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Considering the Fine-Tuning Argument from Probabilities

Photo credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Seán Doran.

This article is the third in a four-part series about the three distinct ways to formulate the argument for an intelligent cause based on the fine-tuning of the constants of nature. Look here for the first and second parts of the series.

Many authors formulate the fine-tuning argument using probabilities and Bayesian analysis (e.g., Swinburne, Collins, Roberts, Barnes). For the sake of simplicity, we’ll discuss a particular formulation — that of Robbin Collins. As we’ll limit our focus to his basic probabilistic line of reasoning, our discussion of the pros and cons of Collins’s formulation will apply equally to other probabilistic formulations as well.

Collins, in his article “God, Design, and Fine-Tuning,” begins by presenting the prime principle of confirmation “that whenever we are considering two competing hypotheses, an observation counts as evidence in favor of the hypothesis under which the observation has the highest probability (or is the least improbable).”

Collins’s Formulation

Using this principle, he formulates the fine-tuning argument as follows:

Premise 1. The existence of the fine-tuning is not improbable under theism. 

Premise 2. The existence of the fine-tuning is very improbable under the atheistic single universe hypothesis. 

Conclusion: From premises (1) and (2) and the prime principle of confirmation, it follows that the fine-tuning data provides strong evidence in favor of the design hypothesis over the atheistic single-universe hypothesis.

His justification for premise 1 is that “since God is an all good being, and it is good for intelligent, conscious beings to exist, it is not surprising or improbable that God would create a world that could support intelligent life.” His justification for premise 2 is the incredibly small likelihood of the constants having the proper values necessary by chance alone. Putting these together, he argues that fine-tuning strongly supports the hypothesis that an intelligent cause set the values of the constants. 

Where the Problem Lies

The biggest advantage of this formulation is its rigor. Using Bayesian analysis, you can legitimately compare the likelihood of the fine-tuned constants given naturalism with their likelihood given theism. Of course, as with any form of analysis, your results are only as good as the initial inputs. And therein lies the problem.

First, can we really find the probability of getting the values of the constants by chance? Since we’ve only observed one instance of each constant, how do we know the likelihood of other values? In other words, since we don’t know the probability distribution of each constant, it would seem that we can’t truly compute the relevant probabilities.

This problem is addressed by Collins, Barnes, and multiverse scientists (who believe that the constants are set by chance). They use plausible upper and lower bounds for the constants and then assume the probability distribution for the constants is linear. Though these seem to be reasonable assumptions, the objection still carries some weight.

“Divine Psychology” 

A second problem with this formulation is, do we really know the probability that God would want to create a complex universe with intelligent, conscious, moral agents? While this approach only needs the supposition that this probability is larger than the vanishingly small probability of fine-tuning assuming no intelligent cause, it could nevertheless be argued that God’s will is inscrutable and positing any knowledge about what God should do is engaging in a form of “divine psychology.” 

Finally, the probabilistic formulation of the fine-tuning argument is surprisingly subject to the problem of evil. This is because once we try to assess the probability of God making our universe, we must consider our entire universe. We must wonder, is it likely that God would make a world with natural disasters, genetic diseases, and so much suffering? While many answers have been given to the problem of evil throughout the generations, the point remains that only the probabilistic formulation of the fine-tuning argument must contend with this challenging problem.

Let us therefore turn to the third formulation that presents fine-tuning as the solution to the intrinsic mystery of the constants and see how it avoids these problems.