How did Max Planck’s work on thermodynamics lead to quantum theory?

Max Planck’s journey toward quantum theory began with his deep commitment to the laws of thermodynamics, which he initially viewed as absolute truths of nature. His research into blackbody radiation—the energy emitted by a perfect absorber—sought to derive a formula that matched experimental observations across all frequencies.12

While classical physics failed to explain the energy distribution at high frequencies (a problem known as the ultraviolet catastrophe), Planck attempted to reconcile existing formulas with the second law of thermodynamics. To derive a successful radiation law, he was forced to abandon his belief that the second law was absolute, instead adopting Ludwig Boltzmann’s interpretation that it is a statistical law.12

Crucially, Planck assumed that the oscillators emitting radiation could only do so in discrete packets, or quanta, with energy $E=h\nu$, where $h$ is Planck’s constant. This departure from the classical assumption of continuous energy emission provided the foundation for quantum mechanics, fundamentally changing how physicists describe the microphysical world.132