Uncertainty principle and observer effect

Today, logical positivism has become unfashionable in many cases, so the explanation of the uncertainty principle in terms of observer effect can be misleading. For one, this explanation makes it seem to the non-positivist that the disturbances are not a property of the particle, but a property of the measurement process — the particle secretly does have a definite position and a definite momentum, but the experimental devices we have are not good enough to find out what these are. This interpretation is not compatible with standard quantum mechanics. In quantum mechanics, states which have both definite position and definite momentum at the same time just don’t exist.

This explanation is misleading in another way, because sometimes it is a failure to measure the particle that produces the disturbance. For example, if a perfect photographic film contains a small hole, and an incident photon is not observed, then its momentum becomes uncertain by a large amount. By not observing the photon, we discover indirectly that it went through the hole, revealing the photon’s position.

— Wikipedia on Uncertainty principle

2011.01.06 Thursday ACHK