Tjalling Charles Koopmans
Koopmans came to Utrecht in 1927, as a student of mathematics and physics. In 1933 he got his degree in the field of theoretical physics, but it was clear that he was searching for a field of study closer to reality, such as psychology, psychiatry or economics. He read Marx's Das Kapital with a circle of socialist friends from Utrecht. While discussing this and other economic works he met Jan Tinbergen (1969 Nobel Prize laureate). Koopmans agreed with Tinbergen that it should be possible to apply the mathematical methods of theoretical physics to economics. Koopmans worked on his dissertation, titled 'Linear regression analysis of economic time-series', in Utrecht but formally received his PhD from Leiden University as his supervising professor had accepted an appointment in Leiden.
After his PhD Koopmans definitely gave up physics and worked as an economist in Rotterdam and Geneva. In 1940, at the start of World War II, he was only just able to leave the country with his family. He went to the United States, where he joined the Cowle Commission and became a professor at Yale.
He received the 1975 Nobel Prize for Economics for his work on the optimal use of resources.