Max Planck's contribution to the development of quantum theory emerged from his investigations into the problem of black-body radiation, which refers to the electromagnetic radiation emitted by a heated object. In the late 19th century, scientists were struggling to explain the observed spectrum of radiation emitted by such objects.
At the time, the prevalent theory suggested that energy was emitted continuously, meaning that an object should emit an infinite amount of energy as its temperature increased. This was known as the "ultraviolet catastrophe" because it failed to match experimental observations.
In 1900, Planck approached the problem from a different perspective. He proposed a radical idea: that energy was not emitted or absorbed continuously but rather in discrete packets or "quanta." These quanta were proportional to the frequency of the radiation and were later named "photons" by Albert Einstein.
Planck introduced a mathematical formula, now known as Planck's law, that described the energy distribution in black-body radiation. To make his formula fit the experimental data, he had to assume that energy was quantized, meaning it could only exist in certain discrete amounts. This was a departure from classical physics, which assumed continuous energy.
Planck's key insight was that energy could only be exchanged in discrete units, and the size of these units was determined by a fundamental constant, now known as Planck's constant (h). The formula he derived successfully explained the observed spectrum of black-body radiation and resolved the ultraviolet catastrophe.
However, it is important to note that at the time, Planck did not fully comprehend the significance of his own proposal. He initially considered his quantization hypothesis as a mere mathematical trick rather than a fundamental physical principle.
It was only later, with the work of Einstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and others, that Planck's quantum hypothesis developed into a comprehensive quantum theory. This theory laid the foundation for a revolutionary understanding of the microscopic world and led to the birth of modern physics.