One of the theories is that inflationary cosmology leads to inflationary cosmology: where one universe's big bang's inflation leads to pockets of inflation that

One of the theories is that inflationary cosmology leads to inflationary cosmology: where one universe's big bang's inflation leads to pockets of inflation that can extend beyond the universe they came from -- effectively creating their own universe. Then a big bang extends from that, which repeats into their own inflationary systems, which repeats into their own system, etc. It's a theory from the 80s IIRC.