The third law is just about the conservation of the momentum. It follows from the translational symmetry of the laws of physics and it holds for any description, whether or not it contains fields. The description in terms of a force, action at a distance, has the same force with the opposite sign acting on both objects. If there are fields, the fields may carry some momentum, too. In quantum field theory, the force comes from virtual particles – virtual quanta of the fields – and they again carry the right momentum so that it is always conserved. So the law always holds. Does it answer “How”?

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— Physics Stack Exchange

— Apr 6 ’11 at 12:17

— Lubos Motl

2013.08.23 Friday ACHK