3 ms·
I'm not really sure that's a useful way of putting it. There are a set of observations which don't match expectations, one idea which explains most of them is t
by rcxdude 3y ago
I'm not really sure that's a useful way of putting it. There are a set of observations which don't match expectations, one idea which explains most of them is that there is some matter present that we can't directly observe (and then there's a wide variety of more specific ideas of what the nature of this matter may be, some of which fit observations better than others). That's in contrast to the idea that our theory of gravity may be incorrect, which also explains some of the observations (including ones which dark matter does not), but less of them overall, and there's a wide variety of specific ideas of how we might modify gravity to fit the observations (and generally I think the difficulty is you can come up with modifications that explain one obversation well but it's hard to explain a lot of them at once).
DM and MOND are referring to different ideas of matching the anomolous observations, not the observations themselves. And each is really a family of different theories, as opposed to one singular theory each.
- chongli 3y agoThat’s not quite right. The theory which MOND is an alternative to is General Relativity. Dark Matter is the name given to the missing mass resulting from our observations (light we observe directly) not according with mass we infer to exist by GR and the amount of gravitational lensing we observe. As an aside, MOND is not doing so well these days. One of the leading proponents of MOND has published a paper showing a need for substantial revision to the theory following observations of wide binary stars [1]. [1] https://academic.oup.com/mnras/article/527/3/4573/7342478 https://academic.oup.com/mnras/article/527/3/4573/7342478
- MattPalmer1086 3y agoThat's not quite right either. MOND is not a relativistic theory. The clue is in the name: MOdified Newtonian Dynamics.
- chongli 3y agoIf my reply implied that MOND was a relativistic theory then that was not intentional. From the first paragraph of the introduction to the paper I linked: Our current best understanding of gravity is encapsulated by the theory of General Relativity (GR; Einstein 1915). This reduces to Newtonian dynamics in the weak-field non-relativistic limit...