Angela Collier
5 HN recommenders · recommended in 7 months, 2023–2024
43:48 · 751K views · Jun 7, 2023
Physicist Angela Collier argues that dark matter is not a theory but a set of observations, covering rotation curves, the CMB and why modified gravity struggles to explain them.
HN links it to correct the common misconception about dark matter and as a counterpoint to popular science coverage, though one commenter found it muddled.
11 comments from Hacker News
This is a dense video, I highly recommend it though: this video TLDW: there's a lot of evidence on why the phenomena we watch is mostly favored to be described as 'something' that is conveniently called dark matter as opposed to a revision of gravity.
If you've got the time, these YouTube videos are a nice counterpoint to a lot of popular communication and discussion on dark matter: Dark matter is not a theory: this video That dark matter video aged like milk: [LINK] the tl;dr is that "dark matter" is a bit of a misnomer. (But also a fun name so it's probably here to stay through sheer memetic momentum.) Dark matter is not actually a hypothesized kind of matter. Dark matter is just an unresolved discrepancy between theory and observation. I'll say that again: "dark matter" is not an attempt at explaining the discrepancy; dark matter is the discrepancy. There are some hypotheses that postulate some kind of as-yet-unobserved matter that could resolve the discrepancy, but these hypotheses are not the actual problem that we call "dark matter". And not all hypotheses postulate unobserved or exotic matter. Some of them suggest alternative physics, others suggest measurement error.
IANAP (physicist) The only the matter portion of the universe is 85% dark matter (26.8% of mass-energy content of the universe). As for the question; I don't think it's right to assume that dark matter really is exotic matter. It's just a set of observations. It's something that behaves like matter (with respect to density scaling) but only seems to interact gravitationally. Some theories posit that it's some unknown particles, others that they are primordial black holes, and some that gravity just behaves differently (MOND). I really enjoyed Dr Angela's videos on Dark Matter [1,2] [1] [LINK] [2] this video
There's a good cosmology YouTuber who basically explains: dark matter is not a theory, it's a set of observations. Galaxies behave like there's a halo of invisible mass surrounding them, one that varies in density per-galaxy. The halos even perturb as expected in galaxy collisions. But nobody's got a coherent theory on what that halo is. this video
If you're interested in learning more I recommend you watch "dark matter is not a theory"[1]. We consistently, across many measures, observe the effect of substantially more mass than we expect using traditional understandings of dynamics. People have been aware of it, under different names, for about 90 years now. [1] this video