Last night, a reader sent me a link to yet another wretched attempt to argue for the existence of God using Bayesian probability. I really hate that. Over the years, I’ve learned to dread Bayesian arguments, because so many of them are things like this, where someone cobbles together a pile of nonsense, dressing it up with a gloss of mathematics by using Bayesian methods. Of course, it’s always based on nonsense data; but even in the face of a lack of data, you can cobble together a Bayesian argument by pretending to analyze things in order to come up with estimates.
You know, if you want to believe in God, go ahead. Religion is ultimately a matter of personal faith and spirituality. Arguments about the existence of God always ultimately come down to that. Why is there this obsessive need to justify your beliefs? Why must science and mathematics be continually misused in order to prop up your belief?
Anyway… Enough of my whining. Let’s get to the article. It’s by a guy named Robin Collins, and it’s called “God, Design, and Fine-Tuning“.
Let’s start right with the beginning.
Suppose we went on a mission to Mars, and found a domed structure in which everything was set up just right for life to exist. The temperature, for example, was set around 70o F and the humidity was at 50%; moreover, there was an oxygen recycling system, an energy gathering system, and a whole system for the production of food. Put simply, the domed structure appeared to be a fully functioning biosphere. What conclusion would we draw from finding this structure? Would we draw the conclusion that it just happened to form by chance? Certainly not. Instead, we would unanimously conclude that it was designed by some intelligent being. Why would we draw this conclusion? Because an intelligent designer appears to be the only plausible explanation for the existence of the structure. That is, the only alternative explanation we can think of–that the structure was formed by some natural process–seems extremely unlikely. Of course, it is possible that, for example, through some volcanic eruption various metals and other compounds could have formed, and then separated out in just the right way to produce the “biosphere,” but such a scenario strikes us as extraordinarily unlikely, thus making this alternative explanation unbelievable.
The universe is analogous to such a “biosphere,” according to recent findings in physics. Almost everything about the basic structure of the universe–for example, the fundamental laws and parameters of physics and the initial distribution of matter and energy–is balanced on a razor’s edge for life to occur. As eminent Princeton physicist Freeman Dyson notes, “There are many . . .lucky accidents in physics. Without such accidents, water could not exist as liquid, chains of carbon atoms could not form complex organic molecules, and hydrogen atoms could not form breakable bridges between molecules” (1979, p.251)–in short, life as we know it would be impossible.
Yes, it’s the good old ID argument about “It looks designed, so it must be”. That’s the basic argument all the way through; they just dress it up later. And as usual, it’s wrapped up in one incredibly important assumption, which they cannot and do not address: that we understand what it would mean to change the fundamental structure of the universe.
What would it mean to change, say, the ratio of the strengths of the electromagnetic force and gravity? What would matter look like if we did? Would stars be able to exist? Would matter be able to form itself into the kinds of complex structures necessary for life?
We don’t know. In fact, we don’t even really have a clue. And not knowing that, we cannot meaningfully make any argument about how likely it is for the universe to support life.
They do pretend to address this:
Various calculations show that the strength of each of the forces of nature must fall into a very small life-permitting region for intelligent life to exist. As our first example, consider gravity. If we increased the strength of gravity on earth a billionfold, for instance, the force of gravity would be so great that any land-based organism anywhere near the size of human beings would be crushed. (The strength of materials depends on the electromagnetic force via the fine-structure constant, which would not be affected by a change in gravity.) As astrophysicist Martin Rees notes, “In an imaginary strong gravity world, even insects would need thick legs to support them, and no animals could get much larger.” (Rees, 2000, p. 30). Now, the above argument assumes that the size of the planet on which life formed would be an earth-sized planet. Could life forms of comparable intelligence to ourselves develop on a much smaller planet in such a strong-gravity world? The answer is no. A planet with a gravitational pull of a thousand times that of earth — which would make the existence of organisms of our size very improbable– would have a diameter of about 40 feet or 12 meters, once again not large enough to sustain the sort of large-scale ecosystem necessary for organisms like us to evolve. Of course, a billion-fold increase in the strength of gravity is a lot, but compared to the total range of strengths of the forces in nature (which span a range of 1040 as we saw above), this still amounts to a fine-tuning of one part in 1031. (Indeed,other calculations show that stars with life-times of more than a billion years, as compared to our sun’s life-time of ten billion years, could not exist if gravity were increased by more than a factor of 3000. This would have significant intelligent life-inhibiting consequences.) (3)
Does this really address the problem? No. How would matter be different if gravity were a billion times stronger, and EM didn’t change? We don’t know. For the sake of this argument, they pretend that mucking about with those ratios wouldn’t alter the nature of matter at all. That’s what they’re going to build their argument on: the universe must support life exactly like us: it’s got to be carbon-based life on a planetary surface that behaves exactly like matter does in our universe. In other words: if you assume that everything has to be exactly as it is in our universe, then only our universe is suitable.
They babble on about this for quite some time; let’s skip forwards a bit, to where they actually get to the Bayesian stuff. What they want to do is use the likelihood principle to argue for design. (Of course, they need to obfuscate, so they cite it under three different names, and finally use the term “the prime principle of confirmation” – after all, it sounds much more convincing than “the likelihood principle”!)
The likelihood principle is a variant of Bayes’ theorem, applied to experimental systems. The basic idea of it is to take the Bayesian principle of modifying an event probability based on a prior observation, and to apply it backwards to allow you to reason about the probability of two possible priors given a final observation. In other words, take the usual Bayesian approach of asking: “Given that Y has already occurred, what’s the probability of X occurring?”; turn it around, and say “X occurred. For it to have occurred, either Y or Z must have occurred as a prior. Given X, what are the relative probabilities for Y and Z as priors?”
There is some controversy over when the likelihood principle is applicable. But let’s ignore that for now.
To further develop the core version of the fine-tuning argument, we will summarize the argument by explicitly listing its two premises and its conclusion:
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. (8)
Conclusion: From premises (1) and (2) and the prime principle of confirmation, it follows that the fine-tuning data provides strong evidence to favor of the design hypothesis over the atheistic single-universe hypothesis.
At this point, we should pause to note two features of this argument. First, the argument does not say that the fine-tuning evidence proves that the universe was designed, or even that it is likely that the universe was designed. Indeed, of itself it does not even show that we are epistemically warranted in believing in theism over the atheistic single-universe hypothesis. In order to justify these sorts of claims, we would have to look at the full range of evidence both for and against the design hypothesis, something we are not doing in this paper. Rather, the argument merely concludes that the fine-tuning strongly supports theism over the atheistic single-universe hypothesis.
That’s pretty much their entire argument. That’s as mathematical as it gets. Doesn’t stop them from arguing that they’ve mathematically demonstrated that theism is a better hypothesis than atheism, but that’s really their whole argument.
Here’s how they argue for their premises:
Support for Premise (1).
Premise (1) is easy to support and fairly uncontroversial. The argument in support of it can be simply stated as follows: since God is an all good being, and it is good for intelligent, conscious beings to exist, it not surprising or improbable that God would create a world that could support intelligent life. Thus, the fine-tuning is not improbable under theism, as premise (1) asserts.
Classic creationist gibberish: pretty much the same stunt that Swinburne pulled. They pretend that there are only two possibilities. Either (a) there’s exactly one God which has exactly the properties that Christianity attributes to it; or (b) there are no gods of any kind.
They’ve got to stick to that – because if they admitted more than two possibilities, they’d have to actually consider why their deity is more likely that any of the other possibilities. They can’t come up with an argument that Christianity is better than atheism if they acknowledge that there are thousands of possibilities as likely as theirs.
Support for Premise (2).
Upon looking at the data, many people find it very obvious that the fine-tuning is highly improbable under the atheistic single-universe hypothesis. And it is easy to see why when we think of the fine-tuning in terms of the analogies offered earlier. In the dart-board analogy, for example, the initial conditions of the universe and the fundamental constants of physics can be thought of as a dart- board that fills the whole galaxy, and the conditions necessary for life to exist as a small one-foot wide target. Accordingly, from this analogy it seems obvious that it would be highly improbable for the fine-tuning to occur under the atheistic single-universe hypothesis–that is, for the dart to hit the board by chance.
Yeah, that’s pretty much it. The whole argument for why fine-tuning is less probably in a universe without a deity than in a universe with one. Because “many people find it obvious”, and because they’ve got a clever dartboard analogy.
They make a sort of token effort to address the obvious problems with this, but they’re really all nothing but more empty hand-waving. I’ll just quote one of them as an example; you can follow the link to the article to see the others if you feel like giving yourself a headache.
Another objection people commonly raise against the fine-tuning argument is that as far as we know, other forms of life could exist even if the constants of physics were different. So, it is claimed, the fine-tuning argument ends up presupposing that all forms of intelligent life must be like us. One answer to this objection is that many cases of fine-tuning do not make this presupposition. Consider, for instance, the cosmological constant. If the cosmological constant were much larger than it is, matter would disperse so rapidly that no planets, and indeed no stars could exist. Without stars, however, there would exist no stable energy sources for complex material systems of any sort to evolve. So, all the fine-tuning argument presupposes in this case is that the evolution of life forms of comparable intelligence to ourselves requires some stable energy source. This is certainly a very reasonable assumption.
Of course, if the laws and constants of nature were changed enough, other forms of embodied intelligent life might be able to exist of which we cannot even conceive. But this is irrelevant to the fine-tuning argument since the judgement of improbability of fine-tuning under the atheistic single-universe hypothesis only requires that, given our current laws of nature, the life-permitting range for the values of the constants of physics (such as gravity) is small compared to the surrounding range of non-life-permitting values.
Like I said at the beginning: the argument comes down to a hand-wave that if the universe didn’t turn out exactly like ours, it must be no good. Why does a lack of hydrogen fusion stars like we have in our universe imply that there can be no other stable energy source? Why is it reasonable to constrain the life-permitting properties of the universe to be narrow based on the observed properties of the laws of nature as observed in our universe?
Their argument? Just because.
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