Could the beginning of the universe be the other side of a black hole?
Not the beginning of the universe under the Big Bang theory. The
constituent matter of our universe represents a lot more mass than
any one Black Hole could contain. However, in a "closed universe",
all mass would eventually re-contract into a single location. The
presence of a universe-worth of mass could conceivably trigger a
process by which the Big Bang would occur again, to spawn yet
another universe. Proponents of "alternate dimensions" of existence
have suggested that the "death" of one dimension's universe might
funnel matter interdimensionally to form the precursor of another
dimension's universe. But this is, of course, a hypothesis
unsupported by any known physical laws.