Does the Puddle Analogy Explain Cosmic Fine-Tuning?

Is the universe fine-tuned for human existence? If so, how do we know it and is such design intentional?

One definition of the anthropic principle states that humanity’s existence places severe constraints on the physical constants and structure and history of the whole cosmos, and specifically on the Milky Way Galaxy, the solar system, Earth, and Earth’s early life.1 Another definition is that the presence of intelligent observers (beings capable of measuring astronomical bodies and phenomena) requires that multiple characteristics of the universe and the laws of physics fit within certain narrowly limited fine-tuned ranges.

Fine-Tuning and the Fine-Tuner
Fine-tuning requires a shaping source. The greater the degree and pervasiveness of fine-tuning, the more capable must be the fine-tuner. Therefore, pursuing evidence of cosmic fine-tuning for the specific benefit of humanity holds profound personal and philosophical significance.

If the observed fine-tuned designs prove to be of little or no consequence, then one could surmise that no intentionality is implied. On the other hand, if the observed fine-tuning is multifaceted and each facet is crucial for making human existence possible, then the fine-tuning source must be more than a mindless, impersonal force or process. The more numerous, specific, and purposeful the fine-tuned requirements, the more these required features reveal about the characteristics and identity of the fine-tuner.

Is Cosmic Fine-Tuning Real?
Not everyone agrees, however, that cosmic fine-tuning is real. Many allege the design is mere anthropomorphism or anthropocentrism. They contend that the observed cosmic fine-tuning is akin to a puddle noting that the hole in which it finds itself is perfectly fit for it. So, the puddle concludes that someone must have precisely manufactured the hole specifically for it.

This puddle argument against cosmic fine-tuning and the implied cosmic fine-tuner dates back at least 50 years to Douglas Adams but has become especially popular in the twenty-first century. I encountered it from one of the anonymous peer reviewers of my recently published paper, “Black Holes as Evidence of God’s Care.” (Open access to the paper is here. Open access to the peer reviewer’s critique is here.) In that paper (and in my book The Creator and the Cosmos2), I cite rebuttals to the puddle argument published by philosophers William Lane Craig3 and Richard Swinburne.4

Problems with “Puddle Thinking”
A few weeks ago, Australian astronomers Geraint Lewis and Luke Barnes published what, in my opinion, is the most eloquent and lay-accessible rebuttal to the puddle argument.5 They begin by giving the puddle the name Doug. Doug the puddle observes an exact match between his shape and the shape of the hole in which he dwells. Doug concludes that Someone must have designed the hole just for him. What Doug fails to realize is that given the fluidity of the water, the solidity of the hole, and the force of gravity, he will always take on the identical shape of his hole. Lewis and Barnes point out the obvious: any hole will do for a puddle.

The puddle analogy for humanity’s existence in the universe is fatally flawed. The two astronomers explain that not every conceivable universe will do for physical life. Physical life is not like a fluid. It will not and cannot adjust to any universe. The fine-tuning that astronomers observe indicates that even very slight alterations to the universe’s characteristics would rule out the possible existence of physical life. For human life, and especially for global human civilization, the constraints on the universe’s characteristics are exponentially more fine-tuned.

Figure: Hot Spring in Yellowstone National Park
Image credit:
Hugh Ross

Characteristics of the Fine-Tuner
Lewis and Barnes conclude that the fallacies in the puddle argument imply that the cosmic fine-tuning that astronomers observe cannot be dismissed as unworthy of our attention. Such features are of utmost importance. Lewis and Barnes suggest the fine-tuner could be a divine mind or a programmer desiring to simulate an interesting universe.

I see an opportunity to proceed further. The degree of fine-tuning will inform us on how intelligent, knowledgable, and powerful is the divine mind or transcendent programmer. Looking beyond the universe as a whole and the laws of physics to explore the fine-tuning of our supercluster of galaxies, our galaxy cluster, our galaxy group, our galactic neighborhood, our star, our planetary system, our moon, and our planet will reveal the extent of the fine-tuning and whether or not the fine-tuning is specific to our species on Earth. These factors have the potential to determine a lower limit to the divine mind’s care and love for our species.

Deepening our exploration of the degree and extent of cosmic fine-tuning likely will reveal multiple purposes for the fine-tuning. When I wrote Why the Universe Is the Way It Is in 2008, I posited 11 distinct purposes for why the divine mind manufactured the universe in the manner that he did. Today, we can identify several more. These distinct purposes tell us much about the characteristics, attributes, and plans of the divine mind. I am particularly impressed that the case for cosmic fine-tuning and a personal, all-powerful, all-loving divine mind is powerfully manifested in a purposeful context. That context is that the features and histories of the universe, the Laniakea Supercluster, the Virgo Cluster, the Local Group, the Local Bubble, the Local Fluff, the Sun, the solar system, the Moon, and Earth must be fine-tuned for billions of humans to possess the opportunity to be eternally redeemed within just thousands of years. Given the fine-tuning evidence, it seems inescapable that the divine mind must be the Creator God of the Bible.


  1. Brandon Carter, “Large Number Coincidences and the Anthropic Principle in Cosmology,” IAU Symposium 63, Krakow, Poland: Confrontation of Cosmological Theories with Observational Data (Dordrecht, Netherlands: D. Reidel Publishing, 1974): 291–298; John D. Barrow and Frank J. Tipler, The Anthropic Cosmological Principle (New York: Oxford University Press, 1986).
  2. Hugh Ross, The Creator and the Cosmos, 4th ed. (Covina, CA: RTB Press, 2018), 153–163.
  3. William Lane Craig, “Barrow and Tipler on the Anthropic Principle vs. Divine Design,” British Journal for the Philosophy of Science 38 (1988): 389–395, doi:10.1093/bjps/39.3.389.
  4. Richard Swinburne, “Argument from the Fine-Tuning of the Universe,” in Physical Cosmology and Philosophy, ed. John Leslie (New York: Macmillan, 1990), 165–166.
  5. Geraint F. Lewis and Luke A. Barnes, “The Trouble with ‘Puddle Thinking’: A User’s Guide to the Anthropic Principle,” Proceedings and Journal of the Royal Society of New South Wales
    154, no. 1 (June 2021), forthcoming.