The Probability of God

Stephen Unwin applied the Bayes formula to calculate the probability of God in his book, "The Probability of God: A Simple Calculation That Proves the Ultimate Truth".

I believe that the question of probability of God has much more to do with philosophy of God than philosophy of probability. Hence, personally, I do not find it particularly interesting. But Unwin's calculation does inspire some thoughts.

It is hard to find a common attribute in all Gods in all religions but a good candidate for such an attribute is the claim that the laws of nature do not (necessarily) apply to God. For example, the laws of chemistry do not always apply - God can turn water into wine. The question whether the Bayes theorem applies to God is a little bit more subtle. Some people consider all mathematics (including the Bayes theorem) to be a part of logic. There is no universal agreement on the question of whether God is limited by logic. Another facet of the problem is whether the Bayes theorem is only a mathematical theorem or whether it is also a law of nature, supported by empirical evidence (in my opinion, it is both). Overall, I do not see why the Bayes theorem should necessarily be applicable to God if the laws of chemistry are not.

I think that we can learn something about applications of probability to natural phenomena by analyzing the problems with probability applied to the supernatural. There are many objects, systems and phenomena that present the same intellectual challenges as God, except to a smaller degree. Examples include economy, financial markets, human brain, an individual person, weather and climate. All these systems are complex and our knowledge of them is incomplete. Direct experiments are often hard or expensive or unethical (or all of these). Simplified theories applied to these systems sometimes fail to account for subtle features that manifest themselves in unpredictable ways.

Going back to God, failures of some probability estimates applied to natural events make me very dubious about any attempt to calculate the probability of God. That is, if there exists objective probability (I believe it does). Subjective probability obviously exists. The subjective probability of God is exactly what you believe it is, and you are welcome to use the Bayes theorem to organize your subjective probabilities related to God into a consistent belief system - I do not see any harm in doing so. Neither do I see any gain.