In 2013 I re-read To Your Scattered Bodies Go, the first part of Farmer's Riverworld saga, having read three or four volumes circa 1979. The setting is an artificial planet where all humans who ever died (for some convenient definitions of ‘human’ and ‘ever’) are simultaneously resurrected, for purposes unknown to them.
It provoked some thoughts. Fashions in scientifictional resurrection have changed since 1971, so here is how I might do it, given enough handwavium. I assume that the resurrection happens in software rather than on a physical planet.
The last version of you may not be the one you'd prefer to restore, even if you never have brain damage.
What if old-you could guide young-you to become a happier old-you, without risking a temporal paradox?
We start with a scan of your brain from each time you slept (made by a friendly posthuman with a time-viewer; this is the least defensible piece of my handwavium). We make two copies of the sequence, ‘joining’ the matching ends to define a loop. Each of these versions of you wakes up in an idealized body, with alternating sexes; thus each scan animates a body of each sex. Metabolism is not simulated (why bother) so there is no hunger.
(Among people who need not eat, what takes the social function of sharing food?)
I would want my pets to get similar treatment (but sexless), accompanied by their littermates because why not.
Each night thereafter, adjacent brains are blended: you wake up remembering two yesterdays. The memory of yesterday in your present body is about twice as strong as the other. The sharing goes around the loop in alternating directions. (I imagine it's much easier to cope with two yesterdays than with three; I'd like to be mistaken about that, because then the process can be symmetric.) Brains get bigger with each merge, but by a small amount: most of each brain already matches its neighbors and thus need not be duplicated.
(I hope the reason for making a loop is now obvious: to avoid exceptions at the ends.)
Thus, if your elderly brain is missing some pieces after a stroke, these are slowly filled in from earlier versions. If you have psychological trauma, it may help you to blend with the you who never had that experience. And if young-you simmered unable to put your unhappiness into words, old-you remembers that unhappiness and can work to remedy it, and ultimately benefit from having had a happier second childhood.
You could reward or punish an instance's behavior by changing its weight in the next blend.
If a body is killed (if that's possible) or voluntarily deleted, its memories blend into its neighbors as usual. A common reason for voluntary deletion, I imagine, is that living half the time in wrong-sexed bodies is intolerable. (How many people will feel that way?)
Sooner or later – perhaps not for years – you (except the eldest and youngest) notice that those around your own age are in two groups that never blend. Do the two branches become rivals? Do they seek each other out, hungry for conversation with peers who do not already share their recent thoughts?
What happens to your Dunbar number when you live quasi-simultaneously in multiple groups?
The blending concept may come ultimately from Greg Egan's Diaspora.
Alternatively: rather than discrete nightly merging, each neuron takes inputs in real time not only from within its own brain but from corresponding neurons in adjacent brains. The weighting of these inputs shifts in the usual way as the brain learns; it usually stays near zero except in the parts of the brain farthest from sensory input and motor output, but rises when adjacent brains are both asleep.
Such multi-brains soon replace some redundancy with specialization.
This concept owes some to Vinge's A Fire Upon the Deep.
Or maybe this is set up by aliens like those of Clarke's Childhood's End, whose longterm goal is to merge all of humanity into a single supermind. Again you have two copies, but they are joined only at the elder end; each baby end is joined to another baby, matched as closely as possible in their tabula rasa state but of a random other culture. After a few years you wonder why your youngest speak two languages unknown to you, though their development in those languages is much slower than in yours.
Even if that is not the plan, perhaps a bug in the system joins identical twins into one loop of four arcs.
You have a world to yourselves, small enough that you could walk a distance equivalent to a great circle in less than a month, yet big enough for some variation in climate; I hope these desiderata are compatible! The laws of physics are fudged as necessary; even with a neutronium core to provide appropriate gravity, such a microplanet would not hold air.
The infrastructure allows each-you to communicate with your contemporaries and make portals from their worlds to yours.
How are your instances initially placed? My favorite idea so far: day zero is a solstice, and each-you wakes up at the latitude where the length of daylight matches that of your respective yesterday, and at a random longitude. (In the polar circles, match the time to next sunrise or sunset.) Thus, instances recorded at a solstice are placed at plus or minus their original latitude; those from an equinox are on the equator. (If you lived most of your life in the tropics, ... we'll think of something.)
Pets are placed beside their human contemporaries. Others also have a claim on many of them, so their loops go through multiple worlds.If you died as a child, there are initially no adults in your private world. To keep such children from growing up feral, up to one-third of your instances (evenly spaced on your loop) live instead in a common big world. Blending goes on all the same.
Farmer places humanity's new home on a world whose surface is one long twisty river valley, wide but confined by high cliffs. Each stretch of riverbank initially has a narrow majority of people from one time and culture, another group half that size from elsewhere and elsewhen, and the remainder are random. Why? An experiment concerning outgroup persecution?
I would place each person near their ancestors. This makes most of the world a dialect continuum: among my neighbors I can find a chain to someone who speaks Proto-Germanic, through pairs who understand each other in their native language; and if I look far enough I can find such a chain to any language, if language was invented only once. (In most places, though, there are a few who cannot speak to their grandparents.) Compromise dialects soon emerge; how far can that process go?
Your instances are placed on a circle, shuffled to bring different ages together. This ring crosses many others, and at least touches each of your parents’.
Rather than having always two instances of each scan, I'm considering making each ring's diameter and population inversely proportional to the square root of world human population during their lifetime. This makes the total area of each generation's rings roughly equal. The minimum size of a ring – for people from the time of peak population – should be four or five thousand. The population of your private world is at least twice that of your ring in the shared world, which can mean more than one pair of sequences make your loop.
Such is my pet fantasy as of 2024 February 10. I began this page on 2022 November 04, incorporating matter from blog posts of 2013 June 15 and 2016 August 20 and 2021 December 30 and 2022 October 24.
Comments? Questions about omitted details?