implications of quantum mechanics, developed the principle of indeterminacy, more commonly known as “the Heisenberg uncertainty principle.” He showed that indeterminacy is unavoidable, because the process of observation invariably changes the observed object, at least minutely.
The following thought experiments demonstrate the uncertainty principle. We know that the only way to observe any object is by bouncing light off of it. In everyday life we ignore an implication of this simple truth: bouncing light off of the object must impart energy and momentum to the object. Analogously, if we throw a rock at the earth we can ignore the fact that the earth’s orbit is minutely deflected by the impact. But what if we bounce light, consisting of photons, off of an electron? Photons will jolt the electron substantially. Our observation invariably and unavoidably affects the object being observed. Therefore, we cannot simultaneously know both where the electron is and what its motion is. Thus we cannot know exactly where the particle will be at any time in the future. The more accurately we measure its location, the less accurately can we measure its momentum, and vice versa.
“Natural science does not simply describe and explain nature; . . . it describes nature as exposed to our method of questioning.” [Heisenberg, 1958]
[Image removed for copyright reasons] (Wikisource contributor note)
Our concepts of reality have already been revised by Einstein, Bohr, Heisenberg, and other atomic physicists; further revisions seem likely. We now know that observations are relative to the observer, that space is curved and time is relative, that observation unavoidably affects the object observed, that probability has replaced strict determinism, and that scientific certainty is an illusion. Is the observational foundation of science unavoidably unreliable, as some non-scientists have concluded?
Seldom can we blame uncontrolled observer-object interaction on atomic physics. The problem may be unintentional, it may be frequent (see the later section on ‘Pitfalls of Subjectivity’), but it is probably avoidable. In our quest for first-order phenomena (such as controls on the earth’s orbit), we can safely neglect trivial influences (such as a tossed rock).
Scientists are, above all, pragmatists. In practice, those of us who are not theoretical particle physicists or astronomers safely assume that time is absolute, that observation can be independent of the object observed, and that determinism is possible. For the vast majority of experimental situations encountered by scientists, these assumptions, though invalid, are amazingly effective working hypotheses. If we are in error by only one quantum, it is cause for celebration rather than worry. The fundamental criterion of science is, after all, what works.
We cannot, however, cling to the comfortable myth of detached observation and impartial evaluation of objectively obtained evidence. The actual process is much more complex and more human (Figure 22):
Expectations, rooted in previous experience or in stereotypes, exert a hidden influence – usually even a control – on both our perceptions and our evaluation of evi-
