Insights on Epicurean Physics
by Erik Anderson

© 1997, 2000, Erik Anderson


The doctrine of atomism, a Greek innovation introduced by philosophers Leucippus of Miletus and Democritus of Abdera in the 5th century BC, describes a universe in which all tangible things are composed of minute indivisible particles of matter: atoms.   Epicurus subsequently developed a modified theory atomism for his own philosophical system, using it as a basis to tie in his epistemological and ethical theories.

Atoms Defined

In our age, the word atom is most typically used to denote a periodical element—a system of protons, neutrons, and electrons, which conjures up the image of a miniature solar system.  These are not atoms in the classical sense.  It was merely by linguistic accident that the elements listed on periodic tables became known as atoms—not unlike how the native Americans became known as Indians.  For just as Christopher Columbus crossed the Atlantic and thought he had arrived at India, chemists in the 19th century isolated such substances as Hydrogen, Carbon, and Oxygen, and thought they had arrived at the ultimate building blocks of all existing things—but in fact, they still had a ways to go, as was confirmed when physicists later “split the atom” in the very next century.

The atoms of the ancient philosophers are what modern particle physicists now call fundamental particles.  Even today, we do not know for sure which of the known particles are indeed fundamental, nor how many different types of them may ultimately exist.  The electron could very well be a fundamental particle—to date, no one has ever “split the electron.”  Protons and neutrons, by contrast, are definitely not fundamental particles—these larger entities turn out to be formed by trios of sub-particles called quarks.  And what are quarks made of?  The mystery continues to unfold.

However, contemporary physicists nearly all agree that particles of matter cannot be broken down for ever and ever—there must be some quantum level at which particles are irreducible.  We can be assured of this because it is apparent that the way that matter behaves at the scale of electrons and quarks, is wholly different from the behavior we see on the scale of billiard balls or planets.  This is because particles exhibit quantum effects—their measured qualities are limited to discrete values.  If particles were infinitely divisible, then any object could be scaled down to any size without being subject to such effects: there would be no reason for matter to group itself together into periodic elements, and, just as in the tales of Gulliver’s Travels, everything we know of could exist in any size: people, cities, worlds, or what-have-you.  But indeed this is not the case.  Scale matters, because the building blocks of all things are discrete entities of fixed sizes.

Permanence of Matter

The atoms of Democritus and Epicurus were also deemed to be eternal, i.e., they can neither be destroyed, nor created.  This universal law is what contemporary physicists deem the “law of conservation”—and it applies equally to mass and energy.

People are born young and grow old, but in one aspect, we are all the same age: all of the matter in our bodies is as old as the universe.  Before they became a part of us, each one of our “personal” atoms had been somewhere else: in the air we eventually breathed, the water we eventually drank, and the food we eventually ate.  And before then, they resided in the soil of the earth, the scattered dust of outer space, and even in the blazing depths of ancient stars.  When we die, our bodies will be dissolved into their elements, which shall continue on without us to be redistributed throughout the world.  The planet Earth itself will eventually break down at some unknown time many eons from now, and all of its elements will be carried away by the exploding sun and strewn throughout space.  From those ashes, new worlds may be formed as the atoms regroup.   But the creation of anything new may only come about by the demolition of something previously existing: you can’t get something from nothing.

If matter cannot be created, how do we then account for the creation of the universe?  It must stand to reason that all matter that exists today has existed for all time.  Does that mean forever—an infinite amount of time?  That is indeed what the ancient Epicureans naturally assumed, but it may not be necessarily so.

Properties of Space

Matter is not the only thing that exists in the universe.  There is also a counterpart to matter, which the ancient atomists called the void.  The term is used to describe the emptiness of unoccupied places, a concept that we usually regard as space.  Just because the void is essentially “nothingness,” it still does exist, as an intangible medium that contains and conducts the transportation of matter.  If only matter existed without the accompaniment of void, the atomists reasoned, then nothing could ever move, because the entire universe would be packed absolutely tight with matter.  But the void is a perfect superconductor, utterly passive, presenting no friction whatsoever to the atoms which pass through it.

Matter and void are the fundamental constituents of all existence, and the Epicureans asserted that no third constituent is possible.  If something is tangible to any degree, then it contains material—what dif not, then it is merely spatial.  All the phenomena that we know of, or that we attempt to discover, or that we care to speculate about, can and must be accounted for in terms of indivisible bodies moving through empty space.

Besides intangibility, another essential property of the void is its boundlessness, meaning that it is not delineated by any boundaries, edges, or extremities.  Does this mean that the reaches of space extend forever and that the universe is infinitely large?   The Epicureans thought so, for if there was indeed an “end of the universe,” what would happen, as Lucretius supposed, if someone went there and threw a spear beyond the point where he was?  One of two things would happen: either the spear would proceed onwards, or something would get in its way.  In either case there would have to be something beyond that point.  In neither case has one arrived at the end of the universe.  This type of persuasive reasoning carried on for ages, and was believed by most every scientific thinker, including the young Albert Einstein.

Modern Cosmological Considerations

However, once Einstein had developed the principles of general relativity in 1915, the way had been paved for a new possibility: a boundless yet finite universe.  What makes this arrangement possible is that the “void” has yet another attribute, unimagined by the ancients, which is: shape.  Gravity, according to General Relativity, is an effect of curved space.  If space can be curved, then the dimensions of the universe could very well be circular, not unlike the dimensions of the Earth.  The analogy is an apt one, because it’s easy for anyone today to realize that the Earth’s surface has no “ends,” but is a continuous plane wrapped upon itself—and in spite of having no such boundaries, the Earth’s surface is definitely not infinite.  We can imagine what would happen if Lucretius departed from Rome to throw his spear off the “edge of the Earth”—in his quest to find it, he would march and sail along a straight path, unwittingly circumnavigating the entire planet, and winding up right back where he started from.  This would happen no matter what direction he traveled: east, north, southwest, etc.  He might be driven to conclude that “all roads lead to Rome” indeed!

Although it is much more difficult to visualize, the same principle can be applied to three-dimensional space curved upon itself.  This implies that a hypothetical expedition across the universe in any particular direction would always lead the imaginary space traveler back to where he started—regardless of his direction of travel.  However, we should not expect such a bold voyage to succeed, because it is now believed that the universe is expanding faster than any spaceship could ever travel.

This most revolutionary discovery came in 1929, at the Mt. Wilson Observatory in California, where astronomer Edwin Hubble measured and cataloged the distances of galaxies.  As he compiled his data, he found a general correlation between distance and space motion: the further away a galaxy was, the faster it receded from Earth (and consequently: from all the other galaxies too).  The immediate implication of this observation was that the universe was spreading itself thin.  So if matter disperses itself over time, an even more profound implication follows: the further back you trace the history of the universe, the denser the universe must have been.  Trace back far enough, somewhere between 12 and 20 billion years ago, and you’ll have reached a point of infinite density.  The entire universe was then contained within the space of a pinprick.  From this infinitesimal spot came pouring forth all the matter that exists, in a violent expulsion that echoes down to the present day.  The big bang theory was born.

Relativity, curved space, and the Big Bang may seem far removed from the humble cosmology of an ancient Greek like Epicurus, but this modern framework will provide us with a novel means of substantiating one of Epicurus’ most controversial conjectures: the atomic swerve.

The Atomic Swerve

In the atomic system of Democritus, cosmology is entirely deterministic, meaning that everything that happens in the universe is the inevitable consequence of what happened before.  According to this view, the trajectory of each and every atom proceeding along straight-line paths that are solely altered by inevitable collisions with other atoms throughout the course of history—all events, past, present, and future, including the fact that you exist and are reading this sentence right now, are dictated by fate.  Epicurus, contrarily, proposed that as atoms traverse the void, they may deviate from a straight-line path at “uncertain times and places.”  These random deviations are very slight, and they occur without any connection to the behavior of other atoms.  In philosophical terms, Epicurus takes on the position of indeterminism, meaning that whatever happens in the universe is incidental, rather than inevitable.

Contemporary physicists still disagree as to whether matter behaves in a fundamentally deterministic or indeterministic manner.  The 1927 discovery of the uncertainty principle, by Werner Heisenberg, has been a prominent catalyst for this debate.  The dilemma which the principle presents, is that it is impossible to ascertain both the position and momentum of any particle with precision—the more accurate determination of the one must entail a less precise measurement of the other.  Because of this inherent imprecision, a degree of “indeterminism” must be factored into predictions, within certain limits of probability.  However, when we speak of “indeterminism” in its full philosophical sense, we are talking about a stronger meaning: random deviations that are axiomatic—a fundamental property of matter itself.  Now because there are limits to what can be measured, as Heisenberg discovered, all this implies is that we can’t make assertions about the events operating beyond those limits.  So the uncertainly principle does not substantiate either side of the argument.

Epicurus’ criticism of Democritus’ determinism, however, stems from a much more blatant observation—an observation as large as the universe itself: if elements never deviated from straight-line paths through the void, how would they have ever found an occasion to collide in the first place?  Why wouldn’t the atoms just rain down in parallel paths forever?  This is exactly the same issue that cosmologists are struggling with today in attempting to describe the early history of the universe.  They want to know how it came about that nature abounds with groupings of galaxies, stars, and planets, rather than an evenly distributed atomic fog.

In 1992, an exciting experiment was undertaken to investigate how the universe evolved the structure it has today: the COBE satellite project.  The microwave detectors onboard this craft mapped the cosmic background radiation which appears at the “edge” of the visible universe in every direction we look.   What we are actually seeing there is the light given off by the receding plasma which constituted the dense early universe (now arriving as microwave energy due to wavelength elongation caused by the Doppler effect). The resulting map depicted minute temperature variances distributed chaotically—regions of higher temperatures signifying areas of higher density.  The areas of higher density would later form the complex structures of galactic clusters that we see today, while the pockets of lower density would become rapidly dispersed in intergalactic space.

The great scientific/philosophic question surrounding these findings is: what would account for these variances?  If, at the initial state of the universe, all matter was packed into a geometric point, then the initial condition of the universe started was a symmetrical, homogenous arrangement—it makes no sense, after all, to speak of a “lop-sided” zero-dimensional point!   But if the evenly spaced atoms of the early universe were to have fanned out in parallel rays, powdering space with equal atomic density, the variances in temperature that we see in the COBE images could not exist—and neither would the galaxies, worlds, nor us!

Hence, the Epicurean theory of the “atomic swerve” provides an accounting for that “initial lateral motion” which made subsequent atomic collisions possible.  It is therefore reasonable to assume that atoms are still “swerving” today.