  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.
