Even an Atheist has to believe something. In The Big Picture, Sean Carroll attempts to construct an atheistic worldview. What he calls poetic naturalism is based on six claims:

There is only one world, the natural world. The world evolves according to unbroken patterns, the laws of nature. The only reliable way of learning about the world is by observing it. There are many ways of talking about the world. [That’s the “poetic” part.] All good ways of talking must be consistent with one another and with the world. Our purposes in the moment determine the best way of talking.

Carroll begins his defense of poetic naturalism with an intriguing argument for the idea that the world is “not caused or sustained or influenced by anything outside itself.” If there is only one world, as 1 affirms, no separate argument is needed to show that there is nothing outside of it. So, is there only the natural world? It is the conservation of momentum that Carroll sees “at the very heart of a shift in how we view the world, from an ancient cosmos of causes and purposes to a modern one of patterns and laws.” Aristotle’s argument for an unmoved mover, Carroll contends, “rests on his idea that motion requires causes. Once we know about conservation of momentum, that idea loses its steam. … [T]he universe doesn’t need a push. It can just keep going.” Carroll acknowledges that, for Aristotle, motion is a far broader concept than movement from one place to another. It refers generally to change or transformation of any sort. But there is no conservation law that applies to all transformations, so conservation of momentum does not explain Aristotelian motion.

Aristotle’s argument for an unmoved mover belongs to the broad and noble class of cosmological arguments. In response to their quest for causes, Carroll argues that causes are emergent. Like fluids and mammals, they are a useful way of talking about the universe, but not fundamental features of reality:

At the deepest level we currently know about, the basic notions are things like “spacetime,” “quantum fields,” “equations of motion” and “interactions.” No causes, whether material, formal, efficient, or final.

You cannot get away from Aristotle that easily. The language that physicists use is not really a good guide to the theories that they can justify. Here is a guide to talking about fundamental physics like an Aristotelian. Instead of saying that the universe consists of quantum fields, say that quantum fields are material causes. Instead of saying that fields interact with each other, say that those fields are efficient causes, ones serving to actualize in the real world what is potential in each quantum field. To answer the question, “What is a quantum field?” is to identify its formal cause.

There is, in any event, something wrong with Carroll’s argument that concepts like cause do not appear in modern formulations of the laws of nature. Concepts don’t appear in equations. Quantities do. The equations describe patterns of natural events. For Carroll, there is only the pattern. On a causal view, the causal abilities of physical substances create, and thus explain, the pattern. But then the observation that there are no causes in our equations is a category error. In a universe with real causes, you wouldn’t find them in equations.

Carroll continues his argument against causality:

Causality is essentially time-asymmetric.

The fundamental laws of nature are time-symmetric.

Thus, causality is not a fundamental feature of our universe.

But, causes create the pattern of the laws of nature; they are not the pattern itself. Sometimes causes create time-symmetric patterns, and sometimes they don’t. The patterns still need an explanation.

Carroll is among the physicists who argue that the world is better understood the less it seems to have any transcendent purpose. To support this sweeping conclusion, Carroll argues that if the universe had a purpose, it would obey teleological laws; but the laws of nature are not formulated in teleological terms. Therefore, by contraposition, the universe has no purpose.

This argument is valid without being sound. The universe could have a purpose without obeying teleological laws. Purpose can be front-loaded into the special initial conditions of the universe, as an arrow shot for the purpose of hitting the bullseye is carefully aimed before being fired. Carroll is placing an arbitrary restriction on how the universe could be purposeful.

The idea that the laws of nature are not inherently teleological is surely not free of difficulties. Carroll says:

The world, according to classical physics, is not fundamentally teleological. … [W]hat matters, in predicting what will happen next, is the current state of the universe. Not a goal in the future, nor any memory of where the system has been.

The problem is that Carroll’s definition of a final cause—“the purpose for which an object exists”—is not Aristotle’s definition: “causes which act for the sake of something.” A conscious purpose is a kind of final cause, but Aristotle’s idea is broader.

We find Aristotelian teleology in nature wherever an efficient cause is directed towards some particular effect. Striking a match is the efficient cause of fire. But since striking a match tends to produce fire, rather than frost, the fire is a final cause of the match. To the extent that the match acts for the sake of anything, it acts for the sake of producing fire. Acorns are the efficient causes of oaks, and oaks are the final causes of acorns. For Aristotle, things that “cannot be the result of coincidence or spontaneity … must be for an end.” Aristotelian teleology is intrinsic, not externally imposed. Acorns have the ability—but not the conscious desire—to grow into oaks; oaks do not happen by chance or coincidence.

If the simple, fundamental constituents of nature display final causality, it would be of a very minimal kind. It might relate mathematical quantities that represent properties of physical causes and their immediate effects. It might relate successive states of the universe separated by infinitesimally small periods of time, rather than something complicated like “in a few years, an oak.” Thus, we might expect differential equations, quantifying statements like “forces act for the sake of producing acceleration.”

To say that final causality in physics must take the form of a boundary condition does not do justice to Aristotle. When he says that the natural place of earth is at the bottom of the universe, and water above earth, air above water, and fire above air, he does not propose a fixed future time when the universe will be perfectly layered like an onion into earth, water, air and fire. Final causes are about the tendencies in elements; they find their residence in the laws of nature, and not in their boundary conditions.

Must we accept the existence of facts that have no explanation, or so-called brute facts? If not, then naturalism, whether poetic or otherwise, should be rejected. This is the core of versions of the cosmological argument that appeal to the principle of sufficient reason, a restricted version of which states that all explainable true propositions have explanations. For example, the theist will argue that the existence of contingent reality is an explainable true fact, and thus has an explanation. But this explanation cannot be another contingent being, and so must be a necessary being.

Carroll rejects this conclusion:

[T]here are no such things as necessary beings. All sorts of versions of reality are possible, some of which have entities one would reasonably identify with God, and some of which don’t.

But this rejection, based on the assumption that what is conceivable is possible, is inconsistent with his reply to the challenge of philosophical zombies in Chapter 41: “[T]he logical possibility of a concept depends on whether this or that ontology turns out to be true.” So with God.

Carroll finds no good arguments for the principle of sufficient reason either:

The usual strategy of defenders of the Principle of Sufficient Reason is not to gather evidence but to proclaim that what we have is a “bedrock metaphysical principle.” That is to say, it’s the kind of thing we can’t even imagine not being true.

Carroll is not quite right about this; it is not in fact the usual strategy. Alexander Pruss, for example, offers eight separate arguments for the principle. If brute facts are possible, Pruss argues, then why aren’t there more of them? There cannot be a reason why brute facts are uncommon, since brute facts do not have reasons. The laws of physics are of no help. All possible brute facts are as inexplicable for the naturalist as the existence of the universe.

The simpler hypothesis is the principle of sufficient reason: there are no brute facts.

“It’s a mistake,” Carroll argues, “to start embracing mystery for its own sake.” This is a remark that Carroll might take to heart. The naturalist, when faced with the fact that anything at all exists, must immediately surrender before an unfathomable mystery. The success of science, the existence of natural laws, every fundamental property of the natural world—are all in principle inexplicable:

Why was the entropy low near the Big Bang? … Why does the universe exist at all? … The secret here is to accept that such questions may or may not have answers. … [F]or some questions, the answer doesn’t go any deeper than “that’s what it is.”

By contrast, Stephen Barr argues:

[T]he complete intelligibility and rationality of reality corresponds to the existence of a supreme intelligence, a supreme reason. The last person, therefore, who would say that there is anything about the world created by God that is inherently irrational is the Jew or Christian.

In Part 4 of The Big Picture, Carroll weighs the evidence for theism and naturalism. In particular, he considers the fine-tuning of the universe for life. Small changes to the fundamental constants of nature can have dramatic consequences: atoms disintegrate; the periodic table disappears; galaxies, stars, and planets are erased; there is no chance for life. If this is so, then Naturalism is vulnerable to two objections. Naturalism is, in the terminology of probability theory, non-informative. Consider a crime scene. Security cameras show the burglar opening the safe on the first attempt, using the twelve-digit code. Detective Alphonse suggests that the burglar guessed the code. This theory is non-informative. A clueless burglar could have guessed anything. Detective Bertrand suggests that the robbery was an inside job. This is informative. Only an informed burglar would have been likely to enter the correct code. This is an important distinction. Non-informative theories are at the mercy of the relevant set of possibilities. We might entertain the probability of guessing a three-digit code. But as we add digits, the set of possible codes grows, and the likelihood of guessing the correct code drops. By contrast, extra digits will not affect the performance of the informed burglar.

Postulating that the world evolves lawfully does not tell us what those laws are. If the world and its laws are brute facts, there cannot be any reason to expect any particular set of possible laws. The predictions of science are not the predictions of naturalism.

Mindful of this objection, Carroll presents the multiverse as a solution to fine-tuning. Perhaps our universe is one among many possible universes. Our existence as observers explains why we observe the conditions required to have observers. Carroll’s defense of the multiverse fails to mention the Boltzmann brain problem. Some possible observers do not need the paraphernalia of fine-tuning, because they form by means of freak stochastic fluctuations. Even in universes that could not support life, Boltzmann brains can form and observe their surroundings for a short time. These kinds of theories predict that typical observers will conclude that they are Boltzmann brains, alone in a dead universe. If small regions of order are more likely than large regions, then Boltzmann brains are vastly more common than observers in large, low entropy universes like ours. If only very special multiverses avoid this problem, then the multiverse itself is fine-tuned. Carroll has published papers on this problem, so its omission from the book is curious, and the statement “we can say with confidence … that if we get a multiverse [via inflation and string theory], any worries about fine-tuning … evaporate” is utterly unjustified.

Carroll attempts to respond to these arguments by showing that the likelihood of a life-permitting universe on theistic grounds is lower than one might expect: “Nobody was able to use the idea of God to predict a vast space with hundreds of billions of stars and galaxies.”

One theory cannot taunt another with evidence that neither explains.

Should we expect a vast universe on naturalistic grounds? Even if theism gives no reason to expect a universe of any particular size, it is no worse than naturalism. The size of the universe is irrelevant. If theism were true, Carroll argues, “it is hard to understand why life seems so unimportant in the final product. … All of this splendor is completely superfluous.” Carroll himself has suggested a good reason for the vastness of the universe—its splendor. For millennia, the immensity and magnificence of the universe has inspired humanity to reach out for the good, the beautiful and the true. “What sort of universe do we demand?” asked C. S. Lewis. “If it were small enough to be cozy, it would not be big enough to be sublime.”

Carroll states that, “If [the fine-tuning argument] is right, we actually are the center of the universe, figuratively speaking.” But this is neither an assumption nor an implication of the argument. We can conclude that the CD player in my car was designed to play music without assuming that the entire car exists solely to play music, even if we do not know what a car is for, or why it makes such a racket when I turn the key. The fine-tuning argument need not assume that our existence is the sole purpose of the universe. The laws of physics, Carroll argues, do not allow us to predict the emergence of life: “if we didn’t know anything about the universe other than the basic numbers of [particle physics] and cosmology, would we predict that life would come about? It seems highly unlikely.” But this is the wrong calculation. We do not know the sufficient conditions for life. But fine-tuning is concerned with its necessary conditions. The rapid expansion of the universe, for example, precludes the formation of any structure at all.

Some of Carroll’s arguments are self-defeating. “There are many different conceptions of God,” he argues, “all of which are somewhat vague on the specifics of God’s intentions about the constants of nature. It’s an inherent problem with any theory that is formulated using words.” Naturalism is also formulated using words. Although physical theories are expressed mathematically, they can fit into both the theistic and naturalistic worldviews. This is surely no proof against vagueness.

“The physical world could behave in any way it pleases,” Carroll correctly observes, adding, “God could still create ‘life’ and associate it with a different collection of matter in whatever way he might choose.” This objection is inconsistent with Carroll’s view of the laws of nature as patterns. It makes sense to say of God that he forces electrons to behave in any way that he pleases. But on a pattern view, one cannot say that the laws of nature are one way and the actual behavior of natural things another. Further, God’s decision to create a rationally discoverable physical environment, rather than one that displays no rhyme or reason, is at least understandable.

Tuned or not, life goes on, and we must interact with people in one way or another. For the poetic naturalist, the search for moral values begins with an examination of the moral instincts. “If we’re discussing ethics and morality,” Carroll asserts, “‘useful’ is closer to ‘offering a consistent systematization of our impulses about right and wrong.’” However, the naturalist seems stuck, for our sentiments are not to be trusted: according to “natural selection, without any divine guidance or interference, we would expect to inherit a wide variety of natural impulses, some for good, some for not so good.”

We need moral values to stand above our animal natures and subconscious passions. If I find in myself an impulse to do something, I cannot suppose that this, by itself, is a moral license to do it. Neither is it reason to suppose that this desire is immoral. We must judge ourselves, but by what standard? Carroll does not shed a great white light on the question. “[W]e need to do better at reconciling how we talk about life’s meaning with what we know about the scientific image of our universe.”

But also, “unlike higher-level scientific descriptions, [values] are not determined by the scientific goal of fitting the data.” On the one hand, “reality guides us”; but, then again, “nature doesn’t guide … Nature is kind of a mess. We can be inspired by it, and occasionally horrified by it, but nature simply is.”

Carroll compares moral rules to the rules of a game, such as basketball. But our moral experience protests: “it’s not like that!” We can change the rules of basketball. But while we can choose to hate, we cannot creatively make hate good, or love evil, or rape an obligation, or gratitude an abomination. Try it sometime. The point applies to Carroll’s opinions about aesthetics. “[B]eauty and goodness,” he claims, “are things we bring to [the world].” Really? Did you bring beauty to the sunset?

Let us imagine that Carroll has an evil twin, someone not nearly so committed to morality as Carroll is. What a very different book he could have written.

Carroll : We certainly haven’t agreed on the best way to live in the world as good human beings.

: We certainly haven’t agreed on the best way to live in the world as good human beings. Evil Twin : Ah, no! There is no best way to live in the world, and thus no such thing as a good human being.

: Ah, no! There is no best way to live in the world, and thus no such thing as a good human being. C : How do we find meaning and purpose in a world that is purely natural?

: How do we find meaning and purpose in a world that is purely natural? ET : Why search for meaning and purpose that do not exist?

: Why search for meaning and purpose that do not exist? C : If we decide that something is deeply wrong, there is no reason why we cannot work to prevent it from happening.

: If we decide that something is deeply wrong, there is no reason why we cannot work to prevent it from happening. ET : Or, we can reverse our decision and decide that it is right.

: Or, we can reverse our decision and decide that it is right. C : Desire is built into life. We can, if we choose, focus our caring on making the world a better place.

: Desire is built into life. We can, if we choose, focus our caring on making the world a better place. ET : Or, focus on getting whatever you desire.

: Or, focus on getting whatever you desire. C : It takes all kinds. People are different, so they’re going to create different things. That’s a feature to be celebrated, not an annoyance to be eradicated.

: It takes all kinds. People are different, so they’re going to create different things. That’s a feature to be celebrated, not an annoyance to be eradicated. ET: Well, except for the people we need to put in prison because they find meaning in their lives by following their innate desires to steal, kill and destroy.

The position that Carroll has adopted seems to be arbitrary. No matter the moral proposition that he means to affirm, its denial is equally plausible.

Naturalism’s commitment to The True, then, cannot support a commitment to The Good. Which kind of naturalist will The Big Picture produce? Carroll, or his twin?