Is the Universe fine-tuned for permitting life?

Reasons given for answering "Yes"
  • Constants of physics are fine-tuned

      Various constants of physics are fine-tuned for permitting life. In particular… [All forthcoming]

      • …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 miniscule 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: [All forthcoming]

      • …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: [All Forthcoming]

      • …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.
  • Reasons given for answering "No"
  • “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 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. Bradly Monton speculates briefly about a brain made of hydrogen atoms (Seeking God in Science (Broadfview, 2009) 83.), but the following judgment seems more sober:

        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 a level. 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 crucifixion; far from explaining away the evidence, it merely kicks 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.].

  • [“Life-friendly Universe are rare but probable”]

      [Brackets] mean “Forthcoming”

  • [“One can't normalize across an infinite range”]

      [Brackets] mean “Forthcoming”

  • “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.])