The fine tuning argument essentially states that there is so much about the universe that is "fine tuned" for life - eg things like the gravitational constant would cause the universe to disintegrate if they were off by 1 part in a million million - that there must be a creator who did the tuning.

The most common response from eg atheists is comparing the situation to water in a puddle remarking on how the hole in the ground is exactly the right shape to hold it. In other words, claiming that rather than the universe being fine tuned, it just fit the existing conditions out of necessity. Whenever this is mentioned in Christian forums, it is pooh-poohed and derided as though it is obviously wrong, but no-one ever seems to actually explain it.

What is the "obvious" refutation of the puddle analogy that everyone seems to know?

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    I see a couple of close votes - I'm aware it's a fringe question at best as the fine tuning argument technically isn't specific to Christianity, but there is no Apologetics SE and Philosophy didn't seem quite right, would that have been the place? Jan 31 at 3:02
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    The puddle analogy is an intuitive and succinct example of the much more intricate and detailed refutations to fine tuning. It shouldn't be considered the strongest form of the refutation. Also, while a Q&A might be useful for finding a response to a specific position in a broader debate, neither a Q&A nor a Christian forum is that good for understanding responses to those responses (which are explicitly banned here), and responses to those. I hope you're trying to whole debate better, from both sides, rather than simply looking for an answer to reassure you that you aren't wrong.
    – NotThatGuy
    Jan 31 at 11:54
  • To make this question not receive any close votes you'd have to make it clear that you want an answer from respected Biblical fundamentalists and scripture scholars who are experts in intelligent design (or whatever underlying system upholds the fine-tuning argument). Basically, you need to provide the connective tissue between ID and Christianity in your question so we can judge the rightness or wrongness of the answers. Otherwise this is soliciting opinions which are sometimes bad, but never wrong.
    – Peter Turner
    Jan 31 at 13:24
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    The linked article talks about "what is widely regarded as the strongest atheist argument against theism, the argument from evil". I'm having trouble understanding the point of this argument or why anyone thinks it's needed. In an atheistic universe, the concepts of "evil", "morality", "purpose", etc. must be artificially created by man, and so don't objectively exist. So any argument related to the existence of "evil" must already be within a theistic universe. So how can such arguments be used to deny the existence of a theistic universe? Feb 1 at 0:13
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    I think the question should be reworded to remove "The most common response from eg atheists is comparing the situation to water in a puddle". This is not true in my experience and I doubt it is true in general. The puddle analogy isn't meant to be an argument in itself - as people have already answered, it is easily refuted. The puddle analogy is only an analogy to give intuition for the Anthropic Principle, which is the real rebuttal to the Fine Tuning Argument. Feb 1 at 0:21

6 Answers 6


Interestingly, the puddle analogy is wrong for exactly the same reasons that the claim that "improbable events happen all the time" does not solve the probabilistic issues inherent in Darwinism. That is, while it's true that any improbable event can happen, only select events are meaningful.

For example, consider drawing 28 letters from a bag of tiles (replacing the drawn letter each time). Even though the probability of drawing, say, "nxkrejvjjlupuhagmbwfxpvsvzpx" is very low, it would not be a surprising result unless it could be shown to convey meaning. Conversely, if you drew the letters "antidisestablishmentarianism", you would rightly suspect that your supposedly "random" process isn't so random. This is the difference between simple complexity and specified complexity.

The problem with the puddle analogy is that it's a puddle. Just as any combination of letters is technically improbable, but most are not surprising, any hole will suffice to hold the puddle. That is, while the puddle's hole is complex, it exhibits only simple complexity. This is not the case with life. In order for the puddle analogy to be "legitimate", one would have to show that life is possible given different physical constants. Actually, it is worse than this, because one would have to show that physical constants which permit life are probable (for some plausible definition thereof). Since, to the best of our knowledge, only very specific physical constants allow for life to exist, this "fine tuning" represents specified complexity. (Of course, the cop-out is to claim that an infinite number of universes having infinite combinations of physical constants exist. However, there is no evidence for this claim, making it purely philosophical in character.)

Put differently... one can change the shape of a puddle in all sorts of ways and still have a puddle. However, it does not follow from this analogy that one can perturb a cell and still have a living organism, or perturb the laws of physics and still have the potential for life to exist.

For further reading, consider:


What is the "obvious" refutation of the puddle analogy that everyone seems to know?

TL;DR: Puddles can exist in holes of any arbitrary shape, but life can exist only in a Universe that has extremely specific fundamental constants.

The puddle analogy relies on the ridiculousness of the belief that the hole either changes, or was specifically created, to match the shape of the puddle.

In reality, it is the shape of the water that changes to match the shape of the hole.

  • Empirically, we see that this happens for billions of puddles, but no one has recorded an instance of a puddle that didn't quite fit into the hole.
  • Scientifically, we know that this effect is caused by the force of gravity acting on a substance that will naturally change shape to minimize its centre of gravity.

Applying that analogy to the Universe, if the fundamental constants changed, they must have very rapidly changed from their initial values in order to become what they are today (telescopic images show what the universe looked like billions of years ago, and the constants appear to be the same then as now). So those constants must have been established at or near the beginning of time.

  • Empirically, we know that the constants are correct, otherwise we wouldn't be here now considering this question.
  • Scientifically, we must conclude that the Universe had the correct values right from its beginning, so it must have been designed to support life.

The puddle comparison claims that this conclusion is just as ridiculous as the idea that the hole's shape was determined by the puddle.

It would be if life (not necessarily in our form) could exist in a universe with arbitrarily different fundamental constants. But we know that almost all other theoretically possible universes would exist for only a brief moment or would be unsuitable for life.

"The Fine-Tuning Design Argument", linked in the Question provides some examples:

  • if gravity had been stronger or weaker by 1 part in 1040 power, then life-sustaining stars like the sun could not exist.
  • If the initial explosion of the big bang had differed in strength by as little as 1 part in 1060, the universe would have either quickly collapsed back on itself, or expanded too rapidly for stars to form. In either case, life would be impossible.

Those two factors alone account for 100 decimal places of precision, and that is only enough to guarantee the existence of suns. Include all the factors that affect what is required to support life and it could be in the thousands of decimal places. That's about as close to impossible as one could imagine.
(E.g. compare 10100 with taking 4 grains of sand from the Sahara and then burying them in random locations throughout northern Africa. Now ask someone else to randomly choose 4 grains of Saharan sand. Would you believe it if they picked the exact same grains?)

By analogy, we could observe that many holes leak and won't hold a puddle. But we can't observe (or even theoretically imagine) any instances of non-leaking holes that won't naturally fit the water that is in them.

Since puddles can exist in holes of any arbitrary shape while life can exist only in a universe that has extremely specific fundamental constants, one must ask: what caused our universe to have those specific values?

It's very difficult to answer that question without either:

  • assuming that an arbitrarily large number of possible universes exist and that this one simply happens to have the right fundamental constants.
  • assuming something from outside-of-universe that already knew the required values.

Each is a concept for which there is no scientifically acceptable proof.
Each is rejected as ad hoc fantasy by believers in the other.

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    – curiousdannii
    Feb 1 at 13:51
  • "Scientifically, we must conclude that the Universe had the correct values right from its beginning, so it must have been designed to support life." - this suggests that the idea that the universe was designed to support life is scientifically accepted, when it is not. It's not even a scientific statement, given that it's not falsifiable.
    – Guy G
    Feb 2 at 11:25
  • @GuyG, I wasn't claiming that statement's validity. Notice that my very next sentence contains "this conclusion is just as ridiculous as the idea that the hole's shape was determined by the puddle". Feb 2 at 14:13
  • The fact remains that all of the scientific evidence that we have supports the fine-tuning argument and no evidence supports the puddle argument. And the fine-tuning argument is accepted among scientists as an unresolved question. The puddle argument is not because it is not even a valid analogy, let alone a scientific hypothesis. Feb 2 at 14:14

I hope this counts as an answer. The puddle idea is just a metaphor or perhaps better stated, a parable. It does not contain or purport to contain the whole of the argument - it merely illustrates it in an easily understandable way.

The actual philosophical debate that the puddle merely illustrates is the Anthropic Principle. I quote:

The anthropic principle, also known as the "observation selection effect", is the hypothesis, first proposed in 1957 by Robert Dicke, that there is a restrictive lower bound on how statistically probable our observations of the universe are, because observations could only happen in a universe capable of developing intelligent life. Proponents of the anthropic principle argue that it explains why this universe has the age and the fundamental physical constants necessary to accommodate conscious life, since if either had been different, we would not have been around to make observations. Anthropic reasoning is often used to deal with the notion that the universe seems to be finely tuned for the existence of life. https://en.wikipedia.org/wiki/Anthropic_principle

Personal note As a radical agnostic (i.e. I profess to know nothing for certain except for my own existence) and a pragmatist, I don't really care about cosmic accidents or creators when it comes to living my daily life. However I often wonder why believers feel the need to justify their faith - especially by science - isn't it enough for them to simply believe? If they have to prove the existence of a god, then that indicates they are doubting Thomases and not true believers.

  • "I profess to know nothing for certain except for my own existence". With whom are you sharing this information? I think believers have an instinctive expectation that their faith should reconcile with science but, oftentimes, the limitations of science are misunderstood and so the reconciliation attempts assume the flavor of justification. Feb 1 at 12:55
  • Christians aren't called to have blind faith. We're called to not only use our God-given rationality, but to be able to give a defense of our faith. It would be irrational to believe in pink unicorns if there is substantial evidence against their existence. Of course, the caricature of Christians as gullible idiots is quite popular among scoffers... (Everyone knows that real unicorns, or at least their living relatives — some debate here whether they qualify as the same animal — are gray.)
    – Matthew
    Feb 1 at 15:40
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    BTW, the Anthropic Principle is absolutely correct. The problem is rather that if physical constants were different, no one would be around to observe their effect. Therefore, the problem of explaining why we are here remains. The usual claim that there are infinite (or at least many) universes — that something "tried and tried again" until our universe happened along by pure chance — merely begs the question, and has no non-philosophical justification. Nor does it explain why conditions are remarkably well-suited for life rather than marginal.
    – Matthew
    Feb 1 at 15:45
  • @Mike Borden - I don't know who I am sharing it with. For all I know, I am God and the entire world is simply a dream I'm having. I don't know whether you exist - I only know that I exist. The point is that I am a pragmatist. Although I don't know if the world exists, I behave as though it does. Feb 1 at 18:57
  • @Matthew - No-one can prove that pink unicorns don't exist. If you have evidence against their existence, what is it? I can't prove that God doesn't exist for a similar reason. I have no idea whether the Christian God exists or whether some other form of god created us or none at all. I don't mind what others believe. I am interested though that you are called to defend your faith. Where is this written? Feb 1 at 19:03

In other words, claiming that rather than the universe being fine tuned, it just fit the existing conditions out of necessity.

No, the puddle argument is a response to the claim that the environment is particularly suited to humans, and it asserts that, rather than the environment being suited to humans, humans are suited to the environment.

The most common response from eg atheists is comparing the situation to water in a puddle remarking on how the hole in the ground is exactly the right shape to hold it.

Really? When I Googled "puddle analogy", I got these results:

  1. Wikipedia article— Explaining the anthropic principle.

  2. Stand to Reason article "Why the Puddle Analogy Fails against Fine-Tuning"—A Christian apologist explaining why the analogy doesn't defeat fine-tuning.

  3. Reasons to Believe article "Does the Puddle Analogy Explain Cosmic Fine-Tuning?"—ditto

  4. Quora question "What does Douglas Adams’ Puddle Analogy mean?"—Question about the analogy

  5. The Truth Will Make You Mad article "The Puzzle of Existence and a Puddle of Doubt"—Christian apologist attacking Douglas Adams, claiming that he misrepresents the fine-tuning argument.

Now, here are the results for "fine-tuning rebuttal":

  1. Why Evolution Is True article "Sean Carroll debunks the “fine-tuning” argument for God"—No mention of "puddle" in the article, although someone brings it up in the comments.

  2. Stanford Encyclopedia of Philosophy article "Fine-Tuning"—No mention of "puddle".

  3. Reasons to Believe article "Fine-Tuning: Responding to a Common Objection"—One of the Christian apologists from above.

  4. The Atheist Voice video "A Rebuttal to the Fine-Tuning Argument"—Does mention puddle, but only once, in passing.

  5. Rashomon Effect video interview "Intelligently Design, Rebuttal To Fine Tuning Argument | Richard Carrier PhD"—No mention of "puddle".

My search for "puddle analogy" was dominated by Christians claiming that it was an argument made by atheists, without any results (at least not in the top 5) of atheists actually making the argument, and my search for rebuttals of the fine-tuning argument was dominated by non-puddle arguments, with a few off-hand mentions of the puddle argument.

Now, let's look at Douglas Adams' original puddle analogy:

Where does the idea of God come from? [...] Now imagine an early man surveying his surroundings at the end of a happy day's tool making. He looks around and he sees a world which pleases him mightily: behind him are mountains with caves in - mountains are great because you can go and hide in the caves and you are out of the rain and the bears can't get you; in front of him there's the forest - it's got nuts and berries and delicious food; there's a stream going by, which is full of water - water's delicious to drink, you can float your boats in it and do all sorts of stuff with it; here's cousin Ug and he's caught a mammoth - mammoth's are great, you can eat them, you can wear their coats, you can use their bones to create weapons to catch other mammoths. I mean this is a great world, it's fantastic. But our early man has a moment to reflect and he thinks to himself, 'well, this is an interesting world that I find myself in' [...] early man is thinking, 'This world fits me very well. Here are all these things that support me and feed me and look after me; yes, this world fits me nicely' and he reaches the inescapable conclusion that whoever made it, made it for him.

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!'

There is absolutely no mention of the fine-tuning argument here. Adams is not responding to the argument that the conditions are the only ones that make life possible, he is responding to what he imagines the belief of early humans to be, namely that the conditions of humans were particularly suited to humans. One can argue that the label "fine-tuning" sort of fits this line of thinking, but it is a particular sort of fine-tuning, and is not the argument that people usually use "fine-tuning" to refer to.

So, all of that is a frame challenge. What about your actual question? Well, the Christian apologist response to the puddle argument is quite simple: they present an argument that it was never presented as a rebuttal to, point out that it's not a rebuttal to that argument, and then smugly pat themselves on the back about how smart they are. In Adams' analogy, the puddle corresponds to humans, the shape of the puddle corresponds to humans' evolutionary adaptations to their environment, and the hole corresponds to that environment. Humans of course couldn't evolve to fit a universe that didn't allow life in the first place, so of course the puddle analogy doesn't address the claim that the universe is uniquely capable of supporting life. There are plenty of other explanations for how the fine-tuning argument is incoherent, fallacious nonsense, such as in Rational wiki's article "Argument from fine tuning" (again, no mentions of puddles).

The fine-tuning argument implicitly (or, more rarely, explicitly) relies on the intuition that is formalized in Bayesian analysis. But for us to do Bayesian analysis on this question, we would have to take the total number of universes with fine-tuning and a God and divide that by the number of universes with fine-tuning with or without a God. Besides the question of what possible meaning this could have, and how we could figure out what number of universes have fine-tuning and a God (and how asserting that this number is large isn't begging the question), the argument pivots crucially on asserting that the number of universes with fine-tuning and no God is minuscule, at least compared to the number with fine-tuning and a God. This is a positive claim, and the burden of proof is squarely on the apologist. And yet when atheists dispute this claim, for instance by pointing out that there are hypotheses under which such a large multitude of universes are created with different constants that it is inevitable that some of them will have "fine-tuning", this is dismissed by apologists as a "cop-out" with "no evidence" and purely "philosophical" "grasping at straws", as if it's the atheists that somehow have the burden of proof.

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    This is good clarification and nullifies much of what has been asked and answered already +1. So the analogy relates to human adaptation to their environment over time without claiming anything about the origins of either the water (humans) or the hole (environment) since, obviously, the hole does not create the water but only sets the boundary for the shape of the puddle (adaptation). Feb 1 at 12:38
  • This answer addresses the puddle analogy well but would be improved by a better source for the refutations against the fine tuning argument. The physical constants section is especially weak, with some vague claims and no citations. Whether or not you believe in the christian God, apparent fine-tuning of physical constants is a serious issue for physics - it's certainly an unsolved problem (and the proposed solutions are a long way off any kind of 'proof': multiverses, as yet unknown dependence between constants that are independent under current theory, etc) Feb 1 at 21:05
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    @BugCatcherNakata "apparent fine-tuning of physical constants is a serious issue for physics - it's certainly an unsolved problem" - that's a misrepresentation. Why the physical constants are what they are may still be an open question, but it is by no means a "serious issue", because science is full of open questions. That's how science works: we're constantly expanding our knowledge further and further, and the edges of that knowledge consists of open questions, until we answer them. (Unless you just meant "serious issue" in the sense that serious physicists have wondered about it.)
    – NotThatGuy
    Feb 1 at 22:06
  • Yep I did meant it in the same sense you did. I should have said "serious issue IN physics" Feb 1 at 22:49

The answer seems simple: consider what happens when you change the parameters. If you make a small change to the shape of a hole in the ground, you still have an almost identical puddle. If you make a small change to the universal gravitational constant, then as you say, the universe falls apart. It's all about the probability of the conditions being right. For a puddle, the probability is close to one; for the universe, it's close to zero. Except, of course, that in an infinite space of possibilities, improbable things are likely to happen quite often.

Whether that gives any validity to the "fine tuning" argument is another question. To me it seems an abrogation of scientific and philosophical enquiry to suggest that the universe "just happened" without any cause, but how closely that cause resembles the "creator" of our imagination is a very open question.

  • There is a scientific Law that states that if something is impossible, no amount of time will make it possible! Appeal to infinite space, universes, or time would then be feckless, scientifically.
    – ray grant
    Feb 14 at 19:35
  • Doesn't quantum theory make pretty well everything possible, just with low probability? Feb 15 at 6:45
  • A humble correction for your consideration: the knowledge about the Cause was not the result of the Christian's imagination; it was the result of God's "self-revelation"! This is what Christmas was all about: the visible incarnation of the invisible God who gave empirical proofs in time-space reality. Mankind is not adrift on the sea of uncertainty , but has a solid Lighthouse built on the Rock to light our understanding (Mt 16:18, 1 Peter 2:4). God is not a figment of man's imagination; rather, man is a figment of God's creation!
    – ray grant
    Feb 16 at 22:43

The argument ignores the narrow range of constraints to permit intelligent life. As water fits in any size of object, the critic assumes that there could be a totally different form of life, other than our carbon based life form. Robin Collins' website is the best source for understanding the fine tuning argument, covering detailed objections.

Objection 2: Other Forms of Life Objection

Another objection people commonly raise to the fine-tuning argument is that as far as we know, other forms of life could exist even if the parameters of physics were different. So, it is claimed, the fine-tuning argument ends up presupposing that all forms of intelligent life must be like us. The answer to this objection is that most cases of fine-tuning do not make this presupposition. Consider, for instance, the case of the fine-tuning of the strong nuclear force. If it were slightly larger or smaller, no atoms could exist other than hydrogen. Contrary to what one might see on Star Trek, an intelligent life form cannot be composed merely of hydrogen gas: there is simply not enough stable complexity. So, in general the fine-tuning argument merely presupposes that intelligent life requires some degree of stable, reproducible organized complexity. This is certainly a very reasonable assumption.

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