Open Journal of Philosophy
2012. Vol.2, No.4, 268-271
Published Online November 2012 in SciRes (http://www.SciRP.org/journal/ojpp) http://dx.doi.org/10.4236/ojpp.2012.24039
268
Reading of “De Rerum Natura” in the Light of Modern Physics
Gualtiero Pisent
Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova, Italy
Received April 28th, 2012; revised May 30th, 2012; accepted J une 10th, 2012
An analysis of the Lucretius atomism is given, that makes particular reference to the naturalistic argu-
ments and contents of the poem. A possible comparison with the atomism of nowadays, based on quite
new, both theoretical (quantum mechanics) and experimental (particle accelerators) grounds, must be
treated with much care. But it seems possible and interesting to compare at least the world outlined by
Lucretius, with the new world, derived by familiarity with modern theories of matter. This is the point I
have tried to stress.
Keywords: Science; Nature; Atomism; Vacuum; Swerve
Introduction
Although Lucretius theories are not fully original (being de-
rived in particular from Epicurus), the poem “De rerum natura”
is so wide, self consistent and miraculously integral in the form
arrived up to our days, that it is worthwhile to be studied and
analyzed as a whole.
The literature about the poem is very wide, and only some ti-
tles are given here for easy reference (Costa, 1984; Kenney,
1971; Smith, 1992).
The interests that promoted these comments are mainly phi-
losophical, poetical, philological and historical, while the aim
of this work is to start directly from the original text, and try to
stress the naturalistic approach of Lucretius, in comparison with
the current ideas about the structure of matter.
It is worthwhile to mention in particular an article recently
published in Physics Today (Gruijv, 2012), that starts the “In-
sights on the classical atoms” from Democritus and Lucretius,
reporting among others the following considerations:
“As fertile as it was, the atomic hypothesis suffered from a
major deficiency: its authors happened to be atheists. Subse-
quent generations were reluctant to accept the atom, and the
concept remained buried in religious animosity for nearly two
millennia.”
Also with reference to this feature of the question, namely
the physics and the meta physics of Lucretius, I hope that some
light should be shed by the present analysis.
From Lucretius to Avogadro
The following analysis will be carried out through comments
on selected quotations of the text (Caro, 1989).
The numeration refers to the Latin edition of the poem.
The translation from Latin to English is more “ad sensum”
than “word for word”.
The first book, on “the Matter”, prepares the audience to ac-
cept the invisible atoms as real components of the world.
“Perhaps you’ll not believe to my words, because these
primitive matter components cannot be detected by eyes. But
I’ll give you clear examples of things that are certainly in the
world, and cannot be seen. The first example is given by the
gust of wind, which lashes the sea, strikes the ships and drag-
sthe clouds [I-265].”
We shall see later on, the reasons that suggest the atomistic
idea, but first of all we must be aware that the assumption, al-
though not trivial, is nevertheless realistic.
“The clothes, left on the seaside, become wet. Then, under
the sunshine, they get dry. But how is water able to penetrate
the cloth, and how to leave it, nobody can see [I-305].”
The arguments make reference to the water and the steam.
The second argument involves explicitly the evaporation
phenomenon, which is a convincing example of something that
we feel as real but we don’t see by eyes.
It is interesting to note (and it is not casual I guess) that when
(after eighteen centuries) the atomistic philosophical assump-
tion becomes a physical theory, this happens because Amedeo
Avogadro (1776-1856) was investigating about the chemistry
of the gaseous state.
Among the three states of matter condensation (solid liquid
and gas), the latter one happens to have the far simplest struc-
ture, and therefore it was, in the history of science, the natural
tool to inquire how the microcosm works.
Avogadro doesn’t see air, like Lucretius didn’t, but Avo-
gadro can work on the interpretation of Boyle’s and Gay Lus-
sac’s experiments.
He owns a technology able to operate on gases by pressure
and temperature variations, and to detect some of their peculiar
properties, without seeing them.
So for the first time in history , (thanks to the di scovery of t he
famous Avogadro’s number), mankind learned that the mole-
cule of a gas, is about 10 exp{–8} cm wide.
Lucretius had no idea about the atom’s dimensions but cer-
tainly he had no reason to suspect that they were so small.
Note that, up to this point, we used the word “atom” in the
sense of Lucretius, namely to designate a microscopic con-
stituent of matter, not better identified. Now, with reference to
Avogadro, we must say “molecules” because, as it is well
known, the chemistry of the gaseous state introduced atoms and
molecules, and discovered that only the molecules of the so
called noble gases, are mono atomic.
From now on we’ll continue to speak of atoms with reference

G. PISENT
to Lucretius, but whenever the modern theory of matter will be
referred to, we’ll introduce the words molecule, atom, nucleus,
electron and so on, in the well defined, modern meaning.
Preliminarily to the introduction of his atoms, Lucretius had
two problems to solve. The first one was the compactness of
matter, which seemed to be an obstacle to the atom’s mobility,
and the second one was the gravity effect, which seemed to
hinder the atomic collisions.
Much space was given by Lucretius to these questions,
which are solved very naturally by modern physics (these
points do not represent serious objections nowadays).
Let us start with the famous “vacuum” problem.
“All things in nature are not at all compact; there is inside
bodies the vacuum .... otherwise, no kind of motion of things
should be possible [I-329]”.
The following statement tries to justify the assumption of
hollow spaces inside matter, that we never can see by eyes, nor
experience directly in some way.
“It is common experience that some bodies are heavier than
others of equal volume .... The heavier body clearly contains
less quantity of vacuum inside [I-358]”.
The line of reasoning is very subtle: the atomic structure it-
self suggests the idea of a matter constant in density. If this is
the case, heavier bodies may exist near lighter ones, only be-
cause they contain a lower amount of empty spaces inside.
It should be interesting but difficult to comment this state-
ment in the light of the modern knowledges, because the struc-
ture of the microcosm happened to be much more complicated
than expected. Three levels were discovered in the micro world,
namely the molecular and the atomic levels (both dominated by
the electromagnetic interaction, and populated by objects as
wide as 10 exp{–8} cm), and the nuclear level (dominated by
the strong interaction and populated by objects as wide as 10
exp{–13} cm). In particular the nuclear density is extremely
high, namely it is equivalent to one aircraft carrier per cubic
millimeter, and this means that inside each atom, large hollow
spaces are left to the flight of the electrons. This kind of vac-
uum was clearly beyond any possible imagination at the time of
Lucretius.
Then, after a long introduction, the author lastly presents his
main play er, namely the atom:
“Bodies are composed by bodies. But we must find some-
thing not capable of further decomposition. If an object like this
exists, it must be solid and timeless [I-624]”.
It follows a very important sentence about the true meaning
and the behavior of this object inside the matter:
“Movements of atoms do not follow primeval projects or
shrewd indications of some mind in the universe. They have
tried and experienced from eternity to now, a huge number of
paths, collisions, deflections, up to find their final state corre-
sponding to the present structure of the world [I-1021]”.
Here we have first something that may be interpreted as a
declaration of atheism in a modern sense: the final state of or-
der reached by the world, is not the effect of Somebody who
has thought and realized a project.
Then it follows the description of what really happened.
The latter statement shows prophetic analogies with the big
bang theory. To explain what I mean, I report a sentence taken
from the famous book of Weinberg on “The first three minutes”
(Weinberg, 1977):
“First frame: the temperature of the Universe is of 100 bil-
lions of Kelvin degrees ... The universe is full of matter and
radiation, and each particle undertakes very fast collisions with
the others ... we have electrons and positrons, photons, neutri-
nos and anti neutrinos”.
The words of Weinberg seem to furnish us the scientific de-
tails, about something, that was well described under wide gen-
eral lines, by Lucretius.
But there is much more about the mechanisms of evolution,
in the quoted phrases.
Sometimes, during a natural development of a system subject
to purely stochastic rules, certain configurations are realized,
whose occurrence seems to be a priori extremely improbable.
But what seems a miracle, is simply explained by the long time
that evolution left to the universe, to try a huge number of at-
tempts.
This concept, very important in physics, has been widely dis-
cussed by Jacques Monod, with reference to biology (Monod,
1971).
The second book of the poem, on “the Atoms”, entered into
the details of the dynamics of atoms; here much attention is
given to the gravity effects, which were considered by Lu-
cretius as an important and unavoidable background in the
whole cosmic phenomenology.
“Bodies in space can not move spontaneously from down to
up ... And this is not contradicted by the blaze of the burning
objects ... Also golden cereals and trees seem to be projected
toward the sky, but heavy bodies cannot avoid falling down ...
Wooden planks are projected up from water, but fall down in
vacuum [II-184]”.
The line of reasoning is very clear: the nature of simple bod-
ies is to fall down. Something may, on the contrary, be pushed
up, but only as a consequence of complicated mechanisms.
Nothing in nature is simpler than atoms, “ergo” atoms fall
down anyway.
It is interesting to analyze the counter examples listed by Lu-
cretius. The first mechanism able to push something up, is the
floating of the wood in water: Archimedes (287-212 BC) is not
explicitly mentioned, but his famous principle was well known
at the time of Lucretius. The mechanism of the blaze is along
the same line, although a little more complicated (air is heated
and climbs, dragging up the blaze itself). But the growing up of
cereals and trees, belongs to quite another phenomenology: we
deal here with living objects (at least at a simple botanical
level), able to distinguish between up and down by virtue of
complicated sensory receptors.
This is a first symptom of a very peculiar feature of Lucretius
philosophy: his atomism first introduced with reference to inert
matter, is then naturally extended to the living bodies and to the
mind. Modern science is much more careful when dealing with
this kind of extension.
At this stage the very important concept of “clinamen” (swerve)
were introduced into the th eory by Lucretius:
“While atoms are driven by their weight in straight vertical
falls through the vacuum, they happen to be casually deflected
from their trajectory. In absence of this swerve, they should fall,
regularly and eternally, like rain drops; no atomic collision, and
consequently no process of generation of the world, should
have been possible [II-216]”.
In other words, the presence of the gravitation on the earth,
was perceived by Lucretius as a severe obstacle to his theory.
His atoms were seen as small material objects, that fall like rain
drops, on vertical parallel trajectories. If this was the picture, it
was clearly hard to imagine how collisions between atoms

G. PISENT
could take place, and this is the reason why he introduced the
swerve.
But nowadays, we know exactly the mass and dimensions of
the gas molecules in the air. They are much smaller and lighter
than Lucretius could imagine, and the consequence is that grav-
ity is totally ineffective on their dynamics.
The mathematical character of modern physics allows us to
demonstrate the statement by a calculat ion.
Let us consider, for example, 1 mole of helium gas, enclosed
in a cubic box, at normal conditions of temperature and pres-
sure. On the basis of the classical theory of ideal gases (de-
scribing the gas molecules as point-like non-interacting parti-
cles), it is easy to calculate the average kinetic energy of one
molecule, namely:




E32KT5610 exp22joule (1)
(where T is the absolute tempera t ure and


K1.3810 exp23  [joule/Kelvin degree], the Boltzmann
constant). On the same footing, we are able to evaluate the
difference in gravitational energy between a molecule on the
top and a molecule on the bottom of the box, namely:


Umgh1810 exp27 joule  (2)
where


m6.6410 exp27  kg, is the mass of the helium
molecule,




g9.81 msec exp 2, is the gravity acceleration
and h = 0.282 m, is the height of the cube containing the mole
of gas.
We can finally calculate the ratio U/E = 1/300,000, which
gives the order of magnitude of the contribution of the gravity
effects on the particle dynamics. The very small value of the
ratio, clearly indicates that the phenomenon is totally unaf-
fected by gravity.
For the details on the calculations, one can see any treatise of
classical thermodynamics, (Piragino, 1983). Our numerical re-
sults refer of course to a particular example, and depend on the
chosen physical conditions; but we are interested only in the
order of magnitude of the results, which doesn’t change very
much.
If one tries to calculate the molecular dynamics within the
liquid or solid (instead of gaseous) state, the job should become
much more difficult, because the strong inter molecular forces
should be taken into account.
But in the latter case, just the internal bounds typical of the
condensed states, should make weaker and weaker the contri-
bution of the gravitational field to the whole dynamics.
Therefore we can say that the above demonstration has wide
limits of generality.
The conclusion is that particles fly free like butterflies, de-
scribing perfect straight lines (whose directions are randomly
distributed in space) between particle-particle or particle-wall
collisions. The random motion is perfectly suitable to generate
collisions and molecular reactions, without the help of any
“clinamen”.
It is worthwhile at this point, to precise better our viewpoint
of modern scientists, about the world outlined by Lucretius.
First of all Lucretius had perfectly in mind the picture of a
chemical reaction within the gaseous state, as it is described by
modern science, but this idea was hardly disturbed by the image
of the rain drops, and the rain drops were the natural phenome-
non, closer to what he thought would happen at the invisible,
microscopic level. His error was derived from an overestima-
tion of the atomic mass, while modern physics shows that his
picture was realistic in spite of gravity, and therefore without
necessity of introducing the swerve.
From the Matter to the Soul
But this is the point that draws on a new (substantially unjus-
tified but very fascinating) line, the whole philosophical system
of Lucretius.
Because, once the new actor (namely “clinamen”) was in-
troduced, it was immediately called by the author, to play a
very fundamental role in the whole universe dynamics, as it is
explained by the following sentence:
“If all atoms movements were internal to a continuous stiff
chain, the new ones deriving with inexorable destiny from the
previous ones, which may be the origin of the freedom, granted
to anybody is breathing on the earth? Where does our will come
from, which is driven by our pleasure’s search and drives our
actions, not subjected to fortune’s laws? ... Everything derives
from this light swerve, which affects the atomic movements in
spaces and times that nobody controls [II-251]”.
As noted before, a fundamental contradiction inside the old
atomism, comes from the continuity of the chain of logic that
goes from inert matter, to living bodies and to human mind,
without any gap.
Lucretius was very aware that somewhere in the chain, it was
necessary to introduce some kind of discontinuity, able to ex-
plain the gap between blind motion of matter and intelligent
human life, and used to solve this problem, the brilliant idea of
the swerve.
Once this serious problem seemed to be satisfactory solved,
he went on (in the third book of the poem, on “the Death”), to
the discussion of the atomic structure of the soul, in the same
framework as he previously discussed the atomic structure of
inert matter:
“What is it possible to say about the soul’s nature? ... No
dynamics in the world is more speedy than the process that
takes place when the mind formulates a project, and acts on the
body to start the relative practical operations... The subject
which is responsible for a so rapid and complicated dynamics,
must be composed by spherically shaped and extremely small
and light elements [III-177]”.
There follows in the poem, a very interesting comparison
among water (a liquid with a low viscosity), honey (which
clearly exhibits a much more dense and viscous flow), and the
things of the ghost. If all of these are rings of a certain logical
chain, all composed by atoms, the atoms of different rings can
not be of the same type. They must exhibit, along the chain,
properties of increasing lightness and mobility, as far as one
proceeds from matter to ghost.
Lucretius’s atomism is naively global and all-inclusive, and
leads naturally to a very rough and worldwide kind of material-
ism:
“Since the soul is part of the body, in the sense that it occu-
pies a precise position within the body, like the eyes, the ears
and the other sensor organs, ... we conclude that the soul can
not exist without the body and the man, who behaves like a
vessel or a container [III-548]”.
In other words the soul dies with the body, and this docks the
poem to higher level considerations “de consolatione philoso-
phiae”.
“Death is nothing for us and doesn’t belong to us, if deadly is
the soul ... When we’ll cease existing, after the divorce be-
270

G. PISENT
tween soul and body whose junction makes our being, be sure
that nothing will be able to reach our senses, even if ground and
sea or sea and sky will mix up [III-830]”.
I mentioned already that “atom’s movements do not follow
projects or indications of some mind in the universe”. The pro-
tection offered by the old gods is therefore rejected, but it is
immediately substituted by the encouraging idea that nothing
bad (or better nothing at all) can happen to us after death.
Nowadays atomism is based on stiff grounds, both theoretic-
cal (mathematics) and experimental (instruments for accelera-
tion and detection of particles); but these grounds are stiff just
because their field of validity is rigorously auto-limited. The
new scientific language is built up around the part of the world
that evolves in such a way that the laws of increasing total en-
tropy are fulfilled. On the other side, the biological world,
whose development is locally anti-entropic, and especially the
world of the mind, must be treated with much care, on a quite
separate footing.
My conclusion is that, in spite of the obvious difficulties of
reading Lucretius (fully justified by twenty centuries of dis-
tance) the poetical descriptions of both the brutal matter and the
divine soul, conserve fully the original fascination and wisdom,
with an important remark. Whilst the physics of the poem looks
(at least somewhere) miraculously prophetic with respect to the
representation of the world that we have now clear in our mind,
much more care is needed in dealing with the associated meta
physics, whose fundamental points seem to be neither convinc-
ing in the old poem, nor satisfactorily solved nowadays (cer-
tainly not as satisfactorily as the physics seems to be).
REFERENCES
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Oxford: Oxford University Press.
Kenney, E. J. (1971), “Introduction”, Lucretius: De Rerum Natura.
Cambridge: Cambridge Uni versity Press.
Smith, M. (1992). “Introduction”, De Rerum Natura. Cambridge: Loeb
Classical Library.
Gruijc, P., & Simonovic, N. (2012). Insight from the classical atom.
Physics Today, 65, 41.
Caro, T. L. (1989). La Natura (Latin text and Italian translation). Mi-
lano: Garzanti Editore.
Weinberg, S. (1977). I primi tre minuti. Milan: Mondadori.
Monod, J. (1971) . Il caso e la necessit’a. Milan : Mondadori.
Piragino, G., & Pisent, G. (1983). Fisica generale e sperimentale (Vol.
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