The current description of light was made by Einstein in 1905 (he recieved the Nobel prize for this in 1921). Even though this work is an important part of the early quantum theory, it can not be said to be part of the later qauntum mechanics which was born in the 1920's. At any rate Einsteins work is 15 years older than quantum mechanics, so in that respect it was for sure thought of without quantum mechanics.
Actually this is not at law of quantum mechanics. Its simply the old rule of conservation of momentum. This is dating back to Newton, though he did of cause not know about photons. If the photon is reflected the sail must gain twice the original photon momentum in order to keep global momentum conserved.
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The current description of light was made by Einstein in 1905 (he recieved the Nobel prize for this in 1921). Even though this work is an important part of the early quantum theory, it can not be said to be part of the later qauntum mechanics which was born in the 1920's.
At any rate Einsteins work is 15 years older than quantum mechanics, so in that respect it was for sure thought of without quantum mechanics.
Actually this is not at law of quantum mechanics. Its simply the old rule of conservation of momentum. This is dating back to Newton, though he did of cause not know about photons.
If the photon is reflected the sail must gain twice the original photon momentum in order to keep global momentum conserved.