You are the same person as 3 years ago, because you remember being that person (not only rationally, but on a deeper level of knowing and feeling that you were that person)
Two things:
1) Can you clarify what you mean by "rationally remembering" here?
2) If you're actually talking about "knowing and feeling that I am that person," then you aren't talking about memory at all. There are many, many events that I do not remember, but which I "know and feel" I was involved in -- my birth, for example.
If you define my "personal identity" as including those things, that's OK with me... I do, as well... but it's not clear to me that there's a sharp line between saying that, and saying that my "personal identity" can include events at which my body was not present but which I "know and feel" I was involved in.
(Just to be clear: I'm not suggesting anything mystical here. I'm talking about the psychological constituents of identity.)
I'm not sure there's anything to say about that other than, if I do identify with those things, then those things are part of my identity.
To put that more affirmitively: if personal identity is a matter of what I "know and feel," then it is a psychological construct very much like cultural identity and family identity, and those constructs flow into one another with no sharp dividing lines, and therefore discussions of where "personal identity" ends and "cultural identity" begins is entirely a discussion of how we choose to define those terms, not actually a discussion about their referents.
This post is not about many worlds. It is somewhat disjointed, but builds to a single point.
If an AI was asked today how many human individuals populate this planet, it may not return a number the several-billions range. In fact I’d be willing to bet it’d return a number in the tens of thousands, with the caveat that the individuals vary wildly in measure.
I agree with Robin Hanson that if two instances of me exist, and one is terminated, I didn’t die, I simply got smaller.
In 1995 Robert Sapolsky wrote in Ego Boundaries “My students usually come with ego boundaries like exoskeletons. […] They want their rituals newly minted and shared horizontally within their age group, not vertically over time,” whereas in older societies “needs transcend individual rights to a bounded ego, and people in traditional communities are named and raised as successive incarnations. In such societies, Abraham always lives 900 years--he simply finds a new body to inhabit now and then. ”
Ego boundaries may be more rigid now, but that doesn’t make people more unique. If anything, people have become more like each other. Memes are powerful shapers of mental agents, and as technology allows memes to breed and compete more freely the most viral ones spread through the species.
Acausal trade allows for amazing efficiencies, not merely on a personal level but also via nationalism and religion. People executing strong acausal trading routines will out-compete those who don’t.
Timeless Decision Theory proscribes making decisions as if choosing the outcome for all actors sufficiently like yourself across all worlds. As competition narrows the field of memeplexes to a handful of powerful and virulent ubermemes, and those memeplexes influence the structure and strength of individual’s mental agents in similar ways, people become more like each other. In so doing they are choosing *as if* a single entity more and more effectively. To an outside observer, there may be very little to differentiate two such humans from each other.
Therefore it may be wrong to think of oneself as a singular person. I am not just me – I am also effectively everyone who is sufficiently like me. It’s been argued that there are only seven stories, and every story can be thought of as an elaboration of one of these. It seems likely there are only a few thousand differentiable people, and everyone is simply one of these with some flare.
If we think of people in these terms, certain behaviors make more sense. Home-schooling is looked down on because institutional schools are about making other people into us. Suicide is considered more sinful than killing outsiders because suicide *always* reduces the size of the Meta-Person that the suicidee belonged to. Argument and rhetoric isn’t just a complete waste of your free time, it’s also an attempt to make Meta-Me larger, and Meta-SomeoneElse smaller. Art finally makes sense.
Added Bonus: You no longer have to have many children to exist. You can instead work on enlarging your Meta-Self’s measure.