What is the Best Explanation for the Fine-Tuning of the Universe for Life?


By David P. Diaz, Ed.D.


Since the 1950s and 60s, fine-tuning has emerged as a scientific term designating certain constants and quantities that appear necessary for the formation of a universe. Moreover, many have pointed out that the initial conditions of the universe and the constants and quantities of physics exist in such a manner that makes life, especially intelligent life, possible.[1] Thus, fine-tuning has been a topic of increasingly intense scientific, philosophical, and theological interest since the 1970s.[2]

While the term “fine-tuning” was originally a religiously neutral one, the designation now incites great debate between those who see fine-tuning as a design feature and those who think of it as a random characteristic of a naturalistic universe. The former group suggests that the existence of fine-tuning should lead us to believe that some form of intelligence has designed the universe, while the latter believe it to be a necessary yet unremarkable feature of a universe resulting from chance.

The Possibility of Life in the Universe

“Life” means that an organism has the capacity to take in food, extract energy, grow, adapt to its environment, and reproduce. Thus, when scientists talk about a universe being “life-permitting,” they mean that the conditions that give rise to life must exist somewhere in the universe before we can ever observe intelligent life. This doesn’t mean, necessarily, that life will arise, it means only that the conditions exist for it to do so.

The anthropic principle asserts that the observation of intelligent life can only occur in a universe capable of supporting such life in the first place. Since the Earth contains intelligent life (e.g., humans), the universe is obviously life-permitting, and therefore, we shouldn’t be surprised to observe such beings.[3] Nevertheless, a significant question presents itself: What best explains the existence of a life-permitting universe?

What is Fine-Tuning?

Within the context of a life-permitting universe, fine-tuning involves “the claim that the laws of nature, the fundamental parameters of physics, and the initial conditions of the universe are set just right for life to occur.”[4] In other words, certain physical constants and quantities exist within an exceedingly narrow range that favors the appearance of life.

This does not mean, necessarily, that the universe was designed but, rather, as physicist Luke Barnes states: “In the set of fundamental parameters (constants and initial conditions) of nature… an extraordinarily small subset would have resulted in a universe able to support the complexity required by life.”[5]

For illustration purposes, there are three categories of fine-tuning found in the universe: (1) the fine-tuning of the laws of nature (e.g., gravitational force, strong nuclear force), (2) the fine-tuning of the constants of physics (e.g., the gravitational constant G, electromagnetic constant), and (3) the fine-tuning of the initial conditions of the universe (e.g., low entropy state of early universe).[6]

Many have suggested that even the tiniest change to any constants or quantities will result in a universe incapable of supporting life. For example, if the gravitational fine structure constant (i.e., a measure of the strength of the interaction between charged particles and the electromagnetic force) was slightly smaller, existing matter would have expanded too far and rapidly to form stars and planets. Hence, no life could have formed. On the other hand, if the gravitational value was too large, the universe would have collapsed on itself, and the stars would have burned out too quickly to allow the evolution of life.[7] Moreover, if the electromagnetic force did not exist, there would be no complex chemistry.[8] The chemicals essential for life would be too unstable to allow proper bonding, and there would be insufficient carbon and oxygen to support life.

While some believe that the many observed constants and quantities seem finely tuned for developing intelligent life, others have suggested that there is no way to scientifically test the effect of fine-tuning since there is no way to adjust the values to observe the consequences. As physicist Sabine Hossenfelder stated, a fine-tuned universe represents “an observational constraint on our parameters.”[9] In other words, our knowledge of fine-tuning is interesting but is of limited scientific value since the parameters cannot be changed.

With so many views regarding the significance (or insignificance) of fine-tuning, it seems prudent to become aware of the different explanations for fine-tuning. The rest of this paper will discuss three possible explanations (although there may be more) for what appears to be a universe that is incomprehensibly well-suited to support intelligent life.

What is the Best Explanation for a Fine-Tuned Universe?

Virtually no scientists dispute the science behind fine-tuning. What they dispute is what it all means. Three popular explanations for the existence of a fine-tuned universe are (1) the multiverse explanation, (2) the claim that fine-tuning is a brute fact of a universe brought about by chance (i.e., single-universe naturalism), and (3) theism (i.e., the design hypothesis).[10]

The multiverse explanation

The multiverse explanation of fine-tuning proposes the existence of a vast, if not infinite, number of universes with different initial conditions or fundamental boundaries of physics and perhaps even different laws of nature.[11] If there were an endless system of universes, we could expect that at least one universe would be structured to support intelligent “observers.” Thus, we shouldn’t be surprised to find human-like life forms or other embodied conscious agents somewhere in a multiverse. In this scenario, we were randomly selected to live in a universe that supports life.

Evaluation: One problem with the multiverse hypothesis is that no scientific evidence supports it. If multiple universes exist, they are unobservable—without observation and testing, there is no way to generate scientific evidence to support a multiverse hypothesis. One cannot test a hypothesis when no data is forthcoming.

According to physicist Sabine Hossenfelder, any universes outside our own would be “causally disconnected from us.”[12] She concludes: “The vast majority of multiverse ideas are presently untestable, and will remain so eternally.”[13] As a result, the multiverse explanation is not a scientific hypothesis; it is a philosophical (metaphysical) one. Philosophical questions such as this lie outside the purview of traditional scientific methods and must be justified in some other way.

Advocates of the multiverse often posit a universe-generating mechanism to explain the origin of other universes.[14] By postulating a universe generator, proponents think that it may increase the probability of getting a life-friendly universe somewhere in the multiverse.[15] However, the speculative cosmologies that are purportedly responsible for generating multiple universes (i.e., string theory, inflationary cosmology) invoke mechanisms that themselves require fine-tuning.[16] Thus, the multiverse hypothesis cannot explain fine-tuning without appealing to some prior fine-tuning mechanism (either the universe generator or whatever generated the generator).

For example, suppose one tries to explain the design of a car by referring to the assembly plant that produces many similar cars. Such a description doesn’t alleviate the need for an explanation for the design of the car. Indeed, it simply points to the need for an explanation of the design of the assembly line that produces the cars. In other words, it shifts the need for explanation to the next level. The shortcoming of this approach is that it leaves one in doubt about the source of all prior fine-tuning processes and mechanisms and still leaves open the question of why these should be random rather than designed.

Even if a multiverse exists, theism may provide a better explanation than naturalism. An infinite set of universes is better explained by an unbounded cause than a random cause. Since there is no good reason to believe that the multiverse must be randomly caused, and since the universe generator must also be finely tuned, a simpler explanation seems more likely: If a multiverse exists at all, then a single transcendent intelligence designed it to support life.

Single-universe naturalism

Philosophical naturalism is a worldview that asserts that the existence of intelligent life in our universe is the result of chance processes governed by natural laws. There are no design influences, only blind material causes. However, naturalism is unproven scientifically and therefore requires a substantial defense to warrant belief.

Single-universe naturalists claim that there is nothing surprising about the fact that we find ourselves in a universe with rational beings because nothing else is possible. Only in a universe that supports life can there be beings capable of observing and reflecting upon fine-tuning. Single-universe naturalists see life in the universe as a brute, inexplicable fact that requires no further explanation. Nobody would be alive to comment on fine-tuning if the universe weren’t life-permitting in the first place. Thus, the existence of human observers is unremarkable.

If one assumes in advance that the fine-tuning found in the universe is the result of chance, then any arrangement of matter is equally improbable (or probable), and there is no reason for one to ask why or how we exist. Naturalists who see fine-tuning as a brute fact say we don’t need to search for a deeper explanation: The universe “just is.”

Evaluation: First, to say that fine-tuning “requires no further explanation” is a matter of opinion. Undoubtedly, many people seek deeper explanations than are readily available. And to say that human existence is “unremarkable” is, at best, arguable. Second, to justify one’s belief that a fine-tuned universe is merely a brute fact, one must know in advance that the universe is solely the result of chance. In other words, one must assume the truth of philosophical naturalism (henceforth, “naturalism”).[17] However, mere assumptions are not self-justifying. To prove that naturalism is true, one must develop and present good reasons to justify such a belief.

Nevertheless, the assumption of naturalism receives no help from science because naturalism is not a scientific position; it is a philosophical one. To merely assume the truth of naturalism amounts to nothing more than a “naturalism-in-the-gap” belief.[18] Thus, single-universe naturalism is a belief that requires evidence and arguments to demonstrate the rationality of naturalism.

When scientists (or anyone else) assume the truth of philosophical naturalism, they naturally begin to reject anything and everything that does not fit their predetermined viewpoint. As candidly admitted by evolutionary biologist Richard C. Lewontin (1997), many people take the side of naturalism simply because of a prior commitment:

It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated.[19]

The design hypothesis

For many theists, it is unsurprising that the universe is fine-tuned for intelligent life. After all, if an intelligent being wanted to create a world where intelligent life exists, it seems reasonable that it would set the initial conditions and physical constants of the universe to favor that outcome. A finely tuned universe—one that supports intelligent, self-reflective, rational beings—is perfectly consistent with a theistic explanation. It is a coherent and simple explanation that need not appeal to unnecessary conjectures (e.g., the multiverse) to support its case.

Theists (specifically monotheists) have historically believed that God created the universe and populated it with all forms of life including intelligent life. This has inspired many theists, as well as non-theists, to seek answers to the “how” question through the study of biology, chemistry, and physics. To theists, fine-tuning leads one to look for an ultimate explanation for the universe and its many features. In a theistic world, the Designer could have used any number of methods to ensure the establishment of intelligent life, including a fine-tuned single universe or a multiverse.

Evaluation: Like the multiverse and chance hypotheses, theism cannot be proven scientifically. In other words, the theistic explanation is not a scientific position but a philosophical one. Nevertheless, many philosophical/theological arguments favor theism, while naturalism has few if any, positive arguments. Therefore, the success of theism depends on demonstrating why it explains fine-tuning better than the other two hypotheses.

Theism receives support in the form of various arguments including, the cosmological argument, the moral argument, the ontological argument, the teleological argument, and many others. Before a theist can be justified in believing that a designing intelligence is responsible for a fine-tuned universe, he must first show that one or more of the arguments for the existence of God are likely to be true while also showing that the multiverse and chance explanations lack sufficient credibility.


Although each of the three explanations offered in this paper is consistent with a fine-tuned universe, none of them can explain fine-tuning with absolute certainty. Nevertheless, the design hypothesis suggests that the exquisitely fine-tuned constants and quantities of the universe favor the influence of a designing intelligence. If true, then the design hypothesis indirectly supports theism but doesn’t at all support naturalism. Moreover, there is no shortage of arguments for the existence of God, each of which may add philosophical weight to the design hypothesis. On the other hand, both the multiverse and chance hypotheses are doubtful. Neither is supported by scientific evidence, and both lack philosophical arguments to support their foundational beliefs.

According to physicist John Polkinghorne, the universe has possessed the potential for life since the Big Bang because of fine-tuning.[20] But, one may ask, “Why is the universe finely tuned?” Polkinghorne states that the universe’s vast collection of finely tuned parameters is too precise to be a “happy accident.” He concludes that fine-tuning leads us past brute facts and toward a context of “deeper intelligibility.”[21] The late English astronomer Fred Hoyle may have said it best: “A commonsense interpretation of the facts suggests that a super-intellect has monkeyed with physics, as well as with chemistry and biology.”[22]

About the author

David P. Diaz, Ed.D., is an independent researcher, retired college professor, and publisher of Things I Believe Project. His writings have spanned the gamut from peer-reviewed technical articles to his memoir, which won the 2006 American Book Award. Dr. Diaz holds a Bachelor’s and Master of Science degree from California Polytechnic State University, a Master of Arts in Philosophical Apologetics from Houston Christian University, and a Doctor of Education specializing in Computing and Information Technology from Nova Southeastern University.

[1] Stephen C. Meyer, “What is the Evidence for Intelligent Design and What Are Its Theological Implications?” in The Comprehensive Guide to Science and Faith: Exploring the Ultimate Questions about Life and the Cosmos, ed. William A. Dembski, Casey Luskin, and Joseph M. Holden, (Eugene, OR: Harvest House Publishers, 2021), 143.

[2] For two classic works on fine-tuning, see Brandon Carter, 1974, in IAU Symposium, Vol. 63, Confrontation of Cosmological Theories with Observational Data, ed. M. S. Longair (Boston: D. Reidel Pub. Co.), 291; and B. J. Carr, and Martin J. Rees, “The anthropic principle and the structure of the physical world,” Nature. 278 (5705): 605–612, 1979.

[3] William Lane Craig, “Excursus on Natural Theology Part 15: The Teleological Argument,” Reasonable Faith, Defenders Class: December 18, 2015, https://youtu.be/pQHnG07r9jw.

[4] Robin Collins, “The Fine-Tuning of the Cosmos: A Fresh Look at Its Implications,” in The Blackwell Companion to Science and Christianity, ed. B. Stump and Alan G. Padgett (Blackwell Pub., 2012), 207.

[5] Luke A. Barnes, “A Reasonable Little Question: A Formulation of the Fine-Tuning Argument,” Ergo, an Open Access Journal of Philosophy 6, no. 42 (2020): 1220–57, https://doi.org/10.3998/ergo.12405314.0006.042, 1220.

[6] Robin Collins, “What Does a Fine-Tuned Universe Mean?” Closer to the Truth video, September 8, 2015, https://youtu.be/o_oIkBdA3Q4.

[7] Alister E. McGrath, Science & Religion a New Introduction, 3rd ed. (Hoboken, NJ: Wiley, Blackwell, 2020), 200–201.

[8] Collins, “What Does a Fine-Tuned Universe Mean?”

[9] Sabine Hossenfelder and Luke Barnes, “The Fine-Tuning of the Universe: Was the Cosmos Made for Us?” Premier Unbelievable? YouTube video, https://youtu.be/5OoYzcxzvvM.

[10] Robin Collins, “Modern Cosmology and Anthropic Fine-Tuning: Three approaches,” in Holder R., Mitton S. (eds) Georges Lemaître: Life, Science and Legacy. (Astrophysics and Space Science Library, vol 395, Springer, Berlin, Heidelberg, 2012), 173.

[11] Ibid., 174.

[12] Sabine Hossenfelder, Lost in Math: How Beauty Leads Physics Astray (New York, NY: Basic Books, 2020), 101.

[13] Ibid., 107.

[14] Meyer, “What is the Evidence for Intelligent Design and What Are Its Theological Implications?” 148.

[15] Ibid.

[16] Ibid.

[17] Philosophical naturalism is a materialistic/naturalistic philosophy that asserts that nothing that is supernatural, or transcendent to the space-time universe, exists. In other words, the natural world is the whole of reality. Philosophical naturalism should not be confused with methodological naturalism. 

[18] By naturalism-in-the-gap, I am referring to a position where one merely assumes the truth of naturalism or takes a position that, given enough time, we will eventually see a naturalistic solution to a problem that currently lacks a solution. This would also be an assumption.

[19] Richard C. Lewontin, “Billions and Billions of Demons,” The New York Review of Books website (January 9, 1997). Retrieved July 14, 2023, from https://www.nybooks.com/articles/1997/01/09/billions-and-billions-of-demons/.

[20] As cited in William Lane Craig and Chad Meister, eds., God Is Great, God Is Good: Why Believing in God Is Reasonable and Responsible (Downers Grove, IL: IVP Books, 2009), 68.

[21] Ibid., 70.

[22] Fred Hoyle, “The Universe: Past and Present Reflections,” Annual Review of Astronomy and Astrophysics 20, no. 1 (1982): 1–36, https://doi.org/10.1146/annurev.aa.20.090182.000245.

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