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If tachyons are faster than light, that means they have passed a certain point before anyone or anything can “see” them. Theories have mentioned that if anything can go faster than light, then it can travel through time. So are tachyons leptons that travel through time constantly?

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  • $\begingroup$ FWIW, even the guy who coined the term "tachyon", Gerald Feinberg, was never a strong believer that tachyons exist in our universe, and over time grew more convinced that they can't exist here. $\endgroup$ – PM 2Ring Jan 24 '19 at 6:06
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So are tachyons leptons that travel through time constantly?

Well, all particles travel through time constantly. (Leptons refer specifically to the electron, muon, tau, and the neutrinos; tachyons probably wouldn't carry lepton number.)

Massive particles have a rest frame in which they have zero momentum, and observers sharing that reference frame see time pass at rate of one second per second. Observers in other, boosted reference frames observe dilated time intervals. How massless particles experience time is an interesting question in its own right.

A tachyonic trajectory in a spacetime diagram connects events that are spacelike-separated. For any pair of spacelike separated events, there exists a reference frame where the events are simultaneous. Other observers would disagree about which end of the trajectory occurred first in time. So it wouldn't make sense to talk about a tachyonic path as moving forward or backward in time. Spacelike trajectories are a different concept altogether, one which doesn't exist in pre-relativistic physics.

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