An impertinent resumé of
the Anthropic Cosmological Principle

by Daniel Berger

While the so-called anthropic coincidences are at least arguably important, the Anthropic Cosmological Principle -- which attempts to answer the anthropic coincidences -- seems a failed enterprise. I will consider four statements of the Anthropic Principle, and reject all of them.
A technical note: I use "universe" to mean the volume of space that is observationally accessible to us. I use "super-universe" to mean a hypothetical infinite spacetime continuum, which obeys laws sufficiently similar to those in our universe that we can make meaningful statements about it.

Weak but defensible

Totally bogus

"If we weren't here, we wouldn't be here."
The Weak Anthropic Principle (WAP) states simply, "If conditions weren't right for us to be here, we wouldn't very well be here to remark on the fact." Of course this is no answer to the presumed improbability of a universe which happens to contain us, or even intelligence at all (much less life!). (1)

WAP advocates may point out that we can't say anything, scientifically, about the likelihood of our particular universe from a single example. This at least puts a respectable face on treating our own existence as a brute fact. However, the underlying premise is that science is the only, or at least the most reliable, way of knowing.

Because this premise is less than certain, many of those who espouse the WAP advocate many universes, so that we just happen to be in the one that contains us. Nick Bostrom (2) points out that the Anthropic Principle may be considered presumptive evidence for many universes "in the absence of any plausible alternative." Unfortunately, there is no observational or experimental ("scientific") evidence whatsoever for any universe besides the one we inhabit. And even the idea has serious problems, both physical and philosophical (I would like to say metaphysical, but that's not always a respectable term, even to philosophers).

Hawking's work on black hole thermodynamics has closed off the possibility of infinite -- or even more than two or three -- serial universes via cycles of alternating Big Bangs and Big Crunches. (3) So advocates of multiple universes usually claim that very many (or infinite) parallel universes are generated as vacuum fluctuations within a super-universe at heat death. This is a respectable hypothesis, since the Universe appears to have zero overall energy within very large observational error bars. (4)

But this just pushes the question back a step: whence came the vacuum? A vacuum is not "nothing," seething as it is with fields and virtual particles governed by definite laws. And whence came those laws? It can be argued that any universe generator which is able to produce occasional fruitful, "fine-tuned" universes must itself be fine-tuned. (5)

"Only a universe with us is possible."
The Strong Anthropic Principle (SAP) attempts to argue, without a shred of evidence, that for some reason fruitfulness is a necessary property of universes. While we can easily conceive of universes that could never develop life or intelligence, the SAP maintains that no such universes are actually possible.

The SAP rests on the so-called Copernican Principle (6), which says that we must not presume to inhabit aught but the most unexceptional of places. Therefore, if we're here, in this particular universe, this universe must be the most probable of all possible universes. Shades of Dr. Pangloss! (7)

Unfortunately, no evidence whatsoever exists for this contention, or for the Copernican Principle, for that matter. Like Occam's Razor (8), it's a presumptive preference which has been known to be fruitful, nothing more.

The SAP should not be confused with the assertion that, if God created the Universe, of course it'll be fruitful, otherwise what'd be the point?

"If we weren't here, the universe couldn't exist."
The Participatory Anthropic Principle (PAP) takes a page from the Copenhagen Interpretation of Quantum Mechanics as well as from the Bell-Bohm idea of deep connectedness between events and objects once in contact. (Of course the Big Bang requires that everything in the universe was once in contact with everything else.)

The Copenhagen Interpretation argues that the quantum world is not actualized until and unless a measurement is made; thus an observer is required to actualize each quantum event as one thing or another (the "collapse of the wave function"). The PAP extends this to the universe as a whole, saying that only universes with observers at some point in their history can become real. The PAP tries to provide a basis for the bald assertion of the SAP.

Apart from some reputedly rather serious philosophical problems with the whole idea, totally unpublicized Nobel-prize-winning experimental work has shown that

  1. The wave function "collapses" very well on its own, thank you very much. No observer appears to be required. (9) This has been given a name: "quantum decoherence."

  2. Particular quantum states can in fact be observed and measured, more than once and reproducibly, without destroying them (or tipping them into one or another alternative). Quantum states therefore have real existence; they're just delicate, like a pencil balanced on its point. Like the pencil, they can decay in any direction; like the pencil, there's nothing mysterious about them. (10)

This is not my own interpretation. The observer-independent reproducibility and collapse of quantum states are central to the field of quantum computing.

"The Universe R Us."
The Final Anthropic Principle pontificates, "Intelligence is a necessary property of Universes, and once Intelligence comes into existence, It can never be destroyed." The first half is simply the SAP; the rest flies off into rather interesting territory.

Frank Tipler and others assert that Intelligence, as dubiously distinct from individual intelligent beings, is self-perpetuating and, at least subjectively, eternal. Furthermore, it will grow more and more powerful until it becomes "God" or something very similar. (11)

Tipler is actually taking a page from Fr. Pierre Teilhard de Chardin, the French Jesuit mystic paleontologist, who decided that God is the culmination of universal evolution (the "Omega Point"). And all the time you thought God created the Universe, not the other way 'round! But then, God (as realized by the Universe) also creates the Universe that brings Him into being... This is the PAP with a vengeance! (12)

Interested readers are referred, not to Teilhard's writings which are impenetrably confusing, but to Robert Heinlein's classic short story, "All You Zombies."

While I have merely cast ridicule on the Final Anthropic Principle, it is possible to do more by way of refuting it. See Milan M. Cirkovic and Nick Bostrom, "The Cosmological Constant and the Final Anthropic Hypothesis," Astrophysics and Space Science, 274, 675-687 (2000). An early draft may be found on the LANL preprint server. Thanks to Professor Cirkovic for calling this article to my attention.


Further reading:

Dan Berger's Anthropic Principle links

John D. Barrow and Frank Tipler, The Anthropic Cosmological Principle, Oxford University Press, 1988.

Excellent discussions of quantum mechanics and its implications are provided by John Polkinghorne, The Quantum World, Princeton University Press, 1984; by Jim Baggott, The Meaning of Quantum Theory, Oxford University Press, 1992; and by Werner Heisenberg, Physics and Philosophy, Harper & Row, 1958.

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References:

  1. Nick Bostrom, a professional philosopher, contends that Baysian probability analysis allows one to take the WAP more seriously; see his site, anthropic-principle.com.

  2. Private correspondence; see Note 1.

  3. I am ashamed to say that I cannot remember my source for this, but the work was published, I think, after A Brief History of Time.

    P.J. Steinhardt and N. Turok (Science, 296, 1436-1439, 2002) offer a theory that gets around the entropic embargo on serial multiple universes by using universe-universe collisions to generate new Big Bangs. No experimental evidence, of course; Alan Guth, originator of the theory of cosmic inflation, says that whether this is plausible depends on how the physics of the hypothetical collisions works out. See the news item in Science, 296, 639 (2002).

  4. See, for example, Martin A. Bucher and David N. Spergel, "Inflation in a Low-Density Universe," Scientific American, January 1999.

  5. The Many Universes Interpretation of quantum mechanics (see the sources listed above) says that every possible quantum event occurs, but when more than one is possible, the different possible events result in the generation of one universe for each possibility. This is sometimes used as a convenient way of generating an infinite number of possible universes. But again, the source of the physical laws which define the ensemble of universes is not addressed.

  6. The Copernican Principle is used to predict the impending extinction of the human race by J.R. Gott, "Implications of the Copernican principle for our future prospects," Nature 363, 315-319 (1993). Gott's argument (based on one by Brandon Carter) is called the Doomsday Argument and is fully discussed here by Nick Bostrom.

  7. Of course, Dr. Pangloss is the Liebnitzean optimist in Voltaire's immortal yet impertinent novel, Candide.

  8. For an analysis of the limitations of Occam's Razor--which says that, of two explanations, the simpler is to be preferred if it explains all the facts -- see Hoffmann, Minkin and Carpenter, "Ockham's Razor and Chemistry," HYLE 3, 3-28 (1997). It seems straightforward to apply this analysis to the Copernican Principle.

  9. See the report in Science 274, 1615 (1996). The original article was published by S. Haroche, J.-M. Raimond, M. Brune et al in Physical Review Letters (9 Dec 1996).

  10. See the report in Science 285, 307 (1999). Original article G. Nogues, A. Rauschenbeutel, S. Osnaghi, M. Brune, J.-M. Raimond and S. Haroche, Nature 400, 239 (1999). Or read about it in Scientific American, October 1999 issue.

  11. I'm strongly reminded of Isaac Asimov's short story, "The Last Question." Perhaps Tipler should pay at least token royalties to the Good Doctor's estate. But I forgot -- Tipler doesn't consider his story to be fiction.

  12. According to John Haught's book, God After Darwin: A Theology of Evolution, the previous paragraph is a caricature of Teilhard -- and indeed, as I note in the next paragraph, I was unable to make head or tail of Teilhard's writings. Haught says that Teilhard merely took the Eternal nature of God seriously: God is as much in the future as in the past.

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Copyright © 1999, 2000, 2001, 2002 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.

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