I think this is what I was grasping for when asking about the recoil as seen by the laser apparatus: (from wikipedia's page "Newton's_laws_of_motion" I'm not allowed to post URL's...)
Quote:
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Newton used the third law to derive the law of conservation of momentum;[24] however from a deeper perspective, conservation of momentum is the more fundamental idea (derived via Noether's theorem from Galilean invariance), and holds in cases where Newton's third law appears to fail, for instance when force fields as well as particles carry momentum, and in quantum mechanics.
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