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 P: 15 In Mandel et Al's most famous experiment (Fig 6 at ‎[url]http://student.science.nus.edu.sg/~g0203645/Atomic%20Molecular%20and%20Optical%20Physics/Quantum%20effects%20in%20one-photon%20and%20two-‎photon%20interference.pdf) the signal beams from two coherent downconverters are ‎observed to interfere only if the two corresponding idler beams are allowed to ‎interfere.‎ Let's say that the a blocking object is inserted or removed in front of idler beam 1 at ‎point A. Let us also say that the signal beams are detected at point B.‎ The direct distance between A and B is x light seconds, and the distance travelled by ‎the idler 1 light beam from the 1 downconverter plus the distance travelled by the ‎signal 1 beam from the 1 downconverter to B is y light seconds.‎ When the object is inserted/removed at A, how long does it take for the interference ‎pattern at B to disappear/appear ?‎ Is it ‎1) Instantaneously ‎2) x seconds later, or‎ ‎3) y seconds later ?‎ ‎(I know that the detector needs to move back and forth to see interference patterns, ‎but assume it can move back and forth and record very quickly).‎ The above is question 1.‎ Question 2:‎ Since light travels at the speed of light, and from Relativity, something travelling at ‎the speed of light experiences simultaneously different times (unlike all less-than-‎light-speed particles/waves), does it make any sense to say that light communicates ‎and interferes with itself at what an outside inertial observer would call different ‎times, due to those different times being experienced by the light beam ‎simultaneously (ie can General Relativity's understanding of the light beams ‎experience of simultaneous time explain some of the Quantum results seen in ‎Question 1) ?‎ ‎(and is there a good [very] basic paper which explains the link ?)‎