Physical Something v. Metaphysical Something

There is an interesting discussion on the RDF forum at the moment entitled Physical Nothing v. Metaphysical Nothing. What struck me was imbedded within a link in the OP - http://plato.stanford.edu/entries/nothingness/

The bit that caught my attention; "Van Inwagen's answer is that we are actually interested in concrete things. A concrete entity has a position in space or time. For instance, a grain of sand, a camel, and an oasis are all concrete entities. Since they have locations, they have boundaries with their environment. (The only exception would be an entity that took up all space and time.)
Admittedly, points in space and time have locations. But concrete entities are only accidentally where and when they are. All concrete entities have intrinsic properties. Their natures are not exhausted by their relationships with other things. Consider Max Black's universe containing nothing but twin iron spheres. The spheres are distinct yet have the same relationships and the same intrinsic properties."

My Italics.

Now it seems to me that the hard-materialist position is essentially posited upon this (mis)apprehension - that there are such things as the 'concrete entities' referred to here. The first thing one might note here is that the evidence for the reality of such entities is Max Black's universe. Clearly (at least I think it is clear) Max Black's universe is not a physical universe, it is a metaphysical universe, so it seems odd that one would argue for a physicalist argument based upon a metaphysical space.

Let me be clear here, that such entities simply cannot physically exist, and this becomes clearer when one considers firstly how we know about any physical entity and secondly how we come to describe those entities. It is the second step that leads to the (mis)apprehension of 'concrete entities'.

So, what constitutes something physically real? We would need to be able to measure it, and to measure it it must have a physical effect, or interaction, with a measuring apparatus. That measuring apparatus might be a human eye, or it might be a weighing scale or it could be a photosensitive cell in a scientific experiment. Without a measurement of something, without an interaction, then that thing is not there.

The allegedly concrete things within our universe are known to us not directly, but because they have a physical interaction with us. An iron sphere, for example, will reflect a stream of photons into my eye and a process within my brain transforms that information into a model. What I actually have, then, is not a real, physical iron sphere in my head but rather a metaphysical interpretation. So one might use this metaphysical iron sphere as a fundamental entity within a metaphysical space. How did this iron sphere come to be, and is it really fundamental? What are the forces that hold the iron atoms together in this sphere? How did the iron atoms come to be?

Now, you could argue that all that I have pointed out is that the iron spheres (or any object) can be relational to other entities, but that doesn't rule out that such a description will not exhaust any description of that entity - in other words that the entity could still have properties that are intrinsic and have no relation to anything else. Okay, perhaps, but just stop and think about that. In order for me to say anything meaningful (physical) about that object I must be able to measure it in some way - otherwise I would be describing something immaterial about the object. The only way that a physical property of an object can be described is in terms of its relationship with some other thing.

So, in terms of our physical universe there can be no 'concrete entities'; any description of an object's physical reality must be made via its relationship with the universe. As far as I can see this is the fundamental error of the hard-materialist position; it is a reductionist argument and, as such, mistakes metaphysical models with physical reality.