Could a future superintelligence bring back the already dead? This discussion has come up a while back (and see the somewhat related); I'd like to resurrect the topic because ... it's potentially quite important.
Algorithmic resurrection is a possibility if we accept the same computational patternist view of identity that suggests cryonics and uploading will work. I see this as the only consistent view of my observations, but if you don't buy this argument/belief set then the rest may not be relevant.
The general implementation idea is to run a forward simulation over some portion of earth's history, constrained to enforce compliance with all recovered historical evidence. The historical evidence would consist mainly of all the scanned brains and the future internet.
The thesis is that to the extent that you can retrace historical reality complete with simulated historical people and their thoughts, memories, and emotions, to this same extent you actually recreate/resurrect the historical people.
So the questions are: is it feasible? is it desirable/ethical/utility-efficient? And finally, why may this matter?
A few decades ago pong was a technical achievement, now we have avatar. The trajectory seems to suggest we are on track to photorealistic simulations fairly soon (decades). Offline graphics for film arguably are already photoreal, real-time rendering is close behind, and the biggest remaining problem is the uncanny valley, which really is just the AI problem by another name. Once we solve that (which we are assuming), the Matrix follows. Superintelligences could help.
There are some general theorems in computer graphics that suggest that simulating an observer optimized world requires resources only in proportion to the observational power of the observers. Video game and film renderers in fact already rely heavily on this strategy.
Criticism from Chaos: We can't even simulate the weather more than a few weeks in advance.
Response: Simulating the exact future state of specific chaotic systems may be hard, but simulating chaotic systems in general is not. In this case we are not simulating the future state, but the past. We already know something of the past state of the system, to some level of detail, and we can simulate the likely (or multiple likely) paths within this configuration space, filling in detail.
Physical Reversibility Criticism: The AI would have to rewind time, it would have to know the exact state of every atom on earth and every photon that has left earth.
Response: Yes the most straightforward brute force way to infer the past state of earth would be to compute the reverse of all physical interactions and would require ridiculously impractical amounts of information and computation. The best algorithm for a given problem is usually not brute force. The specifying data of a human mind is infinitesimal in comparison, and even a random guessing algorithm would probably require less resources than fully reversing history.
Constrained simulation converges much faster to perfectly accurate recovery, but by no means is full perfect recovery even required for (partial) success. The patternist view of identity is fluid and continuous.
If resurrecting a specific historical person is better than creating a hypothetical person, creating a somewhat historical person is also better, and the closer the better.
Humans appear to value other humans, but each human appears to value some more than others. In general humans typically roughly value themselves the most, then kin and family, followed by past contacts, tribal affiliations, and the vaguely similar.
We can generalize this as a valuation in person-space which peaks at the self identity-pattern and then declines in some complex fashion as we move away to more distant locales and less related people.
If we extrapolate this to a future where humans have the power to create new humans and or recreate past humans, we can infer that the distribution of created people may follow the self-centered valuation distribution.
Thus recreating specific ancestors or close relations is better than recreating vaguely historical people which is better than creating non-specific people in general.
Suffering Criticism: An ancestral simulation would recreate a huge amount of suffering.
Response: Humans suffer and live in a world that seems to suffer greatly, and yet very few humans prefer non-existence over their suffering. Evolution culls existential pessimists.
Recreating a past human will recreate their suffering, but it could also grant them an afterlife filled with tremendous joy. The relatively small finite suffering may not add up to much in this consideration. It could even initially relatively enhance subsequent elevation to joyful state, but this is speculative.
The utilitarian calculus seems to be: create non-suffering generic people who we value somewhat less vs recreate initially suffering specific historical people who we value more. In some cases (such as lost love ones), the moral calculus weighs heavily in favor of recreating specific people. Many other historicals may be brought along for the ride.
The vast majority of the hundred billion something humans who have ever lived share the singular misfortune of simply being born too early in earth's history to be saved by cryonics and uploading.
Recreating history up to 2012 would require one hundred billion virtual brains. Simulating history into the phase when uploading and virtual brains become common could vastly increase the simulation costs.
The simulations have the property that they become more accurate as time progresses. If a person is cryonically perserved and then scanned and uploaded, this provides exact information. Simulations will converge to perfect accuracy at that particular moment in time. In addition, the cryonic brain will be unconscious and inactive for a stretch.
Thus the moment of biological death, even if the person is cryonically preserved, could be an opportune time to recycle simulation resources, as there is no loss of unique information (threads converged).
How would such a scenario effect the Simulation Argument? It would seem to shift probabilities such that more (most?) observer moments are in pre-uploading histories, rather than in posthuman timelines. I find this disquieting for some reason, even though I don't suspect it will effect my observational experience.