“Most people would agree with MacAskill that we have moral obligations to future generations. Appeals to fight global warming and save fragile ecosystems often invoke a form of this logic, as do arguments for cultural preservation, such as archiving dying languages or preserving ancient artwork. MacAskill is fully on board with such projects. But longtermism implies a great deal more than that. MacAskill’s book argues that trying to leave a better world for those who come after us isn’t enough—we must also try to ensure that as many people come after us as possible. This is not just about making future generations larger; it’s about maximizing the probability that there are as many of those generations as possible, filled to the brim with happy people. MacAskill is thinking about the truly long term. “To illustrate the potential scale of the future, suppose that we only last as long as the typical mammalian species—that is, around one million years. Also assume our population continues at its current size. In that case, there would be eighty trillion people yet to come; future people would outnumber us ten thousand to one.” 18 (To put that into perspective, that would mean that currently living humans would be outnumbered by our descendants in the same proportion as the residents of San Francisco are outnumbered by the rest of the world.) We have an obligation to try to make the lives of those humans as good as possible, according to MacAskill. And he claims we are uniquely positioned to do so. “If humanity survives to even a fraction of its potential life span, then, strange as it may seem, we are the ancients: we live at the very beginning of history, in the most distant past.… Few people who ever live will have as much power to positively influence the future as we do.” 19
That influence, he claims, extends to whether there will be even more than the aforementioned eighty trillion future humans. About a billion years from now, the Sun’s increased heat will vaporize the Earth’s oceans, kicking off a runaway greenhouse effect that will make the Earth lethal for water-based life. If our species survives until then, somehow maintaining our present population of about eight billion people over that whole span of time, then there will be about one hundred quadrillion (one hundred million billion, or 1017) future people, twelve million for each human alive today. 20 And if, instead of merely being limited to the Earth’s surface, we expand humanity out into space, the numbers of potential future humans become correspondingly astronomical. Over that same billion-year span, spacefaring humans could distribute themselves across the entirety of our Milky Way galaxy, home to at least one hundred billion planets. Even if only 1 percent of those are habitable by humans, that still leaves us with enough room for 1026 future humans over the next billion years, if there’s an average population of eight billion people per planet at any given time. But that isn’t the limit: other planets will have liquid water for far longer than a billion years. And if we can fill the Milky Way, why not the observable universe? If humanity fills the universe to the brim, a burgeoning population across the cosmos until essentially all stars die, the number of future humans could be closer to 1040. That’s ten million billion trillion trillion people, a one with forty zeroes after it. 21 And this all presumes that our descendants remain human, with our bodies and brains of flesh. If we find a way to transfer human minds into computers, or our primary descendants are themselves conscious AIs, there could be a future filled with unnumbered myriads of electronic life, their silicon circuitry silently traversing the intergalactic voids until the heat death of the universe.
For MacAskill, it’s literally the more the merrier. As long as our descendants’ happiness outweighs their misery, his logic demands that the greater their numbers, the better the future is. He argues that we should be aiming for the most maximalist of these futures, as best we can. “The future of civilization could be literally astronomical in scale, and if we will achieve a thriving, flourishing society, then it would be of enormous importance to make it so.” 22 Yet there are so many things that seem unlikely or impossible in these futuristic visions of the final frontier. The idea that our per-world population will remain at an average of eight billion for hundreds of thousands of years, much less millions or billions of years, is already quite suspect. As MacAskill himself notes, this is an unusual period of growth for the human population, and we’re already at an all-time high, which even near-term population forecasts suggest we won’t surpass by much. But putting that objection aside, there are far more serious ones to consider. Living in space is phenomenally difficult. There are no good candidates for long-term human habitation in our solar system, and given the distances involved, sending humans to other star systems is extremely unlikely to be anything other than science fiction. Transferring human minds into computers is probably impossible for a variety of good scientific reasons. Conscious AI may be somewhat more likely, but still far from certain—and sending such an AI into space would come with its own set of practical challenges and ethical concerns.
The likelihood of these futures is small…”
— More Everything Forever: AI Overlords, Space Empires, and Silicon Valley's Crusade to Control the Fate of Humanity by Adam Becker
