Saturday, January 29, 2011

not Evidence against fine-tuning for life

After much interesting e-correspondence Don Page has sent a revised version of his paper, which he has posted on arXiv. It is now called, quite rightly, "Preliminary Inconclusive Hint of Evidence Against Optimal Fine Tuning of the Cosmological Constant for Maximizing the Fraction of Baryons Becoming Life" and not "Evidence Against Fine-Tuning for Life". This will of course disappoint the over-excitable atheists, who have been exulting in the blogosphere that "Evidence Emerges That Laws of Physics Are Not Fine-Tuned For Life: The value of the cosmological constant suggests that the laws of nature could not have been fine-tuned for life by an omnipotent being, says a cosmologist" Ah well.

I do entirely agree that "Maximum likelihood" hypotheses of the type we have been discussing are highly interesting (especially if we can start to explore ones which involve the interaction of multiple levels) and in principle testable, and if thereby we have introduced an interesting new idea into cosmology that will be great.

  1. These are not the same as "fine tuning" in the classic theological/apologetics sense. The point about fine tuning is "it is very unlikely that these constants would have these values by chance, and if the constants had been even slightly different intelligent life would not exist". To simplify, if L is the probability of intelligent life existing and y is the fundamental constant, which has the value 0.5 but which could in principle be uniformly distributed over the range [0,1], then L=A (y-0.5)^2 has y at MaxL, but is not fine tuned, and L= A exp(-100(y-0.501)^2) has y away from MaxL, but is fine-tuned.
  2. Nothing much hangs on them theologically. The idea that we would know the objective function that God is trying to maximise is absurd. And as Don has rightly pointed out, God could well have chosen to so love the multiverse.
  3. I'm not sure they tell us anything much about the universe vs multiverse debate. Any combination of fundamental constants by definition maximises some objective function. And unless there is some credible evidence of interaction between "pocket universes" in the multiverse, any story about an actually existing multiverse M can be re-written as one in which M is simply a set of possible universes.

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