I was reading QED by Richard Feynman and at the end he mentions that:
There is a most profound and beautiful question associated with the observed coupling constant, $e$ – the amplitude for a real electron to emit or absorb a real photon. It is a simple number that has been experimentally determined to be close to 0.08542455. (My physicist friends won't recognize this number, because they like to remember it as the inverse of its square: about 137.03597 with an uncertainty of about 2 in the last decimal place. It has been a mystery ever since it was discovered more than fifty years ago, and all good theoretical physicists put this number up on their wall and worry about it.)
I understand that no mathematical formula exists to compute this number but why is that necessary or even a meaningful question? Could the number just be a fundamental property of nature. Asking for a mathematical basis for this number seems to me like asking why the gravitational constant $G$ is 6.6743 × 10-11 $m^3 kg^{-1} s^{-2}$ or why the average distance from the sun to the earth is one AU? Why is the question concerning the mathematical basis for the fine-structure constant different?