Sunday, September 23, 2012

Act and Potency in Physics

A while back, BeingItself commented on this post by quoting Ed Feser:

The Aristotelian theory of act and potency is the classic example of such a piece of middle ground knowledge. It is grounded in the basic empirical datum, the fact of change. But it is not a description of this or that particular change or this or that particular kind of change but rather of all change as such. Hence while empirically grounded it is not subject to falsification by theorizing in physics, chemistry, etc., because the phenomena dealt with in all such theorizing, since they all involve change, implicitly presuppose the theory of act and potency.

BI then asked,

Do you think that is correct? Do physicists presuppose this metaphysics?

This is a great question, and I thank Mr. Mosis for bumping it back to my attention. I really have no idea what the answer is. Although I've read a fair smattering of philosophy of science and philosophy of physics, I can't recall ever coming across a discussion of the metaphysical assumptions underlying physical theories - not even in discussions of the foundations of quantum mechanics, where some sort of metaphysical groundwork would really be useful. As Feser points out in the linked article,

[F]or most of its history the philosophy of science was essentially concerned with questions about the methodology of science, the logical structure of scientific theories, the meaning of scientific assertions, and the like...
Feser says there has recently been a return to metaphysical issues, and links to some relevant books. Not having read these, though, I'm going to plunge in and try to give you an idea of how physicists go about their business.

(I suspect one reason philosophers avoid these issues is the fear of having the rug pulled out from under them by physicists. Anything any philosopher wrote on time, for instance, probably sounded remarkably silly after Einstein revolutionized our concepts of space and time.)

Let's start with classical mechanics. (Quantum mechanics is a whole different ball of wax, and its interpretation remains very controversial.) The basic entities we work with are:
  • Space - the three-dimensional continuum that is the stage on which everything takes place.
  • Time - is what keeps everything from happening all at once.
  • Point particles -  the actors on the stage. They are idealized objects that have a location in space at a given time. 
  • Fields - extended entities that exist at every point in space. They are produced by (certain types of) particles and they exert influence on  (certain types of) particles.
(Of course, after special relativity we had to stop talking about space and time and start talking about a unified spacetime as the stage on which everything takes place. And after general relativity, we had to get used to curved spacetime. But the basic picture remains the same.)

We then proceed to write equations for how the particles and fields change in time. (Newton's laws for motion of particles, and Maxwell's equations for the changes of fields, for example.) Here the possibility of change is implicit in the fact of a time coordinate: there is no reason to assume that what obtains at one time also obtains at some other time. So, my first reaction to BI's question was to think that of course there's nothing like act and potency in physics. We just talk about change as a fundamental fact about the universe.

When I read Feser and his Aquinas quotes on actuality and potentiality, it seemed as though they were saying that the actual is real, and the potential was sort of real, too, as if it were sitting around somewhere waiting to be pushed into actuality. This seemed like a quaint, medieval idea that had no relevance to modern physics. But the more I thought about it, the more I began to realize that we actually have an approach in physics that very closely resembles this. That is the idea of a state space.

The state space is the collection of all possible states of the system. For a point particle, the state consists of its position and its velocity, or state of motion. For a single particle moving in one dimension, the state space consists of the two-dimensional plane (x,v). The particle's motion is then envisioned as a path in this plane. So, we do indeed think of the possible states of the particle as sort of existing "out there", and the (actual) particle as moving from one of these states to another.

So is Feser right - does modern physics presuppose the notions of actuality and possibility? I'm not convinced. For one thing, the whole notion of state space wasn't developed until the 19th century (by Hamilton, I think). And for another, the state space picture doesn't remove the need for a time coordinate. As I said before, the existence of time already allows for the possibility of change. And we can't even talk about the state space without the notion of velocity, which itself requires time. So it seems to me that the concepts of time and change are metaphysically prior to those of potentiality and state space.


  1. The French physicist, philosopher and historian of physics Pierre Duhem would agree with you, Dr. Oerter, that physical theories do not depend upon a choice of metaphysics. Duhem masterfully shows this, with many historical examples, in his classic philosophy of science work The Aim and Structure of Physical Theory (excerpt). He also treats this in "Physics & Metaphysics," "Physics of a Believer," and this excerpt from To Save the Phenomena.

  2. Thanks, that's very helpful. From the second link:

    "That Physics Logically Precedes Metaphysics

    ...We cannot come to know the essence of things except insofar as that essence is the cause and foundation for phenomena and the laws that govern them. The study of phenomena and laws must therefore precede the investigation of causes."

    That's what I was groping for in my attempts to answer Feser.

    However, I think there's a distinction that must be made between the metaphysical essences that Duhem is talking about and the metaphysical principles that Feser is talking about. Don't we need concepts of cause and change before we can even begin a physical investigation?

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  4. Your question appears to be a question on the method and division of the sciences. Boethius, following Aristotle, proposed that the "Speculative sciences may be divided into three kinds: physics, mathematics, and metaphysics.":

    1. Physics deals with that which is in motion and is material.
    2. Mathematics deals with that which is material and is not in motion [(∵ mathematical objects do not more or change)]
    3. Metaphysics deals with that which is not in motion nor is material.
    (cf. §II of his De Trinitate)

    In this context, Thomas Aquinas writes in his Division and methods of the sciences, a commentary on Boethius's De Trinitate questions V and VI:

    q. 5 a. 1 objection 9: That science on which others depend must be prior to them. Now all the other sciences depend on divine science [(metaphysics)] because it is its business to prove their principles. Therefore Boethius should have placed divine science before the others.

    reply to objection 9: Although divine science is by nature the first of all the sciences, with respect to us the other sciences come before it. For as Avicenna says, the position of […] [metaphysics] is that it be learned after the natural sciences, which explain many things used by metaphysics, such as generation, corruption, motion, and the like [(e.g., actuality, potentiality, matter, form, etc.)]. It should also be learned after mathematics […]. […] Nor is there necessarily a vicious circle because metaphysics presupposes conclusions proved in the other sciences while it itself proves their principles. For the principles that another science (such as natural philosophy) takes from first philosophy [(i.e., from metaphysics)] do not prove the points which the first philosopher [(metaphysician)] takes from the natural philosopher, but they are proved through other self-evident principles. Similarly the first philosopher does not prove the principles he gives the natural philosopher by principles he receives from him, but by other self-evident principles. So there is no vicious circle in their definitions. Moreover, the sensible effects on which the demonstrations of natural science are based are more evident to us in the beginning. But when we come to know the first causes through them, these causes will reveal to us the reason for the effects, from which they were proved by a demonstration
    quia [(i.e., a demonstration a posteriori, a demonstration from effects to causes)]. In this way natural science also contributes something to divine science, and nevertheless it is divine science that explains its principles. That is why Boethius places divine science last, because it is the last relative to us.

    See The Way toward Wisdom by Benedict Ashley (read the first chapter, this excerpt, John Deely's review).

    His main theses are that:
    (1) the natural sciences are epistemologically prior to metaphysics
    (2) metaphysics, which he proposes we term "metascience," is the true philosophy of science.

  5. We ought to support almost all imaginative thought processes ... because ... well, because we do not know to where these thought processes will lead.

    I almost always think there is a 'because clause' ... but I may just be structured that way. Go back to the earliest Greek or Egyptian, Persian, Indian or Asian who first wondered "why?" and try to figure out whether she had an a priori metaphysical precept before she first ground grain, or did grinding grain lead, a posteriori, to her first metaphysical concept.

    Both formulations seem to have possibilities, and are, in my newcomer's opinion, worth pursuing.

    It has been awhile since I followed a blog, but, Dr. Oerter, you spark interesting insights. I have left a second comment under your blog entry "The Moral Instinct" (5/7/11) should you or your readers be interested.

    You are most likely familiar with Journey by Starlight. If not, I commend it to you:

    and its author, Ian Flitcroft:

  6. Thanks for your comments, c. It's a very busy semester for me, and I don't know how much blogging I'll get to do this fall. I'm glad there's at least one person taking the opportunity to look at past posts....

    Having steeped myself in quantum mechanics for my entire adult life, I really think that QM is showing us the limits of human knowledge, the point at which it is no longer sensible to ask, "Why"? (Of course, I might be wrong - possibly I'm brainwashed by other physicists or something.) That's not a reason to stop asking. But I think it's fair to bring up the possibility that there ARE limits to how far we can push the "why" question.

  7. You did not start this particular blog because you felt the 'why' question has reached its logical end (with all due respect ... and thank you ... for responding to my comment).

    Let me quote a bit from P Simon's song "You Can Call Me Al":

    'A man walks down the street
    He says, "Why am I soft in the middle now?
    Why am I soft in the middle?
    The rest of my life is so hard
    Don't want to end up a cartoon
    In a cartoon graveyard"
    Bonedigger, bonedigger
    You know I don't find this stuff
    Amusing anymore'
    (Simon, 1986)

    Outside of our ordinary duties, like quantum mechanics and divorce court, the 'why' question is I suspect all there is. Yes, it's fair to bring up the possibility that there ARE limits to how far we can push the 'Why' question (I think you said that), but we aren't there yet (I think I said that).

    I just read a bunch of the comments under your various Feser entries. At times interesting; at other times painful. Soft in the middle shall we say? But in a strange way necessary. Whether an electron spontaneously (without an efficient or a final cause) alters its energy state is worth pondering over ... at length. It's also just worth gazing at, in our mind's eye. Like the night sky over the Mojave Desert.

    It is not at all clear who the muddle-headed thinkers are in this world. Maybe all of us. Maybe we ARE all just destined to end up as cartoons in a cartoon graveyard. If so, I wonder why.

  8. I believe Feser's position on this amounts to "Physics presupposes change, change can only be explained in the Thomistic-Aristotelian framework, therefore physics presupposes the TA-metaphysics". I think that is fallacious, for two reasons: (a) Aristotelian metaphysics never really succeeded in understanding change, and (b) there are other metaphysical frameworks out there that are at least as good, if not better, at understanding change. Specifically, I think Parmenidean/Eternalism and Herakletian/Becoming as two coherent approaches, although I'm attracted to the former.

    Coming to the physics side - while you restrict your analysis to classical physics, I'd note that the problem becomes more interesting in QM. On the one hand, QM literally takes as its first axiom the "potential" sates of a physical system, using them to construct the Hilbert space. On the other hand, it is far from clear what this entails metaphysically, if anything.

    I think it comes down to the interpretation of QM. If one thinks of measurement-events as constituting reality and virtual-events and unitary evolution as mathematical constructions only, then one is led to claim potentiality is indeed presumed and is used to derive what will happen in practice. If one, on the other hand, adopts a relative or many-world interpretation one is led to believe that there is no potentiality as-such; merely actuality to various degrees/densities. Thus, potentiality plays absolutely no part at the metaphysical level. I belong, hesitantly, to the second camp. And I have other reasons to doubt the metaphysics of potentiality, too - chiefly my support for Eternalism, noted above.

    I agree physics does not necessitate any given metaphysics. But I do believe particular physical theories tend to draw the more philosophically-minded of their practitioners towards particular metaphysics.

    Yair Rezek

  9. Hi, Yair,

    I was going to say something similar about QM. However, as the metaphysical status of the QM states is still extremely unclear, there doesn't seem to be any clear message that can be drawn from that example.

    Except, perhaps, for the point that Alan made above: while metaphysical concepts may be logically prior, knowledge of those metaphysical principles can only come after careful study of the phenomena.

    QM seems to be stuck at the intermediate point: we understand and can describe the phenomena, but we are unsure what metaphysical conclusions to draw from them.

  10. The last 150 years or so of philosophy should perhaps have produced some convergence on a handful of philosophic positions, but this has not occurred. The last 150 years or so of science, on the other hand, has produced such a convergence of scientific positions, despite the growing overall diversity of the scientific enterprise itself. Or is that an illusion?

    But don't both of these exploits, science and philosophy, employ the same tool, namely the human intellect? If so, then why the widely different results?

    I agree with Yair's description of Feser's logical error, namely that the proposition, "Change can only be explained in the Thomistic-Aristotelian framework", is at least either false, unproven, or the framework is in need of modification. I'm just adventurous enough to think if Aristotle were alive today, and were to examine what is presently known or accepted about QM, he would willingly modify his theory about the nature of change, and about the nature of the intellect. Sadly, I do not think that would be true about St. Thomas Aquinas, who strikes me as being committed to, well, different commitments, but I hope I would be wrong about that (him).

    I see that Dr. Oerter has added a comment, so I shall add a point, in keeping with his comments. I believe theorists, whether they be scientists or philosophers, should follow (essentially) the same basic regimen: formulate, then test and re-examine their theories; then modify and again re-examine ad infinitum, or at least until "settled" so to speak. Recalling my anecdotal projections about the prehistoric woman grinding grain, I again suggest we enter a chicken or the egg conundrum as to whether metaphysical precepts are prior or posterior to investigation and modification.

    This is why, as you suggested in a previous post, it is such a risky business to become over-committed to a particular metaphysical stance. New information may just sweep that ground out from under you (or words to that affect) ... which is exactly why I think Aristotle would modify his "apprehended" principles, while Aquinas unfortunately might not ... which is NOT to say Aquinas and Aristotle would necessarily have to abandon their positions (due to QM), but only that they would have to offer a successful explanation (of it) within the constraints of their positions, or adjust (again, not necessarily abandon) their positions to accommodate it (QM).

    So I ask again: why haven't philosophic positions converged?

  11. Prof Oerter,

    At the risk of poisoning the well. BI is largely considered a troll over at Feser's blog who unlike you militantly refuses to do any of the reading on Aristotle, Aquinas, or even read any of Feser's books. From the beginning for him we have to first prove to him studying any philosophy and or classic philosophy all this is somehow worth his while.

    I wouldn't look to him for any intelligent insight. However least you accuse me of say all Atheists critics of AT Philosophy are simply ignorant I must strongly recommend any criticism you come across written by dguller.
    He is an Atheist who has done the relavent reading and has gone beyond it. He has credibility. BI or djindra or Stone Tops are merely amusements. Like any Young Earth Creationist you have ever encountered who tried to give a "scientific" argument for their colorful views.

    I'll catch you later.

  12. BTW briefly

    >Do you think that is correct? Do physicists presuppose this metaphysics?

    It's kind of a stupid question since physicists don't have to presuppose any metaphysics to do physics anymore then I have to presuppose any metaphysics program my DVD player.

    But Feser is clearly talking about the philosophy of science as it is related to the philosophy of nature and of course Positivist Philosophy and Empiricist philosophy are mentioned in the comments being the favorite philosophies of Scientists who happen to be Atheists which are often in practice held as Givens and largely unexamined.

    1. :additionally

      Obviously every Physicist who worked with LHC believed if they recreated to the best of their ability the early conditions of the Big Bang some potency to produce a Higgs particle will be actualized. Or something else might have been actualized or nothing might have been actualized that they would find significant.

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  14. Anything any philosopher wrote on time, for instance, probably sounded remarkably silly after Einstein revolutionized our concepts of space and time.

    Time is metaphysically the measure of change so are you claiming Einstein proved there was no change with relativity?

    At best he showed as one moved toward the speed of light in a particular framework "the measurements of change" seems to slow down as observed by another framework or whatever & that the measurement of a particular change was not constant threw out the universe.

    Yes your problem is confusing the anachronistic physics cited by philosophers way back when and their modeling of it with the philosophy and metaphysics itself.

    Robert are you ever going to not confuse physics with metaphysics? Philosophy of Science with the methodology of science?

    Still I have faith in you.