What are Laws of Nature?

[structureoftruth (Matthew Dickau)]

@vjtorley

I have to say I have a problem here. Either a thing exists or it doesn’t. Virtual existence is a cop-out.

Thomists would probably reply here with something about the analogy of being. But you make excellent points regarding continuity in the substantial change from living body to corpse, and regarding the composition of water molecules.

I think Alexander Pruss makes the suggestion that an Aristotelian can regard fundamental particles composing other substances as still existing and still retaining their own forms, but understanding the particles as transforming from being substances in their own right to mere parts of the composed substance. (And maybe that’s just what “virtual existence” is supposed to mean.) But it does seem to suggest an implausible dependence of the behavior of the microscopic particles on the macroscopic substance of which they are a part.

(Though, given that I am persuaded by the arguments for dualism of human nature, I’m already committed to at least something like what I just called an implausible dependence.)

[dga471 (Daniel)]

@vjtorley

Either a thing exists or it doesn’t. Virtual existence is a cop-out.

Feser would say that for something to to exist virtually in a substance means to be in it potentially, in fact in a stronger sense than in a purely potential sense (as all substances exist potentially in prime matter, but hydrogen and atom exist potentially in a stronger sense in water than in prime matter) (Feser, Aristotle’s Revenge, p. 336). It seems to me that Thomists think there are many different substances, all of which have very different and complex potentialities due to the things existing virtually in them.

Secondly, even if you think this is a cop-out, it appears to me that there’s nothing really wrong with saying that hydrogen and oxygen don’t exist in water. It would be similar to an instrumentalist point of view, where scientific notions are merely useful mental constructs to characterize experimental predictions and results. We model a molecule as a collection of atoms linked by chemical bonds because that is the best way to predict certain properties. An instrumentalist point of view is not uncommon among philosophers of science in general.

@vjtorley

Water is composed of hydrogen and oxygen atoms , which retain the micro-level properties of hydrogen, even if they lack the macro-level ones which we commonly associate with this substance…Whether hydrogen atoms will react with oxygen depends on what (if anything) they’re bonded to. While free-floating hydrogen radicals are highly reactive, hydrogen atoms which are already bonded to oxygen in a water molecule are obviously less so. But that doesn’t make them something other than hydrogen.

I think this is less clear-cut than you think. When hydrogen and oxygen atoms form into a water molecule, they generate a new set of energy levels that are different from hydrogen or oxygen. This is why the emission spectra of water is different than that of hydrogen or oxygen. You cannot experimentally “access” the hydrogen or the oxygen molecule “directly” while they are still in the form of water. (Although maybe some chemists could correct me.)

@vjtorley

But in A-T metaphysics, “system” is not the name of any kind of natural entity, such as a horse or a palm tree. There is no substantial form of a system, as such. Hence it lacks a nature. Do you see now why I am perplexed?

You can replace the word “system” with “substance”. Most of the things we mention here are not (in the Thomist parlance) artifacts, but natural substances. Electrons, atoms, molecules are all natural substances (or existing virtually in them) which can have symmetry properties that cause them to be relevant to Noether’s theorem.

@vjtorley

But it strikes me that quantum fields could be said to perdure through time: they’re always there, even if particles are continually popping into and out of existence. Thoughts?

I can’t find the relevant passage in Scholastic Metaphysics, can you quote a little bit of the context and surrounding sentences?

My first reflex is to point out that the terminology is not quite right. In quantum field theory (QFT), particles are oscillations of quantum fields. As the fields oscillate, they “change” (although you should ask a real Thomist about whether I’m using the word change correctly, in an A-T sense).

Interestingly, I have seen Thomists point to neutrino oscillation as an example of how even fundamental particles can change.

@vjtorley, I think these are all good questions. Keep them coming - I’m going to be attending a 4-day seminar on Thomism where there will be a lot of Thomists around to ask questions. The topic this year happens to do with flux and change!

[vjtorley (Vincent Torley)]

Hi @dga471,

Thank you for your reply. Re QFT: I agree with your points that it is fields (rather than particles) which are fundamental, and that when fields oscillate, they change. My point is that this change is (in A-T terminology) an accidental change, and not a substantial change. The fields are always there: nothing destroys them.

Here’s the relevant passage in Scholastic Metaphysics , page 183:

… The atomist position and its modern variants basically amount to the idea that a kind of secondary matter underlies all change - secondary matter having just those properties that atoms (or some other sort of fundamental particle) are supposed to have.

Quick comment: Feser, when he wrote this book, was evidently unaware that according to modern physics, it is fields, rather than particles, which are fundamental. But the basic point remains the same. Substitute “fields” for “fundamental particles,” and the idea is that it is these fields which underlie all change. As far as I can tell, there is no need to go any further, as these fields are never destroyed: only particles are. Moreover, the fields are well-defined mathematically, and have measurable physical properties. They seem to be the ultimate stuff.

Aquinas wants to dig deeper: evidently he thinks that there is some kind of property-less “I-know-not-what” (i.e. prime matter) which underlies even fields. But to quote Laplace out of context, “I have no need for that hypothesis.” And it seems wildly implausible to claim (as Thomas does) that whenever substance A changes into substance B, it is prime matter alone that survives the change, when the fields appear to be intact.

To continue quoting Feser (p. 183):

But we saw above that this sort of view [i.e. the atomist view that a kind of secondary matter underlies all change - VJT] won’t work. Again, there is no empirical evidence for particles that are incapable of substantial change - even quarks can undergo such change.

Comment: Feser is right if he’s talking about particles, but his point does not apply to quantum fields.

More importantly, there could be no such particles. If a fundamental particle is of such-and-such a form (with its unique causal powers etc.), specifically, rather than some form, then we have limitation and something less than pure actuality. The form is limited to this particle, and that one, and that one, and does not exist where there are no such particles (e.g. in the ancient atomists’ void); the particles are also limited by being actually of this sort rather than that.

Quick comment: whereas particles are countable and individualizable, quantum fields (as I understand them) pervade space and time; hence we cannot speak of individual fields, as we can with particles. We can, however, speak of different kinds of fields, e.g. fields corresponding to different kinds of forces. Each field, like each angel in Aquinas’ angelogy, is one of a kind. And just as angels are (according to Aquinas) all form and no matter, I see no reason why a field should not be likewise.

But what is limited in its actuality is limited by potency. Hence such fundamental particles [or in our updated example, fields - VJT] would be compounds of act and potency; and being fundamental, there would be no yet more basic substances out of which they could be composed. But for a thing to be fundamental in that sense while being composed of act and potency is just for it to be composed of substantial form and prime matter.

Lots of non sequiturs here.

First, the claim that whatever is limited in its actuality is limited by potency appears to be mistaken. To cite a geometric example: a triangle is a totally actual geometrical entity (being a pure form), but it is nonetheless limited, in having three and only three sides. Here, the source of the limitation is the triangle’s actuality. Hence the claim that if quantum fields are limited, they must be compounds of act and potency appears doubtful. And if it be objected that triangles are purely abstract entities, then what about angels, which are (unlike triangles) capable of genuine agency? Thomists claim that an angel is pure form; yet it is limited, by that very form. So why couldn’t a quantum field be limited by its form, without the need to postulate any admixture of act and potency?

Second, Feser’s claim that to be composed of act and potency is to be composed of substantial form and prime matter is a question-begging one. “Potency” does not have to mean “pure passive potency” (i.e. prime matter). There are also active potencies.

Third, a Thomist could of course reply to the examples I have given above by pointing out that an angel, even if it is pure form, is still a composite of essence and existence, and that the same must hold for quantum fields, as God alone is Pure Existence. Granting that point for the sake of argument, a composite of essence and existence is still not the same as a composite of prime matter and substantial form.

To sum up: it seems to me that we do not need to postulate prime matter, as something underlying all change. The arguments put forward for its reality are question-begging and unconvincing.

I’d be very interested to hear what the Thomists at the 4-day seminar on Thomism have to say on these matters. Please keep me posted. Cheers.

[structureoftruth (Matthew Dickau)]

@vjtorley

The claim that whatever is limited in its actuality is limited by potency appears to be mistaken.

As I understand Feser (or, Aquinas via Feser) it’s almost more of a fundamental postulate that actuality is only limited by potency; this is part of the meaning of act and potency for Aquinas. Though this is one of the aspects of Thomistic metaphysics that I find somewhat confusing and unmotivated.

@vjtorley

So why couldn’t a quantum field be limited by its form, without the need to postulate any admixture of act and potency?

Feser says that angels are composed of act and potency, even though they are pure form - there’s a correspondence between form and actuality, and matter and potency, but they aren’t exactly overlapping. According to his system, only God is pure actuality. (Whatever that means, I’m not entirely sure. I don’t see how this conception of God can fail to lead to modal collapse, but that’s another issue.)

Edit: never mind; I see that Aquinas actually does refer to angels as being “pure act”, though only God is absolutely pure act, while angels are only relatively pure act. Again, whatever that means.

[jongarvey]

@structureoftruth

This might be unfair of me since I haven’t read Heisenberg directly (though I have now gotten a hold of Physics and Philosophy and will take a look!), but I feel at least part of the reason Heisenberg takes this position is to support the Copenhagen philosophy of quantum mechanics which had already taken shape.

Matthew, it seems to me rather, from his writing, that Heisenberg was philosophically literate, and appreciated the inadequacy of 19th century reductionism to explain the new phenomena being described and mathematized. Retrieving Aristotelian concepts gave him a language with which to understand better what was going on, and resulted in him and Bohr devising the Copenhagen interpretation.

Now, since all interpretations of quantum theory are philosophical, rather than scientific, it would seem to me that (a) what philosophical tools one has available in ones armoury will affect the preference for interpretation one has and (b) the wider ones grasp of philsophy, the more likely one is to arrive at an interpretation that accounts for all the phenomena.

[Ashwin_s]

@vjtorley

Quick comment: Feser, when he wrote this book, was evidently unaware that according to modern physics, it is fields, rather than particles, which are fundamental. But the basic point remains the same. Substitute “fields” for “fundamental particles,” and the idea is that it is these fields which underlie all change. As far as I can tell, there is no need to go any further, as these fields are never destroyed: only particles are.

@dga471,
Do these “fields” really exist, or is it just a word to describe a concept which explains how fundamental particles pop up?

[structureoftruth (Matthew Dickau)]

@Ashwin_s

Do these “fields” really exist, or is it just a word to describe a concept which explains how fundamental particles pop up?

Depends on how one interprets quantum phenomenon. It is possible under a Bohmian interpretation to say that they really exist.

[structureoftruth (Matthew Dickau)]

@jongarvey

Retrieving Aristotelian concepts gave him a language with which to understand better what was going on, and resulted in him and Bohr devising the Copenhagen interpretation.

Perhaps. I’m a little over halfway through his Physics and Philosophy now and I have yet to come across anything that looks to me like arguments for the Copenhagen interpretation, rather that assertions that it is only way for quantum phenomena to be understood.

You mentioned that he gives aristotelian arguments for privileging the macroscopic world over the microscopic - does he do that in this book or elsewhere in his writings?

[jongarvey]

Read on, McDuff…

[dga471 (Daniel)]

@vjtorley

Aquinas wants to dig deeper: evidently he thinks that there is some kind of property-less “I-know-not-what” (i.e. prime matter) which underlies even fields. But to quote Laplace out of context, “I have no need for that hypothesis.”

Well, as I commented here, I’m not so sure whether particle physics tells us about what the fields actually are, rather than just how they behave:

@dga471

But that’s surely not to be taken literally, right? It’s not that there are literal ball-on-a-spring objects which collectively constitute a field whose oscillations are particles, even if the behavior of these “things” are similar to that of a ball-on-a-spring. What is a field really, then? It surely must be something physical and tangible, not mere Platonic mathematical objects, because particles (and atoms and molecules) are physical and tangible. I don’t think we think about this much in QFT - at some point we just write down an equation (analogous to the plots of oscillations that you drew) and proceed with calculations.

Now if you are a strict empiricist or verificationist, you might hold that the behavior of the fields that is verifiable by experiment is all that could ever matter in a meaningful sense. But as I understand it, the point of thinking about a philosophy of nature (like Thomism) is that it seeks to give a deeper metaphysical understanding of what’s actually happening, instead of the “shut up and calculate” approach.

@vjtorley

And it seems wildly implausible to claim (as Thomas does) that whenever substance A changes into substance B, it is prime matter alone that survives the change, when the fields appear to be intact.

I don’t think this is clear-cut either. When neutrino oscillation happens (as parameterized by the PMNS matrix), do the fields underlying them go through a substantial or accidental change? It’s unclear, because the concept of substantial vs. accidental change hasn’t been defined precisely enough in the context of its application to modern particle physics (AFAIK).

Based on my limited interactions with Thomists, they would probably say that a change is substantial (as opposed to accidental) if there is some sort of discontinuity in the change (like a phase transition). But we don’t have clear-cut analogues to phase transitions in particle physics (again, AFAIK). There definitely is a scholarly gap here that needs to be filled.