As scientific research becomes increasingly cross-disciplinary, many universities seek to support collaborative activity through new buildings and institutions. This study examines the impacts of spatial proximity on collaboration at MIT from 2005 to 2015. By exploiting a shift in the location of researchers due to building renovations, we evaluate how discrete changes in physical proximity affect the likelihood that researchers co-author. The findings suggest that moving researchers into the same building increases their propensity to collaborate, with the effect plateauing five years after the move. The effects are large when compared to the average rate of collaboration among pairs of researchers, which suggests that spatial proximity is an important tool to support cross-disciplinary collaborative science. Furthermore, buildings that host researchers working in the same or related fields and from multiple departments have a larger effect on their propensity to collaborate.