My attention has been drawn to a blog post at The skeptic zone, which in turn discusses a post on strange notions, entitled "Why modern physics does not refute Thomist philosophy." The skeptic zone post instead argued that modern physics does refute Thomist philosophy. This claim obviously not only challenges the original post, but also my own work. Even though I am currently on a brief break from blogging, I couldn't resist formulating a reply. This response started out as intending to be a comment on his blog, but it grew a bit too long, so I have reformatted it to be a bit more self-contained and have posted it here instead.
First of all, I ought to briefly discuss the strange notions post by Dr Bonnette. It can be divided into two parts.
The first part presents the idea that the fundamental principles behind modern science, such as the rationality of the universe and epistemological realism, are also the basis behind Aristotelian philosophy. This is not surprising, since modern science arose out of the medieval university (many trace the history of science back to the likes of Galileo, De Soto and Copernicus -- but who inspired them? Where did they get their ideas from, and draw their basic assumptions? The answer is the high medieval mathematicians and physicists such as Bradwardine, Orseme, and the early experimentalists, who were very much part of the classical tradition).
The point is that there are many modern philosophical traditions which deny these basic assumptions. In this sense, science and Thomism stand on the same side against the postmodern deniers of reality.
The second part of the article addresses certain aspects of modern physics which are stated to contradict Aristotelian premises. For this, it draws heavily on a paper by Castellano. That paper is well worth a read, and makes some good points, although, as is often the case, it has the weakness of focusing on quantum mechanics rather than field theory. But its main point stands well: it is not the physics itself which contradicts Aristotelian philosophy, but the philosophy which is often taught alongside the physics as though it were necessarily linked to it. There is a difference between the mechanical philosophy and Newtonian mechanics. The mechanical philosophy is not the only philosophical interpretation of Newton's physics, even though historically it was the one that inspired Newton as he developed that physics. Similarly, even though the Copenhagen interpretation was held by the founders of quantum mechanics does not mean that it is the only philosophy consistent with quantum physics (or even that it remained consistent with quantum physics as it continued to develop). The link to philosophy from physics is one of induction. And the problem with induction is that even if you find a philosophy that works, you can never be sure that it is the only philosophy that works. So if one particular philosophy of physics disagrees with fundamental principles, then there is a good argument that you should lay it aside until you can find an alternative which does agree with those principles.
My main criticism of the original strange notions post is not that it goes too far, but that it doesn't go far enough. Certainly science (the raw data) and Thomism (a philosophy, i.e. interpretation of raw data) stand side by side against many modern views. But there are other philosophies which stand on that side of the argument. Answering a few points is not enough; one needs to show point by point that the premises behind Thomism are consistent with contemporary physics, and that the premises behind contemporary physics are consistent with Thomism. A superficial discussion is not going to be enough to convince a sceptic. Particularly when that sceptic has a wrong idea of what the premises behind Thomism are (as so many do).
Which brings me nicely to the post I actually want to respond to. I'll do so in my usual way, by quoting various points in the argument which I find particularly troubling, and explaining why I find them troubling.
The overall purpose of the article is (as I understand it) to argue that
- Science uses a different and incompatible class of fundamental concepts compared to Thomism.
- Some basic concepts of Thomism, such as causality, have been proved false by science.
- Thomists tend to use examples and illustrations that are either now obsolete or which don't actually support their case.
- Thomists argue that science cannot disprove their philosophy because the two are disconnected.
My goal here is look at the arguments put forward to support these propositions, and show where those arguments are lacking. For example, the author notes that Thomism uses the concept of act and potency to explain movement.
In science, it is explained in terms of the paradigm of mass, force, and energy, which is no less a metaphysical concept.
- The concept of Force, as it was used in classical physics, is now obsolete. OK, we still use phrases such as "The weak force" and the "The strong force", but the theories underlying that are very different from $F = -GMm/r^2$ and so on. The concept of force as originally constructed no longer plays a role in the most fundamental physics.
- Mass is reduced to interaction between particles, either interaction with the scalar Boson of the standard model, or self-interaction (including internal binding energy). Aquinas/Aristotle has no difficulty with the ideas of particles interacting with each other.
- Energy in modern physics is primarily a label given to distinguish different (meta-)stable states. The label is chosen in such a way that it is conserved through interactions. Aquinas would have been quite happy with the idea of there being different possible states of matter, and us labelling them to distinguish them. The concept of energy is thus a more precise application of Aquinas/Aristotle's metaphysics, rather than a contradiction to it.
But the main problem with this is that act/potency on one hand and force/mass/energy on the other relate to two different concepts in physics. Even in classical mechanics, before we get to things like force, we presuppose a theory of act and potency. A background against which we can measure movement or change. In Newtonian mechanics, this background is provided by what we now describe as two conjugate Hilbert spaces, location and momentum. Additionally, we have a measure that allows us to distinguish the states before and after the change, time, which is also parameterised numerically, and which has its own conjugate variable, Energy. Every specified location and momentum represents one possible state or potentia. At a given time, one of these states is actual. At the next moment in time, another is actual. Of course, we decide which of the states is going to be actual by making use of the concepts of force and so on, but this sits on top of the metaphysical states. The scientists behind classical mechanics might have hidden this background, but it is there.
In quantum physics, of course, the background is different. It is recognised that there are different ways of parametrising space and time, and it is convenient to merge these into a single Hilbert Space, space/time. Similarly energy/momentum form another conjugate Hilbert space. To parametrise the possible states we need one of these (and we can only use one), with space/time being more natural and energy/momentum somewhat easier. We also need a few other parameters such as spin. But once again, this provides us with the background needed to allow any sort of motion, before we get into the mechanics of the motion. We then assume that background when we get to the mathematics, either Dirac's equation in quantum mechanics or the transfer operator in field theory. These equations once again do no more than give us the amplitude that a specified final state will be actual given an initial state. The methods of physics depend on the concept of act and potency (even if not always expressed in these terms by physicists), but build on this to give more precise predictions.
So act and potency refer to the Hilbert space on which we measure change, and "force, mass and energy" allow us to compute which changes can occur. To directly compare one against the other is therefore inadvisable. Modern physicists and mathematicians use different names to describe the background of states rather than "act" and "potency", but the underlying concept is the same. We shouldn't think that just because the words aren't used that the concept isn't there.
The advantage of Aristotle's concept of act and potency is that it is sufficiently general that it can cope with different physical systems. It does not care whether the process of actualisation is driven by classical forces or the exchange of virtual particles. Instead, it tells us that there must be a background against which these processes takes place.
So when the sceptic summarises by writing,
But Thomists disagree with that, because they see metaphysics as being separate and distinct from physical reality,
he is mistaken. Rather, Thomists see metaphysics as underlying physical reality. Metaphysics gives a general framework for what possible universes could be, physics fills in the specific details for this particular universe. Metaphysics tells us that physical theory must assume some sort of background of different states; physics starts by expressing this in a mathematical way.
Dr Bonnette used the principle of non-contradiction to cast doubt on some concepts that often dominate discussions of quantum mechanics, and in particular focusing on wave-particle duality. His point (I think) was that the discussions seem to treat objects as though they are ontologically both waves and particles. However, they are only ever observed as one of these at a time. So rather than adopting a philosophy that embraces a contradiction, we should focus on the observations that at any given time it is either one or the other. Now I don't personally think that Dr Bonnette's example here is particularly good. Quantum objects are neither classical waves nor classical particles, but belong in a different category altogether. But the idea that philosophers shouldn't adopt interpretations of quantum physics which violate fundamental principles such as the principle of non-contradiction when there are alternatives which are consistent with it is a good one.
Our sceptical friend notes that this statement doesn't really advance Dr Bonnette's cause. Here he is in some senses right, and in other senses wrong. He is right in that this particular example doesn't lead us to Thomism, since there are alternative ways of thinking about it. He is wrong in the sense that Dr Bonnette was trying to make a wider claim: that interpretations of quantum physics ought to respect the underlying principles of sound philosophy unless this proves impossible. We should leave aside those interpretations which contradict the philosophical considerations in favour of those which are consistent with it. If the eigenstates that underlie quantum physics can be equated with Aristotelian potentia, then if we adopt an interpretation that contradicts the theory of act and potency, we have a serious problem.
So when the sceptic concludes this section by saying,
So rather than clinging to concepts of physical substance that are contradicted by observation, we need a metaphysical concept of substance that agrees with what we observe,
he isn't helping his own cause. Because Thomists claim firstly that they provide a concept of substance in agreement with observation, and secondly that other approaches to metaphysics fall short, some obviously and dramatically and others more subtly. The concept of substance that agrees with what we observe is one that identifies that particles or systems of particles can exist in different states, and that changes occur when we transition between one state and another. This is just Aristotle's theory of act and potency, albeit expanded in a way that Aristotle himself could never have imagined.
So what of the other bedrock of Aristotle's philosophy, namely the theory of causes. To the Aristotelian, this ultimately is an expression of the rationality of the universe, i.e. that it is possible to understand physical objects. Since science is built on the assumption that we can understand at least in part (otherwise science would be a worthless endeavour), this is not a premise that can reasonably be challenged. But many interpreters of quantum physics do deny this premise, by stating that the physics is inconsistent with all forms of causality. The sceptic is no different:
At the quantum level, things happen on a stochastic basis, and there is no notion of causality in quantum physics. As it happens, this is a major point of disagreement between science and Thomism, despite Bonnette's denial.
I certainly agree that quantum physics is inconsistent with many of the expressions of causality which have been proposed over the past few hundred years. It is also true that quantum physicists don't tend to use the word "cause" in their research papers. But it is a step too far to say that it is therefore inconsistent with all forms of causality. Or that the concept of causality is not invoked even though the word itself is not used.
Let us take the example of a radioactive beta decay, one of the classic cases used to claim that quantum physics is incompatible with notions of causality. A down quark spontaneously decays into a W- Boson and an up-quark. The W- Boson spontaneously decays into an electron and anti-neutrino (there are, of course, also more complicated decay paths leading to the same outcome, but this is the simplest and dominant one). There is no event kicking off this decay. It just happens. So it is claimed that the notion of causality (which is assumed to state that every event needs a cause) is undermined. Except, Aristotelian causality (certainly as it is used in the arguments for God) links substances rather than events. So the W- Boson is the efficient cause of the electron and anti-neutrino. The down quark is the efficient cause of the W- Boson and up quark. Among the final causes of the down quark (its possible decay channels) are the up-quark, electron and anti-neutrino. The conservation of energy ensures that there will always be a cause for every effect. Rather than undermining Aristotelian causality, quantum physics leaves it as the only version of causality still standing.
And, of course, we need some version of causality if we are to suppose that the universe is rational. Dr Bonnette's point stands: our interpretation of quantum physics needs to be consistent with both scientific and metaphysical principles. Which suggests that, if causality is philosophically necessary and only the version of causality found in Aristotelian philosophy is consistent with the science, then we should give at the very least strong consideration to the Aristotelian interpretation of quantum physics.
So the sceptic continues by picking up on a point by Dr Bonnette that science has little direct interaction with many of the the metaphysical concepts. Now, I would certainly state that either Dr Bonnette phrased his statement badly here, or I have misunderstood him, or that I disagree with him. There is a much stronger affinity between the Aristotelian concepts he lists and physical principles. But Dr Bonnette is right to say that equally, materialist denials of form and finality are not scientific. They are built from a philosophy of science, one that doesn't work that well.
But Dr Bonnette certainly seems to be creating a gulf between philosophy and physics which I think is unwise. In part, because he leaves himself open to the sceptic's condemnation:
He has no choice but to make this separation, because these metaphysical principles are in direct contradiction to modern science.
I would fully disagree that the concepts are in direct contradiction to modern science. As I have argued elsewhere, I believe that contemporary physics and Thomism have a very strong affinity with each other. Not quite perfect, but the modifications needed to make the medieval philosophy consistent with the physics are considerably smaller than those needed to be made to the philosophies that inspired atheism consistent. I would also contend that anyone who disputes this either doesn't understand the philosophy (which is the camp the sceptic falls into), or doesn't understand the science (which is the camp that many popularisers of Thomist philosophy unfortunately fall into, even though they are ultimately correct), or hasn't thought it through properly.
The idea of act and potency, for example, is intended to provide a framework in which it is possible to have both change in state and constancy in substance. One can think of the potentia as the different eigenstates of the Hamiltonian; the energy states of the quantum Harmonic oscillator, for example. This is a bit of an oversimplification, but it is close enough to be useful. Let us say we have an electron in a Harmonic potential. A photon hits it, and it is excited to a higher energy level. It then emits a photon, and decays into a lower energy level. In each case, the electron moves from one state to another. Aristotle would say that at any given moment, it is actually in one state, and potentially in the others. A change occurs, and one of the potentials is actualised. His system models the physics quite well so far.
Of course, there is (as Dr. Bonnette's article discussed) one additional feature in the physics not in Aristotle's metaphysics, namely superposition. Here we can either take the approach that Dr. Bonnette seemed to adopt and say that the electron is always actually in one state, but the superposition of the wave-function reflects our uncertainty in knowledge concerning the state. Alternatively, we might try to extend Aristotle's framework, and equate the different possible superpositions as additional potentia. But this is a far smaller modification to Aristotle than would be required to make most non-Aristotelian systems of philosophy, which deny act and potency and thus the whole underlying framework of quantum states, adequately describe the physical system.
Efficient and final causality I have already discussed; the various decay channels of particle physics are examples of final causes. Of course, physics goes further than Aristotle by giving us cross-sections for each of the decays. But Aristotle's system provides us with general principles; physics the specifics, and this is another example of that.
Where an Aristotelian would turn to Form as the abstract principle underlying the properties and possible states of material substances, the physicist would turn to the effective Hamiltonian of more complex materials such as solids and molecules. Again, the philosophical concept of form is a bit broader than that of the effective Hamiltonian, but the physical construction sits within the metaphysical principle. The eigenstates of the Hamiltonian play the same role in the physics as the form does in the philosophy. We are able to establish the accidental and essential properties of a substance from both the Hamiltonian and the form. And so on.
So, having dug himself into a hole, the sceptic keeps digging.
Act and potency do not explain how things move.
Nobody claimed that they by themselves explain the how. That is not what they are there for. They provide a general framework which allows us to think about the concept of motion (change). The concept of things move is prior to question of how things move. But once you accept that there is motion, then it is clear that there is a state from which things move from and a state which they move to. And that is what act and potency do for us. Now we need a physical theory on top of that to address the next question, which is which states could they move to in practice. Even modern physics does not explain how things move (depending on which of the various possible meanings you give to the word how) -- how a down quark undergoes beta decay. It only describes that it can and sometimes does, and what sort of decays and interactions are possible, and the probability amplitudes that they will occur. To go beyond that, we need an interpretation of that theory which might (if we are lucky) give an answer to that how. But if that interpretation conflicts with the notion of act and potency, while at the same time the science that the interpretation is trying to explain depends on it, then we immediately have a self-contradiction.
To support his assertion, the sceptic discusses the idea of essentialism and forms, and how they don't stand up to scrutiny. The example he cites is,
As modern philosophers note, how many grains of sand can you remove from a dune before it is no longer a dune?
A dune is not a single substance, but a collection of substances. Thus this is not a good example to use to deny that there are such things as essences of substances. A more pertinent example would be "How many carbon atoms can you remove from an ethanol molecule before it is no longer an ethanol molecule?" And here, the answer is clearly none. As soon as we remove one atom, it ceases to be that substance and becomes something else. Although I could and perhaps should go into far more detail, it is clear that molecules and the other compound objects of physics and chemistry are not inconsistent with essentialism and forms.
So, as we near the conclusion, we come to this.
Thomists give primacy to metaphysics, and science is not only subordinate to that, but it can have nothing to say about what is real and what isn't in metaphysics. Science, on the other hand, makes observations about reality, and any scientific view of metaphysics would hold that the two must remain in agreement with each other to form a coherent whole. In other words, metaphysics must evolve along with scientific understanding of reality. But to the Thomist, metaphysics is static and unchanging.
We need to distinguish between two different things. Our knowledge of scientific and metaphysical theory, on the one hand, and The true scientific and metaphysical theory on the other. The first of these obviously changes as we gain in knowledge. The latter is static and unchanging. Our hope is that our knowledge gradually approaches the true theory.
It is also a bit unfair to say that Thomists regard our knowledge of metaphysics as static and unchanging. After all, Aquinas himself was a development of Aristotle, and modern Analytical Thomists develop beyond where Aquinas went. All of them, of course, adopt some common principles, but there is much diversity in how they explain those principles. I personally agree that the Thomist community need to engage more with quantum physics, and adapt their philosophy as required. But that isn't to say that there is no such engagement going on. Dr. Bonnette's post, and the article he relies on, is one example. Nor is it to say that any adaptation will be major. It might just be a matter of choosing between different schools or approaches to Thomism. One would have to do the detailed work to find out.
The main point is that Thomists regard some form of Thomism as the true metaphysics. That goes almost without saying; if they didn't think that they wouldn't be Thomists. They might be unsure about precisely which form once we get down into the finer details. The reason for that belief is their understanding that Thomism follows from a few basic, fundamental principles: the existence of change, the rationality of nature, the principle of non-contradiction and so on. Whatever our changing scientific knowledge becomes, it must continue to hold to such principles (after all, if our knowledge of science is changing, then change must be a reality). And it is this idea that gives the Thomist their confidence.
Of course, the frustrating thing is that there seems to be a lack of awareness of contemporary physics, and the continual falling back to Aristotelian examples, in most popular presentations of the philosophy. There is some excuse: they are popular, so can't assume that the readers know how to compute a Feynman diagram, or even what a path integral is. But it is still frustrating, when contemporary physics offers such fertile ground for the Thomist to draw from. But equally, Thomist philosophers get frustrated at the frequent ignorance and misrepresentations of their philosophy in the skeptical and philosophy of science literature. Such works don't present good evidence for disbelieving in Thomism, only evidence that the people who wrote them don't understand Thomism very well, or have never thought about how it can be reconciled with contemporary physics, or interacted with those who do address these issues.
In the Thomistic view, on the other hand, metaphysics deals with a completely separate realm of existence.
No. Precisely the same realm of existence. As the sceptic rightly said, in Aristotle's system, metaphysics and physics were in harmony. That is the goal. There was a divergence when classical mechanics emerged (albeit considerably less so than most people of the time realised, since they had a very inaccurate knowledge of Aristotle's philosophy); now they are coming together again. The problem for Aristotle was that he brought in other concepts, such as the four element theory and that force is proportional to velocity and other such nonsense, which don't depend on his metaphysics and which are clearly wrong. What needs to be done is to combine Aristotle's system with genuine physical principles. Rejecting that which is wrong in Aristotle, but being careful not to throw out that which he got right alongside it. Some have been working on this, and I have taken a few tentative steps myself.
Now, contemporary philosophers of science are, of course, trying to come up with a metaphysics that is in harmony with quantum physics. As far as I am aware, they haven't been making much progress. Perhaps they would make more progress if they tried adopting some aspects of Thomist thought.
Whenever a Thomist tells you that there is no conflict between Thomism and science, what he means is that they are dealing with different things.
No, what they mean is that the premises behind Thomism are a subset of the premises behind modern science. Indeed, the most important premises. The point of difference is not in the science, but in the interpretation of the science. For example, during the scientific revolution the mechanical philosophy was adopted. In the context of classical physics, that's a plausible enough idea. The problem is that it is thoroughly inconsistent with quantum physics. So an alternative is needed. The Copenhagen interpretation? De-Broglie-Bohm? Everett? They all have their problems. The Thomist would argue that the primary reason that they fail is that they are built on inconsistent premises. The Aristotelian assumptions that underlie science, such as the objective rationality of the universe and the existence of change (which ultimately imply formal and final causality), but also other premises which deny form and finality. What we need is an interpretation of quantum physics built on Aristotelian principles. Such as this one.
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