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One Thing Is Certain: Heisenberg's ­Uncertainty Principle Is Not Dead

Heisenberg uncertainty principle on window at Colgate University physics building

The ground floor of the new physics building at Colgate University, which features a version of the Heisenberg uncertainty principle.

Credit: George Musser / Scientific American

What Einstein's E=mc2 is to relativity theory, Heisenberg's uncertainty principle is to quantum mechanics. The principle holds that we cannot know the present state of the world in full detail, let alone predict the future with absolute precision. It marks a clear break from the classical deterministic view of the universe.

Yet the uncertainty principle comes in two superficially similar formulations that even many practicing physicists tend to confuse. Werner Heisenberg's own version is that in observing the world, we inevitably disturb it. And that is wrong, as a research team at the Vienna University of Technology has now vividly demonstrated.

Led by Yuji Hasegawa, the team prepared a stream of neutrons and measured two spin components simultaneously for each, in direct violation of Heisenberg's version of the principle.

From Scientific American
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