Before photons, light was imagined as a hail of tiny bullets

Science · Published 20 October 2026 Swipe more like this →

In short: During the seventeenth century, the world's most prominent thinkers did not view light as a wave. Instead, they imagined it as a mechanical bombardment of tiny particles. This corpuscular theory, championed by Isaac Newton, suggested that light consisted of material corpuscles moving through space with specific masses and velocities.

During the Scientific Revolution, the mechanical philosophy reimagined the universe as a vast machine governed by matter and motion. This worldview was heavily influenced by Epicurean atomism, which posited that everything—including human thoughts—was composed of tiny, moving particles. By the early 1600s, thinkers like Pierre Gassendi began refining these ideas, suggesting that God created a finite number of indivisible atoms moving through a vacuum, a concept that directly challenged the long-standing Aristotelian belief that the universe was entirely full of matter.

Isaac Newton became the primary architect of the corpuscular theory, proposing that light consisted of material "corpuscles" emitted from luminous bodies. To explain why different colors bend at different angles when passing through glass, Newton suggested these particles possessed different masses. While this model successfully explained reflection and rectilinear propagation, it remained a speculative theory on the periphery of his broader work. It was so influential that it dominated 18th-century physics, largely displacing the wave hypotheses proposed by contemporaries like Christiaan Huygens and René Descartes.

The corpuscular theory eventually faced a crisis in the 19th century. New experiments measuring the speed of light in various media provided evidence for wave behavior, and observations of interference and diffraction further undermined the particle model. However, the debate did not end there; the tension between these two opposing views persisted until the 20th century, eventually paving the way for the modern understanding of wave-particle duality. Today, the corpuscular theory serves as a historical forerunner to our modern concept of the photon.

The dominance of Newton's theory was not just a matter of scientific accuracy but of cultural and practical success. Because it could be applied directly to explain visible phenomena, it was adopted almost universally for over a century, even as critics like Leonhard Euler attempted to explain the same optical effects as vibrations in a fluid ether.

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