The probability of God
A reader mailed me a link to a newspaper article about a book purporting to prove that God exists, with a 67% probability.
It is a short review of Stephen Unwin's book The Probability of God, with the ambitious subtitle "A Simple Calculation That Proves The Ultimate Truth."
The "ultimate truth" is apparently that the odds of a Divine Creator is 2 to 1. There must be something about the word "proof" that has escaped me in this case. However, Unwin is apparently a very humorous physicist, and as a math buff he attempts to use Bayesian logic to actually put a probability on God's existence.
Dr Unwin started with the base assumption, the classical Laplace criteria for a priori probabilities, that since we don't know either way, the probability is 0.5 (50%) when there are two outcomes. He then added assumptions, the existence of evil reduces the probability, the existence of unselfish kindness increases it, until he achives the desired result. Dr Unwin is, of course, a believer who personally thinks the chance is 95%.
The 28 percent improvement over the mathematical probability is what Unwin calls his faith.
I am sure that Dr Unwin can teach most people, me included, a lot about mathematics and probability theory. However, I am also pretty certain that I could teach him a bit about theology and theism. Judging by his website, the reviews I have seen, and this short debate on Usenet that occurred when Heather Unwin (his wife?) wanted to promote the book, he is very unwilling or unable to actually explain how he finds arguments for or against God, and perhaps even more important, how he attaches probabilities to them. Yes, I know he will say I should read his book, but there are millions of books around, and before I spend money and time on a particular book, somebody has to give me a good reason to do so.
The one argument for God's existence given in the review does not bode well:
Boldly, Unwin plugs evidence of God into this theorem. He points out, for instance, that giving money to the homeless with no thought of reciprocal reward is evidence of good -- and good is more likely to occur if God is in the universe.
Presuming that is presuming a lot. Based on what your idea of "God" is, it may be true that unselfish goodness is evidence of God, maybe because you learned in sunday school that God is good. But why should God be good? Why could not God be as indifferent to human suffering as most of us are to an insect suffering? There is, as Unwin admits, evil in the world, as well as good, so if God exists, doesn't it make more sense that God doesn't care, or maybe that God is sometimes good and sometimes evil, than blindly asserting he is good?
The existence of unselfish goodness in humans can easily be explained as a side effect of altruism and kin selection. Adding any "god" to the equation doesn't explain anything, even if we presumed that god was good, as this is a phenomenon that no longer begs an explanation.
At another point, Unwin weighs natural disasters -- such as earthquakes, tornadoes and cancer -- to swing the equation against the probability of God.
Again we presume a very specific idea of a deity. Natural disasters are actually a necessity if we want to prove the existence of deities that cause them, like the Norse Thor or the Greek Zevs, both gods of thunder and lightning. In the Torah, Yahweh was a deity associated with causing thunder and earthquakes, not to mention pestilence and other calamities. Apparently, modern theists have moved natural disasters into the category "inconvenient fact", where in earlier times they made people tremble in fear of God's power. For the God of modern Christianity, the existence of natural evil is pretty devastating indeed, but then we have just chosen the form of deity that happens to be popular today.
Does not this tell us that Unwin's theology is very arbitary? Indeed. And while his math may be brilliant, his theology seems to lack reflection. When he assigns probabilities, he is already presuming something about God. But if we don't even know if God exists (he started with a 0.5 probability, remember), how can we know anything about God's personailty and nature that help us assign such probabilities? Stories about God's nature is just hearsay from past believers, for example the men who wrote the Bible, and their description of God is based at least partly on their knowledge about the state of reality. Using the state of reality (like human goodness) as evidence that this God exists is thus pitifully circular logic.
PS: Interestingly, one of the most popular "proofs" for God, the ontological argument after Bishop Anselm, argues that if God exists, he exists by necessity. Thus, if God exists with a probability of 0.67, he doesn't.
10:07:50 AM 
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