whatOne-dimensional Schrodinger, solved honestly: split-step Fourier on 1024 points, unitary to rounding error (the HUD posts the norm ledger). A Gaussian wavepacket rolls toward a rectangular wall TALLER than its energy; the classical verdict is: nothing gets through, ever. What reaches the box edges is absorbed and book-kept per side.
whyThe claim: part of every packet crosses the impassable wall. Watch the probability split -- most reflects, a fraction leaks through and runs. Each run ends in one seeded detection tick on the side the particle turned out to be; the tallies converge to the computed probabilities. The deep signature is measured live: transmission dies exponentially with wall width, ln T falling with slope -2*kappa -- the law behind alpha decay, tunnel diodes, and the sun.
howHalf-potential, full-kinetic, half-potential steps with a hand-rolled radix-2 FFT; an absorbing rim (declared) with exact per-side flux bookkeeping, so transmission counts what escaped right as well as what remains there. Sliders trade wall height and width against transmission; the width scan fits the exponential slope against theory. One integer seeds the detections.