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Everything around us is made up of atoms, tiny units of matter which can be thought of as the basic “building blocks” of the universe. Our understanding of the atom has evolved over the course of several centuries as our ability to explore smaller and smaller length scales has improved. However, the origins of atomic theory actually began with natural philosophers thousands of years ago.
Atoms in Ancient Philosophy The first theories regarding the existence of atoms originated in Ancient Greece and India. The earliest reference to atoms in Greek philosophy is attributed to Democritus and Leucippus in the 5th century B.C. The word “atom” is derived from atomos, the Greek for “unable to be cut.” According to Democritus, Leucippus, and other philosophers at the time, all matter is composed of an infinite number of indestructible, indivisible solids that constantly move about within an infinite “void” of empty space. Around the same time in India, the Hindu philosopher Kanada developed theories of matter that were very similar to those of the Greeks.
The Greeks did not test their predictions through experiment, so the existence of atoms was the subject of centuries of philosophical debate. Plato envisioned the four basic elements (fire, water, earth, and air) as being made up of geometric solids depending on the physical properties of each element. For instance, he associated the nearly spherical icosahedron with water’s ability to flow easily, and the easily packed cube with earth’s more rigid, durable nature. Eventually a fifth solid became associated with the “aether,” an invisible medium that filled the universe (Figure 1).
Figure 1 The Five Platonic solids
The Greeks did not test their predictions through experiment, so the existence of atoms was the subject of centuries of philosophical debate. Plato envisioned the four basic elements (fire, water, earth, and air) as being made up of geometric solids depending on the physical properties of each element. For instance, he associated the nearly spherical icosahedron with water’s ability to flow easily, and the easily packed cube with earth’s more rigid, durable nature. Eventually a fifth solid became associated with the “aether,” an invisible medium that filled the universe (Figure 1).
Figure 1 The Five Platonic solids
During the 3rd century B.C., Aristotle expressed disagreement with the existence of atoms and the void. He argued instead that the basic elements are continuous and infinitely divisible. The different properties of substances in Aristotle’s theory are a result of different ratios of fire, water, earth, and air composing each substance. Although ultimately incorrect, Aristotle’s philosophy proved to be influential, and anti-atomist thinking persisted well into the 17th century.
Although the Middle Ages marked a period of decline for the study of natural philosophy in Europe, atomic ideas flourished elsewhere. During the 11th century, at the height of the Islamic Golden Age, Islamic philosophers attempted to synthesize the Greek and Indian theories into the Asharite school of theology. European interest in atomism was eventually rekindled during the Renaissance. Pierre Gassendi, a Catholic priest, is credited with restoring the atomist view to mainstream European thought by reconciling it with the teachings of the church. Gassendi engaged in frequent debate with René Descartes regarding the exact nature of atoms. Galileo Galilei, known for his contributions to astronomy and physics, also advocated for the existence of atoms.
In the 17th century, one of the founders of modern chemistry, Robert Boyle, proposed the corpuscular theory as an alternative to the atomic theory. In contrast to atoms, corpuscles were theoretically divisible particles that could change the characteristics of other matter. Isaac Newton advocated for the corpuscular theory of light in his 1704 book Opticks. As you can see, without experimental evidence to draw upon, competing theories regarding the nature of matter came and went over the course of more than 2,000 years. That would finally change once experimentation on chemical composition and chemical reactions helped transition the atomic theory from the realm of philosophy to verifiable science.
In the 17th century, one of the founders of modern chemistry, Robert Boyle, proposed the corpuscular theory as an alternative to the atomic theory. In contrast to atoms, corpuscles were theoretically divisible particles that could change the characteristics of other matter. Isaac Newton advocated for the corpuscular theory of light in his 1704 book Opticks. As you can see, without experimental evidence to draw upon, competing theories regarding the nature of matter came and went over the course of more than 2,000 years. That would finally change once experimentation on chemical composition and chemical reactions helped transition the atomic theory from the realm of philosophy to verifiable science.