Interview with David Gunn about his recently published book on the nature of matter and the meaning of modern physical theory.

Release date: Jan 25, 2013

David has higher degrees in physics and philosophy, and has previously been published in the philosophy of physics. His research interests include the interpretation of physical theory, metaphysics and the history of philosophy. He is currently writing his second book.

davidjgunn.com

 

Pneumatology of Matter

I: Your book is called Pneumatology of Matter. It’s a difficult title. The word ‘matter’ is familiar enough, but I’ve not come across ‘pneumatology’ before.

DG: Pneumatology is the science, doctrine, or theory of spirit or spiritual beings.

I: I’m afraid that doesn’t really help me. If anything, it makes your title harder to grasp. How did you come up with it anyway?

DG: I stole it from Hegel.

I: The German philosopher? Did he use that title?

DG: Maybe not, but he used one like it: Phenomenology of Spirit.

I: There’s a superficial resemblance alright, and perhaps more than that. Tell me, does your book contain some kind of inversion of the Hegelian philosophy?

DG: What appealed to me about Hegel’s title was its paradoxical character. You know, spirit is usually held to be invisible, whereas phenomenology is the study of phenomena, including the visible.

I: I see. And your title contains a similar paradox, because matter and spirit are often contrasted with each other, with matter being the visible and spirit the invisible. So now, let me guess: if Hegel’s book is about the appearance of spirit, yours is about the reality or spiritual basis of matter.

DG: Let’s not jump to conclusions. Instead of trying to take in the whole book at once, why don’t we begin with something smaller? A distinction.

I: Which one?

DG: The distinction between mechanical and pneumatical action. Whereas mechanical action is other-determining action, pneumatical action…

I: Pardon me, but you’ll have to speak more plainly.

DG: About?

I: Other-determining action.

DG: By ‘other-determining action’ I mean action which determines the state of something other than that which is acting. Pneumatical action, by contrast, is self-determining action: it is action which determines the state of that very thing which is acting. This is not a new distinction by any means. It goes back to Plato, at least.

I: Okay, so it goes back to Plato. And I think I get it, despite your rather abstract way of putting things. But something still bothers me. You said mechanical action is other-determining action, right? I don’t think you’ve said enough here.

DG: Oh no?

I: No. For shouldn’t you also have said that mechanical action involves contact or touching between that which determines and that which is determined - as occurs between the parts of a clockwork mechanism, and in machines generally?

DG: In fact, the words ‘mechanical’ and ‘mechanism’ are used in a number of different ways, depending on the context. So we need to be careful. Philosophers, for example, typically use them to refer to processes that are devoid of purpose, spontaneity or intelligence. But if you were to ask a logician, a physicist or a biologist what they mean by these words, each of them would have something different and possibly more specific in mind. For the logician a mechanism is just a step-by-step procedure, or algorithm, which takes input of some kind, manipulates it according to specified rules, and spits out the result. Such logical mechanisms are completely abstract. There is no implication as to how they might be physically realized.

I: As in a computer, for example?

DG: Right. For the physicist, on the other hand, a mechanism is a material system whose constituent parts act on one another, changing or endeavoring to change each other’s states. Biologists, meanwhile, often speak of processes that are involved in the growth, maintenance and functioning of living things as ‘mechanisms’. You sometimes even hear talk of social and economic mechanisms.

I: Well, since the book we are discussing is about matter, and since physics is the science of matter, I suppose we should stick to the physicists’ definitions of ‘mechanism’ and ‘mechanical’.

DG: That sounds very reasonable. Nevertheless, I would like us to accept definitions that are a little wider than those of the physicists.

I: How come?

DG: Because I want eventually to apply the words ‘mechanical’ and ‘mechanism’ to systems that are more complex than the ones usually treated in physics: for example, to biological systems. Therefore, I would like us to proceed as we did earlier, and take ‘mechanical’ to refer to any action or process in which things are determined by other things rather than self-determined. I think you can see, from what we have already said, that this usage will include the physicists’ usage of the word ‘mechanical’ as a special case.

I: I can see that.

DG: A mechanism, accordingly, will be any system whose action or behavior is not self-determined - not original to the system as a whole, in other words - but is determined instead by its constituents, perhaps in conjunction with external factors.

I: I’m happy to accept these wider definitions of ‘mechanism’ and ‘mechanical’, but only provisionally. Because I’m still worried that mechanical action necessarily involves contact or touching.

DG: It might interest you to know that not even physicists take contact to be essential to mechanical action. For example, Einstein did not take it to be essential.

I: Oh really? And what is your evidence for Einstein’s view on this matter?

DG: In his book The Evolution of Physics Einstein considers his famous predecessor Isaac Newton to be an exponent of the mechanical philosophy of Nature; and Newton, as is well known, held that bodies can act on one another even if they are not touching.

I: Did he - Newton I mean - give any examples of such action?

DG: Certainly. The action of the moon on the sea, which causes the tides. And the action of the sun on the planets, which holds them in their orbits. In short, gravity.

I: These seem to be genuine examples alright. And there is also the action of magnets on one another, and on other metallic objects. Still, shouldn’t we be cautious and say only that these bodies do not act directly on one another through touching? For they might still act indirectly through touching. Suppose, for example, that some subtle matter existed between these bodies, via which their actions were conveyed to one another… In fact, did not Newton himself caution against unmediated action at a distance?

DG: You are well informed. And yet Newton also rejected the kind of mechanisms involving touching or contact that you just alluded to.

I: Why did he do that?

DG: He had various reasons, some empirical, others more philosophical in nature. But I’m worried that we are now moving too far away from our original subject of discussion.

I: If you could give us just one of Newton’s reasons.

DG: Take the motions of the planets about the sun. Newton explained various features of these motions in terms of an attractive force operating between the sun and planets. But you might instead try to explain them as Descartes originally did, by postulating a swirling vortex of subtle matter, which is centered on the sun and carries the planets around with it. But then you run into difficulties with the comets, which move in highly eccentric orbits. And you also find it hard to account for Kepler’s laws of planetary motion. Both of these difficulties were pointed out by Newton himself.

I: Thank you. I suppose I could consult your book if I wanted to know more about this particular subject.

DG: You could. Or you might consult directly the General Scholium at the end of Book Three of Newton’s Principia.

I: Let’s get back to discussing the difference between mechanical and pneumatical action.

DG: Gladly. Mechanical action, whether or not you take it to involve contact, is essentially other-determining action. That is, it necessarily involves one thing determining or acting upon another thing. As such, it is action from without, or external action. Philosophers would call such action ‘relational’, because it only occurs between things. Pneumatical action, on the other hand, is inner or non-relational, because it is self-determining action.

I: I’m afraid I’m not too familiar with pneumatical action.

DG: You are more familiar with it than you think. Just imagine yourself walking down the street. Is there anything behind you, pushing you on your way? Or anything in front pulling you? No, it is you yourself that is doing the moving.

I: Apparently so. But one might say exactly the same thing about an automobile - and that’s a machine, a mechanism, if anything is.

DG: ‘Auto-mobile’. That means self-moving, doesn’t it? Automobiles have human operators of course. Nevertheless, you have raised a very important objection, one which, if generalized sufficiently, would have it that all such cases of self-motion or self-determining action are at bottom nothing but cases of mechanical or other-determining action. That, indeed, is the essence of the mechanical philosophy of Nature.

I: According to that philosophy, then, human beings, too, would be mechanisms?

DG: Indeed. Their actions would not be original to them, but rather products of their material constituents’ actions, as in the case of the automobile. Unless, of course, one allowed that human beings are not wholly natural or material beings, and that the source of their actions lies in something immaterial.

I: In a soul, for example.

DG: Yes.

I: But then one is faced with the difficulty of explaining how such immaterial things could interact with material things.

DG: Quite so. And there are other difficulties besides. But in any case, that these two kinds of thing - supposing they both exist - have, or are assumed to have, completely different properties, by itself makes it very difficult to explain their interaction.

I: So what’s the alternative? Supposing that immaterial things do not exist, it seems that we are forced to accept the mechanical viewpoint as ultimate, and in doing so abandon all pretense to human autonomy or free will.

DG: It depends.

I: On what?

DG: On whether the mechanical philosophy of Nature is sound.

I: In other words, on whether all cases of pneumatical action can be reduced to cases of mechanical action.

DG: Precisely.

I: Well, then, provide me with a counter-example.

DG: Fortunately, we do not need to go far in order to find one. A counter-example exists even in Newtonian physics.

I: But I thought Newtonian physics was mechanical physics, at least according to Einstein.

DG: So it is. Yet it is not purely mechanical, because Newton had to make a concession to pneumatism in order to make mechanism work.

I: Which concession?

DG: He had to posit inertial force, which is - and I quote - ‘a power of resisting, by which every body, as much as in it lies, continues in its present state, whether it be of rest, or of moving uniformly forwards in a right line’. Newton posited this force in order to make sense of the observed fact that it is more difficult to change the states of heavier than of lighter bodies, even after friction and other retarding forces have been taken into account.

I: So that’s an example of irreducible pneumatical action, is it?

DG: Quite clearly it is. Whereas mechanical force changes, or endeavors to change, a body’s state of motion, inertial force acts to maintain it. In that sense inertial force is opposed to mechanical force, and thus different in kind from mechanical force. What is more, the strength of a body’s inertial force, which is measured by the mass or quantity of matter in the body, does not depend on the body’s relations to other bodies, as the strength of mechanical force does. This confirms that inertial force is a genuinely internal or non-relational power. As such, it differs qualitatively from an automobile’s engine, which is internal only in the familiar, spatial sense.

I: But cannot an automobile’s engine be used to maintain motion?

DG: Yes, but only by setting it in mechanical opposition to retarding forces. And unlike inertial force, an automobile’s engine can also be used to increase motion.

I: Okay, but the postulation of inertial force still seems like rather a minor concession for Newton to have made. However important it was for the development of physics, it carries us no further towards securing free will. In the first place, it does not do away with mechanical action; secondly, even if it did, one could hardly explain the tremendous complexity and variety of human actions on the basis of such a simple material power; and thirdly, the fact that we human beings can change as well as maintain our states of motion, just like automobiles, only seems to confirm that we too are mechanisms of some sort.

DG: You have made some excellent points. Let us consider them in turn.

I: Before we do, would you mind clearing something up? Earlier you defined ‘pneumatology’ as ‘the science of spirit or spiritual beings’. Now such beings are usually assumed to be immaterial, whereas you have just applied the word ‘pneumatical’ to a material power, namely, inertial force. I’m a little confused.

DG: It’s true that philosophers have in the past used words like ‘pneumatology’ and ‘pneumatical’ solely in relation to immaterial powers, because they thought that such powers alone made self-determination possible. However, I do not wish to restrict myself in this way. For me any power of self-determination, immaterial or otherwise, is a pneumatical power, and conversely. I take the opposite of ‘pneumatical’ to be ‘mechanical’ not ‘material’.

I: Alright, if that’s the way you want it.

DG: Let’s return to the three points you made previously, beginning with the first.

I: Which is?

DG: The possibility of “doing away” with mechanical action. Clearly, Newton’s philosophy of Nature does not do away with it, as you said, but there are other natural philosophies which do, in a manner of speaking anyway.

I: You have my undivided attention.

DG: Consider, for example, the natural philosophy of Aristotle, in particular his geocentric cosmology.

I: You mean his theory that the universe is spherical, with the earth at the center, and the sun, moon, planets and stars revolving about the earth?

DG: That’s right. In Aristotle’s cosmology the celestial bodies lie in a set of revolving crystalline spheres centered on the earth, with the moon occupying the innermost and the stars the outermost sphere. The important point for our discussion is that each sphere is moved by the mechanical operation on it of the next highest sphere, whereas the outermost sphere…

I: I get it. The outermost sphere, being outermost, cannot be moved by any higher sphere.

DG: Therefore, this sphere can only be self-moved - assuming, with Aristotle, that there is not anything lying outside the system of spheres that might move it. And there must also be some slippage between the spheres, otherwise they would all turn at the same rate, contrary to the “wandering” of the sun, moon and planets - their apparent motion relative to the stars.

I: I thought every heavenly sphere in Aristotle’s universe was self-moved - that each had its own god, so to speak, or internal principle of movement.

DG: At one point Aristotle does indicate as much, while at other points he indicates that the outermost motion is primary and therefore the only genuine self-motion. However, since our purpose here is not to establish what Aristotle actually believed, but merely to provide an illustration, let us agree, for the moment anyway, to call ‘Aristotelian’ the cosmology I have outlined, in which the outermost heavenly sphere alone is self-moved.

I: As you wish. But what exactly does it illustrate?

DG: That, far from pneumatical or self-determining action being derived from mechanical action, as obtains in the mechanical philosophy, the exact opposite is conceivable.

I: Maybe, but Aristotelian cosmology hardly “does away” with mechanical action.

DG: Agreed. It does not render mechanical action illusory, for example. On the other hand, it does assert the existential priority of pneumatical over mechanical action. For, the self-motion of the outermost crystalline sphere gives rise to the mechanically induced motions of the lower spheres, not the other way round.

I: I can see that. In that sense Aristotle’s cosmology is diametrically opposed to the mechanical philosophy, which holds self-motion to be a product of mechanically induced motion. But look - and I hope you’ll forgive me for pointing this out - geocentric cosmology is obsolete, and has been for centuries. Not even heliocentric, or sun-centered, cosmology is accepted by scientists nowadays. So what’s the point of your example again?

DG: Just this: it illustrates in a simple and visually intuitive way that mechanism, or the mechanical philosophy, is not the sole conceivable philosophy of Nature, and that pneumatism is also possible, even if it does not altogether “do away” with mechanical action.

I: Can you now, then, provide me with a more recent example of pneumatism?

DG: The natural philosophy of Leibniz, Newton’s famous rival, constitutes just such an example. And not only is Leibniz’s pneumatism more recent than Aristotle’s, it is also not tied to an obsolete cosmology, because it does not conceive material self-motion as motion relative to a distinguished place or center in the universe, as Aristotelian cosmology does. For this reason Leibnizean pneumatism will serve as a useful stepping stone to the pneumatical standpoint of modern physics, which likewise does not admit a distinguished place or center.

I: That’s more like it.

DG: Let me point out, to begin with, that although Leibniz considered impact or push-contact mechanical action to be the only way bodies can affect one another, and criticized Newton for not explaining gravity in these terms, he nevertheless agreed with Newton that inertial force must be posited in matter.

I: And for the same reason presumably: that otherwise bodies would not variably resist, but would all be equally affected by, any given mechanical force, contrary to experience.

DG: Yes.

I: So Leibniz made the same concession to pneumatism here that Newton did.

DG: In fact, Leibniz went further than Newton by positing an additional pneumatical power in matter, which he called ‘living force’.

I: What reasons did he give for doing so?

DG: This is where things get a bit tricky, because Leibniz’s reasons were not straightforwardly empirical, but involved considerable input from his metaphysics or general theory of reality. And to explain that theory would take us too far afield.

I: Just do what you can.

DG: On the empirical side, Leibniz noticed that a certain physical quantity, the mass multiplied by the velocity squared, remained constant in various experiments involving moving bodies. From his metaphysical principles, on the other hand, it followed that the total quantity of moving force in matter is conserved. Leibniz therefore took the aforementioned quantity, mass multiplied by velocity squared, to be the measure of a moving force in matter that is distinct from inertial force, this latter being measured by the mass alone.

I: Is not Leibniz’s measure of living force the very same one that physicists now use for kinetic energy?

DG: Pretty much. Leibniz’s measure is actually twice that of kinetic energy. It turns out, however, that neither of these quantities are conserved in general, contrary to what Leibniz believed. But I would like you to ignore that fact for the moment.

I: I seem to recall that Descartes, although he did not posit inertial force, likewise accepted the existence of a conserved moving force in matter.

DG: You are quite right. However, Descartes’ moving force was a force in name only, for its measure or quantity was not distinguished from the quantity of motion of a body, whereas for Leibniz these two quantities were quite distinct. This mathematical distinction signified a difference in philosophical outlook. Whereas Descartes held matter to be inert, or its activity to consist solely in the motions of bodies, Leibniz, like Newton, acknowledged the existence of activity in bodies over and above their motions.

I: Very interesting. But can you tell me why Leibniz’s theory is an example of pneumatism, while Newton’s theory is not?

DG: Newtonian physics, although it recognizes a pneumatical power in matter, is not pneumatical physics, because it does not derive mechanical action from pneumatical action. Specifically, it does not derive the force of gravity, or any other kind of external action, from inertial force. Rather, mechanical force remains irreducible in Newtonian physics, just as inertial force itself does.

I: But this is not the case in Leibnizean physics.

DG: Well, it holds also in Leibnizean physics that mechanical force cannot be derived from inertial force. You see, inertial force, being a force of resistance that opposes mechanical force, is just not suitable as a ground for mechanical force. Furthermore, its measure, which is given by the mass or quantity of matter in a body, is a simple number. And a simple number specifies magnitude only, whereas mechanical force always has direction as well as magnitude. Leibnizean living force, on the other hand, is a pneumatical power more positively and substantially construed. In the first place it is not, like inertial force, a mere reactive complement to mechanical force. Secondly, its measure, although likewise a number, is not a “simple” number. For it depends not only on the mass but also on the velocity of a body - and velocity is a quantity that specifies a direction as well as a magnitude.

I: For that reason, then, Leibniz could take mechanical action to have its basis in pneumatical action, specifically, that of living force?

DG: Yes, and since he held matter to be present everywhere in the universe, it followed that not just mechanical but also pneumatical action occurred everywhere, not just at some distinguished location, as in Aristotelian cosmology.

I: That takes care of my first point anyway. At least, it shows how it is possible, in a modern cosmological setting, for pneumatical action to be not only irreducible to, but also the source of, mechanical action. Indeed, all of the philosophies we have discussed so far - those of Aristotle, Newton and Leibniz - make me wonder whether it is really possible to have mechanical action without pneumatical action, and thus whether pure mechanism itself is possible as a philosophy of Nature.

DG: Even the Newtonian philosophy seems to count against that possibility, does it not? For while mechanical action cannot be derived from pneumatical action in Newtonian physics, pneumatical action remains existentially prior nonetheless. For inertial force, according to Newton, is innate or essential to body. Therefore, if inertial force did not exist, body would not exist, and without body there could hardly be any mechanical force.

I: Agreed. But haven’t we overlooked the case of Descartes? He did not acknowledge inertial force. And if the moving force he posited in matter was a force in name only, as you claimed, did he not then advance a purely mechanical philosophy of Nature?

DG: So it appears, since he denied, in effect, that any pneumatical power of a material nature is responsible for motion and mechanical action. On the other hand, Descartes was quite happy to trace these things back to pneumatical powers that are immaterial.

I: By that you mean God and the human soul.

DG: Yes.

I: So even Descartes took pneumatical action to be fundamental, and mechanical action to be only secondary or derived. I’m very much looking forward to seeing whether something similar holds in physical theory today.

DG: I’m as keen as you are to proceed to that theory. However, I would like to continue our discussion of Leibnizean physics a little longer, in order to address the second point you raised earlier.

I: What was my second point again?

DG: That even if mechanical force could be done away with, or at least conceived as derived rather than fundamental, the pneumatical power replacing it would be too simple a power to be capable of explaining the complexity, variety and supposed autonomy of human actions. Inertial force, for instance, is manifestly inadequate in this respect. But Leibniz’s living force is also inadequate, despite being superior in certain respects to inertial force.

I: If you could say something more about this, by way of clarification.

DG: The pneumatical powers of inertial force and living force vary only quantitatively from body to body, whereas we want to assert, very reasonably, that the actions of the human body differ qualitatively as well as quantitatively from the actions of billiard balls, say, or of planets. To put it another way, inertial force and living force are merely additive powers, meaning that the pneumatical force of a composite body is, in the case of these powers, nothing more than the sum of the pneumatical forces of its parts. What we require, on the other hand, in order to explain human actions and human autonomy scientifically, is a physical force that is not only pneumatical but also non-additive.

I: Did Leibniz himself ever postulate such a force?

DG: Not so far as I am aware. Though he believed in human autonomy, or free will, just the same.

I: Which he explained, presumably, by appealing to an immaterial soul, much like Descartes.

DG: Yes, but with an important qualification. We touched earlier on the difficulty of comprehending interactions between material and immaterial things. Well, Leibniz was especially sensitive to this difficulty, and did not think it capable of resolution by Descartes or anyone else, so long as body and soul continued to be conceived as independently existing things or substances. Leibniz’s solution was to downgrade body from substance to appearance, specifically, to the appearance of soul or mind to itself, and to regard only the latter as substance.

I: Do you mean to say that he took souls to be more real than bodies?

DG: That’s exactly what I mean.

I: That strikes me as very far-fetched, though it does seem to open up a possibility that we didn’t consider earlier. For we took the apparent impossibility of explaining interactions between material and immaterial things to suggest that immaterial things do not exist. But it might instead be that material things do not exist, which in turn might make the notion of free will more intelligible.

DG: The need to make free will understandable was certainly an important factor in the development of Leibniz’s immaterialist philosophy. And we shall have more to say about this philosophy later on. Right now, though, I want to discuss two problems with Leibniz’s physical theory which are especially revealing of its inadequacy, but which are completely overcome in modern physics.

I: I was rather hoping we would have moved on to modern physics by this point. Alas, we seem to be stuck in the eighteenth century.

DG: We should not underestimate what these old masters have to teach us, even when they go wrong - perhaps especially when they go wrong - however eager we might be to discuss the latest discoveries.

I: In that case, please continue.

DG: Leibniz believed, wrongly, that the measure of living force is a conserved quantity, as we said. But it turns out that this measure is also inadequate because of its simple dependence on velocity, which is a relational quantity.

I: And by ‘relational’ here you mean?

DG: That the velocity of a body is not an absolute or invariant quantity but varies from observer to observer. Consequently, observers moving relative to one another will disagree over the amount of living force there is in the body.

I: Okay. But why does that make Leibniz’s measure of living force inadequate?

DG: Because Leibniz held living force to be the phenomenal analogue of primitive spiritual force, which he took to be a thoroughly pneumatical or non-relational power. This means that living force should itself be non-relational, whereas its measure indicates otherwise. Furthermore, living force, like inertial force, is supposed to be essential to body, whereas an observer at rest with respect to a given body will not attribute any living force to it. For that observer, then, the body should not exist, even though it exists for other observers moving relative to the first.

I: Surely Leibniz was aware of this difficulty.

DG: If he was, he might have tried to evade it by claiming that observers are never completely at rest with respect to any body. Or by claiming that observers are only ever momentarily at rest relative to a body - which would have been very convenient, since Leibniz denied that momentary quantities have any reality. Yet the difficulty remains that different observers will attribute different quantities of living force to any given body, whereas force, be it pneumatical or mechanical, is something that should really be objective or independent of observers, in so far as it constitutes real activity in matter. Accordingly, the measure of a force should be an invariant quantity, as mass is in the case of inertial force, or as the inverse square law is in the case of Newtonian gravitational force. This measure should not, in other words, depend explicitly on the time, place or motion of observers relative to the body or physical system in question.

I: Alright. What, then, is your second problem with Leibnizean physics?

DG: That living force is not substantial enough a pneumatical power to act as the ground of any mechanical action except the simple push-contact type. And no-one has ever succeeded in developing a physics that is adequate to the phenomena on the basis of such a restricted notion of mechanism. In particular, no-one has ever succeeded in explaining the motions of the planets in terms of impact or collision mechanisms.

I: With that last example, you seem to be suggesting that a more satisfactory concept of pneumatical action would be allow us to derive Newton’s law of gravity, as well as other mechanical laws that do not depend on the notion of action by contact.

DG: That is precisely what I am suggesting. But let me go further and point out that physics has for a long time now had just such concept of pneumatical action in its possession, and that this concept, unlike Leibniz’s, not only allows us to derive mechanical laws of the generalized Newtonian type, but also overcomes the other difficulties and inadequacies that we found to afflict Leibniz’s concept of living force.

I: You mean that the concept of pneumatical action in modern physics has a corresponding measure that is conserved, invariant and even non-additive?

DG: Precisely that. And more. For this modern concept of physical action is sufficiently powerful that we can even use it to explain the existence of matter.

I: Now you go too far, surely.

DG: Why do you say so?

I: Because I do not think it is possible for science to explain that fact.

DG: Indeed? Have you not heard of the Big Bang, the Higgs boson, or string theory, all of which have been proffered as scientific explanations of the existence of matter?

I: Certainly I have heard of those things, but they have never really impressed me as genuine explanations of material existence, however useful and important they might be in other respects. Consider the Big Bang theory. If one takes it to assert that something - matter - came into being from nothing, then it seems to me that genuine science is here at an end, because the very notion of an intelligible or law-governed connection between successive states is at an end. I mean, why should something rather than nothing have followed nothing in this case? If, on the other hand, the Big Bang does not involve a coming-to-be from nothing, then it simply affords a proximal explanation of matter such as we find it today, not an absolute explanation of matter as such.

DG: Perhaps quantum theory could help us out here, since it appears to undermine the notion that there is law-governed or necessary connection between the successive states of physical systems, and postulates a merely statistical connection. Yet quantum theory is a scientific theory, surely.

I: I believe that the importance of the statistical aspect of quantum theory has been exaggerated. For does not this aspect pertain only to the measured or observed states of physical systems, whereas these same systems evolve in a perfectly deterministic way independently of measurement, according to the theory?

DG: I have to admit, I thought so too. And Dirac, in his famous textbook on the principles of quantum theory, explicitly states as much. But suppose we are wrong about that. There still seem to be serious difficulties with the idea of trying to explain how matter could begin to exist. For, statistical explanations never explain the occurrence of an individual datum. They only ever explain distributions or sets of data. Therefore, they could not answer your question about why something – matter – rather than nothing followed nothing in this case. At most, they could show that a coming-to-be of matter is statistically possible, and that, given infinite time, such a possibility will certainly be realized. But that brings us to a second difficulty. For according to Einstein’s theory of gravity, time is not something that differs radically from matter, or exists independently of matter, but together with space is itself constituted by something material, namely, the gravitational field. If, then, we are to explain how matter began to exist, we must also explain how time began to exist, which implies that there was a time when time was not - a manifest absurdity. But please continue with your reply.

I: As for the Higgs boson, it is plainly inadequate as an explanation of matter. For while this particle is supposed to account for how the other elementary particles of physics acquired mass, what accounts for the existence of the Higgs boson itself? Indeed, what accounts for the existence of the other particles before they acquired mass? Or are such massless particles to be considered immaterial? That would make the photon, the massless particle of light, immaterial. A similar criticism may be directed against string theory, or rather against the proposal that string theory explains the existence of matter. Strings may well end up explaining the observed spectrum of elementary material particles, but what explains the strings themselves? Or are they, likewise, to be considered immaterial entities? My view is that physics, like the other natural sciences, takes matter or Nature as given, and investigates its properties. It does not ask, as philosophy does, whether matter is primitive or explainable in terms of something else

DG: That general viewpoint is held to, I suspect, by a great many persons. However, I intend to overthrow it, or at least show that physics has, with its modern concept of pneumatical action, already overthrown it, and without referring to the Big Bang, the Higgs boson, string theory, or any other specific physical theory or model. The full argument, which is contained in Chapter 7 of my book, is quite involved and technical. But I hope at least I can make my position plausible here, without going into too much detail. After that let’s take another look at the issue of free will, which I know interests you deeply. And if we have time, we might also discuss how it came to pass that pneumatism finally replaced mechanism in physics, and perhaps even touch on the significance of that remarkable development for the other sciences.

I: All of that sounds fine to me.

DG: Let’s begin with what you said about the idea of something coming from nothing. Despite what some physicists have been claiming recently, I agree with you that this idea is contrary to science, that it undermines the notion that Nature is intelligible, which science must assume in order even to get going. On the other hand, I maintain that a scientific explanation of material existence is possible.

I: I honestly do not believe you will be able to reconcile those two statements.

DG: Let us agree, at any rate, that a scientific explanation of the existence of matter will not, indeed cannot, involve showing how matter came into existence from nothing.

I: I’m happy to agree with that.

DG: It follows that a scientific explanation of material existence will show only why matter persists, or continues to exist.

I: You’ve taken me by surprise with that remark, though I admit there seems to be no other option. Either matter began to exist at some point, or it has always existed. And since we have ruled out scientific explanations of the first scenario, we are left with the second. However, does it not seem to you a bit odd to speak of explaining the persistence of matter?

DG: Only if by ‘explanation’ one restricts oneself to accounting for things in terms of antecedent causes, that is, by way of other things that are prior to them in time. For, obviously, if matter has always existed, there couldn’t have been anything which existed before it did. However, there are many examples of explanation in science which do not appeal to antecedent causes. Consider Newton’s explanation of Kepler’s laws of planetary motion. Or the explanation of a material’s gross physical properties in terms of its molecular structure. I hold that the modern scientific explanation of material existence is formally analogous to these cases rather than to the cases involving antecedent causes that philosophers seem to have been most interested in.

I: I see. Please go on with your account.

DG: I said earlier that physics explains the existence of matter in terms of its concept of force or action. But it is clear that no such explanation of material existence is possible in terms of mechanical forces. For these forces, being relational, are existentially posterior to matter, and therefore cannot explain matter’s existence.

I: That seems a perfectly reasonable inference to make.

DG: On the other hand, it is possible to explain the existence of motion in terms of mechanical forces. Newtonian physics, for example, provides just such an explanation.

I: I thought we were interested in explaining matter not motion.

DG: And so we are. However, the Newtonian explanation of motion is not only important in itself, it also introduces in a relatively simple and clear way the key ideas that are needed to understand the modern scientific explanation of matter.

I: I’ll have to take your word on that.

DG: As with the case of matter, we are concerned here to explain the persistence, or continued existence, of motion, not its coming-to-be from nothing - a scenario that we rejected as scientifically unintelligible. In Newtonian physics the persistence of motion is expressed by the principle of the conservation of momentum, where ‘momentum’ is just shorthand for ‘quantity of motion’. What we are looking for, then, is to explain this conservation principle in terms of Newton’s principles of force. This turns out to be very easy, since it follows directly from Newton’s second and third laws of motion. The second law states that the change in momentum of a body is directly proportional to the force impressed on it, while the third law states that for every impressed force there is another such force that is equal in magnitude but opposite in direction to the first force. It follows that the change in momentum induced by the first force is equal in magnitude but opposite in sign to the change in momentum induced by the second force. In other words, these two changes exactly compensate one another, so that the overall change in momentum is zero. The total quantity of motion is therefore conserved, which is what we set out show.

I: That’s a very tidy argument. The decisive factor here seems to be the reciprocal nature of impressed or mechanical force expressed by Newton’s third law of motion. That is, the continued existence of motion has been explained in terms of the reciprocal action of this force.

DG: Exactly right.

I: Does something similar hold, then, in the modern scientific explanation of material existence?

DG: Yes. But it is already apparent that the analogy will not be exact. For mechanical force, being posterior to matter, cannot explain it, as we said. What we require for such an explanation is pneumatical force, because such force is not posterior to matter. However, reciprocal action only makes sense in the case of force that is external or outer, like mechanical force, whereas pneumatical force is internal or self-directed force. As such it cannot have a reciprocal complement, as mechanical force does. What we need to focus on, therefore, is the fact that reciprocal action is a kind of symmetric action, and, more importantly, that this kind of symmetry implies another, which pertains not only to mechanical but also to pneumatical force.

I: I read somewhere that the concept of force is no longer of much use in physics - in fundamental physics anyway.

DG: If the word ‘force’ is taken to denote only Newtonian impressed or mechanical force, then what you read is perfectly correct. However, Newton himself, and also Leibniz, used this word more liberally, for instance, in the terms ‘inertial force’ and ‘living force’, which denote non-mechanical forces. I wish to follow their lead here, even if that seems a bit unconventional. For those old non-mechanical concepts of force have a modern analogue, which, though it is not called ‘force’, is directly descended from those old concepts, and plays much the same role in modern physical theory that the old concepts did in the old physics.

I: But what is to be gained by this unconventional use of the word ‘force’?

DG: Among other things, the knowledge that modern physics posits forces or active principles in matter no less than – and, in fact, even more than – classical physics does. But if you are still worried about my use of the word ‘force’ in a modern context, feel free replace it with the word ‘action’ in each instance, since they are, in this context, virtually interchangeable.

I: I may well make the substitution you suggest.

DG: We were discussing symmetry and reciprocity as they relate to physical force. Let us observe, to begin with, that Newton’s third law of motion, which concerns the reciprocity of mechanical force, implies something else about this force.

I: What exactly?

DG: That the magnitude of mechanical force cannot depend on the positions of bodies, but at most only on their differences in position, that is, on the distances between bodies. For, if the magnitude of this force depended on position merely, you would not get an exact reciprocity in general, as is stipulated in Newton’s third law of motion, since interacting bodies always occupy different positions from one another. In confirmation of what has just been said, observe that Newtonian gravitational force, in particular, is independent of position, that it depends only on the inverse square of the distances between bodies. Now, this position-independence of mechanical force constitutes an invariance or symmetry of the force. But it is qualitatively a different symmetry from that of the aforementioned reciprocity because it is an internal symmetry, and as such need only refer to a single instance of mechanical force, whereas reciprocity, being an external symmetry, always refers to a mechanical force and its reciprocal complement. Clearly, internal symmetry is what will carry over to pneumatical force, and it is this kind of symmetry, furthermore, which in modern physics enables us to explain not only the conservation of momentum but also the conservation of energy, the conservation of electrical charge, and the conservation of those charges - called ‘weak charge’ and ‘color’ - that are involved in nuclear interactions. In short, the persistence or continuing existence of all of those properties that constitute the sources of the fundamental physical interactions are explained in terms symmetric, pneumatical but nonetheless physical action. And this just means that the existence of matter has been explained in terms of such action.

I: I’m afraid you are racing ahead too quickly for me. For did we not agree that inertial force and living force were, or were held to be, pneumatical powers? And yet these forces, although their measures are manifestly independent of position, do not explain the conservation of momentum. Nor, I suspect, do they explain the conservation of any of the other physical quantities you have just mentioned.

DG: You are quite right about that, and I apologize for racing ahead. Those pneumatical powers are indeed too simple to explain even the existence of motion, let alone the existence of that which moves. For this reason Newton and Leibniz, although they took these powers to be essential to matter, could never have explained material existence in terms of their action. It is only in the physics of our day that this has become possible, because in order to explain the existence of matter we require not only a concept of pneumatical action, but also one that is substantial enough to ground mechanical or external actions in the generalized Newtonian sense. In fact, we require more than that. We require symmetries known as ‘field symmetries’ or ‘gauge symmetries’ as well as spatio-temporal symmetries, such as the symmetry with respect to position that we discussed above.

I: Let me get this straight. Are you claiming that physics already enables us to explain the existence of matter, even though it has not yet obtained a unified theory of matter, a so-called ‘theory of everything’?

DG: I am.

I: I find that claim rather implausible. In fact, I know of physicists who hold that even a unified theory will explain only the existence of specific forms of matter, not the existence of matter as such.

DG: Well, I happen to disagree with their pessimistic viewpoint. To see why, recall the Newtonian explanation of the existence of motion in terms of physical force that we discussed earlier. For this explanation, no further specification of physical force was required than what was contained in Newton’s second and third laws of motion. Certainly no unified theory of physical force was required. Not even Newton’s law of gravitational force was required. Now I claim that something analogous obtains in modern physics, and not only for the existence of motion but also for the existence of matter itself.

I: I can see I will have to consult your book, if I really want to understand this subject. I guess there’s only so much that can be covered in an interview. One thing at least is clear: your conclusions have profound consequences for metaphysics and theology. For you have stated that the source of material existence is just the action of physical force, which means that matter has the source of its existence within itself. But that in turn means that external causes are ruled out. There can, in other words, be no transcendent or immaterial causes of material existence.

DG: I quite agree. And I think Newton would have concurred also, for he once stated that ‘however we cast about we find almost no other reason for atheism than this notion of bodies having, as it were, a complete, absolute and independent reality in themselves’. Even so, it is only in modern physics that we have been able, finally, to demonstrate that bodies have this self-sufficiency, this independent reality in themselves, that Newton spoke of.

I: The principal reason for atheism nowadays is surely the theory that living things, instead of having been specifically created, have evolved from more rudimentary forms through natural selection.

DG: You may be right. However, while that theory certainly undermines the idea that species were produced ready-made by a transcendent or immaterial power intervening in Nature, it leaves completely untouched the idea that matter in general, or Nature itself, was originally produced by such a power. Whereas modern physics, by demonstrating the self-sufficiency of matter, confirms that natural science undermines that idea also.

I: That fact, if it is a fact, certainly gives one pause. But do you not also agree that this alleged self-sufficiency, while it implies that matter has no immaterial cause, does not by itself imply that immaterial entities are fictitious or unreal.

DG: I accept what you say. Our result is not sufficient for materialism. Though I think it goes some considerable way towards establishing materialism. To begin with, the self-sufficiency of matter clearly precludes idealism, which holds that matter, in so far as it exists at all, depends on something immaterial for its existence. That means we are left with dualism, which acknowledges the independent reality of both material and immaterial entities.

I: A theory which has deep problems of its own, if I’m not mistaken. For is it not prey to the serious difficulty we discussed earlier, concerning how material and immaterial things are able to interact with one another?

DG: It is so. But instead of us now considering ways in which this difficulty might be circumvented - for example, by positing a dualism of properties rather than of things - I would like to draw your attention to a striking analogy between our present discussion and Newton’s development of the mechanical philosophy. I mentioned earlier that Newton, in order to make mechanism work, had to concede something to the opposite camp, to pneumatism. He had to posit a pneumatical force in matter, namely, inertial force. Just so, in order to make materialism work, we need to make some concession to the opposite camp, to idealism.

I: Just what concession are you referring to? And why is it needed to make materialism work?

DG: I am referring to the explanation of matter in terms of pneumatical principles. Traditionally, only idealists have deemed it important to provide such explanations, whereas materialists have been content simply to assert that matter, and matter alone, is real and self-sufficient, that it does not depend on anything else.

I: You’re not being quite fair here. The materialists I’m acquainted with don’t simply assert that matter alone is real or independent. They make a more substantial claim: that there is no solid evidence for the existence of something else, something immaterial, upon which matter might depend.

DG: Either way, I do not consider the traditional materialist’s position satisfactory.

I: And why not?

DG: Because one can always ask of any given thing or system of things, including even the universe as a whole, why it is thus and not otherwise, and why it even exists at all. And to this question there are just two kinds of answer: either the thing has the reason for its nature and its existence within itself, or it does not, in which case one must look to external causes. So long, therefore, as science has not shown that matter is self-sufficient, its independent existence, indeed its very reality, remain open to doubt. If, on the other hand, as I assert, science has after all demonstrated the self-sufficiency of matter, it will have closed the door on such doubts. In addition, the truth of materialism will have become much more secure, even if it is not yet definitively established.

I: Might not these considerations apply also to physical force? You claim that the existence of matter can be understood in terms of this force. But how in turn are we to understand physical force? Why does it even exist at all?

DG: For my answer to that question, you’ll have to consult my book.

I: This might be a good point for us to put aside the question of material existence, for the time being anyway, and move on to the question of free will.

DG: Let’s do that.

I: With what should we begin our discussion?

DG: We could hardly do better than the third interesting point you made near the beginning of this interview.

I: My third point?

DG: Yes. We have already addressed your first and second points, which concerned the possibility of “doing away” with mechanical action, and the simplicity of inertial force as a pneumatical power, respectively. But you also stated, if I recall, that the ability of human beings to change as well as maintain their states of motion seems only to confirm that they are mechanisms, just like the automobile, rather than autonomous or free beings. Well, I think we have now reached a point where we are able to dispose of that worry quite satisfactorily.

I: Indeed? How so?

DG: You raised that worry in the context of a discussion about Newtonian physics, where mechanical action is not only irreducible to pneumatical action but also the sole origin of real change in matter. It was therefore very reasonable of you, in that context, to consider mechanical actions ultimately responsible for the ability of human beings to change their motions, and thus to treat human beings themselves as mechanisms of some sort. However, the same considerations evidently do not apply in modern physics, where mechanical actions are derived from pneumatical actions. For this just means that change as well as stability ultimately originates in pneumatical actions.

I: So there is no longer the same temptation to regard human beings as mechanisms just because they can change their own states of motion.

DG: Right.

I: Does this apply also to automobiles? I mean, is it now possible that the motions of automobiles are genuine self-motions rather than mere products of their parts’ motions?

DG: In asking that question I suspect you are not being quite serious. Nevertheless, I will give you a serious answer. We human beings have a conviction about ourselves that we do not have about automobiles, which is, that we are the ultimate source of our actions, that we are responsible for them, that they are original to us as human beings and not the mere products our material constituents’ actions, however much those constituents are involved in the carrying out of our actions. What I am claiming is that physics now allows us to explain this conviction of ours without explaining it away. Whereas previously, in Newtonian or Leibnizean physics say, it was simply impossible to make any scientific sense of that conviction, so that immaterial powers had to be called upon to make up for Nature’s apparent lack.

I: But you said, did you not, that all mechanical forces originate in pneumatical force according to modern physics? It follows that the mechanical forces which give rise to an automobile’s motion originate in pneumatical force.

DG: Agreed. But they do not, each of them, originate in the same pneumatical force. Rather, the operation of an automobile involves a number of independent pneumatical forces being brought together, so to speak, in an additive or “mechanical” way. There is no unified pneumatical origin to the automobile’s operation, as we believe there is in the case of a human being.

I: You mean that the self-motion of an automobile is ultimately the product of a number of independent self-motions, including, presumably, that of the automobile’s human operator. Whereas this is not so - or at least we believe it not to be so - of the actions of the human operators themselves.

DG: That is what I mean. The automobile, while it has its motion within itself rather than deriving it from something external, does not have its motion from itself - that is, from something singular and internal that would make the automobile a dynamical unity. The actions of human beings, by contrast, are held to originate in a single pneumatical power that philosophers in the past have termed ‘the will’ or ‘the soul’ or ‘the mind’, but which I hold to be a purely physical power. Of course, in order for this idea to be scientifically credible, we need to recall something that I perhaps should have brought up again earlier: the non-additivity of pneumatical force in modern physics. For, if we are to comprehend scientifically the actions of human beings as free or original to human beings as such, it is not enough that mechanical force be grounded in pneumatical force. We also require that the pneumatical force of a human being is not derivable from the pneumatical forces of its constituents. Otherwise, there could be no real difference between an automobile and its human operator. The actions of both would, necessarily, be mere products of their constituents’ actions.

I: I can see that. But what guarantee do we have that there is an actual difference between automobiles and human beings here?

DG: At this juncture we can only recur to the widely held conviction that there is such a difference; that we human beings have a unity and an autonomy that automobiles, indeed machines generally, do not possess. As to the basis for this conviction, one might point, for example, to the fact that automobiles require human beings to make them go, whereas no human being stands in need of something else in order to act.

I: What you have just said about human beings could also be said about all other natural systems.

DG: I have no wish to dispute that. Although I do not want to give you the impression, either, that I think human autonomy is identical to the autonomy of other beings in Nature. On the contrary, I think there is an important difference, which has to do with rational nature of human beings - with their intelligence. But that’s another very large and controversial subject, which I think we should leave for the book to explicate.

I: Fair enough. But there is still something I want to ask you about free will. From what you have said so far, you seem to think that responsibility or originality is sufficient for human freedom - that it is enough that we are the authors of our actions. Now, I certainly take authorship to be necessary for free will. But it does not seem to me quite sufficient. For does not free will also involve the ability to act otherwise under identical circumstances?

DG: Some persons have thought so, especially in theological circles, because they believed that morality depends on it. But I reject that notion of human freedom, because it seems to involve acknowledging an absolute contingency, which is something utterly unintelligible.

I: An absolute what?

DG: Contingency - something that could be otherwise even though everything else in reality remained exactly the same - which would be possible only if the thing in question were to some degree unconnected to everything else. It’s a bit like the case of something coming from nothing. You asked earlier ‘Why should something rather than nothing have followed nothing in this case?’ No reason can be given. Likewise, no reason can be given as to why a person did one thing rather than another, if their choices have something of the absolutely contingent about them. In my view such contingency, besides being unintelligible, creates as many problems for morality as it solves, if indeed it solves any. It is enough for me, therefore, that we are responsible for our actions in the sense that they are original to us and not simply the products of our material constituents’ actions and external forces.

I: I wonder what you would say, then, to a biologist who maintained that not only our physiological characteristics but also our behavior or actions are just the products of our genes expressing themselves in a particular environment?

DG: I would say something like the following: that a causal relationship between our genes and our behavior does not exist, but at most only a correlation. And that that correlation is due to both of these things, genes and behavior, having their basis in some third thing, namely, physical force.

I: And that seems reasonable to you, because you hold physical force to be the source not only of the actions but also of the existence of material things, and therefore of the existence of genes in particular?

DG: Yes.

I: Would you say, then, that these conclusions of yours, which are based on modern physics, imply that biology needs to be reformed along similar lines?

DG: That’s an interesting one. After all, biology only adopted the mechanical point of view after it had proved successful in physics. Up to that point, indeed right up to the nineteenth century, biologists were still positing souls, vital spirits and other active principles in living beings, in order to explain their differences from non-living beings. With the arrival of genetics and evolutionary biology, however, it seemed possible to account for these differences without referring to such principles. Henceforth, living beings were to be understood mechanically, as products of self-replicating microscopic objects and selective environmental conditions, rather than pneumatically, in terms of active principles. It is rather ironic, therefore, that physics has since abandoned the mechanical model of explanation and returned to the pneumatical model, that is, to a philosophy that was thought to have been discarded once and for all. Now, if you hold, as I do, that physics has a certain priority over biology when it comes to the philosophical significance of scientific theory, you will perhaps agree that the replacement of mechanism by pneumatism in physics indicates that something similar needs to occur in biology.

I: I’ve heard biologists insist that genetics and natural selection are no longer just theories but established facts, like the theory that the earth goes round the sun rather than conversely.

DG: I accept that analogy up to a point. But there is a side to it which is not generally appreciated, and which is relevant to our present discussion.

I: Which side?

DG: I am referring to the fact that the theory that the earth goes around the sun is not basic, but has been explained in terms of deeper theory. In particular, Newton and other scientists have offered mechanical explanations for this theory that are pretty good. But Einstein has since offered a non-mechanical, indeed a pneumatical, explanation that is much better, both theoretically and empirically, than the mechanical explanations. Why, then, couldn’t something similar hold for our understanding of the nature and origin of organisms?

I: I don’t see why it couldn’t, not immediately anyway. Nevertheless, I can imagine a less radical alternative than the one you perhaps have in mind. For might it not be with the evolution of organisms just as it is with the automobile?

DG: And by that you mean?

I: I mean, even if mechanism is, in every instance, reducible to pneumatism, as you are proposing, it doesn’t follow that all actions and processes will originate in a single pneumatical power. Some, like the operation of automobiles, might be mere “mechanical” resultants of several such powers, as we discussed earlier. So why couldn’t organic evolution be such a process, a mere “mechanical” resultant?

DG: That does seem to be a genuine possibility, I admit.

I: In which case, the kind of radical overturning of scientific theory that occurred when Einstein offered a new way of explaining the motion of the earth and other planets around the sun might never occur in evolutionary biology.

DG: Maybe, although I am currently developing an idea which would require the present viewpoint to be explained in terms of a higher one.

I: So long as this higher viewpoint of yours doesn’t revive the notion that species are absolutely fixed or unchanging. For that would surely involve a complete and unwarrantable retrogression in our understanding of the nature and origin of life.

DG: It would seem so.

I: I wonder if you might tell me now about how it came to pass that pneumatism finally replaced mechanism in physics. For this might yet give us some hint as to how biology might improve itself along similar lines, even if it does not provide an altogether accurate blueprint.

DG: I can only make a sketch at this point, since we are short on time.

I: Then a sketch will have to do.

DG: Let’s begin with Newtonian physics, since it was Newton who first recognized that an innate pneumatical force would have to be posited in matter, if the mechanical philosophy were to constitute a viable philosophy of Nature. Now, despite the importance of this innovation, there remained something deeply unsatisfactory about the principles of Newtonian physics. This was their postulation of two radically different kinds of force, pneumatical and mechanical, neither of which could be reduced to or derived from the other. This dualism of force in Newtonian physics resembled the mind-body dualism in metaphysics, which Descartes had been happy to accept, but which most philosophers, then as now, have looked upon with disdain.

I: The difficulty with mind-body dualism is the difficulty of explaining how two radically different kinds of thing, mind and body, can interact and so be united in a human being. Is that the same kind of problem that faces the dualism of force in Newtonian physics?

DG: No. Or rather, not quite. The difficulty is more that this dualism fails to satisfy the philosopher’s demand for rational unity. It would be better, that is, if there were just one kind of force rather than two, or if one of these forces could be derived from the other, because then more would be explained with less, which is always the mark of a superior theory. Of course, an analogous criticism might be directed at the mind-body dualism in metaphysics. Indeed, many philosophers have done just that, and subsequently replaced this dualism with one or other of the diametrically opposed doctrines of idealism and materialism.

I: So the question that now arises is: ‘Is mechanical force to be derived from pneumatical force, or the other way round?’

DG: That is the question alright. And I think you know the answer, given the ground we have traversed to this point.

I: The answer cannot be that pneumatical force is to be reduced to mechanical force.

DG: And why not?

I: Because then one would have, at bottom, a pure mechanism, without even the pneumatical force of inertia. And such a mechanism could not work, as Newton recognized, because no bodies would resist but all would respond equally to any given mechanical force.

DG: Very good. So if there were going to be any reduction, it would have to be a reduction of mechanical to pneumatical force. The first to attempt this was Leibniz, though his attempt was unsatisfactory in several respects, as we have seen. In particular, Leibniz only ever intended to reduce push-contact mechanical force to pneumatical force, whereas what was needed was a reduction of external force more generally, including Newtonian gravitational force. Such a reduction was finally achieved by a number of remarkable successors to Leibniz, although the resulting theory was not recognized by its developers and perfectors for what it was: a radical and powerful alternative to the mechanical theory of matter and motion.

I: Why was it not recognized as such?

DG: Because its development occurred during the heyday of mechanism, so that instead of being identified as an alternative to mechanical physics, or rather as providing mechanical physics with a pneumatical foundation, the exact opposite happened, and the theory was instead treated as little more than a curious result of mechanical principles.

I: As if pneumatism were to be derived from mechanism after all.

DG: Precisely. It was only after the mechanical philosophy began to encounter serious empirical difficulties, that a change of view on this matter could be discerned.

I: What, in particular, caused these difficulties for mechanism?

DG: Principally, it was the repeated failure of attempts to account for electromagnetic phenomena, especially the propagation of electromagnetic waves and their field-theoretic representation, in terms of a hypothetical, space-filling, mechanical medium. Einstein then showed that this problematic medium could be jettisoned, and the electromagnetic phenomena understood in terms of fields alone, if the Newtonian concept of physical time were modified in a certain way.

I: Would you mind clarifying what you mean by the word ‘field’ here?

DG: 'Field', in this context, refers to an elementary material entity that is spread out or non-localized, and as such capable of undulatory or wave-like motion, in contrast to a material particle, which is localized and moves linearly. Originally, such fields were conceived not as substantial or independently existing entities, but merely as dispositional, that is, as waves in something, just like water waves are waves in water. Really, these fields were held to be constituted by the mechanical forces that were allegedly acting between parts of the hypothetical mechanical medium. As such they were mere fields of mechanical force. Einstein’s innovations, however, liberated them from their mechanical substratum, thereby changing their status from dispositional to substantial entities.

I: Did this mean that radiation waves were now taken to exist on their own, without any medium to support them?

DG: Yes.

I: I find that a very difficult idea to grasp. It’s almost as if the wave had been stripped of its matter, leaving only its form behind.

DG: That’s not an altogether bad way of thinking about it. In any case, the approach proved very successful, with an early triumph being Einstein’s field theory of gravity, his so-called ‘general theory of relativity’. Not only did this theory completely surpass Newton’s old mechanical theory, it marked a definitive break with the mechanical philosophy itself. In the first place, the physical field of which it was the theory concerned not only gravity but also the geometrical structure of space, and there was obviously no way such a field could be understood in terms of a space-filling mechanical medium. Secondly, and even more importantly, this field, for the very reason that it concerned the geometry of space, meant that gravitational motions could no longer be understood as mechanically induced motions, as in Newtonian physics, but now had to be conceived as inertial or free, that is to say, pneumatical motions. Einstein, accordingly, lost no time in showing how the aforementioned, much-neglected pneumatical theory of matter and motion could be applied to this case.

I: I see. But so far you have not said anything about quantum theory.

DG: At first quantum theory appeared as a kind of reaction to these new developments, in that it favored the mechanical concept of the material particle over the non-mechanical concept of the physical field, applying the particle concept even to electromagnetic radiation. Before long, however, fields made their way into quantum theory too. And here the field concept was applied not just to radiation but also to the material sources of such. You may have heard of the matter-wave concept of de Broglie and Schroedinger. This was a field-theoretic concept, although there was a good deal of hand-wringing over its interpretation and status, especially from physicists who favored particles over fields. Eventually, however, after a bit of see-sawing between the rival approaches, fields won out, which is why our best theory of matter to date, gravity excepted, is called ‘quantum field theory’. Particles are still recognized by this theory, but only as derived entities, as the observed quanta of fields.

I: I presume that quantum field theory, just like Einstein’s field theory of gravity, is a pneumatical theory?

DG: It is so. And although you sometimes hear opinions to the contrary, quantum fields obey the same pneumatical law of action that the gravitational field does.

I: What about the more speculative theories from the frontier of physics, such as string theory and its rivals, which are attempts to unify quantum theory and gravity theory? If one those theories became established, making the older theories obsolete, would not your entire thesis, your so-called pneumatology of matter, be undermined?

DG: It turns out that string theory in particular, and its most serious rival, loop quantum gravity, employ the same pneumatical concept of physical action that the older theories do. So there appears to be no threat from that quarter, at present anyway.

I: Is there anything in physics, then, any current development at all, that might bring your philosophy down?

DG: None that I am aware of. And the following should also be borne in mind. When it comes to physical action, there are, at the most general level, really only three possibilities. Such action is either completely other-determining, partly other-determining and partly self-determining, or completely self-determining. The first possibility is pure mechanism, a non-starter. The second possibility is represented by Newtonian physics, which is good physics to be sure, but not good enough. The third possibility is what we have in physics today, and has proved far superior to the other two. Can we really envisage future developments in physics taking us away from pure pneumatism and back to one of those other two theories of physical action? In thinking about this, consider the following points: pure pneumatism allows us to explain the existence of both matter and motion scientifically. The hybrid of pneumatism and mechanism allows us to explain the existence of motion only. While pure mechanism does not even allow us to do that. To make up for the deficiencies in these last two theories, we would need, once again, to posit immaterial or supernatural entities, with a consequent loss of rational unity and explanatory power.

I: On that point we’ll have to bring things to a close I’m afraid, since our time is up. Before we finish I would just like to ask you about the origin of the words ‘pneumatical’ and ‘pneumatology’. I’m guessing it has something to do with air.

DG: These words derive from the Greek word pneuma, which means a blowing or breath - as in breath of life - or spirit.

I: Does your pneumatology of matter, then, assert that even so-called ‘non-living’ matter has life in it?

DG: In a sense, yes. And something else besides. But our discussion of that something else will have to wait for another time.