Fundamental physics with LISA

LISA has the potential to make observations that probe deeply into fundamental physics. Not only will it test to exquisite precision the general relativity model for gravitational radiation, but will also test strong-field gravity and in particular the proposition that all black holes are described by the Kerr metric. More research is needed, however, on how to quantify the theoretical meaning of any deviations that might be seen from general relativity. LISA can also make important contributions where cosmology and fundamental physics join. LISA's observations of black-hole coalescences, out to redshifts of 20 or more, provide a completely new distance measure, one that needs no calibration and is independent of the standard cosmological 'distance ladder'. Using this measure, LISA may even begin to measure or limit the time dependence of the dark energy equation of state. Beyond these expected results from LISA is the mission's discovery space: LISA's high sensitivity raises real possibilities that it will discover sources in the dark part of the universe that were completely unexpected.