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According to the results of Michelson–Morley experiment, the speed of light is constant regardless of the velocity of the source. Now, I want someone to correct me if I am mistaking about the following assumptions:

Light(i.e, photons) are massless and thus the law of conservation of momentum doesn't apply to them and that is why it's speed when beamed out of some source will not be affected by the pre-condtions of beaming. But this will rise the question of Why photons are massless?. Because the don't interact with the Higgs-boson field , would be the Dry answer -_- .

Qmechanic
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Fadi
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    "and thus the law of conservation of momentum doesn't apply to them" This is not correct. Even classically light carries momentum and that momentum must be accounted for to maintain the conservation rule. – dmckee --- ex-moderator kitten May 07 '15 at 21:15
  • See http://physics.stackexchange.com/questions/2229/if-photons-have-no-mass-how-can-they-have-momentum?s=6|0.0000 – dmckee --- ex-moderator kitten May 07 '15 at 21:17
  • The conservation of momentum is a direct consequence of the homogeneity of space. As long as light moves trough a homogeneous volume (i.e. vacuum), it can't change its momentum. As soon as that homogeneity is violated (e.g. by the light hitting a mirror), momentum exchange has to take place. That's what causes light pressure on the mirrors. – CuriousOne May 08 '15 at 00:29

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No, the law of conservation of momentum definitely applies to photons. The modification is that the momentum of a lightlike particle is constrained to be equal to its energy divided by $c$. Therefore, for photons, where $E = h f$, then the momentum is equal to $p = \frac{h f}{c}$

Zo the Relativist
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