Questions Does God exist?The fine-tuning of the universe: too perfect a coincidence?

Does God exist?TheismTeleological (design)

The fine-tuning of the universe: too perfect a coincidence?

The fine-tuning argument

Robin Collins born 1961The constants of physics are fine-tuned for life: this is evidence of design.

What it claims

The fine-tuning of the universe is strong evidence for the existence of a designer, God (evidence, not proof: it must still be weighed against the rest).

Why

A universe fine-tuned for life is far more likely if God exists than in a single universe without a designer, where it would be luck.

The same idea through history

William Paley1802Natural Theology: a watch found on the ground implies a watchmaker. Paley starts from living things (the eye), not yet from the laws of physics.

John Leslie1989Universes: he gathers the examples of fine-tuning and argues, with the firing-squad story, that they call for an explanation (design or many universes).

Richard Swinburne2004The Existence of God (2nd ed.), ch. 8: the laws and starting conditions of the universe make the evolution of human bodies probable, which is far more to be expected if God exists than if he does not.

Robin Collins2009"The Teleological Argument" (after a 1999 essay): the most worked-out probabilistic form, based on the likelihood principle, with a long reply to the multiverse.

In short

"The fine-tuning of the universe: too perfect a coincidence?" is an argument by Robin Collins (Collins, "The Teleological Argument" (2009); "The Fine-Tuning Design Argument" (1999), 2009) on the question "Does God exist?" (answer: theism). Its claim: The fine-tuning of the universe is strong evidence for the existence of a designer, God (evidence, not proof: it must still be weighed against the rest). According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P5). AskPhilosophy presents 5 objections, 5 of them with a documented reply, and the original text behind each premise, checked word for word.

Collins, "The Teleological Argument" (2009); "The Fine-Tuning Design Argument" (1999)

Valid with an implicit premise

Since the 1970s, physicists have noticed that several basic numbers of physics (the strength of gravity, the masses of particles, the energy of the vacuum) and the starting state of the universe seem to have to fall within a very narrow range for stars, varied atoms and therefore life to be able to exist. This is called "fine-tuning". For example, according to the physicist Sean Carroll, himself an opponent of the argument, the vacuum energy is tuned to one part in 10 to the power of 120. Robin Collins draws a careful argument from this: he does not say that fine-tuning proves God, but that it is strong evidence, like fingerprints on a weapon. A universe suited to life is not surprising if a good God wanted it; it is extremely improbable if there is only one universe, with no one behind it. The exact extent of fine-tuning is debated among physicists, and the value of the argument among philosophers.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.

Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, the computer finds a situation where everything else is true: fine-tuning does favour God over the chance of a single universe, but another explanation (for example a very large number of universes) explains it just as well. Fine-tuning is then not evidence for God rather than for that other explanation.

The computer confirms that the argument is valid with P5, and invalid without it. Collins himself concludes only that fine-tuning favours God over a single universe with no designer; he deals with the multiverse and the other explanations separately. To move on to "it is evidence for God", full stop, P5 is therefore needed: no other explanation does better. That is where the multiverse objection aims. The debate also concerns P3: can one speak of the probability of the constants, and does our own existence distort the calculation? (anthropic principle, selection effect, normalisation problem). P2 is less discussed, but some ask how we could know what a God would want to create.

Analogy. This is Collins's example. On Mars, explorers find a dome where everything is set up for life: temperature, air, water, food. No one would say volcanoes produced it by chance. A designer makes this dome very probable; chance makes it almost impossible. Collins argues that the universe resembles this dome.

Objections

Each objection is a conversation: click to see who replies and where the debate stands.

Brandon Carter (the anthropic principle) 1974 · attacks premise 3

In 1974 the physicist Brandon Carter formulates the "anthropic principle": what we can expect to observe is restricted by the conditions necessary for our presence as observers. Critics of the argument draw an objection from it: there is nothing surprising in observing a universe fine-tuned for life, since in another universe we would not be there to observe it. Fine-tuning would therefore call for no explanation.

Collins replies

John Leslie 1989 · The firing squad

A condemned man stands before a firing squad of expert marksmen. They all fire, and they all miss. It would be absurd for him to say: "Nothing surprising: had they not missed me, I would not be here to notice." It is true that he can only observe his survival; but his survival remains very improbable by chance, and it calls for an explanation (for example, the marksmen meant to miss). The same goes for fine-tuning.

Robin Collins 1999

The argument can be restated in terms of our own existence. That living, intelligent beings exist is extremely unlikely if there is only one universe with no designer, since our existence requires fine-tuning. But it is not improbable if God exists.

The debate goes on (our summary) Many philosophers, even unbelievers, judge that Leslie's reply defeats the simple version of the objection ("nothing surprising, since we are here"). But Elliott Sober built a more refined version, the "observation selection effect", which argues that the firing-squad case and the fine-tuning case are not alike: see the last objection.

Where the debate stands (our summary)Few philosophers still defend the simple version of the objection ("nothing surprising since we are here"). The debate has moved to Sober's version, below: what should count as already known when calculating probabilities.

Brandon Carter (the "world ensemble"), then defenders of the multiverse 1974 · attacks premise 5

In the same text, Carter considers a "world ensemble": a very large number of universes, with every possible combination of constants. If there are enough universes, it is normal for a few of them to allow life, and we necessarily find ourselves in one of them. This is the multiverse hypothesis, which several physicists defend today. It would explain fine-tuning without a designer, just as a lottery winner is explained if there are millions of players.

Collins replies

Robin Collins 1999 · Who tuned the universe generator?

A multiverse needs a "universe generator", and this generator itself obeys complex physical laws. If those laws were slightly different, it would probably produce no habitable universe. Even a bread machine has to be built just right to work, and it produces only bread, not universes. The multiverse therefore does not remove fine-tuning: it pushes it up one level.

Richard Swinburne 1996 · Ockham's razor

Between two explanations, the simpler one should be preferred. Supposing an immense number of other universes in order to avoid supposing one God, is far less simple: Swinburne judges this choice irrational.

See the rest of the debate (3)

Sean Carroll 2012

The multiverse is not a theory invented to escape fine-tuning: it is a prediction of theories (cosmic inflation, the string theory "landscape") put forward for other reasons. What one posits is not universes but physical laws; if they are simple, the number of universes they produce does not make them less simple.

Roger White 2000 · The inverse gambler's fallacy

Summary: White argues that concluding "there are probably many universes, since ours is fine-tuned for life" commits the inverse gambler's fallacy, described by Ian Hacking in 1987: seeing a double six does not make it probable that the dice were thrown many times before. What must be explained is that THIS universe allows life; and the existence of other universes does not make that more probable.

Neil Manson and Michael Thrush 2003

Summary: Manson and Thrush answer that White's objection is no better than the parallel "this planet" objection: a large number of planets would not explain either why THIS planet is habitable, and yet it does explain why we find ourselves on a habitable planet. They also fault White for assuming that we could not have existed in another universe.

The debate goes on (our summary) The debate continues on two points. First, these theories (inflation, strings) are not yet confirmed by experiment. Second, Carroll himself grants that the multiverse does not explain everything: the starting state of the universe seems far more finely tuned than life requires. Theists see support in this; Carroll replies that it is a bigger problem for the God hypothesis than for the multiverse, and that the explanation will have to come from the detailed properties of the multiverse.

Where the debate stands (our summary)Open point: the multiverse is taken seriously in physics but is not confirmed. The basic disagreements concern its simplicity compared with that of God, the tuning of its "generator", and whether one can move from the multiverse to the explanation of THIS universe (the inverse gambler's fallacy).

Richard Dawkins 2006 · attacks the conclusion

"Who designed the designer?" A God able to fine-tune a universe would himself be at least as complex, and so even more improbable than what he is meant to explain. Invoking God solves nothing: it moves the problem up one level. (See Dawkins's argument, "the ultimate Boeing 747".)

Collins replies

see the argument

Robin Collins 1999 · Collins's reply (written in 1999, against the same objection in Smith and Smart)

The objection only touches another version of the argument, the one that says all organised complexity needs an explanation. Mine only requires that fine-tuning be more probable if God exists than if there is only one universe with no designer. That remains true even if God is inwardly far more complex than the universe.

The debate goes on (our summary) The two sides answer each other at different levels. Collins speaks of what fine-tuning makes more probable; Dawkins speaks of the starting probability of the God hypothesis. Collins grants this: his argument does not say, on its own, that God is probable all things considered. Theists add (Swinburne) that God, a being of unlimited powers, is a very simple hypothesis; critics dispute this.

Where the debate stands (our summary)Collins and Dawkins are talking about different things: what fine-tuning makes more probable, or the starting probability of the God hypothesis. The basic disagreement concerns the simplicity of that hypothesis, which Swinburne asserts and his critics dispute. The rest is in Dawkins's argument.

Timothy McGrew, Lydia McGrew and Eric Vestrup 2001 · attacks premise 3

To say that a constant has "very little chance" of falling in the right range, one must spread the chances over all possible values. But these values run from zero to infinity. On an infinite line, if all values have the same chances, every finite range has zero chance, and the total does not add up to 1: no probability can be defined. And if one ignores this, the argument would work even for a huge range: the narrowness of the range, which gives it all its force, would no longer count.

Collins replies

Robin Collins 2009

The life-permitting range should only be compared with the set of values that current physics really allows us to study (the "illuminated region"), which is finite. And even for an infinite line, the rule that forces the total to add up to 1 by summing infinitely many small ranges is questionable: without it, the argument holds.

Timothy and Lydia McGrew 2005

When the only non-arbitrary spread of chances violates the rules of probability, the most reasonable thing is to suspend judgment: one is not obliged to assign a probability to everything.

The debate goes on (our summary) The question remains open. Restricting the comparison to the "illuminated region" makes the calculation possible, but critics ask why that region should be the right one. It is a technical difficulty, but it touches the heart of P3.

Where the debate stands (our summary)Open point: the technical problem of normalisation has no solution accepted by all. Defenders restrict the comparison to a finite region; their critics judge this choice arbitrary and propose suspending judgment.

Elliott Sober (the observation selection effect) 2004 · attacks premise 3

An example from the astronomer Eddington: I fish with a net whose holes are 10 inches wide, and all the fish caught are bigger than that. I learn nothing about the lake from this, since this net could not catch anything else. Likewise, we could only observe constants favourable to life, whatever their origin. Our observation is filtered: so it cannot decide between design and chance. (Objection put forward in 2004, refined in 2009.)

Collins replies

Jonathan Weisberg 2005 · Weisberg's reply (himself not a theist)

Weisberg also rejects the design hypothesis, but he judges Sober's objection to be mistaken. Applied to the firing squad, it would force the prisoner to reject an obviously correct conclusion. Sober's error concerns what should count as already known when calculating probabilities. Properly understood, our observation of fine-tuning is not rendered uninformative by a selection effect.

Elliott Sober 2009

Sober grants that Weisberg and others convinced him: about the firing squad, he had been wrong. But he maintains that fine-tuning is different. For the prisoner, being alive when the squad fires does not guarantee that he will see himself alive afterwards: the outcome still depends on the shot. For us, being alive is enough to guarantee that we will observe favourable constants, whatever their origin: our existence filters the observation.

The debate goes on (our summary) The debate is not settled. It turns on a technical question: what should count as already known (our own existence) when calculating probabilities. Defenders of the argument reply that our existence itself remains improbable without a designer (Collins's reply to the first objection); Sober judges that this is no longer the fine-tuning argument but another argument, to be examined separately.

Where the debate stands (our summary)Sober has granted that his objection does not hold for the firing squad, but maintains it for fine-tuning. There is no agreement on what should be taken as already known in the calculation.

What today's voices say

Defend it

Brian CoxAsked why the laws of nature allow life, he says one possible answer is a multiverse where every combination of laws exists. He calls it a theory, 'a guess basically'.

Deepak ChopraIn the Puebla debate he asks Dawkins why the universe is fine-tuned and its laws so rational.

John LennoxHe cites the fine-tuning of physical constants, for example Fred Hoyle's point that small changes in nuclear energy levels would prevent life, as a sign of design.

Nick BostromHe says fine-tuning is a fact that "cries out for some sort of explanation" and favors the multiverse plus an observation selection effect; he thinks simulation is a step too far as an explanation. A reviewer notes this is debated.

William Lane CraigHe argues that the constants of the universe are finely tuned for life and that design explains this best. In 2025 he said the choice has come down to a multiverse or God.

Frank TurekHe cites the fine-tuning of gravity (one part in 10^40) and says he does not have enough faith to believe it is chance. In 2026 he calls it the hardest argument for atheists to answer.

Francis CollinsHe points to the universe's physical constants, which make it look 'as if it knew we were coming': 'the knife edge of improbability'. He prefers a mind behind it to a multiverse, but warns that no single argument from nature proves God. (Our argument page is by the philosopher Robin Collins, not by Francis Collins.)

Mohammed HijabHe argues the universe is finely tuned to allow life and uses this to claim that life has a purpose.