In several recent papers we showed that choosing new sets of postulates, including classical (pre-Einstein) physics laws, within the main body of Einstein's special relativity theory (SRT) and applying the relativity principle, enables us to cancel the Lorentz transformation from the main body of SRT. In the present paper, and by following the same approach, we derive Einstein's equation E = mc2 from classical physical laws such as the Lorentz force law and Newton's second law Einstein's equation is obtained without the usual approaches of thought experiment, conservation laws, considering collisions and also without the usual postulates of special relativity.
In this paper we also identify a fundamental conceptual flaw that has persisted for the past 100 years. The flaw is interpreting the formula E = mc2 as the equivalence between inertial mass and any type of energy and in all contexts. It is shown in several recent papers that this is incorrect, that this is a misinterpretation. What Einstein considered to be a central consequence of special relativity is in fact derivable from (pre-Einstein) classical considerations. E = mc2 becomes secondary, not fundamental, and whilst no doubt useful in certain circumstances, need not be valid in all generality.
