I have sometimes thought that there might be an infinite number of universes that contain every possibility that you can think of.
For example (and I realize I'm getting a bit silly here), there may be a universe which is an exact replica of ours except that all the fire hydrants are painted blue instead of read. And that is the only difference. That the fire hydrants are painted blue instead of red. And of course, the people in that universe are probably wondering why we paint fire hydrants red in our universe.
But I digress.
As well as there being an infinite number of parallel universes, an infinite amount of parallel universes continue to branch off from our universe (as well as every other) every single moment. For example, as I am typing this reply, I made a spelling error and I had to backspace to correct it. Well a parellel universe just broke off from this one in which I did not make that spelling error and thus I finished this reply three seconds earlier. Over the course of time, the entire fate of that universe was altered as a direct result of that spelling error! Think about it. In that (now parallel) universe in which I did not make that spelling error, I finished this reply three seconds earlier. As a result, the rest of my life was forever altered and through my interactions with others in that parallel universe, their lives were forever altered as well all because of that three second difference. As time in that parallel universe goes on, everything ends up changing more and more due to that one three-second difference in making this reply. At some point, some tragic auto accident was either prevented or caused as a result of those three seconds! And who knows what else.
I'm sure that everybody on this thread can remember a near miss (auto accident) in their lives. Now think about that near miss. You probably thought to yourself "had I left my driveway just a few seconds sooner (or later as the case may be), I would have been in that accident instead of just missing it."
Well that's what I'm talking about! That three seconds can make all the difference in the world. Now think about that near-miss auto crash again. Even though you missed it in this universe, you didn't miss it in some other parallel universe. In that universe, you happened to be killed in that crash. Aren't you glad you are living in this universe and not that one?
Thinking about parallel universes just boggles the mind. Imagine a parallel universe in which "Imagine" by John Lennon is our national anthem. Now you might be thinking, "that's crazy, how could that be?" Well I'll tell you how that could be. Let's imagine that we lost the Revolutionary War to the Brits and thus remained a collection of British colonies for 200 more years. Now let's imagine that around 1970, we finally get our revolutionizing act together and overthrow those darned Brits. Now due to lower taxes, John Lennon comes to America to live and we are so pleased with that decision that we make one of his songs our national anthem. In this case, "Imagine." Of course, there is another parallel universe in which John Lennon's "Mind Games" is our national anthem instead. And so on and so on.
It sure is strange contemplating all these parallel universes.
That's Everett's "many worlds" interpretation of things, formulated back in 1957: Many-Worlds Interpretation of Quantum Mechanics.
I think you should "contemplate" putting that bong away.