The Probability of God
What’s the probability that God exists?
Here, we’re talking about the God of traditional theism, the O3 world-creator (omniscient, omnipotent, omnibenevolent), or a supremely perfect being. This question recently came up in a debate between Matt Dillahunty and Matthew Adelstein.
Nobody tried to actually give the numerical value, but Matthew suggested that the prior probability was not too low and the probability in light of our evidence was at least >50%. I will not try to give a numerical value either, but I think my prior credence in God (to the extent that I have one?), as well as my posterior credence, is lower than Matthew’s.
I think the Fine Tuning Argument is a reasonable argument for intelligent design, but I think that if there is an intelligent designer, that designer is nevertheless not a triple-omni being.
1. Is God Impossible?
Dillahunty complained that theists have not shown that God is even possible. This was an odd complaint in the absence of any stated reasons why God wouldn’t be possible (which Dillahunty did not give).
I, however, have previously discussed some arguments that the traditional God is metaphysically impossible. E.g.,
“Can he make a stone so heavy he can’t lift it?” This suggests that omnipotence is impossible.
If you know everything you’re ever going to do, then you’re not free to do anything else. Therefore, an omniscient being cannot have free will. But if God lacks free will, then perhaps he is not very powerful at all.
Maybe omnipotence is incompatible with moral perfection, since moral perfection makes you unable to do evil.
Maybe omnipotence and moral perfection are incompatible because there is no best possible world (only a series of better and better possible worlds), yet a morally perfect being must always do the best thing that it can do.
Some theists say that God is by definition a “necessary being,” one who could not have failed to exist. But the idea of a person who could not have failed to exist is obviously nonsensical. (We should probably just avoid this definition.)
Maybe the traditional God requires an impossible kind of infinitude (infinite power, infinite information density), a kind that would enable Him to realize paradoxes. I said little about this in my earlier post, so here is more: Compare these related thoughts about infinity:
An infinite number would be a number larger than every real number, or larger than every natural number. But maybe there are no such numbers; there are just larger and larger real numbers (/natural numbers), going on up forever; there isn’t then another number that comes after these. There are many good arguments that infinity isn’t a number (see my Approaching Infinity).
Compare the fact that there are (on the standard view) points of space arbitrarily far from here—space extends infinitely—but there is no point infinitely far from here. I.e., there are just places farther and farther away, extending out forever; there isn’t some further point that comes after all the points at finite distances.
Similarly, it’s metaphysically possible to have an object traveling at any (finite) velocity. But it is not possible to have an object traveling infinitely fast; “infinity” does not name a possible velocity. (If an object traveled at that speed for one second, where would it end up?)
Or consider the conundrum, “What happens when an irresistible force meets an immovable object?” You could think of this as what happens when you apply infinite force to a thing with infinite inertia. The answer must be that such a scenario is impossible. There can be things with any finite degree of force or inertia, but not infinite.
Similarly, perhaps there is no possibility of “infinite power”; there are only larger and larger possible amounts of power, going on forever. The same goes for knowledge or intelligence.
Of course, if God is impossible for one of these reasons, then His existence has a prior probability of zero. However, all of these are controversial arguments, so you might be unconvinced. If God is possible, then what is the probability that He exists?
2. Prior Probabilities
Nobody has a good general account of how one should assign prior probabilities to things like this—i.e., what’s the initial probability, prior to gathering evidence, that there would be an O-3 world-creator?