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Science & Ultimate Reality
Perhaps the most provocative of Wheeler's ideas is that of the "participatory universe" in which "observership" assumes a central place in the nature of physical reality, and presumably at some level must enter into physical theory. But what exactly constitutes a participant/observer? Is a particle detector enough? A living organism? An information gathering and utilizing system (IGUS)? A human being? A community of physicists?
Melding the participatory universe with "it from bit" reveals the key concept of information at the core, and moreover working both ways. On the one hand an observation involves the acquisition and recording of information. On the other hand an observer, at least of the living variety, is an information processing and replicating system. In both cases it is not information per se that is crucial, but semantic information. An interaction in quantum mechanics becomes a true measurement only if it means something to somebody (made explicit in Wheeler's "meaning circuit"). Similarly, the information in a genome is a set of instructions (say, to build a protein) requiring a molecular milieu that can recognize, decode and act upon it. The base-pair sequence on a strand of DNA is just so much goobledygook without customized cellular machinery to read and interpret it.
Where is there room in physics for the notion of information, not merely in the blind thermodynamic sense, but in the active "life/observation/meaning" sense? How does a lofty, abstract notion like meaning or semantic information emerge from the blundering, purposeless antics of stupid atoms?
Part of the answer must involve the subtle concept of "autonomy." Living organisms are recognized because they really do have "a life of their own." A cell is subject to the laws of physics, but it is not a slave to them: cells harness energy and deploy forces to suit their own ends. How does this quality of autonomy arise? Clearly the system must be open to its environment: there must be a throughput of matter, energy and - crucially
information. But more is needed. When my computer plays chess, the shapes move around on the screen in accordance with the rules of chess. But my computer is also subject to the laws of physics. So are the rules of chess contained in the laws of physics? Of course not. The chess-playing regularities are an emergent property in the computer, manifested at the higher level of software, not in the bottom level of hardware (atoms and electrons). Trace back how the rules of chess work in the computer and you will discover that constraints are the answer. The physical circuitry is constrained to embody the higher-level rules.
Stuart Kauffman has coined the term "autonomous agents" to characterize a program of research aimed at explaining how a system can have "a life of its own." He is a biophysicist and complexity theorist with his own theory of the origin of life based on autocatalytic cycles of chemical reactions. For Kauffman, constraints play a key role in the theory of autonomous agents. Another important quality is a type of Godelian incompleteness that permits the system to display freedom or spontaneity in its behavior. Kauffman's ideas provide a new definition of life. They may even help us understand how, with increasing complexity, a physical system can leap from being mere clod-like matter to being an information-rich participator in a meaningful universe.
Title: Investigations: On the Nature of Autonomous Agents
Author: Stuart Kauffman
"Investigations", my third book, is the strangest intellectual adventure of my life. It began as a notebook in December 1994. I sensed that many strands, each too large to yet be visible, were waiting for exploration. After a year, the notebook was long, and eventually became the book.
I begin with a central image. Consider a bacterium swimming up a glucose gradient. We all readily say, without attributing consciousness, that the bacterium is going to get food. That is, the bacterium is acting on its own behalf in an environment. I will call a system that can act on its own behalf in an environment an "autonomous agent". But the bacterium is "just" a physical system. So my question became: What must a physical system be to constitute an autonomous agent?
I had not expected even the outlines of the answer I would be led to, nor to the expanding web of questions I would be led to explore.
In brief summary, I define an autonomous agent as a system that is able to reproduce and also able to carry out at least one thermodynamic work cycle. Importantly, all free- living organisms fulfill this definition. In trying to find a definition for an autonomous agent, I may have stumbled upon an adequate definition of life itself, but I will not insist on it.
It is interesting that Schrodinger, in his famous "What is Life?", misses the work cycle. Indeed, Schrodinger answered a different initial question, namely, what is the source of order in organisms, and achieved his brilliant insight into the genetic material as an aperiodic crystal that would carry a microcode specifying how to build an organism from its genes. Yet Schrodinger did not answer the question "What is Life?" I suspect that autonomous agents may answer that question. It is, after all, an astonishing fact that autonomous agents do persistently act on the universe on their own behalf. Physics and chemistry will have to contend with the truth of this fact, and lift themselves to that level that allows these fields to talk about life.
Investigations is, at least in part, obviously science. In particular, I am led to propose a class of open thermodynamic chemical reaction networks that are both autocatalytic and carry out work cycles. At a minimum this is a new class of reaction networks that are clearly worthy of study, and might form the basis of a new technology: self-reproducing chemical robots able to build things.
But Investigations took me further, to a critique of the concept of work, the use of Atkin's definition of work as the constrained release of energy, coupled with the puzzled realization that it typically takes work to create constraints, and constraints to create work, to an attempt to portray "propagating work", to the almost certainly true realization that we cannot finitely prestate all the possible Darwinian pre-adaptations that can arise, hence that we cannot prestate the, typically collective, variables that constitute such adaptations, to the realization that, at the level of complex molecules and above, the universe is grossly non-ergodic, to a definition of the "adjacent possible", and a candidate law for biospheres anywhere in the universe: such biospheres may, as a secular trend, tend to expand into the adjacent possible such that the diversity of what can happen next increases, on average, as rapidly as it can.
I find Investigations both deeply interesting, yet deeply puzzling. One of the puzzles is how we can find a mathematical foundation for its basic concepts when we apparently cannot say ahead of time what the variables, the Darwinian pre-adaptations, of a biosphere will be.
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[ 22 February 2002: Message edited by: Moderator ]