Comment on Is The Speed of Light Everywhere the Same?parentComments−lutusp12yThey don't. But the re-emitted photons become part of a coherent wavefront through what Richard P. Feynman called a Path Integral:http://en.wikipedia.org/wiki/Path_integral_formulationSo the reason you have a coherent wavefront moving through a lens, as one example, is not because the photons are emitted in a particular direction, but at a particular time.
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They don't. But the re-emitted photons become part of a coherent wavefront through what Richard P. Feynman called a Path Integral:
http://en.wikipedia.org/wiki/Path_integral_formulation
So the reason you have a coherent wavefront moving through a lens, as one example, is not because the photons are emitted in a particular direction, but at a particular time.