InthelattercasetheeffectofthestimultatedemissiononthemomentumoftheexcitedatomwouldaveragevectoriallytozeroandthiswouldimplythatthedistributionfunctionforblackbodyradiationwouldbeWien'sinsteadofPlanck's.Thuswecanruleouttherandomdirectionoption.
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In the latter case the effect of the stimultated emission on the momentum of the excited atom would average vectorially to zero and this would imply that the distribution function for blackbody radiation would be Wien's instead of Planck's. Thus we can rule out the random direction option.