Summary: The Many-Worlds interpretation of quantum mechanics can help us feel better about choosing between mutually exclusive options.

Previously I’ve suggested that when we think about the ethical implications of the many-worlds interpretation (MWI) of quantum mechanics, the kinds of implications we should expect are ones about how to feel in certain ethical situations, and what kinds of character traits or ‘virtues’ we should try to develop.

In this post I’m going to focus in on the implications it has for how we feel about mutually exclusive life choices.

The Road Not Taken

The fact that the human condition contains mutually exclusive options is often seen as cause for regret and anxiety. Robert Frost’s poem The Road Not Taken is a classic expression of this.

The narrator is “sorry I could not travel both” of the two roads that diverge in a yellow wood, and expects to look back on his choice “with a sigh”.

In addition to being mutually exclusive, the roads are also hard to see down due to the fact that they “bent in the undergrowth”, and are “really about the same” in terms of their attractiveness.

This reflects another aspect of the choices that cause such feelings. It is because both choices seem more or less equally good, given our limited knowledge, that being forced to choose one or the other provokes such anxiety.

The poem strikes a chord because it expresses something we all feel at times. Life does contain such choices.

Often such choices are relatively trivial. Choosing a dessert from a menu, for instance. Choosing a film to watch on a night out. Choosing a holiday destination.

But sometimes they can be significant. Choosing an undergraduate degree. Choosing who to vote for. Choosing a hobby. Choosing between two life partners.

Sometimes too the choice may be whether to take some particular course of action or not to do so. Getting married, for example, or having children.

Travelling both roads

Does MWI allow us to travel both roads, and thereby feel differently about such decisions?

A sceptic might argue that “Decision and decoherence are entirely orthogonal concepts.”

As Eliezer puts it:

You don’t split when you come to a decision in particular, any more than you particularly split when you take a breath. You’re just splitting all the time as the result of decoherence, which has nothing to do with choices….It’s not that one version of you chooses what seems best, and another version chooses what seems worst. In each world, apples go on falling and people go on doing what seems like a good idea.

But the truth is we aren’t currently sure about this. Too little is known about consciousness, and the way that decision-making actually works in the brain.

According to David Wallace, there are three main scenarios in which splitting or decoherence occurs.

1. Deliberate human experiments: Schrödinger’s cat, the two-slit experiment, Geiger counters, and the like.

2. ‘Natural quantum measurements’, such as occur when radiation causes cell mutation.

3. ‘Classically chaotic’ processes: that is, processes governed by Hamiltonians whose classical analogues are chaotic.

Normal decision-making clearly doesn’t fall into category 1.

But it certainly seems possible that decision-making involves chaotic processes (category 3). A research program in cognitive science models the brain as a self-organising dynamic system, in which chaotic processes can occur^[1].

And since chaotic processes are those in which infinitesimally small variations in initial conditions can lead to exponentially divergent outcomes, there is even a possible role for category 2 in decision-making: every human body is bombarded by thousands of ‘cosmic rays’ every second, some of which could cause variations to the relevant initial conditions.

So it is quite possible that whenever we make a decision, the universe does in fact split into numerous worlds: one for each possible outcome of the decision-making process going on in my brain.

It is important to note that cognitive science can’t currently tell us what those possible outcomes might be. It could be that the possible outcomes could vary widely, so that for every good decision I make there are some worlds in which I make very bad ones.

It could also be - and this option perhaps seems more likely - that the possible outcomes are limited to a very narrow range of possible decisions, centered near the decision we actually take in a given world.

But the case of choosing between equally desirable, mutually exclusive options, seems very likely to result in splitting, in this model.

Because the two options are so hard to decide between, a small ‘chaotic’ factor could tip us one way or the other (or perhaps tip the balance in favour of one part of our internal family system).

Real decision-making

It’s true that for our most significant decisions, we sometimes wait for our feelings to ‘settle’ before making the decision, which could make the overall decision less chaotic.

But sometimes this just doesn’t work. You wait, your feelings go this way, then that way. The wedding day comes and you find yourself getting cold feet.

Or maybe there’s pressure to make a decision quickly, and you just go for one or the other.

Real decision-making is bounded in numerous ways. There are always some time constraints (even if it’s a matter of years) and there’s also the opportunity cost of devoting that time to making a better decision. And you can never have access to all relevant information.

So there’s always the chance your decision is shaped by being exposed to new information or arguments, in a way that is governed by chaotic processes in your social environment.

Theories of bounded rationality offer a kind of ideal of decision-making within the constraints we are faced with. But many people fall quite far short of ideals of this sort.

Many real decisions - even significant ones - are made based on incorrect reasoning or a failure to consider relevant information. And beyond a certain point one might even begin to question whether the process involved counts as making a decision.

Someone might look back on a key turning point in their life and think “I was so young and foolish, I never really decided on that”. The decision was essentially made for them, by their social in-group, or other circumstances beyond their control.

The point is that in real decisions there’s no hard boundary between processes happening in your brain and processes in your environment.

So even if you have doubts that the brain-processes are chaotic in the way relevant for quantum-mechanical splitting, it seems pretty clear that the relevant environment-processes are.

Decision and decoherence are not orthogonal, and this is in part because decisions are enmeshed in chaotic environmental processes.

The Multiverse perspective

So it seems for at least some ‘road not taken’ decisions we do take both roads, according to MWI. How should we feel about this?

It’s true that there’s no single stream of consciousness that encompasses experiences of both outcomes, so in this respect the situation remains unchanged. Robert Frost could still be “sorry I could not travel both, and be one traveller”.

But there is an important sense in which the situation has changed. If you believe MWI, you believe that there are other versions of you that made a different degree choice, say, or married a different person.

Some might even go so far as to say that it is you. But these technical questions of personal identity seem rather irrelevant. Whether or not it is you or not, it is a person with an identical history and stream of consciousness up to the point that the two paths diverged, and someone who is presumably enjoying exactly the same experience you would have had, if you had chosen the other path.

So, it seems reasonable to feel at least partial relief from the regret and anxiety that would otherwise come with your choice.

Regret is (among other things) the feeling that you should have done something other than you actually did. But in MWI you (or your counterpart) actually did do the other thing too.

Anxiety is (among other things) the worry that you'll fail to make the right choice. But in MWI you (or your counterpart) take all the options, including the right one.

In addition to relief from negative feelings, the knowledge that one is taking both roads may also bring with positive feelings of plenitude, or a kind of vicarious pleasure.

It seems no less reasonable to feel vicarious pleasure for your multiverse counterpart than it is to feel it for your best friend, or your child. Given the extreme similarities between yourself and your counterpart, it may be more reasonable in fact. (Not to mention vicarious pleasure makes sense even where there's no similarity: your mood could be lifted by a complete stranger across the street dancing along to their headphones.)

So these pleasures, and this relief from regret and anxiety, are rational feelings in MWI. It makes rational sense for us to try to be the kind of wise person who takes the multiverse point of view, and as a result worries less about ‘road not taken’ decisions

Existential physics

So MWI does have valuable implications for the way we think about mutually exclusive life choices.

It's instructive to compare the many-worlds approach here with what may be the only well-known philosophy that's directly addressed this same issue: existentialism.

Existentialist thinkers like Heidegger and Sartre suggested that the difficulties faced when encountering equally attractive but mutually exclusive life choices are characteristic of human freedom more generally.

Here's Heidegger in Being and Time, for example:

Freedom is only in the choice of one possibility - that is, in tolerating one's not having chosen the others and one's not being able to choose them

(The important italics are Heidegger’s).

Both thinkers also explored the specific kinds of anxiety (Heidegger, following Kierkegaard, calls it angst, and Sartre refers to anguish) associated with this freedom.

Each in their own ways, they also proposed ways of responding to this existential anxiety, involving the notion of authenticity.

For Heidegger, by revealing both our historical situatedness and our mortality, existential angst can be made to reveal our ‘ownmost possibilities’, enabling us to make a resolute choice in the face of uncertainty.

Likewise Sartre suggests that his conception of anguished freedom can help us become clear on the ‘fundamental project’ that defines us.

Now, the concept of authenticity here can be understood as a virtue: a disposition or character trait that shapes how we think and feel about fundamental life choices.

And like the approach to MWI I’ve sketched above, existentialism draws conclusions about this virtue from considerations about the basic nature of reality^[2].

But in these respects existentialism seems exactly the inverse of the MWI approach I’ve presented.

While existentialism treats mutually exclusive life choices as part of the fabric of reality, MWI says that at the level of fundamental physics, the apparent exclusivity is an illusion: there’s a sense in which we can make both choices.

And the conclusions of the two approaches diverge as well. While existentialism recommends the virtue of zeroing in on a singular authentic choice, MWI suggests a virtue of zooming out, and attending to the multiple choices we make in multiple worlds.

While both approaches seek a way out from the anxiety and regret of decision-making, existentialism still ends up in a serious mood: we are ‘condemned to be free’ as Sartre put it.

MWI suggests a lighter mood. We should still of course aim to make good choices. Given the constraints of bounded rationality, we may never know if those choices are optimal. But in the grand scheme of the quantum multiverse, that’s no great cause for concern.

^{^}
For example the work of Walter Freeman. His book How Brains Make Up their Minds is an application of this approach to decision-making. This article is a contemporary example of the same paradigm.
^{^}
Both Sartre and Heidegger are influenced by the post-Kantian tradition of German Idealism, in which questions of fundamental ontology are inseparable from apparently psychological questions about human experience. This ultimately derives from Kant's idea that reality must conform to fundamental structures of human consciousness in order to be knowable by us.