Wednesday, February 18, 2015

quantum field theory - Electron Positron annihilation Feynman Diagram



I am having some trouble understanding this fenyman diagram, it seems to indicate that the electron produces the positron, as the arrow of the positron is pointing from the electron.


Additionally the arrow is in directed downwards, implying that the particle is going backwards in time? Is this diagram wrong, or does the arrow mean something else, or does the positron go back in time?!?





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classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

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