Originally Posted by wogoga
Not "should be". Is
First off, your source is basically religious, not scientific. Second, you seem to be confusing the coherence effects that lead to lasers with thermal emissions. This is wrong, very wrong. Stimulated emission does lead to coherence, but it can never dominate emissions unless you've got population inversion, and thermal emissions from a star are very much NOT inverted thermal populations. Third, photons interact with each other very little. As ben explains above, the photon-photon interaction is basically non-existent within the optical range.
It is spatially coherent at long distances simply because the waves have traveled so far that they're basically all traveling parallel to each other. You can only get spatial decoherence when light arrives at your detector from different directions. This is a purely geometric effect, it involves zero interactions between photons. A distant star subtends so little solid angle from our view that it's about as good a point source as you could hope for.
This makes no sense whatsoever.