- #36
Phrak
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To those who have been arguing the point, I fail to see how the exclusion of postulate 2, specifying a finite invariant velocity, would obtain anything but Galilean relativity.
The funny thing is that what we need to resolve that ambiguity is something like..."a coordinate transformation from one inertial frame to another maps the light cone at the origin onto itself", but that's a statement that sounds a lot like the second postulate. It just isn't possible to define "inertial frame" in a way that's appropriate for SR without including (some version of) both of the postulates in the definition.DrGreg said:In fact, that isn't technically quite good enough, because it makes no distinction between orthogonal and skew coordinates, so a bit more is needed to resolve that ambiguity.
The first postulate mentions the equations of electrodynamics explicitly, and Maxwell's equations predict that the speed of an electromagnetic wave is c in all inertial frames. So if we completely ignore that the first postulate actually fails to define what an inertial frame is (which actually seems to be what everyone is doing), then the second is implied by the first.Phrak said:To those who have been arguing the point, I fail to see how the exclusion of postulate 2, specifying a finite invariant velocity, would obtain anything but Galilean relativity.
Phrak said:To those who have been arguing the point, I fail to see how the exclusion of postulate 2, specifying a finite invariant velocity, would obtain anything but Galilean relativity.
Fredrik said:The first postulate mentions the equations of electrodynamics explicitly, and Maxwell's equations predict that the speed of an electromagnetic wave is c in all inertial frames. So if we completely ignore that the first postulate actually fails to define what an inertial frame is (which actually seems to be what everyone is doing), then the second is implied by the first.
If we choose to interpret the first postulate as if it doesn't actually include Maxwell's equations (i.e. if we interpret "electrodynamics" as an unspecified theory of electricity and magnetism), then we still don't get Galilean relativity. To get Galilean relativity, we must at the very least postulate that the invariant speed is infinite.