One popular argument for God's existence is the fine-tuning argument. The most academically respected version roughly runs through the following steps:
This means that, if God doesn't exist, the Universe's being life-permitting is very epistemically improbable; i.e. surprising. (The likelihood is 1 divided by the number of physically possible ways the Universe's laws could have been life prohibiting.)
But it being a life-permitting Universe is not unlikely if God does exist.
Therefore, by the likelihood principle, insofar as a life-permitting Universe is more expected on theism than atheism, it counts as evidence for theism.
Moreover, to the strong degree that it is more expected on theism, it counts as correspondingly strong evidence for theism.
In response to the fine-tuning argument, however, the following objections have been raised: “If the Universe needs a designer, then doesn't God need a designer?”
• George Smith: “If the universe is wonderfully designed, surely God is even more wonderfully designed. He must, therefore, have had a designer even more wonderful than He is. If God did not require a designer, then there is no reason why such a relatively less wonderful thing as the universe needed one.” [Atheism: The Case Against God (Prometheus, 1979), 56.]
• Richard Dawkins: “The divine knob twiddler would himself have to have been at least as improbable as the settings of his knobs.” [“Why there almost certainly is no God”, online at The Edge]
a. This commits a straw man fallacy (or a compound-question fallacy, depending on how it is worded), insofar as the attempted analogue is egregiously disanalogous; it misrepresents the fine-tuning argument: • The fine-tuning argument does not make a design-inference. It does not say anything like “x seems complex/designed, therefore it must be designed.” • In fact, it does not conclude that there is a fine-tuner at all; it merely concludes that the life-permittingness of the Universe evidence for theism using principles from canonical Bayesian probability calculus.
b. This tu quoque argument is also a “red herring” (off-topic). After all, it is at best an argument against God's existence to be discussed elsewhere, and is not an actual response to the fine-tuning argument itself.
c. This also is wildly confused about principles for acceptability in inferences to the best explanation (abductive reasoning). I.e. even if one were making an inference to the best explanation, it happens to be entirely legitimate for x to be a best explanation, even if x itself has no explanation.2
d. This also assumes (at least as traditionally presented) that for any x and any y, if x is more complex than y, then y could not have created x. But there is no evidence for this claim. Moreover, it is entirely conceivable for humans to create something (e.g. a supercomputer intelligence) more complex than themselves.
e. This also assumes God is not simple, despite the fact that most theologians do believe God is simple (very simple).3 Moreover:
Paul Davies (renowned physicist, prof. at London etc.): “A branch of mathematics called algorithmic complexity theory can be used to provide rigorous definitions of simplicity and complexity. One surprising feature of these definitions is that the whole can sometimes be simpler than its component parts. Thus God-plus-universe can be simpler than either God or the universe in isolation.” [“Universes galore: Where will it all end?” in Universe or Multiverse? ed. Carr (Cambridge, 2007) 489-490.]
Michael Behe: “The inference to design can be held with all the firmness that is possible in this world, without knowing anything about the designer” [Darwin's Black Box (Free Press, 2006), 197.]
• William Lane Craig: “As an unembodied mind, God is a remarkably simple entity. As a non-physical entity, a mind is not composed of parts, and its salient properties, like self-consciousness, rationality, and volition, are essential to it. In contrast to the contingent and variegated universe with all its inexplicable quantities and constants, a divine mind is startlingly simple. Certainly such a mind may have complex ideas-it may be thinking, for example, of the infinitesimal calculus-, but the mind itself is a remarkably simple entity. Dawkins has evidently confused a mind's ideas, which may, indeed, be complex, with a mind itself, which is an incredibly simple entity." [Reasonable Faith 3rd (Crossway, 2008), 172.]
• Robert Koons: “…an infinite mind might be extremely simple. God needs no representations and no sense organs: everything (including every possibility) is immediately present to His mind. God needs no inference engines, because God never has to infer anything. …all of God's attributes take values zero or infinity …We need so many parts precisely because our knowledge is limited and mediated by physical processes. God has immediate access to all facts, and so needs no internal complexity at all.” [“LECTURE #15: Objections to Design” online at leader.edu]
• Richard Swinburne (Professor of Philosophy at Oxford): “A finite limitation cries out for an explanation of why there is just that particular limit, in a way that limitlessness does not. As I noted in Chapter 3, scientists have always preferred hypotheses of infinite … when both were equally compatible with the data… [listing multiple examples] There is a neatness about zero and infinity that particular finite numbers lack. Yet a person with zero powers would not be a person at all. So in postulating a person with infinite power the theist is postulating a person with the simplest kind of power possible. God’s beliefs have a similar infinite quality. …” [The Existence of God 2nd (Oxford, 2004), 97.] Swinburne continues to emphasize the point for 13 more pages, covering all God's essential properties.
In fact, as noted by Robin Collins (Physicist, professor of Philosophy): “Medieval philosophers and theologians often went as far as advocating the doctrine of Divine Simplicity, according to which God is claimed to be absolutely simple, without any internal complexity.” [“The Teleological Argument” in The Routledge Companion to Philosophy of Religion eds. Meister & Copan (Routledge, 2007), 417.]