Yes … so slower-than-light
particles can travel either forward or backward
But tachyons can't … their time dilation is imaginary (and minus imaginary is still imaginary
No they don't …
If we see a tachyon going from
B, another observer may see it go from
A … that's all!
Nooo … energy = m0
/√(1 - v2
), so either the energy of tachyons is also imaginary, or their rest-mass is.