The big bang theory is the most accepted theory for the formation of the universe. The “big bang” is a misnomer because there was no explosion, but rather a rapid expansion. It is not known what existed the moment before the big bang, however the evolution of the universe from the first instant after the big bang and onwards is well understood. There is considerable evidence supporting the big bang theory, including the following observations:
- There is an abundance of light elements (hydrogen and helium) in the universe. This is as predicted by the big bang theory.
- The universe cooled as it expanded so that today the Cosmic Microwave Background (CMB) radiation corresponds to a temperature of 2.7 K. This is consistent with scientists’ predictions of that an expanding universe would by now have cooled to a temperature in this range.
- The universe is expanding and the galaxies appear to be moving away from us at speeds directly proportional to their distance from us.
This balloon activity models the universe: once compact but now expanding.