Re:New dark matter map reveals cosmic mystery
by slowmovintarget on Thursday May 27, 2021 @11:29PM
(#27311430)
Dark matter works just fine.
It needs to be "matter" in the cosmological sense [1] because of the ratio of protons and neutrons to photons produced during Big Bang nucleosythesis. We know the ratio of the number of protons to number of photons. We know the number of photons in the universe (most of them are in the CMB), and we therefore know the number of protons. That means we know the amount of "normal" matter in the universe, and it is far less than the total amount of matter in the universe (that must have survived from baryogenesis). This requires there to be "dark matter" in the universe.
The other effects like galaxy formation and stellar motion in galaxies are just things that might be caused by dark matter (though that's come into doubt).
It needs to be "matter" in the cosmological sense [1] because of the ratio of protons and neutrons to photons produced during Big Bang nucleosythesis. We know the ratio of the number of protons to number of photons. We know the number of photons in the universe (most of them are in the CMB), and we therefore know the number of protons. That means we know the amount of "normal" matter in the universe, and it is far less than the total amount of matter in the universe (that must have survived from baryogenesis). This requires there to be "dark matter" in the universe.
The other effects like galaxy formation and stellar motion in galaxies are just things that might be caused by dark matter (though that's come into doubt).
Sean Carroll discusses it here: https://youtu.be/tZQadPmTd84?t=4642
[1] "Matter" in the cosmological sense is "stuff" that moves slower than the speed of light, as opposed to "energy" which moves at the speed of light.