Shine a red laser through a slit thinner than a hair, and the light does not land as a single bright line. It arranges itself into a row of bright and dark bands, with clean stripes of pure darkness carved between them, order appearing where you expected a simple smear. Turn the beam down until only one photon crosses the room at a time, alone, with nothing to interfere with, and the banded pattern still assembles itself, dot by patient dot — as if a single grain of light had quietly traveled every possible route to the wall at once and weighed them all. How can one indivisible particle of light be everywhere at once?
Credit to : Sundown Science
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