In 1900, at age 21, Einstein had his university diploma and was eager to begin his career as a physicist. He struggled to find work, however. After two years of searching, Einstein took a relatively low-level job at the patent office in Bern, Switzerland. Glad for the income and steady work reviewing patent applications--and still able to think about physics after hours—Einstein settled into a comfortable routine. Each day he walked to work through the streets of Bern, a city famous for its medieval architecture and beautiful clock towers.
Einstein passed by the clock towers again on his way home, a route he often took with his closest friend, Michele Besso. The two men regularly discussed science and philosophy—including the nature of time. After one such discussion, Einstein came to a sudden realization: Time is not absolute. In other words, despite our common perception that a second is always a second everywhere in the universe, the rate at which time flows depends upon where you are and how fast you are traveling. Einstein thanked Besso in his first paper on the Special Theory of Relativity.