There is a general distinction between U. S. and European scientists which became patent last week when five Nobel Laureates from Europe* joined two from the U. S.† at the convention of the American Association for the Advancement of Science in Chicago. Americans work primarily with instruments. Europeans with imagination. Thus Danish Niels Bohr's philosophizing about the unmeasurable duality of Nature before the A. A. A. S. was a fascinating novelty which his audience tried hard to understand.
Professor Bohr, who has invented a very useful description of the atom, first pointed to Professor Einstein's relativity laws which say that we can never measure absolute time. Next he referred to Professor Werner Heisenberg's proof that we cannot measure at the same instant both the speed and the position of an electron, that the more exactly we determine the speed of electrons in an atom the less certain we can be of the position of the electrons in an atom. Thus, we can never say precisely what is Cause or what is Effect. The Heisenberg concept of uncertainty is only six years old. Einstein relativity is only 28 years old. Therefore theorists have been busy applying them to comprehension of the atom. But last week Professor Bohr paused to show how they must apply to everyday existence, where an inch is an inch and a gallon is a gallon.
Relativity and uncertainty are absolute facts, reasoned Theorist Bohr in effect. Through them mathematicians are able to describe the tremendous, strange activities within an atom. But only one kind of activity at a time. For, the essential nature of atomic (or quantum) mechanics is duality. You can determine where an electron is or how fast it is moving, but not both facts simultaneously.
Since this essential duality is true for atoms, reasoned Theorist Bohr, it must be true of all things out of which atoms are made. This general duality he called "complementarity," and proceeded to elaborate his thesis abstrusely. The net of his discourse was that if you live inside a ball, you cannot have any conception of its outside convexity, until you get outside. Then you cannot be sure of the internal concavity. Likewise you never can know all the causes of a specific result or all the effects of a single action. With uncertainty of cause & effect goes uncertainty of free will & determinism in human relations, and the impossibility of ever deciding which came first: chicken or egg.
The A. A. A. S. audience felt better when Professor Bohr, fiddling with a loudspeaker cord, short-circuited the apparatus and made it blare. It was much easier, and more pleasant, to understand round-faced young Professor Ernest Orlando Lawrence of the University of California tell how he transmuted elements with "deuton" bullets.