I receive every now and then letters of the following kind:


> While researching the web on Olinto De Pretto I came across your name.

Many web sites claim that De Pretto had Einstein's famous equation before he did. My problem is that the web sites are inaccurate, distorted etc.

My question is: Did De Pretto have the EXACT equation E = mc^2 and not some variation or it could have been corrected to it? Specifically, it was not something to do with inertia, momentum, Lorentz or anything else. None of the sites have the exact quote (even in Italian) that is immaterial, as the equation’s symbols are universal.

If you can spare the time to answer this I would appreciate it.


My reply is that I explained the whole question at the end of my web page:

(points D, E, etc.)

but that unfortunately most of the explanations are written in Italian. Here it is a general, even if synthetic, answer to that kind of mails.


>> It would be difficult for me to explain in a few words and in English the details of a "case" to which I have dedicated many intellectual resources during more than ten years. The risk of misunderstandings is very high, and unfortunately I have never made the effort to translate in English the different papers written about this subject. Anyway, I made De Pretto's essay wholly available on line, at:

and everybody can check by himself that he introduces indeed an original physical hypothesis, concerning a POSSIBLE GREAT AMOUNT OF ENERGY STORED IN EVERY MASS, even when the mass is at rest.

The same amount of energy for every mass, independently from the material, wood, or iron, or glass. In De Pretto's own words (in my poor translation): "Nobody would easily admit that, stored in each kg of each mass, completely concealed to our investigations, there exist such an amount of energy, corresponding to the quantity of energy which can be obatined by millions and millions of Kg of coal; the idea would surely be considered as a foolish one".

He computed this energy starting from the Leibniz's "vis viva", E = mv^2, which corresponds to the famous E = mc^2 when v = c, the light's speed, as he openly conjectured. But it is important to remark that indeed, looking better, he used at last to express this hypothetical energy by means of thermodynamical units, and in doing so he divided the vis viva by a coefficient which is the double of the correct one.

More precisely, he wrote the energy he was conjecturing about, in the form


instead of


4169 was the conversion value in thermodynamical units available at his time: today it is estimated as 4186,05.

This means that he was really thinking of a simple kinetical energy mc^2/2, due to the sum of all moving (at light's speed) aether particles which were in his opinion the ultimate components of any kind of "matter" (by the way, I do believe that De Prettos' conception is much more near to the "truth" than other contemporary more famous physical theories concerning space and matter, but I am a mathematician, and not a physicist!).

De Pretto was not a physicist too, nor an academician, his intuition was founded on a physical conception, the cartesian aether, which Einstein wept out from XXth century's physics, and this explains the general oblivion about his hypothesis, and the fact that his work has never been object until now of the deserved attention from historians of science. I have no problems in accepting that Einstein's approach was more "scientific" in some sense, and coherent with a sophisticated mathematical theory, nevertheless I am sure (as far as one can be sure about historical matters which cannot be fully documented) that De Pretto's idea was a kind of inspiration for Einstein, through his friend Michele Angelo Besso, the only one person mentioned thankfully in the famous 1905 relativity paper. As a matter of fact, it is a rather curious "coincidence" that Besso was the nephew of a beloved uncle (when Michele studied at Rome he was guest of his uncle's house), and that this uncle was a colleague, at the Italian Railways, of one of De Pretto's major brothers! It is very easy to suppose that the general idea of that great amount of energy stored in each matter even at rest, proportional to c^2, went to Einstein throught Besso, and to Besso through his uncle Beniamino from the conversations with De Pretto's brother, which used to talk to everybody of the "foolish physical ideas" of his younger brother.

The fact remains that De Pretto's conception about energy and matter is at least qualitatively, if not strictly quantitatively (namely, leaving that factor 1/2 aside), the unique forerunner of Einstein's famous formula, in the physical interpretation which is today commonly regarded as the correct one. One must not forget that energy is defined just up to an additive coefficient, and that to give a physical meaning to the quantity E = mc^2, when m is the "proper mass" of a material body, is just a matter of physical speculation, and of experiment, and not of a purely theorethical approach.

If it can be helpful for you, in the sense that you have an Italian friend who can translate something for you, I did write a short essay about this case which is available at:

(this page contains different other pieces of information too, some of them even in English).

I hope to have been useful in some way, best wishes,

Umberto Bartocci