Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 exptools 1/6/84; site ihnet.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!ihnp4!ihnet!tjr From: tjr@ihnet.UUCP (Tom Roberts) Newsgroups: net.physics Subject: Re: Quantum mechanics, Aspect experiment, EPR paradox Message-ID: <166@ihnet.UUCP> Date: Wed, 10-Oct-84 10:37:52 EDT Article-I.D.: ihnet.166 Posted: Wed Oct 10 10:37:52 1984 Date-Received: Fri, 12-Oct-84 07:55:47 EDT References: <361@petsd.UUCP> Organization: AT&T Bell Labs, Naperville, IL Lines: 30 The EPR "paradox" in QM is not really a paradox, but merely a way of pointing out that you must be VERY CAREFUL when interpreting experiments involving quantum-mechanical systems. Consider instead the QM system consisting of a single 2-sided coin (heads and tails) after a random coin toss. In order to learn which side is up, you must perform a measurement upon the system (i.e. look at the coin). Assuming a typical coin (i.e. VERY large on the atomic scale), it is no surprise that a single measurement of the system is sufficient to determine its state. You merely look at the top face of the coin; in particular, YOU DO NOT NEED TO LOOK AT THE BOTTOM OF THE COIN, TOO. The EPR gedanken-experiment is merely a different kind of coin-toss. If you wish to determine whether a single particle confined in a box is in one half or the other, it IS sufficient to measure only one half to determine the answer (assuming negligible probability for the particle to change sides after or because of the measurement). The "paradox" arises when you don't keep in mind that you must take account of the ENTIRE system: the left-half of the box, the right-half of the box, and the particle. When you ask "why does a measurement in this half of the box affect the situation in that half of the box (far away) ?" you are NOT thinking of the entire system, but are (erroneously) considering two separated, non-interacting subsystems (the two sides of the box). It isn't clear in which subsystem the particle is in, AND THAT IS THE POINT. In this mode of thinking, you have NOT made a proper separation of the system into non-interacting subsystems. Tom Roberts ihnp4!ihnet!tjr