  Weyl had good reasons for his concern. He analyzed the invariance of  the Maxwell-Dirac equations under the discrete symmetries that  correspond to the transformations now called \(\mathbf{C}, \mathbf{P},  \mathbf{T}\) and \(\mathbf{CPT}\) both for the case of relativistic quantum  mechanics and for the case of relativistic quantum field theory, and  concluded in both cases that the mass of the anti-electron should be  the same as the mass of the electron. That the mass of the proton was so different from the mass of the electron, therefore, appeared to  Weyl to constitute a new serious crisis in physics. 