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Except the evidence of dark matter isn't just about the orbit of a single planet. It goes all the way to predicting the spectrum of the CMB.
by russdill 4y ago
Except the evidence of dark matter isn't just about the orbit of a single planet. It goes all the way to predicting the spectrum of the CMB.
- throwawaymaths 4y agoThe explanatory power of something that has as many free (statistical) parameters as lcdm is so high it's stunning how many things it doesn't explain. You'll surely get some things in there by chance.
- russdill 4y agoThe number of free variables has gone down dramatically due to extensive theoretical and experimental work. And as already mentioned, there are many very different lines of evidence and it's not like different variables are being to fit each one in isolation.
- throwawaymaths 4y agoIt's still way more than 3 > different variables are being to fit each one in isolation. For the big picture, phenomena that get "explained" by dark matter are absolutely being fit by different individual variables. For example, the ratio of dark matter to baryonic matter is different between clusters and individual galaxies by an order of magnitude. I recall the DMD for CMB is also different but I can't substantiate that memory quickly In the small, too, there are many galaxies where we have no idea what dynamical situation led them to have the dark matter content they exhibit.
- naasking 4y ago> The number of free variables has gone down dramatically due to extensive theoretical and experimental work. The number of free variables in MOND is one, visible mass, and it's surprising the number of observations it matches despite that. There is almost certainly something there. The superfluid dark matter idea that incorporated both was a promising unifying idea, but last I checked the proposed models didn't match some observations.
- forgotpwd16 4y ago>You'll surely get some things in there by chance. Usually is tuning the parameters for whatever you want to explain. (And then finding that specific tuning doesn't work for something else.)
- DiogenesKynikos 4y agoLambda CDM has only 6 free parameters.[0] That's pretty amazing for a theory that explains all of cosmology. 0. https://en.wikipedia.org/wiki/Lambda-CDM_model#Parameters https://en.wikipedia.org/wiki/Lambda-CDM_model#Parameters
- naasking 4y agoIt doesn't explain all of cosmology without tuning the distributions of dark matter to reproduce the observations that MOND describes without any parameters aside from visible mass.
- DiogenesKynikos 4y agoThere is only one parameter that tunes the distribution of dark matter, for the entire universe: the spectral index. The spectral index sets the statistics of the overall density distribution in the very early universe. After that, gravity and other physical laws determine the evolution of the universe.
- naasking 4y agoThen this is inconsistent with the recent discovery of galaxies without DM, among other issues. I think you're overstating the consistency of the evidence for DM. I replied with a reference to another of one of your comments.
- Avshalom 4y agoDark matter is statistically distributed, the same as baryonic matter. Galaxies with no dark matter or "too much" dark matter is as consistent as galaxies having different baryonic masses or things like https://en.wikipedia.org/wiki/CfA2_Great_Wall https://en.wikipedia.org/wiki/CfA2_Great_Wall
- lostmsu 4y agoWhy would they be independently distributed?