On the Origin, Development, and Experimental Validation of Relativistic Rest Mass Energy

The equation E = mc2, representing rest mass energy, is one of the foundational pillars of modern physics. It is indeed true that the concept of a relationship between energy and mass existed prior to Einstein. Late 19th-century physicists had laid the groundworks for this through electrodynamic and radioactivity studies. The ‘Thought Experiment’ conducted by Albert Einstein in 1905 was essentially a form of logical imagination. This theoretical framework created in his mind subsequently agreed with laboratory experiments (Experimental Proofs) with hundred percent accuracy. This paper examines the historical roots of pre-Einsteinian mass-energy relationships, Einstein's relativistic derivation of rest mass energy via his thought experiment, and the subsequent experimental evidence that transformed this construct into an established physical reality.