Reproducing a 1976 black-hole radiation calculation from scratch

Author here. This is reproduction, not new physics — Page did it in 1976 and it has been standard ever since.

What I actually wanted to know was how you validate numerical code when there is no experiment to check against. The thing that worked: test against analytic limits the code cannot fit. At low frequency the greybody factor has a known closed-form coefficient of 4/9. My solver extrapolates to 0.44441988, and 4/9 appears nowhere in the code — it can't be tuned to, because it isn't an input.

The other useful habit was keeping a monitor I never optimised. Flux conservation is imposed nowhere in the solver, so it's free. It caught a real bug that the answer itself was hiding — the spectrum looked entirely reasonable.

One correction is in the post. An earlier draft compared against a four-significant-figure value for Page's total power that I had taken from a secondary source and never verified. It is not in his abstract. Retracted, and the comparison now uses his published figures — which are one significant figure, so the honest claim is consistency at that precision, not a 1% validation.