I am currently re-reading Epicurus’ Books On Nature in Les Epicuriens , which is based on lectures given by Epicurus. We know that they were given late in Epicurus’ philosophical career because, in some of the lectures, Epicurus refers back to discussions with Metrodorus that they had years prior “back in the day”, and recognizes previous doctrinal mistakes that had been rectified after years of conversations to clarify their philosophical investigations (particularly concerning their “change of names” practices).

All of this means that we must be careful to not attribute too much authority to any extant writings that may have come from the earlier period. It also means that these books are actually transcripts of advanced lectures given by Epicurus after many years of engaging in philosophical discourse with input from his friends. Let’s try to imagine or re-construct what these lectures or discussions consisted of, so that we can create modern dialogues to replace the literature that is missing.

Book 1

Book One establishes clearly that all things are made of particles and void (cites Against Colotes). Les Epicuriens commentators say that this book is summarized in the Epistle to Herodotus.

Book 2

Book II establishes the existence of particles of light (photons, in modern physics), and establishes clearly that the speed of light is the speed limit of the universe.

Much of the following discussion focuses on how it is that bodies emit these particles (called simulacra in the original text). It is clear that these simulacra are particles by the fact that when they encounter resistance they bounce back, like any other particle. The sun emits light, it reaches water and we see blue because the solar “rays” (photons) do not fully penetrate into the depth of waters. Instead, these photons bounce back and reach our eyes. The denser the water, the less photons penetrate. This is how some solid bodies allow some light through, because they are not as dense as other walls.

A light bulb emits light particles, they bounce against a wall, and our eyes receive the “color”. This color is an emergent property of the photons when they bounce against the particles of the bodies that they touch.

Book II concludes by saying that they have just proven that light is made of these particles and that nothing can move faster than photons, and says here that what follows after this book are the “subjects appropriate to treat after this (subject)”. However, Books 3-9 were never recovered.

The following video follows up on the contents of this book. It helps to connect the nature of light as particles that travel at a certain speed through the void, with interesting repercussions of this insight that include the relativity of time and of all things. If the universe is only 14 billion years old, how can it be 92 billion light years wide?

The video also helps to explain why the ancient Epicureans concluded that time was relative and an emergent property of bodies, which was a very advanced cosmological position for them to assume 2,300 years ago. Epicurus’ Epistle to Herodotus says that “we must not believe that time has any properties other than being an incident to bodies”.

Epicurean cosmology establishes that bodies are made up of particles and void, and their conventional existence and properties are established by the quantity and other properties of the particles that make up the bodies. However, in the process of acquiring increased complexity and interacting with each other, bodies also acquire secondary, relational properties which are no less real than their conventional properties. A magnet’s attraction of certain metals is real. The attraction between two lovers is real, and so is the gravity between a planet and its host star. The chemical interaction that causes an explosion is also real. We observe these phenomena and, although they are not conventionally made up of “particles and void”, they are secondary properties of bodies exhibit according to the observable and measurable laws of nature.

Although those relational / secondary qualities are not eternal, or even essential, the Epistle to Herodotus teaches that we must not banish them from our minds. Incidental qualities do not have a material existence (they are not “atoms and void”), nor do they exist independently in some reality that is beyond our comprehension (some Platonic ether, or heaven, etc.). We must, instead, consider the incidental qualities of bodies as having exactly the character that our sensations reveal them to possess. Today, we are able to measure magnetic forces or gravitational pull, and we know these forces to be emergent properties of the relevant bodies. The epistle then goes on to explain that Time is one such incidental property of nature, that it does not exist apart from bodies:

For example, it is important to grasp firmly that “time” neither has a material existence, nor does it exist independently, apart from bodies. Nor must we think of “time” as a general conception, such as those conceptions which are formed by reasoning in our minds. Instead, we must think of time by referring to our intuitions, our mental apprehensions formed by anticipations, and it is in this context that we speak of a “long time,” or a “short time,” applying our intuitions to time as we do to other incidental qualities. In evaluating time as an incidental quality, we must not search for expressions that we may think are better than those which are in common use, and we must not believe that time has any properties other than being an incident to bodies. We must evaluate time only in accord with our intuitions or anticipations.

Let’s unpack what’s being said here. Epicureans were known for clear, concise speech and for their insistence on calling things by their proper name, and for names to reflect things as they are observed in nature. Poetically addressing Love as Eros (imagined as a baby with diapers throwing arrows) or Time as Chronos (a scary old man whose approach can’t be avoided and who will, in the end, inevitably swallow us) is good in the realm of poetry and myth, but not in the realm of the study of nature.

Time is also not Platonic (that is, unnatural and unreal, a mere idea). It is not a God (as the ancients believed). All things are conventionally made of atoms and void. So the question that the ancient atomists would have been discussing was something like “Does Time not exist, then? If it does, in what way does Time exist“? And it made sense that Time, as a natural phenomenon, must have been an emergent or relational property of bodies. Ancient Epicureans posited that Time is a natural phenomenon and sought diligently to evaluate the nature of Time based on the study of nature by the use of our natural faculties by which we synchronize to nature’s circadian rhythms. The Letter continues:

For indeed, we need no demonstration, but only to reflect, to see that we associate time with days and nights, and with our internal feelings, and with our state of rest. These perceptions of incidental qualities are the root of what we call “time.”

Interesting to note that Epicurus links time to our anticipation of and attunement with the circadian rhythms. Epicurus here was saying that our own organism has a faculty that apprehends time.

Scientists now know that the Moon used to be a planet the size of Mars that collided w Earth early on, and has slowly been moving a ay from Earth in its orbit. Because of this, our Moon used to be much bigger in our sky billions, and later millions of years ago, and will eventually leave our orbit and become a “ploonet”. Also because of this, and because Earth and Moon are still tidally locked, days and nights used to be much shorter in the past (one day used to be only a few hours long), and they will get progressively longer in the future. Our sense of time will continue to evolve with our local planet-moon dance.

I wish to accentuate that to say that Time is incidental / relational to bodies is to relativize it. One light year is the distance a photon travels between two points in a year. This means that the light that we see coming from the stars was emitted millions of years ago. These stellar photons are (together with time) emergent properties of bodies and, since the speed of light is the speed limit of the cosmos, the photons have been traveling through the void together with time from those stellar bodies to our planet, some of them for millions of years.

Time is an emergent, natural process. This is what is meant by the Epicurean doctrine that “we must not believe that time has any properties other than being an incident to bodies”: that Time is neither a God, nor an “absolute” Platonic idea, but a natural, emergent, relational property of bodies (of matter) in space. We can only measure Time in units which–because all things are moving constantly relative to each other–are tied to orbital movements of bodies in space.

Books 3-4

Les Epicuriens says that these books are summarized in paragraphs 49-53 of the Letter to Herodotus, and Book 4 included Epicurus’ theory of memory–about which we get glimpses in the Lucretian “neural pathways” passage, so we do know that such a theory must have existed.

Books 5-9

Les Epicuriens says that these books are summarized in paragraphs 54-73 of the Letter to Herodotus.

Book 10

Discusses a bit about the nature of time, how to measure it (mentions days and nights), on the importance of using conventional language for it, and the fact that time is real.

Further Reading:

Les Epicuriens [Bibliotheque de la Pleiade] (French Edition)

Epicurus’ Letter to Herodotus