The origin and development of the atomic theory

One of the problems that early perplexed the human mind was that of motion. Parmenides, of the Eleatic school, could not conceive of movement of bodies without vacuous space, and for him there could be no vacuum, since the universe is a plenum—the All, the One. Hence there could be no motion, movement of bodies and physical changes being mere delusive appearances.

Leucippus granted that he, likewise, could not conceive of the motion of bodies unless there was empty space for them to move in. But motion he recognized as a fact of nature, as a reality. The Eleatics must, therefore, he said, be in error in supporting the premise that “there is no vacuum.” Given empty space, motion followed.

Neither Parmenides nor Leucippus introduced the conception of the vacuum. It was a pre-existing doctrine fervently attacked by Parmenides and supported on logical grounds by Leucippus. “Nor,” says Professor Gompertz of Leucippus, “did he do more than to refine and to raise to the dignity of a self-sustained system the atomic theory which existed before him, though in a rude, rudimentary and imperfect shape.”

Given atoms of various sizes and forms, their movement in vacuous space was taken as much for granted as their existence. Just as matter itself had no beginning, and can have no ending, so the natural and original condition of atoms was a state of motion. The state of rest was no more “natural” to the Atomists than was the state of motion. They knew nothing of the doctrine which regards matter as an “inert mass.” Matter for them was essentially active and non-quiescent, as it was centuries later for Bruno, Bacon, Leibnitz, Spinoza, and as it is in our own times for all physicists. For energy is synonymous with motion, and matter itself is but a collection of energy units (in constant motion).

DEMOCRITUS’ THEORY

According to Democritus the atoms fall with varying degrees of rapidity, the heavier particles faster, the lighter with less speed, the heavier overtaking and striking against the lighter ones. To quote Lange’s succinct statement:

“As the atoms are of various shapes, and the collision will not take place in the center of the atoms, then, even according to the principles of modern mechanical science, revolutions of the atoms on their axes and lateral motions will be set up. When once set up, these lateral motions must ever become more and more complicated, and as the collision of constant new atoms with a layer of atoms already in lateral motion constantly imparts new forces, so we may suppose that the motion will continually increase. From the lateral motions in connection with the rotation of the atoms are then easily produced cases of retrogressive movement. If now, in a layer of atoms so involved, the heavier—i. e., the larger—atoms continually receive a stronger impetus downwards, they will finally be collected below, while the light ones will form the upper stratum.”[15]

Aristotle said that if there could be such a condition as space devoid of substance (matter), then in such a vacuum all bodies, light or heavy, would fall with equal velocity, which he considered an absurdity. For him the differences in the speed of falling bodies are entirely dependent upon differences in the density of the medium—air or water—through which they fall toward the center of the earth. Epicurus agreed with the Stagirite on the point of equal velocities in a non-resisting medium. But Aristotle not only denied the possibility of the existence of a void anywhere, but asserted that in such a void—were a vacuum possible—no motion could take place!

Epicurus believed that all atoms, of whatever weight, would fall with equal velocity in a vacuum, in simple parallel lines. They are in everlasting movement, originally a perpetual, equable falling through the boundless infinity of vacuous space, with an incomparably greater speed than that of light-rays; though he believed that these traverse the distance from sun to earth in an instant.[16]

While it is true that in infinite space there is neither an “up” nor a “down,” the fact remains, as Epicurus in effect observed, that man considers his head “up” and his feet “down,” and a body as being relatively distant from, or as near or on or within, the earth. So the atoms do converge at the earth, falling downwards unless met by bodies which, by a particular movement and weight, drive them to one side or upwards, or in a spiral or whirling motion—“the commencement of the formation of worlds.” But if the movement of atoms is in straight parallel lines, and all move in the vacuum with equal velocity, how could one atom drive another “to one side or upwards”?

Just here is where the weakness in the atomic theory is introduced by Epicurus. Democritus accounted for the collision and rebound of atoms under law, by a cause, not by chance. Epicurus threw away the cause and introduced “chance collisions.” But no atom was ever deviated from its flight in parallel lines by “chance”—in this case a wholly metaphysical invention. No worlds, no suns or planets could be built up on the theory of particles falling through infinite space in parallel rectilinear paths. There must be collision and recoil of atoms in order that the lateral and whirling movements, or vortices, should be set up, which were supposed to cause the atoms to combine according to their shape, size, and weight, the heavier forming the denser portions of the earth, the lighter constituting the atmosphere.

This difficulty did not escape the astute mind of Lucretius. But in attempting to solve what is really an insoluble problem—the development of worlds under the conditions stated—the great Roman poet only made bad matters worse. For here he introduced the dogma of free will applied to the falling atoms. They were made to deviate from their parallel lines by a voluntary movement!

And it appears that this was done on the authority of Epicurus himself: “In these errors,” says Lange, “Democritus probably had no share; and yet we shall judge them more leniently if we reflect that, even to our own day, the essence of the doctrine of the freedom of the will, with whatever metaphysical subtlety it is elaborated, consists simply of the uncertainty and perplexity of phenomenal appearances.” Again: “Whilst, therefore, it is one of the most important efforts of recent materialism to deduce the whole mass of voluntary movements from mechanical causes, we find Epicurus adopting a quite incalculable element into his system.”[17]

For Democritus a “chance” occurrence would be a causeless event, and this he could not allow under his law of “necessity.” An efficient cause produces always appropriate and calculable results under given conditions, and these results are always uniform, predictable occurrences, given knowledge of the mechanical factors involved.

To the earlier Atomists it seemed clear that particles which are alike in weight and in form would “naturally,” when whirled about in a vortex, be brought to the same location; and because of their peculiar shape, become entangled one with another. Since some atoms were supplied with hooks or even with balls and sockets, some with mortice or dovetail, others with sharp, rough or involuted edges, what more “natural” than that groups or combinations of atoms should be formed, even to the cohesion of some atoms in places not suitable to their nature, resulting in the formation of compound bodies?

Some atoms, indeed, were “unsociable,” having no means of mutual attachment; hence their combination was effected by enclosing them in a shell formed by the “social” particles. Some atoms had means for attachment at two points, which accounts, in part, for the greater or less mobility of the various atoms. The soul consists of the finest and smoothest atoms, akin to those of fire; and since they penetrate the whole body, their motions give rise to the phenomena of life. All objects project into space images of themselves, composed of atoms, which strike against the senses, and are perceived by similar atoms—“like atoms are perceived by like.”

These assumptions were wholly unacceptable to the critical mind of Aristotle,[18] as well as to his distinguished disciple, Strato of Lampsacus, teacher of Ptolemy Philadelphus. The Roman Stoic, Cicero, regarded the Democritean theory of cohesion and compounding of substances as wholly fantastic.[19] Yet the critics of Democritus had no better theory to offer in its place, since they, like the Atomists themselves, had no conception of the electrical, chemical or gravitational attraction of bodies for each other, or of the fact that the pressure of the atmosphere causes the ascent of fire, vapor and heated molecules in general.

To the foregoing objections, others might be offered, but we add only that in modern terms, the impact of indivisible and indeformable atoms upon one another could not produce the required movement of elementary masses. For “if the atoms are rigid, transmission of motion through impact is impossible; if they are elastic, they are then deformable and composed of parts, which is contrary to the hypothesis and implies forces of cohesion and elasticity.”[20]

Democritus, though he was the greatest physicist of his age, could not, of course, be expected to anticipate our modern objections to his doctrine—or his master’s doctrine. The immortal Newton (1642-1727) himself, even Dalton (1766-1844), founder of the modern chemical atomic theory (as distinguished from the physical atomic theories of his predecessors), could not anticipate the advances that have made possible the relentless criticism of modern physics and chemistry. Newton, Boyle and Huygens had no idea that the “atoms” of their conceptions were occupied mostly by “empty space” (using this phrase in its popular meaning—modern science recognizing no actually empty space: for all space contains a gravitational “ether” if not an electromagnetic field of energy).

Thus the “atom” of the chemist is a highly elastic body—highly resilient. Moreover, thanks to the genius of Professor Frederick Soddy, of Oxford, and of Sir F. W. Aston, we now know that what we considered but three years ago to be a homogeneous element—e.g., lead, chlorine, carbon, iron, etc.—is in many cases—if not in all cases excepting hydrogen and helium—a compound body containing particles of different weights (atomic mass). On the other hand, as previously stated, we are reverting to the Democritean theory that all atoms are composed of but one primitive element, the hydrogen atom. And the hydrogen atom in turn is composed of—energy; and energy itself is apparently of atomic structure. All energy is, in the last analysis, electrical in nature, the stuff that lightning, the stars, fire, rocks and metals, the bodies of plants and animals—perhaps the mind of man—are all made of.

With these facts in mind, let us return to Democritus, whose errors—the errors of his age—we may now regard with due allowances.

“SOUL ATOMS”

With Democritus, as with Pythagoras and Heraclitus, fire had a special importance, though it was not, as asserted by some of the ancient writers, regarded by him as an element. The primitive substance, the source of all things, whether fire, earth, air or water, was the world of homogeneous atoms, eternal, unchangeable. Fire, composed of minute, round, smooth atoms, was, on account of its mobility, the living and moving principle of nature, though not the direct cause of motion. But because of the fiery, mobile nature of its atoms, they become a secondary cause of additional motion, from their impact with and recoil from less mobile atoms. Sensation and consciousness are possible because of the extreme mobility of the fiery atoms. They are the “soul atoms,” but sensibility and consciousness arise only as the result of relatively large aggregations of these excessively minute bodies.

“EFFLUENCES”

In order to account for the mutual action or influence of bodies upon one another, when separated by space,—the void,—the Atomists had recourse to the Empedoclean theory of “effluences,” or emanations, which were supposed to be emitted by all bodies (Aristotle, Generatio et Corruptio, i, 8). Penetrating the organs of sense, they excite the appropriate sensation, and, in the case of the brain, they produce images or ideas of things. Hence sensation is the only possible source of knowledge, the origin of all thought being the passage through the sense organs of “effluences” from external objects or organisms, acting mechanically, by contact.

But while affirming that sensation is the source of all knowledge, Democritus, nevertheless, agrees with the Pythagoreans and Socrates in rejecting sensation as such as a source of knowledge. He distinguishes between a “bastard” (skotie) knowledge obtained through the special senses and a true-born (gnesie) knowledge, obtained by direct-contact of external atoms with the body’s “soul atoms.” These are not concentrated in the brain nor are they dependent upon the organs of sense. They are diffused throughout the entire organism, and come into direct contact, without the intervention of the deceptive sense organs, with the reality outside our body.

“Poor Mind,” he makes the senses say (Fragment 125), “it is from us thou hast got the proofs to throw us with. Thy throw is a fall.”[21]

As Burnet points out, the “true-born knowledge is of the same nature as the “bastard,” and “Democritus refused, like Socrates, to make an absolute separation between sense and thought,” the former being, ‘after all, not thought, but a sort of inner sense, and its objects are like the ‘common sensibles’ of Aristotle.’ In the “bastard” knowledge, Democritus included sight, hearing, smell, taste, touch. “True-born” knowledge was obtained directly by the diffused soul atoms from the external objects, and thus made them known as they really are. All phenomena of life and mind are due to the motion of the mobile fiery atoms. Even where Democritus speaks of “the Divine,” he means merely the fiery soul atoms; not a personal being of any kind.

Where there is a large aggregation of the soul atoms, there reason appears, itself a physical phenomenon. Democritus recognized no Nous (Anaxagoras) or World-Soul (Plato), or Deity (Aristotle). The only motive force of the world is gravity, the soul being a secondary cause of motion only by virtue of the fiery atoms’ being most easily moved by pressure and contact. “Spirit” is “only one substance moving side by side with others.”[22]

Every act of the individual, every occurrence in nature, has its efficient cause from which it follows by necessity—or, as we should say, under natural law. All change in things must be reduced to an altered combination of atoms—to new forms and arrangements in space, under the law of “necessity.”

The soul is material and disappears with the disintegration of the body, though there exist invisible beings all around us in the air. But these invisible beings are material bodies also, composed of the finest atoms. At times they project images of themselves which affect our soul atoms, rendering these aerial beings, for the time, visible bodies.