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What is Heisenberg's uncertainty principle?

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Quick answer

Heisenberg's uncertainty principle says you can't know both a particle's exact position and its exact momentum at the same time — the more precisely you measure one, the fuzzier the other becomes. It's a fundamental rule of the quantum world, not a measurement flaw.

Key things to understand

  1. You can't precisely know both position and momentum at once.
  2. Measuring one more precisely blurs the other.
  3. It's a fundamental feature of quantum physics.
  4. It reflects reality's nature, not poor instruments.

People also ask

What is the uncertainty principle?
A quantum rule that you cannot precisely know both a particle's position and momentum simultaneously.
Why does the uncertainty principle exist?
It's built into the wave-like nature of quantum particles, not a result of imperfect measurement.
Who discovered the uncertainty principle?
Physicist Werner Heisenberg, in 1927.