text: if a neutrino has no mass why would it be limited to the speed of light? i admit that this question comes from a layman. einstein showed that the following is true: (m^2)(c^4) = e^2 - (p * c)^2 where m is mass, e is energy, p is momentum, and c is the speed of light.  (it's possible to derive this, but not without a ton of explanation and math.)  for any particle that has no mass, m = 0.  this means that: e = (p*c)  he also showed that v = (p * c^2) / e, where v is velocity. (again, it can be derived with pain.)  so, when e = pc, you get v = c.  what this means is that when all of a particle's energy is due to momentum (and none due to mass), the velocity the particle travels has to be c.  that's the mathematical explanation.