Tachyon

A tachyon () or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists posit that faster-than-light particles cannot exist because they are inconsistent with the known laws of physics. If such particles did exist, they perhaps could be used to send signals faster than light and into the past. According to the theory of relativity, this would violate causality, leading to logical paradoxes such as the grandfather paradox. Tachyons would exhibit the unusual property of increasing in speed as their energy decreases and would require infinite energy to slow to the speed of light. No verifiable experimental evidence has been found to support the existence of such particles. The term "tachyon" is derived from a 1967 paper by Gerald Feinberg about excitations of a quantum field with imaginary mass. Subsequent work has shown that the excitations are not faster-than-light particles, but particle physicists still discuss "tachyons", e.g., in tachyon condensation, when they are referring to tachyonic fields.