DOI: 10.4324/9780415249126-A049-1
Version: v1,  Published online: 1998
Retrieved July 16, 2024, from

2. Foundations of physics

Whatever the universe consists of must be permanent. Nothing comes into being out of nothing or perishes into nothing – two fundamental principles widely regarded as indubitable, but defended by the Epicureans on empirical grounds (Lucretius I 159–264): literal generation would be incompatible with the observed regularities of natural processes, such as the dependence of organic growth on the right material conditions; and literal annihilation would, given the infinity of past time, by now have ensured that nothing at all was left. Nor can the universe (the ‘all’) be changed by addition or subtraction, since by definition it has nothing outside it that could enter or into which bits could escape.

Next comes a statement of what the universe does consist of: bodies and space (Letter to Herodotus 39–40). This is taken to be self-evident, that is, underivatively known and unchallengeable. The reasoning is no doubt that bodies are the things which most obviously have independent existence; and that since that independence is most evident in their ability to move in space, the bits of space which they vacate as they move must exist independently of them.

Space is at this stage simply presented as what the bodies are in, and what they move through – a three-dimensional extension which persists whether occupied or unoccupied. When occupied it gets called ‘place’, when unoccupied ‘void’ (kenon, literally the ‘empty’), and when things move through it ‘room’ (chōra, etymologically linked by Epicurus with chōrein, ‘go’). Epicurus prefers to use these familiar terms rather than a generic one for ‘space’, for which Greek has no precise word (the concept itself being one which had emerged only gradually, with Epicurus perhaps the first to isolate it clearly), and which he manages to capture only by his invented phrase ‘intangible nature’ (anaphēs physis). That there is void, that is, that contrary to the majority ancient view some space is altogether empty, is argued by appeal to such phenomena as motion and permeation. Motion cannot be accounted for, it is argued (Lucretius I 370–83), by the alternative hypothesis of complementary redistribution of matter on the model of a fish exchanging places with the water when it swims. Even the fish would be stuck fast unless there were some void to break the deadlock. Otherwise it would be unable to move until the water had cleared a path for it, or the water until the fish had cleared a path for it.

As for body, it remains for now largely unanalysed, beyond a set of arguments to show that it must exist microscopically as well as macroscopically: its underlying atomic structure cannot be demonstrated until it has been shown that body and space are the sole constituents of the universe. And the next move is to show just that. First, body and space are analysed as contradictory opposites: only three-dimensional things exist per se, and if these are resistant they must be body, if non-resistant void (Lucretius I 430–9). This is the positive proof that body and space are not only irreducibly distinct but also jointly exhaustive. There then follows a supplementary argument (Lucretius I 449–82), in which all other contenders for per se existence – including properties and time – are written off as secondary attributes, parasitic on body and/or space. None of these could exist independently of bodies and/or space. Time is dependent on change, that is, on moving bodies. And even facts about the past (for example, that there was a Trojan War), which might seem to outlive the bodies (Agamemnon and others) of which they are true and therefore to acquire independent existence, are truths about places which still persist (Troy, Mycenae and so on), or, if you prefer, about the universe.

Only now that it is fully established can the body–space dualism be deployed to show that at the lowest level of analysis there will be not only portions of empty space uninterrupted by body but also portions of body uninterrupted by empty space – and therefore, since there is no third thing, totally uninterrupted. Being perfectly solid, these are ‘atoms’, literally ‘uncuttables’. The capacity of a body to disintegrate is directly correlated to the amount of void within it; therefore a body containing no void at all is altogether indestructible (Lucretius I 511–39). That there are such bodies is confirmed both by the evident fact that matter is not completely annihilated by fragmentation, and by the observed regularities of nature, which imply that something altogether unchanging underlies them.

Having mapped the universe out into space occupied by discrete portions of body, Epicurus adds that both space and body are infinite in extent (Letter to Herodotus 41–2, Lucretius I 958–97). First, the infinity of the universe itself (a highly controversial thesis in antiquity, rejected by both the Platonist and the Aristotelian tradition) is argued by appeal to the notion of a limit: it could only be limited if there were something beyond it to limit it, and the notion of the universe (the ‘all’) precludes that. (Lucretius adds the time-honoured argument: what if I go to the supposed edge of the universe and throw something?) Second, it is argued that each of the two constituents of the universe must also, taken on its own, be infinite: finite body in infinite space would be too dissipated to form compounds, while infinite body in finite space would simply not fit.

Citing this article:
Sedley, David. Foundations of physics. Epicureanism, 1998, doi:10.4324/9780415249126-A049-1. Routledge Encyclopedia of Philosophy, Taylor and Francis,
Copyright © 1998-2024 Routledge.

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