Sure, since Einstein formukated SR it's been know that FTL travel causes backwards in time travel.
The reasoning in the article seemed pretty unsophisticated, I was just wondering if someone had known about it before and found any flaws in it. I'll go over the problem myself in a bit, do a few thought expermiments, etc..
I should say that Tachyons have become a part of "pop science" and have suffered because of it. Also I find many of the explanations in the scientific literature to be specious and inaccurate, such as their having an "imaginary mass". Because there isn't a linear relationship between momentum and velocity the concept of inertia simply doesn't apply to them, period.
And I suspect that they may be useful in explaining some things on the larger scale, such as the presence of magnetic fields and solar activity. This would all involve "long wave" tachyons, shortwave ones, those with wavelengths comparable to the electon comptom wavelength for instance, would make the vacuum very unstable and be easily found in experiments. But longwave ones would explain such things as the solar flux tubes, the ambient heating of the Sun's corona, etc., very elegantly.
Special relativity is a simple theory, I didn't check the maths but I can see nothing qualitively wrong with what he said.
In te standard model of a tachyon they DO have an imaginery REST MASS, though I've seen other models that attempt to describe FTL particles with real rest masses. It should be noted though that tachyons are more of an interesting articfact arising from relativity rather than real phenomena.
Here's another link on the subject.
It presents a different interpretation based on Generalized Galilean coordinates which doesn't have the time travel problem.
I've always thought it interesting that while the Lorentz transformation is a symmetry group it has an asymmetry associated with it, namely that it "favors" a special velocity.
I was somewhat doubtful of the conclusion that particles with "rest momentum" would travel faster that light till I solved the equation for the group velocity, but it turned out to be the case.
So far what I have,
first is he's wrong, using the wrong Lorentz transform for the tachyons. There are three Lorentz transforms (the stuff Einstein didn't tell us) one for timelike world lines, one for light like world lines and one for space like world lines. Needless to say the light like one is the limiting case of the other two. When the two contestants are moving away from each other the tachyons speed up, using the proper transformation, so the backward in time business doesn't happen.
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