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Quantum 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.

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Waves & Particles

Quantum Tunnelling

What’s going on

Roll a ball too slowly at a hill and it always rolls back. A quantum particle’s wave doesn’t stop dead at a barrier; it fades away inside it. If the barrier is thin enough, a little of the wave reaches the far side, so there is a small chance of finding the particle there. Tunnelling helps the Sun shine, lets flash memory store your photos, and lets special microscopes see single atoms.

Myth

The particle punches a hole through the barrier.

Fact

The barrier is left untouched.

Learn more

Nobel Prizes in Physics 1973 (tunnelling) and 1986 (scanning tunnelling microscope), nobelprize.org.

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QTM-16 from Quantum Wonders, free quantum physics cards for ages 10 to adult

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