Theists commonly argue that we live on a cosmological knife-edge. Numerous physical constants are said to be so vital to our existence that even the slightest change in any one of them would have produced an eternally lifeless, barren cosmos. If the gravitational constant, for example, had been scaled up or down by only a miniscule factor, or the electromagnetic or cosmological constants perturbed in the slightest, life as we know it could never have come into being.¹ Theologians and religious apologists contend that the probability of the universal constants taking on the exact values needed to sustain life is so low that they could only have been tuned just so by an intelligent agent, who, presumably, must also have called the universe itself into existence.² This, in a nutshell, is the essence of the cosmological fine-tuning argument. Yet, when closely considered, the notion of a universe fine-tuned for humanity leaves theists with more questions than answers.

How Do You Quantify Fine-Tuning?

One of the biggest problems with the fine-tuning argument is that the extent of fine-tuning is, at least presently, utterly impossible to measure. In order to estimate the probability that a given universe could sustain life, one needs at least two pieces of information: first, the number of possible universe configurations; and second, the number of such configurations that are conducive to the development of life, however one may define it.³ Since neither of these quantities is known, no discussion of fine-tuning can begin without a frank acknowledgement that the key premise of the fine-tuning argument is entirely speculative.

Nevertheless, frequent attempts have been made to present the fine-tuning argument in quantitative terms. These attempts have produced a wide range of dubious, and largely inconsistent, results. Often, their underlying assumptions are characterized by shocking failures of the imagination; some, for example, rely upon the conjecture that only carbon- based life is possible; others investigate the effect of changing just one cosmological parameter at a time, while keeping all others fixed, and thereby deny themselves almost the entire space of possible parameter values.⁴

The Anthropocentric Bias

Implicit in the theistic argument for fine-tuning is the belief that the universe was created with humanity in mind as its ultimate end product. Therefore, those advocating this view must not only make the case for a universe fine-tuned to allow for the existence of atoms, molecules, stars, and life; they must argue that the universe was tailored specifically for humans. Hence, the fine-tuning argument cannot be successfully made without simultaneously making a cosmological case for human exceptionalism. This is the ultimate hubris, and the deepest flaw in the argument.

The universe is approximately 13.8 billion years old. Humanity is believed to have evolved to roughly its present form around 200,000 years ago, so our species has existed for only 0.0015% of the age of the universe. From this perspective it is difficult to imagine how one could place humanity at the center of any credible universal narrative. Indeed, if the universe was created with biological life in mind, jellyfish would seem to be a more plausible object of divine attention than our own belated species, given that jellyfish have been around for hundreds of millions of years before humans ever saw the light of day.

Moreover, in terms of both space and time, the vast majority of the cosmos is not merely inhospitable, it is outright hostile to human life. The observable universe, which comprises all the matter and energy that can be seen from our planet, is around 10⁷⁰ cubic miles in volume. Generously estimating the habitable volume of the Earth to be 10⁹ cubic miles,⁵ this means that only one part in 10⁶¹ of the universe is known to be amenable to life (that’s a 1 followed by 61 zeros!). By way of comparison, this is less than the ratio between the volume of a proton and that of our entire solar system.

As well, humans account for merely one part in ~10⁴¹ of the matter in the universe by mass, but even matter itself is far from being the dominant constituent of the cosmos. The universe is overwhelmingly made up of dark energy (~70%) and dark matter (~25%). Ordinary matter makes up a paltry 4–5% of the cosmos, and we, a less-than infinitesimal sliver even of that.⁶ The vast disparity between the human and cosmic scales hardly substantiates the notion of human exceptionalism that is endorsed by theists in the context of fine-tuning. It rather suggests that humanity is, at best, little more than a cosmic speck.

Fine-Tuned for Light

For centuries, physicists have known that nature has a proclivity for disorder. In the absence of outside influence, any physical system in the universe will tend to grow less organized over time. Imagine dropping a cube of salt into a glass of water. Before reaching the water’s surface the salt is arranged in a well-organized crystal, with all of its component sodium and chlorine atoms nestled neatly against one another in a regular pattern. Upon immersion, however, order gives way to chaos and the cube begins to dissolve, as sodium and chloride ions are dispersed throughout the glass in a completely disordered jumble of solvent and solute molecules.

The physical measure of disorder is known as entropy, and the principle of ever-increasing entropy is so well supported by theory and experiment that it is now referred to as the Second Law of Thermodynamics. In essence, the Second Law predicts that the universe of tomorrow will be less orderly—and therefore more entropic—than the universe of today. This has significant cosmological consequences; applied in reverse, it suggests that the universe was far more organized at its birth than it is today. It also means that day-by-day, the universe is working its way towards a state of increasingly higher disorder overall. The prevailing view among cosmologists is that the universe will eventually become so disordered that life, as we know it, will one day cease to be possible.

The inexorable increase in entropy is expected ultimately to result in the transformation of all matter in the universe into a disorganized mix of photons, electrons and neutrinos, whizzing about at random through a vast, and otherwise empty cosmos. There is no room for humans—or, indeed, for life, or interesting structures of any kind—in this terminal state. Yet this, the theologian will insist, is the picture of a universe fine-tuned with humanity in mind as its ultimate end product.

What isn’t There

What would the universe look like if it had been created and fine-tuned from the start with humanity in mind? Certainly, one would expect that the vast swaths of the cosmos that are unnecessary for our existence would be absent. It could be argued that the existence of solar systems other than our own might serve to test believers’ faith to some extent, but the presence of hundreds of billions of completely separate galaxies beyond the Milky Way appears superfluous. The history of the universe up to humanity’s appearance on the scene should also be much more brief—after all, an omnipotent deity could surely conjure a species into existence instantaneously, without consuming the eons of evolutionary time apparently required under the current plan.

If the universe had been fine-tuned for humanity, one might also expect the study of nature to cause scientists to incline more toward faith, not less. This point in particular is one of the more remarkable failures of the theistic argument: as science reveals to us more and more about the world, theistic models of reality increasingly appear so implausible that they must be amended to conform to new discoveries. Too often we forget that the Judeo-Christian position, which was once generally accepted, placed the Earth at the center of the universe, with Heaven and Hell beyond a sphere of fixed stars. Until Charles Darwin’s time, theists held that the origin and diversity of life were best explained by the account of Creation rendered in Genesis. For this reason, from the theistic standpoint it is all the more deplorable that scientists are disproportionately and increasingly irreligious.⁷

Finally, if the universe was fine-tuned for human life by a thoughtful designer, one must acknowledge the appalling inefficiency of the creation process. For one thing, it has been estimated that about 99.9% of all species have gone extinct.⁸ God must therefore be credited with an act of destruction that is as monumental as his mass extinction caused by the global flood. One might be led to wonder why a benevolent and omnipotent deity should be unwilling or unable to fashion a species in his own image, without first preparing the way by eradicating countless lesser ones. God must, then, have created the vast majority of species with the intention of wiping them out well before any biblically relevant timeframe. The pain and suffering experienced by the last dinosaurs as they died from a mixed agony of starvation and thirst 65 million years ago is merely one such example among millions.

All in all, there is no doubt that the discussion surrounding the nature and extent of universal fine-tuning is far from settled. That said, the universe could well have been fine-tuned, but if so it was almost certainly designed without us as its final purpose. Taking a “God’s eye view” of the universe ironically reveals the astronomical scale of our insignificance.

About the Authors

Jérémie Harris is a Ph.D. student in quantum photonics under the Canada Excellence Research Chair in quantum nonlinear optics, at the Max Planck University of Ottawa Centre for Extreme and Quantum Photonics. He holds a Master’s degree in biological physics from the University of Toronto. His work addresses foundational questions and paradoxes in quantum mechanics, and the creation of exotic structured matter waves.

Edouard Harris is a Vanier Scholar and Ph.D. candidate in theoretical and experimental biological physics at the University of Toronto. His research is aimed at applying Bayesian inference techniques to the design and creation of synthetic biological systems.