This is the weekly Q & A blog post by our Research Professor in Philosophy, Dr. William Lane Craig.


I am a Christian theist and working towards a doctorate in philosophy. I have a question that I think is relevant for both laymen and academics, and I would really appreciate your thoughts.

I often find myself "gestalt-shifting" between naturalistic and supernaturalistic (especially theistic) worldviews. When I consider certain things, the theism to which I assent seems eminently reasonable, but when I consider other things naturalism (or at least non-theism) also seems plausible, and it is understandable to me why so many philosophers and scientists are naturalists (or at least non-theists).

For some time I have tried to understand what specifically makes naturalism (or at least non-theism) seem plausible to me (and others), and I think part of it is the following.

Put briefly, so much about the history of the universe and our planet seems arbitrary or random. More precisely, much of natural history seems to lack rational explanation. The universe is billions of years old, and human existence is a mere blip on the cosmic timescale. There are vast, vast numbers of galaxies, and thus tremendous numbers of stars, planets, and other astronomical entities. Moreover, the earth itself is billions of years old, and humans have only existed here for a relatively brief period of time. Great numbers of other species have existed, and many have been extinct for millions of years. Humans seem *so small* relative to the vastness of the universe. As I reflect on these facts and others like them, I can't help but wonder why. Why is the universe and our planet this way rather than some other way? It seems that if the God of traditional (Christian) theism exists, then there should be some rational explanation for these types of facts. There should be some reason why God has created the universe this way, rather than another, these states of the universe, rather than other states. But many of these facts seem pointless and without rational explanation.

Put like this, the ideas are largely rhetorical, but I think they motivate a precise argument. The argument can be put something like this:

  1. If God were to exist, then every state of the universe would be rationally explainable.
  2. It's not the case (or at least it's likely that it's not the case) that every state of the universe is rationally explainable (alternatively, some states of the universe are not rationally explainable).
  3. Therefore, God does not exist.

Important for this argument is a distinction between rational/personal explanation and natural/causal explanation. Natural/causal explanation is the sort of explanation provided when, for example, one explains weather patterns by reference to various natural states and laws of nature. Rational/personal explanation is the sort of explanation provided when one gives a person's reasons for performing some action. For example, what explains my eating a PB&J sandwich is that I like PB&J sandwiches, what explains God's creation of humans is his munificent love, etc. Part of the distinction is that natural/causal explanations are necessitating (in some sense), whereas rational/personal explanations are not.

This distinction is important for premise (2) because the claim is *not* that there are states that lack *any* explanation. In other words, I think the argument is consistent with some form of the principle of sufficient reason (such as the one you use in the Leibnizian Cosmological Argument).

With this in mind, let me mention some of the rationale for the premises. The main support for premise (1) is, roughly, that (a) God is sovereign over every part of the universe, and (b) God is not frivolous. Sovereignty implies control over the universe and the course it takes (except, perhaps, over personal free actions). God not being frivolous implies that God acts for good reasons and not arbitrarily. But these jointly imply that God has control over the states of the universe (i.e. the states are ultimately, or at least partially, explained by God's actions), and God acts to bring about these states for good reasons. Premise (1) seems to follow from these considerations. This is not as precise as it could be, but I trust you can see the thrust of these claims in support of (1).

The main support for premise (2) is, roughly, that we humans cannot see any rational explanation of various states (like the examples given above). And if we cannot see any rational explanation, then it's likely that there isn't one. One might question the move from "we don't know of any" to "there likely is none," but this move is clearly justified in some cases. One might object that it is not justified in this case (i.e. take something like a skeptical theist view with respect to the problem of evil). This is not implausible, but it seems to me that we should at least expect to be able to *conceive* of some good reason for various states of the universe, and I have a hard time of conceiving of good reasons in many cases.

There's a lot more that could, and probably should, be said, but this question is getting long. Since I'm a Christian, I obviously don't think this argument is conclusive. But it seems worthy of serious reflection, and I find it fairly plausible. I suspect also that something like this reasoning is why many (especially scientists and philosophers) find theism implausible. Perhaps they are influenced more by the rhetorical ideas than the precise argument. But I would appreciate your thoughts.

Thank you for your work.



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Dr. William Lane Craig’s Response

Dr. William Lane Craig

D, this very question came up in the Fine-Tuning Seminar last summer at St. Thomas University in which I took part, and I want to share with you a lesson I learned there.

David Manley was making the point that on the cozy, pre-Copernican cosmology—what C. S. Lewis called “the discarded image” of the cosmos—theism seemed vastly more probable than atheism. Like a Fabergé egg, the little universe centered on the Earth, with the spheres of the planets and fixed stars revolving about it, cried out for an explanation in terms of a Cosmic Designer. But if you agree that theism is more likely than atheism on such a view, then, Manley argued, you must also agree that a vast cosmos, such as we observe, counts against God’s existence.

Now I’ve read enough of the philosophical and scientific literature on fine-tuning to know that the vastness of the cosmos is not really surprising on theism. For example, John Barrow and Frank Tipler in their important book The Anthropic Cosmological Principle (Oxford University Press, 1985) emphasize that the size and age of the universe are just what we should expect to observe. For the carbon that makes up our bodies was synthesized in the interior of stars and then distributed throughout the universe via supernovae. It takes aeons for galaxies of stars to form and even more time for the carbon requisite for life to be spread abroad to become the foundation of biological life. No other element could substitute for carbon in this role. So the universe must be as old as it is for life to exist and, hence, as big as it is, since the universe is in a state of cosmic expansion since its inception in the Big Bang 13.7 billion years ago. So the size and age of the universe are just what one ought to expect given the fine-tuning of the initial conditions of the universe, which, many have argued, is best explained through design.

Now, of course, one might ask why the Cosmic Designer chose to create the universe in this manner rather than producing the stars and planets miraculously in a moment. But it seems to me that if the Creator prefers to make a universe endowed with initial conditions and natural laws that forms structures naturally over time rather than to produce a world with the appearance of age (like starlight that never really traveled from the stars to us or fossil fuel deposits that are not actually the vestige of primaeval forests), he can hardly be faulted for preferring such a world over a world with an illusory past. Indeed, once we launch into speculating about universes operating according to different laws of nature, then we have completely lost our tether and have no idea whether such worlds would be preferable to a world like ours, especially in realizing God’s redemptive purposes for creatures created in His image.

Sometimes people complain that a vast cosmos is a waste of space and so would impugn God’s efficiency as a Creator and Designer. But here I’m persuaded by Thomas Morris’ point that efficiency is a value only for someone who has limited time and/or resources, a condition which is just inapplicable to God. That’s why I think that those pressing the efficiency objection are just wrong in thinking of God in terms of an engineer marshaling his resources rather than as an artist, who enjoys splashing His cosmic canvas with dazzling colors and creations. I am in awe as I look at the galactic and cosmic structures photographed by the Hubble telescope. The vastness and beauty of the universe speak to me of God’s majestic greatness and His marvelous condescension in loving and caring about us.

Of course, God’s choosing to create the cosmos in this way raises the problem of so-called natural evil, the suffering that results from living in a cosmos governed by natural laws. You’re cognizant of the relevance of discussions of natural evil to your question, and I won’t reiterate what I’ve written on that topic elsewhere (e.g., Philosophical Foundations for a Christian Worldview). Suffice it to say that I think we’re in no position to make with confidence judgements that it’s probable that God lacks good reasons for the perceived shortcomings of this world. I agree with William Dembski that a world such as ours is a suitable place for fallen and sinful persons like ourselves and for the accomplishment of God’s redemptive plan for the human race. So I reject your premiss (2) without reservation, just as I reject similar inferences concerning natural evil.

So, as I say, I found Manley’s point disquieting. But a personal conversation with Nevin Climenhaga, a former student of Tim McGrew at Western Michigan and a whiz at probability theory, proved to be illuminating. Manley was right, Nevin explained, that if you agree that the existence of a small universe is more probable on theism than on atheism, that is, P(Small Universe | Theism) > P(Small Universe | Atheism), then you must agree that just as the smallness of the universe supports theism, so also the vastness of the universe supports atheism. But—and here’s the rub!—not to the same degree!

This can be seen through the Odds Form of Bayes’ Theorem. (We’ll leave out the background information k for simplicity’s sake.) We want to compare:

Suppose we say P(Small Universe | Theism) = .01 and P(Small Universe | Atheism) = .0001. That reflects our conviction that given a small, pre-Copernican universe, God’s existence is much more probable than atheism. This assumes that the prior or intrinsic probability of theism or atheism is exactly the same; otherwise Manley’s argument collapses. So we’ll just assume for the sake of argument that P(Theism) = 0.5.

Now to figure the probability of a vast universe (that is, a non-small universe) on theism, you subtract the probability of a small universe on theism from 1.0; that is,

P(Vast Universe | Theism) = 1.0 - P(Small Universe | Theism)

So it follows that the probability of theism on a vast universe compared to the probability of atheism on a vast universe is:

Here 1.0 - P(Small Universe | Theism) = .99, and 1.0 - P(Small Universe | Atheism) = .9999. In other words, the degree to which the vastness of the universe increases the probability of atheism is marginal! It scarcely changes the odds at all. So while the smallness of the universe would greatly increase the probability of theism, the vastness of the universe only negligibly increases the probability of atheism. This niggling difference is easily overcome when one factors in other information than the universe’s size, such as its beginning to exist, its being fine-tuned, and so on. Then the universe’s size can become virtually irrelevant.

I think this can help to explain your intuitions, D. Taken in isolation the vastness of the cosmos does count against theism to some degree, but not decisively; indeed, given all the evidence we have, I should say, insignificantly.[1]

[1] I’m grateful to Nevin for his comments on the first draft of this Question of the Week. It’s encouraging to see such gifted, young, Christian philosophers coming up through the system.

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