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Because charge is conserved and the universe appears to have no net charge. You could replace electrons with other negatively charged leptons (because lepton number is also conserved), but these are unstable (in most circumstances) and would decay into electrons. The mass ratio is only relevant in so far as determining things like when and where the protons ...


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Start by considering an isolated hydrogen atom absorbing a photon with an energy of 10.2 eV i.e. undergoing a transition from the 1s to 2p level. The 2p state decays back to the 1s state by emitting a photon because it cannot do anything else. There is simply no other way to release the energy. But now consider a proton absorbing a photon with an energy of ...


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It is a fairly general result that any process that can absorb quanta (such as photons) inelastically can also scatter the same quanta, and the scattering cross section $\sigma_{sc}$ is always at least as great as the inelastic cross section $\sigma_{in}$. For a nucleus, this means that any nucleus that can absorb a photon of energy $E=\hbar\omega$ will also ...


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Charge is a property of matter, so one can only talk of the property and what it does, like equally charged matter repels each other, different charged matter attract each other. Same thing for "mass"! It is a property of everything around us. So charge is always together with matter. The only thing known: there is a smallest amount of charge which ...


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If only we knew what charge is... Actually Quantum Field Theory does not answer that. Charge tells you how different particle fields interact, but it does not arise from the theory in a natural way. Actually, Quantum Electrodynamics is so accurate because it was built upon Classical Electrodynamics, but most of its problems stayed within the new theory (for ...


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