Interesting, thanks for the links. Looking at them, though, it would appear that the two "paths" being interfered differ in length on the order of the separation between the two telescopes -- i.e. meters or kilometers -- rather than astronomical distances. Using the speed of light, this corresponds to a difference in flight time of the light on the order of nanoseconds or seconds. I can imagine how the light traversing the two paths could remain unmolested by stray random, environmental phase shifts during such short times (necessary if you want them to interfere). On the other hand, the double images in the photo would have a difference in flight times of years? But, again, I don't really understand precisely what the astronomer was referring to, or have proper intuition for the conditions of space through which astronomical photons travel...