The speed of light in a vacuum is c in all inertial frames. What about in a medium? Light in a superfluid can be slowed to a few miles per hour, so if this speed was the same for all inertial observers, relativistic effects would be very noticeable on an everyday speed-scale. This doesnt happen, so the speed of light must be frame dependent in a medium. Is there a relation that describes this, or some explanation of why this is the case? Another thing that is confusing me is this: the Lorentz transformation for time is t' = gamma(v)[t-vx/c^2], rearranging gives t = t'/gamma(v)+vx/c^2 which is not what i get from the lorentz transform in reverse t = gamma(-v)[t'+vx/c^2], where gamma(v) = gamma(-v) Hopefully someone can point out my mistake. Thanks.