Long run growth rates cannot be exponential. This is easy to prove. Even mild steady exponential growth rates would quickly exhaust all available matter and energy in the universe within a few million years (see Holden’s post “This can’t go on” for more details).
So a model that tries adjust for marginal utility of resources should also quickly switch towards something other than assumed exponential growth within a few thousand years.
Separately, the expected lifetime of the universe is finite, as is the space we can affect, so I don’t see why you need discount rates (see
a bunch of Bostrom’s work for how much life the energy in the reachable universe can support).
But even if things were infinite, then the right response isn’t to discount the future completely within a few thousand years just because we don’t know how to deal with infinite ethics. The choice of exponential discount rates in time does not strike me as very principled in the face of the ethical problems we would be facing in that case.
Long run growth rates cannot be exponential. This is easy to prove. Even mild steady exponential growth rates would quickly exhaust all available matter and energy in the universe within a few million years (see Holden’s post “This can’t go on” for more details).
So a model that tries adjust for marginal utility of resources should also quickly switch towards something other than assumed exponential growth within a few thousand years.
Separately, the expected lifetime of the universe is finite, as is the space we can affect, so I don’t see why you need discount rates (see a bunch of Bostrom’s work for how much life the energy in the reachable universe can support).
But even if things were infinite, then the right response isn’t to discount the future completely within a few thousand years just because we don’t know how to deal with infinite ethics. The choice of exponential discount rates in time does not strike me as very principled in the face of the ethical problems we would be facing in that case.