The discussion centers around the possibility of particles traveling faster than the speed of light, particularly in relation to concepts like Cerenkov radiation and tachyons. It explores theoretical implications, potential contradictions with Einstein's relativity, and the nature of such particles in different media versus vacuum.
Participants generally agree that particles cannot travel faster than light in a vacuum and that Cerenkov radiation is a distinct phenomenon occurring in media. However, there is disagreement regarding the existence and implications of tachyons, with some viewing them as purely theoretical.
The discussion includes assumptions about the nature of light speed in different contexts and the implications of faster-than-light travel on causality, which remain unresolved.
Lester said:Particles going faster than light in vacuum do not exist. Overcoming speed of light means a violation of causality (even if possible formulations of relativity in this case exist and the corresponding field theories describe the so called tachyonic excitations, but these imply a vacuum instability and then they are never observed in nature).
Cerenkov radiation appears when a particle moves faster than the speed of light in the given medium (not vacuum). In a medium the speed of light is given by v=c/n being n the refraction index of the medium itself and so v is smaller than c. A particle can travel faster than v in the medium producing electromagnetic radiation much in the same way of the sonic bang of an aircraft moving faster than the sound speed in air.
Jon