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Gravity as a field theory shows that particles move because of the curvature of spacetime - the field here is spacetime itself. Electromagnetism is a field theory and light are just waves in the EM field which is cocontiguous with space that bears it. Both the above are classical descriptions. QM, and then QFT showed that we should quantise fields. This ...

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Feynman diagrams are most definitely not a representation of what's going on between the particles. Feynman diagrams are simply a tool to help you remember formulas: if you want to calculate the probability that two electrons will scatter off each other in so-and-so angle, you draw all possible diagrams with two incoming electrons and two outgoing electrons ...

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The angle of the particle lines is irrelevant and it's just a convention. You could as well draw them as straight vertical lines. It doesn't affect the calculation of its contribution to the probability amplitude of scattering. For the same reason, Feynman diagrams do not intent to show attraction nor repulsion. They are just a bookkeeping graphical tool for ...

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Propagators are independent of interactions. They only depend on the free part of the lagrangian. For example, the KG lagrangian reads $$\mathcal L_{KG}=\frac{1}{2}(\partial \phi)^2-\frac{1}{2}m^2\phi^2-\mathcal H_I(\phi)$$ where $\mathcal H_I$ could be, eg, $\frac{g}{4!}\phi^4$. There are different definitions of the propagator (all equivalent, of ...

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