Overview
The Big Bang is the cosmological model of the universe whose primary idea is that the universe has expanded into its current state from an initial state of enormous density and temperature. The Big Bang is a scientific theory, and as such stands or falls by its agreement with observations. But as a theory which addresses the origins of reality, it has always been entangled with theological and philo sophical implications. In the 1920s and '30s almost every major cosmologist was an atheist and preferred an eternal universe for which no explanation is needed of where and when it came from.
