# Tomorrowland movie and tachyons? [duplicate]

Would be possible if tachyonic existed to send info to the past or see the future? since the tachyons according to special relativity could travel to the past?

http://en.wikipedia.org/wiki/Tachyonic_antitelephone

if so could we use the spin of tachyons to send bits of information to the past? :D

## marked as duplicate by John Rennie, user36790, Danu, Qmechanic♦Oct 17 '15 at 13:43

Basically, for the consideration of faster-than-light signalling questions, tachyons are very like light in optical mediums in anomalous dispersion frequency bands where the phase velocity of the light can be greater than $c$. A monochromatic wavetrain with a greater-than-$c$ phas velocity has infinite length (like any monochromatic wavetrain), so it is meaningless to talk about signalling with such a thing. When you try to build localized signalling pulses from superpositions of faster-than-$c$ phase velocity sinusoidal waves the pulse travel / spreading speed is always $c$ or less.