| Background
The key mathematical details are that, under typical mathematics (extended real number line), infinity plus one equals infinity and infinity plus infinity equals infinity. Furthermore, if the probability of there being infinite total utility is positive (i.e. not zero), then the expected amount of total utility is still infinity, even if that's a very low probability. (If that probability is infinitesimal, then the expected value is undefined, and we're still in trouble.)
So, as long as the probability of there being an infinite amount of utility is not zero (and it's not), then nothing we do affects total expected utility. Thus, as Bostrom puts it (p1),
Every possible act of ours then has the same net effect on the total amount of good and bad in the world: none whatsoever.
That makes for one lousy system of ethics. Here's how I'd resolve this:
First, divide decisions into two categories: infinite and finite. Following Bostrom's lingo, we use hyperreals (p13) for the infinite and the causal approach (p16) for the finite.
Infinite
The hyperreals behave a little differently than the extended reals when it comes to the infinite, and that buys us a very good way of assessing certain decisions we face. The key mathematical detail is that, in hyperreals, infinity plus infinity is greater than infinity. (See the ultrapower construction.) What does this buy us? The opportunity to recommend reducing existential risk.
Existential risk is the risk that we will cease to exist. Reducing existential risk means lowering the probability that we will cease to exist. If our continuing to exist would result in a finite amount of utility, than we've got none of these infinity problems in the first place, but if it would result in an infinite amount of utility, then we can use hyperreals to say that reducing existential risk is a good thing.
Quick math, assuming survival means infinite total utility: Let A = 10% chance of survival. Then 2A = 20% chance of survival. Under the extended reals, 2A = A, but under hyperreals, 2A > A. So doing something that leads to a 20% chance of survival can be judged as better than doing something that leads to a 10% chance of survival. Sounds good.
Fanaticism
So far, we have recommendation number one:
1. Reduce existential risk as much as you can. Make any finite sacrifice for any existential risk reduction.
This requires a certain fanaticism for existential risk reduction. So be it. As they say, safety first. Intuitively, this is entirely reasonable. Preventing an existential event means, in colloquial terms, saving the world. I think it's fair to say that any system of ethics that does not recommend we do everything we can to save the world/prevent existential events is suspect.
For a related discussion, see Are We Radicals?.
Finite
If we have the opportunity to reduce existential risk, we should do so. However, if we have no such opportunity, then we can only do a finite amount of good. In this case, the causal approach seems to work well. It says that instead of doing whatever maximizes total utility, we should make the largest increase in utility that we can. This approach breaks down if we can make an infinite increase in utility, but that case has already been handled by hyperreals.
This gives us recommendation number two:
2. If you can't reduce existential risk, increase utility as much as you can.
Again, sounds good.
Uncertainty
In reality, we all may affect existential risk with everything we do. But much of the time, we have no idea how. For example, if I sleep in an extra 30 seconds, I change the chance that I get hit and killed by a car on my walk to work, which would prevent me from getting contributing further to climate change or AI or whatever I end up doing. But I have no idea whether sleeping in will make my getting hit and killed by a car more or less likely, so as far as I'm concerned, I can ignore that matter.
Mathematically, I'm saying that sleeping in has an expected value of zero because I have no information on it. I suspect that this expected value is actually undefined, not zero, but to give it any value other than zero seems counterproductive. Perhaps yinz have better ideas.
Elsewhere in the Universe(s)
There is a chance that there will be infinite total utility even if we Earthlings don't survive, due to utility existing elsewhere in the universe(s). As Bostrom (p2) writes,
Is the cosmos finite or infinite? Cosmological evidence suggests that the latter is probably true. Moreover, if the totality of physical existence is indeed infinite, in the way that cosmology suggests, then it contains an infinite number of galaxies, stars, and planets. If there are an infinite number of planets then there is, with probability one, an infinite number of people. Infinitely many of these people are happy, infinitely many are unhappy...
The approach to uncertainty described above works here as well. With one exception, we have no information about how anything we're doing increases or decreases the utility of anyone that might exist elsewhere in the universe, so it's fair to ignore them. The exception is our efforts to interact with them. A fair question here is how hard we should be trying. There may be no good way of answering this one. I'm comfortable with our current modest efforts. I would be opposed to us not making any effort, as I think we can afford it, as long as it doesn't increase our own existential risk. If nothing else, the SETI project is intriguing for us and thus increases our own, finite, short-term utility.
Bottom Line
A system of ethics is only as good as its recommendations. I think these two recommendations are entirely reasonable and very much keeping with the spirit of utilitarianism. I am not at all concerned with making little tweaks to utilitarianism to keep it from breaking- after all, I'm a moral skeptic. I may actually be more concerned about making little tweaks to mathematics. I'll be curious to hear what you or others have to say about this. |