ABSTRACT

The universe contains radiation in the form of photons moving in all directions with all frequencies. The first observation of the cosmic microwave background, by Penzias and Wilson in 1965, was the most important cosmological discovery since Hubble established the expansion of the universe. The discovery that the background radiation exists opened up the fascinating possibility of measuring the velocity of the Earth relative to the cosmic fluid, that is, relative to the average motion of the local matter of the universe. In the radiation-dominated era, cosmic dynamics based on general relativity is particularly simple. Galaxies probably condensed from primordial density inhomogeneities. Various segregation mechanisms have been proposed and it is conceivable that the matter and antimatter became separated into regions that later condensed into galaxies and antigalaxies.