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April 1st, 2007

FTL drives are crackpot fiction?

originally posted to physics where nice explanations follow</lj>

I was thinking about special relativity and Star Trek at the same time -- the horror! -- and wonder which reason is best for defending the constant speed of light. Here's the usual ones that I've heard, with respect to FTL (faster than light) drives:

1. the Enterprise would need infinite energy to achieve c
2. the Enterprise needs to achieve c instantly (see 1.)
3. the Enterprise would massively expand (see 2.)

And to solve these problems, the Star Trek writers came up with some crackpot fiction:

4. the Enterprise has warp drives instead of FTL drives proper, so we would need some ability to "warp" spacetime (response to 1.)
5. the Enterprise has intertial dampers, so we would need some ability to "damp" g-forces (response to 2.)

That's fine for Rodenberry but what about physics? I mean, if we assume something travels at the speed of light, was it always travelling (and be always travelling) at the speed of light? The deprecated Bohr model comes to mind. There's an emission of energy in that model (ΔE) and we quantized it, but did that photon "start" at the speed of light immediately after the electron(s) changed states? And it instantly achieved c without any need of infinite energy because its massless? So the problem for FTL drives is, fundamentally, trudging around all that matter (a response to 3.) ...

As a thought experiment: if a massless thing accelerates to FTL speeds, then we would have no means to sensibly observe its motion, right?  What I mean is, we "see" most phenomena via instruments of EM bands, whether X-ray or visible, so something FTL would be undetectable ... or at least temporarily undetectable (where I'm thinking of our ability to eventually hear things moving faster than sound).  I recall Einstein using a similar thought experiment and he concluded that since he could never catch up to light -- based on some assumptions that I don't recall -- then light must be a fundamental constant. 

On second thought, anything FTL would be permanently undetectable because whatever EM radiation the thing emits would be slower than its relative faster-than-light speed, so its light would never reach us!  Was that Einstein's reason for setting a maximum speed?! because we do indeed see the universe?