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> Einstein was not the “father of the atomic bomb” as is sometimes still claimed, based on his famous equation, E=mc2, or “Energy equals mass times velocity squared.” His equation itself wasn’t a breakthrough, but it did explain what was going on. Einstein’s theory behind the equation holds that energy and mass are essentially the same thing. In splitting atoms —fission—the energy in their mass is released, producing enormous power.

More than that, the equation is not E= mc^2 except when we are talking about particles with rest mass and are not moving. The equation is really E^2 = (pc)^2 + (mc^2)^2. For example, the second term vanishes for photons without rest mass. I agree that the equation weren't that of a breakthrough in itself until we think about the negative solutions which will lead Dirac to the path of anti-matter.




What Einstein did do for the Atomic Bomb was to co-sign Leo Szilard's letter which got the attention of President Eisenhower and kick-started the Manhattan Project.

https://en.wikipedia.org/wiki/Einstein%E2%80%93Szilard_lette...


You mean Roosevelt, not Eisenhower.


It raised a flicker of polite interest that died, from your own link:

    The Advisory Committee on Uranium was the beginning of the US government's effort to develop an atomic bomb, but it did not vigorously pursue the development of a weapon.
What did move the needle, again from your link:

    The Frisch–Peierls memorandum and the British Maud Reports eventually prompted Roosevelt to authorize a full-scale development effort in January 1942.
In essence, the letter from Einstein did not start the Manhatten Project, it was instead the direct efforts and in person meetings of Oliphant:

https://en.wikipedia.org/wiki/Mark_Oliphant#Manhattan_Projec...


Einstein was, of course, a devout pacifist. It must have turned some heads that he argued for a bomb to be made.


> More than that, the equation is not E= mc^2[...]

Unless 'm' is the relativistic mass. Which, yes, is a perfectly valid and useful concept. See also this discussion: https://news.ycombinator.com/item?id=38425252


People are usually using E=mc^2 equation because it is simpler. Introducing the concept of relativistic mass and Lorenz transformation to get the rest mass (what most people think of mass) will be less intuitive for the common culture.


I used to think so, but these days, I wonder why I used to think that rest mass is more intuitive. For most things we interact with and develop intuitions about, their speeds are so low that relativistic and rest masses are virtually the same, so that intuition can't come from experience. Photons are the exception to that, but we never encounter them at rest, and there's no particular reason we would have an intuition that photons must be massless until we learn about it in school. And then people have to overcome the confusion that photons do still carry momentum despite being massless.

If we think of mass in terms of inertia, the difference between rest mass and relativistic mass only shows up at relativistic speeds (like in a particle accelerator, or cosmic rays). At that point, relativity and Lorentz transforms needs to be taken into account anyway; the half-lives of unstable particles get affected by time dilation, and so on.

The other way that mass shows up in physics is through gravitation. If we think of mass in terms of its gravitational influence, then relativistic mass is all that matters, and rest mass seems to mess with people's intuitions much more, causing all sorts of conceptual mistakes. Like thinking that photons don't gravitate.

Rest mass does has some theory-simplifying mathematical advantages, but I don't think those benefits will matter to the intuitions of non-experts.




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