in the room, but even aside from that, and off the top of my head: the standard model doesn't account for neutrino masses ,matter/antimatter asymmetry, or why the lepton masses are related, and it gets the magnetic moment of the muon wrong. The existence of physics beyond the standard model is certain. We just don't know what it is yet.
      - 3y ago

by uoaei 3y ago

deleted 3y ago

[deleted]

JumpCrisscross 3y ago

Lots of ground between settled science and “no good reason is ever given.” There are strong arguments for dark matter (broadly, not just Lambda CDM). They are inconclusive. The bullet cluster is less strong evidence for dark matter than good evidence against common armchair refutations. (I agree with your author that it doesn’t rule out MOND as is commonly claimed.)

uoaei 3y ago
The arguments inevitably and only boil down to "look, our model converged". The point is, dark matter is not a theory, just a supposition that can always be "proven" with conveniently arbitrarily flexible models (no one can see it so it might be anywhere!). There is no positive theory that has been brought out to explain dark matter, only mere deductive hypothesis about where it would be. Deduction needs a culprit so people keep reaching for different kinds of particles. Jury's out on whether they exist but keeps the experimentalists employed, so at least it's worth that much.
- JumpCrisscross 3y ago
  Fair enough. I think it’s qualitatively different from SUSY, where I tend towards your conclusion of jobs programme masquerading as theory. (I’m much less convinced dark matter is a novel particle.)
- jboy55 3y ago
  There have been actually many positive theories trying to explain what particles dark matter could be, they've all been proven wrong. To me dark matter came about from this, "As we understand gravity we can postulate how galaxies rotate given an estimate on its mass, galaxies do not rotate like this" In this statement there are three elements; 1) Our understanding of gravity 2) Our estimates of the mass of galaxies 3) Our ability to determine how galaxies rotate. At one point in time this last 100 years, we had "solved" gravity with regards to our solar system, and we were finding so many new particles that #2 seemed like a great explanation. However, we are now left with no room in our understanding of particles, I think its time to look at the other elements. Put it this way, if we had never observed the galaxy, but developed the standard model in isolation. Then we looked at the stars and tried to define gravity, I'm not sure we'd be so quick to introduce a new type of matter to define gravity.
  - nyssos 3y ago
    > There have been actually many positive theories trying to explain what particles dark matter could be, they've all been proven wrong. Not at all. Ordinary neutrinos and MACHOs (black holes, rogue gas giants, extremely faint dwarf stars) are mostly ruled out. Supersymmetry is not looking promising but certainly not proven wrong. Sterile neutrinos and axions are very much live candidates. > However, we are now left with no room in our understanding of particles There's plenty of room. Quantum gravity is obviously the elephant in the room, but even aside from that, and off the top of my head: the standard model doesn't account for neutrino masses ,matter/antimatter asymmetry, or why the lepton masses are related, and it gets the magnetic moment of the muon wrong. The existence of physics beyond the standard model is certain. We just don't know what it is yet.
    - 3y ago