An existential risk is a risk “that threatens the premature extinction of Earth-originating intelligent life or the permanent and drastic destruction of its potential for desirable future development,” (Bostrom, 2013). Nick Bostrom has argued that

“[T]he loss in expected value resulting from an existential catastrophe is so enormous that the objective of reducing existential risks should be a dominant consideration whenever we act out of an impersonal concern for humankind as a whole. It may be useful to adopt the following rule of thumb for such impersonal moral action:

Maxipok: Maximize the probability of an “OK outcome,” where an OK outcome is any outcome that avoids existential catastrophe.”

There are a number of people in the effective altruism community who accept this view and cite Bostrom’s argument as their primary justification. Many of these people also believe that the best ways of minimizing existential risk involve making plans to prevent specific existential catastrophes from occurring, and believe that the best giving opportunities must be with charities that primarily focus on reducing existential risk. They also appeal to Bostrom’s argument to support their views. (Edited to add: Note that Bostrom himself sees maxipok as neutral on the question of whether the best methods of reducing existential risk are very broad and general, or highly targeted and specific.) For one example of this, see Luke Muehlhauser’s comment:

“Many humans living today value both current and future people enough that if existential catastrophe is plausible this century, then upon reflection (e.g. after counteracting their unconscious, default scope insensitivity) they would conclude that reducing the risk of existential catastrophe is the most valuable thing they can do — whether through direct work or by donating to support direct work.”

I now think these views require some significant adjustments and qualifications, and given these adjustments and qualifications, their practical implications become very uncertain. I still believe that what matters most about what we do is how our actions affect humanity’s long-term future potential, and I still believe that targeted existential risk reduction and research is a promising cause, but it now seems unclear whether targeted existential risk reduction is the best area to look for ways of making the distant future go as well as possible. It may be and it may not be, and which is right probably depends on many messy details about specific opportunities, as well as general methodological considerations which are, at this point, highly uncertain. Various considerations played a role in my reasoning about this, and I intend to talk about more of them in greater detail in the future. I’ll talk about just a couple of these considerations in this post.

In this post, I argue that:

Though Bostrom’s argument supports the conclusion that maximizing humanity’s long term potential is extremely important, it does not provide strong evidence that reducing existential risk is the best way of maximizing humanity’s future potential. There is a much broader class of actions which may affect humanity’s long-term potential, and Bostrom’s argument does not uniquely favor existential risk over other members in this class. A version of Bostrom’s argument better supports a more general view: what matters most is that we make path-dependent aspects of the far future go as well as possible. There are important questions about whether we should accept this more general view and what its practical significance is, but this more general view seems to be a strict improvement on the view that minimizing existential risk is what matters most. The above points favor very broad, general, and indirect approaches to shaping the far future for the better , rather than thinking about very specific risks and responses, though there are many relevant considerations and the issue is far from settled.

I think some prominent advocates of existential risk reduction already agree with these general points, and believe that other arguments, or other arguments together with Bostrom’s argument, establish that direct existential risk reduction is what matters most. This post is most relevant to people who currently think Bostrom’s arguments may settle the issues discussed above.

Path-dependence and trajectory changes

In thinking about how we might affect the far future, I've found it useful to use the concept of the world's development trajectory, or just trajectory for short. The world's development trajectory, as I use the term, is a rough summary way the future will unfold over time. The summary includes various facts about the world that matter from a macro perspective, such as how rich people are, what technologies are available, how happy people are, how developed our science and culture is along various dimensions, and how well things are going all-things-considered at different points of time. It may help to think of the trajectory as a collection of graphs, where each graph in the collection has time on the x-axis and one of these other variables on the y-axis.

With that concept in place, consider three different types of benefits from doing good. First, doing something good might have proximate benefits—this is the name I give to the fairly short-run, fairly predictable benefits that we ordinarily think about when we cure some child's blindness, save a life, or help an old lady cross the street. Second, there are benefits from speeding up development. In many cases, ripple effects from good ordinary actions speed up development. For example, saving some child's life might cause his country's economy to develop very slightly more quickly, or make certain technological or cultural innovations arrive more quickly. Third, our actions may slightly or significantly alter the world's development trajectory. I call these shifts trajectory changes. If we ever prevent an existential catastrophe, that would be an extreme example of a trajectory change. There may also be smaller trajectory changes. For example, if some species of dolphins that we really loved were destroyed, that would be a much smaller trajectory change.

The concept of a trajectory change is closely related to the concept of path dependence in the social sciences, though when I talk about trajectory changes I am interested in effects that persist much longer than standard examples of path dependence. A classic example of path dependence is our use of QWERTY keyboards. Our keyboards could have been arranged in any number of other possible ways. A large part of the explanation of why we use QWERTY keyboards is that it happened to be convenient for making typewriters, that a lot of people learned to use these keyboards, and there are advantages to having most people use the same kind of keyboard. In essence, there is path dependence whenever some aspect of the future could easily have been way X, but it is arranged in way Y due to something that happened in the past, and now it would be hard or impossible to switch to way X. Path dependence is especially interesting when way X would have been better than way Y. Some political scientists have argued that path dependence is very common in politics. For example, in an influential paper (with over 3000 citations) Pierson (2000, p. 251) argues that:

Specific patterns of timing and sequence matter; a wide range of social outcomes may be possible; large consequences may result from relatively small or contingent events; particular courses of action, once introduced, can be almost impossible to reverse; and consequently, political development is punctuated by critical moments or junctures that shape the basic contours of social life.

The concept of a trajectory change is also closely related to the concept of a historical contingency. If Thomas Edison had not invented the light bulb, someone else would have done it later. In this sense, it is not historically contingent that we have light bulbs, and the most obvious benefits from Thomas Edison inventing the light bulb are proximate benefits and benefits from speeding up development. Something analogous is probably true of many other technological innovations such as computers, candles, wheelbarrows, object-oriented programming, and the printing press. Some important examples of historical contingencies: the rise of Christianity, the creation of the US Constitution, and the writings of Karl Marx. Various aspects of Christian morality influence the world today in significant ways, but the fact that those aspects of morality, in exactly those ways, were part of a dominant world religion was historically contingent. And therefore events like Jesus's death and Paul writing his epistles are examples of trajectory changes. Likewise, the US Constitution was the product of deliberation among a specific set of men, the document affects government policy today and will affect it for the foreseeable future, but it could easily have been a different document. And now that the document exists in its specific legal and historical context, it is challenging to make changes to it, so the change is somewhat self-reinforcing.

Some small trajectory changes could be suboptimal

Persistent trajectory changes that do not involve existential catastrophes could have great significance for shaping the far future. It is unlikely that the far future will inherit many of our institutions exactly as they are, but various aspects of the far future—including social norms, values, political systems, and perhaps even some technologies—may be path dependent on what happens now, and sometimes in suboptimal ways. In general, it is reasonable to assume that if there is some problem that might exist in the future and we can do something to fix it now, future people would also be able to solve that problem. But if values or social norms change, they might not agree that some things we think are problems really are problems. Or, if people make the wrong decisions now, certain standards or conventions may get entrenched, and resulting problems may be too expensive to be worth fixing. For further categories of examples of path-dependent aspects of the far future, see these posts by Robin Hanson.

The astronomical waste argument and trajectory changes

Bostrom’s argument only works if reducing existential risk is the most effective way of maximizing humanity’s future potential. But there is no robust argument that trying to reduce existential risk is a more effective way of shaping the far future than trying to create other positive trajectory changes. Bostrom’s argument for the overwhelming importance of reducing existential risk can be summarized as follows:

The expected size of humanity's future influence is astronomically great. If the expected size of humanity's future influence is astronomically great, then the expected value of the future is astronomically great. If the expected value of the future is astronomically great, then what matters most is that we maximize humanity’s long-term potential. Some of our actions are expected to reduce existential risk in not-ridiculously-small ways. If what matters most is that we maximize humanity’s future potential and some of our actions are expected to reduce existential risk in not-ridiculously-small ways, what it is best to do is primarily determined by how our actions are expected to reduce existential risk. Therefore, what it is best to do is primarily determined by how our actions are expected to reduce existential risk.

Call that the “astronomical waste” argument.

It is unclear whether premise (5) is true because it is unclear whether trying to reduce existential risk is the most effective way of maximizing humanity’s future potential. For all we know, it could be more effective to try to create other positive trajectory changes. Clearly, it would be better to prevent extinction than to improve our social norms in a way that indirectly makes the future go one millionth better, but, in general, “X is a bigger problem than Y” is only a weak argument that “trying to address X is more important than trying to address Y.” To be strong, the argument must be supplemented by looking at many other considerations related to X and Y, such as how much effort is going into solving X and Y, how tractable X and Y are, how much X and Y could use additional resources, and whether there are subsets of X or Y that are especially strong in terms of these considerations.

Bostrom does have arguments that speeding up development and providing proximate benefits are not as important, in themselves, as reducing existential risk. And these arguments, I believe, have some plausibility. Since we don’t have an argument that reducing existential risk is better than trying to create other positive trajectory changes and an existential catastrophe is one type of trajectory change, it seems more reasonable for defenders of the astronomical waste argument to focus on trajectory changes in general. It would be better to replace the last two steps of the above argument with:

4’ Some of our actions are expected to change our development trajectory in not-ridiculously-small ways.

5’. If what matters most is that we maximize humanity’s future potential and some of our actions are expected to change our development trajectory in not-ridiculously-small ways, what it is best to do is primarily determined by how our actions are expected to change our development trajectory.

6’. Therefore, what it is best to do is primarily determined by how our actions are expected to change our development trajectory.

This seems to be a strictly more plausible claim than the original one, though it is less focused.

In response to the arguments in this post, which I e-mailed him in advance, Bostrom wrote a reply (see the end of the post). The key comment, from my perspective, is:

“Many trajectory changes are already encompassed within the notion of an existential catastrophe. Becoming permanently locked into some radically suboptimal state is an xrisk. The notion is more useful to the extent that likely scenarios fall relatively sharply into two distinct categories---very good ones and very bad ones. To the extent that there is a wide range of scenarios that are roughly equally plausible and that vary continuously in the degree to which the trajectory is good, the existential risk concept will be a less useful tool for thinking about our choices. One would then have to resort to a more complicated calculation. However, extinction is quite dichotomous, and there is also a thought that many sufficiently good future civilizations would over time asymptote to the optimal track.”

I agree that a key question here is whether there is a very large range of plausible equilibria for advanced civilizations, or whether civilizations that manage to survive long enough naturally converge on something close to the best possible outcome. The more confidence one has in the second possibility, the more interesting existential risk is as a concept. The less confidence one has in the second possibility, the more interesting trajectory changes in general are. However, I would emphasize that unless we can be highly confident in the second possibility, it seems that we cannot be confident that reducing existential risk is more important than creating other positive trajectory changes because of the astronomical waste argument alone. This would turn on further considerations of the sort I described above.

Broad and narrow strategies for shaping the far future

Both the astronomical waste argument and the fixed up version of that argument conclude that what matters most is how our actions affect the far future. I am very sympathetic to this viewpoint, abstractly considered, but I think its practical implications are highly uncertain. There is a spectrum of strategies for shaping the far future that ranges from the very targeted (e.g., stop that asteroid from hitting the Earth) to very broad (e.g., create economic growth, help the poor, provide education programs for talented youth), with options like “tell powerful people about the importance of shaping the far future” in between. The limiting case of breadth might be just optimizing for proximate benefits or for speeding up development. Defenders of the astronomical waste argument tend to be on the highly targeted end of this spectrum. I think it’s a very interesting question where on this spectrum we should prefer to be, other things being equal, and it’s a topic I plan to return to in the future.

The arguments I’ve offered above favor broader strategies for shaping the far future, though they don’t settle the issue. The main reason I say this is that the best ways of creating positive trajectory changes may be very broad and general, whereas the best ways of reducing existential risk may be more narrow and specific. For example, it may be reasonable to try to assess, in detail, questions like, “What are the largest specific existential risks?” and, “What are the most effective ways of reducing those specific risks?” In contrast, it seems less promising to try to make specific guesses about how we might create smaller positive trajectory changes because there are so many possibilities and many trajectory changes do not have significance that is predictable in advance. No one could have predicted the persistent ripple effects that Jesus's life had, for example. In other cases—such as the framing of the US Constitution—it's clear that a decision has trajectory change potential, but it would be hard to specify, in advance, which concrete measures should be taken. In general, it seems that the worse you are at predicting some phenomenon that is critical to your plans, the less your plans should depend on specific predictions about that phenomenon. Because of this, promising ways to create positive trajectory changes in the world may be more broad than the most promising ways of trying to reduce existential risk specifically. Improving education, improving parenting, improving science, improving our political system, spreading humanitarian values, or otherwise improving our collective wisdom as stewards of the future could, I believe, create many small, unpredictable positive trajectory changes.

I do not mean to suggest that broad approaches are necessarily best, only that people interested in shaping the far future should take them more seriously than they currently do. The way I see the trade-off between highly targeted strategies and highly broad strategies is as follows. Highly targeted strategies for shaping the far future often depend on highly speculative plans, often with many steps, which are hard to execute. We often have very little sense of whether we are making valuable progress on AI risk research or geo-engineering research. On the other hand, highly broad strategies must rely on implicit assumptions about the ripple effects of doing good in more ordinary ways. It is very subtle and speculative to say how ordinary actions are related to positive trajectory changes, and estimating magnitudes seems extremely challenging. Considering these trade-offs in specific cases seems like a promising area for additional research.

Summary

In this post, I argued that:

The astronomical waste argument becomes strictly more plausible if we replace the idea of minimizing existential risk with the idea of creating positive trajectory changes. There are many ways in which our actions could unpredictably affect our general development trajectory, and therefore many ways in which our actions could shape the far future for the better. This is one reason to favor broad strategies for shaping the far future.

The trajectory change perspective may have other strategic implications for people who are concerned about maximizing humanity’s long-term potential. I plan to write about these implications in the future. [i]

[What follows is an e-mail response from Nick Bostrom. He suggested that I share his comment along with the post. Note that I added a couple of small clarifications to this post (noted above) in response to Bostrom's comment.]

One can arrive at a more probably correct principle by weakening, eventually arriving at something like 'do what is best' or 'maximize expected good'. There the well-trained analytic philosopher could rest, having achieved perfect sterility. Of course, to get something fruitful, one has to look at the world not just at our concepts.

Many trajectory changes are already encompassed within the notion of an existential catastrophe. Becoming permanently locked into some radically suboptimal state is an xrisk. The notion is more useful to the extent that likely scenarios fall relatively sharply into two distinct categories---very good ones and very bad ones. To the extent that there is a wide range of scenarios that are roughly equally plausible and that vary continuously in the degree to which the trajectory is good, the existential risk concept will be a less useful tool for thinking about our choices. One would then have to resort to a more complicated calculation. However, extinction is quite dichotomous, and there is also a thought that many sufficiently good future civilizations would over time asymptote to the optimal track.

In a more extended and careful analysis there are good reasons to consider second-order effects that are not captured by the simple concept of existential risk. Reducing the probability of negative-value outcomes is obviously important, and some parameters such as global values and coordination may admit of more-or-less continuous variation in a certain class of scenarios and might affect the value of the long-term outcome in correspondingly continuous ways. (The degree to which these complications loom large also depends on some unsettled issues in axiology; so in an all-things-considered assessment, the proper handling of normative uncertainty becomes important. In fact, creating a future civilization that can be entrusted to resolve normative uncertainty well wherever an epistemic resolution is possible, and to find widely acceptable and mutually beneficial compromises to the extent such resolution is not possible---this seems to me like a promising convergence point for action.)

It is not part of the xrisk concept or the maxipok principle that we ought to adopt some maximally direct and concrete method of reducing existential risk (such as asteroid defense): whether one best reduces xrisk through direct or indirect means is an altogether separate question.