quantum mechanics: answers? (Introduction)

by dhw, Thursday, September 12, 2013, 14:59 (4091 days ago) @ David Turell

DAVID: Searching for answers. A new approach to old equations.-"Pawłowski and his colleagues have found that this postulate is respected by classical physics and by standard quantum mechanics, but not by alternative theories that allow for stronger forms of entanglement-like correlations between information-carrying particles. 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." (my bold)-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."-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. If the authors are saying that Bob will not gain more information from what Alice has sent him than the information she has sent him, it's like saying that if I give you a dollar, I'm not giving you more than a dollar. Not exactly startling. On the other hand, if Bob is given additional information by one of Alice's colleagues, might he not "gain" more than she has sent him? The authors give no further explanation of "information causality", so I hope you can sympathize with my confusion and can tell us what you understand by the term.-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"."-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?