# Heat Radiation

On the evening when Planck first reported the formula to Rubens, he did so on a postcard that was received by Rubens the next morning. After one or two days had passed, Rubens visited Planck and informed him that the new formula was in perfect agreement with his observations.

## The birth of quanta

Sunday **7 October 1900** Rubens together with his wife visited Planck, the discussion turned to the measurements with which Rubens was occupied. Rubens said that for the longest wave-lengths — which he could achieve — the law recently proposed by Lord Rayleigh was valid. On receiving this information from Rubens, Planck set down and studied the theoretical implications for the equilibrium entropy, deriving the radiation formula that carries his name.The text has been adapted from the book *The Historical Development of Quantum Theory. Vol. 1.* by Mehra and Rechenberg.

The same evening Planck reported the formula to Rubens on a postcard, which the latter received the following morning. One or two day later Rubens went to Planck, and was able to bring him the news that the new formula agreed perfectly with his observations.Plank published his formula on paper *Über eine Verbesserung der Wienschen Spektralgleichung* the next 19 October.

## Max Planck

1858-1947

Max Planck was a visionary German physicist renowned for revolutionizing the field of quantum mechanics. His groundbreaking work on the blackbody radiation spectrum laid the foundation for modern physics and earned him the Nobel Prize in Physics in 1918.Planck's discovery marked a pivotal moment in science, paving the way for the development of quantum mechanics. His work challenged classical physics and stimulated the emergence of a new paradigm that redefined our comprehension of the fundamental nature of particles and waves.

In the late 19th century, the prevailing view of radiation's behavior clashed with experimental observations. Planck approached this problem by introducing the radical notion of quantization, proposing that energy exchange occurred in discrete units or "quanta". To explain the blackbody radiation curve, he ingeniously derived a formula that accurately matched experimental data. This formula, now known as Planck's radiation law, revolutionized our understanding of how energy is emitted and absorbed by matter.

Planck's contributions not only established the theoretical framework for modern physics but also laid the groundwork for subsequent generations of physicists to delve deeper into the realm of the subatomic and reshape the landscape of scientific thought.