What best describes the Big Bang theory

The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced

The big bang theory is the origin of the universe. The big bang theory was the beginning of time, mass, energy, space, and eventually humans. Around 14 - 15 million years ago, a giant explosion started the expansion of the universe and this was known as the big bang theory. The origin of the big bang theory can be credited to Edwin Hubble. Edwin Hubble made an observation that the universe is always expanding.