I'm really not understanding your point about Pi. The concept of Pi is quite basic and does not rely on a perfect physical model for the concept to be discovered and examined!...
I don't like the argument about pi. I've mentioned this a couple of times above and nobody seems to want to address my points about the fact that we do not live in Euclidean space. Real circles with the property that ratio of circumference to diameter is a constant and that that constant is exactly equal to the transcendental number we call pi is a complete fairy story. It's just not true physics. It's approximately true physics for sure, but "approximately true" is infinitely far from "perfectly true" when it comes to mathematics. Perhaps this point is too subtle for anyone to notice, but I believe it is the crux of the entire question.
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In the "early science" days of a civilisation they must examine geometric shapes and their characteristics. A square has a circumference of 4 times it's diameter, this does not need a perfect physical model as it can be easily understood. Sure the early scientists would theorise the relationship for a circle, it's a very important relationship. Pi exists and would be discovered and refined in accuracy as the science develops.
Are you really saying you think Pi is "invented"? If so how do you justify that?