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, physicists have pointed out that the initial conditions of the universe and the constants and quantities of physics are finely tuned to make life possible.[1] Fine-tuning has been a topic of increasingly intense scientific, philosophical, and theological interest since the 1970s.[2] Indeed, this subject has incited 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 a Cosmic Fine Tuner has designed the universe to support intelligent life. The latter group sees fine-tuning as a necessary yet unremarkable feature of a universe (or multiverse) resulting from chance.

The Possibility of Life in the Universe

“Life” involves the capacity of any organism 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 these capacities must exist before we can observe intelligent life.

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

What is Fine-Tuning?

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 must exist within an exceedingly narrow range to support life.

“Fine-tuning” is a neutral term. It does not mean 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]

There are three types of fine-tuning found in the universe: (1) the fine-tuning of the laws of nature (e.g., gravity), (2) the fine-tuning of the constants of physics (e.g., the gravitational force constant, electromagnetic constant), and (3) the fine-tuning of the initial conditions of the universe (e.g., low entropy state).[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 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 in the universe, others have suggested that there is no way to scientifically test the effect of fine-tuning since we cannot adjust the values to observe the consequences. As physicist Sabine Hossenfelder stated, a fine-tuned universe represents “an observational constraint on our parameters.” In other words, our knowledge of fine-tuning is interesting but is of limited scientific value since the parameters cannot be changed.[9]

With so many views regarding the significance (or insignificance) of fine-tuning, it seems prudent to become aware of the different explanations suggested for fine-tuning. The rest of this paper will discuss three possible explanations 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?

The three most popular explanations for the existence of fine-tuning in the universe are (1) the multiverse explanation, (2) the claim that fine-tuning is merely 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.

Evaluation: One problem with the multiverse hypothesis is that no scientific evidence supports it. If multiple universes exist, they are unobservable, and without observation and testing, there is no way to generate scientific evidence for a multiverse hypothesis. In other words, if we cannot observe other universes, there is no way to scientifically test the validity of the 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.

As noted above, scientific evidence cannot support the multiverse theory since the question of a multiverse is outside the realm of science. Nevertheless, even if a multiverse existed, theism may provide a better explanation than naturalism.

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.[15] However, the speculative cosmologies that are purportedly responsible for generating other universes (i.e., string theory, inflationary cosmology) invoke mechanisms that 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). The shortcoming of this approach is that it leaves one in doubt about the source of all prior fine-tuning processes and mechanisms.

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 entity (i.e., God) designed it to support life.

Fine-Tuning as a Randomly-Generated Feature of a Single Universe

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 this 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. As we will see, the fact that there is intelligent life in the universe is indeed extraordinary.

Second, to justify one’s belief that a fine-tuned universe is merely a brute fact or the product of chance, one must already know that the universe is solely the result of chance. In other words, one must assume the truth of philosophical naturalism (henceforth, “naturalism”).[17] If one knows that no transcendent causes or entities exist, then it is plausible that the universe is a result of chance. However, mere assumptions are not self-justifying. To prove that naturalism is true, one must develop good reasons to justify such a belief.

However, the assumption of naturalism receives no help from science because naturalism is not a scientific position; it’s a philosophical one. To merely assume the truth of naturalism amounts to nothing more than a “naturalism-in-the-gap” belief.[18] Thus, the chance hypothesis requires evidence or arguments demonstrating the rationality of a belief in naturalism.

Philosophical naturalism is a worldview that asserts that the existence of intelligent life in our universe (and any other existing universes) 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. While it is also true that theism cannot be proven scientifically, many philosophical/theological arguments favor theism, while naturalism has few, if any, supporting arguments.

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 Theistic Explanation

Although some theists reject fine-tuning, it is not necessary to do so. Indeed, for many theists, it is unsurprising that the universe is fine-tuned for human life. After all, if God set the natural processes in motion, then fine-tuning for intelligent life is a reasonable outcome. Therefore, a finely tuned universe that supports intelligent, self-reflective, rational beings is perfectly consistent with a theistic explanation (i.e., creation by a Super-intelligent Being).

Theists have historically believed that God created the universe, which has inspired them 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 universe.

Evaluation: Like the multiverse and chance hypotheses, the theistic explanation is not a scientific position but a philosophical one. Therefore, its success depends on demonstrating why theism explains fine-tuning better than the other two hypotheses.

The theistic explanation receives support from various arguments from natural theology, including the kalam cosmological argument, the moral argument, the ontological 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.

Does Other Life Exist in the Universe?

Many think it is a matter of time until we find intelligent life elsewhere in the universe. This principle has led many to adopt a view called the Copernican presumption of mediocrity. This popular position asserts that humans on Earth “are just typical of life forms throughout our galaxy and the universe.”[20]

Based on the presumption of mediocrity, we should find evidence of other rational beings in the universe, if not now, then in the future. Indeed, we know quite a lot about the potential for intelligent life from our privileged viewpoint within the universe.[21] However, the evidence for the existence of rational beings outside of Earth has not been promising.

After studying thousands of exoplanets,[22] scientists report that none have exhibited conditions sufficient to predict the emergence of life with high confidence.[23] For example, some exoplanets display extreme, elliptical orbits, while others contain giant planets orbiting very close to their stars. Says astrophysicist Howard Smith: “There will be no civilization if a star is too large or too small, if a planet’s orbit or obliquity is wrong, [or] if its size or chemical composition is unsuited.”[24] Moreover, Smith notes that the probabilities of “biological” factors related to the development of life are “very uncertain, and astronomy provides no new evidence to evaluate them.”[25]

Four essential conditions are related to the suitability of a planet to sustain life: “stability, habitability (including the presence of water), planetary mass, and planetary composition.”[26] Smith indicates that all these lines of evidence “argue strongly against the assumption of mediocrity.”[27] He concludes: “The prospects of finding ETI [extraterrestrial intelligence] remain (at best) low….The message of modern research is not that we are ordinary, but the opposite: we appear to be quite extraordinary.”[28] Thus, the current state of cosmology continues to beg for an explanation of why the finely tuned parameters necessary to support life have resulted in intelligent life on Earth but not elsewhere.


In conclusion, 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, which indirectly supports theism. Moreover, there is no shortage of arguments for the existence of God, each of which may add philosophical weight to the “God 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.[29] But this begs the question: “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.” Fine-tuning leads us past brute facts and toward a context of “deeper intelligibility.”[30] 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.”[31]

About the Author

David P. Diaz, Ed.D., is an author, 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 either 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.

[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] Ibid., 500.

[21] To learn how and why the Earth is ideally positioned to study and decipher the universe, see Guillermo Gonzalez and Jay Wesley Richards, The Privileged Planet How Our Place in the Cosmos Is Designed for Discovery (Washington, D.C.: Regnery Pub., 2004).

[22] Our most recent knowledge of the possibility of other intelligent life comes from the study of thousands of exoplanets (i.e., planets outside our solar system), which consist mostly of earth-sized planets revolving around stars like ours (5,462 confirmed exoplanets as of July 5, 2023). Note: NASA keeps a running total of the number of exoplanets on their website: https://exoplanets.nasa.gov/. These numbers change frequently.

[23] The Drake equation is a set of factors that can be used to estimate the probability of life in our galaxy. The equation is the product of five criteria that include: (1) the number of suitable stars, (2) the number of suitable planets around such a star, (3) the probability of life developing on a suitable planet, (4) the probability that life evolves to be intelligent and (5) the typical lifetime of a civilization compared to the lifetime of its star. See Smith, “Alone in the Universe.”

[24] Howard Smith, “Alone in the Universe,” Zygon 51, no. 2 (June 5, 2016): pp. 497-519, https://doi.org/10.1111/zygo.12256, 506.

[25] Ibid., 505.

[26] As cited in Ibid., 504.

[27] Ibid.

[28] Ibid., 509, 517.

[29] 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.

[30] Ibid., 70.

[31] 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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