Is the Universe fine-tuned for permitting life?

“Yes, after all…
  • Constants of physics are fine-tuned

    Various constants of physics are fine-tuned for permitting life.

    This page analyzes five examples:

    • The cosmological constant
    • [The strength of gravity]
    • The strong and electromagnetic force]
    • The weak force]
    • [The proton-neutron mass difference]
    1. “‘To say a constant of physics is fine-tuned is to say that its life-permitting range of values is minuscule relative to the comparison range of possible values which are ‘epistemically illuminated,’ i.e. the range for which we can determine whether the value is life-permitting or not.'” 2.1. Robin Collins discusses these in detail, along with carbon production in stars, in his “The Evidence for Fine-Tuning,” in God and Design: The Teleological Argument and Modern Science, ed. Manson, (Routledge, 2003), 178-199. He devotes five dense pages to covering the cosmological constant in “The Teleological Argument: An Exploration of the Fine-Tuning of the Universe” in The Blackwell Companion to Natural Theology eds. Craig and Moreland (Blackwell, 2009), 215-220.] Collins's forthcoming “The Well-Tempered Universe” will be the definitive source on all things fine-tuning.
  • Initial conditions of the Universe are fine-tuned

    Various initial conditions of physics are fine-tuned for permitting life:

    This article analyzes five examples:

    • [Initial mass-density of the Universe]
    • [Initial distribution of mass-energy]
    • [Big bang “explosion” strength]
    • [Strength of density perturbations yielding star formation]
    • [Density-ratio of radiation to normal matter]
    • [More]
  • Laws of physics are fine-tuned

    Various laws of physics are fine-tuned for permitting life:

    A forthcoming page will analyze these five examples:

    • Gravity1
    • Strong nuclear force
    • …[Electromagnetic force
    • Bohr’s quantization rule
    • …Pauli exclusion principle
    1. Note: Or something relevantly similar to gravity (i.e. a universal attractive force). This same proviso applies to all the examples.
“No, after all…
  • “Changes just yield other forms of life”

    The Universe is only fine-tuned for permitting life as we know it.1 (Supposing otherwise is a kind of “carbon chauvinism.”)2

    By way of response, however, the Universe has to be fine-tuned in several respects in order to permit any kind of life (and certainly intelligent life). Some tamperings prevent chemistry itself, or leave one with a universe consisting of only the lightest elements (hydrogen and helium).3, 4

    1. For examples of individuals raising this objection to fine-tuning:

      Douglas Adams (on “puddle thinking”): “This is rather as 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!’ This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it’s still frantically hanging on to the notion that everything’s going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise.” [Speech at Digital Biota, Cambridge (1998).]
      Victor Stenger: “life as we know it would not exist if any one of several of the constants of physics were just slightly different, [we] cannot prove that some other form of life is feasible with a different set of constants. Anyone who insists that our form of life is the only one conceivable is making a claim based on no evidence and no theory.” [Has Science Found God? (Prometheus, 2003), 156.]
      Sean Carroll: “As skeptical as I am about the ability of physicists to accurately predict gross features of a universe in which the laws of nature are different, I am all the more skeptical of the ability or biologists (or anyone else) to describe the conditions under which intelligence may or may not arise. (Cellular automata, the simple discrete systems popularized by Wolfram and others (Stephen Wolfram, A New Kind of Science (Champaign, IL: Wolfram Media, 2002)., provide an excellent example of how extreme complexity can arise out of fundamentally very simple behaviors.)" [“Why (Almost All) Cosmologists are Atheists” (2003) online at ]
      Michael Ikeda and Bill Jefferys: “Indeed, virtually nothing is known about the possibility of life in universes that are very different from ours. It could well be that most universes could support life, even if it is of a type that is completely unfamiliar to us. To assert that only universes very like our own could support life goes well beyond anything that we know today.” [“The Anthropic Principle Does not Support Supernaturalism” (2004) online at]

    2. A popular alternative put forward is silicon-based life (the next element in carbon's group in the periodic table), but even this seems implausible: “Only two of the natural atoms, carbon and silicon, are known to serve as the back-bones of molecules sufficiently large to carry biological information… [but] unlike silicon [Carbon] can readily engage in the formation of chemical bonds with many other atoms, thereby allowing for the chemical versatility required to conduct the reactions of biological metabolism… [moreover] large silicon molecules are monotonous… [moreover] the electronic properties of carbon, unlike silicon, readily allow the formation of double or even triple bonds with other atoms." [Norman R. Pace “The universal nature of biochemistry” Proceedings of the National Academy of Sciences 98 (2001): 808.] As noted in a Scientific American article by Alexander Jenkins and Gilad Perez, Silicon-based life is very dubious; "no silicon-based molecules of any significant degree of complexity are known to exist.” [Online]
    3. See:

      Stephen Hawking: “Of course, there might be other forms of intelligent life,… Nevertheless, it seems clear that there are relatively few ranges of values for the numbers that would allow the development of any form of intelligent life. Most sets of values would give rise to universes that, although they might be very beautiful, would contain no one able to wonder at that beauty.” [A Brief History of Time (Bantam, 1988), 125.]

    4. Bradley Monton speculates briefly about a brain made of hydrogen atoms (Seeking God in Science (Broadfview, 2009) 83.), but the following judgment seems soberer:

      Graham Oppy (Athest philosophy professor at Monash University): “in a universe in which there is nothing but hydrogen, there plainly won't be life as we know it, and moreover, it seems plausible to suppose that there won't be any other kind of life either.” [Arguing about Gods (Cambridge, 2009) 201.]

  • “The constants can't be different (T.O.E.)”

    Some theory of everything fixes the constants etc. such that there are no free parameters (e.g. M-theory, where it is perhaps naturally impossible for them to be different than what they are).

    So what if that was true? That would just push the improbability up to another level, like the proverbial ruck in the carpet. If the values of the constants are necessary for a given law, that raises the question of why a law like that exists. I.e why should the law be such that it can only produce a fine-tuned system when there are many other possible laws that could exist instead that are not likely to produce a fine-tuned system. To illustrate, imagine some Grand Unified Theory resulted in Jesus uniquely walking on water and resurrecting after his crucifixion. Far from explaining away the evidence, this would obviously just kick the problem upstairs to the superlaw itself.

    • Bernard Carr and Martin Rees (Astrophysicists, professors): “…even if all apparently anthropic coincidences could be explained [in terms of some grand unified theory], it would still be remarkable that the relationships dictated by physical theory happened also to be those propitious for life” [“The Anthropic Cosmological Principle and the Structure of the Physical World” Nature 278 (1979): 612.].
  • 99% of the Universe is hostile to life

    Over 99% of the Universe’s area is uninhabitable.1

    Consider two arguments:

    • Virtually all of its locations do not contain breathable air.
    • Virtually all of its locations are too hot/cold for us to live in.

    This is relevant because if 99% of the Universe is hostile to life (unaided by technology), then the Universe is not very fine-tuned for life.

    But so what if it is 99% hostile?…

    • …our universe is still 100% life-permitting (our physics 100% allows for life).2
    • …if this is evidence against theism, it’s off topic.3
    1. Neil deGrasse Tyson: “Most places in the universe will kill life instantly - instantly! People say, ‘Oh, the forces of nature are just right for life.’ Excuse me. Just look at the volume of the universe where you can't live. You will die instantly.”
    2. The physics of this universe still obviously permits life (or else how are you reading this), and 99.99% of other possible universes don’t. The % of locations where we could live without technology is irrelevant; as long as the universe permits life in any location (which it does) and that “permitting” depends on fine-tuning (i.e. where changing the constants etc. would likely result in a universe that would not permit life anywhere in it.)
    3. Someone might point to the fact we cannot live in 99% of the universe, and say this is unlikely if God exists. The argument insists that, if God exists, God would surely design the universe such that most of it is habitable. (Think of a house designer who designs a house with only 1% of livable space.) By way of response, however, “space” can have more purpose than just livability. So as long as there is more than enough space to live in (which there is), there is no reason to expect all space to be habitable. An omnipotent God's resources are limited not with respect to how much space He creates. So, if space can have any other value aside from habitation, then extra uninhabitable space it is not at all surprising on theism. Sure enough, space plausibly has aesthetic value, worship-inducing value, and an abundance of scientific value in terms of being required for a simple Big Bang universe which through generations of stars is ultimately able to a life-friendly planet. (This is plausibly the most elegant way to bring about a life-permitting planet and many argue that alternative methods would in large part frustrate the possibility of historical cosmology.)
  • [“Life-friendly Universe are rare but probable”]

    [Brackets] mean “Forthcoming”

  • One can't normalize across an infinite range

    There is an unbounded range of possible values that could be taken for a given constant, then no meaningful probability could be assigned to one landing in the life-permitting range. After all, the probability of landing in the life-permitting range will always be 1 over infinity, i.e. zero or undefined. It presumably can't be undefined, because then the fine-tuning argument from probability goes out the window, and it can't be zero, because that is counterintuitive and then all instances of fine-tuning are equally improbable, be they very fine-tuned or hardly fine-tuned at all.

    But no...

    • So-called “countable additivity” (i.e. “finite additivity” applied to the infinite) is false; you can't assume epistemic probability for an entire region is the sum of the individual probabilities of each finite disjoint region.1
    1. Many mathematicians have pointed out problems with countable additivity. • Robin Collins: “This latter principle, however, has been very controversial for almost every type of probability, with many purported counterexamples to it. Consider, for example, the following situation. Suppose that what you firmly believe to be an angel of God tells you that the universe is infinite in extent and that there are a countably infinite number of other planets with civilizations on each planet. Finally, the “angel” tells you that within a billion miles of one and only one of those planets is a golden ball 1 mile in diameter and that it has delivered the identical message to one person on each of those planets. Finally, you decide on the following arbitrary numbering system to identify the planets: you label Earth 1, the planet that is closest to Earth 2, the planet that is next farther out 3, and so forth. Since within current Big Bang cosmology an infinite universe would have no center, there is nothing special about Earth’s location that could figure into one’s probability calculation. Accordingly, it seems obvious that, given that you fully believe the “angel”, for every planet k your confidence that the golden ball is within a billion miles of k should be zero. Yet this probability distribution violates countable additivity. One cannot argue that the scenario I proposed is in any way self-contradictory, unless one wants to argue that an infinite universe is self-contradictory.... [moreover] in some cases it would be irrational to remain agnostic. For example, it would be irrational for a billionaire who received the aforementioned message to spend millions, or even hundreds, of dollars in search of the golden planet, even if it were entirely rational for him to believe what the “angel” told him; it would even be irrational for him to hope to discover the planet. This is radically different than cases where people are legitimately agnostic, such as perhaps about the existence of extraterrestrials or the existence of God; for example, it seems rationally permitted at least to hope for and seek evidence for the existence of extraterrestrials or God. The implausibility of being agnostic in the ‘golden planet case’ is further brought out when one considers that if the billionaire were told that the universe was finite with exactly 10^10,000 planets with civilizations, clearly he should be near certain that the golden planet is not near Earth. But, clearly, if the billionaire is told that there are even more planets – infinitely many – the billionaire should be at least as confident that the planet is not near Earth; and, certainly, it should not become more rational for him to search for it than in the 10^10,000 planets case, as it would if he should switch to being agnostic.” [The Teleological Argument," in The Blackwell Companion to Natural Theology (Blackwell, 2019), 250.]
  • “New knowledge will eliminate fine-tuning”

    The ostensible fine-tuning in the Universe will wash away with new knowledge.1

    By way of response, however, physicists do not seem to think the fine-tuning will wash away, especially not all of it (any more than we think that all the evidences for an old Earth, or for plate tectonics, will wash away). For example,

    • John Leslie (Non-theist philosopher of science, professor at Guelph): “In a book of mine, Universes (1989), I made a long list of such claims about fine-tuning. …What is impressive, I suggest, is not any particular one of the claims about fine-tuning, but the large number of claims that seem plausible, and the consequent implausibility of thinking that every single claim is erroneous.” [“The Meaning of Design” in God and Design Ed. Manson (Routledge, 2003), 56.] (e.g. “clues heaped upon clues can constitute weighty evidence despite doubts about each element in the pile” [Universes (Routledge, 1989), 300.])
  • Restrictiveness becomes irrelevant if the range is infinite

    If the range of values a constant could take fall along an infinite scale of possibilities, then the rational epistemic prior probability of the Universe being life-permitting (on naturalism) is the same regardless of how restrictive the life-permitting range seems to be. In the end, it is all infinitesimal, which renders recent scientific discoveries pertinent to fine-tuning virtually irrelevant to the fine-tuning argument.

    But so what?

    • The range is not infinite.1
    1. Luke Barnes: "Firstly, if one agrees with the usefulness of the Little Question—that we should try to address the Big Question, and that varying the constants is a promising approach—then this is a mere technical setback. If, in our ignorance, we have failed to correctly set up the problem to be solved and do not have appropriate probability distributions, then we should simply try again. There is no in-principle objection that would lead us to abandon the entire project. As argued in Barnes (2018) and outlined above, the two conditions for the normalisability problem—infinite range, flat distribution—are not forced on us for the fundamental constants of nature. Dimensional parameters are bounded by the Planck scale; they cannot vary over an infinite range. This restriction comes from the standard models themselves (L), which are taken as given when we calculate the likelihood in the context of the Little Question. This restriction does not postulate that some principle of logical or metaphysical possibility applies to these quantities, but is rather a consequence of the fact that their status as fundamental constants is bestowed by the standard models, and those models are only mathematically well-defined within the Planck limits. Similarly, we are not forced by any principle to attempt to place a flat distribution from [0,∞) on dimensionless parameters. It is not unreasonable to place a higher expectation on order unity values, which allows us to choose from a range of normalisable distributions."
      [“A Reasonable Little Question” in Ergo, 6.42 (2020): accessed online.]