Lorentz, Einstein et. al. assume time is the variable which changes in a gravity well or as speed approaches $c$. That's the commonly accepted model.
For nearly 50 years I've wondered if anyone else has considered introducing a hypothetical, "universal" rate of reaction U. Wherever t appears in all physical, chemical or electromagnetic formulae, it would be replaced with (U t). The product (U t) behaves precisely as t alone. However, in a case where t slows to 1/2, in this approach t remains the same, but U decreases by 1/2.
For an observer moving close to light speed, their chemical and physical reactions are slowed, including their atomic clock which measures time in their reference frame. From their perspective, the effect is identical to time itself slowing - but time is still progressing as it always has. Only their relative measurement of time has changed.
Since it's only a variable substitution, every formula in the cannon is unchanged. The only difference is that time is linear and universal - with U varying to compensate for relativity.
There is no observable, physical reason to believe in the U factor, but it makes the time ordinate linear and should make all the math easier.
Now, when doing an integral of time in an accelerating reference frame, it's possible to do a simple integration in t without t varying while it's being integrated.
I haven't taken the time to dig into this deeply, but it appears that mass itself might not be changing while its inertial changes because momentum = m v = m/U dx/dt. By factoring U as part of m, them m = m/U and once again, the rate of reaction changed - not the actual mass.
I asked this ages ago in physics classes and the answer was basically "we don't do it that way." That wasn't very satisfying.
Has anyone ever looked at this approach?