Once more unto the breach, dear friends. (Another long fine-tuning post, I’m afraid …)
An oft-cited article on the fine-tuning of the universe for intelligent life was written by Michael Ikeda and Bill Jefferys, and goes by the title: “”The Anthropic Principle Does Not Support Supernaturalism”. It appears online here, and
to the best of my knowledge has not been published anywhere has been published in “The Improbability of God“, edited by Michael Martin and Ricki Monnier (edit: 3/11/2010).
Unless otherwise noted, quotes are from Ikeda and Jefferys (hereafter IJ). Their central argument is as follows. Let:
L = The universe exists and contains Life.
F = The conditions in the universe are ‘life-Friendly,’ that is, the conditions in our universe permit or are compatible with life existing naturalistically.
N = “The universe is governed solely by Naturalistic law.” The negation, ~N, is that it is not governed solely by naturalistic law, that is, some non-naturalistic (supernaturalistic) principle or entity is involved. N and ~N are not assumptions; they are hypotheses to be tested.
L is, of course, true of our universe. For the sake of argument, IJ assume that F is true. N and ~N are taken to have an a priori non-zero probability of being true. Now, the anthropic principle roughly states that living observers must observe conditions that permit the existence of observers. IJ formulate this as:
N appears in the expression just in case a supernatural agent decides to miraculously sustain life in a non-life-friendly universe.
Now, after dealing with the fallacious1 argument , IJ reach their Bayesian climax:
Thus, the fine-tuning of the universe for intelligent life is at best irrelevant to the truth of naturalism, and could actually make it more likely. The fine-tuning of the universe, even if it is true, cannot support supernaturalism. Notice that all probabilities are conditioned on L. As IJ say:
… for an inference to be valid, it is necessary to take into account all known information that may be relevant to the conclusion. In the present case, we happen to know that life exists in our universe (i.e., that L is true). Therefore, it is invalid to make inferences about N if we fail to take into account the fact that L, as well as F, are already known to be true. It follows that any inferences about N must be conditioned upon both F and L … In inferring the probability that N is true, it is entirely irrelevant whether P(F|N) is large or small. It is entirely irrelevant whether the universe is “fine-tuned” or not. Only probabilities conditioned upon L are relevant to our inquiry.
I have two responses. Here I will contend that IJ’s formulation of the argument is incomplete. In the second part, I’ll raise a few issues with this “conditioning on everything” idea.
Here is how I would (roughly) formulate the argument from fine-tuning. Let the “physics” of a universe refer to its laws + initial conditions + physical constants. Let a “universe” be a connected region of spacetime over which physics is effectively constant2. We consider life to be a class of physical phenomena – we won’t need a precise definition. I will drop the ampersand in my notation, i.e. , and typesetting will distinguish my premises from IJ’s. Let:
= this universe contains life
= the physics of this universe includes conditions sufficient for the eXistence of life
= the physics of this universe includes conditions sufficient for the evolution of life
= the natural phenomena of this universe are the causal products of the physics of this universe. (Remember that “physics” includes initial conditions in my terminology.)
= the causes that established the physics of this universe were indifferent to whether our particular physics would allow the survival (evolution) of life.
= in the set of possible physics, the subset that permit the existence (evolution) of life is very small. In other words, the physics of a particular universe must be fine-tuned if that universe is to support the existence (evolution) of life. (I won’t be too worried by the difference between and here.)
The anthropic principle then states: . (2)
A few words on the difference between my formulation and IJ’s.
- The difference between and is clears up a misconception in IJ. They argue that intelligent design advocates simultaneously affirm that the universe is and is not “life-friendly” – Ross says that the universe is so life-friendly that God must have set it up, while Behe says that the universe is not life-friendly so God must have created life supernaturally. But this is simply confused. Ross argues from and , Behe from (“not-E”). In other words, Ross is saying that it’s a miracle to have a stable planet orbiting a stable star in a long-lived universe stocked with atoms that are able to form complex structures. Behe, on the other hand, argues that these conditions are not sufficient to produce all the complexities of life as we know it. Ross and Behe may be mistaken, but they are not contradicting each other.
- IJ’s “N” slightly misses the point. The question is whether physics is fine-tuned and what we can conclude from this, not whether there are any exceptions to the laws of nature3. A deist could affirm that “the universe is governed by naturalistic laws”, and still conclude that fine-tuning is evidence of a cosmic designer of those laws. As a result, the fine-tuning of the universe is a test of the hypothesis , rather than .
- The important observation in the context of this argument is not . The claim that the universe is fine-tuned for intelligent life is more than a claim about this universe. It is a counterfactual claim about how things could have turned out. is almost certainly true – it follows almost inevitably from , which is true. , however, does not follow from .
We can now formulate IJ’s argument in my terminology.
This shows that, given that life exists in this universe, the fact that the physics of this universe includes conditions sufficient for the existence of life makes it not less likely that the continued existence of life is within the causal powers of the physics of this universe. That was a horrendous sentence. In short, life exists. We then learn that physics of the universe is capable of sustaining life. This possibly makes it more likely that life is sustained purely by physical means, without supernatural intervention.
This is all fine, but it has nothing to do with fine-tuning. At best, it could show that the hypothesis that angels push the planets around in their orbits becomes less likely once we learn that Newton’s laws of motion and gravitation can do the job. (Though, as Richard Feynman pointed out, perhaps Newton only showed that the angels push radially rather than tangentially.) It says nothing about what we can conclude from the fact that, if the universe were not three-dimensional, Newtonian gravity would produce unstable planetary orbits.
What we really want to know is the ratio:
Note that we are conditioning on – it is one of the strengths of the argument that we are not appealing to supposed phenomena that are beyond the powers of physical laws.
What effect does the anthropic principle (2) have on ? Using the general principle: for any such that , it follows from (2) that:
Thus, (3) becomes (using Bayes theorem again):
Further, if the life-permitting region of possible-physics-space is small, then it is small independently of whether the physics of our universe is effected indifferently or not. Thus, , which implies:
Putting all together gives:
Then, we argue as follows:
i) Because the life-permitting subset is very small, an indifferent physics-producing process is very unlikely to hit upon a life-permitting universe. This would include simply positing physics as a brute fact. Thus, . (As IJ tell us, is generally not equal to 1, even if we have observed that is true).
ii) There are possible hypotheses under which the physics of this universe is effected with “life in mind”. For the union of all such hypotheses (i.e. ), is not small.
iii) Thus, .
We conclude that learning has increased the probability that whatever set in place the physics of our universe was not indifferent to whether our universe could support life.
None of this proves that is true:
- We could still conclude that is very small or inscrutable, derailing the argument.
- The argument above assumes that this universe is the only universe. As IJ note (and I agree), can also be taken as evidence for a multiverse.
- There are non-supernatural hypotheses consistent with . In “At Home in the Universe” (and elsewhere), John Wheeler argued for the participatory anthropic principle – from the centrality of observership to quantum mechanics (“no elementary phenomenon is a phenomenon until it is a registered phenomenon”), Wheeler proposes that the universe is like a self-excited circuit: “beginning with the big bang, the universe expands and cools. After eons of dynamic development it gives rise to observership. Acts of observer-participancy … in turn give tangible “reality” to the universe not only now but back to the beginning”. The laws of nature are “higgledy-piggledy [built] out of the statistics of billions upon billions of acts of observer-participancy”. Paul Davies favours similar ideas in “The Goldilocks Enigma”. These are admittedly very unorthodox ideas, but they do show that is broader than theism …
- Philosophical arguments from fine-tuning to the existence of God (usually) recognise that is not enough. For example, Swinburne argues that intelligent, moral agents are a kind of entity that God would want to create. Collins has a similar discussion, arguing that at the very least, the conjunction + “only this universe exists” is strongly disfavoured by the fine-tuning of the universe, leaving the atheist (almost all of whom affirm ) needing to produce independent reasons for believing that a life-permitting multiverse exists.
- Of course, could turn out to be false or unknowable.
Note that running the entire argument through assuming instead of doesn’t change much. Equation (3) still holds with this replacement. If anything, the region of possible-physics-space that allows the evolution of life is even smaller than the region that merely allows the existence of life, strengthening our conclusion.
In conclusion, it is possible that the fine-tuning of the universe supports some type of supernaturalism, contrary to the claim of IJ that it is impossible. Whether it actually does is a question for another day. In part 2, I’ll raise a few queries about IJ’s insistence that we condition on everything we know.
1. Which might be a straw man – they don’t cite anyone who actually makes this error, and I’m not aware of any such case. In fact, they don’t cite any of the fine-tuning literature except for Hugh Ross.
2. Footnote: we may wish to stipulate that any observer observes only one universe by definition. These finer points will not effect our discussion.
3. It is possible (i.e. I’m still thinking it through) that the sentence, “a sufficiently powerful supernatural principle or entity (deity) could sustain life in a universe with laws that are not “life-friendly”, simply by virtue of that entity’s will and power” is self-contradictory. In a theistic universe, the laws of nature simply are the way that God runs and sustains the universe. The laws of nature themselves exist “by virtue of that entity’s will and power”. God logically cannot make a consistent exception to the laws of nature – the exception would become the rule. (This doesn’t a priori rule out singular exceptions i.e. miracles). It follows that we don’t need to appear in the anthropic principle i.e. .
More of my posts on fine-tuning are here.