Tachyon

A tachyon ( /ˈtæki.ɒn/) or tachyonic particle is a hypothetical particle that always moves faster than light. The word comes from the Greek: ταχύς or tachys, meaning "swift, quick, fast, rapid", and was coined by Gerald Feinberg in a 1967 paper. Feinberg proposed that tachyonic particles could be quanta of a quantum field with negative squared mass. It was soon realized that excitations of such imaginary mass fields do not in fact propagate faster than light, and instead represent an instability known as tachyon condensation. Nevertheless, they are still commonly referred to as "tachyons", and such fields have come to play an important role in modern physics.