Tuesday, November 4, 2014

Particles

I used to worry for Aristotelian reasons about the particles making up my body. The worry went something like this: Elementary particles are fundamental entities. Fundamental entities are substances. But no substance has substances as parts. The last is, of course, a very controversial bit. However there are good Aristotelian reasons for it.

But I shouldn't have worried much. Elementary particles are not all that likely to be fundamental entities. Quantum mechanics, after all, allows all sorts of superpositions between different particles. But substances either simply exist or simply don't. In the superposition case, they don't simply exist. So they simply don't. But I would expect that the superposition case is more the rule than the exception (if only with small coefficients for all but one one state). I guess we could think that when the wavefunction is in a pure state with respect to the existence of a particle, the particle then pops into existence, and when the state becomes mixed, it pops right out. But notice that the physics behaves in much the same way when we have a pure state and when we have a mixed state that is to a very high approximation pure. So whatever explanatory role the particles play when they pop into existence can be played, it seems, by the wavefunction itself when the particles aren't around. This suggests that the wavefunction is the more explanatorily fundamental entity, not the particles. Of course, the above relies on denying the Bohmian interpretation of quantum mechanics. But it's enough, nonetheless, to establish that elementary particles aren't all that likely to be fundamental entities. And hence they aren't all that likely to be substances.

Of course, it may be that the things that are fundamental physical entities will turn out to be just as problematic for the Aristotelian as the particles were...

15 comments:

elliottroland said...

Re: your original worry, did you not find much comfort in the Scholastic/Thomistic/Aristotelian (not sure when it was introduced) distinction between the actual existence of a substance versus the virtual existence of the parts in the substance?

Heath White said...

What about (what I think is) the Thomistic view:

I am a substance
My soul is a substance
My soul is a part (or, not the whole) of me.

elliottroland said...

Heath, that's not the Thomistic view, but I think something like it was held by some Scholastics (Scotus maybe?)

On the Thomistic view of humans, neither the soul (form) nor the body (matter) are substances. Only the first and third claims are affirmed.

Alexander R Pruss said...

Heath:
1. If Napoleon's soul was a substance distinct from Napoleon, then Napoleon isn't now a soul.
2. Napoleon is now a soul.
3. So, etc.

Elliott:
I think of "virtual existence" as more a name for the problem than a solution to it.
The puzzle is that when food is incorporated into my body, its particles cease to exist as substances, and hence cease to exist (being a substance is surely modally essential), and then when the relevant bit of my body is shed, they come back into substantial existence. And all along there is no sharp empirical change.

Heath White said...

ST I.75.2 seems pretty clearly to say that the soul is a substance ("it is also a substance, that is, something subsistent"), and I.75.4 says pretty clearly that man is composed of soul and body and not a soul only ("man is not a soul only, but something composed of soul and body").

Alexander R Pruss said...

Heath: I.75 is a discussion of a quote from Augustine. I read it as saying this: "Augustine calls the soul a substance. What he means by it is that it's something subsistent."

Aquinas is not endorsing the claim that the soul is a substance in Aquinas' sense of "substance", but only that it is subsistent. I don't know what exactly this means.

But, yes, he does think we are composed of soul and body. Whether this sort of composition is a part-whole composition, though, is not clear to me.

Heath White said...

Alex,

I.75.4 obj 1 and reply will, I think, give you what you want. The soul, like the hand, is a substance in the sense that it exists on its own, without inhering in anything else, but not in the sense that it is “complete in a specific nature” which I think means something like, possesses a form or is a member of a species.

This tells me that in effect you have two different criteria for substances. There is a “bottom up” criterion, according to which fundamental entities are substances, because they exist on their own in a maximal sense. Nothing else composes them. On this criterion, metaphysical fundamentals will be substances and anything they compose will not be, or only in a derivative sense. Then there is a “top down” criterion, according to which it is species-membership or form-possession that makes something a substance. On this criterion, a substance will typically be composed of parts which are not substances.

Which notion do you want?

Alexander R Pruss said...

Unlike Aquinas, I want the two to coincide. :-)

Heath White said...

Why? (Serious question.)

Alexander R Pruss said...

That's a really good question.

I guess it's bound up with my conviction that non-fundamental things like holes and chairs don't really exist. But this bears more thought than that. Thank you.

grodrigues said...

@Alexander Pruss:

"The puzzle is that when food is incorporated into my body, its particles cease to exist as substances, and hence cease to exist (being a substance is surely modally essential), and then when the relevant bit of my body is shed, they come back into substantial existence. And all along there is no sharp empirical change."

Let us try something simpler: a free electron is a substance. An electron bound to a proton makes up an hydrogen atom, another substance. The behaviors of a free electron and a bound electron are radically different, so there does seem to be a sharp empirical change. And if there is such a sharp empirical change, then there is no puzzle, or at least this *particular* puzzle you raise (assuming I am understanding it correctly). And it seems to me that the same can be said about bits of food.

Dagmara Lizlovs said...

Alex:

Here's what the particles in your body are doing:

https://www.youtube.com/watch?v=FzcTgrxMzZk

So stop worrying about the particles making up your body, they've got everything under control. :-)

elliottroland said...

grodrigues and Alex:

I also wonder if, in the food case, it's fair to say that "its particles cease to exist as substances." Surely, on the Thomistic view, at the point of being part of the food the particles are not substances, but rather only exist virtually in the food. As such, they go from being informed by the food's form, to being informed by the soul, to being informed by the form of the cell being shed. Of course, the underlying matter doesn't change much (and in that sense there is no sharp empirical change), but there is significant formal change.


Heath and Alex:

I suspect Aquinas has something like this in mind: something is subsistent if it does not inhere in (or depend ontologically on) something else. In a broad sense we can call anything subsistent a substance, but in a stricter sense we restrict the word to those subsistent things that are mostly complete given their nature. I don't have an account of "completeness" here, but intuitively a human with all limbs is more complete than a human missing an arm, than a human missing all their limbs, than a human missing their body. (Perhaps something is more complete if it is more capable of it's characteristic operations?)

Admittedly, I'm not totally clear on how this differs (if it differs at all) from Heath's suggestion.

grodrigues said...

@elliotroland:

"Surely, on the Thomistic view, at the point of being part of the food the particles are not substances, but rather only exist virtually in the food. As such, they go from being informed by the food's form, to being informed by the soul, to being informed by the form of the cell being shed. Of course, the underlying matter doesn't change much (and in that sense there is no sharp empirical change), but there is significant formal change."

That is also my understanding of Aristotelian-Thomism (with which, insofar as I can understand it, agree with). The substance, say of an electron, ceases to exist qua substance, which just means that the matter is no longer informed by the form of the electron. But on the other hand, the electron has a semi-recognizable existence as a part of the containing substance, of the hydrogen atom say. Its form, powers, etc. are subsumed and harnessed by the containing substantial form.

Oderberg discusses this in "Real Essentialism". In 4.2 "Substantial form", pg. 70, he says:

"Another way of putting the point is to say that substantial form permeates the entirety of the substance that possesses it, not merely horizontally in its parts – there is as much dogginess in Fido’s nose and tail as in Fido as a whole – but also vertically, down to the very chemical elements that constitute Fido’s living flesh. To use the traditional Scholastic terminology, the chemical elements exist virtually in Fido, not as compounds in their own right but as elements fully harnessed to the operations of the organism in which they exist, via the compounds they constitute and the further compounds the latter constitute, through levels of compounds – DNA, the proteins coded for by that DNA, the organelles that make up the cells, the organs made up of the cells, and so on.

Supposing there to be elementary particles (a proposal I deny), and supposing these to be quarks, it does not follow from the fact that every material substance is made of quarks that every substantial form is the form of a bundle of quarks, because in the existing substance the quarks have no substantial identity of their own, their behaviour having been fully yoked to the function and operations of the substance in which they exist. The substantial forms of the particles exist virtually in the substances they constitute. In other words, the quark is ontologically dependent on the whole of which it is a part, but its causal powers persist, albeit in a way radically limited by the whole. The substantial form is what determines the permissible and impermissible behaviour of the quarks in the body, which is why some chemical reactions typically occur, others rarely, and others not at all. Nor is there any particular bundle of quarks of which the form could even be the form, given the familiar fact that every body loses and gains quarks all the time. Again, it is the form that determines the when, how, and how much of the loss and gain may occur, with external circumstances merely operating upon predetermined possibilities."

I am not enough of a Scholar to assert that this is a faithful exegesis of Aquinas, but it is certainly within the spirit.

Alexander R Pruss said...

I wouldn't think there is form in food. I'd think it's just a bunch of particles, if there fundamentally are particles. I know that some Thomists want molecules and atoms to be substances when they exist in isolation, but this seems excessive, since all the interactions of atoms presumably reduce handily to fundamental quantum stuff, even if the math of the interactions is hard to do.

Here I'm assuming the food is dead. That's not always true. Some fresh vegetables and fruit are alive. And it's a good point that there there will be no particles having independent existence.