(Submitted March 01, 1998)
If it is possible to have hundreds of thousands of solar systems,
is it possible to have hundreds of thousands of universes?
People can, and are, going about extensive observing programs looking
for planets around other stars, with a good deal of success recently.
So not only can they exist, but we now know a few that actually do.
On the other hand, there is no way to observe any universe other than
our own. This is not a practical issue (like there not being good
enough telescopes), but rather a fundamental theoretical issue. By
definition, our universe is self-contained. No other universe can
affect anything in our universe, so we cannot gather evidence about its
Applying Einstein's laws of general relativity, it is possible to come
up with solutions that connect one universe to another via a spinning
black hole. However even if we were to observe such a thing, it would
still not tell us if there was another universe on the other side or if
the other side was part of our own universe.
So, from a scientific standpoint the question is moot,
but from a philosophical standpoint, it is fascinating.
for Ask an Astrophysicist