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Wikipedia's bullet cluster article is written in a very misleading way. The bullet cluster is not a hard problem for MOND since regular baryonic gas easily expl

Wikipedia's bullet cluster article is written in a very misleading way. The bullet cluster is not a hard problem for MOND since regular baryonic gas easily explains the lensing. Working out the bullet cluster with LambdaCDM actually took quite a bit longer because there were problems in the initial data set that took astronomers 10 years to work out. In short, the bullet cluster doesn't "disprove" MOND anymore than it "proves" LambdaCDM. NGC 1052-DF2 is as big a problem for LambdaCDM as it is for MOND. LambdaCDM requires dark matter for galaxy formation. Which means either LambdaCDM is wrong about how galaxies form, or there was some event (of which we currently lack evidence) that removed it. As for MOND, it's possible that actually doing the math may show that this galaxy is not particularly weird. There's aren't many folks fluent in MOND, so work on these kinds of issues tends to lag their discovery. As for MOND and cosmology, yeah, MOND sucks at cosmology. The fact that it can so easily explain so many galactic dynamics (far better than LambdaCDM) is really weird though. MOND isn't a great theory, but it's a really interesting model because it really highlights how poorly LambdaCDM predicts (not explains!) the galaxies we see today.

XorNot 2y ago
This is an apple's to oranges comparison. Lambda-CDM is a theory of all cosmology, including galaxy formation. The dark-matterless galaxies are a problem for Lambda CDM because they don't easily fall out of numerical simulation during formation. Supermassive black hole mergers also don't fall out of numerical simulation easily, but we still observe them. They're not a problem for the concept of dark matter in general, since they have good agreement with the idea that the phenomenon creating dark matter appears to be a massive particle of some sort capable of being spatially dislocated from visible mass. So a theory proposing a pervasive but ill-described massive, mostly non-interacting particle may just be under-explored or the ramifications of the full scope of possible dark matter configurations (as pure mass) not explored. It is a problem for MOND, which proposes that all matter is generating this effect which looks like dark matter (and then has an extremely poor ability to explain the rest of cosmology or work within the framework of general relativity).

XorNot 2y ago

This is an apple's to oranges comparison. Lambda-CDM is a theory of all cosmology, including galaxy formation. The dark-matterless galaxies are a problem for Lambda CDM because they don't easily fall out of numerical simulation during formation. Supermassive black hole mergers also don't fall out of numerical simulation easily, but we still observe them. They're not a problem for the concept of dark matter in general, since they have good agreement with the idea that the phenomenon creating dark matter appears to be a massive particle of some sort capable of being spatially dislocated from visible mass. So a theory proposing a pervasive but ill-described massive, mostly non-interacting particle may just be under-explored or the ramifications of the full scope of possible dark matter configurations (as pure mass) not explored. It is a problem for MOND, which proposes that all matter is generating this effect which looks like dark matter (and then has an extremely poor ability to explain the rest of cosmology or work within the framework of general relativity).