I hope this isn't considered too speculative for your guidelines, but I'm very interested to hear what people think would be the implications for QM if Cramer's FTL experiment actually worked. Would it prove or disprove any of the current interrpetations (transactional, Bohmian, MWI)? My thoughts were that it would tend to support MWI and refute any realistic interpretations of QM. If you can send a signal backwards in time, there are only two ways to avoid a paradox: 1) the only signals that can be sent successfully are ones that will not be affected by anything in the past; or 2) the sending of the signal causes a "retroactive" split in the multiverse, where the split occurs at the moment the signal is received. Can any single-universe / realistic interpretation of QM survive if Cramer's "retrocausality" machine worked?