One Electron, Two Paths: From Interference to Which-Path Measurement
The double-slit experiment becomes genuinely quantum when electrons are sent one at a time. A spread of detector hits alone does not prove wave behavior; the crucial evidence is interference between probability amplitudes associated with alternative paths. This note follows the questions of what interferes, where negative phase comes from, whether one electron involves both paths, and what happens when we measure which slit it passes through.
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