Oh, the multi-verse theory is very real. In fact you'll probably stumble across people you might have heard of from books, television or movies. All of those universes are real somewhere.
And, yes. I was in Atlantis last. There, many people from different realities were flung together to fight a war. So, very much like here.
And, time-travel is very much real. I've done it back home, as well as here.