Definition
Plain language
The fact that a camera or light sensor measures brightness — the square of the light wave — not the wave itself.
As stated in the literature
The property of optical intensity detectors that they register the squared magnitude of the incident field; combined with coherent superposition of two beams, it produces a bilinear cross-term encoding the joint structure of the inputs, analogous to the query-key product in attention.
Also called: square-law
Why it matters: This squaring behavior, when two light beams overlap, produces a combined signal that mirrors the kind of product used in attention, hinting at optical ways to compute it.
For example, a phone camera doesn't sense the light wave itself, only how bright it is, which is the wave's strength squared.
Heard on the show
“And square-law detection — the camera measures intensity, not field.”Episode 002 — An AI Ran a Real Optics Lab for 21 Hours and Found a Transformer-Shaped Pattern in Light