Let me preface my answer by saying that I don't take discussion of
tachyons seriously. They have never been experimentally detected, nor
has anbody ever proposed a way in which they might be detectable (to
The answer to your question is no. A negative (rest) mass would imply
that a particle accelerates in the opposite direction to an applied
force. (F=ma is still valid. Or, more correctly, F = dp/dt ). It's
speed would still be below c.
I'm not sure what faster-than-light speeds would require.
Mathematically, it might require that the mass is an imaginary number.
All the more reason why I don't take the whole concept seriously.
The fact that tachyons are represented by *complex* numbers has zero
releveance to wheather they are a viable (existance) concept or not.
This "imaginary" number bit has an amazing amount of bad press. The name
should never have been used in the first place in mathematics. Its why I
never use the term. I use the term "complex". *All* numbers are
imaginary. We represent *all* physical entities with numbers. The fact
that this representation may be with ordered pairs, triplets, 2nd order
tensors, twisters etc, has no baring on the reality of a physical
object. The numbers are just a way of describing the object, they are
not the object itself.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.