Albert Einstein (1879-1955) was a German Jew who had taught himself higher mathematics as a teenager. At the age of 13 he was introduced to the work of Kant, who soon became his favourite philosopher. In 1905, when working as a patent clerk in Switzerland, Einstein published four physics papers that, combined with his 1915 paper on general relativity, provided the foundation for 20th century physics.
The first paper explained the ability of light to knock electrons out of metal (the photoelectric effect). By the late 19th century, the wave theory of light was universally accepted. Einstein's paper was the first hint that it also had particle-like characteristics. Photo-electric experiments had shown that increasing the intensity of a light beam does not increase the amount of energy of each electron knocked out – instead it increases the number of electrons knocked out, while the energy of each remains the same. If, however, you increase the light frequency (which changes its colour along the spectrum from red to blue) then you increase the amount of energy per ejected electron. Einstein's explanation was that light behaves like a shower of particles, each with the energy given by Planck's expression E=hf (an equation that contains Planck's constant quantum of action). Another piece of the puzzle had been found to be digital rather than analogue. It was for this discovery that Einstein was awarded a Nobel prize.
The second paper explained Brownian motion, which was revealed to be not biological at all. Atoms, first hypothesised by Leucippus and Democritus in the 5th century BC, were now accepted by almost everyone to be real, especially after Einstein’s explanation and Jean Perrin’s later experimental confirmation. The energeticists admitted defeat on this question, but there was a twist coming later in the year.
The third paper eclipsed the first two by introducing a completely new concept of space and time. According to Special Relativity, space and time are not absolute but depend on the velocity of the observer, and the speed of light was a new absolute – the same for all observers. This absolute, unchanging speed was also declared to be a limit that no signal can exceed. This theory did not look much like it belonged to classical physics, but there was no quantum element to it either. In spirit, it owed something to Kant, though Einstein did not frame it that way. Special relativity implied a radically new relationship between space and time, which Hermann Minkowski would soon formalise into four-dimensional spacetime, and four-dimensional space time seemed as different to the material world we experience that it should surely count as noumenal rather than phenomenal. However, unlike Kant, Einstein had found a way to place space and time in a realm beyond experience. Einstein's third paper did not cause any immediate metaphysical crisis in science. His fourth paper discussed a consequence of special relativity: the equivalence of energy and matter according to the equation E=mc2. The energeticists, it turned out, weren't completely wrong after all.