The Fine-Tuning Argument for the Existence of God

Author: Thomas Metcalf
Category: Philosophy of Religion
Word count: 987

Here’s a simple experiment to help test whether God exists:

Hold a refrigerator magnet about one inch above a paperclip. If the magnet picks up the paperclip, then that tiny magnet was able to overcome the gravity of an entire planet.[1]

How might this provide evidence that God exists?

Well, if gravity had been as strong as magnetism is now, then you wouldn’t be reading this article, because you never would have existed. The entire universe might just be a huge black hole.

It’s fortunate for us, then, that the physical constants, such as the strength of gravity, have the values they do. Similarly, there are laws of nature that appear to be necessary for our existence.[2]

And a third example of the universe’s being suited for us is its initial conditions, for example, that the universe began in a state with lots of usable energy.[3] Some philosophers and scientists estimate that some of these constants, forces, and conditions couldn’t have varied by more than one part in 1060 (i.e., a one with sixty zeros after it) and still permitted life.

Therefore, perhaps, we should very strongly expect that a universe in which the constants, laws, and conditions formed mindlessly and purposelessly would be one in which life was almost certainly impossible: not just human life, but anything remotely resembling conscious life as we know it.[4] It’s difficult to imagine how any conscious life could be composed of hydrogen alone, or could live in a black hole. And if these facts about the universe are truly universal constants and laws, then if life is impossible anywhere (because of these features), then it’s impossible everywhere.

Arguably, if God exists, then he would intentionally fine-tune a universe’s laws, constants, and conditions so that they permit life like us.[5] A morally perfect God would value life, especially embodied human beings with free will, and so ensure the universe’s physical laws, constants and initial conditions allowed for our existence.[6] This is the basic reasoning behind the Fine-Tuning Argument for God’s existence.[7]

We can summarize the argument as follows:[8]

  1. If God does not exist, then it was extremely unlikely that the universe would permit life.
  2. But if God exists, then it was very likely that the universe would permit life.
  3. Therefore, that the universe permits life is strong evidence that God exists.

Even if that argument is cogent, it doesn’t prove that God exists or that belief in God is justified. For that, we’d need to take into account all the other evidence for or against the existence of God. But the argument does allege to provide powerful evidence for theism.

Critics of the Fine-Tuning Argument, however, have challenged both premises.

Photo from Astronaut Alexander Gerst Aboard The International Space Station
Photo from Astronaut Alexander Gerst aboard the International Space Station

1.      The Probability of a Life-Permitting Universe, Given Atheism

The first challenge argues that a life-permitting universe isn’t improbable, even if there isn’t a God. The three most-popular ways to make this case are as follows.[9]

1.1. The Anthropic Principle

Some objectors argue that it’s not improbable that we would find ourselves in a life-permitting universe, because that’s the only sort of universe we could find ourselves in—otherwise, we wouldn’t exist at all.[10]

One reply: If you were to survive being shot at by a firing-squad of ten expert sharpshooters, you should still be surprised that you survived, even though if they’d killed you, you wouldn’t have been around to notice.[11] So we can still say that something is unlikely, even when, if it had not happened, we wouldn’t have been alive to observe its not happening.

1.2. A Deeper, Fundamental Law

Some suggest that the probability of a life-permitting universe, given atheism, might be much higher than we thought. Perhaps all these constants, laws, and initial conditions are all determined by some deeper, fundamental law, which can only take on a few values.[12]

One reply: Other than this objection’s being a speculative hypothesis, this deeper, fundamental law seems to need its own fine-tuning.[13] Why did we happen to live in a universe that had this deeper, fundamental law at all, instead of having a slightly different deeper, fundamental law, with life-forbidding sets of constants, laws, and initial conditions?

1.3. A Multiverse

Perhaps we live in a multiverse: a set of parallel universes with differing laws, constants, and initial conditions. If so, then it’s not improbable, even given atheism, that at least one of those universes would permit life. And surely if one universe permits life, then we’ll exist in that universe.[14]

One reply: The existence of a multiverse doesn’t raise the probability that this universe (that we’re in right now) would permit life, so it doesn’t really help explain why we would live in such a universe.[15] Think back to the Sharpshooter Analogy: Even if you knew that all over the world, there were many other firing squads shooting at prisoners at the same time, you should still be surprised that you survived. So, the existence of a multiverse doesn’t make it any more likely that our universe would permit life, given atheism.

2. The Probability of Our Universe, Given Theism

The second sort of challenge argues that it’s not really very likely that God would have created a life-permitting universe like ours. Maybe there’s no reason for an omnipotent God to create fragile creatures like us: why not create disembodied minds, and not worry about whether the universe’s constants, laws, and initial conditions permitted physical life?[16]

One reply: perhaps there is something particularly good about the existence of embodied moral agents, who can affect each other’s lives and well-being in predictable ways. Perhaps only physical beings can be seriously harmed and so their acts of free-will are morally significant.[17]

3. Conclusion

There is widespread debate about whether the facts of fine-tuning are evidence for theism. But if the evidence from fine-tuning is a strong as proponents of the argument say it is, then only very powerful evidence against the existence of God could outweigh it.


[1] Collins 2012: §2.3.2.

[2] Ibid., §2.2.

[3] Ibid., §2.4.

[4] Cf. Collins (2012: § 7.4).

[5] Collins 2012: § 5.2.

[6] Swinburne (2004: 168-169).

[7] This is an example of a Design Argument for the existence of God. For a general discussion of such arguments, see Thomas Metcalf’s “Design Arguments for the Existence of God.”

[8] For two of the most-important recent presentations, see Collins (2012) and Swinburne (2004: 172 ff.).

[9] Here I set aside the ‘no probability’ objection (cf. McGrew et al. 2001), according to which we cannot meaningfully assign probabilities when there is only one example (one universe), or when there are infinitely many possible variations between strengths of constants and forces. My reply is that we’re discussing epistemic probabilities, which report the degree to which a person is justified in believing or expecting something. Collins (2012: § 3.1).

[10] See, e.g., Leslie (1989: Ch. 6) and Collins (2012: § 6.1).

[11] Ibid.

[12] Cf. Collins (2012: § 7.2).

[13] Ibid.

[14] Cf. Landsman (2015).

[15] See e.g. White (2000: 271). See also Metcalf (2018) for a more-detailed criticism of the Multiverse Objection.

[16] For example, Philipse (2012: 157) questions both why God would want to create any other minds at all, and why he would want to create physically embodied minds. Here, compare Dougherty and Poston (2008), which examines the interesting relationship between the Fine-Tuning Argument and other design arguments. Metcalf (2018: § VI) considers this objection and argues that it doesn’t seriously threaten the Fine-Tuning Argument.

[17] For this reply, see Collins (2012: § 5.2). See also Swinburne (2004: 99 ff.) for discussion of the value of these embodied moral-agents.


Collins, Robin. “The Teleological Argument,” in Craig, William Lane and Moreland, J. P. (eds.), The Blackwell Companion to Natural Theology (Malden, MA and Oxford, UK: Blackwell, 2012), pp. 202-281.

Dougherty, Trent and Poston, Ted. “A User’s Guide to Design Arguments.Religious Studies 44 (2008): 99-110.

Hacking, Ian. An Introduction to Probability and Inductive Logic. Cambridge, UK: Cambridge University Press, 2001.

Landsman, Klaas. “The Fine-Tuning Argument: Exploring the Improbability of Our Existence.” In Landsman, Klaas and van Wolde, Ellen (eds.), The Challenge of Chance: A Multidisciplinary Approach for Science and the Humanities (Heidelberg: Springer-Verlag, 2016), 111-130.

Leslie, John. Universes. Oxon, UK and New York, NY: Routledge.

McGrew, Timothy, McGrew, Lydia, and Vestrup, Eric. “Probabilities and the Fine-Tuning Argument: A Skeptical View.” Mind 110 (2001): 1027-38.

Metcalf, Thomas. “Fine-Tuning the Multiverse.” Faith and Philosophy 35 (January 2018): 3-32.

Metcalf, Thomas. “Design Arguments for the Existence of God.” 1000 Word Philosophy: An Introductory Anthology. (February 28, 2018).

Philipse, Herman. God in the Age of Science? A Critique of Religious Reason. Oxford, UK: Oxford University Press, 2012.

Swinburne, Richard. The Existence of God, 2nd ed. New York, NY: Oxford University Press, 2004.

White, Roger. “Fine-Tuning and Multiple Universes.” Noûs 34 (2000): 260–76.

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About the Author

Tom Metcalf is an associate professor at Spring Hill College in Mobile, AL. He received his PhD in philosophy from the University of Colorado, Boulder. He specializes in ethics, metaethics, epistemology, and the philosophy of religion. Tom has two cats whose names are Hesperus and Phosphorus. Website:

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