The Nature of Things

De Rerum Natura. Lucretius (98 – 55 BC ?)

Let us now turn our attention to the physical world. Does chance exist in
nature? This question was raised by ancient Greek philosophers.
With them, we are at the fresh start of Philosophy, Mathematics and
Physics. The framework in which classical and modern philosophy and
science will develop is set. For example, Archimedes fundamental
principle of hydrostatics is the first example of physical law. Think of
Newton’s famous quote: “If I have seen further, it is by standing on the
shoulders of giants”.

In this long poem the aim of Lucretius was to set out faithfully the
doctrine of the Greek philosopher Epicurus (Ἐπίκουρος ) (341- 270 BC).
Most of Epicurus work has been lost. Only two long letters summarizing
his doctrine remain.
For the ancient Greeks, physics was a part of philosophy. Mathematics
were first an exercise of philosophical logic.
Lucretius amazing vision of an atomistic, chaotic, infinite universe, has
been influential in building the physical, materialistic conception of
nature which is presently dominant.
The present editions of Lucretius poem are based on two manuscripts
from the ninth century, which were copied from older ones, now almost
certainly lost forever.
We will go through an introduction to his work,1 illustrated by a few
excerpts taken from an English translation.2 They are related to our
inquiry.

1
W.H.D Rouse, M.F. Smith. Loeb Classical Library.
2
Translation by Ronald Melville. Oxford University Press
 Epicurus system
The aim of Epicurus' teaching was to give men a new freedom - not
political freedom, but an individual freedom: he aimed to liberate them
from all fears and disturbances, to make them self-sufficient, and so
enable them to attain tranquillity of mind. Although he was primarily a
moral philosopher, his definition of philosophy being " an activity that
through discussion and reasoning secures the happy life ", he believed that
it is essential to make a scientific study of the nature of the universe. The
purpose of this study is not to acquire scientific knowledge for its own
sake, but solely to free oneself from the unnecessary fears and suspicions
which disturb the mind and preclude the attainment of happiness,
especially fear of the gods and fear of death. Thus, physics is entirely
subordinate to ethics, being merely the necessary means whereby the
ethical goal is achieved. According to Epicurus, desires are unlimited and
impossible to satisfy, and therefore involve pain, and therefore must be
eliminated. Hence his advice concerning a young disciple: « If you wish
to make Pythocles rich, do not increase his means, but diminish his
desire ». The Epicurean attitude to the virtues is utilitarian. It is impossible
to live a pleasant life without living virtuously, and to live virtuously
without living a pleasant life, hence virtue must be practised.

Epicurus' system is divided into three parts: Canonic, Physics, and Ethics.
The Canonic is his theory of knowledge. There are three criteria of truth:
sensation, preconceptions, and feelings. Sensation is the primary standard
of truth. If an error is made, that is not because the sensation is not true,
but because the reason draws a wrong conclusion from the evidence the
sensation provides). With the repetition of sensations, images of each
class of things accumulate in the mind to form a general idea or
preconception to which other examples are referred. (Artificial intelligence is
working in this way).

Without these preconceptions, attainment of scientific knowledge would

be impossible, for sensation by itself is " irrational and incapable of
memory ". As for the third criterion of truth, "there are two feelings,
pleasure and pain, which affect every living creature, it is through these
that choice and avoidance are determined". Thus the feelings of pleasure
and pain are the supreme test in matters of morality and conduct, and since
they are a part of sensation, it is true to say that Epicurus' ethical theory,
like his physical theory, is founded on the validity of sensation.

Physics
Epicurus derived his physical theory from Democritus (Δημόκριτος)
(c. 460 BC – 370 BC) and his master Leucippus (Λεύκιππος).
However, he made some important alterations to Democritus' theory, and
differed from him in making physics subservient to ethics.
The first principles of Epicurean physics are that " nothing is created out
of nothing " (Lucr. 1.150)

For if things came out of nothing, all kinds of things

Could be produced from all things. Nothing would need a seed.
Men could arise from the sea, and scaly fish
From earth, and birds hatch in the sky.

And "nothing is destroyed into nothing " (Lucr. 1.215).

The next great principle is this: that nature

Resolves all things back into their elements
And never reduces anything to nothing.
If anything were mortal in all its parts,
Anything might suddenly perish, snatched from sight.

In other words, Epicurus shared the belief of other ancient physicists in

the conservation of matter. The universe consists of matter and void.
These are the only ultimate realities: nothing that is distinct from them can
exist. That matter exists is proved by sensation; and if there were no void,
matter would be unable to move whereas sensation tells us that it does
move.
And however solid things are thought to be
Here is proof that you can see they are really porous.
In rocky caverns water oozes through,
the whole place weeping with a stream of drops.
Food spreads to every part of an animal's body.
Trees grow and in due time put forth their fruits,
Because all over them through trunks and branches
Right from the deepest roots food Makes its way.
Sounds pass through walls, and fly into closed buildings,

Matter exists in the form of an infinite number of absolutely solid,

indivisible, and unchangeable particles (Lucr. 1.483).

Material objects are of two kinds, partly atoms

And partly also compounds formed from atoms.
The atoms themselves no force can ever quench,
For by their solidity in the end they win.
Though it is difficult to believe that anything
That is completely solid can exist.
For lightning passes through the walls of houses,
And likewise, sound and voices; iron glows
White hot in fire, and boulders burst apart
In the fierce blaze of heat; the solidness
Of gold grows soft and melts, the ice of bronze
Is overcome by fire and liquefied

Being indivisible, the particles are called in Greek atomoi (ἄτoμoι = “that
cannot be cut”).

The indivisible nature of the atom is very important for Epicurus: like the
earlier atomists, he believed that unless there are imperishable elements,
unless there is a point beyond which further division of matter is
impossible, there can be no permanence for the universe; if there were not
something indestructible to survive when compound bodies are dissolved,
everything would long ago have been destroyed into nothing. The atoms
are imperceptibly small

Lest you begin perchance to doubt my words,

Because our eyes can't see first elements,
Learn now of things you must yourself admit
Exist, and yet remain invisible.
The wind, its might aroused, lashes the sea
And sinks great ships and tears the clouds apart.
With whirling tempest sweeping across the plains
It strews them with great trees, the mountain tops.
It rocks amain3 with forest-felling blasts
So fierce the howling fury of the gale,
So wild and menacing the wind's deep roar.

Therefore, they must be investigated with the help of analogy. They are
homogeneous in substance, but differ in shape, size, and weight, and it is
these differences, and also the differences in their movements, positions,
and combinations, which account for all the variety of things in the
universe. Whereas Democritus believed that the number of atomic shapes
and sizes is infinite, Epicurus argued that although the number is
inconceivably large, it is finite, for otherwise some of the atoms would be
visible and even of immeasurable magnitude.
The extent of the void, like the number of the atoms, is infinite, and
naturally the universe which they compose is infinite (Lucr. 1.951).

We find then that the universe is not bounded

In any direction. If it were, it would need to have
An extremity. But nothing can have an extremity
Unless there is something outside to limit it,
Something beyond to bound it, some clear point

3
amain: with great force, haste (archaic)
Further than which our senses cannot reach.
Now since we must admit that there is nothing
Beyond the sum of things, it has no extremity.
Therefore, it has no end, nor any limit.
Nor does it matter in what part of it
You stand: wherever a man takes his place
It stretches always boundless, infinite.

Note this argument is in fact wrong. Think of a circle in one dimension,

or of a sphere in two dimensions. A three-dimensional hypersphere can
be constructed algebraically.

All atoms are always in motion.

And here's a thing that need cause no surprise:

That though all atoms are in ceaseless motion
Their total seems to stand in total rest,
Except so far as individual objects
Make movements by the movements of their bodies.
For all the nature of the primal atoms
Lies hidden far beneath our senses; therefore since
You cannot see them you cannot see their movements.
Indeed, things we can see, if some great distance
Divides them from us, oft conceal their movements.
You see sheep on a hillside creeping forward
Cropping the fresh green grass new-pearled with dew
Where pastures new invite and tempt them on,
And fat lambs play and butt and frisk4 around
We see all this confused and blurred by distance,
A white patch standing still amid the green.
And when in mimic war the mighty legions
Fill all the plain with movements far and wide,
And sheen of armour rises to the sky;

4
frisk:leap in a playful way; butt:push head first
Earth flashes with bronze; the tramp of marching feet
Resounds on high; the hills struck by the noise
Throw back the echoes to the stars of heaven;
And wheeling5 horsemen gallop, and suddenly
Charge, and shake all the plain with their attack—
And yet among high mountains there's a place
From which they seem to stand still, motionless,
A flash of brightness on the plain below.

First let us deal with the motion of atoms moving freely through the void.
Whereas Democritus believed that atoms move in all directions, Epicurus
supposed that they are drawn downwards by their weight. For atomic
compounds to be formed, it is essential for atomic collisions to occur. If
all the atoms are moving straight down in the same direction, how do
collisions occur? One might suppose that the heavier atoms move faster
than the lighter ones and so catch them up, but this answer is unacceptable,
for, as Epicurus brilliantly inferred, objects of different weight falling in
a vacuum fall with equal velocity (Lucr.2.225). Instead he held that, as the
atoms are carried down through the void by their own weight, at random
times and places they swerve slightly from their course as a bus driver
swerves to avoid a cyclist. (Lucr. 2.216)

Now here is another thing I want you to understand.

While atoms move by their own weight straight down
Through the empty void, at quite uncertain times
And uncertain places they swerve slightly from their course.
You might call it no more than a mere change of motion.
If this did not occur, then all of them
Would fall like drops of rain down through the void.
There would be no collisions, no impacts
Of atoms upon atom, so that nature
Would never have created anything.

5
wheeling: turning
The number of worlds is also infinite (Lucr. 2.1048).

Everywhere around us
On either side, above, below, throughout the universe,
There is no end. I have proved this, and the facts themselves
Shout it aloud. Deep space shines clear to see.
Now since space lies in all direction infinite
And seeds in number numberless for ever
Fly all around in countless different ways
Through an unfathomable universe
Perpetually driven by everlasting motion,
It must be deemed in high degree unlikely
That this earth, this sky, alone have been created,
And all those bodies of matter outside do nothing.
And added proof of this lies in the fact
That nature made this world. The seeds of things
In random and spontaneous collision
In countless ways clashed, heedless, purposeless, in vain
Until at last such particles combined
As suddenly united could become in each case
The beginning of mighty things
Of earth and sea and sky, and the generation of living creatures.

This famous theory of an atomic swerve (clinamen) was meant to account

not only for the formation of compound bodies, but also, most
importantly, for free will (Lucr. 2.251).

Again, if movement always is connected,

New motions coming from old in order fixed,
If atoms never swerve and make beginning
Of motions that can break the bonds of fate,
And foil6 the infinite chain of cause and effect,
What is the origin of this free will

6
Foil: defeat
Possessed by living creatures throughout the earth?
Whence comes, I say, this will-power wrested from the fates
Whereby we each proceed where pleasure leads,
Swerving our course at no fixed time or place
But where the bidding of our hearts directs?
For beyond doubt the power of the will
Originates these things and gives them birth
And from the will movements flow through the limbs.
Consider racehorses. The starting gates
Fly open, the horses are strong and keen to go,
But can't break out as fast as their minds would wish.
For all the mass of matter must be stirred
Through the whole body, roused through every limb,
Before it can follow the prompting of the mind.
So you may see that heart begins the motion
Then mind and will join in and drive it on
Until it reaches all the body and limbs.

This is an extremely important point.

Epicurus, as we have already seen, differed from Democritus in regarding

physics as subordinate to ethics. And whereas Democritus was a
determinist, Epicurus believed—and this belief was derived from Socrates
and his followers, especially Plato and Aristotle—that the individual is a
free being with moral responsibility for his own actions. That is why he
could not accept that all the atoms always move predictably and
mechanically in accordance with fixed natural laws: for him the moral fact
of free will is proof that the atoms sometimes move unpredictably and
spontaneously. The great importance which he attached to the
preservation of free will can be judged from the following statement: “It
would be better to subscribe to the legends of the gods than to be a slave
to the determinism of the physicists”.

When atoms collide and interlock with one another, so forming compound
bodies, their motion does not stop (Lucr. 2.80-141), but ceases to be linear
and becomes vibratory: the atoms continually clash together and rebound
at intervals which vary according to the density of the substance. Every
compound body, even such an apparently solid object as a lump of lead,
contains a certain amount of void. The constant motion of the constituent
atoms of objects is imperceptible to us, because the atoms themselves are
imperceptibly small (Lucr. 2.308-322). The ability or inability of atoms
to cohere closely together is determined by their shape: hooked and
branchy atoms form dense substances, round and smooth atoms form rare
substances. Differences in the size and arrangement of the atoms are other
important factors which account for differences in the qualities of
compounds.
Every compound object is a temporary atomic aggregate: it comes into
being, grows, reaches maturity, declines, and is resolved into its
component atoms. Our world is no exception (Lucr. 2.1105): it had a
beginning and will have an end (Lucr. 5.91-109, 235-415). Like every one
of the infinite number of worlds in the universe, it was the result of a
fortuitous concourse of appropriate atoms in a part containing much void:
from the confused, chaotic mass of atoms the different components of the
world gradually separated out, like elements joining like, and the world as
we know it developed.

The constant vibration (πάλσις) of the constituent atoms of each

compound object causes fine atomic films (simulacra), similar in shape to
the object, to be discharged at high speed from its surface. When these
strike our eyes, they produce vision; when they are received by our mind,
they cause thought or, if we are asleep, dreams (Lucr. 4.26-521).
Now I address a matter of great import
For our enquiries, and I show that there
Exist what we call images of things;
Which as it were peeled off from the surfaces
Of objects, fly this way and that through the air;
These same, encountering us in wakeful hours,
Terrify our minds, and also in sleep, as when
We see strange shapes and phantoms of the dead
Which often as in slumber sunk we lay
Have roused us in horror

All sensation involves physical contact between the object perceived and
the body of the perceiver: in the case of taste and touch the contact is
direct; but in the case of hearing and smell), as in the case of vision, the
contact is indirect, being effected by emanations impinging on the
appropriate sense-organ.

Gods live not in our world, but in parts which are as tenuous as their
bodies that is, in the peaceful spaces which extend between the worlds
(μετακόσμια, intermundia), perfectly self-sufficient, tranquil, and happy.
Violent and irregular phenomena such as thunder and lightning,
earthquakes and volcanoes are certainly not sent by them to punish men,
but have purely natural causes (Lucr. 6.43). From the gods, as from all
objects, flows an unceasing stream of simulacra. Simulacra are always of
a very fine texture, but, since the gods are of the finest atomic
composition, the simulacra which emanate from their bodies are
surpassingly tenuous—so tenuous, in fact, that they cannot be received by
the senses at all, but only by the mind (Lucr. 5.148). Even the mind does
not easily perceive them, and it is in sleep, that visions of the gods are
most often seen (Lucr. 5.1169). The person whose mind is not disturbed
by false opinions and fears concerning the gods is best able to receive the
simulacra, which can transmit to him something of the beauty,
tranquillity, and happiness of the gods. The wise man will he will
participate in religious ceremonies, for this will make it easier for him to
concentrate his attention on the divine simulacra.

The vision of Lucretius, rediscovered in early Renaissance, had a deep

influence on the development of modern science.

Let us quote Buffon7 (1783):

7
Georges Lous Leclerc, Comte de Buffon. Famous by his contributions to natural history, cosmology, geology. See
also Buffon’s needle (an exercise of probability involving integral calculus).
"Everything happens,
because with time everything meets,
and in the free range of spaces
and in the continuous succession of movement,
all matter is stirred,
any form given,
all figures printed;
so everything is coming or going,
all is joined or running away,
all is combined or opposed,
everything happens or is destroyed
by relative or contrary forces,
that are the only constants,
and balancing without harm,
they animate the universe
and make it into a theater
with ever new scenes
and objects incessantly reborn ".

However, Epicurus views were far from being shared by all antique
philosophers. One of his harshest critics was Cicero, who also rejected
divination.