Island Universes

Once upon a time, in the early days of astronomy, people who called themselves astronomers referred to galaxies as "Island Universes".  This idea held certain implications that we are now revisiting today -- the idea of a multiverse.  According to the Island Universe theory the large, spiral-shaped objects in the night sky were universes separate from our own, yet completely visible.  No one had any idea there could be another galaxy, after all weren't we privileged in the universe?  But if these objects contained stars like the Milky Way and each star had other objects orbiting them, wouldn't that mean we were no longer special?  That certainly couldn't be the case, so it was hypothesized that those astoundingly bright objects in the sky must have been other universes similar to our own, but different.

An Island Universe visible from our own Universe
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Milky_Way_Galaxy_and_a_meteor.jpg/1024px-Milky_Way_Galaxy_and_a_meteor.jpg

Today, we have a similar idea of multiple, individual universes.  We cannot see the alternate universes today and often refer to them as "alternate realities" assuming that each is parallel to our own.  Many people assume this "parallelness" implies there's an alternate us in an alternate earth in these other universes.  M.R. Franks explains in his book (referenced in the second link) that the alternate universes are less parallel and more every other option for a state of energy.  While it's possible there's a universe with an earth very similar to ours with people very similar to ours, it is not implied that every universe has similar "us's" making the decision opposite every one we make.

Just like many other things in our world we think are new, the idea has already been thought up and dismissed, we're just now providing a different set of rules.  The idea of galaxies not being other universes may seem simple to us now, but imagine what the future will think of us if they discover these other universes are no more than even larger galaxies and the great Milky Way is similar to one of the stars that make it up.  Is it possible there's a multiverse? Yes.  Is it possible these other universes are merely larger celestial bodies we just don't know about yet? Absolutely.

http://ned.ipac.caltech.edu/level5/March02/Gordon/Gordon2.html
http://www.bibliotecapleyades.net/ciencia/ciencia_multiverse04.htm
Mitch Joa