How Quantum Trickery Can Scramble Cause and Effect

Philip Walther’s experiments mash up causality: the idea that one thing leads to another. It is as if the physicists have scrambled the concept of time itself, so that it seems to run in two directions at once. In everyday language, that sounds nonsensical. But within the mathematical formalism of quantum theory, ambiguity about causation emerges in a perfectly logical and consistent way. And by creating systems that lack a clear flow of cause and effect, researchers now think they can tap into a rich realm of possibilities.

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