What is the mass equivalent of all forms of energy in the universe?
According to Einstein’s famous equation E = mc^2, every form of energy is equivalent to a certain amount of mass. This mass is subject to the force of gravity, and it is natural to ask how much mass is present in the universe in all known forms of energy. There are believed to be several important kinds of sources of energy in the universe in addition to the protons, neutrons and electrons that make up all the known forms of matter. All of the following estimates are with respect to the critical density of the universe which is set by its expansion rate. For a ‘Hubble constant’ of 50 km/sec/megaparsecs, the critical density in equivalent grams per cubic centimeter is 5 x 10^-30 grams per cubic centimeter; about equal to one hydrogen atom in a container 130 centimeters on a side averaged over the entire visible universe. This defines the co-called Critical Density of the universe. Cosmic Background Radiation: The famous microwave ‘fireball’ radiation contributed by about 10 billion phot
