General relativity, 6

Authors

David Peak, Utah State UniversityFollow

Document Type

Course

Journal/Book Title/Conference

Physics 3710 – Intermediate Modern Physics, Spring 2018

Publication Date

1-8-2018

First Page

1

Last Page

3

Abstract

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 of hydrogen to helium is about 3:1 in terms of mass and about 10:1 in number of atoms. The total mass in the gas clouds is much larger than in galaxies. On average the density of ordinary, visible mass in the observable universe is equivalent to about one proton per cubic meter. Thus, there is almost no ordinary matter (on average) in the universe.

Recommended Citation

Peak, David, "General relativity, 6" (2018). General Relativity. Paper 6.
https://digitalcommons.usu.edu/intermediate_modernphysics_general/6