I’m going to demonstrate this using Bayes’ Rule. I will represent the hypothesis that (a non-Deist, i.e. an interventionist) God exists as , and the evidence of complex life as . What we want to know is the posterior probability that is true, given , written
which, in English, is: the probability that God exists, given the evidence before us of complex life.
By Bayes rule:
- is the probability of complex life, given that God exists,
- , is our prior belief that God exists, expressed as a probability,
- is the probability of complex life, given that God does not exist, and
- is the probability that God does not exist (which equals .
So first of all we have to set our prior, , the probability that God exists, which I am happy to set high, for instance, at .98.
We also have to set the likelihood of complex life existing, given the existence of an interventionist God (after all, an interventionist God might simply have decided not to bother, or to make something else, like marvellous crystal palaces, instead). However, I will actually set this to 1, as it seems just weird to posit an interventionist God who doesn’t make complex life.
The first thing to note is that the term on the numerator is identical to the first term in the denominator. In our case we have .98*1 on the top, and .98*1 + something on the bottom. I will set the likelihood of Complex life given no interventionist God () at something very small, let’s say .0001. This gives us:
Which gives me a posterior probability that an interventionist God exists of .999998!
So, by setting the probability of complex life, given no God, very small, I have vastly increased my posterior faith that God exists! And if I make it still smaller, then my posterior faith in God grows still further! Take that, atheists! If IDists can show that the probability of complex life, given no God, is sufficiently tiny that it effectively cannot occur within the lifetime of the universe, that second term on the denominator will go to zero, and God becomes a certainty!
So far, so good. Or would be, if it were ever possible to show that something is impossible, which, 500 coins notwithstanding, it isn’t. That’s because there are many different nulls to reject, and there is always likely to be one you haven’t thought of. No matter, that dead horse has been beaten enough in recent posts.
What I want to do here is to look at it the other way round. Let’s say that scientists show that, far from complex life being near-impossible given no God, they discover it’s a virtual certainty – we even manage to do it in a test-tube using conditions known to prevail on early earth, we find all the intermediate fossils we need to fill out the various radiations since dot, and moreoever, get a bunch of SETI signals telling us we aren’t even alone as intelligent beings in the universe.
So instead of setting the likelihood of Complex life given no interventionist God () to something very small, let’s make it 1. Here is our equation now:
What is my posterior probability that God exists? Well, now the denominator simply sums to unity, leaving our belief in God exactly where it started: .98.
In other words, finding out that life is perfectly possible in the absence of an interventionist God tells absolutely nothing at all about whether God exists. It simply leaves us with the faith we had in the first place.
The good news for theists, then, is that there is nothing to fear from naturalist science – it cannot rock your faith, no matter how good a naturalist explanation for anything scientists come up with. If your faith is absolute, absolute, it will remain. If your faith is 50:50, it can only go up, not down.
However, the good news for atheists is that if it starts at near zero, good naturalist explanations will keep it there. Science, therefore, as Dawkins says, allows him to be an “intellectually fulfilled atheist”.
But for theists, it can do absolutely nothing to dent your faith.
So have a very happy Christmas!