3 ms·
- gravitational lensing measurements - velocities in galaxy clusters - getting the fine details of the complicated, wiggly cosmic microwave background spectru
by knzhou 6y ago
- gravitational lensing measurements
- velocities in galaxy clusters
- getting the fine details of the complicated, wiggly cosmic microwave background spectrum right to extreme precision
- getting the fine details of cosmological structure formation (as measured from matter density fluctuations on very large scales) right
- galaxy collisions, like the Bullet cluster (hard to explain with modified gravity)
- the fact that some galaxies have much less dark matter than others (very hard to explain with modified gravity)
- rocqua 6y agoFor the last point. Where do we get our confidence in the (light) mass estimation of a galaxy? Couldn't we be off by a factor of 10?
- knzhou 6y agoMostly the confidence comes from half a century of trying to find such "extra" visible mass! There's a long history of people looking for extra dust or gas or compact objects using a tremendous variety of clever techniques, and yet the deficit has remained. At this point, if you believe that there indeed is extra mass around, it kind of has to be dark matter by definition because it's been so damn hard to see.
- NohatCoder 6y agoThe question is how the f do we know the mass of a galaxy in the first place? We can't have the discrepancy until we have two distinct methods of measuring the mass of a galaxy.