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?