Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!brl-tgr!gwyn From: gwyn@brl-tgr.ARPA (Doug Gwyn) Newsgroups: net.physics Subject: Re: Heisenberg Uncertainty Principle Message-ID: <556@brl-tgr.ARPA> Date: Thu, 8-Aug-85 20:05:18 EDT Article-I.D.: brl-tgr.556 Posted: Thu Aug 8 20:05:18 1985 Date-Received: Sun, 11-Aug-85 07:01:51 EDT References: <3506@decwrl.UUCP> Organization: Ballistic Research Lab Lines: 30 > In over-simplified terms Heisenberg's Uncertainty Principle says that we > cannot know the simultaneous position and momentum of an individual > elementary particle with unlimited accuracy. Yet, we are able to > determine the simultaneous position and momentum of conglomerations of > these elementary particles. No, the same constraint holds. Why do you think otherwise? > Is it strictly a case of the measurement process itself disturbing the > individual particle, or is something else going on here? For example, it > seems to me that if it is simply a matter of the measurement process > disturbing the particles we are trying to measure, then we just have to > find a measurement process that uses small enough particles so that they > won't disturb the particles we are trying to measure. But you can't! > But in my opinion saying that "in principle, > it is impossible to measure the simultaneous position and momentum of a > particle" is quite different than saying that "the means to measure the > simultaneous position and momentum of a particle does not exist". Yes, these are different. QM says that you cannot simultaneously determine (the same component) of the position and the momentum of any object with absolute precision; indeed, because the two are Fourier transform pairs, the simultaneous uncertainties have to obey >= (constant on the order of 1) * h, where h is Planck's constant.
means the RMS uncertainty of a quantity. This is a matter of fundamental principle, not of insufficient cleverness on the part of the measurer.