Open That some of nature’s numbers are sensitive is widely accepted. How sensitive, and what explains it, are open and argued over by physicists and philosophers.
Imagine you are tied to a post in front of fifty trained marksmen. They all fire, and every one of them misses. You are alive. Should you shrug and say, “Well, if they had hit me I wouldn’t be here to wonder about it”? Or should you suspect that something was arranged?
The philosopher John Leslie used this story in 1989 to explain the fine-tuning argument, one of the most discussed arguments for God today. Our science page explains the physics. Here we follow the argument: what it claims, the best replies, and why serious people still disagree.
“Who hath created seven heavens in harmony. Thou (Muhammad) canst see no fault in the Beneficent One's creation; then look again: Canst thou see any rifts? Then look again and yet again, thy sight will return unto thee weakened and made dim.”
Qur'an 67:3–4 · Pickthall (1930)
These verses open the chapter al-Mulk (Sovereignty), which many Muslims recite every night. They do not set out an argument from physics; they invite the reader to look, and to look again. The Psalms, long before, sang their own version: “In wisdom hast Thou made them all; the earth is full of Thy creatures” (Psalm 104:24, JPS 1917).
What the science says, and how the argument works
Physics depends on a handful of numbers that we measure but cannot yet explain, such as the strengths of the forces and the masses of particles. In Just Six Numbers (1999), the Astronomer Royal Martin Rees picked out six that shape the universe. Many physicists have calculated that changing some of them, one at a time, would leave a universe without long-lived stars, without carbon or without chemistry. Our science page explains the examples.
Is it really that delicate? The physicist Fred Adams published a long study in Physics Reports in 2019. He found that stars can work over wide ranges of some constants, and that a universe could even be more friendly to life than ours. Victor Stenger argued in 2011 that changing one number at a time exaggerates the effect, because changes can cancel out. Luke Barnes, an astrophysicist at Western Sydney University, replies that even when many numbers vary together, life-permitting universes remain a tiny region of the possibilities.
In 1973 the physicist Brandon Carter named the ‘anthropic principle’. In its weak form it is a simple truth: we can only ever observe a universe that allows observers. The question is whether that truth explains anything. The firing-squad story is meant to show that it does not: you could not observe being shot, but you would still want to know why you were not.
There is also a technical difficulty. To say a value is ‘improbable’, you need a way to spread probability over all the values it could have taken. For constants with no upper limit, philosophers such as Timothy McGrew, Lydia McGrew and Eric Vestrup argue that this cannot be done, so the probabilities may not mean what they seem to. The Stanford Encyclopedia of Philosophy calls this one of the most serious objections.
Finally, the multiverse. Some versions of cosmic inflation and string theory suggest there may be vast numbers of universes with different values. If so, some would permit life, and we would find ourselves in one of them. No other universe has been observed, and critics say none could be.
The arguments, fairly
Design makes it expected. Philosophers Robin Collins and Richard Swinburne argue that a universe that allows life is far more likely if there is a Designer who values living, thinking creatures than if there is not. On that way of reasoning, fine-tuning counts as evidence for God, even if it is not proof.
The firing squad. John Leslie argued that ‘we would not be here otherwise’ does not remove the need for an explanation. Fifty misses still call for a reason, even if you could only survive to ask about it.
The multiverse does not end the question. Luke Barnes, a Christian, argues that a universe-generating mechanism would itself need finely set laws. And many theists say God could create through a multiverse as easily as through one universe.
Maybe not so fine-tuned. Fred Adams and Victor Stenger argue that the life-permitting ranges are wider than popular accounts say, and that the universe is not especially well suited to life: almost all of it is lethal to us.
A multiverse or a brute fact. Geraint Lewis, Barnes’s co-author, leans towards a multiverse. Others say the constants may simply be what they are, with no deeper explanation, as theists say of God.
Theism predicts nothing in particular. Sean Carroll argues that if God wanted life, God could have made it in any universe at all, so a God would not lead us to expect these particular numbers. He adds that we do not know what kinds of life other universes might allow.
Where it stands
Open. That some features of physics are sensitive is broadly accepted. How sensitive, and whether design, a multiverse or brute fact explains it best, are argued over by able physicists and philosophers. The Stanford Encyclopedia of Philosophy judges it unlikely that new physics will simply make the puzzle disappear.
This argument does not pretend to be proof. Its defenders call it evidence; its critics call it a puzzle that does not point anywhere yet.
One old warning still applies to both sides. Maimonides argued in The Guide for the Perplexed (III:13) that it is a mistake to think the whole universe exists for the sake of human beings. Believers who use fine-tuning today, and critics who mock it, both have to reckon with him.
What each faith says
Judaism
“In wisdom hast Thou made them all; The earth is full of Thy creatures.”
Psalm 104:24 · JPS 1917
The Hebrew Bible praises a world made “in wisdom” (Psalm 104:24), and the book of Proverbs pictures Wisdom present when God “established the heavens” and “set a circle upon the face of the deep” (Proverbs 8:27). A famous midrash, Genesis Rabbah 1:1, compares God to an architect who consults plans before building: God looked into the Torah and created the world.
Jewish thinkers have often been cautious about turning this into a proof. Maimonides saw purpose and order in nature and urged people to study it as a path to love and awe of God, but he warned that we cannot fully know God’s purposes. Rabbi Jonathan Sacks liked to say that science explains how and religion asks why. Fine-tuning, for many Jewish readers, belongs to the ‘why’.
Christianity
“For the invisible things of him since the creation of the world are clearly seen, being perceived through the things that are made, even his everlasting power and divinity.”
Romans 1:20 · WEB
Paul wrote that God’s “invisible things” are “clearly seen, being perceived through the things that are made” (Romans 1:20). William Paley’s watchmaker argument of 1802 drew on living things; Darwin’s theory answered much of it. Fine-tuning is different: it is about the laws and constants of physics, which evolution does not explain.
Christian scientists are themselves divided. John Polkinghorne, the Cambridge physicist who became a priest, called fine-tuning a pointer, not a proof. Luke Barnes argues that a Creator is the best explanation. Others, such as some theologians in the Thomist tradition, are wary of resting faith on any physical argument, in case new physics changes the picture.
Islam
“He unto Whom belongeth the Sovereignty of the heavens and the earth, He hath chosen no son nor hath He any partner in the Sovereignty. He hath created everything and hath meted out for it a measure.”
Qur'an 25:2 · Pickthall (1930)
The Qur’an often speaks of measure. God “hath created everything and hath meted out for it a measure” (25:2, Pickthall), and “Lo! We have created every thing by measure.” (54:49, Pickthall). The Arabic qadar means both measure and decree. The Andalusian philosopher Ibn Rushd set out two arguments for God from nature in the twelfth century: the argument from providence, that the world is suited to human life, and the argument from invention, that living things are made with order.
Muslim scientists such as Nidhal Guessoum take fine-tuning seriously as a source of wonder, while warning against reading modern physics into the Qur’an. Many Muslim scholars stress that the verses invite reflection, tafakkur, rather than offering a scientific proof. Look, says the Qur’an, and look again.
Without religion
“Our planet is a lonely speck in the great enveloping cosmic dark.”
Carl Sagan, Pale Blue Dot (1994) · original English
Non-religious scientists take the puzzle seriously too. Martin Rees, the Astronomer Royal, set out the numbers in Just Six Numbers (1999) and has suggested that a multiverse may explain them. He has no religious belief, though he has said he goes to church out of custom. The physicist Victor Stenger, an atheist, argued in The Fallacy of Fine-Tuning (2011) that the universe is not tuned for us: we are tuned to it, by evolution.
Douglas Adams was a radical atheist by his own description. He told the story of a puddle that wakes one morning and marvels at how perfectly the hole it sits in fits it. Many humanists find the vastness of a universe almost entirely hostile to life humbling rather than troubling. Either way, they say, our home is rare and precious, and worth looking after.
Same and different
Each of the three faiths speaks of a world made with wisdom and measure. Each has thinkers who welcome fine-tuning as a pointer and others who warn against resting faith on it. They share the conviction that order in nature is a reason for gratitude. They differ in emphasis: Christian philosophers have developed the argument most formally; Jewish thought tends to place it under wonder and purpose; Islamic thought speaks of signs and measure. Many non-religious people share the sense that the puzzle is real, and differ on what solves it.
A moment to reflect
- In the firing-squad story, would you want an explanation? Is the universe like that, or different?
- If a multiverse were confirmed, would that make God less likely, or just change the question?
- Should faith rest on arguments from physics at all? What might be lost, and what gained?
- Can a puzzle be real even if it does not point to an answer yet?
We end on a question
If the numbers had been different there would be no one to ask; does that end the question, or is that exactly where it begins?
Watch
A short, even-handed introduction to design arguments and their critics.
Martin Rees, the Astronomer Royal, on why fine-tuning needs explaining and why he leans towards a multiverse.
Luke Barnes, astrophysicist and co-author of A Fortunate Universe, on the philosophy of fine-tuning.
A clear animated guide to the different ideas of a multiverse.
Do it together
Tell John Leslie’s firing-squad story, then vote: does surviving need explaining? Then tell the lottery version (someone has to win). Discuss which story fits the universe better.
Use a free online physics simulator, such as PhET’s gravity or atomic simulations, and change one setting at a time. What breaks first? Talk about what that does and does not tell us about the real universe.
Read Qur’an 67:3–4, Psalm 104 and Romans 1:20 together, then step outside for ten minutes and ‘look again’ at one ordinary thing. Share what you noticed.
Psalm 104 is sung in synagogues at the new moon and read in many churches at harvest. Take it outside and read it aloud verse by verse, pointing at each thing it names: springs, birds, trees, the moon. What would you add?
The Benedicite, ‘O all ye works of the Lord, bless ye the Lord’, is a canticle sung in Anglican and Catholic morning worship. It calls on sun, frost, whales and mountains to praise God. Read it together, then write a modern verse for something science has found since.
Go deeper
- Fine-Tuning (Stanford Encyclopedia of Philosophy) · article
- Adams, The degree of fine-tuning in our universe – and others (arXiv) · paper
- Review of A Fortunate Universe (Notre Dame Philosophical Reviews) · article
- Genesis Rabbah 1:1 (Sefaria) · scripture
- Qur'an 67:1–4 (Quran.com) · scripture
- Maimonides, Guide for the Perplexed III:13 (Sefaria) · book
- Romans 1 (Bible Gateway, WEB) · scripture
- What is humanism? (Humanists UK) · article
Check yourself
Three quick questions. No score, nothing saved.
1. In John Leslie's story, how many marksmen miss?
2. Which three explanations does the page lay out?
3. Who wrote Just Six Numbers (1999)?
Sources (6)
- Rees, Just Six Numbers (1999): Plus Magazine review, 1 Sep 2003
- Adams 2019: stars work over wide ranges; universe could be more life-friendly: Adams, Physics Reports 2019, arXiv:1902.03928
- Stenger one-at-a-time objection; Collins and Swinburne likelihood argument; McGrew, McGrew and Vestrup normalisation problem; Carter 1973; multiverse; SEP judgement on new physics: Friederich, Fine-Tuning, SEP
- Barnes argues for a Creator; Lewis favours a multiverse: Benétreau-Dupin, NDPR, 28 Jun 2017
- Carroll: theism predicts no particular values: Sean Carroll, Post-Debate Reflections, 2014
- Leslie’s firing-squad analogy (Universes, 1989): Friederich, Fine-Tuning, SEP
