[Edit, 4/2/2012: I've written a more complete critique of Stenger's book The Fallacy of Fine-Tuning: Why the Universe Is Not Designed for Us. It's posted on on Arxiv.]
This post is part of a series that responds to internet articles on the fine tuning of the universe. Here I will respond to Prof. Victor Stenger, who is a particle physicist at the University of Hawaii and known for his defence of atheism. Stenger, according to Wikipedia, is currently writing a book on fine-tuning. Here I will respond to a point he made in a debate with Dr. William Lane Craig.
Stenger proposes the following counterexample to the claim that interesting conclusions can be drawn from the improbability of the fine-tuning of the constants/initial conditions/laws of nature:
Low probability events happen every day. What’s the probability that my distinguished opponent exists? You have to calculate the probability that a particular sperm united with a particular egg, then multiply that by the probability that his parents met, and then repeat that calculation for his grandparents and all his ancestors going back to the beginning of life on Earth. Even if you stop the calculation with Adam and Eve, you are going to get a fantastically small number. To use words that Dr Craig has used before, “Improbability is multiplied by improbability by improbability until our minds are reeling in incomprehensible numbers.” Well, Dr Craig has a mind-reeling, incomprehensibly low probability – a priori probability – for existing. Yet here he is before us today.
Stenger’s argument is that sometimes we cannot draw interesting conclusions from low probabilities. The most obvious problem with Stenger’s argument is that sometimes we do, in fact, draw interesting conclusions from low probabilities. For example, British illusionist Derren Brown claimed that he could predict the lottery, and then appeared to do so on national television. From the extremely small probability that he would predict the correct numbers by chance alone, we rightly infer that he didn’t just guess and get lucky.
So what’s the difference between your existence and a lotto draw? The difference is the existence of an independently specified target or pattern.
Let each of the 14 million possible lotto predictions be represented by a ping-pong ball. Place all 14 million balls in a big bag, and shake well. Brown (apparently) reaches blindly into the bag and pulls out the one winning ball. Why is this amazing? It is not just that his ball is unlikely – any ball is unlikely. It is this low probability coupled with the fact that the winning ball is specified independently of Brown’s choice. While the balls are all still in the bag, one is a winner (independent of Brown’s choice) and the rest are losers. He didn’t just pick an unlikely ball; he picked the winning ball. He can’t pull out just any ball and proclaim: “I win”.
Now fill the bag with balls representing the vast number of possible outcomes of different egg-sperm combinations. The hand of fate goes into the bag and out you come. Why isn’t this anything special? Because there is nothing to single out this ball, improbable though it is, while it is still in the bag. We only know who “you” are after you come out of the bag. “You” are not specified independently of the choice of ball. Whatever ball comes out of the bag, the corresponding person can proclaim: “I win”. (In this game, you win by existing.) You can’t lose!
Let me illustrate the difference another way. I shoot an arrow at a huge wall, 100 metres away. When the impact zone is inspected, we find that the arrow has hit the centre of a small red spot. The probability of hitting this point on the wall is tiny. Am I a talented archer? It depends. If I proclaimed: “watch me hit that red spot” before firing the arrow, then I’m the new Robin Hood. However, if I shot the arrow and then took some red paint and painted the spot around my arrow’s impact point, then you can’t reach any conclusion about my archery skills.
So which of these cases does the fine-tuning of the universe resemble? Potential universes can be marked “intelligent life can/cannot live here” independently of the properties of the actual universe. This universe is not special because it is ours. It is special because it can support intelligent life. When we consider the fine-tuning of the universe, we are not considering the probability of this universe. We are considering the probability of a universe that supports intelligent life. Choose a different sperm, you get a different person. Choose a different universe, and you almost certainly do not get a different form of intelligent life. You get no intelligent life at all. The fine-tuning of the universe involves a low probability event and an independently specified target, and thus cannot be dismissed as just another low probability event. Stenger’s counterexample misses the target.
More of my posts on fine-tuning are here.