Math is not a social construct and not a physical one. Math is a
mental construct. There is no inherent relationship whatsoever between math and physics.
Saige (and
Greg Bear) are incorrect to assume that the value of
Pi depends in any way on our physical surroundings. It does not; it is a property of certain idealized entities that exist solely in our minds.
Strictly speaking, any correspondence between mathematical constructs and reality is pure coincidence. Of course, in reality this is a bit different; people prefer to have applications for their thoughts. Additionally, our mind is of course strongly influenced by our physical and social environment. But there are branches of pure mathematics where corrspondences to reality are few and far between, if they exist at all (sometimes, they pop up quite unexpectedly).