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Another great article from Ethan Siegel. I think he makes a pretty strong case for cold dark matter, but it relies pretty heavily on theoretical cosmological ar

Another great article from Ethan Siegel. I think he makes a pretty strong case for cold dark matter, but it relies pretty heavily on theoretical cosmological arguments. For the pro-mond argument, there’s a recent interview with Milgrom on Dr Brian Keating’s physics podcast Into the Impossible [0]. There is also a talk about all the ways DM does not fit observations from Pavel Kroupa (University of Bonn) on youtube [1]. In particular, Kroupa argues that when galaxies pass through one another, DM should cause them to move slower after the collision, because DM would be drawn behind each system in a turbulent wake; but no such slowdown is observed. MOND plus visible matter predicts the motion of these systems well. [0] https://youtu.be/oQ0Cr0hxN40 https://youtu.be/oQ0Cr0hxN40 [1] https://youtu.be/PVgwLWVETIM https://youtu.be/PVgwLWVETIM

andrewflnr 4y ago
Turbulence entirely due to gravitational interaction? Does that work? I guess I should watch it, but I can't take it seriously with the title "On the non-existence of dark matter" when there's so much evidence for dark matter. That's clearly unwarranted confidence in search of attention. That said, if true, I think it more likely indicates that both MOND and LCDM have significant truth. The bar for a theory is "as simple as possible, but no simpler." If the evidence truly demands both MOND and DM, we just have to suck it up.
- wwarner 4y ago
  The DM is moved around by the gravity of the moving galaxy. The DM theory is that each galaxy is surrounded by a huge spherical cloud of DM that (by definition) only experiences gravitation and is invisible and insubstantial in every other way. When Voyager gained speed from passing near Jupiter, it caused Jupiter to slow down by a tiny amount. Similarly, when galaxies pass through each other, the DM should take a measurable amount of momentum from the galaxies. And, yeah, it's a provocative title, but he believes that his measurements falsify DM theory. It's partly a tussle between experimentalists and theoreticians. Kroupa is arguing that the claims of the theory can be tested, and that it doesn't match observations. The theoreticians have a nice story for the big bang, inflation, baryonic nucleosynthesis and the variations seen in the CMB, and the amount of DM it predicts happens to match precisely the amount of DM that we observe.

andrewflnr 4y ago

Turbulence entirely due to gravitational interaction? Does that work? I guess I should watch it, but I can't take it seriously with the title "On the non-existence of dark matter" when there's so much evidence for dark matter. That's clearly unwarranted confidence in search of attention. That said, if true, I think it more likely indicates that both MOND and LCDM have significant truth. The bar for a theory is "as simple as possible, but no simpler." If the evidence truly demands both MOND and DM, we just have to suck it up.

wwarner 4y ago
The DM is moved around by the gravity of the moving galaxy. The DM theory is that each galaxy is surrounded by a huge spherical cloud of DM that (by definition) only experiences gravitation and is invisible and insubstantial in every other way. When Voyager gained speed from passing near Jupiter, it caused Jupiter to slow down by a tiny amount. Similarly, when galaxies pass through each other, the DM should take a measurable amount of momentum from the galaxies. And, yeah, it's a provocative title, but he believes that his measurements falsify DM theory. It's partly a tussle between experimentalists and theoreticians. Kroupa is arguing that the claims of the theory can be tested, and that it doesn't match observations. The theoreticians have a nice story for the big bang, inflation, baryonic nucleosynthesis and the variations seen in the CMB, and the amount of DM it predicts happens to match precisely the amount of DM that we observe.