Atomism

Atomism is a philosophical and scientific view that all matter is composed of small, indivisible units called atoms and of empty space, the void, through which these atoms move. The tradition begins in ancient Greece with Leucippus of Miletus and his pupil Democritus, who proposed that everything observable arises from combinations and motions of atoms of different sizes, shapes, and arrangements within the void.

Key tenets of atomism include the idea that atoms are eternal and indivisible in the original theory, that they differ in properties and natural motion, and that all phenomena result from their interactions and reconfigurations. The void is held to be real in the sense that it provides the space in which atoms move. Changes in the macroscopic world are explained by alterations in the arrangement and connections of atoms rather than by changes in the atoms themselves. Over time, atomism was challenged by other schools, notably Aristotle, whose physics rejected the void and other atomistic assumptions.

In the early modern period, atomistic and corpuscular theories were revived and developed by thinkers such as Gassendi, Boyle, and Newton, contributing to a mechanistic view of nature. By the 19th century, John Dalton’s chemical atomic theory provided a framework for understanding chemical reactions, law of definite proportions, and the conservation of mass, reinforcing the idea that matter is composed of discrete units.

In contemporary science, atomism remains central but its meaning has evolved. Atoms are understood as complex systems that contain subatomic particles and quantum phenomena. While matter is composed of atoms, these atoms themselves are not indivisible in a strict physical sense, and modern theory integrates atomic structure, isotopes, and molecular interactions within quantum mechanics and field theory.