Why Did Classical Physics Fail?

Imagine it's the late 1890s. Physics feels... complete. Newton’s laws govern the planets, Maxwell’s equations describe light, and thermodynamics explains heat and energy. It seems we're just tying up loose ends. Yet, a stubborn, seemingly minor problem remains. When we look at the light—the radiation—emitted by a simple hot object, like a glowing poker from a fire, our most fundamental theories make a prediction that is not just wrong, but catastrophically, infinitely wrong. The equations of classical physics, when applied to this problem, predict that every object in the universe should be radiating an infinite amount of energy at every moment. This implies that the universe should be an inferno of high-frequency radiation. But clearly, it is not. This spectacular failure, this breakdown of everything we thought we knew, is where our story begins. It’s the crack in the edifice of classical physics through which the quantum world first became visible.