There are several tests of general relativity: - gravitional redshift - deflaction of light - perihelion precession of Mercury - Shapiro delay - Lense-Thirring precession - binary pulsars Now comes the part that problems me. These all are based on vacuum solution of Einstein field equations. With vacuum solution EFE is 0 = 0, IMO not that good proof of validity of equations. So is there any real tests of EFE, other than Cosmology? (which have it's problems as we all know) Also looking for good explanations why left side of EFE must equal right side.