Physics Commons^™

General Relativity, 6, David Peak

General Relativity

Modern cosmography

The “normal” matter in the universe—i.e., stuff made of protons, neutrons, and electrons— consists, approximately, of lumps floating in a dilute fog. The lumps are galaxies, clusters of 10⁷ to 10¹¹ stars bound together by gravity. In the currently observable universe, it is estimated that there are roughly 10¹¹ galaxies. The dilute fog is primarily neutral atomic hydrogen gas with some helium-4 mixed in (making up a total of 98% or more of the fog); there are also very small fractions of ²H (deuterium), ³He , and ⁷Li . The ratio …