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Mar31-11, 08:34 PM
P: 242
No, there are proper times and proper lengths, and there are coordinate choices which can lead to different results when those projections are applied to non-boosted frames.

The 2 ly frame is NOT the best solution for describing the problem, it should be nothing more than a sidenote, an "oh, and an observer using his position as the origin of an unaccelerated set of coordinates will project those measurements in such a manner that he will claim the distance is 2 ly", not "this is what happens, there are no invariant properties anywhere, take your beautiful hyperbolic geometry and flush it because we like the description of shrinking rulers and slowing clocks"...

I mean, I suppose your personal taste could lead you to prefer the "contraction/dilation is king" description, but it is not uniquely correct, and it is not the most useful explanation either.

If it had never been put forth in terms of shrinking rulers and slowing clocks we wouldn't have to deal with people getting stuck on silly things like the twin paradox or ladder and barn paradox.

We could have people discussing whether it is better to pronounce "cosh" as (kawsh) or (kose-aytch) instead, ah well.