Atomicism

Atomicism is the philosophical and scientific view that matter consists of small, discrete units called atoms that move through empty space, or the void. In classical atomism, atoms are indivisible and eternal, differing in size, shape, and arrangement, with the properties of substances arising from the organization and motion of these atoms rather than from any intrinsic quality of the matter itself. The void provides the space in which atoms move, collide, and rearrange, allowing change and variety in the physical world.

The idea originates with ancient Greek thinkers Leucippus and Democritus in the 5th century BCE, who proposed that an infinite number of atoms of various kinds exist and interact in a void. The Epicurean school later developed the doctrine, emphasizing mechanical explanations of natural phenomena and the randomness of atomic motion. In the early modern period, the revival of corpuscularianism—an atomistic view of matter—appeared in the works of Pierre Gassendi and Robert Boyle, who argued that matter consists of tiny particles governed by contact and force. Isaac Newton used a corpuscular framework to explain aspects of light and matter, though he did not settle all questions about the nature of atoms.

In the 19th century, John Dalton formalized a coherent atomic theory: elements are composed of atoms, atoms combine in simple whole-number ratios to form compounds, and in chemical reactions atoms are rearranged but conserved. The discovery of subatomic particles and quantum mechanics in the 20th century refined the picture, showing that atoms are divisible and their behavior is governed by probability and wave-like properties. Today, atomic theory remains a foundational concept in science, though its detailed models are described by quantum physics rather than a simple indivisible-atom picture.