Clearing up uncertainty about Heisenberg

The Heisenberg Uncertainty Principle is one of the most important results in quantum theory, dealing with limitations of accurate measurements on two complementary quantities. However, there is a misconception (dating from Heisenberg himself) that the act of measurement is what causes the uncertainty. A new experiment has demonstrated that view is wrong, as I explain in my most recent Ars Technica article.

One of the most important—and famous—results in quantum mechanics is the Heisenberg Uncertainty Principle (HUP). What is less known (at least to non-physicists) is that the HUP exists in two versions. Werner Heisenberg’s original formulation stated that the act of measurement disturbs a physical system, placing strong constraints on (for example) the simultaneous measurement of both the position and momentum of a particle. A more mathematically rigorous version places inherentlimits on the measurement of physical quantities—independent of whether any measurement is actually performed.

While it is often assumed that these different formulations are the same, recent theoretical results have shown the original Heisenberg measurement-based version is incomplete. [Read more!]

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