Login Register Stay Curious Subscribe. The Sciences. Newsletter Sign up for our email newsletter for the latest science news. Sign Up. Already a subscriber? Want more? More From Discover. Recommendations From Our Store. Stay Curious. With these principles footnote: The principle of the constancy of the velocity of light is of course contained in Maxwell's equations as my basis I deduced inter alia the following result:" It is not impossible that with bodies whose energy-content is variable to a high degree e.
If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies. When fuels are burned, rest mass is always lost but the loss is generally barely discernible. Given the huge c2 multiplier, very little fuel is therefore needed to produce a lot of energy.
This is a vast oversimplification. Einstein was neither the first person to consider the equivalence of mass and energy, nor did he actually prove it. Anyone who sits through a freshman electricity and magnetism course learns that charged objects carry electric fields, and that moving charges also create magnetic fields. Hence, moving charged particles carry electromagnetic fields. In J. Thomson , later a discoverer of the electron, made the first attempt to demonstrate how this might come about by explicitly calculating the magnetic field generated by a moving charged sphere and showing that the field in turn induced a mass into the sphere itself.
The effect is entirely analogous to what happens when you drop a beach ball to the ground. But this is not the whole story. Drag or no drag, in order to fall the ball must push the air ahead of it out of the way and this air has mass.
Thomson understood that the field of the sphere should act like the air before the beach ball; in his case the effective mass of the sphere was the entire mass induced by the magnetic field. Although electromagnetic mass required that the object be charged and moving, and so clearly does not apply to all matter, it was nonetheless the first serious attempt to connect mass with energy.
It was not, however, the last. When Englishman John Henry Poynting announced in a celebrated theorem on the conservation of energy for the electromagnetic field, other scientists quickly attempted to extend conservation laws to mass plus energy.
In a particle accelerator, protons are accelerated to almost the speed of light and smashed into each other. The high energy of these collisions allows the formation of new, more massive particles than protons — such as the Higgs boson — that physicists might want to study. Which particles might be formed and how much mass they have can all be calculated using Einstein's equation. It would be nice to think that Einstein's equation became famous simply because of its fundamental importance in making us understand how different the world really is to how we perceived it a century ago.
But its fame is mostly because of its association with one of the most devastating weapons produced by humans — the atomic bomb. The equation appeared in the report, prepared for the US government by physicist Henry DeWolf Smyth in , on the Allied efforts to make an atomic bomb during the Manhattan project.
The result of that project led to the death of hundreds of thousands of Japanese citizens in Hiroshima and Nagasaki. Einstein himself had encouraged the US government to fund research into atomic energy during the second world war but his own involvement in the Manhattan project was limited because of his lack of security clearances.
It is unlikely that Einstein's equation was much use in designing the bomb, beyond making scientists and military leaders realise that such a thing would be theoretically possible, but the association has stuck. Einstein's theory of mass and energy.
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