I'm enjoying this conversation and really like being challenged to dig in and see what I can find. Here's some more info. On the question of experiments that could provide support for string theory, Patrick recently sent out a link to a Northwestern University news release about a detector at the south pole that could provide evidence of string theory. The site is http://www.nupr.neu.edu/1-06/southpole.shtml Also, here's a segment from a Nova report that is archived on the Internet at http://www.pbs.org/wgbh/nova/elegant/view-lykken.html. It's an interview with physicist Joe Lykken of Fermi National Accelerator. This discussion has to do with the possibility of "extra" dimensions, an aspect of string theory. Not only have people come up with experiments, they have tried them. I think a new accelerator being built in Europe is supposed to be more capable of coming up with some answers. -- Joe Lykken: The key to testing extra dimensions in experiments has to do with gravity. The simplest way that you can see evidence for an extra dimension is to try to produce a high-energy graviton, the quantum of gravity, which could then move off into the extra dimensions. In a particle accelerator we try to collide very high-energy particles and hope occasionally to produce a high-energy graviton that moves off into extra dimensions and disappears. This is something we don't see directly-we don't see the graviton that disappears-but we notice that energy and momentum were carried off by some invisible particle and from that we deduce that something strange happened. In this case a high-energy particle, a graviton, moved off into extra dimensions. So this is the simplest kind of experiment you can do, and if you can eliminate other kinds of possibilities for things that carry off energy invisibly, you would then be able to claim that you've seen evidence for extra dimensions of space. NOVA: What are you doing at Fermi Lab to tackle this question? Lykken: The experiments that we're doing right now are colliding protons with anti-protons at the highest energies at which particles have ever been collided. We're hoping that occasionally in these very high-energy collisions we will make a very high-energy graviton that can move off into the extra dimensions, and then we will see the disappearance of a large amount of energy and momentum and deduce from that, we hope, the presence of extra dimensions. NOVA: What would that actually look like? Lykken: In the particle detector what you will see from this collision will look like a jet of high-energy particles, and then you'll see that there is nothing balancing the energy and momentum of that very high-energy jet. There was something there, a high-energy graviton, but it disappeared into the extra dimensions. We see a very high-energy jet of particles going in one direction and nothing balancing it off in the other direction. That's what we call a missing energy signature. That's the kind of thing where we jump up and down and say, "This could be extra dimensions."