Fig 1The double-slit experimentOne electron at a time0 dots
The screen, seen straight on
How many dots landed where · green line = what the maths predicts
The two slits: where the strange part happensGun (top), slits, magnifying lens, screen (bottom)A green flash: one electron landingElectrons leave the gun one at a time, about one each second. Each lands as a single dot, like a tiny ball. But as the dots pile up they make stripes, which only waves can make. So each electron travels like a wave through both slits, then lands like a ball. Watch which slit it uses and the stripes vanish.