Does the Lorentz invariance of Maxwell's equations apply here?

I have the same problem as OP has stated in this question, but more generally; I cannot see how even if Maxwell's equations are lorentz invariant, the principle of relativity still applies.

When we simply use the laws of classical electrodynamics (before the advent of special relativity). It predicts that the moving charge experiences zero force for a frame at rest w.r.t the charge. When we switch to the lab frame, suddenly there is a magnetic force. The second frame will see the test charge collide with some object where the rest frame will not. Doesn't this break some fundamental principle of physics? And if the rest frame observes the test charge also accelerate, then we have a disagreement with Maxwell's laws. I really don't think I have any clue what's going on anymore. How do I interpret Maxwell's laws and the subsequent need for special relativity?

  • $\begingroup$ A reference frame is little more than a state of motion. It isn't something that actually exists. Objects either collide or they don't. Special relativity doesn't have as much to do with electromagnetism as you seem to think. Relative motion is what counts, not relativistic motion. The idea that the current-in-the-wire magnetic field is caused by length contraction is a myth. $\endgroup$ – John Duffield Feb 23 '17 at 13:40

You are correct that it's impossible to see two particles collide in one frame and not collide in another frame - things aren't that crazy in special relativity. There is a magnetic force on the test charge in the frame in which it's moving, but there's an electric force on the test charge in the frame in which it's stationary. So either way, the net Lorentz force on the charge points in the same direction. Electric and magnetic forces change into each other when you boost between frames.


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