Re: modern physics

[Tim Gwinn <***>]

> -----Original Message-----
> From: ROSEN Forum []On Behalf Of Howard
> Pattee
> Sent: Thursday, May 27, 2004 10:32 PM
> Subject: Re: modern physics
>
>
> Tim,
> To keep the postings shorter and to the main points, I will not
> repeat everything.
>
> I said in effect that measurement is an act of the observer who
> chooses what aspect of world he is interested in. That is the
> basic reason why laws cannot usefully describe the process of
> measurement (and why we must make an epistemic cut). In Rosen?s
> terms, coding (measurement) is unentailed by either causal
> natural laws or the inferential models.
>
> Tim replies: First, I would argue, that in Rosen's view, the last
> sentence is incorrect.
>
> HP: I would need some evidence of this. Rosen says (LI p. 61):
> "We can already see some peculiar epistemological issues inherent
> in the diagram of figure 3H.2 that did not arise earlier.
> Specifically: what is the status of the encoding and decoding
> arrows in that diagram? We already saw in the exactly similar
> diagram of figure 3F.2 that the encoding and decoding arrows were
> themselves unentailed. But at least they could themselves be
> considered as formal objects, since at that point we were
> comparing syntactric entailments of two formalisms. But now, we
> are comparing syntactic entailment in a formalism with causal
> entailment in a natural system. The encoding and decoding arrows
> in this case are still unentailed, but it is no longer clear how
> they could be entailed, or from what."
>
> I have stated Rosen's view much more briefly, but I do not see
> how you can reasonably call my statement incorrect.


What I saw as incorrect was spelled out in my subsequent sentence (below),
which Judith affirms in her post today, and which you agree with (below).


> Tim: In the Modeling Relation, encoding and decoding are
> unentailed *within the MR itself*. However, they are not
> therefore unentailed entirely. Modeling Relations do occur within
> the world in which we believe physical laws operate.
>
> HP: This is your statement, not Rosen's. Of course you are
> correct, but the physical entailments on the observer's choice of
> what to measure is very weak and exceptionally difficult to pin
> down. Rosen agrees that in practice the laws we discover are
> largely the result of what we choose to observe. One ultimately
> then has to face the issue of free will in making such a choice.
>
> Tim: It is therefore incumbent upon physics to determine the laws
> appropriate to describe that physical situation and those
> entailments, not to except them from such laws.
>
> HP: Measurement processes are certainly not exempt from laws. In
> principle, there is a lawful description (model) of any
> measurement. What von Neumann and others have shown is that such
> a description of a [system-plus-its-measurement-device] would
> require additional measurements leading to a vacuous regress.
> This can be explained in many ways. Measurement is inherently a
> complex process by Rosen's definition because it has a function
> (creating a record) that cannot be described by state-determined
> dynamics. A complex system, again by Rosen's definition, requires
> more than one inequivalent models. Inequivalent here means that
> neither model is reducible to, or derivable from, the other. In
> physics jargon this is what complementarity means. Consequently,
> laws and measurement require complemtary models.


I am not certain what you mean by "laws" or "description" here. It seems to
me you are equating "laws" with something like "dynamical laws" and
"description" with something like "state description" (particularly in
reference to the infinite regress). In the Rosennean paradigm, I would say
that the neither laws nor descriptions are limited to this state-based view,
so that laws and measurement are not "complementary" in that paradigm.
I am familiar with the term "complementarity", and I personally do not find
it an acceptable substitute for "inequivalent". "Complementarity" seems to
me to have a very specific meaning in physics that "inequivalent" would not
capture.


>
> I agree with everything Rosen says about the necessity of
> relational models. These are timeless, or synchronic models like
> symmetry. We also need dynamical diachronic models. These are
> complementary models. You cannot reduce one to the other or
> derive one from the other. Diachronic models bifurcate into
> time-symmetric (reversible microscopic laws) and the
> complementary time-antisymmetric models (irreversible
> thermodynamics). And so on. There are many cases.


Certainly. I would only add that the scope of Rosen's modeling includes
other kinds of models beyond relational models. If he had restricted himself
by saying that only relational models needed to be added to dynamical
descriptions to provide a complete description, then he would have been
guilty himself of imposing artefactual limits on modeling.


> What Rosen says about the limits of state-determined dynamics is
> certainly true. My only disagreement with Rosen is his view that
> physics limits itself to state-determined dynamics. That is just
> not the case.
>
> Howard


If modern physics is a program, as you stated in your previous post, that
begins with "epistemic principles" that "support the ideal of objectivity
which simply means that these aspects or laws do not change when the
observers change, nor can they be changed by the observer", then physics is
tacitly asserting a world-as-mechanism view, whether it acknowledges it or
not. And such a world is coincident with one described in state-based terms.

Tim