A one-parameter version of the fine-tuning argument

In the previous post I tried to explain what the cosmological constant (abbreviated as CC from now on) is, why we think we need it to explain  the faintness of distant supernovae, and why galaxies and other structures would not have been able to form if the CC were substantially larger than the value required to explain the observations.  I also indicated how straightforward attempts at calculating the value of the CC from first principles give nonsensical answers.

The existence of galaxies depends crucially on the value of the CC, but we have no theoretical understanding of why the CC isn't much larger than its observed value.  If we accept that we need some kind of material structures in the Universe for complex life to exist, our existence then seems to balance on the edge of a knife.  It is almost as if the value of the CC had been selected by a supernatural intelligence who created the Universe for us (and from there I suppose it is easy to prove that his name is Yahweh).  If we think syllogisms make bad arguments look impressive, and especially if our initials are WLC, we might feel tempted to put it as follows:

1. The fine-tuning of the CC is due to either physical necessity, chance, or design.
2. It is not due to physical necessity or chance.
3. Therefore, it is due to design.

A few comments are in order here.  First of all I would like to point out the emotional background of the argument.  I can imagine a situation where our models of the Universe contained a parameter X which value was completely irrelevant to the existence of life, and which had a particular, unexplained value in our Universe.  If the value of X were important for some other feature of the universe, would we then feel that it made sense to invoke Yahweh as an explanation?  I don't think so.  So the fine-tuning argument makes the assumption that complex life needs explanation over and beyond other features of the Universe.

The second comment I want to make is that there are more parameters which, like the CC, have values that cannot be derived from theory, and where a small change from their measured values would make life impossible.  I will have deal with those later, but for I while I will stick to the one-parameter version of the argument, just to keep things simple.  Much of what I will say will apply equally to the general case.

Finally, the list of alternatives in the premises is not exhaustive.  For example, our Universe might be a result of naturalistic design (as opposed to supernatural design).  That would be the case if we were part of a simulation run by some other advanced life-form on their computers.  Proponents of supernatural fine-tuning will have to show that all alternatives are less probable than goddidit.

I will discuss how theists defend the second premise in later posts.  What I want to do in closing here is to voice one of the concerns I have about the meaning of fine-tuning.

In the previous post we saw that in our universe the CC is equal to 1 (in suitably defined units), and I claimed that if it were larger than about 100, galaxies wouldn't have formed.  I also gave the "best" theoretical estimate of the CC as 10 to the power of 120.  This must be why apologists like William Lane Craig say that the CC is fine-tuned to a precision of (roughly) one in 10 to the 120.  But if we accept that the CC is a tunable parameter, it could in principle take on any value between negative and positive infinity.  So it is in fact tuned to infinite precision.  At this point WLC's grin may widen so as to light up the entire solar system, but I tend to see this as a problem with the whole argument.  Since the range of possible values is infinite, the life-permitting range of values of the CC will always be insignificant in comparison.  It will always be possible to claim that the CC is fine-tuned.

A further problem is the unstated assumption that all possible values of the CC are a priori equally probable, technically referred to as a uniform prior.  It could be the case that a more complete physical theory, while not allowing us to calculate the CC, predicts a probability distribution for it which is peaked around the observed value.  I am not saying that this situation is likely to arise, but the theist needs to give some justification for why a uniform prior should be preferred.

So, in order to make the notion of fine-tuning precise, both a range and a probability distribution for the CC need to be specified and argued for.  To me that seems to entail having some knowledge about the mechanism that got the Universe started, and that is knowledge we don't have.