Do numbers and other mathematical entities actually exist, or are they made up by the human mind?
This is a question I've asked in a number of forums before and have only gotten one interesting reply. Derek Abbott said he doesn't know, but thought it was a paradox. To paraphrase Derek: "Nowhere in the universe does a perfect circle exist; only approximations. Yet we can imagine a perfect circle in our minds, and unless you believe cognition is epiphenomenal, our minds exist in the universe, and thus so do perfect circles...."
I struggled on whether to post this in Physics or Math, but I'm more curious as to the physicist's answer. Anyone?