Pre-Einstein physics split over whether light was a wave or a particle.

Evidence

For centuries, light had divided the best minds, he said. Some, like Aristotle and James Maxwell, thought of light as a kind of disturbance in the ether, a wave that spreads outwards from an initial source – like sound does. Others, such as Democritus and Isaac Newton pointed out that, unlike sound, light cannot bend round corners – something waves do by their very nature – and thus it must be made of tiny things, or particles, travelling in a straight line before hitting our eye’s retina. Who was right? — Yanis Varoufakis, Technofeudalism, 55

Categorization

• CANDY: The historical wave-vs-particle split with Aristotle/Maxwell against Democritus/Newton is a genuinely fun, low-context explainer fact.
• corroborated: 2 independent passages support this claim — Yanis Varoufakis, Technofeudalism: What Killed Capitalism, 55
• XREF: connects to: Einstein proved light is simultaneously particles and waves, reconciling opposites. — Yanis Varoufakis, Technofeudalism: What Killed Capitalism, 56