Nothing can travel faster than light. It's one of the fundamental constants of our universe, and as such, it's kind of a big deal. We've got a bit of an issue here, then, since scientists at CERN have just announced that they've spotted some subatomic particles blowing past the light speed barrier. Physics, we have a problem.
Researchers at CERN have been running an experiment which involved sending a beam of neutrinos about 450 miles straight through the Earth from Switzerland to Italy. Neutrinos are small subatomic particles that are made from regular matter (and have mass), but since they don't have any charge, they can pass straight through just about everything. Typically, they move very, very fast: close to (but not at) the speed of light.
Over the course of the last three years, the researchers noticed that their neutrino pulses were arriving in Italy early. And by "early," they mean about 60 billionths of a second earlier than it would take a beam of light to travel the same distance. They repeated the experiment some 15,000 times, and have reached a statistical level of confidence in this result that qualifies it as a formal discovery. What this is saying is that neutrinos, which are made of matter and have mass, can travel faster than the speed of light, which they are most definitely not supposed to be able to do.
Here's why this is really, really important: if it is in fact possible for something to travel faster than the speed of light, Einstein's special theory of relativity says that it could lead to a causality violation. In other words, an object could travel back in time and create one of those nasty time-travel paradoxes. And this is just one of many reasons why special relativity states that light is the ultimate cosmic speed limit.
So what happens now? Well, a bunch of really, really smart people are going to try to figure out if there's any other explanation for the result of the CERN neutrino experiment. And honestly, that's probably what's most likely to happen: maybe there was some slight error to the experiment, or there's some special-case property of neutrinos that makes them behave in a strange manner that somehow doesn't violate the speed of light. Relativity is a theory that's held up to a lot of scrutiny over the years, and it's hard to believe that there's something so fundamentally wrong with it.
That said, we definitely don't know everything there is to know about physics, and it's entirely possible that we've been missing something. If it's ultimately proven that neutrinos can travel faster than light, it's going to mean that a lot of what we thought we knew about the universe is, if not completely wrong, then at least not exactly right.
Relativity as a concept will need to be rethought, textbooks will need to be rewritten, and we'll all have to start accepting the fact that our universe is an even weirder place than we thought it was.