Does the anthropic principle explain away fine-tuning?

  • Clarifying the question

    Question: An observer selection effect is a kind of selection bias. It occurs when evaluating data in a way that fails to take into account that the very existence of observers is correlated with said data.

    The [Weak] Anthropic Principle is the observer selection effect as applied to the cosmic “fine-tuning problem.” It is often phrased as:

    We shouldn't be surprised to find that the Universe is compatible with our existence. Otherwise, we wouldn't be here to observe it!1

    Should this consideration rationally prompt someone to be unsurprised at the existence of life, given knowledge of fine-tuning?

    1. As classically put:

      John Barrow & Frank Tipler: “The observed values of all physical and cosmological 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,” [The Anthropic Cosmological Principle (Oxford, 1986), 16.]

  • What experts say

    Philosophers seem to widely agree that the anthropic principle, as an explanion for why the Universe permits life (or conscious observers), is tautologous and only relevant given a suitably varied multiverse or cyclic universe hypothesis (i.e., whereby it is not surprising that some universe/cycle won the life-permitting lottery).

“No, after all…
  • Selection biases are not explanations

    Selection biases as such do not explain anything here, and so cannot function as explanations.1

    Luke Barnes: “A selection bias alone cannot explain anything.… [For example] how are quasars so luminous? The (best) answer is: because quasars are powered by gravitational energy released by matter falling into a super-massive black hole… The answer is not: because otherwise we wouldn’t see them.” [“The Fine-Tuning of the Universe for Intelligent Life”, Online]

    There are clearly many situations where we ought to be surprised to find that we are alive, and this is not challenged by the trivial fact that we should not be surprised that we are not observing our death.

    1. Here is one way a philosopher has argued that it is not an explanation:

      Alvin Plantinga: “It’s no explanation to point out that these constants have to be fine-tuned for us to observe that they are fine-tuned—any more than I can ‘explain’ the fact that God decided to create me… by pointing out that if God had not thus decided, I wouldn’t be here to raise the question.” [“Methodological Naturalism?” Origins & Design 18:1 (1997).] The quote from Luke Barnes above, however, seems to better capture what is going on.

    2. Consider a famous illustration:

      Richard Swinburne (Philosophy professor at Oxford): “On a certain occasion the firing squad aim their rifles at the prisoner to be executed. There are twelve expert marksmen in the firing squad, and they fire twelve rounds each. However, on this occasion all 144 shots miss. The prisoner laughs and comments that the event is not something requiring any explanation because if the marksmen had not missed, he would not be here to observe them having done so. But of course, the prisoner’s comment is absurd;” [“Argument from the Fine-tuning of the Universe,” in Physical Cosmology and Philosophy, e.d. Leslie (Macmillan, 1990), 165]1

      This is a spin-off of the sharpshooter analogy originally proposed by John Leslie, “Anthropic Principle, World Ensemble, Design,” American Philosophical Quarterly 19 (1982): 150.

  • It's not about “observers”

    The most sophisticated version of the fine-tuning argument is less interested in mere observers simpliciter and more interested in the possibility of societies of interacting moral agents.1

    1. See Robin Collins's “Modern Cosmology in Philosophical and Theological Perspective: Three Methodological Approaches”; Alternative Title: “The Fine-tuning of the Cosmos: A Fresh Look at its Implications” online.
  • [Boltzmann brains are observers]

    [Brackets] mean “forthcoming.”