# Einstein Relatively Easy

### What's Up As we have seen in our previous article, Einstein published for the first time in 1905 a demonstration to try set the equivalence of inertia and energy, or mass and energy.

However, it is only in 1912 in the Manuscript of Special Relativity, that the famous formula E=mc2 appears in its well known form. In this draft, however, the equation, which demonstrates that mass is a form of energy, appears in a somewhat different form. Originally, Einstein used the variable "L" for energy (the "L" stood for Lagrangian, a general form of energy); later, he crossed out the "L" and changed it to "E." The letter q stands for the velocity of the moving body.

In the below english translated extract corresponding to the above original manuscrit, we recognize the formula E=mc2, with m=γm0 (rest mass) as seen in our article Introduction to Four-momentum vector and E = mc2

Then Einstein makes the supposition that the body is moving with a velocity q<<c, and expands in a Taylors series We recognize the equation we have exposed in our article Introduction to Four-momentum vector and E = mc2 ### Quotes

"The essence of my theory is precisely that no independent properties are attributed to space on its own. It can be put jokingly this way. If I allow all things to vanish from the world, then following Newton, the Galilean inertial space remains; following my interpretation, however, nothing remains.."
Letter from A.Einstein to Karl Schwarzschild - Berlin, 9 January 1916

"Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the 'old one'. I, at any rate, am convinced that He is not playing at dice."
Einstein to Max Born, letter 52, 4th december 1926