Program / Course 14: Arguments for the Existence of God / Lesson 5.4
What you will learn
- State the fine-tuning claim in physics and the argument built on it.
- Distinguish the scientific claim from the philosophical inference.
- Explain the probability and observer-selection objections.
- Say which parts of the debate are settled and which are open.
The big idea
Physicists have found that if certain constants of nature or starting conditions had differed slightly, a universe able to support life would not exist. The fine-tuning argument says this is more to be expected if a purposeful creator exists than if the universe is the product of chance. Critics reply that the physics claim is more uncertain than it sounds, that only a life-permitting universe could be observed a life-permitting universe, and that probabilities for physical constants cannot be calculated. Both the science and the inference are disputed.
Key terms
- Fine-tuning
- The claim that the laws, constants or initial conditions of the universe must lie within narrow ranges for life to be possible.
- Physical constant
- A number in physics that is not derived from other numbers, such as the strength of gravity or the mass of the electron.
- Life-permitting range
- The set of values of a constant for which life of some kind could exist.
- Anthropic principle
- The observation that observers can only find themselves in a universe that permits observers. In its weak form it is a consequence of selection, not a claim about purpose.
- Likelihood
- In probability, how expected the evidence is on a given hypothesis.
- Cosmological constant
- A number describing the energy of empty space, which affects how fast the universe expands. Its observed value is very small compared with some theoretical estimates.
- Normalizability problem
- The difficulty that probabilities cannot be assigned over an unlimited range of possible values, since they must add up to one.
Background
The astronomer Fred Hoyle, a skeptic of conventional religion who favored the steady state theory, noted in the 1950s that carbon can form in stars only because of a special energy level in the nucleus. He later said that a superintellect seemed to have monkeyed with physics. Since the 1970s, physicists including Brandon Carter, Martin Rees and Paul Davies have discussed how sensitive the conditions for life are to the constants. Rees’s book Just Six Numbers (1999) is a clear popular account. Rees is not a theist.
Philosophers have developed the argument in several ways. Robin Collins, Richard Swinburne and others state it with probability theory. Critics include Elliott Sober, Neil Manson, Timothy McGrew, Lydia McGrew and Eric Vestrup, who have questioned the probabilities, and Victor Stenger, who argued that the physics claim is exaggerated.
Step-by-step explanation
Step 1: The scientific claim
Examples often cited include the strength of the strong nuclear force (a small change could prevent the formation of stable atoms), the expansion rate of the early universe (too fast and no galaxies form, too slow and the universe collapses), and the cosmological constant, whose observed value is far smaller than theory would naively predict. Physicists agree that some constants are sensitive in these ways. They disagree on how narrow the ranges are and whether other kinds of life could exist in other conditions.
Step 2: The argument in numbered form
1. The universe’s constants and initial conditions fall in a very narrow life-permitting range. 2. The probability of this is very low if it arose by chance, with no purpose. 3. The probability is not low if a purposeful creator wanted life. 4. So the evidence supports the creator hypothesis over the chance hypothesis.
This is a probabilistic argument. It does not claim to prove that a creator exists. It claims that the evidence favors one hypothesis over another.
Step 3: The observer selection reply
Critics note that observers could not exist in a universe that does not permit life, so finding oneself in a life-permitting universe is no surprise. Douglas Adams’s image of a puddle that marvels at how well the hole fits it illustrates the point. Defenders reply that this confuses two things. The fact that observers exist explains why they observe a life-permitting universe, but does not explain why such a universe exists. An analogy: a person facing a firing squad who survives would still ask why all the shooters missed.
Step 4: The probability problem
To say the life-permitting range is improbable, one needs a measure of the whole range of possible values. But the range of possible values of a constant has no natural limit, and probability cannot be spread evenly over an infinite range. Critics say that this makes the claim of improbability meaningless. Defenders reply that one can use finite ranges set by physics, or compare ranges relative to the scale of natural units, and that the argument needs only that the range is small compared with plausible values. The debate is technical and unresolved.
Step 5: Physics may explain the constants
Some physicists hope a deeper theory will show that the constants could not have been otherwise, which would make the fine-tuning only apparent. Others think the constants are free parameters. A deeper theory has not been found. Defenders reply that even a law that fixes the constants would itself call for explanation. This reply is another case of the question of ultimate explanation from Module 3.
- Which part of the argument is physics, and which is philosophy?
- Why might a life-permitting universe not surprise anyone at all?
- What does the firing squad example show, and what does it not show?
- Can there be life of other kinds in universes with other constants?
- How should a person weigh a physicist’s opinion on a philosophical inference?
- Is a purposeful creator a better explanation than brute chance?
Examples
Hoyle and carbon
Carbon is needed for life as it is known, and stars make it in a process that requires a very particular energy level in the carbon nucleus. Hoyle predicted this level in 1951 and it was found. He later said it looked as if someone had tinkered with the numbers. He remained an unbeliever in the God of the churches.
The puddle
Douglas Adams imagined a puddle that wakes and marvels at how well the hole it lies in fits its shape, and concludes the hole was made for it. The image is used to say that life suits its world because it adapted to it. Defenders say it does not apply to the physical constants, which were fixed before life began.
The firing squad
John Leslie’s example imagines a prisoner before a firing squad of a hundred marksmen, who all miss. The prisoner cannot be surprised not to be dead, since he would not be there to notice otherwise. Yet he would still reasonably suspect that something arranged the result.
Different perspectives
Catholic
Catholic writers have used fine-tuning in line with the Church’s teaching that creation shows the Creator. Pope John Paul II spoke of the harmony of creation. The Church has no official view on the argument, and Catholic physicists such as George Coyne (a Jesuit astronomer) have urged caution about its use.
Orthodox
Orthodox theologians tend to treat the order of the cosmos as a sign of God’s wisdom, in line with the Fathers, but are reluctant to use probability arguments. Some, like Alexei Nesteruk, write on theology and cosmology without making fine-tuning a proof.
Protestant
Robin Collins (a Protestant) and others defend the argument. William Lane Craig uses it. Some Protestants, including Reformed theologians, note that the God who is argued to is not yet the God of the Bible. Young-earth creationists often reject the cosmology involved.
Scientific views
Cosmologists such as Rees and Leonard Susskind accept that some constants appear fine-tuned, and often prefer the multiverse as an explanation. Others, such as Stenger, hold that the claim is overstated. There is no consensus.
Skeptical views
Skeptical philosophers argue that there is no way to assign probabilities to universes, that observer selection reduces the surprise, and that it is premature to infer a creator. Some also say that if God wanted life, a universe so hostile to life in most of its parts is odd.
Why it matters
Fine-tuning is currently the most discussed design argument. Because it blends physics with philosophy, it is easy to overstate or to dismiss. Learning to separate the physics claim from the probability inference helps in judging many public debates.
Common misunderstandings
Misunderstanding: Scientists have proved the universe was designed.
Correction: Physicists describe sensitivity of life to constants. Whether this needs a designer is a philosophical question on which scientists disagree.
Misunderstanding: Fine-tuning has been refuted by the multiverse.
Correction: The multiverse is one proposed answer. It is speculative and has its own problems, as the next lesson shows.
Misunderstanding: The argument says life could not exist under any other laws.
Correction: It says life as known is sensitive to certain constants. Other forms of life under other laws are not ruled out, but are not known either.
Misunderstanding: The anthropic principle explains the universe.
Correction: It explains why observers see a life-permitting universe, but not why there is one. Its force depends on other ideas such as a multiverse.
Knowledge check
State the fine-tuning argument.
The constants and initial conditions of the universe lie in a narrow range that permits life. This is unlikely if it arose by chance, and much more expected if a purposeful creator wanted life. So the evidence favors the creator hypothesis. It is a probabilistic argument, not a deductive proof, and it depends on both the physics and the probabilities.
What is the observer selection objection, and how is it answered?
It says observers can only observe a universe that permits observers, so the finding is no surprise. Defenders reply that this explains why observers see it but not why it exists, and give the firing squad example: surviving explains why one notices, but not why all the shooters missed.
What is the probability problem?
To call a life-permitting range improbable, one needs a measure over all possible values of a constant. There is no natural limit to that range, and probability cannot be spread evenly over an unlimited range. Critics say this makes the claim empty. Defenders suggest using finite ranges from physics, and the matter is technical and unsettled.
Why might a deeper physical theory affect the argument?
A future theory might show that the constants could not have been otherwise, making the fine-tuning only apparent. Defenders reply that a law fixing the constants would itself need an explanation, which returns to the question of ultimate explanation. No such theory exists, so the question remains open.
Think it through
- Does the idea of a fine-tuned universe move you, or leave you cold?
- Is it reasonable to infer from the structure of the universe to its cause?
- How should a believer treat a physics result that may change?
- Would a universe designed for life look different from this one?
Independent assignment
Physics and philosophy
In your own notebook, write 350 to 500 words. Divide a page into two columns headed physics claims and philosophical claims. Place each part of the fine-tuning argument in a column. Then write which column carries the weaker premise, and what evidence would strengthen it. Do not send this to anyone.
Further study
- Stanford Encyclopedia of Philosophy, Fine-Tuning Read for a careful statement of the claim and the main objections.
- Stanford Encyclopedia of Philosophy, Teleological Arguments for God’s Existence Read the section on fine-tuning in the history of design arguments.
- Richard Swinburne, The Existence of God Read for the probabilistic form of the argument.
- William Lane Craig, Reasonable Faith: Christian Truth and Apologetics Read for a defender’s use of fine-tuning.
- Isaiah 45 Verse 18 says that God formed the earth to be inhabited.
- Psalm 8 A meditation on the heavens and humanity.