>>12740456>how do we know it exists?There are three classical lines of evidence for dark-matter:
Rotation curves: galaxy rotation curves (the speed of stars at different distances from the center) are mapped by blueshift analysis of spectral-lines at various distances from the center, a reliable method, and this shows that the rotational speed doesn't obey Kepler's law with the visible matter as the major source of gravity. The conclusion, assuming standard gravity, is that the galaxy is surrounded by a uniform cloud of dark matter
Zwicky's estimate of galaxy-cluster binding: when you consider the velocities of galaxies in bound clusters, you can figure out how deep the potential well is. The galaxies should be bound, or else it would be a conspiracy that we observe them together right now (they would be flying past by coincidence), and from the velocities, you get a sense of the total mass in the cluster. The result is that there is about 30% of the closure density in dark matter plus ordinary matter, but the ordinary matter is only about 5%.
Cosmological bounds: The mapping of the blackbody radiation fluctuations allows you to quantify the cosmological model, and this reveals that there is a 70/30 split of the universe into cosmological constant and matter. The total amount is the closure density, and this is consistent with Zwicky's dark-matter estimate. Simulations of the structure formation in the universe gets roughly right global density distributions of galaxies with the dark matter content as it is, and no modifications in gravity.
These three lines all converged to the same answer, since the rotation curves also showed a certain amount of dark matter at least 3 times the ordinary matter in a cloud around a galaxy.
>>12740351>defies expectations from particle physicsDark matter interacts gravitationally, so by making a beam of high energy gravitons, and scanning the sky, you can find all the dark matter particles-- they'll scatter the gravitons.
