User blog comment:Bigtymerxg4/Existentialism/@comment-Tab.-20091020134735

Relativity 101: Maxwell’s equations for electromagnetism have certain symmetries that show that transformations that leave the laws unchanged cannot be applied to space or time independently. In other words, a change in time has a compensating chance in space and vice versa. That can be ignored in certain special cases – basically when an object is stationary, however any motion will result in an effect on time, although the effects are more or less negligible for the kind of motion that regularly takes place, which is where Newtonian mechanics is a suitable model.

Long story short, Maxwell’s equations are not the same in all inertial frames. The main thing is symmetry, changing from one frame of reference to another is a symmetry operation on space-time – to say Newtonian mechanics is the same in any inertial frame is to say that the laws are symmetric under translations at uniform speed, which doesn’t hold for Maxwell’s equations, which suggests that some inertial frames are more inertial than others. The result of all of this was some experimental evidence that light doesn’t obey the general rules for relative motion (if you’re moving at 30 mph, someone else is moving in the same direction at 40 mph, they’re moving at 10 mph relative to you, etc), more specifically that the speed of light is absolute – if you’re stationary, the speed of light relative to you will be c. If you’re moving at 50 mph, it’s still c relative to you, not c – 50.

The consequences are basically that the symmetries of Maxwell’s equations preserve not only the equations, they preserve the speed of light - again, that the speed of light is absolute. You can’t travel faster than the speed of light. Near light speed, lengths shrink, time slows down, and mass increases without limit (hypothetically speaking, if you were actually travelling at near the speed of light, this wouldn’t actually be recognisable, as measuring equipment also gets transformed etc, which explains why light isn’t relative – changes in length and time at varying speeds compensate for the difference).

If you want the actual theory – curvature of space-time is related to mass and energy (mass-energy equivalence is a consequence of relativity). The curvature of space-time at any given point is related by the field equations to the four-momentum of whatever matter and energy is there, and the curvature of space-time explains gravity. Under relativity, space-time is represented as a (four-dimensional) semi-Riemannian manifold, and the geodesics of the manifold represent the paths of particles and light.

Have a nice day.

ps when the fuck did pvx get blogs