Most of the familiar physical properties vary according to the relativistic observer's reference frame - speed, mass, energy, time, length, etc. Which properties remain invariant, so everybody will always measure the same value?
Electric and colour charges appear to be. Width, orthogonal to any resultant gravitational/velocity vector, appears to be. Causality is in practice, although there is some debate over the niceties of interactions with entangled states. Is this list correct, and are there any others?
(Possibly relevant; This question asks about "objects" rather than properties in general, but has not been answered yet)
