Well, keep in mind that some people used to think that neutrinos were massless. It wasn't for sure, there really wasn't any real evidence either way. Then they figured out that they were oscillating between types. In order for them to be able to oscillate they must be experiencing time. Therefore they must be traveling at less than C. Therefore they must have mass. So the idea that massless particles don't experience time is not at all new.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.