Constraining Mach's principle with high precision astrometry
  The analyses of high precision astrometric surveys, such as Gaia, implicitly
assume a modern version of Mach's Principle: the local inertial frame of our
Solar System should be non-rotating in the frame of distant quasars. On the
contrary, Einstein's General Relativity allows a rotating universe. Thus,
relaxing the assumption of Mach's Principle will allow placing a constraint on
a class of rotating cosmologies by comparing high precision astrometry of
quasars with well-measured solar system orbits. Constraining global rotation
will test General Relativity, inflation, and the isotropy of cosmological
initial conditions.
