Applied Physics, Vol. 2, Issue 1, Sep  2019, Pages 21-35; DOI: 10.31058/j.ap.2019.21004 10.31058/j.ap.2019.21004

Physicalism is a Key Item of Current Scientific Knowledge

, Vol. 2, Issue 1, Sep  2019, Pages 21-35.

DOI: 10.31058/j.ap.2019.21004

Nicholas Maxwell 1*

1 Science and Technology Studies, University College London, London, England

Received: 6 July 2019; Accepted: 30 September 2019; Published: 5 November 2019

Abstract

This paper gives a specific interpretation to physicalism, and argues that physicalism, in this sense, is a key item of scientific knowledge.  Physicalism is interpreted to be the thesis that the universe is such that there is a not yet discovered true physical theory of everything that is unified.  What it means for a physical theory to be unified is then explicated.  Physicalism, interpreted along these lines, is implicit in the way in which in physics only unified theories are ever accepted, even though endlessly many empirically more successful, disunified rivals always exist.  In order to give ourselves the best chance of improving this implicit, problematic, metaphysical thesis, we need to adopt a new conception of science, aim-oriented empiricism, which construes physics as making a hierarchy of assumptions concerning the knowability and comprehensibility of the universe.  Physicalism is one of these assumptions.

Keywords

Physicalism

1. Introduction

Physicalism is a part of current scientific knowledge. This assertion immediately provokes two questions. First, what is physicalism? What does the thesis assert? Second, what possible grounds can there be for holding that physicalism is a part of scientific knowledge given that physicalism is, presumably, an unfalsifiable thesis, thus metaphysical, and thus to be excluded from science in accordance with Karl Popper' s demarcation criterion? [1] In what follows, these two questions are answered.

2. What Physicalism Means

The term physicalism has been used to stand for different doctrines by a number of authors. Otto Neurath interpreted the term to mean that any meaningful statement is equivalent to some physical statement. [2] For J.J.C. Smart, physicalism is the doctrine that everything is physical – such that it can in principle be depicted by physics. [3] In 1966, physicalism was characterized as the doctrine that: “(a) the world is made up entirely of only a few different sorts of things—the fundamental physical entities. (b) Precise, exceptionless laws govern the way in which these entities change. (c) Human perception is almost entirely deceptive: almost all perceptual qualities, e.g. qualities such as colours, sounds and smells, have no real, no objective existence” [4]. For David Chalmers, physicalism is the doctrine that “all the positive facts about the world are globally logically supervenient on the physical facts. This captures the intuitive notion that if [physicalism] is true, then once God fixed the physical facts about the world, all the facts were fixed” [5].

Here, physicalism is interpreted in such a way that it asserts that the physical universe is such that there is a not-yet discovered physical " theory of everything" that, if discovered, would in principle predict all physical phenomena. This theory would be both unified and true.

Physicalism in this sense implies physicalism as it is rather more generally understood, to mean roughly " everything is made up of physical entities" - as long as this latter doctrine includes, as a special case, the idea that everything is made up of just one physical entity, some kind of all-pervasive, unified field. In what follows, questions about whether anything else exists besides the physical, and if it does how precisely it is related to the physical, are left open. It is required, as a minimum, that if anything non-physical does exist, if it changes there are physical changes as well.

Physicalism, understood as interpreted here, asserts that the physical universe consists of two parts, U and V. U is the same everywhere, throughout all space and time, throughout all actual and physically possible phenomena, in an invariant form. Its physical nature is specified by the true, unified physical " theory of everything" . V is what varies, from place to place and from time to time. U, plus V at any instant throughout the universe determine, perhaps probabilistically, values of V at subsequent instants.

But what, it may well be asked, in the above characterization of physicalism, does it mean to say of a physical theory that it is " unified" ? This is especially problematic because one and the same theory may be formulated in endlessly many different ways, some unified, others horribly disunified.

Here, a view is adopted that has been expounded and defended elsewhere: see [6], [7], [8], [9], [10], [11]. A physical theory is disunified if what it asserts about the world differs from one range of phenomena to another. If what a theory, T, asserts about all actual and possible physical phenomena to which it applies falls into N distinct regions, what the theory asserts about how phenomena evolve in any one region being different from what it asserts about phenomena in all the other regions, and then T is disunified to degree N. For unity, it is required that N = 1.

Note that a physical theory that is unified in this sense may well be formulated in any number of different ways, some formulations seeming unified, others seeming horribly disunified. But as long as all these different formulations have the same physical content, so they assert the same about the actual and possible physical phenomena to which they apply, then they are all unified. Changing the formulation of a theory does not change its degree of unity or disunity, as long as its content remains the same.

The true " theory of everything" (if it exists), unified in the above sense, asserts that U is precisely the same at all times and places, throughout all actual and possible phenomena. The theory specifies how U determines change in changing V.

There is, however, a refinement. What a physical theory asserts, its content, may differ, from one range of phenomena to another, in different ways, some differences of content being more serious than others.

There are at least eight different ways, in which the content of a physical theory, T, may differ, from one region of phenomena to another.

(1) T may make different assertions for different space-time regions. Thus T might assert " All phenomena occur in accordance with Newton' s law of gravitation up till the first moment of 2050; after that date they occur in accordance with F = Gm1m2/d3. In this case, T is disunified to degree N = 2 in a type (1) way.

(2) T differs in N distinct ranges of physical variables other than position or time. Example:

F = Gm1m2/d2 for all bodies except for those made of gold of mass greater than 1,000 tons in outer space within a region of 1 mile of each other, in which case F = Gm1m2/d4. Here, T is disunified to degree N = 2 in a type (2) way.

(3) T postulates N-1 distinct, spatially localized objects, each with its own unique dynamic properties. Example: T asserts that everything occurs as Newtonian theory asserts, except there is one object in the universe, of mass 8 tons, such that, for any matter up to 8 miles from the centre of mass of this object, gravitation is a repulsive rather than attractive force. The object only interacts by means of gravitation. Here, T is disunified to degree N = 2, in a type (3) way.

(4) T postulates N distinct forces. Example: T postulates particles that interact by means of Newtonian gravitation; some of these also interact by means of an electrostatic force F = Kq1q2/d2, this force being attractive if q1 and q2 are oppositely charged, otherwise being repulsive. Here, T is disunified to degree N = 2 in a type (4) way.

(5) T postulates one force but N distinct kinds of particle. Example: T postulates particles that interact by means of Newtonian gravitation, there being three kinds of particles, of mass m, 2m and 3m. Here, T is disunified to degree N = 3 in a type (5) way.

(6) Consider a theory, T, that postulates N distinct kinds of entity (e.g. particles or fields), but these N entities can be regarded as arising because T exhibits some symmetry (in the way that the electric and magnetic fields of classical electromagnetism can be regarded as arising because of the symmetry of Lorentz invariance, or the eight gluons of chromodynamics can be regarded as arising as a result of the local gauge symmetry of SU(3)). If the symmetry group, G, is not a direct product of subgroups, T is fully unified; if G is a direct product of subgroups, T lacks full unity; and if the N entities are such that they cannot be regarded as arising as a result of some symmetry of T, with some group structure G, then T is disunified to degree N.

(7) If the (apparent) disunity of there being N distinct kinds of particle or distinct fields has emerged as a result of a series of cosmic spontaneous symmetry-breaking events, there being manifest unity before these occurred, then the relevant theory, T, is unified. If current (apparent) disunity has not emerged from unity in this way, as a result of spontaneous symmetry-breaking, then the relevant theory, T, is disunified.

(8) According to GR, Newton' s force of gravitation is merely an aspect of the curvature of space-time. As a result of a change in our ideas about the nature of space-time, so that its geometric properties become dynamic, a physical force disappears, or becomes unified with space-time. This suggests the following requirement for unity: space-time on the one hand, and physical particles-and-forces on the other, must be unified into a single self-interacting entity, U. If T postulates space-time and physical " particles-and-forces" as two fundamentally distinct kinds of entity, then T is not unified in this respect, with N = 2.

For unity, in each case, it is required that N = 1. As one goes from (1) to (8), the requirements for unity are intended to be accumulative: each presupposes that N = 1 for previous requirements. As far as (6) and (7) are concerned, if there are N distinct kinds of entity which are not unified by a symmetry, whether broken or not, then the degree of disunity is the same as that for (4) and (5), depending on whether there are N distinct forces, or one force but N distinct kinds of entity between which the force acts.

(8) introduces, not a new kind of unity, but rather a new, more severe way of counting different kinds of entity. (1) to (7) taken together require, for unity, that there is one kind of self-interacting physical entity evolving in a distinct space-time, the way this entity evolves being specified, of course, by a consistent physical theory. According to (1) to (7), even though there are, in a sense, two kinds of entity, matter (or particles-and-forces) on the one hand, and space-time on the other, nevertheless N = 1. According to (8), this would yield N = 2. For N = 1, (8) requires matter and space-time to be unified into one basic entity (unified by means of a spontaneously broken symmetry, perhaps).

As one goes from (1) to (8), then, requirements for unity become increasingly demanding, with (6) and (7) being at least as demanding as (4) and (5), as explained above. It is important to appreciate, however, that (1) to (8) are all versions of the same basic idea that T is unified if and only if the content of T is the same throughout the range of possible phenomena to which it applies. When T is disunified, (1) to (8) specify different kinds of difference in the content of T in diverse regions of the space, S, of all possible phenomena to which T applies. Or, equivalently, (1) to (8) divide S into sub-regions in different ways, T having a different content in each sub-region.

A physical theory may be unified (or disunified) to extent (n,N), where n stands for the kind of unity, n = 1, 2, ... or 8; and N standing for the degree of unity in each case, N = 1, 2 ... ∞. For perfect unity, it is required that n = 8 and N = 1. Equally, physicalism can be interpreted to be infinitely many different theses physicalism(n,N). Physicalism(n,N) asserts that the universe is such that some not yet discovered physical " theory of everything" is true and is unified in a type n way to degree N. In what follows " physicalism" will be taken to mean physicalism (n=8, N=1).

There are at least four significant features about this account of unity of theory. First, it reveals that there is no absolute distinction between the worst kind of disunity, with n = 1, and the best, with n = 8. Second, it reveals that the symmetry of theory is no more than an aspect of its unity. Third, this account of unity is also an account of what it means to say of a physical theory that it is explanatory. The greater the empirical content and unity of a physical theory, so the greater its explanatory power. This explicates what it means to say, not just of a theory, but also of a possible (or actual) universe, that it is physically comprehensible. Fourth, the account of unity just given enables us to throw a two-dimensional grid over all possible partially physically comprehensible universes – the grid partially ordering universes with respect to kind, n, and degree, N, of unity, or of physical comprehensibility. Chaos is partially ordered!

One final point concerning what physicalism means. If physicalism, in the above sense, is true, does this mean that everything is physicalistic in character? The answer is: No. As has been demonstrated long ago, physics cannot predict or explain the experiential: colours, sounds, tactile qualities as human beings experience these things, and have inner experiences of these things. Physics is concerned only with a highly selected aspect of all that there is: that aspect of things which determines (perhaps probabilistically) how events evolve in time. [4,12] Years later, Thomas Nagel [13] and Frank Jackson [14] made similar points.

3. Physicalism is a Part of Scientific Knowledge

It is clear that physicalism, as just interpreted, is neither verifiable not falsifiable empirically. It is thus a metaphysical thesis, and hence cannot be a part of scientific knowledge, if Popper' s demarcation criterion is accepted. What possible grounds, then, can there be for holding that physicalism, in this sense, is a part of scientific knowledge?

Once again, use is made of arguments that have developed elsewhere. It has been shown decisively that Popper' s demarcation criterion must be rejected. Metaphysical theses must be regarded as an integral part of current scientific knowledge, and physicalism, in the above sense, is one of these theses: see [6-11], [15-18].

In recent years there has been an explosion of literature devoted to the metaphysics of science – and to the metaphysics of physics more specifically: see, for example, [19]; Chakravartty [20], [21]; Maudlin [22]; Morganti [23]; Mumford and Tugby [24]; Ross et al. [25]; Slater and Yudell [26]. It is striking that none of this work avails itself of the argument for the view expounded in this paper. None of this work is thus able to provide the strong grounds for holding that physicalism are a part of scientific knowledge indicated in this paper: see [18] for an elaboration of this point.

What, then, is my argument in support of the thesis that the metaphysical thesis of physicalism is an integral part of current scientific knowledge? The argument, in outline, proceeds as follows. Physicists only ever accept (more or less) unified theories, even though endlessly many empirically more successful but seriously disunified rivals always exist. In persistently accepting unified theories only, even though endlessly many empirically more successful disunified rivals exist, physicists thereby make a substantial, implicit assumption: the universe is such that all seriously disunified theories are false.

Let T be any accepted fundamental physical theory – Newtonian theory, classical electrodynamics, quantum theory, general relativity, quantum electrodynamics, quantum electroweak theory, quantum chromodynamics, or the standard model. There are, to begin with, infinitely many disunified rivals to T – T1, T2, … T – that are just as empirically successful as T. In order to concoct such a rival, T1 say, all that needs to be done is modify T in an entirely ad hoc way for phenomena that occur after some future date. Thus, if T is Newtonian theory (NT), NT1 might assert: everything occurs as NT predicts until the first moment of 2050, when an inverse cube law of gravitation comes into operation: F = Gm1m2/d3. It is possible also to concoct endlessly many disunified rivals to T by modifying the predictions of T for just one kind of system that has never observed. Thus, if T is, as before, NT, then NT2 might assert: everything occurs as NT predicts except for any system of pure gold spheres, each of mass greater than 1,000 tons, moving in a vacuum, centres no more than 1,000 miles apart, when Newton’s law becomes F = Gm1m2/d4. Yet again, we may concoct further endlessly many equally empirically successful disunified rivals to T by taking any standard experiment that corroborates T and modifying it in some trivial, irrelevant fashion – painting the apparatus purple, for example, or sprinkling diamond dust in a circle around the apparatus. T can then be modified in an ad hoc way so that the modified theory, T3 say, agrees with T for all phenomena except for the trivially modified experiment. For this experiment, not yet performed, T3 predicts – whatever may be chosen. Endlessly many different outcomes may be chosen, thus creating endlessly many different modifications of T associated with this one trivially modified experiment. On top of that, of course, endlessly many further experiments can be trivially modified, each of which generates endlessly many further disunified rivals to T.

Each of these equally empirically successful, disunified rivals to T – T1, T2, … T – can now be modified further, so that each becomes empirically more successful than T. Any accepted fundamental physical theory is almost bound to face some empirical difficulties, and is thus, on the face of it, refuted – by phenomena A. There will be phenomena, B, which come within the scope of the theory but which cannot be predicted because the equations of the theory cannot (as yet) be solved. And there will be other phenomena (C) that fall outside the scope of the theory altogether. Any one of the disunified rivals to T, T1 say, can be modified further so that the new theory, T1*, differs further from T in predicting, in an entirely ad hoc way, that phenomena A, B and C occur in accordance with empirically established laws LA, LB and LC. T1* successfully predicts all that T has successfully predicted; T1* successfully predicts phenomena A that ostensibly refute T; and T1* successfully predicts phenomena B and C that T fails to predict. On empirical grounds alone, T1* is clearly more successful and better corroborated, than T. And all this can be repeated as far as all the other disunified rivals of T are concerned, to generate infinitely many empirically more successful disunified rivals to T: T1*, T2*, … T*.

But even though all of T1*, T2*, … T* are more successful empirically than T, they are all, quite correctly, ignored by physics because they are all horribly disunified. They postulate different laws for different phenomena in a wholly ad hoc fashion, and are just assumed to be false. But this means physics makes a big, implicit assumption about the universe: it is such that all such grossly disunified, theories are false. If physics seeks truth, as it surely does, and at the same time persistently accepts unified theories only, even though endlessly many empirically more successful disunified rivals are always available, this can only mean that physics implicitly assumes: all these disunified rivals are false. It is implicitly assumed: the universe is such that all disunified theories are false.

At once the questions arise: What precisely ought this assumption to be? And on what grounds is it to be made? It is of profound significance for physics that a good assumption is made since this assumption influences both what theories are accepted in physics, and what kind of new theories are sought. Yet here, since this assumption concerns the ultimate nature of the physical universe, that about which humanity is most ignorant, it is almost bound to be the case that an assumption will be made that is false. And the historical record reveals that physicists have changed their minds a number of times since modern physics began. In the 17th century the view was that the universe is made of corpuscles that interact by contact; this gave way to the view that the universe is made of point-particles that interact by means of rigid forces at a distance; this in turn gave way to Einstein' s view that there is a unified field, which in turn succumbed to the view that everything is made up of quantum particles. Nowadays there is the view that the universe consists of tiny quantum strings in ten or eleven dimensions of space-time.

In these circumstances, physics needs a new methodology which best helps physicists improve the metaphysical assumption that is made. Physics needs to be seen and so natural science more generally, as making a hierarchy of metaphysical assumptions, these assumptions becoming less and less substantial as the hierarchy is ascended, and so more and is required for science, or the pursuit of knowledge, to be possible at all. This view, which may be called aim-oriented empiricism (AOE), is depicted in Figure 1.

<a href=Figure 1 Aim-Oriented Empiricism (AOE)" _src="/ueditor/asp/upload/image/20200122/15796291217126356.png"/>

Figure 1. Aim-Oriented Empiricism (AOE).

At the top there is the relatively insubstantial assumption that the universe is such that humanity can acquire some knowledge of its local circumstances. If this assumption is false, it will not be possible to acquire knowledge whatever is assumed. Scientists are justified in accepting this assumption permanently as a part of scientific knowledge, even though they have no grounds for holding it to be true. As the hierarchy is descended, the assumptions become increasingly substantial and thus increasingly likely to be false. At level 6 there is the more substantial thesis that there is some rationally discoverable thesis about the nature of the universe which, if true and if accepted, makes it possible progressively to improve methods for the improvement of knowledge. “Rationally discoverable”, here, means at least that the thesis is not an arbitrary choice from infinitely many analogous theses. At level 5 there is the even more substantial thesis that the universe is comprehensible in some way or other, whether physically or in some other way. This thesis asserts that the universe is such that there is something (God, tribe of gods, cosmic goal, physical entity, cosmic programme or whatever), which exists everywhere in an unchanging form and which, in some sense, determines or is responsible for everything that changes (all change and diversity in the world in principle being explicable and understandable in terms of the underlying unchanging something). A universe of this type deserves to be called “comprehensible” because it is such that everything that occurs, all change and diversity, can in principle be explained and understood as being the outcome of the operations of the one underlying something, present throughout all phenomena. At level 4 there is the still more substantial thesis that the universe is physically comprehensible in some way or other – physicalism (n=8, N=1) in other words. At level 3, there is an even more substantial thesis, the best, currently available specific idea as to how the universe is physically comprehensible. This asserts that everything is made of some specific kind of physical entity: corpuscle, point-particle, classical field, quantum field, convoluted space-time, string, or whatever. Given the historical record of dramatically changing ideas at this level, and given the relatively highly specific and substantial character of successive assumptions made at this level, scientists can be reasonably confident that the best assumption available at any stage in the development of physics at this level will be false, and will need future revision. Here, ideas evolve with evolving knowledge. At level 2 there are the accepted fundamental theories of physics, currently general relativity and the standard model. Finally, at level 1 there are accepted empirical data, low level, and corroborated, empirical laws.

I first expounded and defended a version of this hierarchical view of aim-oriented empiricism in [27]. It was further elaborated in Maxwell [28] and [29]. A more elaborate version still is expounded and defended in great detail in Maxwell [6]. For a more detailed defence of the version indicated here, see Maxwell [7] (chs. 1, 2, and appendix). [30] argues that this view is a sort of synthesis of the views of Popper, Kuhn and Lakatos, but an improvement over the views of all three. [8] (ch. 14) gives a detailed exposition of AOE, and argue, in some detail, that AOE succeeds in solving major problems in the philosophy of science, including the problems of induction, simplicity and verisimilitude. For an account of how AOE was developed, partly as a result of criticisms of Popper’s falsificationism, see [31]. For the most recent expositions of, and arguments for, AOE see [11,18].

The basic idea of aim-oriented empiricism is to separate out what is most likely to be true, and not in need of revision, at and near the top of the hierarchy, from what is most likely to be false, and most in need of criticism and revision, near the bottom of the hierarchy. Evidence, at level 1, and assumptions high up in the hierarchy, are rather firmly accepted, as being most likely to be true (although still open to revision): this is then used to criticize, and to try to improve, theses at levels 2 and 3 (and perhaps 4), where falsity is most likely to be located.

In order to be acceptable, an assumption at any level from 6 to 3 must (as far as possible) be compatible with, and a special case of, the assumption above in the hierarchy; at the same time it must be (or promise to be) empirically fruitful in the sense that successive accepted physical theories increasingly successfully accord with (or exemplify) the assumption. At level 2, those physical theories are accepted which are sufficiently (a) empirically successful and (b) in accord with the best available assumption at level 3 (or level 4). Corresponding to each assumption, at any level from 7 to 3, there is a methodological principle, represented by sloping dotted lines in figure 1, requiring that theses lower down in the hierarchy are compatible with the given assumption.

When theoretical physics has completed its central task, and the true theory of everything, T, has been discovered, then T will (in principle) successfully predict all empirical phenomena at level 1, and will entail the assumption at level 3, which will in turn entail the assumption at level 4, and so on up the hierarchy. As it is, physics has not completed its task, T has not (yet) been discovered, and humanity is ignorant of the nature of the universe. This ignorance is reflected in clashes between theses at different levels of AOE. There are clashes between levels 1 and 2, 2 and 3, and 3 and 4. And the two fundamental theories at level 2, the standard model and general relativity, clash as well. The attempt to resolve these clashes drives physics forward.

In seeking to resolve clashes between levels, influences can go in both directions. Thus, given a clash between levels 1 and 2, this may lead to the modification or replacement of the relevant theory at level 2; but, on the other hand, it may lead to the discovery that the relevant experimental result is not correct for any of a number of possible reasons, and needs to be modified. In general, however, such a clash leads to the rejection of the level 2 theory rather than the level 1 experimental result; the latter are held onto more firmly than the former, in part because experimental results have vastly less empirical content than theories, in part because of our confidence in the results of observation and direct experimental manipulation (especially after repetition and expert critical examination). Again, given a clash between levels 2 and 3, this may lead to the rejection of the relevant level 2 theory (because it is disunified, ad hoc, at odds with the current metaphysics of physics); but, on the other hand, it may lead to the rejection of the level 3 assumption and the adoption, instead, of a new assumption (as has happened a number of times in the history of physics, as was seen in section 5 above). The rejection of the current level 3 assumption is likely to take place if the level 2 theory, which clashes with it, is highly successful empirically, and furthermore has the effect of increasing unity in the totality of fundamental physical theory overall, so that clashes between levels 2 and 4 are decreased. In general, however, clashes between levels 2 and 3 are resolved by the rejection or modification of theories at level 2 rather than the assumption at level 3, in part because of the vastly greater empirical content of level 2 theories, in part because of the empirical fruitfulness of the level 3 assumption (in the sense indicated above).

It is conceivable that the clash between level 2 theories and the level 4 assumption might lead to the revision of the latter rather than the former. This happened when Galileo rejected the then current level 4 assumption of Aristotelianism, and replaced it with the idea that “the book of nature is written in the language of mathematics” (an early precursor of our current level 4 assumption). The whole idea, however, is that as one goes up the hierarchy of assumptions one is increasingly unlikely to encounter error, and the need for revision. The higher up one goes, the more firmly assumptions are upheld, the more resistance there is to modification.

The idea of representing the metaphysical presuppositions of physics (concerning the nature of the universe) as a hierarchy of theses, increasingly insubstantial as one goes up the hierarchy, gains some support from the fact that something somewhat similar exists informally at the empirical level – level 1 of figure 1 – and for much the same reason. There are, at the lowest level, the results of experiments performed at specific times and places. Then, above these, there are low-level experimental laws, asserting that each experimental result is a repeatable effect. Next up, there are empirical laws such as Hooke’s law, Ohm’s law or the gas laws. Above these there are such physical laws as those of electrostatics or of thermodynamics. And above these there are theories which have been refuted, but which can be “derived”, when appropriate limits are taken, from accepted fundamental theory – as Newtonian theory can be “derived” from general relativity. This informal hierarchy at the empirical level exists for the same reason as the hierarchy is needed at the metaphysical level: so that relatively contentless and secure theses (at the bottom of the empirical hierarchy) may be distinguished from more contentful and insecure theses (further up the hierarchy) to facilitate pinpointing what needs to be revised, and how, should the need for revision arise. That such a hierarchy exists at the empirical level provides some support for the claim that the hierarchy at the metaphysical level needs to be adopted.

AOE, as depicted in Figure 1, provides physics with a meta-methodology which facilitates improvement of the metaphysical assumptions, and associated methods, as physics advances, in the light of which seem to be the most fruitful empirically, and other considerations. As knowledge in physics improves, so metaphysical assumptions and methods improve as well or, in other words, knowledge about how to improve knowledge. There is something like positive feedback between improving knowledge of the universe, and improving aims and methods, improving knowledge about how to improve knowledge. Everyone would acknowledge that this kind of positive feedback goes on at the empirical level. New empirical knowledge can lead to new methods, via the development of new instruments, new experimental techniques, which in turn lead to further acquisition of new knowledge. AOE provides methods which facilitate such positive feedback at the metaphysical and theoretical level as well. As humanity increases its scientific knowledge and understanding of the universe, it increases its knowledge of how to increase knowledge – the very nub of scientific rationality which helps explain the explosive, and apparently ever accelerating, growth of scientific knowledge. Scientists adapt the nature of science to what they find out about the nature of the universe. All this has gone on in science to some extent implicitly: what the transition from orthodox empiricism to AOE does is to make the implicit explicit – science becoming more rigorous and even more successful as a result.

In providing grounds for accepting theses at levels 7 to 4, no attempt whatsoever is made to establish that these theses are true, or are likely to be true. Ultimately, all our scientific knowledge is conjectural in character, as Popper tirelessly stressed. Rather, reasons are given for accepting these theses granted that our concern is to improve knowledge of truth. As has been indicated above, level 7 is to be accepted because its acceptance can only help, and cannot in any circumstances harm, the pursuit of knowledge of truth. Level 6 is accepted because it may be able very substantially to help the pursuit of knowledge, and can scarcely harm this pursuit, if false. Theses lower down in the hierarchy are accepted on the grounds that (a) they comply with theses at levels 7 and 6; (b) they provide the best help, if true, of promoting empirical knowledge of truth; and (c) they have actually promoted empirical knowledge of truth better than any other rival hypothesis at that level.

Physicalism (8,1) satisfies these requirements better than any rival thesis at this level. Physicalism (8,1) holds out the hope of great empirical progress in that it tells us that as physicists capture the nature of U - the unchanging physical entity that runs through all phenomena - more and more accurately, so accepted physical theories will successfully predict wider and wider ranges of phenomena more and more accurately. It tells us that, as physics gets clearer about the nature of U, so the methods of physics are likely to improve - methods which specify what kind of theories need to be developed and accepted. But of far greater significance than the promise that physicalism (8,1) holds out for empirical progress, very strikingly all the great advances in theoretical knowledge and understanding in physics at least since Galileo' s time have all been in accordance with the empirical research programme that physicalism (8,1) indicates. All these successive theories draw closer to capturing physicalism (8,1) as a unified, falsifiable " theory of everything" .

All advances in theory in physics since the scientific revolution have been advances in unification, in the sense of (1) to (8) above. Thus Newtonian theory (NT) unifies Galileo' s laws of terrestrial motion and Kepler' s laws of planetary motion (and much else besides): this is unification in senses (1) to (3). Maxwellian classical electrodynamics, (CEM), unifies electricity, magnetism and light (plus radio, infrared, ultra violet, X and gamma rays): this is unification in sense (4). Special relativity (SR) brings greater unity to CEM, in revealing that the way one divides up the electromagnetic field into the electric and magnetic fields depends on one' s reference frame: this is unification in sense (6). SR is also a step towards unifying NT and CEM in that it transforms space and time so as to make CEM satisfy a basic principle fundamental to NT, namely the (restricted) principle of relativity. SR also brings about a unification of matter and energy, via the most famous equation of modern physics, E = mc2, and partially unifies space and time into Minkowskian space-time. General relativity (GR) unifies space-time and gravitation, in that, according to GR, gravitation is no more than an effect of the curvature of space-time – a step towards unification in sense (8). Quantum theory (QM) and atomic theory unify a mass of phenomena having to do with the structure and properties of matter, and the way matter interacts with light: this is unification in senses (4) and (5). Quantum electrodynamics unifies QM, CEM and SR. Quantum electroweak theory unifies (partially) electromagnetism and the weak force: this is (partial) unification in sense (7). Quantum chromodynamics brings unity to hadron physics (via quarks) and brings unity to the eight kinds of gluons of the strong force: this is unification in sense (6). The standard model (SM) unifies to a considerable extent all known phenomena associated with fundamental particles and the forces between them (apart from gravitation): partial unification in senses (4) to (7). The theory unifies to some extent its two component quantum field theories in that both are locally gauge invariant (the symmetry group being U(1)xSU(2)xSU(3)). All the current programmes to unify SM and GR known to me, including string theory or M-theory, seek to unify in senses (4) to (8).

In short, all advances in fundamental theory since Galileo have invariably brought greater unity to theoretical physics in one or other, or all, of senses (1) to (8): all successive theories have increasingly successfully exemplified and given precision to physicalism (8,1) to an extent which cannot be said of any rival metaphysical thesis, at that level of generality. The whole way theoretical physics has developed points towards physicalism (8,1), in other words, as the goal towards which physics has developed. Furthermore, what it means to say this is given precision by the account of theoretical unity given above.

It is this astonishing empirical progressiveness of the research programme to which physicalism (8,1) gives rise that justifies acceptance of this thesis, within the framework of AOE, in preference to any rival thesis at this level.

Physicalism(8,1) in effect determines, along with empirical considerations, what theories are accepted and rejected in physics. In order to be acceptable, a new theory must (a) be sufficiently empirically successful and (b) must, when added to the totality of current theory, have the consequence that that totality accords better with physicalism (8,1), in that its kind and degree of unity increases (n increases towards 8, and N decreases towards 1).

For a much more detailed argument for accepting physicalism as a part of current scientific knowledge - and for the argument that AOE provides us with the solution to the problem of induction - see Maxwell [6], [7], [8], [11], [16].

Two final points:

First, Thomas Kuhn and others have expressed doubts about whether anything theoretical persists through scientific revolutions. If science is viewed from the perspective of AOE, however, it is clear that much persists through theoretical revolutions in physics: namely, metaphysical theses at levels 4, 5, 6 and 7. Indeed as has been remarked elsewhere “Far from obliterating the idea that there is a persisting theoretical idea in physics, revolutions do just the opposite in that they all themselves actually exemplify the persisting idea of underlying unity!” [6].

Second, as many have noted, physics tends to advance from one false theory to another. Thus Galileo’s laws of terrestrial motion and Kepler’s laws of planetary motion are corrected by Newtonian theory, in turn corrected by general relativity. Classical physics is corrected by quantum theory, in turn corrected by quantum field theory. Philosophers of science, viewing this matter from an orthodox empiricist perspective, tend to regard the fact that physics advances from one false theory to another as having very negative implications for scientific progress. That physics will continue in this way has even been dubbed “the pessimistic induction” [32]. But viewed from the perspective of AOE, this manner of progression is actually to be expected, if physics really is making progress, and the universe really is physically comprehensible. For, if a theory, To, is precisely true throughout some restricted domain of phenomena D then, granted physicalism (8,1), To must specify precisely what does not change, U, throughout all phenomena in D, and the way U determines how things change in D. But, according to physicalism, U exists unchanged throughout all phenomena. Thus, if To specifies the nature of U in D, it will be a straightforward matter to extend To so that it specifies U for all physically possible phenomena, To thus becoming the true theory of everything, T. Conversely, if To cannot be extended in this way to apply correctly to all phenomena, then To cannot be precisely true within D: To must be false. In brief, physicalism (8,1) implies that a dynamical physical theory can only be precisely true of anything if it is (capable of being) precisely true of everything.

Granted, then, that physics proceeds, not by attaining T in one bound, but rather by developing a succession of theories that apply, with ever increasing accuracy, to ever wider ranges of phenomena until eventually a theory of everything is attained, it is inevitable, granted physicalism, that physics will progress by the development of theories that are all false throughout their domains of application until the ultimate, unified true theory of everything is attained (which will be precisely true about everything). Since physicalism predicts that physics will progress in this way, the fact that physics has so far thus progressed can only count in favour of physicalism (8,1): it cannot count against physicalism and AOE, as some have supposed: see [32] and [33].

4. Conclusions

Physicalism, despite being an untestable, metaphysical conjecture, is a key component of current scientific knowledge. In order to be acceptable, a new theory must be sufficiently empirically successful, and it must accord sufficiently well with physicalism (8,1) - that is, when added to other accepted fundamental physical theories, the totality of theory must have a kind of unity as near to n = 8 as possible, and its degree of unity must be as near to N = 1 as possible. Physicalism, here, is to be interpreted as asserting that the universe is such that the not yet discovered true physical theory of everything does exist, and is unified with n = 8 and N = 1. Physicalism is, however, only about a highly selected aspect of all that exists - that aspect which determines (perhaps probabilistically) how events evolve in time. Physicalism does not deny that the experiential exists - our whole human world of experience, consciousness, free will, meaning and value.

Conflicts of Interest

The author declares that there is no conflict of interest regarding the publication of this article.

Acknowledgments

The authors would like to acknowledge intellectual support and encouragement, over the years, from Leemon McHenry, Matthew Iredale, Agustin Vicente, Tim McGettigan, Peeter Müürsepp, Agnieszka Lekka-Kowalik, Michael Matthews, David Lorimer and Harald Walach.

Copyright

© 2017 by the authors. Licensee International Technology and Science Press Limited. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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