Shannon asked:

Could you explain Epicurus' theory of atoms and the void, and its consequences?

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Epicurus (341 — 271/70 BC) holds that atoms (tiny, unbreakable portion of matter) are the basic
physical constituents of the universe; they move in a void of empty space. Atom literally translates as
'uncuttable' — atoms are the fundamental building blocks of objects that cannot be cut. Macroscopic
objects consist of atoms grouped together and the properties of all physical objects are to be
explained in terms of the way atoms behave.

His argument goes along these lines: (1) it is obvious that there are bodies in motion (2) nothing
comes into being from what does not exist. The first point is an empirical one, the second a general
tenet of Greek philosophy, derived from the Principle of Sufficient Reason (the rule that for everything
that occurs there is a reason why it happened the way it did).

We might draw the following out: (1) because bodies move there must be an empty space in which
they move. To counter Epicurus however, this is not true of the universe as a whole. If we consider
that the universe might be expanding, this is an expansion ofspace rather than an expansion into
some other void. (2) The bodies we can see are made up of other bodies — they are compounded
from other smaller pieces; physical objects can be broken into smaller parts. This cannot go on
forever, Epicurus thought because otherwise matter would disappear into nothingness.

He also thought that the basic and immutable building blocks (the atoms) explain the regularities of
nature. Nowadays talk of regularities of nature requires qualification; at the most fundamental
sub-atomic level, many physicists believe that the behaviour of electrons is governed not by strict
laws but by probability. Yet irregularities generally cancel each other out at the macroscopic level,
which allows us to make certain scientific predictions based on perceived regularities. We also know
that atoms are not uncuttable; there are more fundamental constituents of reality than atoms —
heavily theoretical things like quarks and gluons.

According to Epicurus, bodies and void exist uncontingently; properties such as colour, temporality
and the good are to be explained in terms of bodies. since Epicurus accepted that nothing can come
from a nothing, he held that the universe has no beginning and will have no end. Atoms likewise must
always have existed; our world is only one of in infinite number of possible worlds. Each comes into
existence and then dies away; the universe is not limited in size — there is no edge . There are
limitless atoms and limitless space.

Adam Gatward

Epicurus thought that physical atoms must be indivisible, impassive and imperceptible. Since atoms
are a mass, they must be very small to be imperceptible. The Presocratic philosopher Democritus
had thought that atoms were of variable size, but Epicurus thought that if there were large atoms we
would be aware of them. Epicurus wrote in his Letter to Herodotus that atoms must be indivisible or
they would have been pulverised and disintegrated into nothing.

It follows from physical indivisibility that atoms contain no void. In order to physically divide an atom
there must be some internal split — a void within the atom — although Jonathan Barnes in The
Presocratic Philosophersnotes that this is not a logical requirement, but a physical requirement that
an atom is not porous.

Sorabji in Time, Creation and the Continuumsays that Epicurus' novel position is that atoms were
conceptually (as opposed to physically) divisible although there must be minimal parts because if an
atom was infinitely divisible there must be infinite parts and an atom would then be infinitely large.
Also in thinking about an atom we would be thinking about infinity which is impossible. The minimal
part is to be understood on an analogy with the smallest perceptible part. The physical atom is
actually imperceptible, but if we can think of a smallest perceptible part, Epicurus thought that we
should be able to accept, by analogy, a smallest conceivable size because as he says in Letter to
Herodotus "even the idea that the atom has a size was predicated on the analogy of the things before
our eyes".

We might use Aristotle's distinction between the potential and actual to understand this since it may
have been this distinction that led Epicurus to distinguish between physical and conceptual atoms.
The analogy is a strange one and has given rise to discussion on the shape of the smallest part.
Epicurus speaks of "uncompounded edges", so it may be that atoms had no edges or shape — which
is Sorabji's view, although to follow through the analogy, edges and shape must be assumed to be
there even if it is not clear what or how they are, and if the Epicurean conceptual atom is divisible it
seems to be a presupposition that there are edges to the minimal parts — and with these, voids.

As for consequences, given the indivisibility of physical atoms — and the assumption that they are
distinct from one another — it should be the case that they can be joined and parted. But if two are
joined in such way that there is no gap, or void, then they cannot be parted. Another consequence is
for change. Aristotle had held that if atoms were impassive and indivisible, there could be no
movement or change.

The divisibility of conceptual atoms avoids these consequences. While the minimal part of an
Epicurean conceptual atom has uncompounded edges, the atom in itself is not denied edges. Edges
are made up of the minimal parts. If an atom has edges then it has a void — or gap — by which it can
be said to be joined to another, and hence it can be parted. And because the conceptual atom is
divisible, it is possible that it is subject to change.

Rachel Browne