Ultimate Symmetry

If we want to consider mass to be variable with speed as in early Special Relativity, and distinguish between rest mass:  and relativistic mass: , according to the standard equation that uses Lorenz factor: , then we can arrive to the equation  by calculating the derivative  which in this case will not be equal to zero as we required in equation 3.7 above. However, the above relativistic equation of mass () is only obtained based on the same mass-energy equivalence relation that we are trying to prove here, so in this case it will be a circular argument. Therefore, the two equations:  and  are equivalent, and deriving one of them will lead to the other.