Einstein graduated from his teachers' training program at the Zurich Polytechnic in August 1900, along with three other students. Two of these students immediately obtained positions as assistants at the Polytechnic, but Einstein was not so fortunate; Professor Weber, a German, was not particularly fond of the student who had renounced his citizenship and relied on his friend's lecture notes to pass all his classes. Unable to find employment immediately after graduation, Einstein spent the summer of 1900 living with his family in Milan.
Over the next three years, Einstein obtained temporary teaching positions while working on his doctoral dissertation on the kinetic theory of gases. His job search became less difficult following the publication of three papers in the prestigious Annalen der Physik. These papers, along with his dissertation, reflect Einstein's frustrations with the mechanical worldview that dominated physics throughout the nineteenth century and into the twentieth.
The mechanical worldview refers to the Newtonian view of the universe, according to which all natural phenomena arise from the interactions among moving matter. This matter obeys Newton's three laws of motion, involving action and reaction, force and acceleration, and inertia. According to Newton, all matter consists of small particles, which the English chemist John Dalton referred to as "atoms" in the first decade of the nineteenth century. The motion of atoms was set against a background of an infinitely flat "absolute space" and a strictly linear "absolute time." Over the course of the century, chemists and physicists struggled to come to terms with the existence of atoms and their properties.
Even Newton had not been completely comfortable with a strictly mechanical view of the universe, because mechanics seemed unable to account for his law of universal gravitation: how could this force act across space given the vacuum between atoms? Even more serious challenges to the mechanical worldview arose with the formulation of electromagnetic theory by Michael Faraday, James Clerk Maxwell, and Heinrich Hertz over the course of the nineteenth century. The greatest contribution to this theory was Maxwell's famous equations explaining the propagation of electromagnetic waves. Maxwell equations unified electricity and magnetism to define the nature of light. Light had previously been considered a wave that propagated through the ether, a mysterious substance that pervaded the whole universe. The ether, like Newton's absolute space, served as a reference frame against which motion could be measured. One of the most important problems facing physicists like Einstein at the turn of the century was to find a complete mechanical account of Maxwell's equations that was consistent with the Newtonian worldview.
Einstein's early papers represent his attempt to extend the atomic, mechanical perspective to several phenomena in physical chemistry. His first two papers, published in 1901 and 1902, deal with the nature of forces between molecules. Einstein based his calculations on the principle that these molecules obey a universal law such as gravity, though today we know that these interactions are governed by the actual size of the molecules. Although his early papers had their flaws, Einstein successfully applied the laws of statistical mechanics to atoms, thus achieving a "general molecular theory of heat." In his dissertation, he developed a statistical molecular theory of liquids and showed how the laws governing the dynamics of heat flow (thermodynamics) could be understood in terms of the motions and collisions of Newtonian atoms.
Einstein's attempt to unify thermodynamics and mechanics demonstrates an overriding philosophical trend in his work as a whole: from the very beginning of his career, he was determined to find unifying themes in physics; this drive for unity would figure centrally in his formulation of relativity. Moreover, the context of Einstein's desire for unity was larger than the field of physics alone: a "unifying spirit" pervaded central European thought at the turn of the century and shaped ideas such as German idealism, Romanticism, and Historicism. One of the most famous and influential nineteenth-century German poets, Johann Wolfgang von Goethe, passionately articulated a longing for unity, wholeness, and the interconnection of all parts of nature. Likewise, philosophers from Kant to Dilthey had pointed to a transcendent higher unity. Einstein's drive for unity was thus not just a response to the state of physics in his day, but also the product of a broader cultural milieu.