Tachyon

Tachyons are hypothetical particles that, according to some theories in physics, can travel faster than the speed of light. Unlike ordinary particles, which have mass and move at or below light speed, tachyons would possess imaginary mass, allowing them to accelerate as they lose energy. While they appear in some aspects of theoretical physics, particularly in discussions about quantum mechanics and relativity, tachyons have never been observed, and their existence remains purely speculative. If they were real, they could challenge our understanding of causality and time.