In the late 19^th century, there was a crisis in Physics. This story contains all the usual beats, a reluctant hero, a seemingly impossible task, and numerous sequel opportunities. Our story starts in 1896 with a middle-aged German Physicist called Max Planck who had taken particular interest in his colleague’s formula (A possible love triangle?). This colleague, Wilhelm Wien, had developed a formula to predict the relation between the radiation spectrum of a ‘blackbody’ and its temperature.

λmax= (0.0029 m.K)/T

Planck was fascinated with Wien’s formula and made multiple attempts to derive it from the second law of Thermodynamics. Despite his attempts, Wien’s law wouldn’t budge. Now, before we reach the hero of our story, we must also mention two other characters, Lord John Rayleigh, and James Jeans. In June of 1900 using statistical mechanics they co-developed the Rayleigh-Jeans formula, when plotting this formula, they found something quite troubling, it predicted that as the temperature rose the blackbody would emit light of at higher and higher frequencies continuing onto infinity.

ρ (λ,T)=8π/(λ^4) kT

This result is known as the ultraviolet catastrophe and was a huge problem for Physics. If we couldn’t understand what happens as we heat objects up how could we ever hope to understand the processes which drive the industrial revolution. Furthermore, in October of 1900 Wien’s law had been experimentally shown to fall apart at low frequencies.

Enter our hero, Max Planck, his hypothesis was that energy could only be emitted in certain discrete packets or quanta and from this he found the following formula:

ρ (λ,T)= (8π/λ^4) (hc/(λ(exp⁡(hc/λkT)-1))

Planck’s formula matches perfectly to experiment and resolved the ultraviolet catastrophe, however even Planck thought his formula to be a hack. The idea that light existed in discrete quanta and wasn’t continuous was unheard of. Yet, a few years later another German Physicist used the same idea to discover the Photoelectric effect and Quantum Mechanics was born.

References:

Chodos, Alan . “October 1900: Planck’s Formula for Black Body Radiation.” Www.aps.org, www.aps.org/publications/apsnews/200210/history.cfm.

Mavani, Himanshu, et al. A Concise History of the Black-Body Radiation Problem. 2022.

“The Nobel Prize in Physics 1911.” NobelPrize.org, www.nobelprize.org/prizes/physics/1911/wien/facts/.

TY – BOOK AU – Faizan, Mohammed PY – 2020/08/01 SP – T1 – Microwave Radiometry VL – DO – 10.13140/RG.2.2.14759.37280 ER –