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The Cosmic Anthropic Principle

The Anthropic Cosmological Principle", by John D. Barrow and Frank J. Tipler, Oxford University Press, 1986


If you want to learn about the Anthropic Principle, this is the book to read. However I must warn you that the style is turgid, that a substantial degree of scientific literacy is required, and that the conclusions and arguments are often dubious. It is not an easy read for the informed layman. The anthropic principle comes in two flavors, the weak anthropic principle, and the strong anthropic principle. The following definitions are from TACP:

Weak Anthropic Principle: The observed values of all physical and comso- logical quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirement that the Universe be old enough for it to have already done so.

Strong Anthropic Principle: The Universe must have those properties which allow life to develop within it at some stage in its history. (Carter)

Participatory Anthropic Principle: Observors are necessary to bring the Universe into being. (Wheeler)

Final Anthropic Principle: Intelligent information-processing must come into existence in the Universe, and, once it comes into existence, it will never die out.

The WAP is not, as it might seem, simply a tautology. It does allow us to account for some the observed properties of the universe. For example, the observed age of the universe can be predicted from the fact that we exist. This is turn accounts for many of the "large number" coincidences. There is an extensive analysis which indicates that the various physical constants must be fairly close to their observed values. The WAP can be taken as a useful heuristic for those concerned with speculative cosmology.

The various forms of SAP are more speculative, to put it politely. Wheeler's arguments are based on QM considerations that I do not feel competent to evaluate. In the book the FAP is combined with a lot of heavy duty cosmology to build some of the most grandiose castles in the air since Olaf Stapledon.

Tipler is noted for arguing that We Are Alone; that we are the only intelligent species in this Galaxy, and probably in the entire universe. A notable fraction of the book is spent on this theme. I suspect that this is simply a matter of Tipler working his favorite hobby horse, since I did not see where any essential connection was made between We Are Alone and the Anthropic Principle.

TACP cites a number of evolutionary theorists to claim that the develop of intelligence is inordinately improbable. The arguments given are mostly a misuse of quotation. There is an extended discussion of Tipler's "Von Neumann Machine Dispersion" argument. (Tippler assumes the possiblity of AI type Von Newmann machines -- he does not seem to recognize that this is not essential to his argument; an intelligent species constitutes a collection of Von Neumann machines in their own right.) Tippler's general argument is important in analyzing the Fermi Silence question; however it is much less conclusive than he believes.

An interesting argument by Carter is presented. Briefly, if the development of intelligent life depends on several very improbable steps, then it will, with high probability, appear shortly before the end of the window of opportunity. This provides the prediction that, if we don't do something about it, that Earth will cease to be a hospitable environment for land based life in a few hundred million years (or less). One of the possibilities suggested is that the atmospheric Oxygen level will rise to too high a level. Carter's arguments have some major holes; however they do provide a falsifiable prediction.

There is an extensive discussion of various teleological principles that have appeared in different theologies and cultures. It should be noted that these are not the same animal as the SAP.

In summary, the WAP is a useful heuristic whose value is overstated in the book. The SAP is interesting, but it and the speculations derived from it are decidedly premature in view of our present stage of knowledge about the universe.


This page was last updated July 1, 2002.

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