This is pure conjecture but I was thinking about it and wanted to ask people who know more about tachyons than I do: In a vacuum: Particles with mass can only travel with v < c Mass-less particles can only travel with v = c Tachyons can only travel with v > c If you refract light by passing it through a medium with a refractive index > 1 it slows down. I have heard of experiments where light is slowed to virtually a complete stand still, so my question is this: What would happen if you can slow a tachyon down to the speed of light? Would it give up its energy and instantaneously create mass-less particles? Or does that violate the laws of physics? If it did could you use that result to detect tachyons?