Monday, June 17, 2013

An Answer to the Anthropic Principle?

The anthropic principle is based upon the fact that the parameters of the universe (such things as the gravitational constant, the charge of the electron, etc.) are just right. If they were even slightly different, atoms could not exist. How likely is it that our one and only universe just happens to have parameters within these limits? You can see why intelligent-design proponents love the anthropic principle. I’m surprised they don’t spend more time on this rather than on bacterial flagella.

One explanation that astronomers offer is the multiverse model: all possible universes exist somewhere, somehow, and somewhen, and of course if a universe has no atoms it has no brains to think about such questions. However unlikely our universe is, if there is an infinite number of universes, then the existence of ours is an absolute certainty. I cannot refute this argument, but it leaves me unfulfilled: it is sort of like the woman who believed that the world was on the back of a turtle, which was on the back of another turtle…and she told Bertrand Russell, “It’s turtles all the way down.” Just slide through a wormhole and you might find a universe that is just different enough from ours to make an interesting TV program.

A mere 15 years after it was published, I got around to reading a book by Lee Smolin. The Life of the Cosmos made a proposition that really caught my attention. He proposed a natural selection model to explain our unlikely universe. (Unlikely is an understatement. According to Smolin, the chances of a universe having the range of parameters that allow the existence of atoms is one in ten to the 239th power.)

Here is my summary of his proposal. A universe came into existence, sometime before time, and there was a 10 to the 239th power chance that it had the wrong parameters and collapsed back upon itself, stillborn, as it were. The collapse of a defective universe might not have taken very long, just a few Planck times (a Planck time is 10 to the -43 seconds). And then it would explode back into existence. This could have happened even more than 10 to the 239th power times. But finally a universe popped into existence that had parameters that were not too far off from what we observe. Let’s call him LUCA, the last universal common ancestor, and I do mean universal. This universe would not collapse upon itself immediately; instead, it would expand and produce lots of massive stars. The collapse of a massive star produces a black hole. Now within the event horizon of a black hole, a new universe can form. Such a universe can have billions of black holes, each with a universe inside. That is, viable universes reproduce, and have fitness.

Suppose, says Smolin, that each time a new universe forms, it has parameters that are just a little bit different from those of the universe in which its natal black hole formed. This would be the equivalent of genetic variation among progeny universes. Eventually, the overwhelming majority of universes will be those that have parameters that are very close to the perfect values. Therefore, universes like ours are the most common, for the same reason that complex life forms are common: they are the ones with the highest fitness. You don’t need an infinite number of universes. This would be a kind of multiversal Darwinism. The anthropic principle, as an intelligent design argument, therefore makes no more sense than to say that the odds against the existence of insulin is 20 to the 51st power (20 amino acids, 51 residues).

I have no idea whether Smolin’s proposal makes any sense. My understanding of cosmology is pretty much limited to the summaries of Scientific American articles. I admit, further, that I have not read Stephen Hawking’s books. But I thought I would pass on to you what seemed to me an exciting idea. Feel free to comment!


  1. I've always understood the anthropic prinicple a little differently, or perhaps I understand it not at all. The only universe, assuming others could exist with different parameters, that has set of parameters appropriate for life is the one in which we find ourselves the observers. So you can only find yourself in one flavor of universe, so the odds aren't very long at all.

    1. Good point. I was just summarizing Smolin's ideas for what they are worth. Thanks for commenting.

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  3. For a long discussion of the facts relating to the anthropic principle
    and cosmic fine tuning, with many links to scientific papers and quotes
    from scientists, see my recent blog post
    Cosmic Fine-Tuning Visualized