C that is, as in E = MC2, the speed of light.
Newspapers are breathlessly reporting that scientists have measured neutrinos travelling at faster that the speed of light, in seeming contradiction to the theory of relativity which tells us that the speed of light is the universe's speed limit.
I'm no particle physicist, but I'm sure that this result will not be reproducible, which is of course the standard for validating a scientific finding, and will prove to be a measurement error.
How can I be so sure? Simple logic (Or should I say "elementary my Dear Watson?")
If C isn't really the speed limit and the neutrinos really were able to exceed the speed of light they could pick any speed between 299 792 458 m/s and well, infinity. They they would pick a speed that is only just a tiny teeny bit bigger than what the scientists think is their margin of error simply does not pass the somebody screwed up somewhere test.