[UnbelievingScumOnTheOtherSide]

You cannot travel at the speed of light.

I wonder about that. The Heisenberg Uncertainty Principle says you cannot know precisely the location of a particle. In principle, there is a finite, albeit remote, possibility for a particle to suddenly be on the other side of the universe. Suppose a particle improving its odds by moving near the speed of light were to occupy a point just ahead of its median position? Then it is beyond the speed of light and off to the races (relative to the observer.) More like the sound barrier then.

[Cboldt]

-- The Heisenberg Uncertainty Principle says you cannot know precisely the location of a particle. --

IIRC, it's that you can't know BOTH, the location, and the momentum/energy.

[ctdonath2]

Problem with that is what constitutes a “particle” is a lot stranger than you think. That line of thinking just doesn’t work that way near such boundary conditions.

[ErnstStavroBlofeld]

A Tachyon is a hypothetical subatomic particle which moves faster than light. In the language of special relativity, a tachyon is a particle with space-like four-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds.