In the context of general relativity, space almost is a substance. It can bend and twist and stretch, and probably the best way to think about space is to just kind of imagine a big piece of rubber that you can pull and twist and bend.
Alan GuthDespite its name, the big bang theory is not really a theory of a bang at all. It is really only a theory of the aftermath of a bang.
Alan GuthThe Big Bang theory says nothing about what banged, why it banged, or what happened before it banged.
Alan Guth