Gravity waves

BBC News: Lab tuned to gravity's 'ripples'.

One of the great scientific experiments of our age is now fully underway.  A German/UK team has put the giant GEO 600 gravitational wave detector in a continuous observational mode.  The Hanover lab is trying to detect the ripples created in the fabric of space-time that sweep out from merging black holes or exploding stars.  Success would confirm fundamental physical theories and open a new window on the Universe, enabling scientists to probe the moment of creation itself.  GEO 600 is working alongside a US project known as Ligo (Laser Interferometer Gravitational Wave Observatory).  It may also be joined in the hunt by an Italian lab within a year.  A confirmed detection would require the super-sensitive equipment at more than one of these widely spaced facilities to record an event simultaneously.

No-one's detected a gravity wave yet because we didn't have the equipment, but we have theories.

Edit:

Gravity is not a strong force, as forces go.  That's the hard part of these experiments, finding nothing isn't proof of anything.  If the theory is wrong, and you're looking for the wrong thing, you're not going to find it.  If the theory is right but the equipment isn't sensitive enough, you won't find it either.  And these events they hope to monitor (coalescing black holes and the like) aren't everyday occurrences.  I don't expect results anytime soon, but it's good that they're looking.