quantum mechanics: answers? (Introduction)

by dhw, Friday, September 13, 2013, 19:53 (3880 days ago) @ David Turell

DAVID: (quote): " For that reason, the group writes in their paper, "information causality might be one of the foundational properties of nature" — in other words, an axiom of some future, reconstructed quantum theory." (David's bold)-dhw: Apparently information causality says "that if one experimenter (call her Alice) sends m bits of information about her data to another observer (Bob), then Bob can gain no more than m classical bits of information about that data — no matter how much he may know about Alice's experiment."-dhw: As you have put the sentence in bold, it's clearly important to you, but I'm totally flummoxed. I'd be grateful if first you would explain what is meant by "classical" information.-DAVID: Classical information is the information at the non-quantum level. It is Newton's classical science.-Thank you. Sadly I remain just as confused. Now the authors seem to be saying that if Alice sends Bob m bits of information about her quantum experiment, Bob can't gain more than m bits of information about the non-quantum world. Is it not possible for Bob to see connections that Alice doesn't see? After all, the authors think that every construct is subjective (see below). And I still don't know what is meant by "information causality". Perhaps you can define it and explain why it is so important.-http://www.nature.com/news/physics-quantum-quest-1.13711?WT.ec_id=NATURE-20130912-QUOTE: "Still, this does seem an odd way for the Universe to behave. And this is what prompted Fuchs to call for a fresh approach to quantum foundations. He rejected the idea, held by many in the field, that wave functions, entanglement and all the rest represent something real out in the world (see Nature 485, 157...158; 2012). Instead, extending a line of argument that dates back to the Copenhagen interpretation, he insisted that these mathematical constructs are just a way to quantify "observers' personal information, expectations, degrees of belief"."-dhw: In other words, as we discussed on our epistemological thread, whatever conclusions are drawn will be subjective. I had great difficulty following Ruth's arguments against subjectivism in her Chapter 7, and if experts in the field can't agree, how can a layman possibly know what is true and what is not?-DAVID: Your confusion is because these folks are ignoring Ruth. She recognizes more than they do Heisenberg's wall of uncertainty and the confusion it brings. These folks keep trying to interpret quantum phenomena as if they are fully within our reality and they are not. They are probabilities and one can only average what to expect. Copenhagen was just a way to go forward and not worry about the confusion.-On the contrary, these folks REJECT the idea that all of this represents "something real out in the world", and insist that the constructs are subjective! Ruth regards quantum states as "ontologically real possibilities existing in a pre-spacetime realm [...] These possibilities are taken as real because they are physically efficacious, leading indeterministically to transactions which give rise to the empirical events of the spacetime theatre." And the problem of subjectivism "evaporates" because the transaction "is simply observed differently by the different observers" (which in my book = subjectivism). Yes, I am mightily confused.