Here's the thing about relativity.
Well, there are several things about it. The first is that the things it tells you are simultaneously absurd and obvious from principles.
But the one I mean is that if you just decide "oh yeah I'll accept this even though it's ridiculous" and then you go ahead and follow the math, it tells you things that are completely ridiculous, that then turn out to be completely true.
(So, why are they ridiculous? Because these effects are so tiny in the conditions we're exposed to that we'd never notice if we hadn't predicted them first, and our brains built an inaccurate internal model of gravispacetime. And also because in the normal conditions we're expose to, these things even out like the age/planetary rotation/orbit/precession thing from the other toot.)
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