Mainstream academic physics has completely eliminated the concept of non-rest, variable mass. Mass and energy are equivalent, so you CAN apply mass values to th

Mainstream academic physics has completely eliminated the concept of non-rest, variable mass. Mass and energy are equivalent, so you CAN apply mass values to the kinetic energy of a particle, but it turns out to be more confusing than its worth. To be clear, it's just a reformulation of the math involved. Both formulations of GR/SR with and without variable mass create the same predictions. It's just that it keeps the concept of mass more coherent to stick with "mass is the energy of a particle at rest".