I’m looking for help on a project connected with Rovelli’s Relational Quantum Mechanics, which has been talked over a few times in this forum (see links below). The original papers on this are – http://arxiv.org/abs/quant-ph/9609002v2" [Broken] (“Relational Quantum Mechanics”) http://arxiv.org/abs/quant-ph/0604064v3" [Broken] (“Relational EPR”) There’s a lot going on in these papers, especially the first, and they open up more issues than they resolve. But they aim at a basic shift in perspective that I want to explore. To summarize – (A) Usually physics operates from the common-sense assumption that things like particles, fields and spacetime structure are just “given” in reality, and have definite properties “in themselves”. Obviously this notion works very well for most practical and theoretical purposes, but not so well when it comes to QM, where we end up with descriptions of reality in terms of superpositions. Because the idea of a given objective reality is so basic to how we think, though, for the most part physicists just learn to accept that reality is weird and paradoxical, at the quantum scale, and move on. (B) Rovelli’s reading of QM, on the other hand, is that we need to give up on “reality” as a basic assumption. Physical entities are not real “in themselves” but only insofar as they affect each other, i.e. exchange information through physical interactions. So basically, physics isn’t modeling the structure of a given reality, but the structure of “how things look to each other”, each from its own point of view in the interaction-web. RQM, p.7 – “A complete description of the world is exhausted by the relevant information that systems have about each other.” In RQM every physical system is an “observer” of the other systems it interacts with, and all types of physical interaction are “measurements” to the extent that they convey information. The question is, does this approach lead to anything new, or is it just another way of trying to get comfortable with the weirdness of QM? The (A) perspective can be thought of as a “hardware” view, where the world consists of things with “built in” properties and intrinsic modes of behavior. We as observers have no direct perception of this underlying hardware, but we can make reasonable inferences about it based on observation, and verify hypotheses by experiment. This is standard physics. The (B) perspective of RQM is more like a “software” view. Here the physical world is made of communicative interaction-events – “observations”. That means ultimately physics is describing the same world that we all actually experience – the “informational environment” from the standpoint of each individual system in communication with others. Yet we’re not talking about something subjective, in the sense of mind-dependent, “in our heads”. We’re talking about the physical world “out there” as the information-defining interactional environment we all live in, moment to moment. Now clearly, to the extent that the (A) hardware description works, we should use it. It’s vastly more efficient to say what a thing really is, than to say how it looks from the changing perspectives of each thing it interacts with. To say “the electron has mass Me” (a hardware description) summarizes in a single datum many different regularities occurring in countless individual interaction-events. So the goal of RQM can not be to do away with (A) descriptions of reality. However, it raises the question of why the (A) description generally works so well. If Rovelli is right, and the software view is ultimately more fundamental, then QM must be showing us how the real-time network of communications-events defines, maintains and constantly updates this consistent, verifiable picture of reality we all share. In other words, it’s possible that without discovering new data or inventing new theories, we could learn to interpret the known physics as describing not only the “content” of this messaging system – the picture of reality it sustains – but also the functionality of the system itself. That could open up a much more powerful way of explaining the complex structure of known physics. So long as we’re just describing reality as a body of given fact, ultimately the best our theories can do is develop a compact, efficient way of summarizing all the facts in a minimal set of equations. On the other hand, if what we’re dealing with is not just given facts but a functional system, this gives us (at the least) an approach to understanding the multi-faceted “fine-tuning” of the universe. We can guess that the universe has to be more or less like this, in order to define itself as a coherent body of communicated information, and see if that leads anywhere. We don’t need to suppose the universe exists so we humans can observe it – in RQM “observing” is how every entity participates in defining a collective reality. Beyond that, there’s the possibility of developing an evolutionary explanation for base-level physics. If we can describe how this self-defining, self-communicating information system works, we might be able to see how something like this could evolve by “natural selection” out of the chaotic background of a quantum vacuum – i.e. out of a random superposition of all possible interaction-webs (most of which wouldn’t succeed in defining any information). So I think what RQM offers us is the possibility that a much more profound understanding of existing theory might be reachable, without introducing any new assumptions. Essentially we know two things about the world. One is that it looks very much like a given, objective (and nearly Euclidean / Newtonian) reality. The other is that it functions as a real-time informational environment that consistently supports that picture of reality. Because regardless of how we choose to interpret QM, it’s clear that the physical world does operate as a communications system. Not only can we humans send messages to each other, but everything anyone can know about the world gets physically defined / communicated through interaction. The question is just whether this is just a trivial fact about the world, to be taken for granted, or something important for physics to analyze and understand. Rovelli’s RQM papers don’t analyze this functionality, but they do certainly open up the question – how does the interaction-web described by the QM formalism coordinate the data exchanged between different observers, to produce a shared picture of reality? And despite their limited focus on interpreting QM, I think there are important indications in these papers about the structure of a quantum communications system. I’ll try to summarize some of those in separate posts. I’m very interested in your thoughts on this, and also in other approaches to informational functionality in physics. What I’m after here is to clarify a certain perspective for thinking about physics, rather than advocate for a particular theory. Just as one other example of work that might point in this direction, I’ll mention a recent paper of Zurek’s on “quantum Darwinism” – an outgrowth of the decoherence approach: http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.2832v1.pdf" [Broken] _________ FYI, here are links to some previous PF threads on RQM. These are mainly about Rovelli’s second paper interpreting the EPR “paradox”, and about the relationship of RQM to the many-worlds interpretation. https://www.physicsforums.com/showthread.php?t=128364" https://www.physicsforums.com/showthread.php?t=117286" https://www.physicsforums.com/showthread.php?t=120485"