Trope-ing the light fantastic (FTL)

Nothing goes faster than light, right? Relativity theory settled that, surely.

Okay, that's orthodoxy. But quantum mechanics is also orthodoxy, and physics has yet to reconcile relativity with QM. So there's something basic we don't understand. (I'll look at string theory, the brave new hope for reconciliation, in another post. It isn't pretty.)

Must SF prove relativity wrong to use FTL as anything other than a trope? In my opinion, no. It's sufficient to rely (implicitly or explicitly) on issues with and ambiguities in accepted theory. To name a couple:

Maybe the speed of light, even if we can't exceed it, isn't a constant. Check out Faster than the Speed of Light by physicist Jaoa Magueijo. Variable light speed does away with the kludge to Big Bang theory that is cosmic inflation. And some of Magueijo's variable-light-speed theories envision faster light speed in the vicinity of cosmic strings. (These aren't the strings of string theory. The terminology is unfortunate.)

And string theory -- despite its lack of concrete success -- is mainstream physics. String theory envisions extra dimensions beyond the 4-D space-time continuum of relativity. Maybe the 4-D universe we experience is afloat in up to (in the predominant theory) 11 dimensions. As long as string theory remains mainstream physics, it's hard to see why science fiction can't use some sort of subspace, hyperspace, or extra-dimensional (see [membrane theory) shortcut with the net effect in this universe of faster-than-light travel.