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Flipping Out

April 14, 1985

Flipping a coin produces a random result, right? Wrong, say Vladimir Vulovic and Richard E. Prange, physicists at the University of Maryland in College Park. They argue that, far from being random, the outcome of a coin toss is as determined as anything can be. If someone could only know the exact starting position of the coin, including its height above the floor, and the exact impetus and direction of the thumb that flips the coin (and the exact status of the air that the coin will traverse), heads or tails could be predicted with certainty.

Vulovic and Prange may be right in theory, but, as a practical matter, the starting position and strength of a flip cannot be known exactly--much less the vagaries of the air. So, for all useful purposes, flipping a coin remains a random event.

There are many other phenomena that fall into the category of theoretically possible but practically impossible. The laws of physics, as currently understood, hold that if a fire is lit under a tea kettle, all the water in the kettle, instead of boiling, may rush to one corner and freeze. This result is so unlikely that it has never happened, and is never likely to happen. But it is possible, leading to a number of questions--among them: What does it mean for something to be possible if it cannot be done?

The immediate answer is that if something is at least possible it might someday happen. And in the meantime? What is the status of something that is possible but very improbable? It can't be ruled out, but it can't be ruled in.

The work of Vulovic and Prange harks back to the 17th Century, when modern science really got going and people were struck with the idea that the universe was a great clock, wound up by God at the Creation, which has been running since by the preordained rules built into it. If only one could know the starting position and motion of every molecule in the universe, it was said, all of history could have been predicted, and all of the future could be known. Various social sciences are still smitten with this goal today.

The success of this project is as unlikely as water freezing in a heated tea kettle. The future remains unknowable in the small and in the large. Heads or tails?

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