Inertial mass = gravitational mass, what about momentum?
  It has been tested precisely that the inertial and gravitational masses are equal. Here we reveal that the inertial and gravitational momenta may differ. More generally, the inertial and gravitational energy-momentum tensors may not coincide: Einstein's general relativity requires the gravitational energy-momentum tensor to be symmetric, but we show that a symmetric inertial energy-momentum tensor would ruin the concordance between conservations of quantized energy and charge. The nonsymmetric feature of the inertial energy-momentum tensor can be verified unambiguously by measuring the transverse flux of a collimated spin-polarized electron beam, and leads to a serious implication that the equivalence principle and Einstein's gravitational theory cannot be both exact. 
Xiang-Song Chen
gr-qc