I pretty much figured, before the book was released, that I would take up the task of writing a review. I felt this way because Carroll is an extremely articulate and modest philosophical naturalist and has been securing more of a secular following as of late--especially since he debated William Lane Craig, and, in my opinion, won--and I was very curious as to how he would make a cumulative case for a coherent naturalist metaphysic. And after beginning to read the book I do in fact feel that there are many things to comment on, as I had hoped. Though I obviously disagree with Carroll on many of his positions, Carroll's humble and unboastful attitude coupled with his articulate writing make this a great read.
So, on with the review, then. Carroll's book is split into six sections: Cosmos, Understanding, Essence, Complexity, Thinking, and Caring. I am, so far, planning to write a review on each section individually, though it might be the case that I don't have many comments to make on a particular section, and thus I might not review all of them. This Part I review will focus on the section labeled Cosmos.
[O]ur best approach to describing the universe is not a single, unified story but an interconnected series of models appropriate at different levels. Each model has a domain in which it is applicable, and the ideas that appear as essential parts of each story have every right to be thought of as "real." Our task is to assemble an interlocking set of descriptions, based on some fundamental ideas, that fit together to form a stable planet of belief. (p. 4)This explication of poetic naturalism is very similar to two theories I've surveyed in the past, namely Model-Dependent Realism, as promulgated by Hawking, and Embodied realism, as promulgated by Lakoff. The key aspects of this philosophy are that we, as humans, talk about and describe different aspects or "levels" of the world using different models and different vocabularies, and that, as long as these models are consistent and coherent, they can overlap and reconcile with one another.
Unfortunately, Carroll doesn't delve too deep into this philosophy in the first section. Rather, he spends more space expounding this perspective in his second section Understanding--which should make sense since the "poetic" aspect of this philosophy is mostly epistemic. Therefore, I will save my comments on poetic naturalism until the next installment of the review.
One way that Carroll attempts to demonstrate the "layered" models of reality we conceptualize, as predicated by PN, is with Aristotle's notions of natures and causes. For Aristotle famously promulgated the principle of causality, which stated that something can only be "moved" if it was caused to do so by something else in motion. (Of course, by "motion" Aristotle really meant change, and by change he really meant something which is being reduced from potency to act.) But Carroll claims that the conservation of momentum has relegated such notions to mere useful macroscopic descriptions and constructions:
[T]he whole structure of Aristotle's argument for an unmoved mover rests on his idea that motions require causes. Once we know about conservation of momentum, that idea loses its steam. [...] What matters is that the new physics of Galileo and his friends implied an entirely new ontology, a deep shift in how we thought about the nature of reality. "Causes" didn't have the central role that they once did. The universe doesn't need a push; it can just keep going. [...] Of course, even today, we talk about causes and effects all the time. But if you open the contemporary equivalent of Aristotle's Physics--a textbook on quantum field theory, for example--words like that are nowhere to be found. We, still, with good reason, talk about causes in everyday speech, but they're no longer part of our best fundamental ontology. (p. 28-29)I have a couple comments at this point. First, the conservation of momentum--which is embedded in Newton's law of inertia--doesn't, at all, call Aristotle's idea of motion into question. For, again, Aristotle said that when something changed, this required something responsible for that change. But uniform inertial motion is seen, as explicated by physicists, as a state in itself, and not a change per se. That is, the state of motion of an object is its velocity, and thus an object with a uniform state of motion is an object that is moving at a constant velocity--as long as it is not being acted upon by an unbalanced force--and thus is not changing, according to physics. Therefore, the conservation of momentum does not at all run counter to Aristotle's metaphysical principle, in fact, it is completely irrelevant to the principle.
Second, it is simply not true that talk of causality, at least efficient causality, is absent from contemporary scientific textbooks. In fact, it's ironic that Carroll specifically mentions quantum field theory textbooks since in An Introduction to Quantum Field Theory the authors write the following: The necessity of having a multiparticle theory also arises in a less obvious way, from considerations of causality[...] In a relativistic theory, this conclusion would signal a violation of causality. (p. 14)
These points may seem peripheral, but I believe they are important for a couple of reasons. First, the unmoved mover argument of Aristotle, if valid, would defeat a naturalist ontology, which Carroll holds. Yet, Carroll quickly dismisses Aristotle's unmoved mover argument, in light of the supposed irrelevance of concepts of causality, yet he does so fallaciously. Again, this isn't that big a deal since Carroll's thesis is not predicated on discussing Aristotle's proofs for God. Nevertheless, his fallaciously swift dismissal of the efficacy of causality is still a strike against his case.
Second, Carroll is trying to score a point for poetic naturalism by claiming that the language of causality is only a folk theory constructed from interactions at the macroscopic level, and isn't part of our "fundamental ontology" and has no utility in the domain of physics. Yet the fact that this has been demonstrated to be false with the quote above (one of many) already begins to poke holes in Carroll's form of naturalism. That is, we see that a concept like causality is not simply a model that only applies in one limited domain. Rather, it in itself should be part of one's fundamental ontology.
Carroll also makes much of the fact that causality is nowhere to be found in the laws of physics, and claims that such concepts are "emergent":
We look at the world around us and describe it in terms of causes and effects, reasons why, purposes and goals. None of those concepts exists as part of the fundamental furniture of reality at its deepest. They emerge as we zoom out from the microscopic level to the level of the everyday. (p. 54)This is not correct, though. While it is true that causality is not palpable in the mathematical equations of physics and quantum physics--though we shouldn't expect it to be, since causality is not quantitative--this does not mean that causality is not operative and efficacious as it pertains to "reality at its deepest." I maintain that causality is ubiquitous at every turn, in the microscopic and macroscopic levels of reality.
To see this, consider the famous experiment conducted by physicist Hendrick Casimir in 1948. Casimir placed two metal plates one ten-thousandth of a centimeter apart in a quantum vacuum. As one might logically theorize, these plates would stay put, since the space is empty and thus there are no forces to affect the plates. But they didn't stay put, rather they were driven towards each other! And the first question that should come to one's mind is "Well, what was the cause of this effect?" It turns out that the cause is that there is an imbalance between the quantum fluctuations in between and outside the plates, and this imbalance yields a pressure imbalance, which pushes the plates together.
The point here is that, contra Carroll, causality is no less efficacious in a quantum vacuum than in our familiar everyday lives, and causality does simply emerge as we "zoom out" from the microscopic to the macroscopic.
Carroll also spends a good amount of the first section discussing our constant search for "reasons why" things happen or why facts obtain. He agrees that the search for explanations is extremely rational and makes sense in our everyday lives. Where Carroll draws the line is when one makes this search for explanation a metaphysical principle (e.g. the Principle of Sufficient Reason) that pronounces that everything must admit of explanation, or a "reason why." This is, no doubt, a very modest and logical position to take. Carroll is not committing one way or another to whether all things and facts admit of explanation. He humbly claims that they might or might not, and leaves the door open to the possibility of brute facts.
However, as one who does in fact believe that all things and facts must necessarily and logically admit of explanation, I do not agree with Carroll here. And I find that his arguments against the PSR to be rather weak. Carroll claims that "[o]ur standards for promoting a commonsensical observation to a 'metaphysical principle' should be very high indeed. "(p. 41) Now, I would agree here, but Carroll really doesn't survey any concrete arguments actually given (besides Leibniz's Principle of the Best) that would attempt to demonstrate why the PSR should be taken as a metaphysical principle. He merely says the following:
[F]or every fact we notice about the universe: as soon as we apprehend it, we think there must be a reason behind it. This isn't an argument that the Principle of Sufficient Reason is logically incontrovertible; it only implies that we often act as if something like it were true. If we're honest, it's an empirical, evidence-based argument, not an a priori one. (p. 42)I agree with Carroll that this argument he has articulated is not a priori, and is not logically incontrovertible. The problem is that no (logical) person attempting to establish the PSR as a metaphysical principle would use this argument, especially since it's just an inductive argument which cannot form an immutable principle at all.
The type of arguments that are given in favor of the PSR (and that are a priori) consider the nature of epistemic chains of explanation themselves. And they argue that explanation forms an instrumental and transitive chain, so that if even one member of a chain is unexplained (i.e. is a brute fact) then the chain as a whole loses efficacy. (Indeed, I have argued that very thing here, though I don't expect Carroll to have read my own specific post.) The point is that Carroll has not done the appropriate philosophical leg-work to dismiss the PSR as casually as he has done. And again this is important because the PSR puts a wrench in the works of his poetic naturalism, and also calls into question many other pronouncements he makes in the book, as we'll see in subsequent reviews.
The arrow of time
More importantly, in Carroll's eyes, the denial of the immutability of causality and explanation, as well as the displacement of their existence as a mere human convention of utility, is ultimately illuminated by the increase in entropy and the arrow of time:
"Memories" and "causes" aren't pieces of our fundamental ontology describing our world that we discover through careful research. They are concepts that we invent in order to provide useful descriptions of the macroscopic world. The arrow of time plays a crucial role in how those contexts relate to the underlying time-symmetric laws of physics. (p. 66)Carroll's point is that we only utilize concepts like causality and explanation because events progress from past to future, due to the arrow of time. This is to say that such concepts are contingent upon the direction of time, which is itself a contingent fact of the universe and could have been otherwise. But the laws of physics, on the other hand, do not have an arrow of time imprinted into them, and thus, as Carroll claims, concepts like causality and explanation are not carving reality at its joints, but are only concepts that humans constructed in order to make sense of the world as we interpret it. For had the arrow of time been in the opposite direction, things would be very different, as would our concepts and models.
Now, while it is true that if the arrow of time were pointing in the reverse direction, from future to past, events in the world would unfold in a completely counterintuitive and foreign manner, this would still not remove the necessity for concepts like causality and explanation. For explanation and causality are always present wherever things exist and behave, and wherever events and processes occur. And even in a universe where the arrow of time were reversed, you would still have things which exist and events which transpire; and as long as you have that, you have causes and effects, as well as explanations.
So I maintain that Carroll has not demonstrated how humans "invent" these concepts, and again, this is important, because Carroll's poetic naturalism in founded on the idea that these concepts are human constructs and models, invented through our interaction with the world on the macroscopic level due to utility. However, if these concepts are not cognitive constructs but are immutable principles embedded in the fabric of reality, then Carroll's form of naturalism loses ground.