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I take the case of Alice and Bob in the EPR experiment. Here Bob does not measure spin projections but make a Young's double slit experiment. What Alice does on her side will not be known by Bob. She can decide to let her particles go freely to the left (in the environment of Bob).

Bob will see no interference. he cans suppose two things:

1) the which path information is known by Alice but he ignores the result so he is in a classical case of a probability problem , no more in quantum problem with ampkllitudes.

2) Bob knows what is decoherence , and how to use a reduced diagonal density matrix after decoherence.

in the two cases nothing can explain why the particle follow one path or the other. But is it still a collapse problem? we are now in the case where there is a lottery in Tokyo and that you read the results later in London. Would you talk about collapse problem.