Einsteins hole dilemma and gauge freedom
  The issue of the physical equivalence between the different coordinate system in Einstein theory is revised. Gauge fixing influences results of measurements and physics are different in two different coordinate system. Spacetime metric generated by static spherically symmetric distribution of matter can be matched with wide family of vacuum solution and the exterior spacetime geometry could not be deduced directly from the interior perfect fluid solution, without reference to a gauge fixing or viceversa. The property of sollutions in general relativity is indeed an observer dependent concept. 
Sergey M. Kozyrev, Rinat A. Daishev
physics.gen-ph