Pythagoras taught how to survey using x, y,… to find a space interval
Pythagoras taught how to survey using x, y,… to find a space interval
s2 = x2 + y2 + … Einstein-Minkowski taught how to survey in space-time:
s2 = x2 + y2 +… -c2t2 —an “invariant”
s2 = 0 is “on the light-cone”
The intervals s are independent of the system of the observer, (inertial, non-accelerating systems, as in Galileo) and only these are physically meaningful, just as in surveying only the distance intervals are meaningful, not x,y etc, since these depend on arbitrary coordinate systems. Same for other observables, like m2c4=E2 - p2c2