Superstring theory is hot with scientists trying to understand the entire nature of the universe (as opposed to, say, inventing a way to block cellphone reception in cinemas). The idea is that all the particles and forces in the universe are different notes on appallingly tiny strings. A key tenet of this theory is that there are at least ten dimensions, that's six more than the four we can access, but that the others can't be measured or in any way observed because they're too small. Seriously, that's the entire argument. And an invisible and untouchable dog ate their homework. Also, the dog cannot be smelled.
One of the main arguments in favor of string theory is that it correctly predicts the existence of the graviton; this would be the graviton that nobody has ever actually detected, by the way. The graviton we only "know" about at all because another theory (Quantum Field Theory) says it exists. Oh, but that theory stops working if you actually try to use the gravitons in it. It's like saying elves have to exist otherwise there'd be nobody to make toys for Santa.
The problem is that gravitons are points, and as soon as you bring the field theory down to a point the probabilites of something or other become infinite. Since it's only actually possible for something to be 100% probable, you don't have to be a mathematician to understand that an answer of 101% is probably wrong, 200% is definitely wrong, and infinity-% is indescribably moon-bendingly wrong.
Superstring theory solves this by saying that gravitons aren't points; they (and everything else) are little strings around those points, so you never get there. That's right. The geniuses, the guys who would have been rocket scientists a couple of generations ago, the frontline in humanities quest for cosmic knowledge solved a problem in the theory by drawing a little string circle around the point and saying "Don't go here or our stuff breaks". Good thing they weren't rocket scientists or we'd have star charts marked "Don't go this way because planes stop working".
After that the evidence gets even weaker, as if that was possible. Some starry-eyed scholars who may have spent a little too much time indoors point to the inherent symmetry and beauty of the mathematics, and how it fits in with the other graceful theories that describe the universe. I have two things to say:
1) Anybody who thinks mathematics is pure art and elegance simply hasn't done enough integration.
2) The concept that all particles and forces are made up of different notes on the same string all throughout the grand totality is very nice, but given the choice on how to arrive at it, I'll choose a joint and a bean bag over ten years of fiendishly difficult mathematics.
Of course the real support for superstring theory is that it would be really nice if it was true. Alas, the same factor has not given my "Lots of hot cheerleaders doing my bidding" theory the same financial and public support. But when you can't provide a shred of evidence for your belief system (other than the fact you like it better than the alternatives), and certain parts of that system actually refuse the idea of being experimentally tested - well, there's only one thing to say:
Welcome to the Church of Superstring.