The Big Bang model is that the universe began in an extremely dense and hot condition and has expanded. The theory suggests that redshift proves the universe is expanding.

The Big Bang is a physical theory about how the universe started expanding, and then made the stars and galaxies we see today. The Big Bang is the name that scientists use for the most common theory of the universe, from the very early stages to the present day.The most commonly considered alternatives are called the Steady State theory and Plasma cosmology, according to both of which the universe has no beginning or end.