Is the "mass means rest mass" (MMRM) school of thought within relativity theory still "Einstein's theory of relativity"?
I have read that both MMRM and "mass depends on velocity" relativity predict experimental results equally well.
I think Karl Popper said that when two theories both predict experimental results equally well you should choose the simpler theory. Is the "MMRM" theory simpler than the old "mass increases with speed" theory, and adopted by some/all for that reason, or is it just easier, mathematically?
I have read that MMRM allows use of a unified system based on tensors instead of different math for different tranformations, making the math easier.