Experiments
Double-Slit Experiment
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Thomas Young shone light through two closely spaced slits in 1801 and showed the light landing on a screen beyond formed alternating bright and dark bands, a pattern that only makes sense if light waves passing through the two slits interfere with each other, and his result argued strongly for light as a wave rather than a stream of particles. The experiment was repeated in the twentieth century sending single electrons or photons through one at a time, and even individual particles, arriving one by one, build up the same interference pattern over time. Placing a detector at the slits to learn which one a particle passed through destroys the pattern completely, a result that shows particles behave as waves except when measured directly, the demonstration now used to introduce wave-particle duality.
Facts
YearSourced to the subject's own account MethodSourced to the subject's own accountCoherent light (or, in later versions, individual photons, electrons or other particles sent through one at a time) is directed at a plate pierced by two closely spaced parallel slits, and the pattern formed on a screen behind the plate is recorded, with or without a detector at the slits identifying which slit each particle passed through. 1 Key FindingSourced to the subject's own accountLight and matter build up an interference pattern characteristic of waves when no measurement identifies which slit a particle used, but the pattern disappears the moment a detector determines which-path information, demonstrating wave-particle duality at the heart of quantum mechanics. 1 Cross-Tradition Connections
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