Appleton Professor of Natural Philosophy, Dartmouth College; Author, The Island of Knowledge

Atomism: Reconciling Change with No-Change

In contributing to this volume, I decided to go back to the basics, literally to the beginnings of Western scientific thought. For already in Ancient Greece we find the striving for ideas with beauty and elegance that remains so important to our culture. As we will see, their influence is more than merely historical.

So, back to the late pre-Socratic philosophers we go, to around 450 BCE. (Thus, not quite "pre" Socrates, as he was born c. 469 BCE.) At the time, there were two warring views of reality, which had been developed and refined for some 200 years. On the one hand, the Ionians—Thales of Miletus being the first—claimed that what was essential in Nature was change: nothing was permanent, everything was in flux. "You cannot step in the same river twice," proclaimed Heraclitus of Ephesus (although not in so direct a manner). Later on, Aristotle commented on this view of perpetual change in his Physics: "some say…that all things are in motion all the time, but that this escapes our attention." This Ionian philosophy is known as a philosophy of "becoming," focusing on transformation and the transient nature of natural phenomena.

On the other hand, the Eleatics—Parmenides of Elea being the first—claimed the exact opposite: what is essential is that which doesn't change. So, to find the true nature of things we look for what is permanent. Among the Eleatics we find Zeno, whose famous paradoxes aimed at proving that motion was an illusion. This was a philosophy of "being," focusing on the unchangeable.

If you were an ambitious young philosopher starting out around 450 BCE, what were you to do? Two schools (let's leave the Pythagoreans out), two opposite views of reality. It is here that Leucippus came in, a man who, like Thales, was probably also from Miletus. He and his prolific pupil Democritus came up with a beautifully simple solution to the change vs. no-change dilemma. What if, they reasoned, everything was made from tiny bits of matter, like pieces of a Lego set? The bits are indestructible and indivisible—the eternal atoms, and thus give material existence to the Eleatic notion of "being". On the other hand, the bits can combine in myriad ways, giving rise to the changing shapes and forms of all objects in Nature. So, objects of being combine to forge the changing nature of reality: being and becoming are unified!

Fast forward to the present. Atoms are now very different entities: not indivisible, but made of yet smaller bits. Not uncountable, but with a total number of 94 naturally-occurring and a few others made artificially in labs. Notwithstanding the differences between ancient and modern atoms, the core notions that all objects are made of smaller bits and that the properties of composite objects can be understood studying the properties of these bits—the essence of reductionism— has served science extremely well.

Yet, as science marched on to describe the properties of the elementary bits of matter, the elementary particles, a new notion came to substitute that of small bits, the concept of "field". Nowadays, particles are seen as excitations of underlying fields: electrons are excitations of the electron field, quarks of the quark field, and so on. The fields are fundamental, not the particles. Furthermore, many scientists today express their discontent with reductionism, stating that a more holistic approach to science may open new avenues of understanding. There is much truth to this, since it's impracticable to think that we can understand the behavior of, say, a DNA molecule—a huge entity with hundreds of billions of atoms—by integrating the behavior of each one of its atoms. Matter organizes in different ways at different levels of complexity, and new laws are needed to describe each of these different levels.

Are we then done with Atomism's intellectual inheritance? Not if we look at its essence, as an attempt to reconcile change and no-change, which necessarily coexist. Our modern view of physical reality remains a construction built upon these twin concepts: on the one hand, the material world, made of changing fields, their excitations, and their interactions. On the other, we know that these interactions are ruled by certain laws which, by their very nature, are unchangeable: the laws of nature. Thus, we still understand the world based on the twin pillars of being and becoming, as pre-Socratic philosophers did some two and a half millennia ago. The tools have changed, the rules have changed, but the beauty and elegant simplicity of the idea that change and no-change coexist remains as vivid today as it was then.