# Tachyon Speed

1. Apr 15, 2015

### Garlic

Hello,
I heard that theoretical particles that have negative mass (techyons) are predicted to tend to speed up to infinite, if their energies are low enough. I don't understand why infinite speed instead of 2c (double the speed of light) are predicted?
Note: I don't know whose/which theory it is. Sorry if my question is irrelevant.
Thank you

2. Apr 15, 2015

### Orodruin

Staff Emeritus
Tachyons have negative squared masses.

Why would you think that the speed should be 2c for a low energy tachyon? Generally, for any particle, $v = pc^2/E$. All particles satisfy $E^2 = (pc)^2 + (mc^2)^2$ and so if the tachyon has negative mass squared, the energy of the tachyon can be zero. Its velocity would then informally be $v = pc^2/0 = \infty$.

3. Apr 15, 2015

### Garlic

Okay. Thank you. Is there any possibility that a particle has an imaginary mass?

4. Apr 15, 2015

### Orodruin

Staff Emeritus
Tachyons generally come with a lot of theoretical problems, such as violations of causality. That is not saying they do not exist, but I believe most physicists would be very surprised if they did.