The Big Bang Theory is our best guess about how the universe began. The Big Bang Theory is the leading explanation for how the universe began. Simply put, it says the universe as we know it started with an infinitely hot and dense single point that inflated and stretched — first at unimaginable speeds, and then at a more measurable rate — over the next 13.8 billion years to the still-expanding cosmos that we know today. Existing technology doesn't yet allow astronomers to literally peer back at

The Big Bang Explained | ABC Science