Einstein's theory is completely incorrect. Famous equation E=mc2 is incorrect as well. "The proof" of formula's accuracy is based upon experimental fact that derrivative of energy released in atomic fusion (dE) equals derrivative of product of mass and speed of light squared (dmc2). However, _integral_ of this equation equals E=mc2+C, with C being a constant, so Einstein's formula would be correct only if mentioned constant equals zero.
Contemporary theorethical physics is meeting a dead end mainly because of incorrect assumption that interstellar space is empty, meaning its energy equals absolute zero (constant C equals zero in Einstein's equation). In reality, interstellar space is filled with vast energy and matter of great density, whereas mass represents effect of local changes in basic density and basic energy.
Much more about this, including calculated gravitational constant, can be read online in my book: