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Given some of the discussions, lately, about aspects of my
father's work, I thought it would be both useful and entirely appropriate to
post a few passages of his own thoughts on these same subjects. The first is
from "Life, Itself; A Comprehensive Inquiry Into the Nature, Origin, and
Fabrication of Life", pages 202/203:
Robert Rosen wrote:
... In chapter 7, I introduced the idea of a simulation of
a formalism. Roughly speaking, I showed that a formalism can be simulated if its
inferential structure could be expressed as software to a mathematical machine,
in particular, as program. As I suggested, this places severe restrictions on
that inferential structure; simulability of a formalism is a strong condition to
be mandated of it.
We are now in a position to put these apparently
unrelated ideas together and see what happens.
8B MACHINES AND MECHANISMS
As we have seen, given a natural system N [here, "natural" means actual or real, as opposed to
formalisms], we have formalisms F associated with it as models,
simply by virtue of Natural Law itself [meaning that
appropriate inferential entailment in a model will commute to the
corresponding natural system's causal entailment and the model will then
accurately predict behaviors of/in the natural system]. We now also
have a condition (simulability) that may be mandated of formalisms. Putting the
two together defines for us a class of natural systems, those whose models, as
formalisms, satisfy that condition.
Let us give a name to this class. We shall say that a
natural system N is a mechanism if and only if all of its models are
simulable.
We shall further say that a natural system N is a
machine if and only if it is a mechanism, such that at least one of its
models is already a mathematical machine.
On the face of it, these seem peculiar ways of
characterizing mechanisms and machines from among the class of natural systems.
But this peculiarity stems only from my _expression_ of these concepts in terms of
the models of N, rather than try to talk directly about N itself. This is all
Natural Law entitles us to do. We have so far in this volume nothing that
transcends those entitlements, and I shall do nothing in what follows that
transcends them; on the other hand, it is my aim to utilize precisely these
entitlements to the full extent. It is my main contention, in fact, that
contemporary science, as a whole, does not do this; by the time we are
done, this fact and its consequences will be quite apparent."
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