Exceeding the Speed Limit

For Columbia University Physicist Gerald Feinberg, the monthly magazine Fantasy and Science Fiction is as compelling as any learned scientific journal.

It has printed a continuing debate be tween Authors Isaac Asimov and Ar thur C. Clarke over the existence of a particle that travels faster than light.

"Impossible, that's all," Asimov insisted in 1967. "Possible, that's all," retorted Clarke in a recent issue. Feinberg's fascination is understandable. The particle is his conception, although he is still not certain that it really exists.

Feinberg has long felt frustrated by Einstein's 1905 conclusion that velocities greater than the speed of light (186,000 miles per second) are absolutely im possible. Such speeds must be approached before man will ever be able to travel to distant stars, and Feinberg says that he does not "like the thought of being permanently confined by lim ited velocities to a small region around our solar system."

Tedious Trip. Spurred on by that hemmed-in feeling, Feinberg brazenly began questioning the inviolable Einsteinian speed limit more than a dec ade ago. But no matter how he analyzed the set of mathematical equations that define relativity, he could not es cape the conclusion that matter cannot be accelerated to the speed of light, to say nothing of higher velocities. The equations showed that at the velocity of light, the mass and energy of any ordinary particle would become infinite --a clearly impossible situation. Beyond it, his mathematics suggested, the mass and energy of the particle can only be represented by the kind of number that mathematicians call imaginary*-- also an inconceivable state of affairs.

Feinberg was unable to get around this mathematical roadblock until he was struck by an ingenious idea. If mass becomes imaginary at high velocities, why not see what happens when an imaginary number is substituted for mass at rest? When he made the substitution, he was able to derive a real number for the energy of a particle traveling above the speed of light. Translating this concept into physical terms, Feinberg conjured up a strange particle that seemed to exist only on the other side of the speed-of-light barrier; it could move at velocities greater than 186,000 m.p.s., but never at that speed or slower. Thus, because it could never stop, its rest mass was irrelevant and could indeed be an imaginary number.

According to the relativity equations, that "tachyon" (a name that Feinberg coined from the Greek word for "swift") should have other strange characteristics. Unlike familiar particles, which gam mass and energy as they accelerate toward the speed of light, Femberg's particle would lose mass and energy as it accelerated beyond the light barrier. At infinite speeds, it would theoretically have no mass or energy at all. Like a plane going faster than the speed of sound, a tachyon with an electrical charge would generate a "light boom" as it traveled faster than 186,000 m.p.s. The boom would take the form of visible light that might well be detectable.

Unbelievable Velocity. With these characteristics in mind, researchers in Sweden, at Princeton and at Indiana State University have been working on a variety of complex experiments designed to detect tachyons--so far without success. Feinberg himself has suggested a massive, computer-aided survey of existing bubble-chamber pictures of particle collisions, hoping that someone may find a pattern that will confirm the presence of tachyons.

If tachyons are some day found--and somehow harnessed--Feinberg's dreamed-of trip to the distant stars may yet be possible. The Einstein barrier to higher speeds would still be unbreakable by man and his spacecraft, but with their unbelievable speeds, the particles could serve to accelerate men closer to the velocity of light.

* Any multiple of the square root of minus one.

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