In June of 1902, Einstein was offered a job as a technical expert (third class) at the Bern Patent Office. For an annual salary of 3,500 francs, he was responsible for deciding whether submitted inventions were deserving of patent protection, whether they infringed on existing patents, and whether the products actually worked. Einstein could complete his tasks so quickly and so well that he had ample spare time in which to pursue his scientific work, and was even granted a raise of 400 francs soon after being hired.
While living in Bern, Einstein met regularly with a close circle of friends who shared his interests in physics and philosophy. These individuals included the Romanian student Maurice Solovine, his old friend Conrad Habicht, an electrical engineer Lucien Chavan, and Einstein's closest friend from the Polytechnic, Michele Angelo Besso. These men met late into the night to discuss their intellectual interests and referred to themselves as the Olympia Academy.
At the end of 1902, Einstein's father suffered a heart attack and Einstein returned to Milan to visit him. On his deathbed, Hermann Einstein finally consented to Einstein's marriage to Mileva Maric, and the couple wed on January 6, 1903. By this point, Mileva had lost much of her interest in science and had become a housewife. The couple's first son, Hans Albert, was born in May 1904.
The years 1903-1905 were arguably the most productive years of Einstein's entire career. In 1905, he published three papers that would transform physics in the twentieth century. The subjects of these papers were Brownian motion, quantum theory, and special relativity, each of which represented a groundbreaking solution to the most pressing problems facing physicists in Einstein's day.
The paper on Brownian motion, entitled "On the Movement, Demanded by Molecular-Kinetic Theory, of Particles Suspended in Liquids at Rest," tied in closely with Einstein's dissertation on the statistical molecular theory of liquids. Brownian motion referred to the permanent erratic movement of particles suspended in a liquid, first noticed by the English botanist Robert Brown in 1828. Einstein predicted that the random motions of molecules in a liquid impacting on larger suspended particles--such as bits of pollen--would result in irregular, random motions of the particles. From these particles' motion, he then could determine the dimensions of the hypothetical molecules causing the motions. This paper, published in the Annalen in 1905, brought Einstein numerous admiring letters from scientists throughout Europe and helped establish his reputation as a significant contributor to physical theory.
Einstein's paper on Brownian motion was conservative in its application of statistical methods to the random motions of Newtonian atoms. However, far more revolutionary (Einstein used the term himself) was his paper entitled "Concerning a Heuristic Point of View about the Creation and Transformation of Light." In this paper, Einstein argued that under certain circumstances, light behaves not as continuous waves but rather as discontinuous, individual particles called quanta. Einstein was driven to formulate this quantum hypothesis in response to an experimental puzzle that had challenged physicists throughout the nineteenth century.