Since I am writing this and you are reading it, the world seems to still exist in spite of recent claims that the end was here. When you saw the billboards announcing the end of the world, did you decide it was true? Probably not, but why not? This post is about decisions. How did you decide the end was not near?

Philosopher David Hume long ago observed that even if you have seen the sun come up everyday, and know from history that it has come up as long as records have been kept, that you have no logical reason to assume absolutely that the sun will rise tomorrow. Nonetheless, I bet that you are more confident the sun will rise tomorrow than that the world will cease to exist on the date the next person of note predicts. Why is that?

In this series, I sometimes post puzzles based on a pretend Earth ruled by logic. For example, a castaway lands on an island known to be inhabited by two tribes; one always tells the truth and the other always lies. The castaway meets a native at a fork in the road and wants to know the way to the nearest village to get help. How can he find the right path by asking a single question? (Only one question is permitted in these puzzles.) The normal answer assumes only logic. It is more interesting to ask what is the purpose of telling a lie. Do the liars want to conceal the truth or respond logically? If they are perverse and want to conceal the truth, then the puzzle cannot be solved exactly. The best one can do is ask the native if he knows there is free beer in the village. Then he can follow the native to town, or if the native sees through the ploy, at least know the native thinks he might be missing free beer.

Real decisions made in our real world are more complex than purely logical ones. Real decisions always involve probability. The probability of the sun will rise tomorrow is so high based on past observations, that we accept it as a proven fact regardless of Hume’s warnings.

All this brings us to one of the basic problems of philosophy. What is the nature of the world in which we make decisions? Some philosophers assume the world we experience through our senses is an illusion. The “real” world can only be accessed through non-sensory means. Others are agnostic about an underlying reality different from what we sense. This argument over duality has raged for millennia.

Prophets who predict the end of the world belong to the school that believes in (at least) two worlds. Knowledge of the coming end is transmitted to them in some way from the ideal world to our everyday world. For instance, a prophet might hear the voice of God warning of the end. For that person, the warning seems valid, but to everyone he/she warns, the relayed warning is sensory data and should be judged as such. The probability that someone who predicts the end of the world on a particular day is insane or lying is much higher than the probability that it will happen.

This is so obvious we wonder how anyone can believe end of the world predictions, yet it happens.