The Observer Effect

Abstract

The observer effect is the fact that observing a situation or phenomenon necessarily changes it. Observer effects are especially prominent in physics where observation and uncertainty are fundamental aspects of modern quantum mechanics. Observer effects are well known in fields other than physics, such as sociology, psychology, linguistics and computer science, but none of these other fields have experienced the same level of publicity and controversy as physics. This may be responsible for the widely held implicit assumption that “real” observer effects are exhibited only by quantum objects and not by classical objects. This misunderstanding may be due, to some extent, to confusing the observer effect with the Heisenberg uncertainty principle and with other quantum uncertainty principles. In fact, observer effects occur in both classical and quantum systems. This article presents a number of examples of observer effects in purely classical processes. It also introduces a framework for understanding and analyzing many of such effects for classical systems. Ignoring observer effects can cause errors in experiments at a macroscopic level where no quantum effects would be discernible. Consequently, there are practical reasons for being careful to address observer effects.