5. Eyeglasses and the lens equations

Not only does QED allow you to beautify yourself accurately, it allows you to fry ants on pavement and fix blurry eyesight.

The idea that light travels along the path of least time explains why lenses work. Light travels slower in substances such as glass than in air or a vacuum. By inserting thick glass along straight-line paths from A to B and barely any glass along outside paths, you can make all these paths from A to B take exactly the same time. Their probability amplitudes will be pointing in the same direction, creating a large resultant amplitude, meaning that light from all paths is very likely to "focus" at B.

Differently shaped lenses (the above example is not a normal thin converging lens) could correct eyesight or focus light on parallel paths to burn ants and chickens.

Based on this concept, it's possible to replicate the experimentally-created "laws" of refraction such as Snell's Law: . While the Thin Lens Equation: assumes that lenses act like the one at left (so it can be proved without QED), quantum electrodynamics explains the basic physics behind the assumption.

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