# Question on parallel multi. theories

1. Dec 3, 2008

### rpcarroll

Ok, I haven't studied the subject at all (yet), but a professor of mine was explaining some of the theories behind string, brane, etc. to me. So bear with me here; I'm confused by this idea that came into my head earlier:
If there are an infinite number of universes where every possible outcome has happened someplace in one of them... shouldn't something in one of them have found a way to travel between other parallel universes and into ours?

2. Dec 3, 2008

### tbourner

Hi, n00b here too, just looking around.

Surely if there are infinite 'verses then technically there are infinite universes where that is possible, and even infinite universes where it has happened!

Maybe when they say 'infinite' they actually mean slightly less than infinite?

3. Dec 4, 2008

### michael879

There can be impossible events even if there are infinite universes. For example, 1+1 = 2 in all universes. Similarly, it could and probably is the case that in every universe, travel to other universes is prohibited by the laws of physics.

4. Dec 4, 2008

### Hurkyl

Staff Emeritus
Only if such a thing is a "possible outcome".

Incidentally, I'm accepting the premise is true only for the sake of argument. Really, I think your professor is just outlining some of the counterintuitive facts about probability when infinitely many samples are involved. And incidentally, I think he should have said "has happened with probability 1" rather than "has happened" -- probability 1 isn't the same thing as a guarantee!

5. Dec 4, 2008

### p-brane

Hi rpcarroll,

Too bad you're not in one of the universes where you ignore this part of your professor's lecture. However, maybe this is one of the universes in which it isn't on the exam anyway.