Could they have made the atom bomb without einsteins e=mc2?
Of course they could. To build the atom bomb you just have to understand radioactivity and you need to know that atoms, when they decay, release vast amounts of energy. The knowledge that this energy release also leads to a loss in mass is not important. e=mc2 is always true even when the energy involved is small. So when black powder explodes it also looses a tiny amount of mass because it doesn’t matter if the energy comes from the nuclear forces that hold the core of atoms together or if it comes from electrical forces that power chemical reactions. Energy is always equivalent to mass. But no one would say you need to know e=mc2 to build a black powder bomb.
