Euler, the Basel Problem, and the Art of Knowing More Than One Can Prove
An interesting and genuinely stimulating issue: the Basel_Problem and the Riemann_zeta_function. By the way, and at the risk of sounding reflective rather than revisionist, my own view is this:
Despite its elegance, Euler’s treatment of the zeta function—and much early work that followed—lacked a unifying conceptual framework. He handled ζ(s) more as a pliant formal expression than as a structured mathematical object. Infinite series were freely rearranged, divergent sums tamed, and analytic continuation used long before anyone defined it. Euler often knew the answer so well he scarcely felt compelled to justify it.
Crucially, neither he nor his successors had
- a structural reason for the appearance of π in even zeta values,
- a geometric or spectral view of ζ(s),
- or a principled account of how arithmetic data mesh with analytic behaviour.
Rigor eventually arrived with Cauchy, Riemann, and others, but it merely tidied the theory rather than explaining its deeper architecture.
Further progress on the Basel Problem and the zeta function may require shifting attention from sums to spectra. The presence of π² hints at eigenvalues, boundary conditions, and hidden operators, much like the Laplacian on an interval. From this angle, ζ(2) becomes the trace of an operator on an appropriate space rather than a numerical curiosity.
A promising line of inquiry is to identify a canonical dynamical or geometric system whose spectral invariants encode the special values of ζ(s) across the complex plane. This would situate the zeta function in a natural mathematical setting, not one built from ad hoc analytic continuations. It would place the Basel Problem within broader themes such as spectral geometry, non‑commutative spaces, and the elusive bridge between arithmetic and analysis. Instead of asking how Euler reached the right answer, we ask what sort of mathematical universe renders his result inevitable.
To be clear: Euler’s solution was not mistaken but premature—an inspired success achieved before its conceptual foundations existed. He delivered the destination; it has fallen to later mathematics to build the road and explain why the route must look as it does.
