• Fine Tuning as an Argument for Prior Probability

    In my last post I discussed why the fine tuning argument could never be an evidential argument. Every workable way in which we’ve tried to state it simply works out such that fine-tuning cannot make the evidence we have unlikely under the atheist’s perspective. And if it can’t do that, then it can’t show that theism predicts any evidence related to this issue better than atheism, which means there’s no evidential argument to be had.

    What about an argument from prior probability? That is, could fine-tuning argument be used in some way to show that God has a high prior probability of existing?

    To determine a prior probability, we have to ask “When it is the case that fine-tuning exists, how likely is it that God was the cause instead of some other possible explanation?”

    We might be tempted to think that the prior probability is low, since naturalistic explanations have proven successful over a long period of time whereas supernatural explanations have a bad track record. However, many believers expect to find a universe that works largely or wholly in accordance with observed laws of the universe. Deists come to mind. And there are others: some believers think God controls everything that happens in the universe, and so observed regularities in the behavior of matter and energy are simply the way God chooses for them to work, and God makes similar choices throughout time and space. One may not find these views plausible or likely to be true, but I don’t want to beg the question by leaving them out.

    So, how might we obtain a prior probability? To use an analogy, if we were doctors with a medical patient who showed symptom A, figuring out a prior probability for which disease was the cause could be done by looking at a large number of solved medical cases in which patients showed symptom A, and how often the symptom was caused by disease X and disease Y. if disease X was at work 70% percent of the time, the prior probability that our new patient has disease X is .7

    I think something along these lines can be done with the fine-tuning argument. Let’s suppose that there is a 50% chance that there is a god and a fifty percent chance that there is not. We can create a fictional representation of what these numbers mean by imagining a dividing line: on one side of the dividing line is a large number of models of what reality would be with a god, on the other side is an equal number of models of what reality would look like if there was not. For the sake of argument, we’ll grant that every model of reality that has a god also has a fine-tuned universe.

    So, if we go back to our fictional set of models and imagine picking fifty random potential models of reality that have a god, collectively those models would have produced fifty fine-tuned universes, possibly more, if God wanted to create them.

    What about the models of reality that don’t have a god? The fine-tuning argument can only give the god hypothesis a high prior probability if it is the case that fifty random atheistic models of reality could be expected to produce far less than fifty fine-tuned universes. If we buy what the fine-tuning argument says thus far, then we must believe that a godless reality would only rarely produce a fine-tuned universe. However, it does not follow from “godless universes are rarely fine-tuned” that “fine-tuning means god.” That would be just as illogical as saying “Luck rarely produces a winning lottery ticket, so this winning lottery ticket I have must have been something other than luck.” In any case, the rarity of fine-tuned universes under atheism means that the only way atheistic models of reality will be likely to produce a fine-tuned universe is if they are expected to contain a huge, huge number of universes with random variations in their laws of physics. Are there any reasons to suppose atheistic realities would have a huge number of universes? Richard Carrier has suggested two reasons which I have adapted and modified from his chapter on design in The End of Christianity:

    1. It is a logical possibility that reality might be filled with many universes, whether or not there is a god. In fact, under atheism, any number of universes might exist, from zero all the way to infinity. If one assumes that all possibilities are equally likely, as the fine-tuning argument does,* then that means that each amount of universes (from zero to infinity) has an equal chance of obtaining. If that’s true, then that means it is nearly 100% certain that there will be a vast, vast number of universes in an atheistic reality. This is so because between zero and infinity the vast majority of numbers are large ones; for example, a googol (which is 10 to the hundredth power) or less universes would represent a large but finite number of possibilities, while the numbers greater than a googol would represent an infinite number of possibilities, and an infinite number is always much larger than a finite number! [Note: Carrier has summarized his argument on his blog here]

    So, regardless of how rare a fine-tuned universe is an atheistic reality, the odds are that there will be one or more, simply because there will be so many universes: if fine-tuned universes are one out of a trillion trillion trillion, that’s no problem, because atheistic realities will usually contain more than a trillion trillion trillion universes, and so at least one will hit the jackpot. You can substitute “a trillion trillion trillion” with whatever number you like, and the conclusion remains the same.

    It should also be the case that the physical constants of these universes will be randomly ordered: if the universes don’t come about through a previous cause, then the only thing to determine what form they will take are the laws of logic. Since the laws of logic allow for all manner of variation in the physical constants (so say fine-tuning proponents) then the universes could have any possible set of physical constants, and with no previous cause to determine what exact value those constants will have, they could just as well have any possible value as any other.

    2. Carrier also brings up the point that Quantum mechanics tells us that random quantum fluctuations might produce another big bang singularity or a concentrated high energy state like the one that in the first moments of the Big Bang’s expansion (which I think is right, from my own understanding of the process). Of course the frequency with which we would expect this to happen is extraordinarily small, it’d be so infrequent that we’d never expect to observe it if we watched the entire universe for a hundred trillion trillion years. Nonetheless, it would happen in time. If an atheistic model has at least a single universe to start with, such a universe in the eternity of time would eventually produce another big bang within itself, if the universe doesn’t already produce baby universes through black holes. The only question remaining is whether a new big bang inside our universe could wind up with different physical constants than the universe it is born in. I personally find it hard to believe that the physical constants would remain fixed. I would think that if it is possible for the physical constants to be other than what they are in our universe presently (as the fine-tuning argument assumes) then there would have to be some possible physical differences in the early moments of the universe that would produce different values for the physical laws, and if that’s so then I’d think that variations in the quantum origin of a universe would produce those. In the absence of any good scientific evidence against that proposal, I think it’s fine for us to favor this assumption, since it seems intuitively correct. After all, someone making the fine-tuning argument can’t hang their case on a counter-intuitive assumption without any evidence or reason to justify making such an assumption. This proposal works out to basically the same result that the previous proposal worked out to: an atheistic reality will contain an infinite number of universes with randomly ordered physical constants, and as such it will produce one or more fine-tuned universes, making it even with the theistic models.

    3. Max Tegmark has written an article on the different multiverse theories in modern cosmology and the evidence for them. While we may not be able to say that any of these theories are more likely than not to be true, we can say that there is a strong possibility than one of these theories is true, as some of them have been tested multiple times (like the Everett interpretation of Quantum Mechanics). So, a universe that looks like ours has a decent chance of being part of a reality that contains many other universes. This consideration, on its own, may not defeat an argument for a high prior probability of fine-tuning by God. But it would weaken it to a very great degree. The calculations behind such reasoning would be largely subjective, but I think it might be arguable that God would have a prior probability greater than 50% if we’re only looking at this consideration and leaving the other two out. That said, I doubt one could argue all the way to the conclusion that the no-god hypothesis has an absurdly small prior probability, certainly not on intuition alone.

    Here’s something else to think about: I’ve chosen to have a one-to-one ratio of godless and god-having realities. Arguably, though, it shouldn’t be done that way. Many atheists have arguments to the effect that it is extraordinarily unlikely a priori that God exists (most notably, the argument to design for the nonexistence of God). If arguments like that one are right, then it’s extremely unlikely that God exists, and the way this would translate into our fictional representation of possible realities would be to have one God-having reality for every billion or so godless realities. If you did it like that, and if you allowed, for example, that one out of every ten thousand godless realities like ours had a giant multiverse, then it would work out that for every one God-having reality, the godless realities would produce upwards of hundred million fine-tuned universes (one billion godless realities, divided by ten thousand so that we can find the fraction of those that have a multiverse, and when there is a multiverse there will be one or more fine-tuned universes, which means there will be at least a hundred million).


    At the present, the fine-tuning argument utterly fails as an evidential argument. As an argument for prior probability, my tentative conclusion is that it is a failure. If we had more knowledge about physics we’d be able to say something about whether the laws of physics can change and whether new big bangs produced by quantum fluctuations might come out with new physical constants so that possibility 2 would work out. But we don’t have that information, and so we can either call agnosticism on this problem or simply fall back on the intuitions we have about these kinds of things in order to see what conclusion we come to. If we claim agnosticism, the fine-tuning argument fails. If we use intuition to take us to some conclusion then it seems to me the fine-tuning argument still fails, and has no chance of success unless updates in our knowledge of physics (and philosophy, as well) were to close the ways in which a godless cosmos can have many universes with random variation.

    Are there any good arguments from design left? I don’t think so. The only things in the physical universe that have left people with an impression of intelligent creation are (1) biological organisms, and (2) the values of physical constants. We have abundant evidence that biological organisms resulted from an unintelligent process of evolution by natural selection, so the biological argument from design fails. As for (2), the anthropic principle ensures that we can’t observe a universe inhospitable to life, so physical constants cannot be evidence of a designer, even in principle. It is at least logically possible to make an argument for the existence of God having a high prior probability on the basis of the physical constants, but there are many problems with attempting to do this.

    It is logically possible that there might have been a really good argument to design. If we found a planet, for example, with the words “God is real” written in every human language on its surface, we could have a really good design argument. We’d have a natural artifact that showed evidence of intelligent creation which could not be the result of evolution by natural selection, and such an observation would not be entailed by the anthropic principle. Of course, no one has ever found anything like this, and we can explain the absence of such design easily under atheism.

    * End note: Fine-tuning proponent Robin Collins lays out how the fine-tuning argument depends on the principle of indifference in The Blackwell Companion to Natural Theology. I suspect the argument could never be made without the principle of indifference, because without assuming all possibilities are equally likely, we wouldn’t have any way at all to estimate how frequently life supporting universes are supposed to be under atheism, it’s not as if we can make observations of how frequently life-supporting universes occur without the existence of God.

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    Article by: Nicholas Covington

    I am an armchair philosopher with interests in Ethics, Epistemology (that's philosophy of knowledge), Philosophy of Religion, Politics and what I call "Optimal Lifestyle Habits."