In reality, a piece of glass is a terrible
monster of complexity—huge numbers of
electrons are jiggling about. When a photon
comes down, it interacts with electrons
throughout the glass, not just on the
surface. The photon and electrons do some
kind of dance, the net result of which is
the same as if the photon hit only the surface.

—Richard P. Feynman
QED: The Strange Theory
of Light and Matter

Gutenberg:
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