Pair of postage stamps commemorating the centenary of the birth of Max Planck

Historical Significance: Max Karl Ernst Ludwig Planck, FRS (1858 - 1947) was a German theoretical physicist who originated quantum theory, which won him the Nobel Prize in Physics in 1918. This theory revolutionised human understanding of atomic and subatomic processes, just as Albert Einstein's theory of relativity revolutionised the understanding of space and time. Together they constitute the fundamental theories of 20th century physics. In 1894 Planck had turned his attention to the problem of black-body radiation. He had been commissioned by electric companies to create maximum light from light bulbs with minimum energy. The problem had been stated by Kirchhoff in 1859: "how does the intensity of the electromagnetic radiation emitted by a black body (a perfect absorber, also known as a cavity radiator) depend on the frequency of the radiation (i.e., the colour of the light) and the temperature of the body?" Planck's law proposed in 1900 provides the answer. It describes the electromagnetic radiation emitted by a black body in thermal equilibrium at a definite temperature. The formula includes the constant h, known as Planck's constant.