Question: what's before the big bang ?

Joel Goldstein answered on 27 Feb 2023:

A great question! The short answer is that no-one knows.

Our current best understanding is that about 14 billion years ago, the universe was incredibly hot, incredibly dense, and expanding incredibly rapidly. Since then, it has continued expanding and cooling to produce what we can see around us.

How this incredibly hot, dense, expanding universe got there is something we just can’t say at the moment. The laws of physics we know can’t describe it, and there is not sufficient information in astrophysical observations to deduce anything.

Of course, there are lots of theories. In some theories the universe (including time) is entirely self-contained, and asking what came “before” it makes as much sense as asking what happens at the end of a circle. In other theories, the universe repeatedly cycles: a big bang is followed by expansion, then contraction and finally a “big crunch”, before it starts all over again. There are also several different theories in which our entire universe is just part of something much larger, often called a “multiverse”. This multiverse may contain huge numbers of universes, some of which are like ours, but others might have very different laws of nature.