Something that was never mentioned (that I recall) in any physics classes I took…
It turns out that Lorentz contraction (though not time dilation) can be predicted without recourse to special relativity. If you do enough horrible math, you can show that Maxwell’s Equations require that hunks o’ matter composed of particles which solely interact electromagnetically will be Lorentz-contracted in the direction of motion. Special relativity makes a more general claim, of course, saying that anything and everything will be Lorentz-contracted in the direction of motion, regardless of what forces are between the matter particles.
In retrospect, this isn’t that surprising. Maxwell’s Equations turned out to be relativistically correct from the start and in fact were a major part of what inspired Einstein to come up with SR. Maxwell’s Equations require that light travel at c in any inertial frame, which is at odds with Galilean relativity. That conflict is what lead to Einstein formulating SR which is actually based on only two postulates:
- The laws of physics have the same form in all inertial frames.
- Light travels at c in all inertial frames.
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I first learned this amazing fact in a nifty book titled “The Science Of Radio” by Paul Nahin.
I didn’t know that Einstein cited Maxwell as inspiration, however.
Another curious fact is that Maxwell apparently had this mental model of the physics behind electromagnetism which was wildly wrong, but it didn’t matter because it lead him to the correct mathematics. I might have read that in a collection of Feynman lectures, perhaps it was The Character of Physical Law. Highly recommended.
Now, if you find even a semi-accessible explanation of General Relativity which doesn’t require mastery of tensors, I’d love to know about it.
Someone once recommended “Spacetime Physics” by Wheeler, but this turns out to be almost entirely about SR with a tiny bit of GR explanation towards the end.