Multiple Universes, Fine-Tuning, and Well-Aimed Bullets

When it comes to the apparent “fine-tuning” of the universe for the existence embodied life, naturalists typically appeal to multiple universes (or a multiverse) to explain why the fine-tuning is not really surprising at all.

A Visual Representation of the Multiverse Option (MVO)

As the story goes, if there are a virtually infinite number of baby universes inside a multiverse – each with different initial conditions and different values for the constants and variables in the known laws of physics – then one of those baby universes is bound to be hospitable to life, however unlikely this might appear from the perspective of human observers.

My aim in this post is not to explore the empirical merits of the multiverse option (MVO) but to examine what I suspect to be an explanatory weakness in it – insofar as the worldview of naturalism enlists it to increase the probability that this universe would exhibit fine-tuning. The possibility still remains that as quantum physics and cosmology progress, new empirical discoveries will one day confirm the existence of universes other than our own. Therefore, I think it wise to offer a philosophical examination of how the MVO can be enlisted to shore up the explanatory resources of naturalism without trying to forecast whether (or to what extent) future scientific research will support or undermine the MVO.

In my view, the main weakness in using the MVO to provide a naturalistic explanation of fine-tuning is not that it accounts for too little, but rather that it can (ironically?) account for anything we observe! It can explain any physical feature or fact about this universe as unsurprising, even virtually certain, insofar as this universe is merely one among infinitely many others.[1] No matter how improbable some physical feature may be on naturalism, the MVO can come to the rescue by showing how at least one world in the cosmic pool of multiple worlds had to exhibit that feature. But why, you might ask, is this a weakness?

Well, one of the virtues of a good explanation is its ability to operate like a “well aimed bullet” – not only by making certain phenomena more likely (or expected) than its competitors, but also by leading us to expect them independently of which ones we actually observe in this universe. An explanation that gives us reasons to believe the actual universe would look a certain way (independent of how it does look) is better than one that can accommodate virtually anything we happen to find after observing the fact.

How does this apply to the theism vs. naturalism debate?

First, on naturalism + the multiverse, there is no reason to expect that this universe would exhibit fine-tuning, apart from the fact that it does. Had the universe been inhospitable to life-forms, we would, of course, not be around to observe this fact, but the lack of fine-tuning (or the presence of it) would still cry out for explanation, even if no observers were around to wonder about it. What’s worse, because the “naturalism + multiverse” hypothesis fits so easily with any physical fact that could be observed, it seems to lack explanatory power. A view that is compatible with anything explains nothing.

Second, on theism, the likelihood of any universe is somewhat low given that (1) God could have decided not to create anything and that (2) other universes may also be consistent with his creative purposes. At any rate, any universe God did create would likely contain orderliness, aesthetic and moral beauty, as well as finite creatures capable of enjoying valuable states of affairs (including divine love). Such a universe would require a lot of “stage-setting” (or fine-tuning) in order to be exhibit these features.

In other words, if we can imagine a target that consist of points which represent possible universes, theism operates like a well-aimed bullet by narrowing down the space on the target where the bullet is likely to hit. By contrast, naturalism (+ the multiverse) cannot predict beforehand where (on the target) a particular bullet will likely hit. Rather, it predicts that every point on the target will be hit because an infinite number of randomly aimed bullets are being fired!

Does Naturalism really have this many “bullets” in its explanatory arsenal to explain fine-tuning? Is theism a better explanation because it doesn’t need so many “bullets” to do the explaining?

What kind of explanation do you, the reader, believe is better: a well-aimed bullet or an infinite spread of randomly aimed bullets? How would your answer to this question impact the theism vs. naturalism debate over the fine-tuning of the universe?


[1] M-Theory currently allows for 10 to the 500th possible worlds within a multiverse, which is a far cry from an actually infinite number of worlds, but that is beside my point in this blog post.

4 thoughts on “Multiple Universes, Fine-Tuning, and Well-Aimed Bullets”

  1. Very nice post!

    One question I have is this (It’s purely a *question* – I do not have an answer myself).

    You write “A view that is compatible with anything explains nothing.”

    An explanation can be true or false. It could happen that both views X and Y are both able to explain Z, but that X would also be able to explain *any* non-Z. It might also perfectly well be that X is actually the *true* explanation of Z.

    If we would have independent reason to believe that X holds while we have independent reason to believe that Y doesn’t hold, wouldn’t we then have better reason to consider X a good explanation of Z (even though X is not a well-aimed bullet at all)?

    …maybe this is all very confused 🙂

  2. That’s a difficult questions Dominic:
    Insofar that X is compatible with any Z or non-Z (I won’t say “explain” Z since that is the question at hand), then what counts as an “independent” reason would have to be of an order that is distinct from Z’s and non-Z’s. Perhaps X is simpler than Y, or has a higher prior probability, or lacks add hoc assumptions that Y posits? For what it’s worth, the X that you describe is severely limited as an explanation because no factors other than simplicity, prior probability, or ad hoc purity could increase or decrease its likelihood.

    After some further thought, I doubt that the multiverse or some variation of it satisfies X. I’m inclined to believe that empirical data will one day reveal the existence of other worlds (though perhaps only a finite number) – so it isn’t empirically neutral as my last post suggested. But it seems crucial, though, to specify what kind of explaining the MVO is supposed to do. As an explanation of fine-tuning, it functions more conservatively. As an explanation of any physical event within this universe, no matter how improbable, it functions too extravagantly. Would you agree?

  3. Following the bullet analogy, I suppose an objector can argue as follows: whether a narrow point on the target is hit by one bullet or an infinite bunch of random bullets, what difference does it make? The narrow point got hit, period, end of story.

  4. Here are some final thoughts. In the above post entitled, “Multiple Universes, Fine-Tuning, and Well-Aimed Bullets,” I claimed that (1) an explanation is more powerful if it operates like a well-aimed bullet by leading us to expect certain phenomena independently of which ones we actually observe. On the basis of (1), I argued that (2) the multiverse option (MVO) lacks explanatory power because it is compatible with virtually any physical fact we happen to observe and therefore cannot lead us to expect such facts independently of our observing them. Put simply, the MVO lacks explanatory power because it is not a well-aimed bullet.

    In retrospect, I suspect that (1) might be too stringent a requirement for hitting targets (i.e. for explanatory power). Why? Because whether a target gets hit by a well-aimed bullet or by a multitude of randomly aimed bullets makes little difference: the target got hit, end of story! This conclusion would thereby undermine (2) because whether the existence of a finely-tuned universe is explained by appealing to God’s independent reasons for creating a hospitable world or by a multitude of worlds which is bound to contain one like ours makes little difference to explanatory power. Note: I have said nothing about other features of good explanations, such as simplicity, scope, and outside corroboration, etc.

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