Past As Uncertain As Future

Before Albert Einstein ended his recent visit at California Institute of Technology, he--with Drs. Richard Chace Tolman and Boris Podolsky of the institute--wrote a letter to The Physical Review. This letter, published last week, answers in a measure a persistent query: What good did Professor Einstein's U. S. visit do Science? In the letter he proved that the Past is as unascertainable as the Future.

The uncertainty of the future has been accepted by physics. Physicists can foretell the general action of a vast aggregate of, say, electrons. But they cannot say how any individual electron will behave. Their difficulty lies in the fact that the instant they recognize an electron, the electron disappears or changes its condition by reaction with the measuring device.

Now Savants Einstein, Tolman & Podolsky prove that it is impossible to say exactly where that electron was before it struck the measuring device.

Their proof depends upon the abstrusities of quantum physics. An analogy simplifies the idea:

An observer watches a vast throng pushing through an amusement district. By the law of averages he knows that a certain proportion will attend one theatre, other proportions other theatres. But he cannot tell which person will enter any particular theatre. Many of the people themselves could not enlighten him. Whim or the pressure of the crowd might change their direction.

In the crowd are identical triplets-- Mary, Marie, Marion--dressed exactly alike. The observer thinks he recognizes Mary (an electron). He taps her on the shoulder. She turns around. Now the observer does not know whether she is Mary, Marie or Marion. Her identity is uncertain. The tapped girl pauses and may decide not to go to the show that evening. As a theatre-going electron she therefore disappears.

Or the interruption of her walk may make her decide to go to some performance other than the one she predicted. Her future is uncertain. Nor does she know whence she came. The crowd pushed her willy-nilly until she encountered Mr. Observer.

Philosophers, theologians, sociologists and others dealing with the affairs of men may derive despair from the uncertainty of past as well as of future. Physicists are for the present content. Statistical studies of average group action have helped them to probe marvelously deep into Nature.

Yet Dr. Einstein, snug last week in his Berlin Tower, was somewhat restless. "[We do] not describe Nature, but merely expectations from Nature," he said. "Whereas the aim of Science is to describe the things themselves, not merely the probability of their happening. . . ." He is confident that there is a cause for every phenomenon; that some day some scientist will be able to explain precisely why Mary started for the theatre, why she turned at the observer's tap, why she did or did not proceed to a particular performance.

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