## Fundamental Reality II: Causes and Explanations

With sufficiently robust assumptions about how causation works, it is possible to formulate various Cosmological Arguments (there's more than one) in a strictly deductive way.  But in our age there isn't enough of a consensus about how causation works, or even whether it really exists, to create an argument with broad popular appeal.  Some people even say that Science has refuted the idea of causality and replaced it with other concepts.

Instead I'm going to go the long way around and focus on the concept of explanations.  It seems utterly clear to me that Science is in the business of finding explanations for certain phenomena.  If it can't do that, it loses any claim to make sense out of the world.  If you want your theory to explain even one single thing about the world, then that requires you to give an account of what circumstances explain that thing.  Then we say that the thing happened because of those circumstances.  And as you can see, that word “because” has the word cause sitting inside of it.  Grammar itself teaches us that Science requires some notion of causation.

For example, we say things like “the planets all rotate around the sun in the same direction because the solar system formed from a rotating disk of gas”, or “the heat capacity of matter is finite because it is made out of atoms”, or “electrons attract protons because they have negative charge”, or “energy is conserved because the laws of nature are invariant under time translation.”  It is not obvious that these various senses of “because” all correspond to the exact same concept, but we can take almost any of them as examples for what I am going to say.  (Except perhaps for the “because” of pure logical deduction from definitions, i.e. “cold is the absence of heat because that is what the word cold means; 2+2 = 4 because 4 is twice two.  But pure logic is not enough to explain everything that happens, since avoidance of strict logical inconsistency is a rather weak constraint.)

Aristotle famously said that there are four different types of causes: material, formal, efficient, and final.  As a classification of the types of "because" answers we give to various questions, this seems fairly reasonable.  But some people would argue that the physical sciences only use some of these types of explanations.  In particular, it is disputed whether final causes, which express purposes—e.g. that the sun exists in order to produce light, or that the animals eat in order to receive nourishment—really exist in reality outside of our own minds.  This question will pop up later when we discuss Ethics, not to mention the Fine-Tuning Argument.  For the time being, let's consider less controversial notions of causation, without assuming Aristotle’s division to be correct.

In order to side-step some possible misunderstandings about what I mean by an explanation, let me make it clear that I am using the term explanation in a broad sense, so that:

A. Explanations can be Nondeterministic.   An explanation does not need to be deterministic, in the sense that the effect invariably follows from the cause.  It is enough if the explanation produces a framework, in which it makes sense that the cause might be produced.  For example, Quantum Mechanics is a nondeterministic theory, in the sense that if you start with a given initial condition, and you know the laws of physics, there is generally more than one possible final outcome, and you can only predict their probabilities.  So long as the probability of what happens is not so low as to indicate that the theory is probably wrong, I'm going to count this type of thing as an explanation of the experimental outcome.  That's because it seems that the universe is not deterministic, and if it isn't, then probabilistic explanation is the best that we can do.

For example, if a radioactive atom decays, you can't predict exactly when it will decay, but you can still explain why it can decay with reference to the forces and particles in the nucleus.  It's not like the decay occurs in an explanatory void.  So I think in a quantum mechanical theory, we need to generalize our notions of "explanation" and/or "causation" to allow for such nondeterministic explanations.  Just because you can't predict exactly what happens, doesn't mean there isn't a set of circumstances which causes whatever does happens to happen.  It's just that there's more than one possible outcome that set of circumstances could have produced.  That's different from something happening without any causes at all.

B. Explanations can be Unknown.  Similarly, there obviously exist some phenomena which do have an explanation, but we don't know what it is yet.  In that case, I want the term “explanation” to refer to the actual reason why the thing occurs, and not merely to those explanations which are currently known to our limited human minds.  Maybe we will never find out the full explanation for something, but that doesn't mean it doesn't exist.  This point is important because Cosmological Reasoning, as I understand it, involves the attempt to push back the concept of explanation back to its ultimate fundamentals, to see what a fundamental explanation would have to look like in principle.  For example, a Naturalist doesn't necessarily need to know what the most fundamental theory of physics should look like, to propose that if we did know it fully, it would then explain everything else.

On the other hand:

C. Explanations are not just Regularities.  I reject the Humean view that causality is just a name for the constant conjunction of events.  In the end, I think this boils down to a renunciation of the possibility of explaining anything.  “Rocks have always fallen down before” is simply not an explanation for why the next rock falls down.  It doesn't have the right form to be an explanation.  It may make it rational to believe that the next rock will fall down, but the reason it does so is that we believe that there are underlying causes (in this case, gravitational attraction to the Earth) which remain roughly the same for each rock.  Conversely, there are many types of regularities (e.g. as of 2014, a woman has never been U.S. President) which may be unbroken in our experience, but that doesn't make those recurrences Laws of Nature.  Hence, when we seek to explain things, we ought to demand more than just the occurrence of regularities.

This seems to me to be elementary common sense, and I don't think the mathematization of physics (which merely describes these regularities, in increasing generality and detail) should change this conclusion.  But even if you accept the Regularity View, you still can't do Science at all unless you try to figure out how to describe these regularities with the most fundamental and deep laws possible.  On any reasonable view of causation, we can ask whether this process of explaining things finally terminates; and that will be the topic of the next section.

Next: Chains, Parsimony, and Magic

Posted in Metaphysics, Theological Method | 1 Comment

## Fundamental Reality I: Prologue, or Why Even Bother?

Looks like I've got to tell you now what I think about the Cosmological Argument.  I believe that Cosmological Arguments can give us a good reason to believe in some type of fundamental entity which causes the universe to exist.  In Theism that fundamental entity is taken to be God.  However, I think that the Cosmological Argument by itself, apart from other considerations, does not necessarily imply either Theism or Supernaturalism.  That is because there are also candidates within Naturalism for what that entity might be.  But there are related considerations, having to do with consciousness and ethics, which in my view tip the scales towards Theism, and I will try to also explain what these are.

Before I begin, let me tell you right away that this isn't my preferred approach for doing Apologetics.  I generally prefer a more empirical approach based on examining historical records for things like, oh, people being raised from the dead.  That's not just because that type of data can potentially get you to Christianity instead of just Theism.  It's also because, as a scientist, I've been trained to prefer the data to purely theoretical reasoning. Also, as someone who has studied the history of Philosophy, I'm well aware of just how far astray one can be led by so-called “armchair reasoning”, where you try to figure out how it makes sense for the universe to work, based only on broad aspects of reality.

There's way too many examples of philosophers (I'm looking at you, Kant) who say that things logically follow necessarily from premises, when in fact they don't.  They're sneaking in extra assumptions on the side: relying on intuitions and then calling it Reason.  It's not irrational to have intuitions—without them reasoning would never get off the ground—but not everyone necessarily shares those intuitions.  That's just how it is in Philosophy.  Any strictly deductive arguments for the existence of God necessarily rest on premises that not everyone is going to accept.

So I'm not going to even try to make deductive claims for most of what I'm going to say, but instead I'll try to tell you why I find Theism plausible, from an armchair reasoning point of view.  There are plenty of places where you'll be able to dissent from me.  I will argue that Theism makes better sense out of the world than any rival view, but not that all other views are inconsistent or absurd.

The English idealist F.H. Bradley said that “Metaphysics is the finding of bad reasons for what we believe upon instinct; but to find these reasons is no less an instinct.”  Well, I'm going to indulge that instinct here. I'm well aware that what I say isn't going to convince everyone.

I've been told that the perfect philosophical argument would be one where if the hearer understood the argument but failed to accept the conclusion, they would just die.  The struggle to accept the incoherence would just be too much, and their brain would shut down.  Well, there aren't any arguments like that, but I think Metaphysics is still worth doing anyway.

In fact, we must do Metaphysics.  Even if you decide to focus on empirical evidence such as miracle claims, you still have to decide how much empirical evidence you actually need to accept a conclusion that may seem weird to you. But just how weird is God's existence? Bayes' Theorem says that the assignment of prior probabilities is a necessary step in evaluating any claim.

So that means, when deciding whether something exists or not, we always need to have some set of plausibility heuristics in our mind which say how likely that thing is to be.  In cases where we are talking about the fundamental nature of existence, that means we've got to do Metaphysics.  Even if there are no strictly deductive arguments (from indisputable premises), there are still going to be plausibility arguments pointing in various directions.  It's irrational to put too much faith in plausibility arguments, but it's also irrational to be completely insensible to them.  We must assess the plausibility of propositions in order to evaluate them properly.

If at any point you think I am handling things badly and going beyond my evidence, I ask only to be judged by fair standards.  It's easy enough to just take a negative point of view, and criticize unwarranted assumptions in other people's arguments.  But suppose that someone asked you to stand up and defend your own metaphysical beliefs (say, materialism) with arguments capable of persuading others.  Not just something offhand like “This makes sense to me, and I've never seen any good reason to believe otherwise”, but some robust intellectual argument for certain types of existence or nonexistence claims. You'll quickly find that it's a hard thing to do.  Yet some particular specific set of metaphysical statements must in fact be true, even if it is hard to see which ones.

So if you disagree, please do not just say, “There's a hole in your reasoning at line 278, therefore you are being illogical and religion is irrational.”  Instead tell me what metaphysical view you find more plausible and why.

From this perspective, I find it interesting that it is possible to argue for the existence of God as well as we can.  There are no compelling armchair arguments for the existence of quarks, jaguars, and so on, yet these exist and are observationally measurable.  Only in the case of the most fundamental being, God, can we make any kind of purely philosophical argument for his existence.  And that is precisely because he is so fundamental, that he is part of the background for everything else that we can or do experience.

I hasten to repeat that this type of considerations I'm about to present are not the primary reasons why I believe in God.  God has shown himself through explicit divine revelations, recorded in the Bible and elsewhere.  So it is not necessary to approach him through purely philosophical means. And there are many important things about God which we cannot hope to learn without revelation.  Nevertheless, there are some people who have argued themselves into Theism for reasons similar to those I am going to describe.  I also think it gives some helpful background motivations for Christian theology, even though it is not the primary source of it.

But I don't think Cosmological Argument type reasoning should be exclusively thought of as an argument for Theism, as though it had no other applicability except as a religious tool.  I think there are several different types of Cosmological considerations, and that anyone trying to think through Metaphysics seriously, will have to do some type of reasoning not completely unlike what I am going to say.  Indeed, quite a bit of what I am going to say should be acceptable even to atheists, and I would continue to accept several of the arguments even if I ceased to be religious.

None of what follows is intended to be particularly original, except for the presentation, and perhaps also the modesty with which I wish to assert the following claims as plausibility arguments, rather than any kind of strict deductions.  Broadly speaking, the types of arguments being considered have been around for a long time (longer than Christianity has been around), although I'm going to present them in the form I find most plausible even at the cost of a bit of originality.

One might worry that such arguments are a post hoc attempt to justify, through specious reasoning, conclusions which really came from certain religious texts.   But historically speaking, this is not at all what happened.  The arguments were developed primarily by Greek philosophers such as Plato, Aristotle, and the Stoics.  These arguments tended to support a monotheistic view of the world, which was actually in conflict with the polytheistic view of their surrounding culture.  (Other Greek philosophers developed something more akin to Naturalism, which was of course also in conflict with popular Greek religion.)  It is therefore quite interesting that the Greek arguments supported something much closer to the Hebrew conception of divinity, which the Hebrews had received by Revelation rather than Reason.  Western culture as we know it is really the synthesis of the Greek mind with the Jewish heart, without which there is no theo-logy.

But that combination is also not the origin of Christianity.  Rather, it is the cultural milieu in which Christianity started.  The compatibility of these two sets of ideas was just starting to be appreciated, when something far stranger than either of them came into the world to save it.

Next: Causes and Explanations.

(Update: edited the sentence about the perfect philosophical argument.)

Posted in Metaphysics, Theological Method | 13 Comments

## Construct your own Cosmological Argument

First read this piece by St. Feser:
So you think you understand the Cosmological Argument?

Now take the following argument scheme, making suitable choices as needed:

1. (Major Premise) Every [thing/event] with property X needs a [cause/explanation/reason] outside of itself to [cause/explain/be the reason of it]
.
2. (Minor Premise) There is at least one [thing/event] with property X.
.
3. (Inductive Principle) You have a choice...
A.  argue that an infinite regress of [causes/explanations/reasons] for the X's is unreasonable, OR
B. argue that such an infinite causal chain would itself have property X, OR
C.  argue that the entire set of X's taken together (which might, depending on X, include the entire physical universe we know and love) has property X.
.
4. (Conclusion) Tracing back the [causes/explanations/reasons] back to their ultimate origin, we find that there is [one/at least one] thing which does not have property X, which, taken [singly/together], [causes/explains/gives the reason for] all the things which do have property X.
.
5. (Atheist Baiting) Add the famous words: "And this all men call God".  Works best if ~X is a traditional divine attribute, or even better if you can collect several such ~X's and can argue that they all refer to one and the same Exalted Being!

For example, in the debate, St. Craig's kalam argument used "comes into existence" as X, and then used a lumping strategy (3C) to talk about the universe as a whole and ask whether it had a cause.  This form of the Cosmological Argument ended up being strongly dependent on what the Science of the Big Bang actually shows, but most forms don't really depend that strongly on Science.

Other traditional X's include "changing with time", "contingent" (something that might or might not exist), "composite", and some other possibilities mentioned in the link above.   The idea is that there are some features of objects which make us seek out causes for them, for example if an object is composed of several disparate objects, we naturally want to know what brought them together.  Depending on what you pick for X, the Cosmological Argument may be more or less plausible.

You will also want to consider what type of causal concept you want to include in your argument.  A key question is how we know there is such a thing as causation?  If it is primarily for empirical reasons, then presumably we know about it through some type of inductive argument from experience, in which case we could wonder how applicable it will be in unusual situations.  On the other hand, if it is primarily motivated by reason, through analyzing what types of explanations would make sense of the universe, it may be less dependent on observation.  Or perhaps the truth is somewhere in the middle.

Another thing to figure out is what types of entities are connected by cause-effect relationships.  Does a cause have to determine the effect with certainty, or is it sufficient if it in some way produces it?  For example, if we want to argue that all contingent things were caused by something which is necessary, this is a contradiction in terms unless a necessary thing can produce contingent things, i.e. if causes don't have to be deterministic.  A related question: when we talk about causes, are we primarily talking about beings causing things to happen (a.k.a. agent-causation), or states of affairs causing things to happen (a.k.a. event-causation), or both?

Regarding step (5), note that excessively glib atheist baiting obscures the fact that nearly everyone should accept some type of Cosmological Argument, even if they don't necessarily take it to a Theistic conclusion!  If you are going to talk about causes/explanations/reasons AT ALL (and I really don't see how to avoid this) then you really need an account concerning the domain to which the concept is applicable.  And then it is an interesting fact, that either you must accept infinite or circular chains of [causation/explanation/reasons] or you end up going outside the domain to something else which is different.

This type of reasoning should be interesting, even if you are an atheist.  The trouble is, if people only encounter Cosmological Arguments in the context of Theism, then Atheists adopt an argumentative approach where they just feel the need to poke a few holes in the arguments and then retreat to where they were before.  This doesn't do justice to the fact that there are numerous X's for which the argument's premises are at least plausible, even for people who don't start out committed to any particular religious doctrine.

For example, Carroll himself gives an account of the scope of causation when he says:

Why should we expect that there are causes or explanations or a reason why in the universe in which we live? It’s because the physical world inside of which we’re embedded has two important features. There are unbreakable patterns, laws of physics—things don’t just happen, they obey the laws—and there is an arrow of time stretching from the past to the future. The entropy was lower in the past and increases towards the future. Therefore, when you find some event or state of affairs B today, we can very often trace it back in time to one or a couple of possible predecessor events that we therefore call the cause of that, which leads to B according to the laws of physics. But crucially, both of these features of the universe that allow us to speak the language of causes and effects are completely absent when we talk about the universe as a whole. We don’t think that our universe is part of a bigger ensemble that obeys laws. Even if it’s part of the multiverse, the multiverse is not part of a bigger ensemble that obeys laws. Therefore, nothing gives us the right to demand some kind of external cause.

There seem to be some question-begging moves in this paragraph, but leave that aside.  My point is that Carroll gives a positive account of when he thinks makes the notion of [cause/explanations] make sense.  He endorses a version of (1) whereby the concept of causation makes sense if (a) there are laws of nature, understood as unbreakable regularities, and (b) there is a thermodynamical arrow of time whereby entropy increases, making a distinction between the past and the future.  (Since causes normally precede effects, but the laws of physics don't strongly distinguish between the two directions of time except through thermodynamics, it seems clear that the arrow of time has to play some role in distinguishing causes from effects in physics.)

He also allows (2) that this concept—though not fundamental in his opinion—nevertheless makes sense for certain particular cases.

Then for (3) he allows us to lump together the universe taken as a whole, but claims that this whole does not meet his criterion (1).  He thus comes to an object—the whole universe, apparently—for which, in his view, it wouldn't make sense for it to have a cause (4), although he does not identify it with God (5).  Thus his reasoning has an implicit atheist version of the Cosmological Argument behind it.  Though one can certainly question whether the metaphysical assumptions behind this claim are right.

But it's just possible you came here hoping, not to construct your own Cosmological Argument, nor to deconstruct Carroll's, but instead to find out what I think about it, something which you may think I have postponed saying for quite long enough.  Well, it just so happens that I've written a 16,000 word essay on the Cosmological Argument and related topics, and will be posting it in installments over the course of the next few weeks.

## Explanation needed

I've been discussing Sean Carroll's claim 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.

In my last post, Models and Metaphysics, I tried to argue that there are substantive philosophical questions about causality which Carroll is dismissing unduly as pre-scientific.

But in this post, I thought I'd give a concrete example of a situation where we would not declare victory and go home, even with a complete and consistent model of the universe.  While at some point fairly soon I'd like to give my own take on the Cosmological Argument, my counterexample in this post isn't going to depend on any seriously heavy-duty metaphysics.  Instead I'd like to try to focus on something fairly quantitative and precise, something  "rational almost to the verge of rationalism", in short, an argument that even someone steeped in scientism could love.

Let's imagine that in the future, we come up with a seeming Theory of Everything™ which explains almost everything about the world.  Every single physical phenomenon which has ever been observed has now been explained by a simple equation.  Let us stipulate that the initial state of the universe is itself determined by these equations, leading to a cosmology consistent with what we observe.  If you like, we can also pretend that no supernatural events have ever been verified, and that (after the Great Riot of 2438 C.E., when all the metaphysicians and philosophers were confined to the tops of their Ivory Towers and forbidden to communicate with the ordinary citizens outside) we have all agreed not to inquire to closely into the question of why certain physical states of the brain correspond to conscious experiences.  It is indeed a great triumph for the Scientific Method.

There's one catch.  The remaining (non-meta)physicists tell us that there is one universal constant of nature in the theory, designated by a capital alpha $A$, whose numerical value needs to be fixed before any predictions can be made.  This constant is dimensionless, meaning that all the units cancel out, so that it isn't measured in meters per gram, or joule-seconds, or anything like that, but is just a real number.  For example, it might be the ratio of two things with the same units.  Because this constant $A$ is dimensionless, it's numerical value is independent of the choice of units used to measure this parameter.

(In real life there are currently about 26 or so dimensionless constants in the Standard Model plus General Relativity—not counting inflation or dark matter—the most famous of these constants being the fine structure constant, which is approximately $1/137.036\ldots$.)

Since the equations work equally well no matter what the value of $A$ is, we have no choice but to do experiments to see what its value is.  Let us suppose (rather unrealistically) that the scientists have measured this parameter to 800 decimal places, and that—lo and behold!—the answer is exactly

No one knows why, that's just the way things are.

(Note: this situation is different from the usual Fine-Tuning Argument, because I am not supposing that there is any reason why life requires the constant to take on this precise value.)

I submit to you that, notwithstanding the fact that this TOE™ gives a complete description of everything in the universe, we ought not to declare victory and go home.  Because it is plain as day that this number $2\pi / 7$ requires some sort of explanation which has not yet been given.  In other words, we don't just demand that our models completely explain the data.  We also demand that they be complete in the sense of providing explanations for anything which seems to require an explanation.

True, $2\pi / 7$ is not an extremely complicated number; in most computer languages one can write a fairly short computer program that spits out this number.  But I didn't become a physicist in order to compress my sense-data into as few bits of information as possible; WinZip does a better job of data compression than I ever could.  I became a physicist in order to understand how and why the world works the way that it does.

So I wouldn't be completely satisfied with this TOE™ as it stands, even though it would be a big improvement on our current best theories of physics.  Instead I would start asking naïve questions like:

"Why is there a $2\pi$ in the formula for $A$, given that we all know that $2\pi$ is the ratio between a circle's circumference and its radius?  Where do circles come into it?"

and

"What's so special about $7$?  Is this just a random whole number that was pulled out of a hat?!?  Why is the denominator even an integer at all?  What is $7$—a sufficiently awkward prime that it seldom comes up in physics formulae—doing in the most fundamental equation of the universe?"

Now I don't know whether all of these mutterings about sevenths of circles would get me shoved up a Tower or not.  But I am convinced that this question would be meaningful, that it must have an answer, and that any red-blooded human being with basic curiosity about the world should hope to find the answer.

Or, to speak in Bayesian terms, nearly all of my prior probability would be placed on there is an explanation for this odd fact that I don't know yet, and nearly none on this is just an inexplicable basic fact about the universe which has no explanation at all.  I'm not sure how to convey this intuition to you if you don't already share it.  But it seems to me that basic inexplicable facts about the universe shouldn't fall into patterns which seem to indicate the existence of a deeper layer of reality, unless there actually is a deeper layer of reality behind the shadows we see on the cave wall...

"What's that? Yes officer, I was just headed for that Tower over there right now!  Please don't let me trouble you any further.  No, I just stepped out for a moment.  Yes.  Look I'm heading back right now.  See?"

Of course, just because I would think that there must be an explanation, doesn't mean that we would ever find out what that explanation is.  Life can be a bummer that way:

All this I have proved by wisdom.
I said, “I will be wise”;
But it was far from me.
As for that which is far off and exceedingly deep,
Who can find it out?
(Ecclesiastes 7:23-24)

I would be potentially open to any explanation involving either "natural" or "supernatural" elements, so long as it in fact explained the parameter.

Of course, if the explanation involved more ad hoc elements than the thing being explained, then that would raise questions about whether it was really the best or simplest explanation.  And even if I thought of a good explanation, I might wonder if there were some other equally good explanation. Or conversely, I might not be able to think of any good explanation at all.  So at the end of the day I might have to be an agnostic about what type of explanation should be considered.

But that wouldn't change the fact that I'd think there'd be one.

## Models and Metaphysics

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 $x$ and the other in position $y$ is minus the amplitude for the first to be at $y$ and the other at $x$.  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!