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© Copyright 2002, Jim Loy
When one thing causes another, that is a cause and effect relationship. If A causes B, then B is the result of A. Cause and effect may intrude upon philosophy. Does time run forward (as we perceive it to do), or does it run backward (and our perception is fooling us)? Science suggests that it runs forward, as the simpler of the two options (See Occam's Razor). Regardless, we can merely pretend that time runs forward, and almost all of science works more simply.
A causes B implies that A happens before B does. In fact, that seems to be built into time and the universe; that is how nature works. That is how you can tell if a movie is being run backwards: a gunshot makes the bad guy's gun fall to the ground; a person jumping into a swimming pool makes water splash. Detectives find clues to what caused what. But just because B follows A does not mean that A caused B. They may be unrelated, or they may have a common cause. It is a common mistake to assume that of two related events, the earlier one caused the other:
1. Bill hit the ball, in the direction of center field, right out of the park, and his team won 1-0. Was Bill the hero of the day? It turns out that Bill missed second base, and was called out; and Bill was not the hero of the day.
2. A man is killed in Seattle. Two hours later, a man is killed in New York, in exactly the same manner, and his killer is caught. He is the cause of at least one murder. The coincidence is so great that the detectives strongly suspect that he killed both men, and try to figure out how he could get to New York in two hours. It turns out that it was a copycat crime, and both murders are similar to a well-publicized murder a week previously in California. The similarity of both later murders has a common cause, the earlier murder.
The Second Law of Thermodynamics has a great deal to do with cause and effect. As I said in my article about the Second Law, "The Second Law of Thermodynamics says that ... energy goes from a usable form to a less usable form. Things run downhill, flywheels slow to a stop, useful kinetic energy becomes useless heat. No physical process, no machine, is ever 100% efficient." That is the main cause and effect relationship in science. Chemical reactions are predictable mainly because we can keep track of the conversions from one form of energy to another. The same is true of nuclear reactions and the trajectories of projectiles.