``I didn't mean that there haven't been practices (experimentation or industry) that prove the mathematical theories of gravity. I meant that the way you happened to state the two examples differently incidently illustrated the idea of practice as the test of theory. There's no way to prove the truth of a theory by only discussing it. And I didn't meant that you intended to prove it by just stating it. Sorry.'' Charles
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Don't be sorry. I saw the difference you pointed out immediately, and it me made go back and think about clear, easy examples that demonstrate the idea that there are physical universals out there and all cultures come to terms with them by working with them.
Gravity and light are among my favorite `things'. It took me a long time to figure out just how entrained the biological world is on the orders of the physical world. I tend to go off into theory land over gravity. It is one of those features of the world that nobody notices, and therefore do not consider fundamental, that is to say constitutive for their thought processes.
CG