This post provides a summary of my working paper “Welfare and Felt Duration.” The goal is to make the content of the paper more accessible and to add context and framing for an EA audience, including a more concrete summary of practical implications. It’s also an invitation for you to ask questions about the paper and/or my summary of it, to which I’ll try to reply as best I can below.

What’s the paper about? 

The paper is about how duration affects the goodness and badness of experiences that feel good or bad. For simplicity, I mostly focus on how duration affects the badness of pain. 

In some obvious sense, pains that go on for longer are worse for you. But we can draw some kind of intuitive distinction between how long something really takes and how long it is felt as taking. Suppose you could choose between two pains: one feels longer but is objectively shorter, and the other feels shorter but is objectively longer. Now the choice isn’t quite so obvious. Still, some people are quite confident that you ought to choose the second: the one that feels shorter. They think it’s how long a pain feels that’s important, not how long it is. The goal of the paper is to argue that that confidence isn’t warranted.  

Why is this important? 

This issue affects the moral weights assigned to non-human animals and digital minds. 

The case for thinking that subjective time experience varies across the animal kingdom is summarized in this excellent post by Jason Schukraft, which was a huge inspiration for this paper.  One particular line of evidence comes from variation in the critical-flicker fusion frequency (CFF), the frequency at which a light source that’s blinking on and off is perceived as continuously illuminated. Some birds and insects can detect flickering that you and I would completely miss unless we watched a slow motion recording. That might be taken to indicate that time passes more slowly from their subjective perspective, and so, if felt duration is what matters, that suggests we should give additional weight to the lifetime welfare of those animals. In line with that idea, Jason’s research has motivated using CFFs to inform the assignment of moral weights at Rethink Priorities, as outlined here. 

A number of people also argue that digital minds could experience time very differently from us, and here the differences could get really extreme. Because of the speed advantages of digital hardware over neural wetware, a digital mind could conceivably be run at speeds many orders of magnitude higher than the brain’s own processing speed, which might again lead us to expect that time will be felt as passing much more slowly. As above, this may be taken to suggest that we should give those experiences significantly greater moral weight. Among other places, this issue is discussed by Carl Shulman and Nick Bostrom in their paper on digital minds. 

What’s the argument? 

You can think of the argument of the paper as having three key parts.

Part 1: What is felt duration?

The first thing I want to do in the paper is emphasize that we don’t really have a very strong idea of what we’re talking about when we talk about the subjective experience of time. That should make us skeptical of our intuitions about the ethical importance of felt duration.

It seems clear that it doesn’t matter in itself how much time you think has passed: e.g., if you think the pain went on for six minutes, but actually it lasted five. If subjective duration is going to matter, it can’t be just a matter of your beliefs about time’s passage. Something about the way the pain is experienced has got to be different. But what exactly? I expect you probably don’t have an obvious answer to that question at your fingertips. I certainly don’t. It’s also worth noting that some psychologists who study time perception claim that we can’t distinguish empirically between judged and felt duration, whereas others who think we can make this distinction also claim that people frequently mix them up, especially when it comes to reported feelings of time passing quickly. 

Part 2: What felt duration could be

At the next stage, I look at theories of what felt duration consists in. The idea is that once we have a theory of what the subjective rate of experience really is, we’ll be in a much better position to say whether it’s the sort of thing we ought to care about for its own sake. I claim it isn’t.

One theory I consider is the cognitivist theory of felt duration, favoured by Valtteri Arstila and Ian Phillips. Very roughly, this says that our experience of the passage of time arises from the fact that we’re aware of external events in relation to our own stream of conscious thoughts. When there’s a big speed-up in the volume of conscious thought occurring alongside some experienced event, the event feels longer. That seems plausible enough. But it also seems plausible that it doesn’t matter in and of itself how quickly your conscious thoughts move in relation to external events while you’re in pain. If there's a suitable change in the content of your thoughts and the way they interact with your pain experience, that could potentially make a difference for better or for worse, but the speed of conscious thought relative to external processes surely doesn’t matter in and of itself to pain’s badness. 

Another theory I consider is the quantum theory of felt duration, favoured historically by Karl Ernst von Baer and more recently by Carla Merino-Rajme. This theory assumes that experience isn’t continuous. It’s divided up across discrete experiential frames, a bit like the frames in a film reel. The more of these experiential frames that make up your experience of an event, the longer it feels. This also strikes me as plausible. But the only plausible explanation I can think of for why it should matter how many of these frames divide up your experience is something like the following. If your pain experience isn’t continuously ‘on’, but instead made up of lots of little bursts of pain, then it could be that those bursts of pain are packed more densely in time when time feels like it’s passing slowly, as a result of which more time overall could end up being filled with pain as opposed to non-pain. That does sound like it’s got to be worse for you. But this is also extremely speculative. It’s also ultimately a story on which the pain is worse because it fills more objective time, so it doesn’t actually support the view that subjective time experience matters in itself. 

Part Three: Rebutting an argument from digital simulations

The final part addresses a thought experiment that a lot of people raised when I was discussing the ideas in the paper. Imagine a digital simulation of someone’s experience. Imagine varying the speed at which the simulation runs by changing the clock speed on the hardware running it. A lot of people have the intuition that that doesn’t make any difference for how good or bad it is for the simulated people we’re creating. After all, they can’t tell the difference: their experiences are subjectively indistinguishable. 

I reject the assumption that subjectively indistinguishable experiences of pleasure or pain are equally good or bad. Suppose, plausibly, that what it is for two experiences to be subjectively indistinguishable is that there exists some one-to-one mapping among the instants that make up those experiences so that you can’t tell apart any instants mapped to one another. Insofar as that’s right, we should reject the idea that subjectively indistinguishable pains are equally good or bad. Note, for example, that $f\left(t\right):=2t$ is a one-to-one mapping between $[0,1]$ and $[0,2]$ and so if there is a pain (one that’s continuously ‘on’) lasting exactly one second and another lasting exactly two seconds, and if those pain experiences are qualitatively exactly the same at every instant they occur, then they’re subjectively indistinguishable on this analysis. But the two-second pain is surely worse. 

The arguments given in the paper itself are obviously more careful and detailed. There are also a bunch of issues covered in the paper that I’ve completely left out of this summary: whether the theory of relativity makes it impossible to assign an objective duration to a valenced experience; whether we really have evidence that conscious experience is discrete as opposed to continuous, and in what sense; whether the 'amount' of conscious thought occurring in a given time period can be meaningfully defined and measured in a way that allows for interspecies comparisons; and much more besides. 

What are the practical upshots? 

I think we should significantly reduce our credence that subjective time experience modulates welfare. As a result, we should give less weight to subjective time experience when assigning moral weights to animals and digital minds in order to set priorities. 

To give some sense of this, in 2020 Jason Schukraft reported a 70% credence that there exist morally relevant differences in the rate of subjective experience across the animal kingdom. I currently think something in the range of 10-30% is more plausible, though I don’t think my views on this are very stable or especially well-considered. What’s important to note is that the lower range I favour isn’t explained by the fact that I think we should be more skeptical than Jason that there is variation in the rate of subjective experience. Instead, I think we should be more skeptical that that kind of variation is morally significant. That means putting less weight than we might have done on the welfare of small, high-metabolism animals, such as birds like the pied fly-catcher (CFF: 146 Hz), and more weight than we might have done on the welfare of larger, slower animals, like the leatherback turtle (CFF: 15 Hz). It also means putting significantly less weight on the welfare of fast-paced digital minds than we might have done, and thus potentially significantly reducing our estimate of the contribution of digital minds to total welfare over future time.

Still, it’s important to keep in mind some caveats and limitations of the conclusions I draw. In particular, a lot of what I focus on is the question of whether subjective time experience matters in and of itself, i.e., holding fixed things like objective duration, intensity, etc. It’s compatible with that idea that differences in the rate of subjective time experience tend to bring about other kinds of changes that are morally significant in their own right, like differences in felt intensity or differences in objective duration. I don’t think we currently have good evidence that that’s the case, but it’s also very much an open question. 

Bonus content

Jason gives an argument for thinking that it’s subjectively experienced time that matters, which appeals to an analogy with intensity; John Firth at GPI also pressed me on this in conversation. I didn’t address this argument in the paper, as it’s already longer than many philosophy journals are happy to consider. Instead, I’ll address the argument now. 

Here’s the argument from Jason: 

“Two subjects might be exposed to a negative stimulus (an electric shock, say) of the same intensity but differ with respect to the felt badness of the subsequent pain. Such a difference is subjective (in that the painfulness of the shock is relative to the subject being shocked) but no less genuine in virtue of the subjectivity. What matters morally is not the objective intensity of the stimulus, but the subjective badness of the experience. ... [I]f it is the perceived intensity of a stimulus that matters morally, rather than any objective feature of the stimulus, it’s unclear why we shouldn’t apply the same reasoning to duration.”

(The dots here link parts of the original post that are actually somewhat far apart, but that strike me as parts of a single argument.)

In my view, applying the same reasoning to duration does not support using subjective time experience as opposed to objective duration to assign moral weights. When it comes to intensity, we can talk about the intensity of the noxious stimulus - e.g., the temperature of the stove you accidentally touch - or of the painful sensation it evokes. When it comes to duration, we can draw a similar distinction: a distinction between the duration of the noxious stimulus - how long you held your hand on the stove - and the duration of the painful sensation it evokes. As I see it, the analogue of saying that we don’t care about the intensity of the stimulus, but of the sensation, is that we shouldn’t care about the duration of the noxious stimulus but only the duration of the painful sensation. That seems right: it doesn’t matter how long your hand was actually in contact with the stove; what matters is how long the painful burning sensation endures thereafter. But that’s totally compatible with measuring the duration of a pain in clock time. 

The analogue of caring about the subjective time filled by an experience of pain rather than its objective duration would seem to be saying that you shouldn’t care about how intense a sensation is, but how intense it seems. It’s not clear if that’s a meaningful claim, let alone a plausible one.