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MAN AND THE INDETERMINACIES* JOHN R. PLATTf Understanding the external world is the objective of science, and accurate prediction is the test ofit. Ifwe really understand genetics, we can breed better hybrid corn. Ifwe really understand geology, we can locate minerals and oil. If we really understand the motion of the atmosphere and its water vapor, we can predict the weather. But some ofthe most thought-provoking problems ofscience are those involving "indeterminacy," where accurate prediction for some reason becomes impossible. It is as though a sign said, "Nonsense!—Your prying or your prediction at this point interferes with itself, so your supposed observations orpredictions can no longer be made objectively or meaningfully ." Many ofthese problems are a little bit like my answer to your question whether I will wear my red tie tomorrow morning. I may tell you that I will, but this is an intention, not an objective prediction like predicting rain—and you will immediately show that you know this by laughing at me ifI try to bet with you on it. It is obvious that my knowledge ofthe prediction and the bet would change my performance, and I am likely to wear the red tie or not, as the case may be,just so I will win—or to do the converse to prove my unpredictability. Everyone knows, really, that predictions of one's own conscious decisions are not objective predictions in any scientific sense. The most famous case ofindeterminacy, where getting data for a prediction interacts with the outcome in somewhat the same way, is that of the Heisenberg "uncertainty principle" in atomic physics, which upset the whole philosophical world forty years ago. But indeterminacy and * A chapter from the book The Step to Man, published byJohn Wiley & Sons, Inc.,June, 1966; reprinted by permission. t Acting Director, Mental Health Research Institute, University ofMichigan, Ann Arbor. 67 related questions of prediction also touch many other problems, for example , in areas such as biology and psychology. It is interesting to look at some ofthese problems to seejust what goes wrong with deterministic predictions, and why. This gives us a much clearer view ofwhat questions objective science can meaningfully ask and what it cannot, and what parts oflife must be left out ofthe scientific equation. It appears that several of the non-classical conclusions may be ofcentral importance in understanding the relations between manandman and between man and the universe. The Areas ofDeterminism The concept ofdeterminismis closely bound up with the concept ofthe "isolated system." An isolated system, in astronomy or physics or chemistry , is a body or collection ofbodies—for example, the sun and planets, or the chemicals in a flask—which are supposed to interact in some respect only with each other. It is a system which an observer can either start off or can observe accurately at some initial time, and which can then continue to be observed indefinitely without any appreciable disturbance to its motions or behavior from interactions with the observer himself or with the rest ofthe universe. These conditions are evidently essential in order for determinism to hold, that is, in order for our specification of the initial state ofthe system to suffice for determining its final state accurately at any later time. Ofcourse, isolation from the surroundings is never perfect. The chemicals in the flask boil offinto the air. The earth's tides slow down the moon by amounts that can be measured. Nevertheless, the "isolated system" is a useful and accurate approximation for most ofthe problems we know how to solve in physics and chemistry and engineering; and in fact, that is why we know how to solve them. Ifwe correct for the small disturbances , Newton's laws will predict eclipses and the motions ofplanets or man-made satellites for years or centuries ahead. The planets are heavy bodies, not much affected by the dust in their paths or the sunbeams by which we observe them. Few other predictions in science are as certain as those of the planets, but in most cases the uncertainties are not believed to be due to any breakdown of determinism. Forecasting the weather, for example, is difficult apparently because of the great complexity of...


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