I was recently asked to explain my estimate (or better, my “guesstimate”) for the probability of the existence of any god. As I wrote in a recent post, my guesstimate for the existence of any god is somewhere around 1 chance in 10 to the 500th power; that is, 1 part in 10^500; i.e.,
0.000000…[continue for a total of 499 zeros]…001
which is the smallest probability I’ve ever encountered. That’s why I also wrote that the probability that any god exists (or has ever existed) is “zilch” or “zip” (or “zippo”). Perhaps my explanation (see below), for why I say that the probability of the existence of any god is so miniscule as to be ignorable, would be of interest to others.
It’s not simple to explain briefly. I’ve written two chapters on the topic in my free, online book, namely, Chapter Ih (dealing with “Hypotheses, Probabilities, and Evidence” and introducing Bayes’ method) and Chapter Ii (entitled “Indoctrination in Ignorance”, where I show the method used). To try to cut those two (long!) chapters down to a single (long!) paragraph, I’d try this.
Whereas Bayes’ method can’t be used to estimate the probability of the existence of any god (in spite of Unwin’s silly attempt to do so, in his book The Probability of God) – because there’s no reliable evidence to support the existence of any god – therefore, one is left with estimating the probability that any god COULD exist. In outline, the argument contains the following two steps.
(1) The probability that YOU could ever come into existence is certainly less than 1 part in 10^100 (using a very crude estimate for the probability that a symmetry-breaking fluctuation in the original “total nothingness” could have created the universe). I expect that the probability that any particular person could ever come into existence is the range from 1 part in 10^100 to 1 part in 10^200. Yet, the evidence supporting the proposition that you exist confirms your existence to within about 1 part in 10^25. It’s not “certainty”, as Descartes claimed, because (for example) we all could be simulations in some humongous computer game!
(2) The probability that “the original nothingness” could have proceeded directly to popping a god into existence is very much smaller than the probability that it could have created you – unless, of course, you have the capabilities that a god allegedly has. My “guesstimate” is that the probability that “nothingness” could have popped a god into existence is in the range of 1 part in 10^200 to 1 part in 10^1000, which for discussion purposes, I use 1 part in 10^500. But the evidence supporting the proposition that any god exists (in contrast to the evidence supporting the proposition that you exist) is zip. Therefore, if I’m to base my beliefs on evidence (as I desire), then consistent with Sagan’s “extraordinary claims require extraordinary evidence”, I conclude that the probability of the existence any god is the same as the probability that a god could have ever come into existence, i.e., ~1 part in 10^500.
If theists (aka “unscientific antihumans”, aka “god believers”, i.e., those who “wish” that their god exists) would like to find some comfort in such an argument, they might be pleased to know that string theory (or brane theory) suggests the existences of somewhere around 10^500 possible universes (or better, ‘multiverses’, or just plain ‘verses’, meaning ‘turns’). If that’s correct, then such a result plus the above guesstimate for the existence of any god would suggest that, in one of the verses, there might be a god – but then, the chance that there’s a god in ours is back down to the ~1 chance in 10^500.
I’ll add that the counter-argument that “God has always existed” can be dismissed for lack of evidence. In fact, in reality, no data support the contention of the existence of any infinity, such as the proposed infinite lifetime of any god (or for that matter, anyone’s “immortal” soul). Even adding together the numbers for all sand grains at all seashores, stars in the sky, and hydrogen atoms in our universe, all evidence supports the proposition that infinities occur only in games, such as pure mathematics and religions.