MATTER

The term "matter" and its cognates ("material," "materialist," "materialistic," and the like) have played active parts in philosophical debate throughout intellectual history. Natural philosophers have studied material objects and contrasted them with such immaterial agencies as energy and fields of force; metaphysicians and mathematical philosophers have distinguished the material or tangible aspects of things from their formal or intangible aspects, their physical properties from their geometrical ones. Again, the terms "matter" and "material" have played a humble part not only in science but also in moral philosophy and even theology. Matter has thus been placed in opposition to life and mind, soul and spirit, and a preoccupation with worldly pleasures and bodily comforts, as opposed to the "higher" pleasures of the mind, has been condemned as "materialistic" and unworthy of spiritual beings. In thinking about matter, accordingly, the question of how far—if at all—these various distinctions can actually be justified and reconciled must always be borne in mind.

This question immediately poses a historical problem, for ideas about matter have not been static. On the contrary, they have been subject to continual development, and it is highly doubtful whether one can isolate a single concept of matter shared by, say, Anaximander and Thomas Aquinas, Democritus and René Descartes, Epicurus and Albert Einstein. Thus, for instance, a seventeenth-century philosophical thesis about the relations between mind and matter must be interpreted in relation to seventeenth-century ideas about physics and chemistry. Such a thesis can be transplanted into the intellectual environment of the twentieth century only by taking into account changes in the fundamental concepts of science during the intervening years. We must therefore consider how the concept of matter has been progressively refined and modified in the course of intellectual history.

Greek Philosophy

As far as we can judge from the surviving texts and the testimony of Aristotle, the idea of a constituent or material ingredient (hyle ) common to things of all kinds was a central concept of the Ionian school of philosophy. The Ionian philosophers, beginning with Thales of Miletus, disagreed about the nature of this common ingredient. Some likened it to water, others to air or breath, others to fire; some insisted that it could have no properties analogous to those of any familiar substance but must be entirely undifferentiated or unlimited. Yet they agreed, at any rate, in their statement of the basic philosophical problem: "What universal, permanent substance underlies the variety and change of the physical world?"

It would be a mistake, however, to think of the Ionians as materialists in the modern sense. As they conceived it, the universal material of things was far from being brute, inorganic, passive, mindless stuff intrinsically devoid of all higher properties or capabilities. Water, for instance, was, for them, not a sterile, inorganic chemical but a fertilizing fluid, and in their system it was quite open to consideration whether the basic stuff of the world might not be provided by either spirit (pneuma) or mind (nous). At this initial stage in philosophical speculation, indeed, the questions preoccupying philosophers cut across many of the distinctions that later generations were to treat as fundamental.

We first find these distinctions being drawn explicitly and insisted on by the Athenian philosophers, following the examples of Plato and Aristotle. For instance, Plato and his fellow mathematicians at the Academy explained the properties of homogeneous material substances in one way, those of organized, functional systems in another. Like the Sicilian philosopher Empedocles, they classified material substances into four contrasted states or kinds—solid (earth), aeriform (air), liquid (water), and fiery (fire)—but they added a novel mathematical theory to account for the contrasted properties of these four kinds of substance. Each kind, they supposed, had atoms of a distinct geometrical shape, and they hypothetically identified these shapes with four of the five regular convex solids—tetrahedron, cube, octahedron, and icosahedron—whose mathematical properties had been studied by Plato's associate Theaetetus. (The fifth solid, the dodecahedron, they associated with the twelve constellations of the outer heavens.) The characteristic properties of organisms, on the other hand, they explained in functional rather than material terms. The form of any bodily organ must be accounted for as reflecting its role in the life of the organism; this form should be thought of as created specifically to perform a particular function as effectively as the available materials permitted.

Aristotle went further. He distinguished sharply between the material substance of which an object was composed and the form imposed on it, and he questioned whether the characteristic properties of any substance or system could be usefully explained in either atomistic or geometrical terms. In order to understand the properties and behavior of any individual object, it was first necessary to recognize it as an object of a particular kind. Each kind of object existing in nature had properties determined by its own special form or essence, so that any universal primary stuff (hyle ) must be devoid of any particular distinguishing characteristic. For Aristotle and his followers the problem of distinguishing substances became primarily a matter of taxonomy, of qualitative classification, rather than a quantitative, physicochemical problem. Weight, from this point of view, was just one possible quality among others. Aristotle's views went beyond those of Plato in one other respect that was to have profound implications for cosmology. He drew a clear distinction between the sublunary world, whose objects were composed of the four terrestrial elements—earth, air, fire, and water—and could be created and destroyed, and the superlunary or celestial world of the outer heavens, whose inhabitants were composed of the quintessence (fifth essence) and exempted from change and decay. Of all terrestrial things only the souls of rational beings in any way shared this immutability.

Later Classical and Medieval Periods

Subsequent philosophers—whether in Hellenistic Alexandria (200 BCE–550 CE), the Islamic centers of learning (650–1150), or the newly founded universities of western Europe (950–1500)—introduced a number of variations into the debate about matter without adding any fundamentally new themes. For both the Stoics and the Epicureans, ideas about matter were closely associated with religious beliefs. Epicurus and his followers—notably, the Roman poet Lucretius—developed the more fragmentary speculations of Democritus and Leucippus about the atomic structure of matter into a complete philosophical system. But the atoms of the Greek philosophers differed from those of nineteenth-century European science in three crucial respects. First, they had an indefinitely large range of sizes and shapes instead of a limited number of fixed forms, one for each chemical "element." Next, they interacted only by direct contact or impact rather than by exerting forces of attraction or repulsion on one another. And, finally, they existed in special varieties—atoms of magnetism, of life, of mind, and of soul—to explain all sorts of activities—physical, biological, psychological, and even spiritual. The collisions and conjunctions of these atoms were regarded by Epicurus as an autonomous physical process, for his fundamental aim was to attack any belief in external interference by divine agencies in the affairs of the natural world.

The Stoics, such as Zeno of Citium and Chrysippus, rejected atoms in favor of three kinds of continuous physical medium or spirit (pneuma) for both scientific and religious purposes. The pneuma was an integrative agency, analogous to a field of force, capable of maintaining a stable pattern of properties and behavior in a physical system; in addition, it was capable of existing in separation from the solid and liquid frame of the "body" and could probably be identified with the soul. Instead of rejecting the traditional deities, like the Epicureans, the Stoics reinterpreted them as incorporeal agencies comparable to the pneuma. Yet though the Stoics and the Epicureans differed about many things, they agreed that every agency capable of producing physical effects—even the mind—must be regarded as a material body (soma). As a result for Lucretius pure mind was composed of very smooth and mobile atoms; for Chrysippus it consisted of undiluted fire.

The alchemical philosophers, for their part, introduced an experimental element into the study of matter. Beginning with the Democritean Bolos of Mendes (c. 200 BCE), going on through Maria the Jewess and Zozimos of Alexandria (second and third centuries CE), the alchemists exploited the traditional craft techniques of the Middle Eastern metallurgists, dyers, and jewelers and attempted to find ways of separating and isolating the essences or spirits in things. In this way they were led to contrast volatile and chemically active substances, such as alcohol and ether (spirits), with solid and passive ones, such as earths and calces (bodies). The association of the soul and the body in living creatures was thus treated as analogous to the association of volatile and gaseous with solid and earthy substances in a chemical compound. When freed from this association, incorporeal spirits naturally tended to rise toward the heavens and corporeal bodies to sink to the earth, a fact that apparently harmonized with the traditional Aristotelian contrast between the celestial and terrestrial worlds.

Nevertheless, philosophers and theologians in the strictly orthodox Aristotelian tradition rejected Stoic, Epicurean, and alchemical ideas as being excessively materialistic. In their view the soul was not in any way a subject for chemical or quasi-chemical speculation. The forms or essences of things were not themselves composed of any material stuff, even of the highly tenuous kinds conceived by the Stoics and alchemists. Accordingly, for Thomas Aquinas and the other philosophers of the high Middle Ages, the relation between matter and form was a problem in metaphysics or theology rather than one in natural philosophy.

New Theories: 1550–1750

Thus, the revival of the physical sciences during the Renaissance started from a position in which no single doctrine about the nature of matter was clearly established and generally accepted. All supporters of the new mechanical philosophy were attracted to an atomistic or corpuscular view of matter, but most of them took care to dissociate themselves from the original atomistic doctrines of Democritus and Epicurus, which were still suspected of having atheistical implications. Thus, Johannes Kepler explained the crystalline structure of snowflakes by reference to a geometrical theory of atoms modeled on that of Plato, Galileo Galilei embraced atomism as a physical embodiment for the points of geometry, and Descartes treated all matter as corpuscular in structure, at the same time denying the theoretical possibility of a void or vacuum. All of them regarded such mechanical interactions as collisions as the basic model for physical processes and sought to build up a theory of forces (dynamics) capable of explaining the established generalizations about the motions of physical objects.

However, attempts to work out an effective and comprehensive system of physical theory without going beyond the categories of atomism inherited from the Greeks encountered a number of difficulties. These sprang ultimately from the dual axiom that any agency capable of producing physical effects must be composed of a corresponding type of material object and that these objects could influence one another only by direct mechanical action, which required that the bodies be in contact. To deny the first half of this axiom implied accepting the notion of nonmaterial physical agencies; to deny the second implied accepting action at a distance. Both these notions were widely rejected as being incompatible with sound natural philosophy.

The immediate outcome of this dual axiom was to commit the advocates of the new mechanical corpuscular philosophy to a proliferation of new kinds of atom—for instance, magnetic, calorific, and frigorific corpuscles—introduced to account for the corresponding physical phenomena of magnetism, heat, cold, and so on. Although some philosophers, including Descartes, saw the possibility of cutting down the types of atoms—for example, by explaining heat as a consequence of the internal agitation of the material atoms composing hot bodies—even Descartes felt bound to accept that light, magnetism, and the like were carried by subtle fluids made up of corpuscles of insensible weight. Matter, he declared, came in three kinds, of which only "third matter" was subject to gravity and thus had any weight.

An indirect but even more profound outcome of the corpuscularian axiom was to support Descartes's fundamental division between mind and matter as absolutely distinct substances. The least plausible element in traditional atomism had been its psychology. Christian theology had added its own objections to any explanation of mental activity that regarded the mind as composed of atoms, no matter how light or mobile, for this, it was generally agreed, came perilously close to denying the immortality of the soul. The new physical science of the seventeenth and eighteenth centuries accordingly limited its aim. The realm of nature consisted of material bodies interacting mechanically by contact and impact and could be studied by science. The realm of spirit—including, at least, the intellectual activities of human beings—was a distinct and separate object of speculation to which the categories of physical science were not directly relevant. Much of the debate in subsequent epistemology can be traced to this point.

Accordingly, for two hundred years beginning around 1700, the concept of matter kept a central place in physical theory but was set aside as irrelevant to the study of mind. In physics the first major break with traditional ideas came through the work of Sir Isaac Newton. By his theories of dynamics and gravitation, Newton established a sharp distinction between material objects in a strict sense, whose mass conferred on them both inertia and weight, and forces, which were a measure of the way in which material objects interacted rather than a special kind of material thing. In the case of gravity, as he showed in his Philosophiae Naturalis Principia Mathematica (1687), these forces had to be supposed capable of acting over distances of many million miles, though Newton himself was inclined to believe that some invisible mechanical link existed by which the sun, for instance, exerted its gravitational action on the planets. In the later editions of his Opticks (especially those published after Gottfried Wilhelm Leibniz's death in 1716) he extended this idea to explain other physical phenomena. Electrical, magnetic, and chemical action also, he argued, might prove to be manifestations of forces of attraction and repulsion acting across the spaces between the massive corpuscles of bodies. Thus, the traditional system of atoms and the void was amended to become a theory of material corpuscles interacting by centrally directed forces.

Classical Physics

Newton's program for natural philosophy made its way only slowly to begin with, but it met with no grave check until the late nineteenth century. At first, his insistence on mass as the essential property of matter was not found universally convincing. Others continued to regard extension, impenetrability, weight, or the capacity to produce physical effects as the indispensable criterion. As a result, throughout the eighteenth century there was an element of cross-purposes in debates about the corporeal nature of, for example, light and fire. Two developments particularly helped to clarify the intellectual situation and established the Newtonian categories as the basis of physical science. First, Antoine Lavoisier and his followers—notably, John Dalton—demonstrated that the phenomena of chemistry as well as those of physics could be unraveled on the assumption that all genuine material substances possessed mass and were composed of corpuscles or atoms. Second, the mathematical work of Leonhard Euler and his successors transformed Newton's account of forces of attraction and repulsion into the modern theory of fields of force.

After 1800, then, physical scientists went ahead rapidly with the experimental and mathematical work that culminated in the so-called classical physics and chemistry of the late nineteenth century. In this system the agents responsible for physical action were divided into two sharply contrasted categories. On the one hand, there was matter; this consisted of massive atoms that combined to form molecules in accordance with the principles of chemical combination. The mechanical energy associated with the motion of the molecules within any body accounted for its temperature; the fields of force between them explained gravitational, electric, and magnetic attraction and repulsion. On the other hand, there were those agencies—such as light and radiant heat—that apparently lacked both mass and weight and that were transmitted in the form of waves across the empty space between the material atoms. Gravitation apart, these various agencies turned out, as was shown by James Clerk Maxwell's electromagnetic theory of light, to be all of one general kind. By combining the established theories of the electrical and magnetic fields of force into a single mathematical system having the same degree of generality as Newton's dynamics, Maxwell demonstrated that electromagnetic waves would share the known properties of light and radiant heat and would move across space with the same velocity that had actually been measured in the case of light. This interpretation gained greatly in strength when Heinrich Hertz used an intermittent electrical spark to produce artificial electromagnetic waves, the so-called radio waves.

Though devoid of mass, these various forms of radiation nevertheless carried energy. Numerically, the sum total of all forms of energy in any isolated system (like the sum total of the masses of all the material bodies involved) was apparently conserved unchanged throughout all physical and chemical changes. As a result it seemed for several decades that the whole of natural philosophy could successfully be built on the central distinction between matter and energy and on the two independent axioms of the conservation of mass and the conservation of energy. Thus, Newton's program for physical science came close to being finally fulfilled in classical physics and chemistry.

Twentieth-Century Reconsiderations

This intellectual equilibrium was short-lived. As Sir John Squire put it:

Nature and all her Laws lay hid in Night.
God said "Let Newton be, and all was Light."

It could not last. The Devil, shouting "Ho!
Let Einstein be," restored the status quo.

To do Einstein justice, the difficulties in the classical system that he resolved had been considered residual embarrassments for some time, and many of the conceptual changes for which he argued have since established themselves as indispensable features of physical theory. Still, they did undoubtedly have the effect of blurring the sharp distinctions and tidy certitudes of nineteenth-century science.

The effect of these conceptual changes on our concept of matter has been profound. Physicists have been compelled to reconsider and modify all the fundamental planks in the program enunciated for natural science by the mechanical philosophers of the seventeenth century. To begin with, Einstein displaced the seventeenth-century model of mechanical action as the universal pattern for intelligible physical processes by a new model based on electromagnetic theory. The embarrassments facing physicists in the 1890s arose, he showed, from a mathematical conflict between Maxwell's theory of electromagnetism and the mechanics of Galileo and Newton. Einstein circumvented these difficulties in his theory of relativity by giving priority to the theory of electromagnetic fields and by amending the principles of Newtonian mechanics to conform to the Maxwellian pattern. As a result the attitudes of a representative late nineteenth-century physicist, such as William Thomson, Lord Kelvin (who declined to accept Maxwell's theories, declaring that he could embrace a physical explanation of a phenomenon wholeheartedly only if he could make a mechanical model to demonstrate it), have since come to seem excessively narrow.

As a result of this initial change, however, certain other fundamental elements in classical physics have had to be called in question. The absolute distinction between matter and energy, for instance, has gone by the board. It now appears that any quantity of energy (E ) is in certain respects equivalent to a proportional quantity of mass (m = E/c ², where c is Maxwell's constant, equal to the measured velocity of electromagnetic radiation); that for theoretical purposes the twin conservation principles of nineteenth-century physics and chemistry should be joined in a single axiom, according to which the sum total of energy and mass (combined according to the formula E + mc ²) was conserved in all physical processes; and that in appropriate circumstances a quantity of electromagnetic energy can be transformed into the corresponding quantity of matter or vice versa. This implication was confirmed in the 1930s from a detailed study of individual actions between atomic nuclei and other particles, and it was dramatically reinforced by the explosion of the first atomic bombs, whose energy was derived from the marginal loss of mass involved in the nuclear fission of such heavy elements as uranium.

Meanwhile, the earlier contrast between matter, which was assumed to exist in discrete atomic units, and radiation, which traveled in the form of continuous waves, was under criticism for quite different reasons. First, Max Planck showed that bodies exchanged light-energy in the form of bundles or wave-packets. Einstein, going further, argued that electromagnetic energy always existed in the form of these photons. Then, in the early 1920s, Louis de Broglie put forward the idea that the subatomic particles into which Niels Bohr and Ernest Rutherford had analyzed the fundamental material units of earlier chemistry might themselves manifest some of the properties of wave-packets. This was confirmed in 1927, when it was shown that a beam of electrons passed through a crystal lattice produced a diffraction pattern just as a beam of light of the corresponding wavelength and velocity would have done. By the 1960s it began to appear that matter-particles might differ from the energy-packets of light or other kinds of radiation only in having part of their energy frozen in the form of inertial mass.

Finally, the theory of quantum mechanics, first formulated between 1926 and 1932 by Werner Heisenberg, Erwin Schrödinger, and P. A. M. Dirac, has radically undercut one last presupposition, which had underlain physical science since the time of Galileo. From 1600 on, the fundamental units of matter—whether called corpuscles, particles, or atoms—had been regarded as intrinsically brute, inert, and passive. They might be constituted in such a way that they are capable of exerting forces on one another by virtue of their relative motions and positions, but one had to seek the ultimate source of this capacity—as of their motion—in God who created them. (This was one point on which Newton, Descartes, and Maxwell all agreed.) Since 1926 the final unit of analysis in physics has ceased to bear any serious resemblance to these inert corpuscles. Instead, the quantum physicists begin with certain wave functions or eigenfunctions, which characterize the activity of, say, an electron or an atom as much as they do its structure and position. Just as mass has ceased to be entirely distinct from energy, so the particles of Newton's physics have ceased to be absolutely distinct from the forces of attraction and repulsion acting between them. On the contrary, according to the principles of contemporary physical theory, every kind of fundamental particle—whether of matter or energy—should be associated with a corresponding mode of interaction and force field. Photons, electrons, mesons, nucleons—all these have a dual aspect, being characterized partly by their inertial mass or intrinsic energy and partly by their pattern of interaction with the environment. One outstanding and at present unsettled question is whether the transmission of gravitational forces, from which the whole notion of a field began, also involves the propagation of particles ("gravitons") at a finite speed. If it proves that "gravitons" do in fact exist and travel at the same speed as photons, this will tie up one of the more notorious loose ends of mid-twentieth-century physics.

Implications of New Theories

Today almost all the axioms of earlier natural philosophy have been qualified, if not abandoned. Mass has ceased to be the essential, unalterable characteristic of all physical objects and now appears to be one variant of the wider category of energy. No longer can any determinate amount of this energy be localized with absolute precision (Heisenberg's principle), and we are left with a picture of a natural world whose fundamental elements are not so much passive bricks as units of activity. This transformation—as Samuel Sambursky has argued—involves a reaction against the axioms of seventeenth-century physics as radical as the Stoics' rejection of the atomism of Epicurus. Indeed, Sambursky points out, there is a strong parallel between the two reactions. As in the Stoic theory, physicists today also consider matter essentially active rather than passive and explain its behavior as the outcome of patterns of energy and excitation associated with any given state or condition.

The full implications of this change for our other ideas are beginning to become apparent only now. In biology, at any rate, a considerable change has come about since 1950 by the extension of physical theories about molecular structure into the fields of genetics, embryology, and bacteriology. Here the intimate association of structure and function characteristic of modern subatomic theory is reproduced in the association of specific biological activities with particular configurations (and, thus, eigenfunctions) of the complex molecules involved. The extensions of the new ideas about matter into the theory of organic development and human behavior are still at a speculative stage.

This much can, however, be said. During the centuries that have elapsed since the revival of natural philosophy at the Renaissance, the concept of matter has changed its character quite fundamentally. In the present state of scientific thought, accordingly, all earlier questions about, for instance, the relation of matter, life, and mind need to be entirely reconsidered. When, for instance, Descartes classified matter and mind as distinct substances, he was putting the concept of mind and mental activities in opposition to a concept of matter as inert extension, a concept that is now discredited. To that extent the extreme dualism of Descartes's philosophy has been not so much refuted by later science as made irrelevant; its categories no longer fit our situation.

Similarly, other long-standing debates concerning, for example, the reality of the material world or the relation between material objects and our sensations will need to be reappraised in the light of changes in our concept of matter. But this is a task for the future.

See also Anaximander; Aristotle; Atomism; Bohr, Niels; Chrysippus; Descartes, René; Dynamism; Empedocles; Energy; Epicurus; Einstein, Albert; Ether; Galileo Galilei; Heisenberg, Werner; Hertz, Heinrich Rudolf; Kepler, Johannes; Lavoisier, Antoine; Leucippus and Democritus; Mass; Maxwell, James Clerk; Newton, Isaac; Plato; Renaissance; Schrödinger, Erwin; Thales of Miletus; Thomas Aquinas, St.; Zeno of Citium.

Bibliography

In general, this article follows the argument of Stephen Toulmin and June Goodfield, The Architecture of Matter (London: Harper and Row, 1962), in which the development of the concept of matter is fully analyzed but discussed without serious technicalities. For the various periods covered here the reader is referred to the following works.

greek philosophy

S. Sambursky, The Physical World of the Greeks (London: Routledge and Paul, 1956), is an outstanding survey for the general reader. W. K. C. Guthrie, A History of Greek Philosophy, Vol. 1 (Cambridge, U.K.: Cambridge University Press, 1962), and G. S. Kirk and J. E. Raven, The Presocratic Philosophers (Cambridge, U.K.: Cambridge University Press, 1957), are up-to-date scholarly discussions of the Ionian natural philosophers. F. M. Cornford, Plato's Cosmology (London: K. Paul, Trench, Trubner, 1937), is the most convenient existing version of the Timaeus, in which Plato's views about matter are expounded. J. H. Randall Jr., Aristotle (New York: Columbia University Press, 1960), provides an illuminating account of that philosopher's scientific ideas; it is useful for the nonspecialist.

later classical and medieval period

S. Sambursky's The Physics of the Stoics (London: Routledge and Paul, 1959) and The Physical World of Late Antiquity (London, 1962) complete the story begun in his Physical World of the Greeks (see above). Cyril Bailey, The Greek Atomists and Epicurus (Oxford, 1928), and A. J. Hopkins, Alchemy, Child of Greek Philosophy (New York: Columbia University Press, 1934), are scholarly but readable: Both books remain stimulating and full of interest. E. J. Holmyard, Alchemy (London, 1957), and A. C. Crombie, Medieval and Early Modern Science (Garden City, NY: Doubleday, 1959), are readable popular surveys.

new theories: 1550–1750

H. T. Pledge, Science since 1500 (London: H. M. Stationery Office, 1939; reprinted, New York: Harper, 1959), and A. R. Hall, From Galileo to Newton (London, 1963), are general histories, both of which include useful material on the new theories. Mary B. Hesse, Forces and Fields (Edinburgh, 1961); Marie Boas, Robert Boyle and Seventeenth Century Chemistry (Cambridge, U.K.: Cambridge University Press, 1958); Hélène Metzger, Les doctrines chimiques (Paris, 1923) and Newton, Stahl, Boerhaave (Paris: F. Alcan, 1930); I. Bernard Cohen. Franklin and Newton (Philadelphia: American Philosophical Society, 1956); and E. J. Dijksterhuis, The Mechanization of the World Picture, translated by C. Dikshoorn (Oxford: Clarendon Press, 1961), are scholarly books dealing in a penetrating way with more detailed aspects of the subject.

classical physics

Edmund Whittaker, History of the Theories of Aether and Electricity, 2 vols. (Edinburgh, 1951–1953), and Mary B. Hesse, Forces and Fields (see above), are the best specialist surveys. For the general reader Charles C. Gillispie, The Edge of Objectivity (Princeton, NJ: Princeton University Press, 1960), N. R. Campbell, What Is Science? (London: Methuen, 1921; reprinted, New York: Dover, 1952), Albert Einstein and Leopold Infeld, The Evolution of Physics (New York: Simon and Schuster, 1938), and George Gamow, Biography of Physics (New York, 1963), may be selected from many others as being particularly useful.

twentieth-century reconsiderations

A great many books of general interest have been published about the twentieth-century transformation in physical theory. Apart from Einstein and Infeld, op. cit., and Gamow, op. cit., one of especial merit is Banesh Hoffmann, The Strange Story of the Quantum (New York: Harper, 1947). Many of the physicists directly involved have written interestingly about the changes—notably, Werner Heisenberg, Philosophical Problems of Nuclear Science (London: Faber, 1952). The analogy between Stoic matter theory and wave mechanics is pursued in Sambursky, The Physics of the Stoics (see above).

Stephen E. Toulmin (1967)

Matter

Matter is anything that takes up space and has mass (or weight which is the influence of gravity on mass.) It is distinguished from energy, which causes objects to move or change, but which has no volume or mass of its own. Matter and energy interact, and under certain circumstances behave similarly, but for the most part remain separate phenomena. They are, however, inter-convertible according to Einstein’s equation E=mc², where E is the amount of energy that is equivalent to an amount of mass m, and c is a constant: the speed of light in a vacuum. Thus, modern physics states that matter can be converted to energy and energy converted to matter. Classical physics and the other sciences, however, continue to distinguish between the two concepts for their own purposes. How science got to this point with respect to the definition of matter is a story in itself.

In ancient Greece, some philosophers, most notably Heraclitus (c.535–c.475 BC), believed that everything in the world was in a state of fluctuation. Others argued that there must be some permanence, otherwise it would not be possible to see anything as being real.

The fifth century Greeks were apparently the first to attribute structure to matter. They postulated that matter consisted of very small particles that were firmly bound together in the solid state, but which could change position to accommodate compression and deformation. At higher temperatures, these particles were thought to slide past each other and to eventually separate as the material object underwent melting and evaporation. The Greeks called these particles atoms, Greek for indivisible. This philosophical position offered a reconciliation between the views of a world in fluctuation and one that is permanent.

In 1687, English physicist and mathematician Sir Isaac Newton (1642–1727) published his Principia, in which he described his laws of motion. As had his Greek predecessors, Newton viewed matter as passive and inert, and as consisting of “solid, massy, impenetrable, movable particles.” Thus, for Newton and his contemporaries, there was little distinction between the properties of matter in the material world and the building blocks of which it was composed.

In 1785, French chemist Antoine Laurent Lavoisier (1743–1794) proposed his Law of Conservation of Matter, which states that matter can neither be created nor destroyed, only changed into different forms. This law has since been superseded by the Law of Conservation of Mass and Energy, which takes into account the observations of Einstein that mass and energy are interchangeable under certain conditions.

In 1804, the English scientist John Dalton formulated the atomic theory, which set out some fundamental characteristics of matter, and which is still used today. According to this theory, matter is composed of extremely small particles called atoms, which can be neither created nor destroyed. Atoms can, however, attach themselves (bond) to each other in various arrangements to form molecules. A material composed entirely of atoms of one type is an element, and different elements are made of different atoms. A material composed entirely of molecules of one type is a compound, and different compounds are made of different molecules. Pure elements and pure compounds are often referred to collectively as pure substances, as opposed to a mixture in which atoms or molecules of more than one type are jumbled together in no particular arrangement.

Elements and compounds can undergo chemical processes (reactions), which rearrange, break, or form bonds between atoms. Substances can also change by physical processes, which may alter the observable characteristics of the substance, but do not rearrange the internal structures of any molecules. The chemical compound water, for example, can be split into the element hydrogen and oxygen by electricity. That is a chemical reaction, because bonds in the water molecules break, and new bonds form. Water can also freeze into ice, or boil into vapor. Those are both physical processes because the water molecules do not change their internal bonding.

In the case of ordinary chemical transformations, the mass of the products always equals the mass of the reactants. If, for example, three oxygen (O₂) molecules (six atoms in total) go into a reaction, then six oxygen atoms must be found somewhere in the product. Thus, matter is neither created nor destroyed, but only transformed. By careful measurement of the mass of reactants before a reaction and the mass of the products after, chemists were able to devise the law of definite proportions and the notion that matter is conserved.

At the Earth’s surface, matter exists in one of three physical states (or phases)—solid, liquid, or gas—categorized by the extent of attraction between the molecules or atoms of the substance. (Other intermediate states are possible under more extreme conditions.) Solids have a very orderly, rigid arrangement of their atoms or molecules, with strong forces holding the atoms or molecules together. Gas molecules or atoms, on the other hand, have almost no intermolecular forces holding them together. Liquids have intermediate properties; their molecules or atoms have some attractive force for each other, but are not fixed in place like those of a solid.

Even though matter seems to be an easy concept to understand and an easier concept to define, there is nothing simple about matter. Although empty space (space devoid of matter) is often loosely talked about, there is really nothing in the universe that scientists consider empty space. Light from distant stars and gravitational fields from stars, planets, and galaxies permeate the far reaches of the universe. Ultimately, all of these things relate back to matter.

See also Element, chemical.

mat·ter / ˈmatər/ • n. 1. physical substance in general, as distinct from mind and spirit; (in physics) that which occupies space and possesses rest mass, esp. as distinct from energy: the structure and properties of matter. ∎  a substance or material: organic matter vegetable matter. ∎  a substance in or discharged from the body: fecal matter waste matter. ∎  written or printed material: reading matter.2. an affair or situation under consideration; a topic: a great deal of work was done on this matter financial matters. ∎  Law something that is to be tried or proved in court; a case. ∎  (matters) the present situation or state of affairs: we can do nothing to change matters. ∎  (a matter for/of) something that evokes a specified feeling: it's a matter of complete indifference to me. ∎  (a matter for) something that is the concern of a specified person or agency: the evidence is a matter for the courts.3. (the matter) the reason for distress or a problem: what's the matter? pretend that nothing's the matter.4. the substance or content of a text as distinct from its manner or form. ∎  Printing the body of a printed work, as distinct from titles, headings, etc. ∎  Logic the particular content of a proposition, as distinct from its form.• v. [intr.] 1. be of importance; have significance: it doesn't matter what the guests wear what did it matter to them? to him, animals mattered more than human beings. ∎  (of a person) be important or influential: she was trying to get known by the people who matter.2. rare (of a wound) secrete or discharge pus.PHRASES: for that matter used to indicate that a subject or category, though mentioned second, is as relevant or important as the first: I am not sure what value it adds to determining public, or for that matter private, policy.in the matter of as regards: the British are given preeminence in the matter of tea.it is only a matter of time there will not be long to wait: it's only a matter of time before the general is removed.a matter of1. no more than (a specified period of time): they were shown the door in a matter of minutes.2. a thing that involves or depends on: it's a matter of working out how to get something done.a matter of course the natural or expected thing: the reports are published as a matter of course.a matter of form a point of correct procedure: they must as a matter of proper form check to see that there is no tax liability.a matter of record see record.no matter1. regardless of: no matter what the government calls them, they are cuts.2. it is of no importance: “No matter, I'll go myself.”to make matters worse with the result that a bad situation is made worse.

Matter

Matter is anything that takes up space and has mass (or weight which is the influence of gravity on mass.) It is distinguished from energy , which causes objects to move or change, but which has no volume or mass of its own. Matter and energy interact, and under certain circumstances behave similarly, but for the most part remain separate phenomena. They are, however, inter-convertible according to Einstein's equation E=mc2, where E is the amount of energy that is equivalent to an amount of mass m, and c is a constant: the speed of light in a vacuum .

In 1804, the English scientist John Dalton formulated the atomic theory , which set out some fundamental characteristics of matter, and which is still used today. According to this theory, matter is composed of extremely small particles called atoms , which can be neither created nor destroyed. Atoms can, however, attach themselves (bond) to each other in various arrangements to form molecules. A material composed entirely of atoms of one type is an element, and different elements are made of different atoms. A material composed entirely of molecules of one type is a compound, and different compounds are made of different molecules. Pure elements and pure compounds are often referred to collectively as pure substances, as opposed to a mixture in which atoms or molecules of more than one type are jumbled together in no particular arrangement.

Elements and compounds can undergo chemical processes (reactions), which rearrange, break, or form bonds between atoms. Substances can also change by physical processes, which may alter the observable characteristics of the substance, but do not rearrange the internal structures of any molecules. The chemical compound water , for example, can be split into the element hydrogen and oxygen by electricity . That is a chemical reaction, because bonds in the water molecules break, and new bonds form. Water can also freeze into ice , or boil into vapor. Those are both physical processes because the water molecules do not change their internal bonding.

At Earth 's surface, matter exists in one of three physical states (or phases)—solid, liquid, or gas—categorized by the extent of attraction between the molecules or atoms of the substance. (Other intermediate states are possible under more extreme conditions.) Solids have a very orderly, rigid arrangement of their atoms or molecules, with strong forces holding the atoms or molecules together. Gas molecules or atoms, on the other hand, have almost no intermolecular forces holding them together. Liquids have intermediate properties; their molecules or atoms have some attractive force for each other, but are not fixed in place like those of a solid.

See also Element, chemical.

263. Matter

See also 261. MATERIALS, PROPERTIES OF ;316. PHYSICS .

allomorphism

variant crystalline structure in a chemical compound. —allomorphic , adj.

allotropism, allotropy

the quality of certain substances to exist in more than one form, with different properties in each form. — allotropic, allotropical , adj.

hylozoism

Philosophy. the doctrine that all matter has life. —hylozoist , n. —hylozoistic , adj.

materialism

1. the philosophical theory that regards matter and its phenomena as the only reality and explains all occurrences, including the mental, as due to material agencies.

2. attention to or emphasis on material objects, needs, and considerations, with a disinterest in or rejection of intellectual and spiritual values. —materialist , n. —materialistic , adj.

monism

Metaphysics. any of various theories holding that there is only one basic substance or principle that is the ground of reality. —monist , n. — monistic, monistical , adj.

rheology

Chemistry and Geology. the study of the flow and deformation of colloids, especially pastes. —rheologist , n. —rheologic, rheological , adj.

somatology

Obsolete, the branch of physics that studies the properties of matter. Also called somatics .