If you conceive of the Universe as the full suite of matter and energy we know, and the early stages had it all compressed into a tiny region of space, then why didn’t it collapse into a black hole? (Birmingham Libraries)

This Is Why Our Universe Didn’t Collapse Into A Black Hole

If everything was hot, dense, and super close-together at the Big Bang, what kept us from collapsing into a singularity?

The Big Bang is one of the most counterintuitive ideas out there. If you think about taking all the matter and energy in the Universe, and starting it off in a tiny region of space, doesn’t it seem rather unlikely that it would expand at the exact rate needed to give us the Universe we see today? Wouldn’t it be far more likely to simply collapse, gravitationally, into the densest type of object the Universe can contain: a black hole? Clearly, that didn’t happen. But understanding why that didn’t happen might just be one of the most profound questions you can ask to help make sense of the Universe we inhabit.

The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. Why the Universe expanded as it did, rather than collapsing into a black hole, demands an explanation. (C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47))

If you knew, from first principles, what the laws of physics were everywhere and at all times in our Universe, that still wouldn’t be enough for you to come up with the prediction that the Universe as we see it ought to exist. Because while the laws of physics set the rules for how a system evolves over time, it still needs a set of initial conditions…