He lived in Switzerland between 1895 and 1914, except for one year in Prague, and he received his academic diploma from the Swiss federal polytechnic school (later the Eidgenössische Technische Hochschule, ETH) in Zürich in 1900. He taught theoretical physics there between 1912 and 1914 before he left for Berlin. He acquired Swiss citizenship in 1901, which he kept for the rest of his life after being stateless for more than five years. In 1905, he was awarded a PhD by the University of Zurich. The same year, he published four groundbreaking papers during his renowned annus mirabilis (miracle year) which brought him to the notice of the academic world at the age of 26.