Recent experiments at CERN suggest that faster than light speeds may be possible, at least for a certain class of particles. In today's shouts, a debate concerning the subject took an unfortunate turn when FIBS's master troll decided to join. I'm therefore putting up some thoughts about it here.

Relativity theory starts with the results of the Michelson-Morley experiment which demonstrated the constancy of lightspeed relative to moving frames of reference. Based on this finding, Einstein remodelled physics's concepts of time and space to make theory conform to experimental results. A consequence of this remodelling is the impossibility of exceeding the speed of light for particles with non zero mass. If this conclusion turned out to be wrong, as the recent neutrino experiments suggest, the premise from which it follows would necessarily have to be called into question as well, that is, Einstein's remodelled concepts of time and space. Those would have to be remodelled again, and in a way to be able to incorporate time travel into the past as well as events in which effect comes before cause, both phenomena made possible by the existence of tachyons (= faster than light particles). This is a much more formidable task (if any sense can be made of it at all) than even the step from Newtonian mechanics to relativity theory.

A point that was given in shouts was that faster than light speed (ftl) cannot invalidate the application of relativity theory in scenarios for which relativity theory has been experimentally confirmed. While that is not wrong, it is entirely trivial. Obviously, no new discovery could possibly do that (*). The real point is that ftl speed is a huge conceptual challenge for relativity theory. A bigger challenge in fact than relativity theory was for Newtonian mechanics (and that challenge was rather big already). There is a way to retain the classical concepts of mechanics (mass, force, etc.) in relativity theory in a somewhat modified form. However it is much harder to see a way to do the same for ftl speed within relativity theory, since to relativity theory lightspeed being an upper limit is conceptually fundamental. If one took away the idea of "force" from Newtonian mechanics, a working theory might still be available, but the kind of picture it would give of the physical world would be very different. A similar thing would happen if ftl speeds had to be introduced to relativity theory. If the CERN experiments turned out to be accurate, it would be nothing short of revolutionary to physics, not in the sense that old theories would suddenly become useless (Newtonian mechanics are quite sufficient for many problems, such as getting a satellite into earth orbit), but regarding the change in how we think about the physical foundations of the universe we inhabit. As CERN theoretical physicist Alvaro de Rujula remarked, "If it is true, then we truly haven't understood anything about anything".

(*) By the same argument, one might hold that relativity theory does not invalidate Newtonian mechanics.

There once was a young lady from Flyte,
who said she could go faster than light.
She set off one day
and, in a relative way,
arrived the previous night.