Spaces and places are at the center of the science studies scholarship. Some scholars focus on the spatial circulation of written traces; others focus on the socio-cultural hierarchies reflected in the spatial organization of the laboratories. But most privilege single-case studies as their research method. While single-case studies offer the advantage of providing rich and detailed ethnographic description of spaces, they often fail to explain how imaginary spaces of science are turned into concrete social settings, often with unexpected deviations from their creators’ initial purposes. This paper argues that a comparative approach, which I call “paired biographies,” can help us study the tensions between imaginary and real spaces of science. This method of paired biographies is applied here to trace the attempts (both failed and successful) by two prominent physicists (J.R. Oppenheimer and E.O. Lawrence) to turn their imaginary scientific spaces into concrete places. This comparative approach, based upon paired biographies of various laboratory lives taken at different points in time, highlights the tensions between imaginary spaces of science and concrete architectural forms (themselves located in broader environments), and shows which unexpected outcomes derive from these tensions.