In reply to Eric Walker's message of Sat, 3 Feb 2018 15:56:35 -0700: Hi, [snip] >On Sat, Feb 3, 2018 at 3:49 PM, <mix...@bigpond.com> wrote: > >When you look at the night sky, it is mostly black, so there don't seem to >> be as >> many photons around as would be needed to account for dark matter (or dark >> energy for that matter ;). Of course, I could be wrong, but that's my first >> impression. >> > >Your eyes do not see the radio, infrared or microwave backgrounds, nor the >high-energy gamma rays that are present. :)
True, but the number of gamma/x rays is way fewer than the number of visible light/heat photons, and the radio waves carry far less energy. Given that most of the photons in the Universe come from stars, of which our Sun is reasonably typical, we could expect most of the photons in the Universe to have a spectrum roughly the same as that of our Sun. Another way to look at it is that if most of the photons come from stars, then the total mass/energy of all photons can't exceed the total mass loss of all stars over the life of the Universe, and since the mass loss of stars is due to fusion reactions, and is only a fraction of the total mass of stars, the total photon mass must be (much) less than the total baryonic mass of the Universe, thus insufficient to account for dark matter/energy (which must exceed baryonic matter by a large margin IIRC). Regards, Robin van Spaandonk local asymmetry = temporary success
