What can LISA tell us about General Relativity?
• We know General Relativity (GR) is an extremely good approximation to Nature in the weak field. In the strong field we have only rather circumstantial evidence for the validity of GR, and no clear demonstration that massive compact objects are really described by the vacuum uncharged Kerr metric. Nonlinear GR is so complicated that we can’t be sure that there are not other stable solutions that ordinary matter might produce. Furthermore even if Einstein was right and Gμν=8πTμν, GR does not tell us what the stress-energy tensor is for highly relativistic compact objects that generate strong (and therefore non-linear) gravitational fields Tμν. Unexpected nearby matter, charge configurations or exotic new fields (soliton stars, boson stars) might exist near or in some or all massive compact objects which we call “black holes”.
