By 1909 Einstein was recognized as a leading scientific thinker and in that year he resigned from the patent office. He was appointed a full professor at the Karl-Ferdinand University in Prague in 1911. Albert was the youngest one to attend the invitation-only Solvay Conference in Brussels, the first world physics conference.
In fact 1911 was a very significant year for Einstein since he was able to make preliminary predictions about how a ray of light from a distant star, passing near the Sun, would appear to be bent slightly, in the direction of the Sun.
About 1912, Einstein began a new phase of his gravitational research, with the help of his mathematician friend Marcel Grossmann. Einstein called his new work the general theory of relativity. He moved from Prague to Zurich in 1912 to take up a chair at the “Eidgenössische Technische Hochschule” in Zurich.
Einstein returned to Germany in 1914 but did not reapply for German citizenship. What he accepted was an impressive offer. It was a research position in the Prussian Academy of Sciences together with a chair (but no teaching duties) at the University of Berlin. After a number of false starts, Einstein published late in 1915 the definitive version of the general theory of relativity.