Designed for Life? Is Fine-Tuning Due to God, or the Multiverse?
A summary of the fine-tuning argument and response to key objections
The standard models of particle physics and cosmology contain 31 fundamental constants. (1) Many scientists expected that life would be possible for a range of universes. It turns out this is not the case.
For example, physicist Luke Barnes (1) points out:
…if gravity were repulsive, matter wouldn’t clump into complex structures. In a universe of Newtonian gravitating masses (with no other forces), unless the initial conditions are exquisitely fine-tuned, collections of particles either exhibit boring periodic motion or unstable chaotic motion, but not the kind of complexity of arrangement required by life.” (p1231)
Another example is from philosopher John Leslie (2):
The nuclear strong force, too, must be neither over-strong nor over-weak for stars to operate life-encouragingly”. As small an increase as 2 % in its strength “would block the formation of protons out of quarks,” preventing the existence even of hydrogen atoms let alone others…Slight decreases could be equally ruinous.” (p119)
Likelihood of a life-permitting universe given naturalism
Mathematical models provide a rigorous method for exploring the likelihood of a life-permitting universe. For each fundamental constant, physicists define parameters based on standard models in the field. Varying the values of these parameters, allows us to predict how the universe would be in different scenarios.
Naturalism gives no reason to expect the fundamental constants will take any particular values. Therefore, a non-informative prior distribution (making as limited assumptions as we can about the likely value of the constant before seeing the data) is most appropriate.
Barnes found the likelihood of such a universe extremely small (1 in 10–136) given naturalism (1). Many other physicists such as Roger Penrose (2) and Lee Smolin suggest the probability is even lower (3).
Likelihood of a life-permitting universe given theism
If God exists, a life-permitting universe is not certain, but also not implausible:
But surely life is at least modestly plausible given theism…This is not to say that one should expect a theistic universe to contain fine-tuned life (even conditional on life). But one shouldn’t think fine-tuned life fantastically unlikely either. (Hawthorne and Isaacs (4), p145–146)
Therefore, fine-tuning supports the validity of theism compared with naturalism. Since fine-tuning is much more likely given theism.
Objection: the puddle argument
The anthropic principle is a popular criticism of fine-tuning. Douglas Adams (5), a science fiction writer, provided a nice illustration:
If you imagine a puddle waking up one morning and thinking, “This is an interesting world I find myself in — an interesting hole I find myself in — fits me rather neatly, doesn’t it? In fact it fits me staggeringly well, must have been made to have me in it!”
The only evidence of a life-affirming universe is that we exist. So there is a selection effect. We wouldn’t be alive to observe another kind of universe.
However, this criticism is irrelevant to fine-tuning. The basis of the argument is not that we exist — we all know that! The starting point is evidence from physics. Life is possible only in a narrow range of values for the fundamental physical constants.
Therefore, given these very narrow constants, the probability of a life-affirming universe is low. We require an explanation for why our universe is life-permitting.
Objection: multiverse
Another response to fine-tuning is positing a multiverse.
…given a large enough number of other universes with sufficiently variegated properties, the right conditions for life are likely to turn up somewhere. And secondly, of course, intelligent physical life forms could only exist in a universe where just the right conditions prevailed. The fine-tuning of the universe for life is just our local slice of luck. (1)
The problem with this strategy is that the primary evidence for the multiverse is fine-tuning. In addition, the multiverse is currently untestable (6). Therefore this explanation is based largely on speculation.
Philosopher Phillip Goff (7) has argued even if there was evidence for the multiverse, this could not account for fine-tuning. Such an explanation commits the ‘inverse gambler’s fallacy’.
The gambler’s fallacy is what my dad used to call the “law of averages”. Let’s say I’ve tossed a coin three times, and there were three heads. By the “law of averages”, I expect the next coin to come up tails. However, the probability of tails is the same every time I toss the coin (0.5 or ½). The result of previous coin tosses have no impact on the probability of the next coin toss.
The inverse gambler’s fallacy is a version of the gambler’s fallacy. Both assume a rare event (R) happens after a long chain of previous non-events (not-R). The gambler’s fallacy uses the “law of averages” to predict a future event. The inverse gambler’s fallacy uses the same assumption to provide an explanation of the rare event (8).
An example may help. I have been lucky enough to observe a black swan. In the UK, there are approximately 40 black swans out of a total population of around 32,000 swans (approximately 1 in 800).
All the information you have about my experience with swans:
- I’ve seen one black swan.
- Data suggests black swans are rare.
Now this may lead you to speculate I am an avid swan watcher. To have observed something so rare, I must have seen a lot of swans. If so, you would have committed the inverse gambler’s fallacy.
That I’ve seen a black swan tells you nothing about the number of other swans I’ve observed. There is an important piece of information not yet factored in. I used to work at the University of York in the UK from 2011 to 2022. A male black swan was a prominent feature on the campus until his death in 2014. So the probability of me seeing a black swan is not that low!
Similar principles hold when applied to fine-tuning:
…The reason some scientists take seriously the possibility of a multiverse in which the constants vary in different universes is that it seems to explain the fine-tuning. But on closer examination, the inference from fine-tuning to the multiverse proves to be instance of flawed reasoning. (7)
References
- Barnes L. A Reasonable Little Question: A Formulation of the Fine-Tuning Argument. Ergo 2019; 6:42
- Leslie J. The Pre-Requisites of Life in our Universe. In Craig WL, Meeker K, Murray M, O’Connor T. Philosophy of Religion (Eds.). Edinburgh University Press.
- Smolin L. The Life of the Cosmos. Oxford University Press.
- Hawthorne J, Isaacs Y. Fine- Tuning. In: Benton M, Hawthorne J, Rabinowitz D (Eds). Knowledge, Belief and God. Oxford University Press.
- Adams D. The Salmon of Doubt. William Heinemann Ltd.
- Ellis G. Does the Multiverse Really Exist? Scientific American 2011;https://www.scientificamerican.com/article/does-the-multiverse-really-exist/
7. Goff P. Our Improbable Existence Is No Evidence for a Multiverse. Scientific American 2021; https://www.scientificamerican.com/article/our-improbable-existence-is-no-evidence-for-a-multiverse/
8. Hacking I. The Inverse Gambler’s Fallacy: The Argument from Design. The Anthropic Principle Applied to Wheeler Universes. Mind 1987; 96:331–340.
