Why is it that mathematics, which is a human construct in the form of theorems and equations, can possibly be so successful at describing in a quantitative manner the physical world?
Here are a couple of attempts at answering this:
Eugene Wigner: The Unreasonable Effectiveness of Mathematics in the Natural Sciences.
Richard Hamming: The Unreasonable Effectiveness of Mathematics.
and more recently.
Kevin H Knuth: The Deeper Roles of Mathematics in Physical Laws.