Press a curved lens onto a flat plate and a wafer-thin wedge of air is trapped between them. Where the gap is a whole number of half-wavelengths the light cancels; between, it survives — so the same white light that made the oil slick above draws itself as a target of colored rings. The centre, where the two glasses touch and the gap is nothing, is dark: there is no room left for a color to stand.
Drag up / down to press harder — the wedge steepens and the rings crowd inward. Drag left / right to slide the contact point. This is the hero film's own physics, held still enough to count.