A pastor I know tells me that ‘fine-tuning’ proves the existence of a Creator. If the fundamental laws and constants of our universe were much different, life as we know it would not exist.
Fundamental laws, such as those describing gravity, tell us how physical things behave through cause and effect, such as why an apple falls to the ground. Fundamental constants set some of the numerical values within those laws. According to astrophysicist Ethan Siegel, there are 26 fundamental constants needed to explain our universe.
Examples are the masses of the up and down quarks, the particles that make up protons and neutrons. Their different masses help make the neutron just 0.14% heavier than the proton. Alter those relative masses sufficiently and ordinary hydrogen could become unstable, as Physics Today explains. This would radically change stars, chemistry and the prospects for life as we know it. This illustrates that the fine-tuning question is not purely abstract. Perhaps the pastor has a point?
Physicists postulate that a scientific multiverse might address this fine-tuning argument. However, on deeper examination, such multiverses as eternal inflation (EI) and the many-worlds interpretation (MWI) do not support all possible physical laws and constants. EI and standard MWI only realise possibilities permitted by their underlying laws and starting conditions. MWI does not vary laws or constants at all. EI may allow some variation in constants and in the laws operating within individual universes, but this is only within possibilities permitted by its underlying physics. It does not entail that every physically possible set of laws and constants is realised.
This then raises a question: why those specific laws and constants, and why that range of possibilities? What is the selection mechanism for which elements are changeable, and which are not? Why should reality realise one physically possible universe while excluding others? No established principle currently explains why reality should privilege this particular set of laws and constants over others.
Philosophers have posited broader multiverses, such as Max Tegmark’s Level IV Multiverse, in which every mathematical structure has physical existence, and David Lewis’s modal realism, the view that every possible world is real. These would entail a vast range of universes. All physically possible universes would exist, but so would possibilities extending beyond coherent physical worlds governed by cause and effect, perhaps even a Wonderland in which a grin remains after the Cheshire cat has disappeared. These additional possibilities go beyond what an explanation of fine-tuning requires.
It might then be worth considering a ‘Goldilocks’ compromise. This is what I term here the Metaphysical Multiverse (MM) – a multiverse in which every physically possible universe exists, each with a coherent set of physical laws and constants, but not every mathematical or modal possibility.
With MM, a physically possible universe is one whose laws and constants form a coherent physical system of cause and effect. It does not need to resemble our universe in its dimensions, forces or constants. Mathematical consistency on its own, as in the Level IV Multiverse, is insufficient. MM postulates every physically possible universe. A universe with our laws and constants is included by definition. In a multiverse containing all physically possible universes, we find ourselves in a life-permitting one – because only those can contain observers.
A possible objection to MM is the inverse gambler’s fallacy. This is the mistaken belief that observing a rare event implies the process producing it has occurred many times. Applied here, the fallacy would be: ‘Because our universe is life-permitting, many universes must exist’. But MM makes no such inference. It does not deduce many worlds from fine-tuning. Rather, it starts from the principle that all physically possible universes exist. It then uses that to explain why we observe a life-permitting one.
But could such a multiverse be compatible with future scientific developments? MM may also be more than a Goldilocks compromise. Because it concerns only physically possible worlds, future science might help clarify its scope, or provide a model approaching it. Like Democritus’s atomism, it could conceivably be absorbed into science. For example, in 2026 Edward J. Shaya published The Topological Multiverse as the Self-Consistent Extension of Everettian QM to Quantum Gravity – a speculative proposal illustrating how quantum cosmology might accommodate variation in laws and constants in an extended MWI.
The idea of such a metaphysical multiverse has ancient precedents. In his Letter to Herodotus (c. 300 BCE), Epicurus affirmed that “there are infinite worlds both like and unlike this world of ours”. Epicurus’s vision of innumerable worlds anticipates a similar intuition behind MM. If a world’s physically possible, there’s no obvious reason why reality would exclude it.
Returning to my pastor’s Creator, Aaron Rabinowitz writes in his recent Skeptic book review that he finds it “uncompelling” when such theists argue that everything must have a cause – hence god – then posit that god, uniquely, can be “uncaused”.
Invoking a Creator raises another question. Why would that Creator choose these laws and constants over others? Perhaps it has reasons of which we are unaware? But such unspecified reasons do not explain this particular choice.
Perhaps Ockham’s razor might help. A tutor once explained it to me like this: imagine waking up in the morning to find the grass wet. You might say fairies came in the night, waved their magic wands and sprinkled water. Or you might say it rained. Both could explain the wet grass, but Ockham’s razor favours the latter because it makes fewer assumptions.
MM, in its current form as a metaphysical framework, cannot be assessed by empirical test (testable by observation). It has to be judged by coherence, explanatory power, and parsimony (few assumptions, as per Ockham’s razor). MM is parsimonious in the kinds of entities it posits, not their number. One might feel this multiplies worlds beyond necessity. However, a brute fine‑tuned universe or a creator may be a less simple endpoint. The brute‑universe view treats the fundamental constants as unexplained givens, like a large set of free parameters.
A creator, in turn, posits an unexplained complex mind capable of setting those parameters. Of the three, MM is arguably the leanest in assumptions – and thus the most in keeping with Ockham’s razor – even if it’s most extravagant in instances.
MM appears to offer a potential explanation of the fine-tuning problem without invoking a Creator, unifying worlds under a general, exceptionless principle – all physically possible frameworks are realised. This replaces the need to privilege one apparently arbitrary set of constants, or to posit an unexplained selector. It requires no common starting condition from which all universes are generated, and no mechanism selecting which physically possible universes exist: it postulates them all.
Whether that would persuade my pastor is another question.
