1. "Maybe there are an infinite number of universes and this just happens to be the one with all the necessary conditions for life." This is known as the multiverse hypothesis (also called the "many worlds" or "world ensemble" hypothesis; Humphrey's been blogging on it lately), and it has some gynormous problems. The first is that it violates Occam's Razor. This is the idea that the simpler explanation is more likely to be the correct one. Often, atheists misunderstand this to mean that a qualitatively simpler explanation is preferable, and then argue that an omniscient and omnipotent God would be the most complex explanation imaginable. Unfortunately, at least for their case, there are two difficulties with such an understanding. First, it just flies in the face of the doctrine of divine simplicity. This is the view that God is the least complex entity in existence, and was held by most of the Christian theologians and philosophers in history, although it's fallen on hard times recently. But even if we ignore that, this argument completely misunderstands what is meant by simplicity. It's not that the cause of an effect must be understood as ontologically simple; it's that it must be numerically simple: the more entities you have to posit, the less likely your theory is correct. In other words, Occam's Razor is the claim that the quantitatively, not qualitatively, simpler explanation is more likely to be true.
To apply it to the case in point, the multiverse hypothesis has to posit an unfathomable or infinite number of universes in order to account for one universe having the necessary conditions for life. By contrast, Monotheism posits the existence of one causal agent who brought the universe into existence with the necessary conditions. Obviously, the latter is the simpler explanation, and so according to Occam's Razor, we should prefer it to the multiverse hypothesis.
The second problem with the multiverse is as follows: if you watched someone flip a coin a million times and it came up heads each time, you could either conclude that it's fixed in some way (maybe it's a two-headed coin) or you could conclude that there are an infinite number of coins being flipped and you just happened to see the one that came up with a million heads in a row. The gambler takes the chance on the latter and so bets that the coin is due to come up tails on the next flip. But 1) even if it is an honest coin, it only ever has a 50-50 chance of coming up tails at any particular flip. It isn't "due." This is the gambler's fallacy. The multiverse hypothesis, however, does not commit the gambler's fallacy, it commits 2) the inverse gambler's fallacy. Basically, regardless of whether the gambler was right to think the coin is due to come up tails, his assumption that it's an honest coin would only be valid if he actually saw all the other infinite number of coins coming up with all their different results. When you have a sample of one, it is much more rational to conclude that the game is fixed. (This, incidentally, is a further response to the third objection in part 2, that we cannot draw any conclusions about probability because we only have the one universe to work with.) So the fact that we have a universe that appears rigged is best explained by the hypothesis that it is, in fact, rigged. The universe is the way it is because someone decided it should be.
Third, no one has been able to come up with a multiverse that does not itself have a beginning as well as numerous anthropic coincidences of its own. So it doesn't evade the question of why the universe can support life; it just forces us to ask it again with slightly different terminology.
Fourth, the supposition of other universes by itself does not evidently lead to a solution of the Anthropic Principle. As William Lane Craig writes,
even if we conceded that a multiple universe scenario is unobjectionable, would such a move succeed in rescuing us from teleology and a cosmic Designer? This is not at all obvious. The fundamental assumption behind the Anthropic philosopher's reasoning in this regard seems to be something along the lines ofFinally, the multiverse hypothesis is just as metaphysical as the monothestic hypothesis. For those who don't like metaphysics in their science, the multiverse is no better than saying "God did it." So it's not a choice between one theory that's metaphysical and one that's not (or perhaps one that's less so); it's a choice between two equally metaphysical solutions, one of which commits fallacies and one which does not.8. If the Universe contains an exhaustively random and infinite number of universes, then anything that can occur with non-vanishing probability will occur somewhere.But why should we think that the number of universes is actually infinite? This is by no means inevitable, not to mention the paradoxical nature of the existence of an actually infinite number of things. And why should we think that the multiple universes are exhaustively random? Again, this is not a necessary condition of many-worlds hypotheses. In order to elude the teleological argument, we are being asked to assume much more than the mere existence of multiple universes.
2. "These characteristics are just for life as we know it." Another way of stating this objection is that life accommodates itself to its surroundings. Observing how the universe just happens to meet the necessary criteria for life is like a puddle observing how the pot hole just happens to be shaped for the puddle to fit in it.
So let's clarify our terms. When we refer to life in this context we mean physical life, life that is composed of matter, i.e. atoms. Moreover, in order for something to be physically alive it must be capable of processing physical energy to perform work; when a living thing stops processing energy we call it death. Now of course, one may simply say that there may be non-physical life out there. Certainly. In fact, most religions maintain that there are entities that are not physical. They're called angels. Or one could say that non-living material entities are alive in some sense; perhaps each rock is conscious for example. But this would merely be ascribing an occult property (rather than a physical property) called "life" to physical objects; as such it would also be a form of non-physical life. And if one is willing to accept the existence of a non-physical realm in order to explain the Anthropic Principle, there can be no objection to the monotheistic explanation of it. In order to avoid such an explanation, therefore, this objection must say that the Anthropic Principle only applies to physical life as we know it.
In order for a physical entity to process energy, it must have complex molecules which are physically capable of such processes. Complex molecules are those that are based on atoms that are able to form a large number of bonds with other atoms. There are only three elements capable of forming complex molecules: silicon, boron and carbon. Silicon can only form about a hundred amino acids, which is insufficient for physical life. Boron is rare, and poisonous to life where it does exist in concentration; plus, wherever boron exists, carbon exists in much greater abundance, so it's not very likely to happen. Thus, when we discuss the necessary parameters for life, we refer to carbon-based life. One might think if the laws of nature were different it would change the situation. True. The Anthropic Principle shows that if the laws of nature were different, physical life could not exist at all.
Now some might suggest that I'm simply not taking the concept of "life as we know it" far enough. I'm still working in terms of atoms, and perhaps if we look into the subatomic realm, we would find ways for different types of atoms to form into different types of molecules that could then form living creatures. The problem here is that the ability of atoms to form bonds is directly related to the configuration and properties of its electrons. So the capacity for something to be alive in a physical sense is based on the basic properties of atoms, and thus of matter. Now the question arises: would it be possible to alter the basic properties of electrons or other subatomic particles in such a way that they would still be able to form into complex molecules capable of processing energy to perform work? To the best of my knowledge, the answer is no. The properties of electrons, protons, and neutrons as well as their interaction are some of the most dramatic examples of anthropic coincidences. Their masses must be precisely what they are, their decay processes must be precisely what they are, their ratios to each other must be precisely what they are, etc. in order for life to exist. For example, the ratio of electrons to protons that were created in the Big Bang must be exactly the same number to within one part in 1037 in order for their charges to balance out. Otherwise, the electromagnetic force would have dominated gravity and prevented the formation of planets, stars, and galaxies.
One might still object, though, that if completely different subatomic particles were created in the Big Bang which then formed completely different atoms and molecules, it would be possible to have a different type of life. But as soon as we're positing a completely different type of matter, it becomes difficult to continue calling it matter. In other words, this would (again) be just as metaphysical a solution as the monotheistic one. Moreover, at this point, we're positing different universes in order to explain the Anthropic Principle, so for this suggestion to have any force it must be wedded to the multiverse hypothesis with all of its failings. Thus, the monotheistic solution to the Anthropic Principle is preferable.
There's one more installment to go. Stay tuned.
Update (13 Feb): See also part 1, part 2, and part 4.
(cross-posted at Quodlibeta)