Philosophy Professor John T. Roberts, of the University of North Carolina, Chapel Hill, has recently put forward a new version of the fine-tuning argument, entitled, Fine-Tuning and the Infrared Bull’s-Eye (Philosophical Studies 160(2):287-303, 2012). What makes Roberts’ version of the argument particularly interesting is that it is not only much clearer in its formulation than other versions, but also invulnerable to the standard objections that are usually leveled against the fine-tuning argument. As Roberts puts it in the Abstract:
I argue that the standard way of formalizing the fine-tuning argument for design is flawed, and I present an alternative formalization. On the alternative formalization, the existence of life is not treated as the evidence that confirms design; instead it is treated as part of the background knowledge, while the fact that fine tuning is required for life serves as the evidence. I argue that the alternative better captures the informal line of thought that gives the fine-tuning argument its intuitive plausibility, and I show that the alternative formalization avoids all of the most prominent objections to the fine-tuning argument, including the objection from observation selection effects, the problem of old evidence, the problem of non-normalizable probability measures and a further objection due to Monton. I conclude that the alternative formalization is the one that attention should be focused on.
I intend to keep technical jargon to an absolute minimum in this post, so that readers of various backgrounds will be able to digest it. Let’s begin with a few statements which figure in the argument. Roberts abbreviates these statements as R (for restricted range), V (for values), L (for life), D (for design) and C (for chance). In layperson’s language, the propositions read as follows.
R: Fine-tuning is required for life. Life depends on a set of conditions. Each of these conditions can be described by a physical parameter – e.g. the ratio of the strength of gravity to that of electromagnetism; or the strength of the force binding protons and neutrons within the nucleus of the atom; and so on. Each of these parameters falls within a very narrow range, outside of which life would be impossible. As Roberts puts it, life is balanced on the head of a pin. That is, if anything, an under-statement. Indeed, Dr. Robin Collins, in his memorable 2009 essay, The Telelogical Argument: An Exploration of the Fine-Tuning of the Universe, discusses three kinds of fine-tuning: The (i) the fine-tuning of the laws of nature, (ii) the fine-tuning of the constants of nature, and (iii) the fine-tuning of the initial conditions of the universe. Roberts’ argument mainly relates to fine-tuning of the second kind. Just to give one example: the force of gravity is fine-tuned to a precision of 1 in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, or 1 in 10^60. (I should add that fine-tuning is something that scientists have only known about for the last 30 years, although physicist Robert H. Dicke first suggested it, back in 1961.)
V: In our universe, the value of each physical parameter lies within the corresponding range required for life. (That’s pretty obvious: if it weren’t true, we wouldn’t be here.)
L: Life exists in our universe. (Once again, this is an obvious fact.)
D: In our universe, the values of the parameters are set or influenced by the intentional actions of a purposive and intelligent being – in other words, a Designer. (This is what theists believe.)
C: In our universe, the values of the parameters are a matter of chance. (This is what atheists believe.)
The problem with the standard formulation of the fine-tuning argument – and how Roberts proposes to fix it
In his article, Roberts identifies a vital flaw in the way that the fine-tuning argument is commonly presented. The argument proceeds as if we already know that fine-tuning is required for any sort of life to exist, and then suddenly discover that (surprise!) our own universe contains life. In reality, we already know that life exists in our universe; the surprise is the fine-tuning of the constants of Nature. As Roberts puts it:
On the standard way of formulating the fine-tuning argument, the fact that fine-tuning is required for life – what I called R – is treated as part of the background knowledge B. L on the other hand (or, on the alternative version, V) is treated as the new evidence we are considering. This suggests that we have known all along that fine tuning is required for life to exist in our universe, and then one day we discovered that life does exist in our universe – a striking discovery that forced us to reconsider the case for a designer. Of course, that gets things exactly backwards. We have known all along that our universe is life-sustaining (L). What comes as a surprise and makes us think that maybe we should rethink the matter of chance vs. design is the more recent discovery that fine tuning was required for life.
The flaw identified by Roberts in the standard version of the fine-tuning argument is what underlies two common objections to the argument in the literature. The first (formulated by the philosopher Elliott Sober) is the objection that excluding the fact that the universe contains life (i.e. L) renders the argument vulnerable to an observational bias, which is known in the philosophical literature as an observation selection effect. After all, in order to make an observation in the first place, you have to be alive, so there’s something fishy about leaving the existence of life (L) out of our background knowledge B. The second objection is that the fact that our universe contains life is old evidence: it’s something we’ve long been acquainted with, so it should form part of our background knowledge, instead of being treated as new evidence.
Atheist philosopher Bradley Monton also objects to the fine-tuning argument, but on somewhat different grounds. Even if the fact that our cosmos contains life makes the existence of a Designer more likely, he says, it doesn’t necessarily follow that fine-tuning has anything to do with that. The existence of life might make the existence of a Designer more likely for a host of other reasons – e.g. religious experience, our sense of morality and our sense of beauty – that have nothing to do with fine-tuning.
So, how does Roberts think the argument should be re-formulated, to render it invulnerabe to these objections? By making the “surprising” fact the discovery of fine-tuning, rather than the existence of life.
This suggests that when we treat the fine-tuning argument as a likelihood argument (or more generally, when we formulate it in Bayesian terms), we should let our background knowledge include L, and let R be the item that plays the role of evidence. After all, the thing that we discovered which suddenly seemed to favor the hypothesis of a designer over the chance hypothesis in a new way was not that there is life in the universe, nor that e.g. the ratio of the strengths of the gravitational and electromagnetic forces has the value it does, but rather that the life we know to exist in the universe depended on a set of conditions balanced on the head of a pin in a way we had never suspected before. So, the crucial move in the argument is this: The precariously-balanced nature of life in our universe is far less surprising given a designer than it would be given chance, and so it evidentially favors design over chance.
But is the fine-tuning of life really new evidence?
At this point an atheist might ask: “How can the fine-tuning of life constitute new evidence?” If it’s a logical implication of what we already know about physics, then it should be considered old evidence. Roberts replies that regardless of whether fine-tuning was already implied by our existing theories of physics or not, it wasn’t discovered until relatively recently, and when it was, it came as a surprise:
One worry is that R (the proposition that fine-tuning is required for life) is not really “new evidence”; the discovery of it was really the discovery that it was a consequence of theories we had already accepted. But what is really doing the evidential work here is the discovery that there are certain real-valued physical parameters which need to be within surprisingly narrow boundaries in order for life to exist – in other words, the fact of R. That fact, of course, is something that was discovered empirically, albeit over a long period of time rather than all at once. But evidence propositions need not be discovered instantaneously in order to serve as evidence. And by the time the discovery of this fact began, it was already well-known that life exists. So there is no problem with considering a context in which the background knowledge includes L, and the new evidence under consideration is R.
Roberts’ new, intuitive version of the fine-tuning argument
Roberts is now ready to put forward his own version of the fine-tuning argument. Before we examine it, there’s just one more principle that we need to be familiar with: the Likelihood Principle. It goes as follows. Suppose you’re considering two rival hypotheses: hypothesis 1 and hypothesis 2. Then we can say that a new piece of evidence E favors hypothesis 1 over hypothesis 2, whenever (and only whenever) the probability of that evidence occurring is higher under hypothesis 1 than it is under hypothesis 2.
Putting it in mathematical jargon: in a context where our background knowledge is B, a piece of evidence E favors hypothesis H1 over hypothesis H2 if and only if the probability of E given hypothesis H1 and background knowledge B, or Pr(E|H1 & B) is greater than the probability of E given hypothesis H2 and background knowledge B, or Pr(E|H2 & B)].
The Likelihood Principle is not at all controversial, philosophically speaking: it simply describes the standard way of adjudicating between rival hypotheses.
Let’s now have a look at Roberts’ formulation of the fine-tuning argument. I’ve translated the steps into layperson’s language, in my bracketed comments:
The fine-tuning argument, then, claims that when our background knowledge includes L (which of course it always does), the discovery of the truth of R evidentially favors design over chance, because R is more likely given design than it is given chance. So here’s how we should reformulate the fine-tuning argument:
Premise 1+: L belongs to our background knowledge B.
[Plain English translation: we already know that life exists in our universe – VJT.]
Premise 2+: If L belongs to our background knowledge B, then Pr(R|D & B) > Pr(R|C & B).
[Plain English translation: if we already know that life exists, then the probability that life would require fine-tuning is higher if there’s a Designer than it would be if everything is ultimately the product of blind chance – VJT.]
Step 3, by 1+ and 2+: Pr(R|D & B) > Pr(R|C & B)
[Plain English translation: since we know that life exists in our universe, it follows that the probability that life would require fine-tuning is higher if there’s a Designer than it would be if everything is ultimately the product of blind chance – VJT.]
Conclusion, by 3 and the Likelihood Principle: Given our background knowledge, R evidentially favors D over C.
[Plain English translation: therefore the discovery of fine-tuning favors the hypothesis that there’s a Designer over the hypothesis that everything is ultimately the product of blind chance – VJT.]
In other words, the discovery of fine-tuning makes it more likely (from our perspective) that there is a God, if by “God,” we mean a purposeful and intelligent being outside the cosmos. And as scientists discover more and more fine-tuning in our scientific investigations of the cosmos, it will appear increasingly likely to us that there really is such a God.
Night vision: why fine-tuning renders the existence of a Designer more likely
Roberts anticipates a possible objection to his new version of the fine-tuning argument: how do we know that the second premise is true? The second premise stipulated that if we already know that life exists, then the probability that life would require fine-tuning is higher if there’s a Designer than it would be if everything is ultimately the product of blind chance. But why should this be so? Why should the occurrence of fine-tuning render the existence of a Designer more likely?
To make this premise appear plausible, Roberts tells a little story about someone who receives a birthday present of a set of infra-red goggles (which they haven’t opened yet), and who is also standing in front of a large wall:
Imagine that you are standing in front of an extremely large wall, which as far as you can tell is homogeneously white, with nothing to distinguish one part of it from another. From somewhere behind you, a dart is launched, and it zooms over your head and then hits a point on the wall. It occurs to you to wonder whether the dart was thrown carefully by a skillful aimer or flung up there by some chance process. You might reason as follows:
… [T]he skillful-aimer hypothesis doesn’t make the dart’s hitting this point any more likely than the random-flinger hypothesis does. And so, thus far, all my evidence seems to be neutral between the skillful-aimer hypothesis and the random-flinger hypothesis.
Then you open your birthday present, and it’s a pair of infrared-vision goggles. You put them on, and when you look at the wall again, you see that it bears a standard dartboard design done in infrared paint, and the center of the bull’s-eye is at precisely the point where the dart is sticking out of the wall. Now what do you think? It seems obvious that the only reasonable thing to think at this point is that you now have excellent evidence that the dart was carefully aimed. (And by someone or something that can see in the infrared part of the spectrum.) Why? We can reconstruct your reasoning as a likelihood argument: There being something special and aim-worthy about the point where the dart struck the wall is much less surprising and much more to have been suspected if the dart were thrown by a skillful aimer than if it were flung up there by some random process…
The analogy between this case and that of the fine-tuning argument is obvious. Our discovery of R corresponds to the discovery of the infrared bull’s-eye: It shows us that there was something intelligibly (even if not uniquely) aim-worthy or choiceworthy about the values of our universe’s parameters which they do not share with generic possible parameter-values. Just as the discovery of the heretofore invisible bull’s-eye ought to strike us as more likely given a skillful aimer than given a random flinger, so should the special feature of the actual parameter-values strike us as more likely given that they were set by design than given that they were set by chance.
This is an excellent illustration, which seems to render the second premise of Roberts’ argument intuitively plausible. But we might still want to ask: precisely what is it that makes it rational to infer that the dart is thrown by an intentional agent? Roberts thinks he has the answer: the target was choiceworthy or aim-worthy in a way that other spots on the wall were not.
In both the case of the fine-tuning argument and the case of the inference to the skillful aimer, the defense of the crucial likelihood inequality stands or falls with this assumption:
Assumption: Suppose that event X has happened, rather than the alternatives Y, Z, etc…. Consider the proposition that X has some feature which distinguishes it from Y, Z etc. and makes it intelligibly choiceworthy or aim-worthy in a way that not all of Y, Z etc. are. This proposition is more likely given that X was the result of an intentional act of an agent than it is given that X was the result of chance.
Roberts then proceeds to show that this Assumption can be justified by appealing to two very plausible premises. The first premise (labeled (3) in his article) “just says that it is much more likely for X to occur as the result of an agent’s action if X is particularly (though not necessarily uniquely) choiceworthy for an agent than it is otherwise.” In other words, agents are more likely to aim for aim-worthy targets. Roberts comments: “This is surely correct: Agents are much more likely to do choiceworthy things than they are to do things in general.”
The second premise (labeled (4) in the article) which Roberts uses to justify his Assumption simply says that “the likelihood of X occurring as a matter of chance is unaffected (or anyhow, affected very little) by whether X is particularly choiceworthy.” In other words, blind chance doesn’t aim at anything. That’s why we call it blind. Adds Roberts: “This is overwhelmingly plausible.”
What is choiceworthy about the physical parameters of our cosmos is that they are life-supporting parameters. As such, they are the sort of target that a Designer might well aim to realize.
Why the new formulation of the fine-tuning argument is superior to the old one
Roberts points out that his new formulation of the fine-tuning argument has a conspicuous advantage over the standard version, since it is invulnerable to objections that are commonly leveled against the standard formulation of the argument:
None of the objections considered in the preceding section carry any weight against this argument. Note first that this argument clearly depends on fine tuning as such: What serves as evidence here is the very fact that there are physical parameters that need to be fine-tuned in order for life to exist… Next note that the likelihoods that figure in this argument are already conditionalized on a background that includes the existence of life. Adding the fact that life exists to the background knowledge is not going to change anything, because that fact is already in the background knowledge. This shows that neither the old-evidence objection nor the observation-selection-effect objection even arises for this form of the fine-tuning argument.
Roberts can also rebut Bradley Monton’s objection, that even if the fact that our cosmos contains life makes the existence of a Designer more likely, it doesn’t necessarily follow that fine-tuning has anything to do with that. Roberts has given us an independent reason as to why the occurrence of fine-tuning makes the existence of a Designer more likely.
My only comment at this point is that the foregoing “night vision” illustration isn’t really an argument for the second premise of Roberts’ argument as for the third: the probability that life would require fine-tuning is higher if there’s a Designer than it would be if everything is ultimately the product of blind chance. So much the better for the argument, then: it brings the conclusion one step closer.
An Objection: How do we know what a Designer would do?
We are not done yet, however. An atheist might object that we are making assumptions about what the Designer would and wouldn’t choose. But how do we know that? In reply, Roberts says that he is making only one modest assumption: that an agent who creates a universe is more likely to want to make a universe that can sustain life than just any old random universe. Of course, there may be other goals that a Designer might have – e.g. the production of a universe containing nothing but diamonds. But the production of a universe that can sustain life is surely an interesting goal in itself. In Roberts’ words:
There is a common objection to the fine-tuning argument that might appear to raise trouble here. The case for (3) [the premise agents are more likely to aim for aim-worthy targets – VJT] depends on the assumption that an agent is more likely to do a given thing if that thing is intelligibly choiceworthy than it is if that thing isn’t intelligibly choiceworthy. But what do we know about what an agent capable of setting up a universe would or would not find choiceworthy? … It shouldn’t be controversial that such a being could see a life-sustaining universe as choiceworthy. And it isn’t necessary to make the much stronger assumption that any such being would necessarily see such a universe as choiceworthy – let alone the assumption that any such being would want a universe with human beings in it. All that is necessary for the argument to go through is that a life-sustaining universe is intelligibly choiceworthy in a way that not all kinds of universe are. And this seems obviously true.
An Objection: Would a Designer Make Fine-Tuning Necessary?
But the atheist has another ace up his sleeve. “Doesn’t it seem odd,” he might ask, “to claim that if a Designer wanted to create a universe capable of supporting life, then He would create a finely-balanced one, in which life would be annihilated if the physical parameters describing our universe were changed even a little? Why would He do that?” Roberts responds that even if it were unlikely that a Designer would make a finely-tuned cosmos that was balanced on a knife-edge, rather than another kind of cosmos, the occurrence of fine-tuning is still more likely if the parameters describing our universe are set by a Designer than if the parameters are set by chance. To make his point, he uses another illustration, this time relating to screen-savers:
What the fine-tuning argument needs in order to work is not for it to be more likely than not that a designer would make R be true if it could; rather, it needs it to be more likely that R is true given both L and D than it is given L and C. This latter claim is perfectly compatible with its being the case that if there is a Designer, it would most likely make a world where fine tuning is not required.
It might be helpful to consider an analogy. I have an uncle who is not at all famous, is not a model, and does not work in the computer industry or know anybody who does. So if you notice that my screen saver features a picture of my uncle, you can reasonably be quite confident that I set up my own screen saver, instead of just using the one that came pre-installed on the computer. This doesn’t change if you also happen to know that my uncle and I are not particularly close, so that it is rather unlikely that I would choose a picture of him for a screen saver if I were setting it up myself. That doesn’t matter: As unlikely as it is that my uncle’s photo would be in my screen saver had I set it up myself, it is surely far more unlikely that his photo would be in my screen saver had my screen saver been the one provided by the manufacturer. (After all, I am at least related to the guy.) So when you see my uncle’s photo there, you have excellent grounds for favoring the hypothesis that I set up my own screen saver over the hypothesis that I used the one that came pre-installed – even though what you see is quite surprising, given the hypothesis thus favored.
How should the probabilities in the argument be understood?
Finally, Roberts addresses the epistemic question: how should we construe the probabilities which figure in his version of the fine-tuning argument? Are they objective? Surely not: what could it possibly mean to say that there’s an objective likelihood that the universe should be fine-tuned, given that there is a Designer, and that the universe He designed contains life? And how would we compute such a likelihood? We can’t use a “Bell curve” here, as the range of values for these parameters is potentially infinite. In mathematical jargon, the probability distributions are non-normalizable.
Instead, Roberts suggests interpreting the probabilities in his argument as subjective states of belief, or what he calls “credences.” Some philosophers (e.g. Tim and Lydia McGrew and E. Vestrup) have argued that subjective credences weaken the fine-tuning argument by making it depend on assumptions about the prior likelihood of a Designer’s existence. Not so, replies Roberts: all his argument assumes is that if a Designer exists, then He would view the production of a life-sustaining universe as a choiceworthy target. No assumption is made about the inherent likelihood of such a Designer existing in the first place.
Roberts now argues that by modestly construing the probabilities as subjective credences, he can successfully overcome a powerful mathematical objection to the Fine-Tuning argument:
The formulation of the fine-tuning argument I have presented, with the probabilities interpreted as credences, is also immune to another common objection against fine-tuning arguments: namely, that they make illegitimate use of probability theory since they employ non-normalizable probability distributions. The idea is that the fine-tuning argument needs to assign probabilities to the various possible values of the parameters P1 … PN. But these parameters can take any real numbers as their values. So there is no way to distribute probabilities over them uniformly, and any non-uniform distribution would be arbitrary. But in the new version of the argument I have just presented, this is not a problem: The only probability distribution that we need to use assigns a probability of 1 to the proposition that all of our universe’s parameters are in their life-permitting ranges, and to the proposition that there is life in our universe… The great, infinite space of possible parameter-values plays a role in the argument – the non-life-permitting regions within that space play the role of Y, Z etc. in Assumption [i.e. the premise above, that a choiceworthy occurrence is more likely, if it was produced by an intentional agent, than if it was produced by chance – VJT.]. But at no point does the argument need to employ a probability distribution defined over this space.
Roberts closes by acknowledging that while his new intuitive formulation of the fine-tuning argument shows that fine-tuning lends support to the existence of a Designer, that’s about as far as it can take us:
Where should we go from here? I’ll close by saying a few things about this argument that, for whatever it’s worth, seem obviously correct to me. First of all, the argument really does show that the phenomenon of fine tuning (assuming it to be genuine) provides some evidence in favor of the existence of a designer. Second, on its own, this argument certainly does not establish that we ought to believe that there is a designer — that depends on what other evidence is available and on the prior plausibility of the hypothesis, matters that the fine-tuning argument does not address. Third, the fine-tuning argument lends no support to any hypotheses about the desires or motives of the designer, except that it must be enough like us for us to be able to recognize it as a purposive agent at all, and enough like us for it to be able to share our sense that a life-sustaining universe is a particularly (if perhaps not uniquely) choiceworthy kind of universe to make. Fourth, the fine-tuning argument lends no support to any hypotheses about how powerful the designer is, except that it had the power to influence the values of the finely-tuned parameters. (So in particular, there is no support here for a being with the power to create the universe ex nihilo, or even to determine the mathematical form of the laws of physics.) Fifth, the fine-tuning argument lends little if any support to any hypotheses about how much knowledge the designer had, except that it must have thought it likely that a universe with parameter-values within the life-permitting range would lead to something interesting. Despite these limitations, the argument does seem
to show something interesting and surprising.
The fine-tuning argument, then, cannot by itself take us to belief in God. But what about Roberts’ claim that it can’t even establish the existence of a Designer? In Roberts’ words, that depends on “what other evidence is available and on the prior plausibility of the hypothesis.”
I’d like to respond here by proposing that we can put a floor or minimum, on the prior likelihood of there being a Designer. Here’s why. Consider some argument or set of arguments A against the existence of a Designer. What will these arguments appeal to? One of two things: logic or experience. If it’s logic, then it should be possible to show on purely logical grounds that the universe can have no Designer. So far no-one has presented such a proof. But if the argument is based on experience, then we need to ask: how many experiences tell against the existence of a Designer? The number of humans who have ever lived is 100 billion, or 10^11. If we count every episode of 0.1 seconds as a distinct experience, and the length of an average lifetime as (generously) 2,000,000,000 seconds, then we get 20 billion experiences, or 2 x 10^10. Thus the total number of experiences in human history is at most 2 x 10^21, and if all of these tell against the existence of a Designer, then we might say that the likelihood of a Designer is at least 0.5 x 10^(-21). That’s low, but consider the fine-tuning of gravity alone: 1 part in 10^60, according to Collins’ 2009 essay on the fine-tuning argument. 10^60 dwarfs numbers like 10^21. Thus we can say that the fact that the number of experiences we’ve had is finite, coupled with the fine-tuning argument, is sufficient to render the existence of a Designer likely. What’s more, the Designer would have to be supernatural, even if the fine-tuning argument alone is unable to establish that this Designer is an ex nihilo Creator of the cosmos. In other words, it seems that the fine-tuning argument, combined with the finitude of human experience, gets us to belief in some kind of God.
What do readers think?