Fundamental physics with the ESA mission GAIA

ESA advisory committees have selected the astrometry mission GAIA as one of the future cornerstones of the science program. GAIA is primarily a mission to study the history, formation and evolution of the Galaxy from astrometric, photometric and spectroscopic measurements, but it also displays remarkable capabilities in some areas of fundamental physics. After introducing briefly the measurement principles and the expected accuracy, I focus on the three topics most relevant for the physicists: the definition and realization of a quasi-inertial machian frame, the testing of the PPN formulation of the gravitational theory and finally a determination of the possible time change of the gravitational constant. (C) 2001 Academic des sciences/Editions scientifiques et medicales Elsevier SAS.