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Quantum Wonders card QTM-22, The Uncertainty Principle, with a glowing paper-cut illustration. It reads: A particle can’t have both a perfectly sharp position and a perfectly sharp motion at the same time.

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Chance & Measurement

The Uncertainty Principle

What’s going on

In 1927 Werner Heisenberg showed that position and momentum (mass times velocity) trade off: squeeze one to a precise value and the other must spread out. This comes from particles being waves. A wave squeezed into a tiny spot is made of many different wavelengths, and wavelength sets momentum. For everyday objects the blur is far too small to notice.

Myth

The uncertainty is only caused by clumsy measuring tools.

Fact

The limit holds even for a perfect measurement.

Learn more

The Feynman Lectures on Physics, Vol. III, ch. 2.

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QTM-22 from Quantum Wonders, free quantum physics cards for ages 10 to adult

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All 18 Quantum Wonders cards

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