Expert: James Gort - 12/27/2006

Question
Hi Prof. Gort.  I have a question related to the idea of a multiverse.  I realize this is probably considered more fringe science, which is perhaps why it interests me.  I'm having a hard time grasping the concept of what is meant by multiverse.  I've read up on this a bit and it usually ends up either too technical or paranormal for me to understand.  So my question is this:  If the universe is all of space and time, how can another one exist?  How can something exist separate from all that exists?  Doesn't that contradict the meaning of the word universe?  What evidence exists to support this idea?  Sorry for such an abstract type question.  I appreciate your time.

Answer
Hi Jim,

You've asked a very interesting and intriguing question.  But one we may never know the "answer" to.  But I'll give you a short summary of the latest ideas, at least from my understanding.

Our senses are tuned to a 4-dimensional universe.  Dimensions are measured in space-time, where space normally means the familiar 3 spatial distances (length, width, height, or simply X, Y, Z) and time.  We can comprehend those and define our universe by those dimensions.  

But suppose we were 2-dimensional "flat worms" living on the surface of a large ball.  In such a universe, our flat worm scientists may find that the universe is somehow curved, and  if we went far enough, we could even wind up where we started.  But it would be impossible, as 2-dimensional creatures, to imagine another ball a distance away.  Or even imagine what was "inside" of our ball.  That third dimension would be unknown to us.  A whole universe of other flat worms could be living on a second ball, and we could never have contact with them.  They would forever be beyond our universe.

Well, a similar thing could be in play in our 4-dimensional universe.  A theory which has gained some acceptance in order to understand the nature of elementary particles is "string theory".  This theory implies that all matter is comprised of vibrating strings, but those strings vibrate in 10 or more dimensions.  We can never observe those other dimensions (in fact, the entire theory may forever be unprovable!), but the mathematics requires it.  So, presumably, other universes could exist in some of those other dimensions, and we could never observe them or have contact with any beings which may exist there.  This sounds like "paranormal", but it is really allowed according to currently understood physical laws.

Another way to think about it is with the Big Bang theory.  According to that theory, space and time itself originated at some finite time in the past (about 13 billion years ago).  We can't speak about "what's beyond" 13 billion light-years, because space and time itself didn't exist then.  But does that mean there's "nothing"?  Maybe not.  Although our 4 dimensions don't exist outside our space-time sphere (our universe), there could be other dimensions which do exist.  Other universes.  At least in "theory".

I hope that gives you some food for thought.  This verges on not being true "science", because it's (probably) untestable and doesn't make predictions.  The worth of a scientific theory is in the testable predictions it makes.  But it's fun to think about these possibilities, anyway!

Prof. James Gort