At Antonio’s suggestion in his comments on the last post, I reviewed more of Ulrich Mohrhoff’s work on interpreting quantum physics contained in this paper and on his website, thisquantumworld. I also plowed through some of the debate between Mohrhoff (posting as koantum) and Patrick Van Esch (vanesch) on this thread at physicsforums. This was extremely fascinating although often over my head.
From my reading so far, Mohrhoff is saying two things which I think have some merit:
1. He rejects the assumption that the wave function represents something real. Many physicists extrapolate from the elegance of the idea of the deterministically evolving wave function to an ontological interpretation of QM (many-worlds or many minds) which tries to elevate this side of the story and minimize the measurement process. There is no quantum theory without measurements!
I’m sympathetic here, since while I believe the both of the quantum processes are fundamental, I think the measurement events are the “more real”: they constitute our concrete world while wave functions are the abstract possibility space available to be actualized by measurements (they are “real”, too, but not in a concrete sense).
2. While rejecting the naïve assumption that the wave function represents something real, Mohrhoff does want to find an objective description of reality which doesn’t appeal to consciousness. QM gives the probability distribution for unperformed measurements. It is a mistake to see these as subjective probabilities. They are objective probabilities.
I agree with this to an extent: I don’t see full-blown human consciousness as the sole avenue to measurement, and think natural systems implement measurements ubiquitously. However, in my view, the phenomenon of first-person consciousness is rooted in an experiential quality which is part of all measurement events (in the spirit of panexperientialist proposals such as Whitehead's or Gregg Rosenberg's).
But what is Mohrhoff’s positive proposal? What is “this quantum world”?
Here are some notes I took from his writing with my editorial comments in italics.
1. The world is intrinsically non-local. (Don’t be confused by thinking about the existence of a space-time background of points and instants – we contribute that to the theory, its not intrinsic).
2. Identical particles cannot be distinguished from each other independent of their possession of properties which can be distinguished.
So, these two statements imply that the quantum world cannot be built from the bottom up.
So how is it built? From the top-down.
“What ultimately exists is one. Call it whatever you like. Matter and space both come into being when this enters into (more or less fuzzy) spatial relations with itself…””…the relations are self-relations,”
This sounds like the world possesses a power of self-measurement. This is certainly an interesting rearrangement of the mystery, but I don’t see how it increases our understanding of reality.
Nothing has a property until it is measured (including the property of existing in a space-time continuum). Measurements create their outcomes (it isn’t that these properties are ontologically carried by the wave function between measurements). No measurements/no world.
OK (although I would say the wave function carries properties in their form as possibilities, and they are not created but made concrete when measured).
The macroscopic world is real in a way the microscopic world is not, since the probability of finding macro-objects where classically they should not be is very low. “… we must be allowed to look upon the positions of macroscopic objects – macroscopic positions, for short—as instrinsic, as self-indicating, or as real per se.” “The ‘foundation’ is the macroworld… not the micro-world.” “As philosophers would say, the properties of the quantum domain supervene on the goings-on in the classical domain.”
But the existence of macroscopic objects is just a primitive in this interpretation. This top-down view is equivalent to saying we just can't explain macroscopic events or objects. I find this unsatisfactory. I want to see us build an improved bottom-up explanation of the world, where the raw material is a property dualism matching the properties embedded in the quantum probability space with an “ability to measure” property possessed by natural systems.