Tue, 15 Mar 2005

On the probability of past events

Apparently, creationists are trying to use probability to prove that life did not come from not-life (that abiogenesis is impossible). They refer to a "Borel's law" as proof. This is a philosophically empty idea. Evolutionists should not accept the idea that probability analysis can have any relationship to something that has already happened. The creationists are trying to argue that something which manifestly happened -- abiogenesis -- could not have happened because it was too improbable.

Philosophically, that is like saying that once you flip a coin, the coin cannot be in either state because both are improbable. Obviously, you can look at the coin and see that it indeed is either heads or tails. The creationist would say "No, no, the probability has to be much smaller to say it's impossible. That's Borel's law." No, that's nonsense.

Let's say that you want to show that something is impossible because the probability of its happening is too small. Let's pick some number, 1 of N. Make N large enough that you are satisfied that it is impossible for that event to occur. Now, flip M coins such that 2^M > N. The probability of that exact combination of flips is sufficiently small that it could not have happened. And yet, it manifestly did happen. You can look at the coins and verify that they have been flipped.

The creationist would say "No, no, that's not our argument at all. Only one particular combination of coins will result in life." So what? Obviously, we are having this discussion; we are alive; the past event, however improbable, occurred. Let's say that you believe in the branching universe theory -- where every possibility has been taken and there are correspondingly many universes. In all the universes in which life didn't happen, there is no controversy because there is no life. There are unspeakably many universes in which there is no life; there are also unspeakably many in which there is. The improbability of it all is a moot point. It happened. Deal with it. Don't try to rewrite history with some entity capable of violating the physical laws of the universe.

UPDATE: TM Lutas comments. Matt Cline disagrees with TM.

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