CoachEvery other visible thing is a diffusing object: it receives light and re-sends — diffuses — part of it in all directions. The page, the apple, the Moon, your own face: none makes a glimmer of its own; each scatters received light generously to every side. A diffuser in the dark is simply invisible.
Examples
Example 49.3 (Diffusion is not mirroring)
Both mirrors and pages send received light back — but with opposite manners. The mirror bounces in one disciplined direction (equal angles — your old bounce rule), preserving the picture; the page’s microscopic roughness sprays light everywhere, destroying the picture but offering itself to every eye at once. That is why a mirror shows the lamp, while the page merely shows itself, from wherever you stand.
Example 49.4 (The Moon’s file, closed)
The childhood verdict now has its formal words: the Moon is no primary source; it is a diffusing object of planetary size — gray rock scattering sunlight in all directions, our way included. So moonlight is secondhand sunshine, and the “dark side” is simply the half whose file holds, at that moment, no light to forward.