Einstein enrolled in the Zurich Polytechnic in October 1896, although he was still six months short of the official minimum age of 18. He participated in a four-year teachers' training program that would qualify him as a specialized high school teacher of mathematics and physics. He lived in student lodgings in the bourgeois district of Hottingen, first in the apartment of Frau Henriette Hagi and then at a small pension run by Stephanie Markwalder. Throughout his four years of study, he lived on the modest income of 100 Swiss francs per month, most of which was provided by his maternal grandparents, the Kochs.
Einstein's decision to enroll in a teachers' training program may seem surprising in light of his own unhappiness as a schoolboy in Munich; the joy he took in learning came from his informal education at home, not from his experiences in a school with formally trained instructors. However, his teaching course may have been an attempt to reach a compromise with his family, which was in financial trouble at the time. The factory run by his father and uncle had failed in 1896 and most of the family funds were lost. Thus, despite Einstein's desire to master the frontiers of physics, he also recognized the importance of securing a steady income.
Einstein did not abandon physics, however, indeed studying it seriously in the laboratory of the head physics professor at the Polytechnic, Heinrich Friedrich Weber, who was best known for his contributions to electrical engineering. Yet although Einstein admired the professor's achievements, he was distressed to learn that Weber, a staunch believer in classical physics, was hopelessly old- fashioned, dismissing of all the advancements in electricity and magnetism since Helmholtz's discoveries of the 1850s. Once again, as in high school, Einstein relied on independent study: he read widely the works of Maxwell, Kirchoff, Hertz, Helmholtz, and contemporary physicists. Einstein also benefited from his studies with his mathematics lecturer, Hermann Minkowski, who would later prove instrumental in devising a strict mathematical formalism to support Einstein's theory of relativity.
Although Einstein did not have a large social circle in Zurich, he made several close friends who would have a strong impact on his future. One such friend was Marcel Grossman, a mathematics student one year his senior. Grossman's father was a factory owner in Zurich and Marcel was the product of a liberal Swiss environment. Einstein viewed his friend as a model student and relied heavily on his lecture notes whenever it came time for final examinations. Grossman continued to come to Einstein's aid in later years, first by helping him to secure a position at a patent office in Bern following his graduation, and then by working on the mathematical calculations of the general relativity theory.
Another of Einstein's closest friends was Michele Angelo Besso, a mechanical engineer living in Zurich. Einstein met Besso through an amateur music group in Zurich, which Einstein often joined on Saturday afternoons to play his violin. He encouraged Einstein to read the works of Ernst Mach, a contemporary Austrian philosopher. Mach's empirical positivism and distrust of metaphysical speculation would have a strong impact on Einstein's theory of special relativity.
Finally, Einstein also became very close with Mileva Maric, a Hungarian student three years his senior at the Zurich Polytechnic. Mileva was not a brilliant student, but a hard and determined worker. Although Einstein was popular with many of the women at the Polytechnic, his relationship with Mileva became particularly intense between the autumn of 1899 and the summer of 1900. Then, in July 1901, not long after their graduation, Mileva informed Einstein that she was pregnant. Einstein intended to marry her, but his parents were vehemently opposed on the grounds that she was beneath their social standing. Mileva's parents, in contrast, encouraged the relationship between Einstein and their daughter, especially when they learned that she was pregnant. When Mileva gave birth to an illegitimate child at the end of January, 1902, Mileva's parents took responsibility for the young Lieserl and, it is believed, soon put her up for adoption. Although Einstein and Mileva remained on good terms throughout the pregnancy, it was not until January 1903, when Einstein had a secure and well-paying job at the patent office in Bern, that the couple finally married.
The relationship between Einstein and Mileva has been a subject of extensive historical interest, especially following the publication of their romantic correspondence. Einstein's love letters to his fiancee contain detailed descriptions of his scientific work and his reactions to his studies, often interjected amidst more prosaic personal details such as his decision to shave and his fondness for sausages. Although the Einstein scholar Dr. Evan Harris Walker argued in 1990 that Mileva was crucial in the development of relativity theory, it is unlikely that she made any significant intellectual contribution to Einstein's research. While Einstein referred in his letters to "our work" when discussing his latest ideas, this term was most likely a testament to his desire to involve her in his work, not to the actual fact of her involvement. It should be noted that Mileva did help her husband by checking his calculations, and therefore participated directly in his research even though she probably did not shape its development. In any case, historians agree that Mileva was one of the most important individuals in Einstein's life during his years at the Zurich Polytechnic and immediately thereafter.