Before talking about the famous formula’s history, it is good to understand what E=mc2 means. In physics, mass–energy equivalence is the concept that the mass of an object or system is a measure of its energy content.

For instance, adding 25 kilowatt-hours (90 megajoules) of any form of energy to any object increases its mass by 1 microgram even though no matter has been added.

A physical system has a property called energy and a corresponding property called mass; the two properties are equivalent in that they are always both present in the same (i.e. constant) proportion to one another. Mass–energy equivalence arose originally from special relativity as a paradox described by Henri Poincaré. The equivalence of energy E and mass m is reliant on the speed of light c and is described by the famous equation: E=MC2

What is interesting to learn in the history of E=MC2, it’s that this concept has it’s own life, and the paternity of it, is source of polemics.

H. Poincaré, 1887, A. Einstein 1921

Those who discovered the theory of restrained relativity had the chance to express themselves, so let’s see first what they have to say :

Lorentz in 1921: « I didn’t established the principal of relativity as rigorously and universally true. Poincaré, on the contrary, obtained a perfect invariance of the equations of electrodynamisme and he was the first to formulate the postulate of relativity, term that he was the first to use »

Einstein in 1946: « It is out of any doubt that if we look retrospectively on its evolution, the theory of relativity was already mature in 1905. Lorentz had already discovered by the analysis of the equations of Maxwell, the transformation that has his name. On his side, H. Poincaré had penetrated more deeply in the nature of these relations. Me, I had knowledge only about Lorentz great work, but not the work of Poincaré. In this sense, my work is independent… »

Facts commonly admitted:

- In 1900, Henri Poincaré published an article in which he affirms that a ray that could be considered as a fictive fluid of a mass equivalent to m = E/C2. He inspired by the theories of electrons by Lorentz.
- In 1905, Albert Einstein is the first to suggest that when a material looses its energy E, the mass decrease of a value equal to E/c25.
- In June 1905, Poincaré completes the transformation of Lorentz equations and proves the invariance of Maxwell equations.
- In September 1905, the article of Einstein doesn’t mention any other reference. There is no reference to Poincaré, but he mentions Lorentz relations.
- In 1902, Einstein read « La Science et l’Hypothèse » by Henri Poincaré.
- H. Poincaré died in 1912. A. Einstein died in 1955.

E=Mc2 is a concept that had a life of it’s own, just like the reality that it describes. Indeed, if the equation is quite recent, so the paternity of it, the phenomenon itself exists since way before humain being even appeared on earth.