If there were really a Marvel Vs. DC movie, many would die to see it. Until that day comes true, we can enjoy what could it be like with this fantastic fan made movie trailer by Alex Luthor.
I must say, that is some fine video editing there. Sit back and watch.
The multiverse theory of quantum physics posits the existence of parallel universes — an infinite number of ever-growing realities that exist concurrently with our own. The theory holds that anything than can happen will happen; if not in this reality, then in another.