How did Max Planck’s idea of quanta differ from classical ideas about energy?

Max Planck’s concept of quanta represented a fundamental departure from classical physics, which viewed energy as continuous.1

In classical physics, energy—including light—was understood to move as continuous waves, allowing matter to absorb or emit energy at any value across a spectrum. This framework, exemplified by the Rayleigh-Jeans law, suggested that energy intensity would increase indefinitely with frequency, a theoretical failure known as the ultraviolet catastrophe.1

Planck revolutionized this understanding by proposing that energy is instead exchanged in discrete, finite packets called quanta. He theorized that matter can only absorb or emit energy at specific, equally spaced levels. The energy of these quanta is determined by the formula $E=h\nu$, where $\nu$ is the frequency of the radiation and $h$ is Planck’s constant.213

By introducing this quantization, Planck provided a mathematical solution that matched experimental observations of blackbody radiation, effectively replacing the classical assumption of continuous energy with a model where energy values are restricted to discrete, integer multiples of a base unit.21