Research in theoretical questions includes topology and signature change in the early universe, and quantum gravity using the tool of path integration. Observational/experimental studies include tests of General Relativistic effects via laser-ranging to dense geodetic satellites. Matzner is a Co-I member of the LARES satellite team, and of the recently approved LARES 2 satellite team. (LARES, the densest artificial satellite in orbit, was launched in 2012; LARES 2 is expected to be launched in 2021).