The Big Bang is the leading scientific theory explaining the origin of the universe. It posits that around 13.8 billion years ago, the universe began as an incredibly hot and dense point, often referred to as a singularity. This point rapidly expanded in a massive explosion, causing space itself to stretch and evolve.

As the universe expanded, it cooled down, allowing for the formation of fundamental particles and, eventually, atoms. Over time, these atoms coalesced to form stars, galaxies, and larger structures. The evidence for the Big Bang includes the cosmic microwave background radiation, which is the afterglow of that initial explosion, and the observed redshift of galaxies, indicating that the universe is still expanding.

The theory has profound implications for understanding the cosmos, the formation of elements, and the fate of the universe itself.