Matt McIrvin's Freaky Alternate Reality

The always engaging David Appell takes issue with some hopeful statements by Wesley Clark about faster-than-light travel. I tend to take a dim view of the possibility of faster-than-light travel based on everything I know about physics, and Appell is almost completely right. But a few points need clarification.

Clark is confused. Well, OK: he's wrong. In fact, one can't believe in both E=mc2 and the possibility of faster of light travel, because one of the assumptions behind Einstein's derivation of E=mc2 is that nothing can travel faster than the speed of light ("c").

Well, as a hair-splitting objection, I suppose one could believe in the formula E=mc² but not in Einstein's derivation of it, though this would be odd, since the whole theory Einstein developed is spectacularly well-supported.

But beyond that, what Einstein actually assumed was not that the speed of light is an absolute limit, but that the speed of light is invariant in all inertial frames, which furthermore exhibit the same physics in every other way. From that, the speed-of-light barrier is a derived consequence, and so is the rest-energy associated with a given mass.

That said, science-fiction writers who know their physics know a million handwaving ways around it. For instance, in general relativity, it's not completely ruled out that there's some way to make wormhole shortcuts that could take you across faster-than-light intervals in space-time without requiring you to go faster than light in Einstein's sense. Such a possibility would raise all sorts of disturbing problems with causality that make theorists yell at each other (since they could be used to make a "closed timelike loop" that would allow backwards time travel), but its impossibility is not a given.

Or... it's possible (though I personally doubt it) that there are some currently unknown, exotic, super-weak interactions that actually violate relativity and have a preferred reference frame, across which influences might travel faster than light without violating causality, in which case Einstein's theory is just a very good approximation applying to the matter and interactions we know. When you get down to it, what Einstein proposed was a universal symmetry of nature, that of Lorentz invariance. Apparently universal symmetries have fallen to experiment before.

But that's not to say that any of these are terribly likely as physics or promising as a technical possibility. They're more in the nature of science-fiction-plot-device physics, wherein you start with the consequence you want and reason backward to some semi-plausible extension of known science that gets you there. Real scientists don't reason this way, but science-fiction writers often do (the really hard-headed ones, at least), and when handled well, made-up physics can be a pleasure to read.

I don't think that it's worth spending much, or anything even, to develop technologies on spec based on evidentially unsupported violations of known physics; that Breakthrough Propulsion Physics project at NASA that spent thousands on developing ill-supported antigravity concepts was a real embarrassment. On the other hand, looking for subtle violations in a systematic manner might be an interesting thing to do. Fortunately all Clark was advocating was "higher and applied mathematics", something I'm all in favor of since it pays off in lots of ways, whether or not you end up using it to build a star drive.

I haven't jumped on the Wesley Clark bandwagon-- I think he's one of a few pretty good candidates for president-- but lately there's been an annoying effort (of which Appell's post was not a part!) to portray him as a Ross Perot-grade loony, and this remark of his is no doubt going to be used for that purpose. Personally I suspect that it's the admittedly nonrational daydream of a fairly knowledgeable science-fiction fan, but I wouldn't hold that against anybody.