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Quantum Wonders card QTM-10, Wave–Particle Duality, with a glowing paper-cut illustration. It reads: Light and electrons travel like waves but arrive like particles, one dot at a time.

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Waves & Particles

Wave–Particle Duality

What’s going on

Send light through two narrow slits and you get stripes, the signature of waves. Turn the light down until only one photon arrives at a time, and the screen records single dots. Wait, and the dots build up the stripes. Electrons, atoms and even molecules do the same. Quantum things aren’t tiny balls or ripples; they are something new that shows both sides.

Myth

A photon keeps switching between being a wave and being a particle.

Fact

It is one kind of thing that our everyday words don’t quite fit.

Learn more

The Feynman Lectures on Physics, Vol. III, ch. 1 (free at feynmanlectures.caltech.edu).

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QTM-10 from Quantum Wonders, free quantum physics cards for ages 10 to adult

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More from Waves & Particles

All 18 Quantum Wonders cards

Quantum Wonders card QTM-11, The Double-Slit Experiment, with a glowing paper-cut illustration. It reads: Send electrons one at a time toward two slits, and a striped pattern still builds up — as if each went through both. The Double-Slit ExperimentQTM-11Quantum Wonders card QTM-16, Quantum Tunnelling, with a glowing paper-cut illustration. It reads: A particle can sometimes turn up on the far side of a barrier it doesn’t have the energy to climb. Quantum TunnellingQTM-1618 cards in six groupsSee them all