User:Wwheaton/test5

From (ca Sept 2007) version of Thermoeconomics

See Living systems, and Living systems theory, and James Grier Miller

From User:TimVickers, 1/19/2009 on Talk:Life.

A physical definition of life based on information ratios
Knowing little of the literature, yet I have the effrontery to propose that life is fundamentally a phenomenon by which information expands and propagates itself.

An information structure, or organism, exists in an environment which is favorable (mild?) enough that the organism is able to maintain its own organization and preserve its core information kernel. The organism furthermore copies its information kernel, not necessarily with perfect accuracy, into the environment, producing new organisms. The complexity of the organism is measured partly by the information content of the kernel, but also by the information content of the environment in which it is able to survive and propagate, both being quantified in accordance with statistical mechanics and information theory.

The ratio, of the information content in the kernel to the information content in the necessary surrounding environment, gives a measure of the complexity of the organism, and its status in the Tree of life.

Some examples:


 * A prion may have an information content of about 1 bit (protein folded in one of two alternate configurations), and requires a complex organism (say a 1 GB cow) to inhabit, so its information ratio might be as little as 10-10.


 * A virus can survive and replicate in the environment of a living cell. The kernel/environment ratio might be tentatively said to be on the order of 1 MByte/1 GByte, or 0.001. (It might be better to express these ratios in logarithmic form; -10 in base 2).


 * A computer virus, with a length of 1 MB, living in a (machine/operating system) environment of 1 GB, might come in at 0.001, like a natural virus.


 * An environment lately discovered at a depth of ≥2 km in a gold mine in South Africa seems to contain only a single species of sulfate-reducing bacteria, living in a purely mineral environment.  Here the determination of the information ratio appears particularly simple and feasible to evaluate.


 * A human can survive in a very wide range of environments, much less restrictive than a virus requires. The genetic information content in the (individual) human kernel may be on the order of 1 GB.  The environmental information is more difficult to quantify (though it should be possible in principle) but it is clearly much less restrictive than for a virus, so the information content should be correspondingly less.  Since humans can inhabit a wider range of environments than any other form of life we know, it appears that the environmental information for homo sapiens is actually likely to be less than for any other life form yet observed.

The above schema has the consequence that organisms must have an energy source in order to copy their information kernel, by the Second Law of Thermodynamics, from the viewpoint of statistical mechanics and information theory. For classical biology, this means organisms must metabolize. It also requires that the environment be not in thermal equilibrium, but must present sources of free energy that can be used to support this organizational necessity. Absent perfect accuracy of kernel copying and preservation, it also brings the evolution of organisms and species diversification along as a natural consequence. This idea in principle appears to allow a natural path to the classification of life forms, natural and artificial, terrestrial and alien, into a physically-based hierarchy of complexity.

The chief difficulty I see lies in the accurate quantification of the information contents required. This in turn inevitably involves the boundaries one draws in specifying the environment and the organism, introducing an element of ambiguity. What is the organism? What is the environment? Should we include one organism, or the entire species? A single organism often cannot survive, and, if sexual, cannot reproduce. A hive of bees is a superorganism, and as such fits naturally into this system. But its environment must include flowers and all that is needed to support them. A modern malware computer virus may require the entire World Wide Web to thrive. A human floating in a spacesuit has a particularly simple environment, but perhaps we ought to consider the industrial infrastructure that is required to support him before being too quick. The Gaia Hypothesis proposes that the entire planetary system of Earth is a single living organism. Obviously its information content is huge, and its environmental specification is uniquely simple. Fundamentally it appears to me that the organism should be defined broadly enough so that it is able to reproduce and grow independently, and the environment should include every external thing necessary to support the survival of the life-form, but nothing beyond that minimal requirement. But, considering the environment and organism together as a physical system, the boundary one chooses to draw between the environment and the organism seems unclear, possibly essentially so.

I apologize for what probably appears to be flagrant original research, but I actually expect there must be much in the literature (with which I am only slightly familiar) that is relevant to the above arguments. If it can be sourced, then so much as may be would be allowable for this article. Thus I appeal to other more expert editors for comments and suggestions along these lines. Thanks, Wwheaton (talk) 22:49, 7 December 2008 (UTC)

Discussion w/ Mitra
Re your question on cave paintings of 19 Jan on Talk:Life, in my suggested definition, one must distinguish between the organism, and the surrounding environment it which it lives. Admittedly this can be difficult to do without some arbitrariness or ambiguity (which is a problem, needing work). But having made that division and drawn that boundary, one must estimate the information content (in bits, say) in the organism necessary to sustain its necessary functions of protecting and reproducing its core information. Similarly, one must estimate the information necessary to define the minimal environment necessary for the organism to function successfully in it. Then the dimensionless ratio of those two is the interesting number. If it is small, the proposed bioform is not very lifelike; conversely, if the ratio is large, the proposed object has a strong case to be called "life". I think the cave painting hardly qualifies at all, because it cannot actively protect its core information or reproduce it, unless you include the artist as part of the organism (it which case it obviously becomes pretty lively, but not just "a painting"). If you say just the painting is the organism, and the artist is part of the environment, then the ratio is very small, because the information in the artist is huge, and in the painting much much smaller. Wwheaton (talk) 19:52, 22 January 2009 (UTC)