The isotropy of the cosmic microwave background radiation (same temperature in all directions)indicates that
A) the universe has always been dominated by matter.
B) the universe had an early period of inflation in which regions initially in contact were carried out of contact with each other.
C) the universe did not begin to expand significantly until after the era of recombination.
D) regions that appear to us to be on opposite sides of the visible universe are in fact in close contact with each other.

Question

Quizplus · Accepted Answer

The isotropy of the cosmic microwave background radiation indicates that regions of the universe that appear to be on opposite sides (i.e. in different directions) of the visible universe have the same temperature, suggesting that they were once in contact with each other. This supports the idea of an early period of inflation in which the universe rapidly expanded, carrying initially in-contact regions out of contact with each other and smoothing out the universe on large scales.

The Isotropy of the Cosmic Microwave Background Radiation (Same Temperature