# How could the “Big Bang” singularity have actually expanded? [duplicate]

We have mountains of evidence about singularities and how they work, and we have mountains of evidence that the "Big Bang" was the origin of the universe as we know it. But if compressing enough matter into a small space causes an inescapable singularity (i.e., a black hole), why does compressing all matter into a small space lead to a sudden expansion?

## marked as duplicate by John Rennie, Kyle Kanos, fibonatic, Jim, Qmechanic♦Feb 11 '15 at 19:34

• "We have mountains of evidence about singularities and how they work" Citation needed? We have a lot of math and the math is grounded in experiment (sometimes subtle and beautiful experiments, too), but we don't have singularities to do experiments on. – dmckee Feb 11 '15 at 14:57
• You don't have a singularity just lying around? Get with the times :P Seriously though, what I meant was we have done so many experiments and made so many observations, that the existence of singularities isn't really disputed despite us not having directly observed one (that I know of). – thanby Feb 11 '15 at 15:22
• I would say the actual existence of singularities is pretty far from established :) It's a sign that the equations break down, that's about as far as the "not disputed" goes I think. – BjornW Feb 11 '15 at 16:46
• The Big Bang didn't happen at a point. It is very different from the singularity in a black hole. – John Rennie Feb 11 '15 at 16:58
• possible duplicate of Big Bang snuffed by a black hole? – John Rennie Feb 11 '15 at 16:59

The "explosion" wasn't caused by matter being under high pressure. It is thought that during the first few moments after the creation of the Universe, it went through a phase called "inflation", where there was no matter or radiation or anything else, only potential energy, which lasted $\sim10^{-34}$–$10^{-32}$ seconds and blew space up by a factor of at least $e^{60}$. See e.g. this post for more on inflation. When inflation ended, the Universe continued to expand but slowly decelerated due to the gravitational attraction of its matter. Recently, though, it started accelerating again due to something called dark energy.