First of all, there seem to be lots of ways in which we might fail to develop such technology. We might go extinct or our civilization collapse or something of the kind (outright extinction seems really unlikely, but collapse of technological civilization much more likely). It might turn out that computational superpowers just aren't really available -- that there's only so much processing power we have any realistic way of harnessing. It might turn out that such things are possible but we simply aren't smart enough to find our way to them.

Absolutely. I think this is where this thing most likely fails. Somewhere in the first disjunct. My gut does not think I am in a simulation, and while that is not at all a valid way to acquire knowledge, it is the case that it leans me heavily into this.

Second, if we (or more precisely our successors, whoever or whatever they are) develop such computational superpowers, why on earth use them for ancestor simulations? In this sort of scenario, maybe we're all living in some kind of virtual universe; wouldn't it be better to make other minds like ours sharing our glorious virtual universe rather than grubbily simulating our ancestors in their grotty early 21st-century world?

So I am not saying that they WOULD do it, I actually can think of a lot of pretty compelling reasons why they MIGHT. If the people who are around then are at all like us, then I think that a subset of them would likely do it for the one-boxer reasons I mentioned in the first post (which I have since updated with a note at the bottom to clarify some things I should have included in the post originally.) Whether or not their intuitions are valid, there is an internal logic, based on these intuitions, which would push for this. Reasons include hedging against the teletransportation paradox (which also applies to self-uploading) and hoping to increase their credence of an afterlife in which those already dead can join in. This is clearer I think in my update. The main confusion is that I am not talking about attempting to simulate or recreate specific dead people, which I do not think is possible. The key to my argument is to create self-locating doubt.

Also, in my argument, the people who create the simulation are never joined with the people in the simulation. These people stay in their simulation computer. The idea is that we are “hoping” we are similarly in a simulation computer, and have been the whole time, and that when we die, we will be transferred (whole) into the simulations afterlife component along with everyone who died before us in our world. Should we be in a simulation, and yet develop some sort of “glorious virtual universe” that we upload into, there are several options. Two ones that quickly come to mind: 1) We might stay in it until we die, then go into the afterlife component, 2) We might at some point be “raptured” by the simulation out of our virtual universe into the existent “glorious virtual afterlife” of the simulation computer we are in.

As it is likely that the technology for simulations will come about at about the same time as for a “glorious virtual universe” we could even treat it as our last big hurrah before we upload ourselves. This makes sense as the people who exist when this technology becomes available will know a large number of loved ones who just missed it. They will also potentially be in especially imminent fear of the teletransportation paradox. I do not think there is any inherent conflict between doing both of these things.

Someone else -- entirelyuseless? -- observed earlier in the thread that some such simulation might be necessary in order to figure out enough about our ancestors' minds to simulate them anywhere else, so it's just possible that grotty 21st-century ancestor sims might be a necessary precursor to glorious 25th-century ancestor sims; but why ancestors anyway? What's so special about them, compared with all the other possible minds?

Just to be clear, I am not talking about our actual individual ancestors. I actually avoided using the term intentionally as I think it is a bit confusing. I am pretty sure this is how Bostrom meant it as well in the original paper, with the word “ancestor” being used in the looser sense, like how we say “homo erectus where our ancestors.” That might be my misinterpretation, but I do not think so. While I could be convinced, I am personally, currently, very skeptical that it would be possible to do any meaningful sort of replication of a person after they die. I think the only way that someone who has already died has any chance of an afterlife is if we are already in a simulation. This is also why my personal, atheistic mind could be susceptible to donating to such a cause when in grief. I wrote an update to my original post at the bottom where I clarify this. The point of the simulation is to change our credence regarding our self-location. If the vast majority of “people like us” (which can be REALLY broadly construed) exist in simulations with afterlives, and do not know it, we have reason to think we might also exist in such a simulation. If this is still not clear after the update, please let me know, as I am trying to pin down something difficult and am not sure if I am continuing to privilege brevity to the detriment of clarity.

Third, supposing that we have computational superpowers and want to simulate our ancestors, I see no good reason to think it's possible. The information it would take to simulate my great-great-grandparents is dispersed and tangled up with other information, and figuring out enough about my great-great-grandparents to simulate them will be no easier than locating the exact oxygen atoms that were in Julius Caesar's last breath. All the relevant systems are chaotic, measurement is imprecise, and surely there's just no reconstructing our ancestors at this point.

I agree with your point so strongly that I am a little surprised to have been interpreted as meaning this. I think that it seems theoretically feasible to simulate a world full of individual people as they advance their way up from simple stone tools onward, each with their own unique life and identity, each existing in a unique world with its own history. Trying to somehow make this the EXACT SAME as ours does not seem at all possible. I also do not see what the advantage of it would be, as it is not more informative or helpful for our purposes to know that we are the same or not as the people above us, so why would be try to “send that down” below us. We do not care about that as a feature of our world, and so would have no reason to try to instill it in the worlds below us. There is sort of a “golden rule” aspect to this in that you do to the simulation below you the best feasible, reality-conforming version of what you want done to you.

Fourth, it seems quite likely that our superpowered successors, if we have them, will be no more like us than we are like chimpanzees. Perhaps you find it credible that we might want to simulate our ancestors; do you think we would be interested in simulating our ancestors 5 million years ago who were as much like chimps as like us?

Maybe? I think that one of the interesting parts about this is where we would choose to draw policy lines around it. Do dogs go to the afterlife? How about fetuses? How about AI? What is heaven like? Who gets to decide this? These are all live questions. It could be that they take a consequential hedonistic approach that is mostly neutral between “who” gets the heaven. It could be that they feel obligated to go back further in gratitude of all those (“types”) who worked for advancement as a species and made their lives possible. It could be that we are actually not too far from superintelligent AI, and that this is going to become a live question in the next century or so, in which case “we” are that class of people they want to simulate in order to increase their credence of others similar to us (their relatives, friends who missed the revolution) being simulated.

As far as how far back you bother to simulate people, it might actually be easier to start off with some very small bands of people in a very primitive setting then to try to go through and make a complex world for people to “start” in without the benefit of cultural knowledge or tradition. It might even be that the “first people” are based on some survivalist hobby back-to-basics types who volunteered to be emulated, copied, and placed in different combinations in primitive earth environments in order to live simple hunter-gatherer lives and have their children go on to populate an earth (possible date of start? https://en.wikipedia.org/wiki/Population_bottleneck). That said, this is deep into the weeds of extremely low-probability speculation. Fun to do, but increasingly meaningless.