In my previous posts about the Carroll-Craig debate, I've been skirting around the edges of an important claim by Carroll which summarizes the main reason he doesn't buy the Cosmological Argument. That's because I was focusing on the question of whether the universe had a beginning. Now I want to grapple with his more philosophical claim.
Carroll says this:
So, I think I can make these points basically by following Dr. Craig’s organization starting with the kalam cosmological argument, and unlike what he said I should be doing I want to challenge the first of the premises: If the universe began to exist it has a transcendent cause. The problem with this premise is that it is false. There’s almost no explanation or justification given for this premise in Dr. Craig’s presentation. But there’s a bigger problem with it, which is that it is not even false. The real problem is that these are not the right vocabulary words to be using when we discuss fundamental physics and cosmology. This kind of Aristotelian analysis of causation was cutting edge stuff 2,500 years ago. Today we know better. Our metaphysics must follow our physics. That’s what the word metaphysics means.
[Well, many scholars think that Aristotle's book on causation/God was called Metaphysics because it was the book immediately following his Physics in the traditional order of the canon. But perhaps Carroll knows this and is simply introducing his thesis in a joking way...]
And in modern physics, you open a quantum field theory textbook or a general relativity textbook, you will not find the words “transcendent cause” anywhere. What you find are differential equations.
[Of course, because QFT and GR concern the interactions between various material entities (excitations of fields). Their interactions (i.e. their causal relationships) are indeed described by differential equations. And therefore the subject matter does not concern transcendental or ultimate causes, any more than economics or psychology textbooks discuss the weak force. What he really ought to say to make his argument, is that the term "cause" does not appear in many modern physics textbooks (apart from the use to mean "logically implies") due to its lack of usefulness in specifying the precise form of the laws of physics.
It is, however, a separate question whether concepts of causation are implicit in the fact that some particular differential equation holds. It does not seem outrageous to state that the state of the fields at a given point are caused by the state of the fields just beforehand in the past lightcone; indeed this concept is called causality in contemporary physics. This concept may indeed be different in some ways from traditional philosophical ideas of causality, but it is not sheerly different, and there is room for argument about the precise relationship between these ideas of causation. Carroll continues:]
This reflects the fact that the way physics is known to work these days is in terms of patterns, unbreakable rules, laws of nature. Given the world at one point in time we will tell you what happens next. There is no need for any extra metaphysical baggage, like transcendent causes, on top of that. It’s precisely the wrong way to think about how the fundamental reality works. The question you should be asking is, “What is the best model of the universe that science can come up with?” By a model I mean a formal mathematical system that purports to match on to what we observe. So if you want to know whether something is possible in cosmology or physics you ask, “Can I build a model?” Can I build a model where the universe had a beginning but did not have a cause? The answer is yes. It’s been done. Thirty years ago, very famously, Stephen Hawking and Jim Hartle presented the no-boundary quantum cosmology model.
[See here for my discussion of the claim that the Hartle-Hawking model leaves no room for a Creator.]
The point about this model is not that it’s the right model, I don’t think that we’re anywhere near the right model yet. The point is that it’s completely self-contained. It is an entire history of the universe that does not rely on anything outside. It just is like that. The demand for more than a complete and consistent model that fits the data is a relic of a pre-scientific view of the world. My claim is that if you had a perfect cosmological model that accounted for the data you would go home and declare yourself having been victorious.
Carroll seems to be saying that the ability to construct a mathematically precise and consistent model of the universe is the only important criterion for the fundamental laws of physics, aside from fitting the data. Presumably he would add something about simplicity if we were considering two rival models which both accounted for the same data, but I think he doesn't mention that since his primary concern is saying what counts as a possible model according to the contemporary set of informal procedures that cosmologists use, rather than asking how we decide between models once we have them.
This is probably the most important claim that Carroll made during the debate. I appreciate the fact that he was able to state his view in such a clear and accessible way. Now, there is one important point in which I agree with Carroll, and one important way in which I disagree.
I agree that Modern Science has involved some shifts in how we think about causation in the physical universe. This shift, which occurred sometime around the beginning of the 20th century (give or take a couple hundred years) involved a move away from mechanistic notions of causation, towards more abstract mathematical models. As a characteristic example, in the 19th century it was presumed that light waves couldn't exist unless they were supported by a medium, called the luminiferous aether. When Einstein developed special relativity, he showed that no such aether was necessary. If you can write down a satisfactory equation for the way the electromagnetic field propagates, there's no need to ask questions like "In what medium does it propagate?" (Of course, this philosophical point could have been made in the time of St. Maxwell as well, but it wouldn't have been as compelling then, since before Einstein's theory of relativity an aether was needed to preserve the principle of relativity).
Another example concerns normal forces of the sort that prevent two solid bodies from occupying the same space. A premodern physicist would have said that solid bodies have a property of solidity or massiness which, using our everyday intuitions, prevents two bodies from occupying the same position. In Lucretius' atomic theory, the atoms were in solid shapes like billiard balls (but not necessarily round) which excluded each other due to their solidity. Very different was St. Roger Joseph Boscovich's 1763 proposal that atoms are merely mathematical points exerting force on other mathematical points.
In modern physics, there's nothing inherently wrong in general with two objects occupying the same position, since you can write down equations in which this is allowed. The default, in the absence of interactions, is for two bodies to pass right through each other. That this does not occur for real solid bodies is due to a combination of electromagnetic forces and the Pauli exclusion principle for electrons.†
So I agree with Carroll that there have been changes in our attitude to causality in Physics. Now let's see whether this should change our views about Metaphysics. As a reminder, Metaphysics is the branch of philosophy which studies the fundamental nature and relationships between various beings (abstracting from the particular descriptions of the particular things as studied by more specialized fields like Physics or Biology). It asks questions like these:
Do individual things have a particular essence or nature which does things?
In what sense does causality exist, and if so what kinds are there?
Is there really a physical universe?
Are there really minds?
Can everything be reduced to physics, or can everything be reduced to mental properties, or are these two independent realities, or are they both dependent on something else?
In what sense do mathematical entites like "7" or "isoscoles triangles" exist?
In what sense does morality exist?
Does some type of God exist, and if so what is he/she/it like?
What are the relationships between these different types of existence?
Do the "holes" in doughnuts really exist, or are they merely the absence of doughnut?
Are the questions I just asked even meaningful, or are some of them silly word games?
(The subset of questions about what exists are also sometimes also called Ontology. In case you're wondering, analytic philosophers really do debate the one about holes. Personally I consider the one about God to be more important. But I figured that given my last question, I needed to include at least one question which I consider to be a silly word game...)
Now, these questions raise some difficult and contentious issues, and philosophers have been debating them for thousands of years. But rather then tackle them head-on, let's ask to what extent developments in Physics and other Sciences help answer these questions.
There are two opposite extreme approaches one might take:
1. One is the view that our Metaphysics should essentially follow immediately from our Physics. Once we learn from experiment what specific Laws of Physics are true, that tells us everything we need to know about Metaphysics. People with this view tend to be scientistic and dismissive of philosophical arguments. (You might think from the quotation above that this is Sean Carroll's view, that once we work out the correct physical model there are no more interesting questions to ask. But in fact his view is more subtle, since he acknowledges that there are interesting philosophical questions not obviously resolved by Science.)
2. The opposite extreme would be to say that developments in Physics have little or no bearing on Metaphysics. For example, there are modern day followers of St. Thomas Aquinas (typically but not always Roman Catholics) who believe that something similar to Aristotle's metaphysical views follow necessarily, given that the world is rationally explicable at all, and that the very possibility of doing Science depends implicitly on accepting them. In this view, the basic concepts of metaphysical reality such as substance/accident or act/potency are written in stone, although identifying the particular "substances"‡ which actually exist, and their properties, depends on empirical Science. One such philosopher is St. Ed Feser, whose blog is on my sidebar. (I recently read his book Scholastic Metaphysics in which he presents his arguments for this position. On a first pass, I found it serious and interesting but ultimately unconvincing, though giving my reasons would take this post too far afield.)
But it seems to me that the correct view is in the middle, that Physics has some bearing on Metaphysics but it doesn't fully determine it. Physical models and metaphysical views have, not a 1-to-1 relationship, or even a 1-to-many relationship, but a many-to-many relationship!
People who agree on the Laws of Physics (to the extent that we are able to discover them at present) can still have radical disagreements about Metaphysics. Of these metaphysical views, some seem irrational and silly, like the Monadic view that all distinctions are illusory and that only one thing exists. But it seems to me that there are several possible reasonable (i.e. non-crazy) views. So even after we agree on a single physics model, multiple metaphysical views can be reasonable. The variety of interpretations of Quantum Mechanics is one prominent example. Choosing between these interpretations requires philosophical arguments; doing an experiment is not enough.
On the other hand, it seems rather unlikely that the philosophical considerations by themselves are sufficient to pin down an exact Metaphysics either. That would be to say that every single view about the nature of Being, besides one, can be decisively refuted by philosophical arguments. That would seem to me almost as surprising as a claim that the Laws of Physics can be deduced from pure Reason. There are just too many possible sets of belief, and logical consistency plus noncraziness is too weak of a constraint. (Especially since our notion of noncraziness needs to be flexible enough to include things like interpretations of QM and the mind-body problem, where nearly all views seem "crazy" in one way or another.)
Given that there are multiple possible views about Metaphysics, we need all the help we can get to choose one. So it would be absurd not to rely on Physics to some extent, especially as it impinges on relevant questions. How could anyone have an informed position on the nature of time without thinking about what General Relativity says about spacetime? But we also need to recognize that Physics is not enough, and that abstract arguments about what "makes sense" are also called for. Even together these are not sufficient to bring all reasonable Philosophers into agreement.
That means that Carroll is moving much too quickly when he says that "This kind of Aristotelian analysis of causation was cutting edge stuff 2,500 years ago. Today we know better. Our metaphysics must follow our physics."
If there are multiple possible metaphysical views, then we can't just dismiss the views of Aristotle (or whoever) just for being old, without carefully thinking about their compatibility with Modern Science. Maybe people switched to modern views because of updates in physical knowledge (some of which, like Determinism, may themselves be out of date!). Or maybe they changed because of philosophical arguments, in which case we need to check whether those arguments are good or bad. Or maybe the old views simply became unfashionable. Most likely, it was some combination of these four causes, and we need to be careful! As St. Lewis writes concerning Owen Barfield:
In the first place he made short work of what I have called my "chronological snobbery", the uncritical acceptance of the intellectual climate common to our age and the assumption that whatever has gone out of date is on that account discredited. You must find out why it went out of date. Was it ever refuted (and if so by whom, where, and how conclusively?) or did it merely die away as fashions do? If the latter, this tells us nothing about its truth or falsehood. From seeing this, one passes to the realization that our own age is also a "period", and certainly has, like all ages, its characteristic illusions. They are the likeliest to lurk in those widespread assumptions which are so ingrained in the age that no one dares to attack or feels necessary to defend them.
While I don't accept St. Feser's arguments that Aristotelianism is compulsory, I think that studying it is a useful antidote to thinking that there's only one possible view. Certain aspects of modern thought might be unreasonable inheritances from the Enlightenment, or from Positivism. The easiest way to notice that we are making unnecessary presuppositions, is by comparison to what previous thinkers have thought. If we dismiss previous metaphysical views out of hand, that makes it hard to notice our own modern blindness towards certain issues and problems.
We need to be especially careful given the tendency for theories to be expressed in the language of the existing philosophical structures. This can cause us to think that those theories depend on a certain Metaphysics, when really they don't. Just because theologians expressed Trinitarian doctrines using Aristotelian terminology, or early 20th century physicists expressed QM using Positivist concepts, doesn't necessarily mean that these ideas can't be transplanted to certain other systems.
Aristotelianism became unpopular long before QM was discovered. But suppose that somehow the medieval European or Muslim world had discovered QM. I bet that their "interpretations" would have been radically different from anything we have now, even if the mathematics which they developed ultimately turned out to be equivalent to ours (as happened to Heisenberg and Schrödinger)!
None of what I have said here is a positive argument for Theism. It is merely my attempt to sweep away Carroll's strong claim that once we have a physical model, all of our work is done and there is no place to ask further metaphysical questions. On the contrary, we can continue to ask questions, and we can judge possible answers to those questions by whether they make logical or intuitive sense to us.
Perhaps at the end of the day, a person might conclude that the certain questions about the origin of the Universe are meaningless, or that that they are meaningful but that Theism is not the correct answer to them. But that has to come after considering the merits of different rival views, not beforehand.
Notes:
† The Pauli exclusion principle forbids two fermions from occupying the same state, which sounds a bit like the principle that solid objects cannot occupy the same space, except that:
(i) ``state'' refers not just to position but rather to all properties including both position and velocity (to the extent that both can be simultaneously measured in Quantum Mechanics).
(ii) It follows from a much more abstract mathematical principle, which I will cite without explaining, that identical types of fermions (e.g. electrons) have antisymmetric wavefunctions. This means that the complex number describing the quantum mechanical amplitude for one electron to be in position 
and the other in position 
is minus the amplitude for the first to be at and the other at . This is called Fermi-Dirac statistics.
(iii) It doesn't apply to bosons, which have symmetric wavefunctions. Therefore you can have a bunch of identical bosons in the same state, as in lasers or Bose-Einstein condensates.
‡ "Substance" is a technical term in Aristotelian metaphysics. It means an individual entity which possesses existence independently, as opposed to an "accident" which "inheres" in a substance and can be changed without affecting the underlying nature of the thing in question. Sort of like the difference between nouns and adjectives. Not to be confused with the more recent chemical notion of substances. This confusion of terminology causes great misunderstanding when Roman Catholics try to explain their doctrine of transubstantiation to modern people!
