A very interesting fact came up in a Communication Engineering lecture. Usually the root mean square pulse broadening of light increases through all mediums; Air, space, perspex etc. However my lecturer posed a very intriguing question. Is there a medium through which the root mean square pulse broadening of light decreases?
Thinking about the question, I considered all materials I could think of with a low dispersion coefficient. But these were still not pure enough to let light speed up through them. Physics logically states an object essentially needs to have no mass in order to travel at or faster than the speed of light. Was our lecturer playing games?
The answer was released to us. Fire! Through research conducted by our lecturer and other communication engineering academics, tests showed that the pulse broadening becomes a negative value and light speeds up through a flame from a controlled gas burn path. Discussion in the class lead to the hypothesis this could occur due to the state of the flame at its concentration point being somewhat of a plasma state rather than a solid or gas.