While doing research for an upcoming article on string theory (a "big idea" if we ever saw one), I ran across this interview with Lisa Randall. It contains the following wonderfully wacky three questions, in which Randall applies her brain to "branes," higher dimensions, and alternate universes. Gotta love physics:
If there are more than three dimensions out there, how does that change our picture of the universe?
What I'm studying is branes, membranelike objects in higher-dimensional space. Particles could be stuck to a three-dimensional brane, sort of like things could be stuck to the two-dimensional surface of a shower curtain in our three-dimensional space. Maybe electromagnetism spreads out only over three dimensions because it's trapped on a three-dimensional brane. It could be that everything we know is stuck on a brane, except for gravity.
Yet we very clearly see only three dimensions when we look around. Where could the other dimensions be hiding?
The old answer was that the extra dimensions were tiny: If something is sufficiently small, you just don't experience it. That's the way things stood until the 1990s, when Raman Sundrum and I realized you could have an infinite extra dimension if space-time is warped. Then with Andreas Karch, I found something even more dramatic—that we could live in a pocket of three dimensions in a higher-dimensional universe. It could be that where we are it looks as if there's only three dimensions in space, but elsewhere it looks like there's four or even more dimensions in space.
And there could be a whole other universe set up that way?
Possibly. It would be a different universe because, for example, bound orbits [like Earth's path around the sun] work only in three dimensions of space. And the other universe could have different laws of physics. For example, they could have a completely different force that we are immune to. We don't experience that force, and they don't experience, say, electromagnetism. So it could be that we're made of quarks and electrons, while they're made up of totally different stuff. It could be a completely different chemistry, different forces—except for gravity, which we believe would be shared.
Finally, for those of you who think that theoretical physicists are all nerdy old men wearing pocket protectors: check out Randall's picture after the jump, which could inspire a person who make all kinds of jokes about gravity and attraction.