Parallel worlds are a lot more than Vulcans with really boss facial hair. Time to break it down.
The concept of a universe outside of our own is cool, but complicated. Did you read X-Men comics in the '90s? Then you know that readers (and writers, let's be honest) get lost trying to deal with such a mind-bending premise.
That's where science comes in. We may not have theories that have been proved yet, but there are three possibilities out there that could all, in some way, at least be put to the test. And we've found a very handy video that explains it all in one nice, easily digested package.
In your heart of hearts -- which one of these do you want to be true? Or do you have a theory all your own?
via Minute Physics)