How is it that a tachyon is faster than $c$?

Question

I remember reading that a tachyon is faster than light, but am still confused as to how and if they could exist in our universe?

Answer 1

If there were a particle that traveled faster than $c$, we would call it a tachyon. Such a particle would indicate that we fundamentally misunderstand the structure of spacetime, since travel faster than $c$ is forbidden in special and general relativity. There is no experimental evidence for any such particle.

More realistically, tachyons indicate problems with a theoretical model. I have had discussions with string theorists who are working to modify the such-and-such model so that it no longer predicts tachyons.