Also see [1], a follow up post by Stacy McGaugh, a MOND proponent, who is quoted in the Quanta article. He does not agree with the evidence as presented in that article.
> DF2 has consistently been portrayed as fatal for MOND despite consistently being shown not to be a problem. I’ve given up writing formal papers showing this, as nobody cares. They just hear what they want to hear, which is that MOND is wrong. Indeed, after the 2018& incident I swore off doing so.
This should set off crank alarms when you read it.
Professor McGaugh has commented many times on the sociology of science and how the dominant paradigm tends to be hostile or indifferent to alternate views. He is also quite frank about the limitations of MOND as well, although he is definitely in the MOND camp overall.
> If two typical galaxies met in a head-on collision, the dark matter would experience very little friction, or drag, and would keep on rocketing by. But ordinary matter, which interacts using all four fundamental forces, would get all tangled up.
Isn't a galaxy mostly empty space? I thought I read before that when galaxies collide there's actually very little physical contact between the matter. Stars mostly pass through affected predominantly only by change in surrounding gravity. Is this not the case?
The mean free path of a hydrogen molecule in the "warm interstellar medium" is about 0.03 light years, much smaller than the diameter of a galaxy. So if gas clouds collide they will interact strongly.
They don't collide but they do get "tangled" in each other's gravity. Small things (stars) get tossed in random directions and big things (gas clouds) pass into each other and start condensing into smaller/brighter things.
[1] https://tritonstation.com/2026/10/15/ghostly-galaxies-in-the...
Ok then
This should set off crank alarms when you read it.
Isn't a galaxy mostly empty space? I thought I read before that when galaxies collide there's actually very little physical contact between the matter. Stars mostly pass through affected predominantly only by change in surrounding gravity. Is this not the case?