Monday, July 7, 2014

Link: Richard Dawkins and Circular Reasoning

Over at The Cumulative Case, I've made a recent post about Richard Dawkins and his circular reasoning, which echoes a post from a while back here at the Two Books Approach.  In essence, I have attributed a statement to Dr. Dawkins that, if followed to its logical conclusion, means to deny that the fine-tuning of the universe implies the existence of God, is predicated on first assuming God cannot exist.  That is, the probability of God existing is identically zero.  Of course, this isn't logic or reasoning, it is simply blind faith.  Now, I don't suppose I'll know for sure if Dr. Dawkins really holds to this view, so for the benefit of the doubt, I will say that he does not.  Even so, I think it is interesting to unpack what the following statement means: "No matter how improbable this universe is by chance, the probability of God is even less."

An excerpt from the relevant post from The Cumulative Case:
If you start off assuming that God cannot exist, then no amount of evidence, no matter how strong, can budge you.  Dawkins is essentially saying, "I don't care what the scientific evidence for fine tuning says, I will choose to believe that God does not exist." That is not reason or rationality, that is blind belief. Belief, as it were, in spite of the evidence.
For the readers' convenience, I've pasted the relevant point from my old post (note the edit where I have made my statements more circumspect by inserting [many] where the word "all" used to be):
[T]he statement "no matter how improbable this universe is by chance, the probability of God is even less" is tantamount to saying "the probability of God existing is zero." Think about it. The only non-negative number that is guaranteed to be smaller than all positive numbers is zero. This is quite a strong statement. It goes far beyond saying God doesn't exist. It says that God cannot exist. In other words, Dawkins is using an assumption that God cannot exist to try to prove that God does not exist. It is a completely circular argument.
Here's another way to think about it, for the more math-oriented folks. In probability and statistics, the proof we're trying to make is something called a conditional probability. We see an improbable universe around us. What is the probability that God exists given we live in an improbable universe (ie, what's P(G|U))? Using Bayesian inference, we can easily come up with:
P(G|U) = P(G)/(epsilon + P(G)).
Here P(G) is the prior probability that God exists, and "epsilon" is the small chance that this universe came together by coincidence ([many] scientists would agree that epsilon is very small...something like 10^-50 or less). When doing Bayesian inference, you often have to bring in some a priori assumptions to assign prior probabilities (hence the name), so we have to guess at what P(G) is. But you never outright assume that P(G) is identically zero (or one). That would be the same as saying "no matter what our studies tell me, I will choose to believe X." (That's called blind faith.) Usually, when you don't know, you simply set your prior probabilities equal to 1/2. It's easy to see that P(G|U) (the probability that God exists given the universe we live in) would be extremely close to one for any reasonable choice of P(G). The only choice that makes P(G|U) small is P(G) = 0. Which is apparently what Dawkins wants to say.