Of all the sciencey buzzwords to come out in recent years, this sounds like the one that is most likely to have been lifted from the latest Avengers script; but what does "dark matter" actually mean? Well, this is kinda embarrassing, but it doesn't really mean anything. The thing is, according to our calculations, there's a lot more gravity in the universe than should be generated by the amount of matter in it. By all rights, the universe should be coming apart at the seams, because it doesn't appear to have enough mass to hold it all together in the structures that we can observe. The "dark matter" basically refers to the thing that should be generating the gravity, but we haven't the foggiest idea what it is. We don't even know if its one single thing, and there's nothing to say that it should even be matter at all - it could be a force, a field, a forcefield, it could be something else entirely. We do know one thing about it though: It exists. We know this because we can observe its interactions with gravity, notably its lensing effect which causes the light from other cosmic objects to bend with spacetime. That's all we got for the moment though. Right now, it's basically a shortcut to make the maths work.
