Ufologists who believe in the ETH point to claims that various developments and shortcuts might lead to faster than light travel. The two physicist authors of this book have been examining the possibilities for a good number of years, and present their conclusions here. This is not an easy read, and a good knowledge of physics is probably needed to appreciate the arguments in full, but the basic conclusion is that none of the suggested processes could actually work in practice.
They examine tachyons, sub-atomic particles supposed to always travel faster than light, and show how they might be able to send messages into the past in certain circumstances, which would create paradoxes of varying degrees of nastiness. It is by no means clear that this would be the case, or that one could transmit a tachyon back along the path one had been received from, though this idea causes problems over something called ‘preferred direction’. Tachyons have not actually been detected. (This was before the claims about superluminary neutrinos, but this now appears to be probably an artefact of the measuring process, and in any case these ‘superluminary’ neutrinos did not possess one of the main properties of tachyons, that of going ever faster as they lose energy.
They examine various ways of creating time travel through wormholes and warp drives of various kinds. Unfortunately these all involve having to have large supplies of exotic matter with negative energy. In the case of the warp drives it turns out that this would be the negative equivalent of the energy output of several galaxies, to say nothing of other more esoteric physical difficulties. Worm holes of various kinds all have what look like insuperable problems when the maths are gone into with due thoroughness.
Travelling back in time through wormholes of course leads to all sorts of weird paradoxes like being able to shoot your own grandmother and prevent yourself getting born, in which case you didn’t shoot your grandmother. One way out of this was to assume that the time traveller would end up in the past of a parallel universe, an interesting prospect. Oh dear, on close inspection it turns out that the process would actually rip you apart, subatomic particle by subatomic particle, each one ending in a different parallel universe. You couldn’t even send a message by Morse code into a parallel universe. All that could come out of a time machine is incoherent white noise.
There have been suggestions to build time machines using rotating cylinders, rotating laser beams and the like. Alas the said cylinders and beams have to be at the very least longer than the observable universe by hyperastronomical orders of magnitude, and probably would have to be infinitely long.
The authors also point out that while forward time travel by relativistic velocities is theoretically possible, that does not mean that it is practical proposition.
If these authors are right, then that really is the end for the ETH, and for time travel, visitors from parallel universes, brane hopping and etc., at least by any means we could remotely comprehend. One thing we can be certain of, is that it will not by anything resembling ultra high performance aircraft. -- Peter Rogerson.