The Bohr Complementarity Principle

• A complete classical description of microscopic phenomena (like electron or photon) requires complete knowledge of two “complementary” quantities (like momentum and position).

• Measuring one of a complementary pair always destroys information about the other.

• Therefore it is impossible to know everything about a microscopic physical system.

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Bohr extended his famous Principle of Complementarity to other fields of endeavor. He said, for example, that all great truths come in complementary pairs -- the greater the truth, the greater is it’s opposite. You might summarize it by saying “you can’t win without losing, because winning and losing are complementary aspects of playing the game.”