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The universe consists of bodies and void: that bodies exist, perception itself in all men bears witness; it is through the senses that we must by necessity form a judgment about the imperceptible by means of reason.

—Epicurus 1

DEFINING ATOMISM

In his exhaustive study Atomism and Its Critics: Problem Areas Associated with the Development of the Atomic Theory of Matter from Democritus to Newton, philosopher Andrew Pyle lists what he defines as the ideal central claims of atomism:

A commitment to indivisibles, particles of matter either conceptually indivisible (i.e., such that one cannot conceive of their division) or physically unsplittable.
Belief in the existence of vacuum or “Non-Being,” purely empty space in which the atoms are free to move.
Reductionism: explanation of the coming-to-be, ceasing-to-be and qualitative alternation of sensible bodies in terms of the local motion of atoms which lack many (most) of the sensible properties of those bodies.
Mechanism. This is the thesis about the nature of physical agency: it claims in effect that no body is ever moved except by an external impulse from another body.²

The book is Pyle's doctoral dissertation at the University of Bristol. Its chapters deal with each of the above four issues over three periods: classical antiquity (ca. 500 BCE–500 CE), the Middle Ages and Renaissance (ca. 500–1600), and the seventeenth century.

Pyle tells us that many Renaissance thinkers accepted (3) but not (4), “insisting that the movements of minute bodies that constitute the generation and alteration of sensible bodies are guided by purposive, spiritual agencies of some kind.”3

In this book, I will carry this discussion on to the present day, showing how atomism—including item (4)—constitutes our best description of the observations we make of the world. We will see how material atomism was resisted by many of the greatest thinkers of all time, from Aristotle and Plato to Augustine and Aquinas, and then on to the present day, where we find it under attack by those who refuse to believe that matter and natural forces are all there is to observable reality.

The reductionism in item (3) that forms a part of the doctrine of atomism is highly unpopular. Time and again, we hear from scientists, philosophers, theologians, spiritualist gurus, and laypeople that “the whole is greater than the sum of its parts.” We will see that while this statement is technically true, it is far less profound than its proponents claim. As Alex Rosenberg notes in Darwinian Reductionism; or, How to Stop Worrying and Love Molecular Biology:

[The] whole has properties which no individual part has: the property of wetness that water has is not a property that any H₂O molecule has. But this is no reason to deny the reducibility of wetness to properties of H₂O molecules. Wetness is identical to the weak adhesion of these molecules to one another, owing to the polar bonds between the molecules; and these bonds are the result of the distribution of electrons in the outer shells of the constituent atoms of the H₂O molecules.⁴

In other words, the whole still results from the action of its parts. Try as they might, the anti-reductionists have been unable to find any evidence to support their distaste for atomism. No special holistic forces have been shown to come into play with the aggregation of large numbers of parts; just new properties develop or, in the common parlance of today, “emerge” from the interaction of the parts.5

LEUCIPPUS AND DEMOCRITUS

Leucippus, who lived in Miletus (or possibly Elea or Abdera) in Ionia in the early fifth century before the Common Era, is usually credited with inventing the theory of atoms and the void, at least the Greek version that has come down to us. Little is known about him, and none of his writing has survived. More is known about Democritus of Abdera, who is thought to have been Leucippus's student, or at least a much younger colleague, and he appears in the anecdotes of many ancient texts. He is reported to have produced a large number of works on many subjects, but these have only survived in secondhand reports.⁶

The atomic theory of Leucippus and Democritus can be characterized by the simple phrase “atoms and the void.” Everything is made of atoms, even gods and the soul. While today we think of atoms as moving around in empty space, or “nothing,” Leucippus and Democritus did not regard the void as “nothing.” It is just as much a part of reality as “something.” A single, infinite entity exists in reality. That reality breaks up into an infinite number of infinitesimal parts—atoms and the void. In this way, the concept of a unique elementary substance is retained while accounting for diversity and the potential for change.

According to these early atomists, the atoms themselves are hard, incompressible, and indivisible. They have no parts. Although lacking any substructure, they have different gross geometrical characteristics: size, weight, shape, order, and position. It is not clear whether the property of weight was introduced by Democritus or later by Epicurus.

They argued that the motions of atoms are endless and largely random, with a tendency to move toward some point such as the center of Earth. Everything happens by either chance or necessity. When they collide, atoms either recoil from one another or coalesce according to their various shapes. For example, they may have hooks that enable them to grab onto one another. When they join to form new, compound identities, individual atoms still retain their original identities.

In the third century of the Common Era, the historian Diogenes Laertius summarized Democritus's atomic model as follows:

The principles of all things are atoms and the void, and everything else exists only by convention. The worlds are unlimited and subject to generation and corruption. Nothing could come to be from nonbeing, and nothing could return by corruption to nonbeing. Atoms are unlimited in size and number, and are the seat of a vortex motion in the universe, which results in the creation of all compounds: fire, water, air, and earth, which are simply organizations of certain atoms, themselves resistant to change and alteration by virtue of their hardness. The sun and the moon are composed of such particles, smooth and round, as is the soul, which is the same thing as the intellect.7

Note that fire, water, air, and earth are not the basic elements in this scheme, as they were held to be in almost all other ancient natural philosophy, either as the individual primal stuff, or in combination. Even in the Middle Ages, alchemy was based on the principle that you could combine these elements to make other compounds. In particular, by adding fire to earth (stone), you could make gold. That never succeeded, but in the twentieth century, physicists were able to combine the nuclei of baser elements, what I will call chemical atoms, to make gold. Unfortunately, they couldn't make enough of the precious metal to pay for the experiment, much less generate riches.

The vortex mentioned above is suggestive of the swirling nebula of interstellar matter that contracted under gravity to produce our solar system. Atoms tended to move in that direction.

We will have more to say later about whether nothing can come from nonbeing. The basic point here is that atoms, as described by Democritus, always existed and are indestructible, while the compounds they form, including the soul, can come and go.

ATOMS AND GODS

From the beginning, atomism has been an anathema to religious belief. According to philosopher David Sedley:

Atomism [is] the first Presocratic philosophy to eliminate intelligent causation at the primary level. Instead of making intelligence either an irreducible feature of matter, or, with Anaxagoras, a discrete power acting upon matter, early Greek atomism treats atoms and void alone as the primary realities, and relegates intelligence to a secondary status: intelligence, along with color, flavor, and innumerable other attributes, is among the properties that supervene on complex structures of atoms and the void.8

Democritus was a contemporary of Socrates, so he was well aware of the dangers of public impiety. However, he assigned a limited role to the gods. They did not intervene in a world governed by natural laws. Furthermore, since the soul is made of atoms, it is not immortal and humans can never become gods.

ATOMS AND THE SENSES

In The Presocratic Philosophers, philosophers Geoffrey Kirk, John Raven, and Malcolm Schofield explain how Democritus viewed the senses:

Democritus sometimes does away with what appears to the senses, and says that none of these appears according to truth but only according to opinion: the truth in real things is that there are atoms and the void. “By convention sweet,” he says, “by convention bitter, by convention hot, by convention cold, by convention color; but in reality atoms and the void.”9

Democritus regarded observations such as color and taste as conventions and, thus, not real. Only atoms and the void are real, and these he could not see.

Although he quite correctly questioned the reliability of the senses, Democritus hardly ignored them. In fact, he proposed an atomic mechanism to explain how the senses operate. According to Democritus, visual perception results from atomic emanations from the body colliding with atoms in the eye. This is essentially as we understand sight today. Particles, or atoms, of light called photons are emitted from bodies. If the body is the sun or a lamp, the photons are energetic enough to excite electrons in the chemical atoms of the eye and produce a signal to the brain. Colder bodies, such as you and I, also emit photons, but these are in the lower energy infrared region of the spectrum, where our eyes are insensitive. In order to see human bodies directly by their emissions, our eyes must be aided by special night-vision goggles that detect infrared light. Since most of the objects surrounding us are not as hot as the sun, we see them by means of the higher energy photons from the sun or lamps as they scatter off the object and into our eyes.

The senses of sound and smell were also correctly viewed in ancient atomism as the emanation and absorption of atoms. The sense of touch was also accurately described as a collision of the atoms of the hand, for example, with the atoms of the object being touched.

LATE NIGHT WITH LEDERMAN

In his highly entertaining book, The God Particle, to which I will refer several times in this book (which I wish I could make half as entertaining), Nobel-laureate physicist and former Fermilab director Leon Lederman imagines a dream in which he takes Democritus on a tour of the accelerator.10 Here are two related excerpts:

Lederman: How did you imagine the indivisibility of atoms?

Democritus: It took place in the mind. Imagine a knife of polished bronze. We ask our servant to spend an entire day honing the edge until it can sever a blade of grass held at its distant end. Finally satisfied, I begin to act. I take a piece of cheese…

Lederman: Feta?

Democritus: Of course. Then I cut the cheese in two with the knife. Then again and again, until I have a speck of cheese too small to hold. Now, I think that if I myself were much smaller, the speck would appear large to me, and I could hold it, and with my knife honed even sharper, cut it again and again. Now I must again, in my mind, reduce myself to the size of a pimple on an ant's nose. I continue cutting the cheese. If I repeat the process enough, do you know what the result will be?

Lederman: Sure, a feta-compli.

And a little later in the dream…

Lederman: Today we can almost define a good scientist by how skeptical he is of the establishment.

Democritus: By Zeus, this is good news. What do you pay mature scientists who don't do windows or experiments?

Lederman: Obviously you're applying for a job as a theorist. I don't hire too many of those, though the hours are good. Theorists never schedule meetings on Wednesday because it kills two weekends. Besides, you're not as anti-experiment as you make yourself out to be. Whether you like it or not, you did conduct experiments.

Democritus: I did?

Lederman: Sure. Your knife. It was a mind experiment, but an experiment nonetheless. By cutting a piece of cheese in your mind over and over again, you reached your theory of the atom.

Democritus: Yes, but it was all in the mind. Pure reason.

Lederman: What if I could show you that knife?

Democritus: What are you talking about?

Lederman: What if I could show you the knife that can cut matter forever, until it finally cut off an a-tom?

Democritus: You found a knife that can cut off an atom? In this town?

Lederman: [nodding] We're sitting on the main nerve right now.

Democritus: This laboratory is your knife?

Lederman: The particle accelerator.

ATOMISM IN ANCIENT INDIA

A form of atomism can also be found in ancient India. Although more closely tied to religion in very important ways than Greek atomism, enough similarities exist to lead one to suspect some contact between the two distant cultures.

According to historian Bernard Pullman, six major philosophical systems emerged from Hindu Brahmanism. Of these, the Nyaya-Vaisheshika movement was the strongest defender of atomism. A doctrine of atoms can be found in the Vaisheshika sutra, written by Kanada in the first century BCE. Other Hindu schools were receptive to the idea, while Vedanta was opposed.11

Kanada's atoms, like those of Democritus, were eternal, indestructible, innumerable, and without parts. However, they included the classical four elements—fire, air, water, and earth—along with aether, space, time, and two kinds of souls. Gods and individual humans contain eternal, omniscient souls, while another form of soul called manas is an organ of thought that acts as the link between the god-human soul and external objects.¹²

The Buddhist school of Hinayana held to an atomic doctrine similar to Nyaya-Vaisheshika. It also regarded the four elements as atoms, although it considered soul and conscience to be outside the realm of atoms. Jainism, on the other hand, seemed to hold views similar to the Greek atomists in not regarding the four elements as atoms.

All these philosophies viewed the soul as eternal and incorruptible, while the Greek atomists said the soul was a composite of atoms and thus disintegrates upon death along with the rest of the body.¹³ In short, the atomism that came out of ancient India maintained the dualism of matter and mind/soul/spirit that is present in most religions while Greek atomism, although accepting the existence of remote gods uninterested in humanity, was distinctly atheistic—at least as the term is used today. In this book, I will take theism to be a belief in a superhuman god or superhuman gods existing outside the material world but still very much active in the operation of the universe and in human affairs. Atheism is nonbelief in such a god or gods, or in any kind of external, immaterial supernatural force. The gods of Greek atomism were not supernatural. They were made of atoms, too, and did not remotely resemble the superhuman gods of the Iliad and the Odyssey or the gods of India. Because of its duality, Indian atomism should not be considered comparable to that of the Greeks.

EPICURUS

Epicurus was born on the island of Samos in 341 BCE to poor Athenian parents. After compulsory military service, he studied philosophy for ten years in Teos in Ionia under Nausiphanes, from whom he learned the atomism of Democritus. Epicurus never acknowledged any contribution from Leucippus.

The Epicurean movement began after Epicurus moved to Colophon in Ionia. Gathering disciples along the way, he briefly taught on the island of Lesbos and in Lampsacus in Ionia, where he gained many more disciples and financial support. In 306 BCE, he settled in Athens where he held meetings in the garden of his house. Because of this, his movement became known as “The Garden.”

Students of The Garden, which (scandalously) included both sexes, were expected to live a simple life of quiet study and to withdraw from politics. Epicurus developed a unique world-system based on atomism that repudiated most of the teachings of Aristotle, Plato, and all the other philosophical schools of his time and place: Our earthly life is all there is. The punishing and vengeful gods of myth do not exist. What gods do exist have no concern for humans because they live outside our world in a state of perfect happiness. Humans decide proper conduct by reasoning about the best actions to pursue. Justice is defined as dealing with others for mutual advantage and can change as circumstances change.

Epicurus died at age seventy in 271 BCE. He left behind over three hundred books, including On Atoms and Void. Unfortunately, only a small portion of his work remains, mostly fragmentary. These fragments can be found in The Essential Epicurus: Letters, Principal Doctrines, Vatican Sayings, and Fragments by Eugene O'Connor, which has been my primary reference for this section.14 Pieces of Epicurus's masterwork On Nature were recovered from the ashes of Herculaneum, which was destroyed in the eruption of Mount Vesuvius that destroyed Pompeii in 79 CE. Unfortunately, so far these have not been widely available.

As you can imagine, Epicurus had many enemies and Epicureanism has long been wrongfully associated with a debauched life in the hedonistic pursuit of pleasure. In fact, while Epicurus regarded pleasure as an ultimate good, he was mainly concerned with avoidance of fear and pain by limiting desires and living modestly. Tranquility and freedom from fear and pain resulted from living a simple life of friendship, learning, and temperance.

In Lives of the Eminent Philosophers, Diogenes Laertius says that Epicurus had legions of followers and was honored in Athens with bronze statues. Early Christians approved of Epicurus's denouncing of pagan superstition, but his teachings were ultimately suppressed in medieval Christendom. In his epic fourteenth-century poem Inferno, Dante Alighieri (ca. 1265–1321) consigned Epicurus to the sixth circle of hell for denying the immortality of the soul (canto 10.13–15). Epicurus is the only ancient philosopher in Dante's hell.

As we will see later, the Renaissance saw a revival in interest in Epicurus, especially after the discovery of Lucretius's De rerum natura. In 1647 Pierre Gassendi published Eight Books on the Life and Manners of Epicurus that had great success, especially in England where it influenced Thomas Hobbes, John Locke, and other important figures.

De rerum natura is the main source we have today for Epicurus's teachings on atomism. However, before we get to that, let us look at some of his teachings by quoting directly from Epicurus's surviving works as translated by O'Connor. (The page numbers from that reference are given in parentheses.)

Quotations from Epicurus on atomism come from “Letter to Herodotus” (a friend of Epicurus's, not the ancient historian).

The universe is without limit.…Also, the universe is boundless both in the number of bodies and the magnitude of the void.…Moreover, there are infinite worlds, both like and unlike this one. (22–23)

Atoms exhibit none of the qualities belonging to visible things except shape, mass, and size, and what is necessarily related to shape. For every quality changes; but the atoms do not change, since, in the dissolution of compound substances, there must remain something solid and indestructible. (27)

The atoms must possess equal velocity whenever they move through the void, with nothing coming into collision with them. (30)

Let us also look at some of the words of Epicurus concerning religion. In his “Letter to Menoeceus,” he talks about an immortal god but tells us not to apply anything to him “foreign to his immortality or out of keeping with his blessedness.” He says that the assertions made about gods by the many are “grounded not in experience but in false assumptions” that the gods are responsible for good and evil. (62)

Epicurus is most eloquent when he speaks of death:

Grow accustomed to the belief that death is nothing to us, since every good and evil lie in sensation. However, death is the deprivation of sensation. Therefore, correct understanding that death is nothing to us makes a mortal life enjoyable, not by adding an endless span of time but by taking away the longing for immortality. For there is nothing dreadful for the man who has truly comprehended that there is nothing terrible in not living. Therefore, foolish is the man who says he fears death, not because it will cause pain when it arrives but because anticipation of it is painful. What is no trouble when it arrives is an idle worry in anticipation. Death, therefore—the most dreadful of evils—is nothing to us, since while we exist death is not present, and whenever death is present, we do not exist. It is nothing to the living or the dead, since it does not exist for the living and the dead no longer are. (63)

DIFFERENCES WITH DEMOCRITUS

According to the peer-reviewed Internet Encyclopedia of Philosophy, Epicurus modified the teachings of Democritus in three important ways:15

Weight. Aristotle had criticized Democritus for not explaining why atoms moved in the first place. Epicurus said that atoms had a natural motion—that is, “downward”—and proposes weight as the atomic property that accounts for this motion.
The Swerve. If atoms all just moved downward, they would never collide. So Epicurus added the notion that at random times they swerve to the side.
Sensible Qualities. As we have seen, Democritus said only invisible atoms and the void exist and sensible qualities such as sweetness are simply conventions. This led him to be pessimistic about our ability to obtain any knowledge about the world through our senses. Epicurus agreed that the properties of macroscopic bodies result from their structures as groups of atoms, but they are still real in a relational way. For example, cyanide is not intrinsically deadly, but it is still a real property when ingested by human beings.

POST-EPICUREAN ATOMISM

According to ancient historian Richard Carrier (he's not ancient, his history is), significant scientific progress was made in the period between Epicurus and Constantine, when Christianity took control of the Roman Empire. In personal correspondence, Carrier told me, “By influencing even non-atomist scientists and driving many of the debates (between atomist and non-atomist scientists), atomism was a major contributor to all the scientific progress in antiquity after Aristotle.”¹⁶

Let me just briefly mention some of the scientific accomplishments of Greek and Roman scientists that occurred during this period. They are not recognized as well as they should be because the Church suppressed their writings due to their real or implied atheism.

Strato of Lampsacus (ca. 335–ca. 268 BCE) was the third director of the Lyceum founded by Aristotle. He wrote mostly on physics and disagreed with many of Aristotle's views, especially his teleology (final cause). He was an atomist, a materialist, and an atheist.

Ctesibius of Alexandria (fl. 285–222 BCE) founded the science of pneumatics, and his improved water clock was more accurate than any clock ever built until the pendulum clock invented by Christiaan Huygens in the seventeenth century.

Eratosthenes of Cyrene (ca. 276–ca. 195 BCE) invented the science of geography and was the first person to accurately estimate the circumference of Earth.

Archimedes of Syracuse (ca. 287–ca. 212 BCE) was one of the greatest scientists in the ancient world. His numerous achievements are well enough known that they need not be cataloged here.

Aristarchus of Samos (310–ca. 230 BCE) was the first known person to propose the heliocentric model of the solar system.

Hipparchus of Alexandria (ca. 190–ca. 120 BCE) developed trigonometry, discovered the precession of the equinoxes, and compiled the first comprehensive star catalog.

Hero (or Heron) of Alexandria (ca. 10–70 CE) was a geometer and inventor. He collected geometric formulas from a variety of ancient sources on the areas and volumes of various solid and planar figures. He also invented over a hundred pneumatic devices, that is, machines that work by air, steam, or water pressure. These included a fire engine, a wind organ, and a steam-powered engine that was the first known device to transform steam into rotary motion. He also proposed mechanical devices that used levers, wedges, pulleys, and screws.

Claudius Ptolemy (ca. 90–ca. 168 CE) developed the detailed geocentric model of the solar system that enabled astronomers to predict the positions of planets, the rising and setting of stars, and eclipses of the sun and Earth's moon.

LUCRETIUS

Titus Lucretius Carus was a Roman citizen who lived around 100–50 BCE. While little is known of him, he wrote a 7,400-line poem, De rerum natura (The Nature of Things) that is considered one of the great works of the ages. It is also the most unusual of poems. It is not an epic tale of human or superhuman adventure. Nor is it myth or history, but a philosophical and scientific treatise written in Latin hexameter. Furthermore, the message is atheistic and materialistic, denying the existence of anything magical or supernatural, including an immortal soul, and proclaiming the evils of religion.17

The poem introduces few philosophical or scientific ideas original to the author but rather presents the worldview of Epicurus and the atomic theory as the master elaborated on what had been taught by Democritus. By putting the teachings of Epicurus in poetic form, Lucretius made them more palatable—indeed, he made them majestic and inspiring.

Many translations of De rerum natura now exist, although as we will see in the next chapter, that almost did not happen. In the seventeenth century, the great English poet John Dryden (1631–1700) translated selected portions, 615 lines out of 7,400, essentially rewriting them so they would be pleasing to the reader in English. He focused on subjects that appealed to him, such as the progress of love, the advantages of reason and moderation, and the inevitability of death. He ignored the philosophical passages, which offer the translator less freedom.¹⁸

I particularly enjoy these passages:

So when our mortal frame shall be disjoin'd

The lifeless lump uncoupled from the mind,

From sense of grief and pain we shall be free;

We shall not feel, because we will not be.

Nay, though our atoms should revolve by chance,

And matter leap into the former dance;

Though time our life and motion could restore

And make our bodies what they were before.

What gain to us would all this bustle bring?

The new-made man would be another thing;

When once an interrupting pause is made,

That individual Being is decayed.

We who are dead and gone, shall bear no part

In all the pleasures, nor shall feel the smart,

Which to that other Mortal shall accrue,

Whom of our matter time shall mold anew.

These passages recognize a fact that many scholars today fail to comprehend. Every event that happens in the universe is fundamentally reversible. The air in a room can rush out an opened door, leaving behind a perfect vacuum. All that has to occur is that the air molecules in the room, which are in random motion, be simultaneously moving in the direction of the door when the door is opened. That we never observe this to occur is purely a matter of chance. It is enormously unlikely, given the large number of molecules in the room, but technically not impossible.

However, if our “selves” are solely composed of all the atoms in our bodies, most particularly our brains, then why wouldn't the full self be restored? Dryden seems to hold a dualistic view, certainly common in his time as now, when he talks about “the lifeless lump uncoupled from the mind.” I don't think Lucretius meant that.

In what follows, I will provide some selected quotations from De rerum natura using a recent line-by-line translation in rhyme by A. E. Stallings that attempts to give some of the feel of the poetry of the work without departing too far from what Lucretius actually wrote.20

Let me begin very early in the poem, when Lucretius talks about how religion “breeds wickedness” and “gives rise to wrongful deeds.” He uses the tale in the Iliad where Agamemnon sacrifices his daughter Iphigenia as his ships sail to Troy:

With solemn ceremony, to the accompanying strain

Of loud-sung bridal hymns, but as a maiden, pure of stain,

To be impurely slaughtered, at the age when she should wed,

Sorrowful sacrifice slain at her father's hand instead.

All this for fair and favorable winds to sail the fleet along!—

So potent was Religion in persuading to do wrong. (1.96–101)

The poem tells us to observe nature in order to eliminate religious darkness:

This dread, these shadows of the mind, must be swept away

Not by rays of the sun nor by the brilliant beams of day,

But by observing Nature and her laws. And this will lay

The warp out for us—her first principle: that nothing's brought

Forth by any supernatural power out of naught. (1.146–50).

At this point, I want to correct a common misunderstanding. Ancient atomism has been interpreted, even to the present day, to imply that the existence of atoms was inferred by reason alone, thus providing a counterexample to the common view held by most scientists and philosophers of science that we can learn about the world only through observation. For example, in a 2012 op-ed piece in the New York Times titled, “Physicists, Stop the Churlishness,” essayist Jim Holt criticizes the public disdain that several top contemporary physicists hold for philosophy.21

Holt quotes Richard Feynman as mocking “cocktail-party philosophers” for thinking they can discover things about the world “by brainwork rather than experiment.” I have not been able to find the precise quotation, which Holt does not cite. However, Feynman does mention “cocktail-party philosophers” several times in chapter 16, volume 1, of his classic “Lectures on Physics.”²² Note that he did not say professional philosophers. In any case, Holt remarks, “Leucippus and Democritus…didn't come up with [the idea of atoms] by doing experiments.”

I agree that physicists should not disparage philosophy, which performs a valuable service in clarifying and interpreting scientific results. However, I do not know of any professional philosophers today who claim that we can discover things about the universe by thought alone. Yet, Holt seems to think just that. If Holt is implying that knowledge of the universe can be obtained by thought and reason alone, he is surely at odds with the thinking of most scientists and philosophers.

Certainly Leucippus and Democritus, or any ancients, did not do the type of carefully controlled experiments that mark science today. Indeed, virtually all ancient philosophers, including Plato and Aristotle as well as the atomists, expressed distrust in the senses and believed that they could be overruled by reason. It was not until almost two millennia later that Galileo (1564–1642) reversed the inequality and established the rule of observation over pure thought (as well as revelation), which then became the governing principle of the scientific revolution that followed.

Still, even after that, philosopher Immanuel Kant (1724–1804), in his Critique of Pure Reason, argued that the mind had access to truths about the universe that did not depend on observation, what he called synthetic a priori knowledge. One of his major examples was our intuition that space is described by Euclidean geometry. We now know that other geometries exist and that Einstein used non-Euclidean geometry to describe space in his general theory of relativity.

While general relativity was certainly a remarkable achievement of the human intellect, it was pursued because of the failure of Newton's theory of gravity to explain certain observations, such as the precession of the perihelion of Mercury, and was only accepted after it had explained these and successfully predicted other observations.

No one knows how the atomists arrived at the idea of atoms, but they weren't just brains in a vat operating by thought alone. They were living, experiencing human beings.

The following quotation from Lucretius shows that at least he, writing almost three centuries after Democritus, sought empirical justification for the atomic model.

Just in case you start to think this theory [atoms] is a lie,

Because these atoms can't be made out by the naked eye,

You yourself have to admit there are particles

Which are but which cannot be seen…(1.165–69)

For example,

Thus clearly there are particles of wind you cannot spy

That sweep the ocean and the land and clouds up in the sky. (1.277, 278)

Further, in book 2 he adds,

There's a model, you should realize,

A paradigm of this that's dancing right before your eyes—

For look well when you let the sun peep in a shuttered room

Pouring forth the brilliance of its beams into the gloom,

And you'll see myriads of motes all moving many ways

Throughout the void and intermingling in the golden rays. (2.112–17)…

Such turmoil means that there are secret motions, out of sight,

That lie concealed in matter. For you'll see the motes careen

Off course, and then bound back again, by means of blows unseen. (2.126–28)

This remarkable passage is suggestive of the motion that we now know as Brownian motion. Einstein and Jean Baptiste Perrin used Brownian motion in the early twentieth century to demonstrate conclusively the existence of atoms. French philosopher Gaston Bachelard (1884–1962) was of the opinion that observations involving dust provided the essential notion of atoms so that it was not just a product of pure thought:

Without this special experience, atomism would never have evolved into anything more than a clever doctrine, entirely speculative, in which the initial gamble of thought would have been justified by no observation. Instead, by virtue of the existence of dust, atomism was able to receive from the time of its inception an intuitive basis that is both permanent and richly evocative.23

However, in this case, the dust motes are also moved around by air currents. In the Brownian motion observed in other media, currents are negligible.

Continuing with the poem, Lucretius follows Epicurus in contradicting Aristotle on the existence of the void:

For if there were no emptiness, nothing could move; since it's

The property of matter to obstruct and resist,

And matter would be everywhere at all times. So I say

Nothing could move forward because nothing would give way. (1.331–36)

Here he also gives basically the definition of matter that I always state as follows: matter is what kicks back when you kick it.

Lucretius also anticipates modern physics in his view of time:

As slavery, penury and riches, freedom, war and peace,

Whatever comes and goes while natures stay unchanging, these

We rightly tend to term as ‘consequences’ or ‘events’.

Nor does Time exist in its own right. But there's a sense

Derived from things themselves as to what's happened in the past,

And what is here and now, and what will come about at last.

No one perceives Time in and of itself, you must attest,

And something apart from things at motion and from things at rest. (1.455–63)

The notion of time expressed above clashes with the common—sense view but is very suggestive of the meaning of time implied by the theories of relativity.

We saw above that Epicurus had introduced the idea that atoms randomly “swerve” to the side during their natural downward motion, so that they could interact with other atoms. Here's how Lucretius describes it:

…when bodies fall through empty space

Straight down, under their own weight, at a random time and place,

They swerve a little. Just enough of a swerve for you to call

It a change of course. Unless inclined to swerve, all things would fall

Right through the deep abyss like drops of rain. There would be no

Collisions, and no atom would meet atom with a blow. (2.216–23)

Richard Carrier has listed twenty-two “predictions” made by Lucretius that have been verified by modern science. Carrier has also provided the exact locations with the poem.24 Of course, these were not the type of precise, falsifiable predictions we see in science today, and they are, in some cases, stretching it a bit. Nevertheless, they illustrate that the successful prediction of atoms was not simply a lucky random occurrence that might have been made by an astrologer or an alchemist, but that it is part of the larger worldview that follows naturally from the assumption that everything is particles and the void. Now that the atomic model has been fully verified by modern science, that worldview is ready to be taken seriously.

Finally, I mentioned in the preface that the atomists anticipated evolution by natural selection. Lucretius talks about how, in the beginning, there were many freaks with various deformities that made them unable to reproduce or forage for food and so their species died off. You will get objections from some scholars that this was not really evolution, so I will just provide the following excerpt:

Many kinds of creatures must have vanished with no trace

Because they could not reproduce or hammer out their race.

For any beast you look upon that drinks life-giving air,

Has either wits, or bravery, or fleetness of foot to spare,

Ensuring its survival from its genesis to now. (5.855–59)

THE ANTIATOMISTS

Aristotle

Aristotle had no sympathy for atomism. He refined the model attributed to the pre-Socratic Empedocles (ca. 490–430 BCE) that fire, earth, air, and water constitute the basic elements out of which everything else is formed.

Aristotle disagreed with the atomist view that observable qualities such as color and smell were “conventions” and that only atoms are real. Rather, he insisted these were intrinsic properties of bodies that had nothing to do with the observer. Aristotle's primary reason for rejecting atomism was his conviction that a void was logically impossible. Putting it in modern terms, he also thought that the natural speed of a body was inversely proportional to some resisting factor. Since the void has no resisting power, atomic speeds are infinite, which Aristotle considered absurd. It followed, then, that there is no void.

Aristotle's argument was based on his theory of motion, which was grossly wrong, where by “grossly wrong” I mean totally inconsistent with observations.

What were Aristotle's gross errors?

He failed to grasp the principle of inertia, in which a body in motion can remain in motion. He assumed that in order to move, a body must be pushed along by some agent or motive power.
He assumed there were two types of motion: “natural” and “forced.” The basic elements fire and air move naturally upward, while earth and water move naturally downward. Celestial bodies move naturally in circles. The agent for these motions was Aristotle's “final cause,” the teleological principle in which everything has a purpose toward which it naturally progresses. All other motion is forced.

These views led Aristotle to believe that atoms and the void is necessarily a false theory. He reasoned that if an object were placed all by itself in a void, there could be no natural motion since there was no up or down. The object would not know where to go. Furthermore, being alone, it had no forces acting on it. It followed that motion in a void is impossible.

Aristotle's second misconception led to a third error that would also have far-ranging consequences on scholarship in the Middle Ages. Aristotle concluded that a different set of dynamical principles governed Earth and the heavens. Here he actually retrogressed from the views of the Milesian philosophers. It was only with the discoveries of Kepler, Galileo, and Newton two millennia later that it was established that physics is universal.25 It is surely significant that the scientific revolution of the seventeenth and eighteenth centuries occurred outside the Church-controlled universities in Europe where Aristotelian scholasticism was being taught as dogma.

The Stoics

Pullman identifies the physics doctrines of the Stoic philosophers as “the clearest expression of opposition to the teachings of the atomists.”²⁶ Stoicism was founded in Athens by Zeno of Cittium in the third century BCE and had adherents well into the Common Era, including the Roman emperor Marcus Aurelius (121–180). Stoicism fizzled out in 529 when the emperor Justinian I (482–565) shut down all philosophical schools so that Christianity would have no opposition.

As we have already seen in the case of atomism, a philosophy of the nature of the universe affects thinking in other areas such as religion and morality. Such was the case with the Stoics. While the atomists divided the universe into discrete parts separated by empty space, the Stoics viewed it as a continuum without any void. While the atomists believed in an impersonal universe, the Stoics were pantheists, holding that the universe was an active, reasoning substance.

In his work De Natura Deorem (The Nature of the Gods), the great Roman statesman and philosopher Cicero (106–43 BCE) explains the Stoic view this way:

The universe itself is god and the universal outpouring of its soul; it is this same world's guiding principle, operating in mind and reason, together with the common nature of things and the totality which embraces all existence.

Unlike the atomists, who believed that material atoms are unlimited and eternal, the Stoics’ entire world was finite and corruptible. Unlike the atomists, who believed that chance played a role in the evolution of the world, to the Stoics, everything was predetermined by the ultimate organizing force. Out of this belief came the well-known characteristic that today is commonly called stoicism, the acceptance of fate. Atomism fully accepts human free will, although to the atomists it is the result of the random swerve, which is not exactly what Christianity and other religions think of as free will.27

Like so many people today, the Stoics could not see how the complexity of the world could arise by chance. Cicero scoffed at the notion, comparing it with tossing a vast quantity of the twenty-one letters of the Latin alphabet on the ground and having it produce Ennius's Annals.²⁸

Cicero also did not accept the Epicurean notion of the swerve, as described previously. What causes an atom to deviate from its path? Once again, we see how difficult it is to accept the notion that not everything requires a cause, that some things simply happen by chance.

The Neoplatonists

The Neoplatonists constituted the final group of early antiatomists. Their school was founded by Plotinus of Lykopolis (205–270 CE). His collected writings appear in the six Enneads and were a great influence on Christian theology as incorporated by Augustine of Hippo in the fifth century CE.

Although the Neoplatonists did not support stoicism, they agreed that it was absurd to think the world could be the result of spontaneity and chance, that everything simply arose from the movements of atoms. In Enneads 2.1, Plotinus asks,

What motion of atoms can one attribute to the actions and passions of the soul?…What movements of atoms stir the thought of the geometer, the arithmetician, or the astronomer? What movements are the source of wisdom?

Plotinus anticipates many modern theological arguments when he insists the following in Enneads 4.4:

It is impossible for the association of material bodies to produce life and for things devoid of intelligence to engender intelligence.…For there would be no composite bodies and not even simple bodies in the reality of the world, were it not for the pervasive soul of the universe.

As we will see, in every important respect, the atomists were so right and the antiatomists so wrong.