Along with the cosmological argument, the design argument is one of the oldest philosophical arguments for the existence of God. It moves from the seemingly purposeful features of the natural world to the existence of a supernatural designer of that world. Unlike the cosmological argument, the design (or “teleological”) argument relies on data from the sciences. Prior to Darwin, this data came primarily from terrestrial biology. Up through the nineteenth century it was widely held that organisms and their parts could not have arisen naturally — that only the supreme artifice of a benign Creator could account for the eyes of the eagle and the hands of the human. Though philosophers objected to the inference from apparent design to God’s existence (David Hume’s Dialogues on Natural Religion is a tour de force), there really was no good non-supernatural explanation of the apparent design of organisms. Then Darwin proposed evolution by natural selection, and biological design arguments were deemed refuted. They have re-emerged on occasion in the 150+ years since the publication of On the Origin of Species. Notably, so-called “Intelligent Design Theory” got a great deal of attention starting about 25 years ago, though it has waned as a movement due to unfavorable court rulings regarding the teaching of it in U.S. public schools. But, for the most part, design arguments from terrestrial biology have been abandoned by serious theists.
Despite the success of evolutionary biology in explaining biological complexity, however, an important question about life remained unanswered. Why is the universe the sort of place in which life can even arise? The universe might have been such that complex life could not have evolved anywhere at any time. It might have collapsed back in on itself moments after the Big Bang. It might have been far too hot. Its matter might have been too diffuse. Yet the “cosmic parameters” — the particles, forces, and constants that determine the universe’s general structure and delimit what is possible in it — are such that there is enough time and material for life to arise through a long evolutionary process. Why?
The physicists who initially explored these questions in the twentieth century made a surprising discovery: the numbers describing the universe seem adjusted to perfection. They compared getting a life-permitting universe to finding the just-right spot on an old-style radio. The dials of the universe are turned just so, away from the static of lifelessness and perfectly centered on the music of being. How should we explain this seeming “fine-tuning”? Perhaps there is no explanation and it is just a fluke. Design proponents reject that idea. There is an explanation, they say. Cosmic fine-tuning implies the existence of a Tuner. This “fine-tuning argument” for the existence of God is perhaps the most popular philosophical argument for God’s existence nowadays.
To understand the fine-tuning argument more fully we must dip our toes into modern physics and cosmology. Consider first particle physics. Quarks, leptons, and bosons are thought to be the most basic of all particles. They constitute the protons and neutrons that, with electrons, make up the atoms that make up the molecules that make up the biochemical building blocks of all life. These fundamental particles have very exact characteristics. There are precise numbers describing them and the forces governing them. These numbers seem completely arbitrary. Why, for example, is the mass of the proton 1.67262 thousandth of a trillionth of a trillionth of a kilogram? For all we know, its mass could have been totally different. Likewise, the universe as a whole has very exact characteristics. Its average temperature is -270.42 Celsius, its age is 13.8 billion years (+/- 20 million years), and its current rate of expansion is 74 kilometers per second per megaparsec. Why exactly those numbers? Right now, there is no theory or approach that tells us that those exact values have to be what they actually are.
And yet, these cosmic parameters taking those precise values is often a requirement for the universe’s being hospitable to life. For example, the cosmological constant (symbolised by the Greek letter “”) is an essential cosmic parameter. It is a crucial term in Einstein’s equations for the General Theory of Relativity. When is positive, it acts as a repulsive force, causing space to expand. When is negative, it acts as an attractive force, causing space to contract. If the value of were not precisely what it is, either space would have expanded at such an enormous rate after the Big Bang that complex objects would never have had a chance to form, or the universe would have collapsed back in on itself immediately after the Big Bang. Either way, life could not possibly have emerged anywhere in the universe. Some calculations put the odds that took a life-permitting value at well below one chance in a trillion trillion trillion trillion.
Similar calculations have been made showing that the odds of the universe’s having the right kind of stars for life are also unimaginably low. Consider that every molecule in your body contains elements that were formed within the interior of a star through nucleosynthesis. Carbon, oxygen, iron, calcium — none of these elements existed at the beginning of the universe. They all came to exist only after the stars formed them and then ejected them at their deaths. If the universe did not have the sorts of stars that engage in the process of nucleosynthesis, then there would be no carbon, no oxygen, no iron, no calcium — and so no life like ours anywhere in the universe.
To grasp just how astounding this fine-tuning is, compare the luck involved in getting a life-permitting universe to winning the Range Game on the long-running U.S. television show “The Price Is Right.” [You are encouraged to look at one of the many video clips of the Range Game on YouTube; the game perfectly illustrates the dynamics of fine-tuning.] Contestants try to win a prize by guessing at the actual retail price of the prize. A range of possible prices is pre-specified in order to make winning easier. For example, a $150 winning range (indicated by a clear red shield) might start at $3100 and slide its way up, possibly to the top price of $3700. When contestants think the actual price of the prize falls within the $150 range, they press a button to stop the sliding shield. If the actual price falls within the $150 range, the player wins the prize.
What if the winning window on the Range Game were narrowed to one penny? And what if the contestant had to bid, not on a modest prize, but on all of the gold in the Bank of England, its cash value calculated down to the last penny? The odds of winning that game are over a trillion to one. Suppose this game really were played, but just once, and the first contestant won it. Would you attribute the result to good luck? Of course not. You would suspect the game was rigged.
Proponents of the fine-tuning argument apply the same line of thinking to the life-conduciveness of the universe. The exceptional improbability of getting a universe that allows for the evolution of life indicates that the result was consciously chosen rather than random. Whoever or whatever did the selecting must exist outside of the universe, have immense knowledge and power, and want there to be life. That certainly sounds like God. And that, in short, is the fine-tuning argument for the existence of God.
Note the conception of God’s creative activity that is implicit in the fine-tuning argument. God did not specially create life in a discrete miraculous act, contrary to the opening verses of the Book of Genesis. Instead, God selected the very structure of the physical universe from amongst an array of possibilities, choosing to bring into real existence one in which life would evolve on its own in some place at some time. Since the creation of the physical universe is not itself something that happens within the physical universe, and since the laws of nature only apply to what happens within the physical universe, making a universe that is just right for life violates no laws of nature. Proponents of the fine-tuning argument can say that, far from denying science, they fully respect its integrity and universality. In particular, they can say that they in no way reject modern evolutionary biology. That is, they believe in “theistic evolution.” Theistic evolutionism gives its adherents a way to say both that God is the Creator and that modern science fully explains the events inside the universe. Consonance with theistic evolutionism accounts for a good deal of the popularity of the fine-tuning argument amongst scientifically literate theists today.
If life is not specially created by God, what about human life? Is it, too, wholly the product of evolutionary forces, or was there some special act of God along the pathway to human life? If the former, does that mean we lack souls? If the latter, is that not just the sort of miracle belief in which theistic evolutionists eschew? These are very difficult questions for theistic evolutionists. Yet how to answer them will be peculiar to each theistic tradition, and so these questions lie outside the scope of this essay. So, too, do scientific objections to the fine-tuning calculations themselves. [Some reputable physicists maintain that the calculations behind the fine-tuning claims are largely mistaken and that life-permitting possible universes are far less rare than advertised.] Furthermore, generic objections to theism as an explanation — of why there is anything at all, of why the universe is fine-tuned for life, of why we ought to be moral — are so numerous, various, and old that they cannot be surveyed without writing a separate article. In the remainder of this essay, let us focus instead on the most common objection to the fine-tuning argument. It is that there is a perfectly good explanation of cosmic fine-tuning for life that does not bring God into the discussion at all.
The fine-tuning argument rests on the assumption that our universe is the only one. Some physicists deny this. They say that the existence of other universes is a natural consequence of much of contemporary physics. According to “the multiverse hypothesis”, there is some mechanism for the production of a vast number of universes. [Suggested mechanisms include “chaotic inflation”, “bubble universes”, and “oscillating universes”.] These universes vary randomly in their basic characteristics. Most of them are duds — for example, they recollapse a few milliseconds after the Big Bang. But there are enough of them to make it likely that at least one has just the right conditions for the evolution of life. The reason the cosmic parameters in our universe are just right for life is that we could not observe them to be otherwise. We must not neglect “observational selection effects” when thinking about cosmic fine-tuning for life.
An observational selection effect is any factor that filters an experience of yours based on the need for you to meet certain conditions in order for you to have that experience. For example, if you have ever watched a parkour video, you may have wondered “How is it that all of those daring young people completed all of those amazing stunts?” The wonder diminishes when you change the question to “How is it that I am observing a video of all of those daring young people completing all of those amazing stunts?” Once you frame the question that way, the answer is clear. The daring young people you see are taking a lot of video of themselves trying to get it right. The failures do not end up on the parkour videos. Only the successes do. That is, a precondition for ending up on a parkour video is that the attempted stunt is completed successfully. If the attempt is not a success, you do not see it.
According to what is called “the anthropic principle”, there is an observational selection effect acting upon us when we engage in physics, astronomy, and cosmology. We are guaranteed to observe that the universe meets whatever conditions are necessary for there to be life in it, simply because if the universe did not meet those conditions, we would not be around to observe it. Awareness of this observational selection effect should guide our attempts to understand the significance of the observed fine-tuning for life of the cosmic parameters. According to proponents of the multiverse hypothesis, if there are many other universes, then probably at least one of them is just right for life. Only a universe that is just right for life will ever become “ours” for intelligent inhabitants like us. Keeping the anthropic principle in mind, we will realise that within the multiverse, a fine-tuned universe is the only kind of universe we could possibly observe. Thus given the truth of the multiverse hypothesis, observing our universe to be fine-tuned for life is not at all surprising. Just as the seeming design of the eyes or the wings of an eagle can being explained in terms of natural selection operating over immensely many, immensely varied organisms, the seeming design of the universe itself can be explained in terms of observational selection acting against the background of immensely many, immensely varied universes.
Do we have any independent evidence for the existence of the multiverse? Defenders of the fine-tuning argument (as well as some neutral observers) say we do not. They say that the multiverse hypothesis is unscientific because it is untestable. Some go so far as to say that the multiverse hypothesis was dreamed up by irreligious physicists simply to avoid the obvious conclusion that God exists. It is, they claim, the last resort of the desperate atheist. Yet defenders of the multiverse hypothesis respond that it is perfectly scientific and that it is possible to gain observational evidence of the existence of other universes. Survey evidence gathered by this author indicates that the relevant scientific experts — cosmologists — do take the multiverse hypothesis very seriously as a scientific idea. They judge that physicists have developed the multiverse hypothesis, not out of a desire to deprive theists of a good argument, but because the multiverse hypothesis is a natural consequence of widely accepted aspects of the best current theories in physics. Even if no one were making the fine-tuning argument, they would still be developing multiverse models. Furthermore, for the most part the cosmologists surveyed regard the multiverse hypothesis as scientifically testable, either now or in the future. If the multiverse hypothesis is a fully respectable scientific hypothesis, we have a plausible alternative explanation of cosmic fine-tuning for life. That would greatly reduce, if not wholly eliminate, the force of the fine-tuning argument for the existence of God.