Our money goes further in the future, giving us an initial reason to invest to spend later. Unless we live at an especially important time.
“At a 5% real rate of return, over 200 years our invested financial resources would be 17,000 times as large. What’s more, because the rate of return on investment exceeds the growth rate, these resources would also be much larger as a proportion of the world economy: if the rate of return is one percentage point larger than the growth rate of the world economy, after 200 years the invested resources would be 7 times as large, when measured as a fraction of the world economy. Other things being equal, greater resources would allow us (or our inheritors) to do much more good. So there seems to be a strong pro tanto reason for impartial and longtermist altruists to invest their resources rather than donating now.” (P. 6)
“Because civilisation has such a long future ahead of it, and because resources grow over time (both in absolute terms, as a fraction of the world economy), there is a strong prima facie case for impartial altruists to invest their resources, passing them on to future people to use philanthropically. However, if we thought that the present time was exceptionally influential— or even the most influential time — this would be a strong counterargument.” (p. 24)
But it seems we should have an exceptionally low prior that we do live in such an especially important time:
“If we don’t go extinct in the next few centuries, then there are plausibly a vast number of people in the future. The Earth will remain habitable for something on the order of a billion years. Even if current population levels reduced to a tenth of what they are today (i.e. to about 1 billion people per century), that would mean that there would be ten thousand trillion people to come. If, as Parfit suggests, we would subsequently take to the stars, that number would get far higher: there are one hundred billion stars in the Milky Way; settling just 0.1% of them with the same population as on Earth would mean that there are a trillion trillion people to come. If we consider also the 8 billion other galaxies that we could access, the numbers get correspondingly higher again.
For the purposes of my argument, what matters is not these precise numbers, but that any of them are astronomical. If there are a trillion trillion people to come, then the a priori probability that we are among the million most influential people ever is one in a million trillion. This is about the same probability as dealing a Royal Flush from a well-shuffled pack of cards three times in a row.” (p. 10-11)
In fact, we also have some reasons to think that people in the future will do a better job than we can with the resources we send them:
“As a general matter, people in the future, who we could pass our resources to, will plausibly be far smarter and more informed than even the most brilliant minds of today: they may be the beneficiaries of enhancement technologies, more powerful intelligence-augmenting tools like computers and artificial intelligence, better educational methods and better nutrition. And they will very likely have a radically larger edifice of scientific knowledge to base their decisions on, with decades or centuries of further moral progress, including on the very particular question of how best to use resources to make the world better.” (p. 18)
William MacAskill (2021) Are we living at the hinge of history? Ethics and Existence: The Legacy of Derek Parfit Oxford University Press, edited by Jeff McMahan, Tim Campbell, James Goodrich, and Ketan Ramakrishnan.
Quotes are from the working paper.