Atomism

ATOMISM. - Philosophical and scientific theory that resolves reality into an aggregate of indivisible primary elements, called atoms (from the Greek ἄνωσις, "indivisible").

I. PHILOSOPHY

Atomism, as a philosophical-physical doctrine, arose for the first time in Greece around the middle of the 5th century through the work of Leucippus (probably of Miletus) and his disciple Democritus of Abdera (v.), who developed its theories into a system, taken up and continued in the 3rd century by Epicurus. Between Democritus and Epicurus tradition gives in continuous succession the following names: Nessa, Metrodorus of Chios, Diogenes of Smyrna, Anaxarchus and Pyrrho of Elis, head of the sceptical school, then Nausiphanes his pupil and teacher of Epicurus, and Hecataeus of Abdera: besides these, Apollodorus, Diotimus and Bion of Abdera are named as belonging to the Democritean school.

The atomism of Leucippus and Democritus was born as a consequence of the Parmenidean doctrine of being, and was, after that of Empedocles (v.) and Anaxagoras (v.), the most grandiose attempt to resolve the problem that the concept of being one and immutable had opened with respect to the manifold and mutable reality of the sensible world. The solution given by Empedocles and Anaxagoras, whose work occupies the first half of the 5th century, had been to multiply being and explain change by the union and separation of parts, the first positing the four elements as the foundation of this, the second raising to the rank of original substances everything that, quantitatively divided, remains qualitatively one: the so-called "homoeomeries." This solution, by denying division under the category of quality, can itself be considered atomistic, that is, as qualitative atomism. Both Empedocles and Anaxagoras admitted divisibility to infinity in the category of quantity.

The solution put forward for the first time by Leucippus was simpler. Being is and non-being is not, Parmenides had said. Being is being, and non-being is non-being, Leucippus distinguished, but non-being exists no less than being: it is the void, while being is the full. The same proposition was thus formulated by Democritus: "the ente (τὸ δὲν) does not exist any more (οὐ μᾶλλον) than nothing (ὃς τὸ μῆδεν)" (fr. 156). The formula "no more" recurs also at other points in the fragments of Democritus and must be considered as one of the most important logical principles of the atomistic deduction. Probably on its basis the multiplicity of entities was demonstrated: if there exists an "entity" and it is limited by "nothing," there is no reason why another should not exist, and so on to infinity. However that may be, Leucippus and Democritus taught that entities are infinite, as infinite is space, and move ab aeterno in all its directions. Equally infinite are their forms and varieties of size and therefore of weight, "there being no reason why an entity should have one form rather than another." These entities, excluding nothing from themselves, are indivisible, that is, atoms.

To demonstrate the necessity of admitting the existence of indivisible bodies, we find in Democritus two arguments: the first is that from one the two cannot be born and vice versa, a typically Eleatic argument founded on the identity of the one and of being; the second is that, if a body were entirely divisible, since, to be such, it would already have to be actually divided, the last term of the division being nothing, the body would itself be nothing. This argument reflects the problem that troubled the mathematics of the 5th and 4th centuries, namely that of the infinitesimal, whose solution came only in the Aristotelian theory of the continuum (cf. Met., IX, 6, 1408 b 15 ff.). From it we gather that the atomism of Leucippus and Democritus was only physical and not mathematical. Concerning movement, Aristotle reproached the two philosophers for not having indicated its cause. In some testimonies the cause is given as impact; but impact is a consequence of movement, and since the motion of the atoms is ab aeterno, one must conclude that they considered movement as an immediate consequence of the opposition between full and void, and in impact they placed the cause of its determination, not of its origin. But the atoms, moving ab aeterno, ab aeterno collide, and in this sense every aggregation has as its immediate cause precisely impact. Weight, which will later be assumed by Epicurus as the cause of natural motion in opposition to that of impact and declination, was considered by Leucippus and Democritus only as a coefficient, together with form and size, of the separation that determines aggregates. Infinite the atoms and infinite space, infinite too are the worlds, which succeed one another as they dissolve into one another.

According to the concordant declaration of all the testimonies, the formation and disintegration of the worlds would have been attributed by Democritus to chance ("Democritus who places the world by chance," according to Dante's verse, Inf., IV, 126). That, given the principles, this is in fact true, is something that can be denied only by those modern interpreters who exclude every form of teleologism as contrary to the concept of science. Historically it must be said that the concept of chance, at the time when Democritus was writing, was already known and entirely defined. As for Leucippus, he had affirmed that "everything happens according to reason and necessity" (fr. 2). Earlier than Democritus and closer to the Eleatics, he was still ignorant of the opposition between logical and mechanical necessity. His theory was rigorously deduced and rationally intelligible. That the Eleatic identity of being, being maintained only for matter, the cosmos, as the order assumed by it, should come from non-being, and therefore contradict the very principle to which the whole system was obedient, was something of which he could not have been conscious. For Democritus this cannot be said, and his theory of human progress, which he had taken up and developed from Anaxagoras, considered chance as the natural complement of intelligence and art.

In reality every atomistic system, by reducing the complex to the simple and the whole to the parts, can in no case go beyond matter, and must of necessity sacrifice form, that is, in the last analysis, spirit. In the system of Democritus (of Leucippus we know less) there is place neither for God nor for the soul. Everything is the result of a temporary and contingent aggregation, and everything is mortal. Plato and Aristotle combated atomism on the basis of the same Eleatic principle from which it had been deduced: if nothing comes from non-being, this impossibility must be affirmed above all for form: the reason of the part is in the whole and not vice versa.

Epicurus, who came after Aristotle and who had in view not so much the scientific problem as the practical one, in taking up again the system of Leucippus and Democritus, sought to modernize it according to the new concepts brought by Platonic and Aristotelian speculation. The principal modification was that of distinguishing in atoms a natural motion, a forced motion, and a free motion. The first he made to consist in the fall along a straight line due to gravity, which naturally put him in conflict with the concept of the infinite, in which there is neither high nor low. Considering therefore that bodies in a void fall with equal velocity, in order to be able to explain collisions and impacts, he assumed that atoms could indefinitely deviate "somewhat" from the straight line: this is the second form of motion, which received from him the name of declination (παρέγκλισις), the "clinamen" of Lucretius. This second form of motion, which Diogenes of Oenoanda (2nd or 3rd century A.D.) calls free motion ("libera potestas" in Lucretius), allowed him to explain the freedom of the will. The third form of motion is that of impact, a motion necessary and casual at the same time (ἡ κατὰ τὸ αὐτόματον ἀνάγκη). Another fundamental modification was that of considering the number of atomic forms to be finite, whereas his predecessors had made it infinite, and this in order to be able to explain the fixity of species, that is, the limitation of qualities. As regards the problem of divisibility, Epicurus, while maintaining the physical indivisibility of atoms on the same grounds as Leucippus and Democritus, also professed, in contrast with the mathematics of his time, which had by then progressed, a mathematical atomism in the theory of minima, at which every division stops and which constitute the unit of measure of magnitudes. The negation of all teleology of the universe is for Epicurus a dogma, but, as a substitute for Aristotelian finalism, he elaborated in his theory of the universal equilibrium of forces (isonomía) the concept of a constant cyclical identity of becoming, which served him as a basis for the concept of natural necessity.

After the end of the ancient world, down to the Middle Ages, no trace is any longer found of any philosophical elaboration of atomism. The Arab philosophers, through their knowledge of the works of Aristotle, took up again the atomistic theory, affirming that bodies are composed of punctual atoms, devoid of extension, all homogeneous. Through the Arabs the atomistic doctrine reappears in the European philosophy of the West in certain realist thinkers: William of Conches, d. 1150, a Platonist, Adelard of Bath, who also in atomism seeks the reconciliation between Aristotle and Plato (1115), Hugh of St. Victor, d. 1141, author of the first Summa, Nicholas of Autrecourt and others; for them the material atom is the last residue of division in a chaotic matter which an immanent principle, form, causes to undergo a series of transformations. The four elements are reduced to combinations of homogeneous and invisible particles, and all the works of nature, including the human body, take their origin from this plasticity of atoms.

In Renaissance thought atomism finds a supporter in Fracastoro and then in Bruno (doctrine of minima); it is upheld by P. Gassendi and opposed by Descartes. Bacon criticizes the doctrine of Democritus, but ends up upholding a corpuscular theory very similar to that of the Abderite.

Atomism is taken up again with scientific criteria by Boyle and by Newton in order to explain the constitution and structure of matter. From that epoch down to the present, scientific atomism has had a continuous development until it rose, with the hypotheses of Rutherford and Bohr, to a general theory accepted by all, which also represents the most fertile field of new discoveries of the modern sciences, for which reference is made to the entries CHIMICA, FISICA and MATERIA.

Carlo Diano - Emilio Bodrero

II. SCIENCES

Atomism, which in the Middle Ages had almost entirely yielded the field to hylomorphism (v.), flourished again with the rise of the experimental sciences, in which it became increasingly established until today it permeates every part of physics and chemistry. However, if contact with the positive sciences led to such a valid affirmation of atomism, this did not happen without serious difficulties and genuine crises, which could be overcome only at the price of profound mutations in its own fundamental conceptions.

The reasons why scientists showed themselves in general very inclined toward atomism were at first predominantly philosophical in nature, and only later were properly experimental reasons added to them. Among the former we must count the tendency toward the visualization of one's own schemata, which naturally led to mechanism, to which atomism lent itself very well. Add to this anti-Aristotelianism, due in part to the Scholastics' estrangement from the new scientific currents, in part to their having misunderstood the Aristotelian concept of form, with the consequent error regarding occult qualities, and therefore regarding every change that was not reducible to changes of figure and place.

To these principal reasons are often added arguments drawn from the nature of the continuum (v.). Only in the 19th century did reasons of a scientific character become established, principally the kinetic theory (v. GAS, TEORIA CINETICA dei) and the interpretation of the stoichiometric laws of chemistry.

The atomistic movement in science may be said to have been initiated by Gassendi (v.), who linked himself directly to Epicurus, whose doctrines he attempted to re-establish, placing, in place of eternal atoms governed solely by chance, atoms created by God and directed toward determinate ends according to a divine plan. To the same form of atheistic atomism adhered in the 17th century Bacon, Galileo, Hooke, Boyle, Newton... Decidedly opposed was instead Descartes (v.), despite his rigid mechanism. Forms of atomism may in a certain way also be considered the dynamism of Boscovich (v.) and the monadism of Leibniz (v.).

However, atomism had until then remained more a philosophical system than a scientific theory. This character it instead assumes with Bernoulli, who in his Hydrodinamica (1783), starting from the hypothesis that a gas is constituted by corpuscles in disordered motion, and applying the laws of mechanics, succeeds in explaining the pressure of the gas as due to the impact of the corpuscles against the walls and in deducing mathematically from it the law of Boyle and Mariotte. Thus were laid the foundations of the kinetic theory, which only a century later was to be taken up again with the works of Clausius and Maxwell, and was to have such influence in the affirmation of atomism in physics. On the other hand, in 1808 Dalton lays the foundations of chemical atomism with his New system of chemical philosophy, in which however to the classical atomistic conception he was forced to add a postulate that finds in it no explanation, namely that the atoms of each element have their own characteristic weight.

The victory of atomism was nevertheless neither easy nor rapid. In the kinetic theory, in fact, a serious difficulty was encountered when, having interpreted heat as due to the motion of molecules, one sought to explain mechanically the second law of thermodynamics, according to which an isolated body constitutes an irreversible physical system, whereas the laws of mechanics are essentially reversible. This was one of the principal reasons that induced certain physicists — Rankine, Mach, Ostwald, Duhem — to abandon mechanism and therefore atomism, in order to entrench themselves in energeticism (v. DINAMIEMO), a position of more prudent positivism that denies all ontological value to the hypotheses and schemata of physics. The difficulty was however brilliantly overcome by Boltzmann on the basis of the calculus of probabilities, recognizing the statistical value of the second law of thermodynamics.

Even graver difficulties arose in chemistry when one sought to pass to the determination of atomic weights. Among some concordant data, such uncertainties and confusions were reached as to make Dumas say that, had it been possible, he would gladly have erased the word atom from chemistry; and even greater opposition was raised by Berthelot. Yet the solution of the difficulties already existed in certain memoirs of Avogadro and of Ampère to which chemists had paid no attention. It fell to a young Italian chemist, Cannizzaro (v.), to call their attention to this theory (1860), which, if on the one hand it was to mark the definitive triumph of atomism in chemistry, on the other constituted a new conception in comparison with the atomism of Democritus: simple bodies were no longer constituted by absolutely indivisible atoms. With the work of Cannizzaro begins a particularly fruitful period for chemical atomism (v. MATERIA, CHIMICA). Not only had the molecule revealed itself resolvable into atoms, but the atom itself had revealed itself to be a complex edifice. But precisely through these marvelous developments, atomism, under the pressure of experience and theory, was rapidly evolving toward new forms that preserved ever less of the old Democritean schema.

III. THE A IN TODAY'S PHYSICS

Summing up the results of physics on this point, it is perhaps not an exaggeration to say that of the original a. only the name remains, and even this is used in an anachronistic sense. The atom is anything but indivisible, and even its ultimate components, the elementary particles, are something other than the simple, immutable, clearly visualizable corpuscles of Democritus's philosophy. Hence the judgment, still frequent in scientific and philosophical literature, which attributes to Democritus the paternity of the scientific a., must be accepted with great reservation.

As regards the atomic structure of matter and many data relating to it, we can readily accept Planck's statement: «To these objections [against the atomic hypothesis and the electron theory] I oppose the resolute affirmation (and in this I know I am not alone) that atoms, even if we know nothing about their nature, are real no more and no less than the celestial bodies and terrestrial objects that surround us. When I say that the hydrogen atom weighs 1.6. 10⁻²⁴ g, I have no greater chance of being wrong than when I say that the moon weighs 7. 10³⁰ g». But if the question is raised concerning the nature of atoms, and especially of their ultimate components, the problem becomes ever more obscure and obliges us to suspend any definitive judgment (v. TEORIE FISICHE, QUANTISTICA, MECCANICA).

IV. ATOMISM AND SCHOLASTICISM

In general Scholasticism showed itself opposed to atomism, insofar as it considered the system in its materialistic and mechanistic form as proposed by Democritus, and this judgment of its is still fully valid. More recent authors ordinarily distinguish between philosophical atomism and atomic theory, but this distinction seems rather vague unless it is made clearer what is meant by the name atomic theory. On the other hand, the task of sifting out the elements of truth contained in modern theories is, as has been said, exceedingly arduous. One may nevertheless attempt to establish certain sure cornerstones that allow at least a better delimitation of the controverted questions: a. It is certain that the living being enjoys a substantial unity, and therefore the atoms cannot in it be considered as natural individualities complete and independent in themselves.

b. The metaphysical arguments in favor of the hylomorphic composition of bodies in general, at least with regard to their ultimate components, retain their intrinsic value, insofar as they prescind from physical scientific theories (v. ILEMORFISMO).

c. No opposition, in principle, exists between the traditional Scholastic position, which recognizes a substantial unity even in macroscopic inorganic bodies, and physical-chemical atomism, which recognizes in them an atomic structure, since this can be due to a simple accidental heterogeneity like the organic structure of the living being.

d. An attempt has been made to find an interpretation of atomic theory in the theory of natural minima of the ancient Scholastics: the rapprochement is perhaps suggestive, but it ought to be examined more deeply also in relation to the nature of isotopes.

Mario Viganò