A Beginner’s Guide to the Fine-Tuning Argument

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In the past few decades a broad consensus has emerged among physicists that a number of aspects of the physical cosmos appear to be ‘fine-tuned’ for life, which is to say, various aspects of its basic structure and of the fundamental laws that govern it are balanced on a knife-edge. If any of them had differed by only a very tiny amount, the universe would not have been capable of supporting life at all. Some of these ‘fine-tuned’ features of the universe are such that had they differed only very slightly, the universe would not even have contained galaxies and stars, let alone complex conscious creatures like ourselves.
There are many specific examples of fine-tuning.[1] Let’s look at just a couple. It’s been estimated by physicists that if the strength of gravity were different by just one part in 1060, there could be no stars and galaxies. A tiny bit stronger and all the matter would have collapsed back in on itself; a tiny bit weaker and the matter would have spread out too quickly for anything like galaxies or stars to be able to form. Another example is what’s known as the cosmological constant. The cosmological constant governs how fast space itself expands or contracts. A tiny bit too strong and the universe would have collapsed back on itself; a tiny bit too weak and the universe would have expanded too quickly for galaxies to be able to form. It’s estimated that the chance of the cosmological constant having a value that would permit life is roughly 1 in 1053.
To be sure, whilst physicists are broadly agreed that the universe exhibits fine-tuning, they don’t agree on the interpretation of this fact. Is it evidence that an intelligent mind stands behind the cosmos? Or does it even call our for explanation at all? These sorts of questions, I would suggest, fall not within the domain of physics but of philosophy.
Here’s one reason that someone might suggest that fine-tuning doesn’t call out for any explanation at all: “If the universe hadn’t been fine-tuned for life then we wouldn’t be here to notice that fact; there’s no other kind of universe we could have observed other than a fine-tuned universe; and so we shouldn’t be surprised to find ourselves in a fine-tuned universe.” The philosopher John Leslie has responded to this objection by way of an analogy.[2] Suppose that you’re about to be executed by a firing squad made up of fifty of the world’s finest marksmen. Each one of them has a live round in his rifle, and each of them has a fantastic aim. They raise their rifles, take aim, and fire, but to your amazement, you’re still alive — every single one of them has missed.
Obviously, you’d think, “this cries out for explanation; there must have been a setup; they must have all missed on purpose.” But suppose someone said to you, “Actually, you shouldn’t be amazed, after all, if the marksmen hadn’t all missed then you wouldn’t be here to wonder about it.” This is a flawed line of reasoning. It’s true that the only scenario you could witness is one in which the marksmen all miss. But the fact that they all missed is very improbable given the hypothesis that they all intended to kill you, and so you should look for another hypothesis to account for what happened. Similarly, it’s true that the only kind of universe we could observe is one which is fine-tuned, but the existence of a fine-tuned universe is very, very improbable given the hypothesis of sheer chance, and so we should look for another hypothesis.
What other hypotheses are on the table? One is that the fine-tuning of the universe is not the result of chance, but rather, the deliberate choice of a rational mind who stands behind the universe. Let’s call this the design hypothesis. But recently another hypothesis has received considerable attention. This is the multiverse hypothesis. The multiverse hypothesis postulates that our universe isn’t the only one, but that instead there exists a whole vast ensemble of universes, differing from one another with respect to their fundamental laws of physics and initial conditions. Given enough universes, the thought goes, at least one of them will have physical laws and initial conditions which make possible the emergence of life.
So the question is: does the multiverse hypothesis account for fine-tuning at least as well as the design hypothesis? The philosopher Robin Collins has written extensively on this question, suggesting that the multiverse hypothesis faces the following dilemma.[3] Either the multiverse is unrestricted — containing every logically possible universe — or it is restricted — containing only some of the logically possible universes. If the multiverse is restricted, then there remains an unanswered question about why the multiverse contains this set of universes rather than any other set, and so the fine-tuning problem is simply pushed up a level. On the other hand, if we appeal to an unrestricted multiverse to explain fine-tuning, this poses serious problems for the very idea of scientific explanation. In a nutshell, the problem is that if the unrestricted multiverse hypothesis is true, then every event that is logically possible is 100% probable — that is, if something is logically possible, then it actually happens somewhere in the multiverse. Suppose you roll a die 100 times and it lands on six every time. Normally, we would regard such an event as calling for an explanation in terms of the die being rigged. But if the unrestricted multiverse hypothesis is true, everything that is logically possible actually occurs, and that includes a fair die landing on six 100 times in a row. It seems like whenever something very surprising happens, the explanation will always just be “oh well, everything that is logically possible actually happens in an unrestricted multiverse, so don’t worry about it.” And that spells the end of scientific investigation. In short, the multiverse hypothesis has serious flaws that render it doubtful whether it really does rival the design hypothesis.
Finally, it’s important to note the limitations of the fine-tuning argument. Just taken on its own, the fine-tuning argument doesn’t show that the God of the Bible exists. But it does, arguably, give a fair amount of support to the hypothesis of an extremely powerful and extremely wise designer, and as such, the fine-tuning argument can form part of a wider cumulative case for Christian theism.



Dr Max Baker-Hytch received his doctorate in Philosophy from Oxford University in 2014. He is Tutor in Philosophy at Wycliffe Hall, Oxford University. He is also Senior Academic Tutor at the Oxford Centre for Christian Apologetics.

Further reading:

Neil Manson (ed.), God and Design: The Teleological Argument and Modern Science (London: Routledge, 2003)
John Hawthorne and Yoaav Isaacs, “Fine-Tuning Fine-Tuning,” in Knowledge, Belief, and God: New Insights in Religious Epistemology (Oxford: Oxford University Press, 2018)
Robin Collins, “The Teleological Argument: An Exploration of the Fine-Tuning of the Universe,” in The Blackwell Companion to Natural Theology, ed. William Lane Craig and J. P. Moreland (Oxford: Blackwell, 2012)

[1] For an overview, see Martin Rees, Just Six Numbers: The Deep Forces that Shape the Universe (New York: Basic Books, 2000)
[2] John Leslie, “Anthropic Principle, World Ensemble, Design,” American Philosophical Quarterly, 19 (1982), pp. 141-51.
[3] Robin Collins, “The Teleological Argument: An Exploration of the Fine-Tuning of the Universe,” in The Blackwell Companion to Natural Theology, ed. William Lane Craig and J. P. Moreland, (Oxford: Blackwell, 2012)