Uniformity and Variability:. The development of the science and engineering of materials in this century has many aspects which promise to enrich the conceptual reservoir of the philosopher of matter. In this essay I would like to explore a few of the philosophical issues raised by new developments in materials science, particularly the new awareness of the importance of studying the behaviour of matter in its full complexity. This awareness has, in turn, resulted in part from the creation and experimentation with materials which involve a heterogenous meshwork of components, such as fiberglass and other composites, as opposed to the simpler and more predictable behaviour of uniform, homogeneous materials such as industrial-quality steel.

Cyril Stanley Smith, a metallurgist and an expert in the history of materials, has explored the development of the philosophy of matter in the West, from the ancient Greeks to the present day, and has concluded that for the most part, the study of the complexity and variability of behaviour of materials has always been the concern of empirically oriented craftmen or engineers, not of philosophers or scientists. In his own words:

"Through most of history, matter has been a concern of metaphysics more than physics, and materials of neither. Classical physics at its best turned matter into mass, while chemistry discovered the atom and lost interest in properties...[In both metaphysical speculation and scientific research] sensitivity to the wonderful diversity of real materials was lost, at first because philosophical thought despised the senses, later because the . . . the new science could only deal with one thing at a time. It was atomistic, or at least, simplistic, in its very essence." {1}

This author claims that by the time Greek philosophers like Democritus or Aristotle developed their philosophies of matter, practically everything about the behaviour of metals and alloys that could be explored with pre-industrial technology, was already known to craftmen and blacksmiths. For at least a thousand years before philosophers began their speculations, this knowledge was developed on a purely empirical basis, through a direct interaction with the complex behaviour of materials. Indeed, the early philosophies of matter may have been derived from observation and conversation with those "whose eyes had seen and whose fingers had felt the intricacies of the behaviour of materials during thermal processing or as they were shaped by chipping, cutting or plastic deformation." {2} For instance, Aristotleis famous four elements, fire, earth, water and air, may be said to reflect a sensual awareness of what today we know as energy and the three main states of aggregation of matter, the solid, liquid and gas states.

As metaphysical speculation gave special meanings to these four elementary qualities, their original physical meaning was lost, and the variability and complexity of real materials was replaced with the uniform behaviour of a philosophically simplified matter about which one could only speculate symbolically. It is true that sixteen-century alchemists recovered a certain respect for a direct interaction with matter and energy, and that seventeen-century Cartesian philosophers intensely speculated about the variable properties of different ways of aggregating material components. But these early attempts at capturing the complexity of physical transmutations and of the effect of physical structure on the complex properties of materials, eventually lost to the emergent science of chemistry, and its almost total concentration on simple behaviour: that of individual components (such as Lavoisieris oxygen) or of substances that conform to the law of definite proportions (as in Daltonis atomic theory).

There was, as Cyril Stanley Smith observes, an "immense gain" in these simplifications, since the exact sciences could not have developed without them, but the triumph of chemistry was accompanied by a "not insignificant loss". In particular, the complete concentration of analysis at the level of molecules caused an almost total disregard for higher levels of aggregation in solids, but it is there where most complex properties of interest to todayis material scientist occurr. {3} As it is usual in the history of science, there were several exceptions. Galileo studied the strenght of materials in the sixteen-century, and in the seventeenth while Newton was reducing the variability of material behaviour to questions of mass, his arch-enemy Robert Hooke was developing the first theory of elasticity. As materials scientist James Edward Gordon has remarked, "unlike Newton, Hooke was intensely interested in what went on in kitchens, dockyards, and buildings -the mundane mechanical arenas of life...Nor did Hooke despised craftmen, and he probably got the inspiration for at least some of his ideas from his friend the great London clockmaker Thomas Tompion...". {4} Despite the imporatnt exceptions, I believe it is fair to say that, at least in England, much more prestige was attached to scientific fields that were not concerned with these mundane mechanical arenas where materials displayed their full complex behaviour. This may be one reason why conceptual advances in the study of materials, such as the key conceptual distinction between stress and strain (one refering to the forces acting on a material structure, the other to the behaviour of the structure in response to those forces), were made in France where applied science was encouraged both officially and socially. {5}

James Gordon has called the study of the strenght of materials the Cinderella of science, partly because much of the knowledge was developed by craftmen, metallurgists and engineers (that is the flow of ideas often ran from the applied to the pure fields), and partly because by its very nature, the study of materials involved an interaction between many scientific disciplines, an interdisciplinary approach which ran counter to the more prestigious tradition of "pure" specialization. {6} Today, of course, the interdisciplinary study of complexity, not only in materials but in many other areas of science, from physics and ecology to economics, is finally taking its place at the cutting-edge of scientific research. We are begining to understand that any complex system, whether composed of interacting molecules, organic creatures or economic agents, is capable of spontaneoulsy generating order and of actively organizing itself into new structures and forms. It is precisely this ability of matter and energy to self-organize that is of greatest significance to the philosopher. Let me illustrate this with an example from materials science.

Long ago, practical metallurgists understood that a given piece of metal can be made to change its behaviour, from ductile and tough to strong and brittle, by hammering it while cold. The opposite transmutation, from hard to ductile, could also be achieved by heating the piece of metal again and then allowing it to cool down slowly (that is, by annealing it). Yet, although blacksmiths knew empirically how to cause these metamorphoses, it was not until a few decades ago that scientists understood its actual microscopic mechanism. As it turns out, explaining the physical basis of ductility involved a radical conceptual change: scientists had to stop viewing metals in static terms, that is, as deriving their strenghth in a simple way from the chemical bonds between their composing atoms, and begin seeing them as dynamical systems. In particular, the real cause of brittleness in rigid materials, and the reason why ductile ones can resist being broken, has to do with the complex dynamics of spreading cracks.

A crack or fracture needs energy to spread through a piece of material and so any mechanism that takes away energy from the crack will make the material tough. In metals, the mechanism seems to be based on certain defects or imperfections within the component crystals called dislocations. Dislocations not only trap energy locally but moreover, are highly mobile and may be brought into existance in large quantities by the very concentrations of stress which tend to break a piece of material. Roughly, if populations of these line defects are free to move in a material they will endow it with the capacity to yield locally without breaking, that is, they will make the material tough. On the other hand, restricted movement of dislocations will result in a stronger but more brittle material. {7} Both of these properties may be desirable for different tools, and even within one and the same tool: in a sword or knife, for instance, the body must be tough while the cutting edge must be strong.

What matters from the philosophical point of view is precisely that toughness or strength are emergent properties of a metallic material that result from the complex dynamical behaviour of some of its components. An even deeper philosophical insight is related to the fact that the dynamics of populations of dislocations are very closely related to the population dynamics of very different entities, such as molecules in a rhythmic chemical reaction, termites in a nest-building colony, and perhaps even human agents in a market. In other words, despite the great difference in the nature and behaviour of the components, a given population of interacting entities will tend to display similar collective behaviour as long as there is some feedback in the interactions between components (that is, the interactions must be nonlinear) and as long as there is an intense enough flow of energy rushing through the system (that is, the population in question must operate far from thermodynamic equilibrium). As I will argue in a moment, the idea that many different material and energetic systems may have a common source of spontaneous order is now playing a key role in the development of a new philosophy of matter. But for materials scientists this commonality of behaviour is of direct practical significance since it means that as they begin to confront increasingly more complex material properties, they can make use of tools coming from nonlinear dynamics and nonequilibrium thermodynamics, tools that may have been developed to deal with completly different problems. In the words of one author:

". . . during the last years the whole field of materials science and related technologies has experienced a complete renewal. Effectively, by using techniques corresponding to strong nonequilibrium conditions, it is now possible to escape from the constraints of equilibrium thermodynamics and to process totally new material structures including different types of glasses, nano- and quasi-crystals, superlaticces . . . As materials with increased resistance to fatigue and fracture are sought for actual applications, a fundamental understanding of the collective behaviour of dislocations and point defects is highly desirable. Since the usual thermodynamic and mechanical concepts are not adapted to describe those situations, progress in this direction should be related to the explicit use of genuine nonequilibrium techniques, nonlinear dynamics and instability theory". {8}

Thus, to the extent that the self-organizing behaviour of populations of dislocations within ductile metals is basically similar to the spontaneous collective behaviour in other populations, tools and concepts developed in very different disciplines may apply across the board, and this may help legitimize the intrinsic interdisciplinary approach of materials science. As I just said, however, the common behaviour of different collectivities in nonlinear, nonequilibrium conditions is of even greater importance to the philosopher of matter. This is very clear in the philosophy of Gilles Deleuze and Felix Guattari who are perhaps the most radical contemporary representatives of this branch of philosophy. Inspired in part by some early versions of complexity theory (e.g. Rene Thomis catastrophe theory, and the theories of technology of Gilbert Simondon) these authors arrived at the idea that all structures, whether natural or social, are indeed different expressions of a single matter-energy behaving dynamically, that is, matter-energy in flux, to which they have given the name of "machinic phylum". In their words: ". . .the machinic phylum is materiality, natural or artificial, and both simultaneoulsy; it is matter in movement, in flux, in variation. . ." {9}

The term "phylum" is used in biology to refer to the common body-plan of many different creatures. Human beings, for example, belong to the phylum "chordata", as do all other vertebrate animals. The basic idea is that of a common source of form, a body-plan which through different foldings and stretchings during embryological development, is capable of generating a wide variety of specific forms, from snakes, to giraffes to humans. Deleuze and Guattari, aware that nonlinear population processes are common not only to animals and plants but to metals and other inorganic materials, have extended this meaning to refer to a common source of spontaneoulsy generated form across all material entities. I began this essay by quoting the opinion of a metallurgist, Cyril Stanley Smith, on the historical importance of sensually aquired knowledge about the complex behaviour of metals and other materials. And indeed, in Deleuze and Guattariis philosophy of matter, metallurgists play an important role:

". . . what metal and metallurgy bring to light is a life proper to matter, a vital state of matter as such, a material vitalism that doubtless exists everywhere but is ordinarly hidden or covered, rendered unrecognizable . . . Metallurgy is the consciousness or thought of the matter-flow, and metal the correlate of this consciousness. As expressed in panmetallism, metal is coextensive to the whole of matter, and the whole of matter to metallurgy. Even the waters, the grasses and varieties of wood, the animals are populated by salts or mineral elements. Not everything is metal, but metal is everywhere. . . The machinic phylum is metallurgical, or at least has a metallic head, as its itinerant probe-head or guidance device." {9}

One aspect of the definition of the machinic phylum is of special interest to our discussion of contemporary materials science. Not only is the phylum defined in dynamic terms (that is, as matter in motion) but also as "matter in continuous variation". Indeed, these philosophers define the term "machinic" precisely as the process through which structures can be created by bringing together heterogenous materials, that is, by articulating the diverse as such, without homogenization. In other words, the emphasis here is not only on the spontaneous generation of form, but on the fact that this morphogenetic potential is best expressed not by the simple and uniform behaviour of materials, but by their complex and variable behaviour. In this sense, contemporary industrial metals, such as mild steel, may not be the best illustration of this new philosophical conception of matter. While naturally ocurring metals contain all kinds of impurities that change their mechanical behaviour in different ways, steel and other industrial metals have undergone in the last two hundred years an intense process of uniformation and homogenization in both their chemical composition and their physical structure. The rationale behind this process was partly based on questions of reliability and quality control, but it had also a social component: both human workers and the materials they used needed to be disciplined and their behaviour made predictable. Only then the full efficiencies and economies of scale of mass production techniques could be realized. But this homogenization also affected the engineers that designed structures using this well disciplined materials. In the words of James E. Gordon:

"The widespread use of steel for so many purposes in the modern world is only partly due to technical causes. Steel, especially mild steel, might euphemistically be described as a material that facilitates the dilution of skills. . . Manufacturing processes can be broken down into many separate stages, each requiring a minimum of skill or intelligence. . . At a higher mental level, the design process becomes a good deal easier and more foolproof by the use of a ductile, isotropic, and practically uniform material with which there is already a great deal of accumulated experience. The design of many components, such as gear wheels, can be reduced to a routine that can be looked up in handbooks." {10}

Gordon sees in the spread of the use of steel in the late nineteen- and early twenty centuries, a double danger for the creativity of structural designers. The first danger is the idea that a single, universal material is good for all different kinds of structure, some of which may be supporting loads in compression, some in tension, some withstanding shear stresses and others torsional stresses. But as Gordon points out, given that the roles which a structure may play can be highly heterogenous, the repertoir of materials that a designer uses should reflect this complexity. On the other hand, he points out that, much as in the case of biological materials like bone, new designs may involve structures with properties that are in continuous variation, with some portions of the structure better able to deal with compression while others deal with tension. Intrinsically heterogenous materials, such as fiberglass and the newer hi-tech composites, afford designers this possibility. As Gordon says, "it is scarcely practicable to tabulate elaborate sets of "typical mechanical properties" for the new composites. In theory, the whole point of such materials is that, unlike metals, they do not have "typical properties, because the material is designed to suit not only each individual structure, but each place in that structure." {11}

I do not mean to imply that there are no legitimate roles to be played by homogenous materials with simple and predictable behaviour, such as bearing loads in compression. And similarly for the institutional and economic arrangements that were behind the quest for uniformity: the economies of scale achieved by routinizing production and some design tasks, were certainly very significant. As with the already mentioned homogenizations performed by scientists in their conceptions of matter, there were undoubtedly some gains. The question is, what got lost in the process. I can think of several things.

First, the nineteenth century process of transfering skills from the human worker to the machine, and the task of homogenizing metallic behaviour went hand in hand. As Cyril Stanley Smith remarks "The craftman can compensate for differences in the qualities of his material, for he can adjust the precise strength and pattern of application of his tools to the materialis local vagaries. Conversely, the constant motion of a machine requires constant materials." {12} If its is true as I said at the beggining of this essay that much of the knowledge about the complex behaviour of materials was developed outside science by empirically oriented individuals, the deskilling of craftmen that accompanied mechanization may be seen as involving a loss of at least part of that knowledge, since in many cases empirical know-how is stored in the form of skills.

Second, as I just said, not only the production process was routinized this way, so was to a lesser extent the design process. Many professionals who design load-bearing structures lost their ability to design with materials that are not isotropic, that is, that do not have identical properties in all directions. But it is precisely those abilities to deal with complex, continuously variable bahaviour that are now needed to design structures with the new composites. Hence, we may need to nurture again our ability to deal with variation as a creative force, and to think of structures that incorporate heterogenous elements as a challenge to be met by innovative design.

Third, the quest for uniformity in human and metallic behaviour went beyond the specific disciplinary devices used in assembly-line factories. Many other things became homogenized in the last few centuries. To give only two examples: the genetic materials of our farm animals and crops have become much more uniform, at first due to the spread of the "pedigree mystique", and later in this century, by the development and diffusion of miracle crops, like hybrid corn. Our linguistic materials also became more uniform as the meshworks of heterogenous dialects which existed in most countries began to yield to the spread of standard languages, through compulsory education systems and the effects mass media. As before, the question is not whether we achieved some efficiencies through genetic and linguisitic standarization. We did. The problem is that in the process we came to view heterogeneity and variation as something to be avoided, as something pathological to be cured or uprooted since it endangered the unity of the nation state.

Finally, as Deleuze and Guattari point out, the nineteen-century quest for uniformity may had had damaging effects for the philosophy of matter by making the machinic phylum effectively unrecognizable. As the behaviour of metals and other mineral materials became routine, and hence, unremarkable, philosophical attention became redirected to the more interesting behaviour of living creatures, as in early twenty-century forms of vitalism, and later on, to the behaviour of symbols, discourses and texts, in which any consideration of material or energetic factors was completly lost. Today, thanks in part to the new theories of self-organization that have revealed the potential complexity of behaviour of even the humbler forms of matter-energy, we are begining to recover a certain philosophical respect for the inherent morphogenetic potential of all materials. And we may now be in a position to think about the origin of form and structure, not as something imposed from the outside on an inert matter, not as a hierarchical command from above as in an assembly line, but as something that may come from within the materials, a form that we tease out of those materials as we allow them to have their say in the structures we create.

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