Brent: I'm suspicious of these fantasy thought experiments. But however detailed it may be doesn't answer my question as to what it would mean to erase the welcher weg but not the memory that the weg was detected. I noted that this is not like a classical erasure of a memory because in this case the coherence is maintained, sowhen the welcher weg is erased there is no long any fact-of-the-matter as to which way it went. There is no fact-of-the-matter that it was detected to go left or right. So the "memory" if it exists, is a false memory.
----- https://www.nature.com/news/how-quantum-trickery-can-scramble-cause-and-effect-1.22208 <<Last year, Walther and his colleagues devised a way to measure the photon as it passes through the two gates without immediately changing what they know about it. They encode the result of the measurement in the photon itself, but do not read it out at the time. Because the photon goes through the whole circuit before it is detected and the measurement is revealed, that information can't be used to reconstruct the gate order. It's as if you asked someone to keep a record of how they feel during a trip and then relay the information to you later — so that you can't deduce exactly when and where they were when they wrote it down. As the Vienna researchers showed, this ignorance preserves the causal superposition. “We don't extract any information about the measurement result until the very end of the entire process, when the final readout takes place,” says Walther. “So the outcome of the measurement process, and the time when it was made, are hidden but still affect the final result.”>> The specific experiment is here https://arxiv.org/abs/1608.01683. Not an easy read ... SWITCH, "causal witness", and so on -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
