I have been contemplating this experiment for quite some time now, and I have some questions. http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdf is a preliminary copy of the paper describing the experiment, for reference. The first and most obvious question would be whether it is possible to actually predict the future, by replacing the beam splitters in the idler photon paths with movable (actually, my thought was LCD electrically switchable) mirrors, and making the idler path longer than the signal path; I believe that the answer to this must almost certainly be "no," because the interference shown by the signal photons cannot be separated left from right without the correlation of the idler photon impacts, but there is a vanishingly small chance based on the data in the paper (and I have seen a more complete version of the paper, and the results were the same) that there might be a way to see the difference between the interference and non-interference cases without reference to the idlers. As I say, I don't believe it will pan out, but the data presented in the paper do not exclude the possibility. But the first part that I really wanted some feedback on is: The positions of the mirrors that would replace the beam splitters in the left and right idler paths obviously determine whether the idler photons will go to the which-path detectors, or through the quantum eraser to the eraser detectors. Is the probability distribution of the signal photons that creates the interference interpreted as the effect, and the probability distribution of the idler photons either to the which-path detectors or to the eraser and eraser detectors interpreted as the cause of that effect? I have some reasons for interpreting it that way. First, there is obviously a correlation between the probability distribution of the signal photons and the probability distribution of the idler photons. Second, there is no other variable correlated to the probability distribution of the signal photons. Third, a change in the probability distribution of the idler photons such that they are all sent to the eraser and eraser detectors always results in a probability distribution of the signal photons that shows interference, and a change in the probability distribution of the idlers such that they all go to the which path detectors always results in a probability distribution of the signal photons that does not show interference. While I do know that the correlations between the probability distributions of the signal and idler photons prove a causal link between them, I do not know whether these three facts together constitute proof that the idler distribution is the cause and the signal distribution is the effect, and that is my question. There is more, but this post is long enough for now.