This was a period of cosmic inflation that lasted mere fractions of a second — about 10 Existing technology doesn't yet allow astronomers to literally peer back at the universe's birth, much of what we understand about the Big Bang comes from mathematical formulas and models. While the majority of the astronomical community accepts the theory, there are some theorists who have alternative explanations besides the Big Bang— such as eternal inflation or an oscillating universe. 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. Suddenly, an explosive expansion began, ballooning our universe outwards faster than the speed of light.

Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.