Newtonian-- From my own reading they travel backwards in time.... <br /><br />Here's what John Gribbin says:<br /><br />"At first sight, the special theory of relativity seems to forbid faster-than-light (FTL) travel. If you start out moving slower than the speed of light and go faster and faster, time runs more and more slowly until, at the speed of light itself, it comes to a stop. You can't go any faster, because the speed of light itself is an impenetrable barrier -- if you try to increase your speed any more, there is no time left in which to make the increase. But just on the other side of that barrier, according to the equations, lies a bizarre counter-clock world. There, if you are moving at just over the speed of light, time runs very slowly backwards. There is a certain logic to this -- after all, if time runs slower as you approach the speed of light, and stands still at the speed of light, then it must run backwards ('slower than standing still') above the speed of light. The faster you go, in the tachyonic world, the more rapidly time runs backwards -- and the more energy of motion such a particle has, the slower it goes (that is, adding energy always pushes a particle closer to the speed-of-light barrier, from either side of the barrier). So as a tachyon <i>loses</i> energy it goes faster and faster, rushing backwards in time as it does so. Amazingly, this bizarre possibility was first put forward just <i>before</i> Einstein published his special theory of relativity. At the beginning of the twentieth century, Arnold Sommerfeld (who had been a <i>Privatdozent</i> at Gottingen University, but was then a professor at the Technical Institute in Aachen and went on to gain fame in Munich as a pioneer of quantum theory) realized that Maxwell's theory of electromagnetism required FTL particles to speed up as they lost energy. He published this conclusion in 1904; since the special theory, published in 1905, is also largely based on Maxwell's theory, it is no real