Radiant heat from hot objects was considered a form of electromagnetic radiation, but classical theory of electromagnetic radiation could not explain this spectrum. The German physicist Max Planck (1858 - 1947) suggested that energy from a hot body could only be released in discrete amounts, proportional to the frequency (inversely proportional to the wavelength) of the emitted radiation, according to the formula E = hf ( where 'f' is the frequency and 'h' is what quickly came to be known as Planck's constant). Thus the quantum was born. Planck stopped short of proposing that the radiation itself was quantized as the classical wave theory of light still stood supreme.
The discoveries in atomic physics and radiation were enough to shake classical physics to its core, but more was to come. In 1905, Einstein came forward with his revolutionary proposal that neither time nor space was absolute, that they were related to one another, and that both depended on measurements made with respect to a chosen frame of reference, which had to be identified. This special theory of relativity was particularly troubling to the traditionalists who assumed that a hypothetical medium is essential as the carrier of light and all other kinds of electromagnetic waves. Physicists had to get used to the idea that electromagnetic waves did not need a medium to wave in.