Uncertainty principle and observer effect

The uncertainty principle is often stated this way:

The measurement of position necessarily disturbs a particle’s momentum, and vice versa.

This makes the uncertainty principle a kind of observer effect.

This explanation is not incorrect, and was used by both Heisenberg and Bohr. But they were working within the philosophical framework of logical positivism. In this way of looking at the world, the true nature of a physical system, inasmuch as it exists, is defined by the answers to the best-possible measurements which can be made in principle. To state this differently, if a certain property of a system cannot be measured beyond a certain level of accuracy (in principle), then this limitation is a limitation of the system and not the limitation of the devices used to make this measurements. So when they made arguments about unavoidable disturbances in any conceivable measurement, it was obvious to them that this uncertainty was a property of the system, not of the devices.

Today, logical positivism has become unfashionable in many cases, so the explanation of the uncertainty principle in terms of observer effect can be misleading.

— Wikipedia on Uncertainty principle

2010.08.12 Thursday ACHK