The background imagery of the magazine cover has the equation E = mc2 embossed on a mushroom cloud that rises above an inferno.
After the very public demonstration of huge energies released from nuclear fission after the atomic bombings of Hiroshima and Nagasaki in 1945, the equation E = mc2 became directly linked in the public eye with the power and peril of nuclear weapons.
The equation was featured as early as page 2 of the Smyth Report, the official 1945 release by the US government on the development of the atomic bomb, and by 1946 the equation was linked closely enough with Einstein’s work that the cover of Time magazine prominently featured a picture of Einstein next to an image of a mushroom cloud emblazoned with the equation.
The Einstein Franchise promoted by Time magazine was very strange because Einstein’s scientific contribution to the Manhattan Project was “inconsequential”.
Einstein himself had only a minor role in the Manhattan Project: he had cosigned a letter to the U.S. President in 1939 urging funding for research into atomic energy, warning that an atomic bomb was theoretically possible.
The letter persuaded Roosevelt to devote a significant portion of the wartime budget to atomic research.
Without a security clearance, Einstein’s only scientific contribution was an analysis of an isotope separation method in theoretical terms.
It was inconsequential, on account of Einstein not being given sufficient information (for security reasons) to fully work on the problem.
Furthermore, the Einstein Franchise promoted by Time magazine was “in no way an explanation of the large energies released in radioactive decay” and “is not required in discussing fission”.
Einstein’s equation is in no way an explanation of the large energies released in radioactive decay (this comes from the powerful nuclear forces involved; forces that were still unknown in 1905).
In any case, the enormous energy released from radioactive decay (which had been measured by Rutherford) was much more easily measured than the (still small) change in the gross mass of materials, as a result.
As the physicist and Manhattan Project participant Robert Serber put it:
Somehow the popular notion took hold long ago that Einstein’s theory of relativity, in particular his famous equation E = mc2, plays some essential role in the theory of fission.
Albert Einstein had a part in alerting the United States government to the possibility of building an atomic bomb, but his theory of relativity is not required in discussing fission.
The theory of fission is what physicists call a non-relativistic theory, meaning that relativistic effects are too small to affect the dynamics of the fission process significantly.
And, just to confuse matters even further, the Einstein Franchise equation promoted by Time magazine was not the equation Einstein published in 1905.
Albert Einstein did not formulate exactly the formula E = mc2 in his 1905 Annus Mirabilis paper “Does the Inertia of an object Depend Upon Its Energy Content?”; rather, the paper states that if a body gives off the energy L in the form of radiation, its mass diminishes by L/c2.
Does the inertia of a body depend upon its energy content? – A. Einstein – 27 Sept 1905
Wikipedia explains away the rebranding of the Einstein Franchise in the 1940s as a “simple expression of the ideas of Albert Einstein”.
However the association between E = mc2 and nuclear energy has since stuck, and because of this association, and its simple expression of the ideas of Albert Einstein himself, it has become “the world’s most famous equation”.
Wikipedia [also] cleverly glosses over any misunderstanding the reader may have regarding “the origin of energy in nuclear processes” by stating that “such processes” can be understood “without the need to invoke mass–energy equivalence”.
E = mc2 has frequently been used as an explanation for the origin of energy in nuclear processes, but such processes can be understood as simply converting nuclear potential energy, without the need to invoke mass–energy equivalence.
Therefore, for anyone who is confused by this rebranding it is helpful to remember that Einstein’s original 1905 equation:
1) Does not define an absolute relationship between mass and energy.
2) Only defines a relationship between changes in mass and changes in energy when the energy is electromagnetic.
(Here, “radiation” means electromagnetic radiation, or light, and mass means the ordinary Newtonian mass of a slow-moving object.)
This formulation relates only a change Δm in mass to a change L in energy without requiring the absolute relationship.
Einstein’s equation, by theory, can give these energies by measuring mass differences before and after reactions, but in practice, these mass differences in 1905 were still too small to be measured in bulk.
Additionally, it is only Einstein’s original 1905 equation that has been experimentally tested.
In 1933, the energy released from the reaction of lithium-7 plus protons giving rise to 2 alpha particles (as noted above by Rutherford), allowed Einstein’s equation to be tested to an error of ± 0.5%.
Instead, mass–energy equivalence merely indicates that the large amounts of energy released in such reactions may exhibit enough mass that the mass loss may be measured, when the released energy (and its mass) have been removed from the system.
For example, the loss of mass to an atom and a neutron, as a result of the capture of the neutron and the production of a gamma ray, has been used to test mass–energy equivalence to high precision, as the energy of the gamma ray may be compared with the mass defect after capture.
In 2005, these were found to agree to 0.0004%, the most precise test of the equivalence of mass and energy to date. This test was performed in the World Year of Physics 2005, a centennial celebration of Albert Einstein’s achievements in 1905.
Finally, because Einstein plucked c2 out of thin air it is probably worthwhile to remember Max Planck’s observation that Einstein’s 1905 derivation “is only valid to first approximation”.
The correctness of Einstein’s 1905 derivation of E = mc2 was criticized by Max Planck (1907), who argued that it is only valid to first approximation.