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Author Topic:   Fine tuning: a discussion for the rest of us mortals
Slim Jim
Junior Member (Idle past 6244 days)
Posts: 26
Joined: 05-06-2005


Message 15 of 83 (261171)
11-18-2005 11:43 PM
Reply to: Message 1 by coffee_addict
11-18-2005 5:26 PM


From a Bayesian probabilistic point of view, I've always been rather fond of the Fine-tuning argument for it seems to undermine ID more than validate it.
Consider the following propositions:
L: the universe exists and contains life.
F: the conditions of the universe are compatible with life existing naturalistically.
N: the universe is solely naturalistic.
WAP: (Weak Anthropic Principle) life can exist in a naturalistic universe only if the conditions of that universe are compatible with life existing naturalistically.
We can comfortably agree that proposition L is true. The claim that the universe is fine-tuned for life (vacuously) implies that life can thereafter exist naturalistically. Thus we can safely agree that proposition F is true. Proposition N is more contentious, so let's assume that either of N (the universe is solely naturalistic) and ~N (the universe is not solely naturalistic) are possible for the moment. Thus both N and ~N have non-zero probabilities of being true. The Weak Anthropic Principle states that L&N -> F, or in probabilistic terms P(F|L&N) = 1.
Things become very interesting when we apply Bayes theorem. This allows us to conclude:
P(N|L&F) = P(F|L&N) * P(N|L) / P(F|L)
         = P(N|L) / P(F|L)
         >= P(N|L)
i.e. the probability that the universe is solely naturalistic given the universe exists, contains life and the conditions of the universe are compatible with life existing naturalistically is greater than the probability that the universe is solely naturalistic given the universe exists and contains life. Thus the Weak Anthropic Principle does not impede the premise that the universe is solely naturalistic.
And since P(~N|L&F) = 1 - P(N|L&F) we can conclude that P(~N|L&F) <= P(~N|L). i.e. the probability that the universe is not solely naturalistic given the universe exists, contains life and the conditions of the universe are compatible with life existing naturalistically is less than the probability that the universe is not solely naturalistic given the universe exists and contains life. Thus fine-tuning does not support supernaturalism.
This is quite ironic - we have arrived at the rather curious position where fine-tuning increases the likelihood of a naturalistic universe.
ID proponents may say "Whoa! Hang on minute Slim. There are two arguments that undermine a solely naturalistic universe. 1. Irreducible Complexity implies that the conditions of the universe are not compatible with life arising by solely naturalistic mechanisms. And 2. the Anthropic argument implies that the universe is so finely-tuned to the existence of life that the universe cannot be considered solely naturalistic."
Ok. Let's have a look what happens when we assume Irreducible Complexity (i.e. ~F):
~F -> ~(L&N) = ~F -> ~N
i.e. given that the conditions of the universe are not compatible with life arising by solely naturalistic mechanisms, it follows that we cannot have both life and a solely naturalistic universe. Since the universe does exists and contains life (L is true), we have that given that the conditions of the universe are not compatible with life arising by solely naturalistic mechanisms, it follows that we cannot have a solely naturalistic universe. Thus Irreducible Complexity tells us that ~F undermines a solely naturalistic universe:
P(N|L&~F) < P(N|L).
Now let's have a look what happens when we assume the Anthropic argument (and hence F is true):
F -> ~(L&N) = F -> ~N
i.e. given that the conditions of the universe are so finely tuned to the existence of life, it follows that we cannot have both life and a solely naturalistic universe. Thus Fine-tuning tells us that F also undermines a solely naturalistic universe:
P(N|L&F) < P(N|L).
This puts the ID proponents in a real statistical bind:
P(L&N) = P(L&N&~F) + P(L&N&F)
       < P(N|L) * (P(L&~F) + P(L&F))
       = P(N|L) * P(L)
       = P(L&N)
which is a contradiction. Ouch!
It would seem that ID proponents would do well to stay away from such naturalistic arguments like Fine-Tuning.

This message is a reply to:
 Message 1 by coffee_addict, posted 11-18-2005 5:26 PM coffee_addict has not replied

  
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