The Failure of the Puddle Analogy

And some other replies to fine-tuning

1 Introduction

I think the fine-tuning argument is one of the best arguments for God’s existence, but I’ll readily admit: there are complicated and tricky issues that one needs to sort out to decide if it works. All is not smooth sailing. To get to the bottom of the various objections, you have to do lots of thinking.

Many objections to fine-tuning are serious. The multiverse reply, electrons in love, the measure problem—all these are tricky to figure out. I’ve talked about them (plus some less serious objection) here in more detail.

But there are also lots of very popular objections to fine-tuning that obviously totally fail and have exactly zero force. I thought I’d explain why a lot of the common replies don’t work. The worst offender is the puddle analogy.

2 Muddles with puddles

The puddle analogy came from Douglas Adams. He wrote some pretty funny books like Hitchhiker’s Guide to the Galaxy, but sadly being good at making quips and writing science fiction does not give one any special expertise on fine-tuning (unlike being a 21-year-old undergraduate, which gives one deep insight into fine-tuning). The original quote from which the argument is drawn is:

“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, 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. I think this may be something we need to be on the watch out for.”

The thing that’s irritating about the puddle analogy is that it’s not quite clear what the point is. The above paragraph gives one analogy involving a puddle that seems to have a great number of possible lessons. Each lesson, however, isn’t an adequate reply to fine-tuning.

Consider the bit at the end. Adams seems to think that because the puddle will go extinct eventually, it should think the universe was not made for it. Analogously, because heat death will end all life, we shouldn’t think the universe was made for us.

But this is a bad inference. First of all, sometimes the world might be made for a creature even if the creature will not last. Human experimenters make petri dishes to study E. coli. Eventually these petri dishes are destroyed—they are not made to last. Nonetheless, a sentient E. coli would not be irrational to think a human petri dish was made for it if it observed parameters set just right for it.

Second of all, all that we know is that in the distant future, if the laws continue working as they have before, we will not continue to exist in this location. But we do not know that we will be destroyed. Christians tend to think that God will raise us all from the dead and usher in a new creation. Theists can—and should—believe in the afterlife.

If one’s objection to fine-tuning is that we will not be around forever, this is straightforwardly question-begging. If theism is true, this is almost certainly false. A perfect being would have no reason to snuff us out after just a few decades. Adams’ analogy is like an E. coli. seeing that though the petri dish is perfectly suited for them in lots of improbable ways, because the petri dish will not last it must not be for them—even though on the hypothesis it was made for them, there’s every reason to suspect that they will be transferred to another nicer location after this life ends.

But this is not the part of the analogy that people tend to focus on. They care more about the puddle bit. The idea seems to be that the puddle is reasoning poorly. The universe is not made for them, instead they are made for the universe. Evolution is claimed to be similar—the universe is not built so that we can survive, we are built so that we can survive through the process of evolution by natural selection.

But this simply fails to grapple with fine-tuning. Proponents of fine-tuning are not advocates of traditional intelligent design. They do not claim that we should believe in God because his existence is the only way to explain why humans have such developed capabilities that enable us to survive.

Instead, they claim that we should believe in God because his existence is the best explanation of a universe that is capable of harboring life in the first place—or any complex structure. If the cosmological constant were different, for instance, the evolutionary process could never have gotten started. No two particles would ever interact. If no particles ever interacted, it’s rather difficult to see how life could have begun.

The puddle errs because the sets of conditions capable of sustaining a puddle are not actually very rare. Most containers of most shapes could contain a puddle of water (this is how liquid works!) If, in contrast, there was a rare type of sentient gas that needed some extremely specific configuration that had a one in googol probability of forming by chance—well, then it would seem obvious that such a gas should think the conditions around them were made for them after finding itself in such a container.¹

The puddle goes wrong in falsely assuming that the conditions that will produce them are very rare. But this is true in the case of fine-tuning, and has been established to be so by physicists.

(Of course, it may be that the puddle should think someone finely-tuned the constants because only a world with a finely-tuned cosmological constant could produce puddles or any other structure. But then the puddle analogy amounts to little more than the claim that a sentient puddle shouldn’t buy the fine-tuning argument—which would only be persuasive to one who thinks other creatures shouldn’t buy the fine-tuning argument. A sentient puddle should equally think God finely-tuned the cosmological constant).

So that is why the puddle analogy is not a good objection. It differs from the fine-tuning argument in a crucial respect: the probability of finely-tuned constants is actually very low. The probability of the universe having some structures that contain puddles are not.

3 But we only have one universe!

Another common reply to fine-tuning is the following: how can we declare fine-tuning unlikely. We only have one universe. It’s not like we can say that fine-tuning is statistically rare, because we only have one universe to sample from. You can’t do probability on a sample of one.

This sounds plausible at first but turns out to be false. Not only can you do probability on a sample of one, we do it all the time.

Why do scientists believe in continental drift—the notion that the continents were all part of one supercontinent that drifted apart? There are a few different reasons but the big ones are:

1. Fossils on different continents were very similar in the distant past. However, after various dates (differing between different continents) the species on continents started to diverge. This is positively expected if continents broke apart but utterly bizarre if they didn’t—why the heck would two different continents separated by an ocean have similar plant and animal life until some discrete time period after which they break apart.

2. The continental shelves of the various continents line up like puzzle pieces. Again, this is striking. By chance one would not expect continents to fit together like pieces of a jigsaw puzzle.

We can rightly say that if continental drift didn’t happen these things are really improbable. But how can we say that? We only have one universe! It’s not like we have a large sample of continents drifting apart—plus a large sample of them not.

The reason we can declare it improbable is that if there was no continental drift, one could imagine fossils taking on any pattern. If something could conceivably take on any pattern, but it takes on some highly specific pattern that matches with some other hypothesis, then that fact is evidence for that other hypothesis. This is why even though we don’t have a big sample of aliens, if we found binaristic incoding of digits of pi from a distant star, we’d assume it was aliens and not chance.

Similarly, to give an analogy from Michael Huemer, imagine that the initial conditions spelled out “made by God.” Surely this would be strong evidence of a designer. This isn’t because we’ve observed that most universes without designers spell that out. It’s because out of all the conceivable arrangements it could take on, the odds it would take on that particular highly specific arrangement are very low.

4 That’s just a God of the gaps fallacy

Fine-tuning is commonly claimed to be a God of the gaps fallacy. The core idea seems to be that it’s fallacious to assume that just because we don’t know how something happened God must have done it.

I think the phrase “God of the gaps” is hopelessly confused and needs to die.

Why is it fallacious to use God to plug a gap in our knowledge? Does one commit an “evolution of the gaps fallacy,” whenever they use evolution to explain some phenomenon in the world like nested hierarchies and transitional fossils. Of course not! Some fact is evidence for a hypothesis if that fact is likelier given the hypothesis than given its falsity! If there’s some otherwise mysterious fact about the world that is likelier if there’s a God than if there’s not, then that fact is evidence for God’s existence.

Anytime we get evidence for a hypothesis, it comes from that hypothesis plugging a gap. We rightly believe in evolution because it plugs a lot of gaps—explaining many biological features that would otherwise be utterly mysterious.

It wouldn’t be wise to simply use God to explain random things we don’t know about. To give an analogy Aron gave, up until a few years ago, we didn’t really know what caused holes in swiss cheese. No one said that God must directly send out emissaries to bore holes in swiss cheese. But that’s because the probability of there being holes in cheese are no higher given theism than atheism. It does no good to point to random theistic explanations of things if there’s no reason to think they’re likelier given God’s existence than given atheism.

The way to reason about evidence is Bayesian—a fact is evidence for theories on which it’s least improbable. Provided some theory like theism naturally explains some phenomena, then if it’s otherwise surprising, that phenomena is evidence for theism.

I’ve discussed this in more detail here, if you’re interested. I’ve also explained, in that article, why claiming that arguments commit the appeal to incredulity fallacy is basically always confused.

5 Conclusion

I have just scratched the surface of bad objections to fine-tuning. There are many, many more. There are enough to fill all the libraries of the world (okay, not really unless people are writing in really big letters). But hopefully I’ve adequately explained why at least many of the common ones fail.

1. To be more precise, and more analogous to fine-tuning, assume that that the odds are around one in googol that it would be possible for such a gas to form anywhere in the universe.