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In school we learn about optics and how rays of light reflect off of surfaces and travel through lenses. These trajectories depend 100% on the shape of the surface (convex, concave, angle of incidence, etc). But how does this work on a microscopic/quantum level? When a photon reaches an object, assuming it doesn't just pass through, it will hit some electron or maybe a proton or a neutron. But there's no concept of a "surface" there. That's a macroscopic phenomenon. Even more, any realistic surface will have plenty of imperfections - it will never be perfectly smooth. And yet all our optical devices work. How?

Added: There's a duplicate question that asks something very similar, but is tagged as and thus the answer is also from a classical standpoint and doesn't consider quantum effects. My question is more from a quantum-mechanics standpoint, because light is fundamentally a quantum phenomenon and reflecting also happens in the quantum realm at a scale where indeed the concepts of "curvature" or even "plane" disappear. Or at least that's what my layman knowledge suggests.

Vilx-
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Rays are one way to think about light. They are very useful for lens design. But you never have just one ray.

Light is a wave. Even a single photon is described by a wave and is spread out over a region.

Reflecting a wave requires an object that has size. The wave is an oscillating electric and magnetic field. These fields cause charges in the surface to oscillate. Oscillating charges radiate. This radiation is the reflected wave. The surface has to be big enough for the charges to oscillate. Typically, the surface must be bigger than a wavelength of light. See If we repeatedly divide a colorful solid in half, at what point will the color disappear?

mmesser314
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