Dissolving the Thread of Personal Identity

by Skeptityke6 min read25th May 201432 comments


Personal Blog

(Background: I got interested in anthropics about a week ago. It has tormented my waking thoughts ever since in a cycle of “be confused, develop idea, work it out a bit, realize that it fails, repeat” and it is seriously driving me berserk by this point. While drawing a bunch of “thread of personal continuity” diagrams to try to flesh out my next idea, I suspected that it was a fairly nonsensical idea, came up with a thought experiment that showed it was definitely a nonsensical idea, realized I was trying to answer the question “Is there any meaningful sense in which I can expect to wake up as myself tomorrow, rather than Brittany Spears?”, kept thinking anyways for about an hour, and eventually came up with this possible reduction of personal identity over time. It differs somewhat from Kaj Sotala’s. And I still have no idea what the hell to do about anthropics, but I figured I should write up this intermediate result. It takes the form of a mental dialogue with myself, because that’s what happened.)

Doubt: Hang on, this whole notion of “thread of personal continuity” looks sort of fishy. Self, can you try to clarify what it is?

Self: Let’s see… I have a causal link to my past and future self, and this causal link is the thread of personal identity!

Current Me: Please notice Past Self’s use of the cached thought from “Timeless Identity” even though it doesn’t fit.

Doubt: Causal links can’t possibly be the thread of personal continuity. Your state at time t+1 is not just caused by your state at time t, lots of events in your surroundings also cause the t+1 state as well. A whole hell of a lot of stuff has a causal link to you. That can’t possibly be it. And when you die, alive you has a causal link to dead you.

Doubt: And another thing, personal continuity isn’t just an on-off thing. There’s a gradient to it.

Self: What do you mean?

Doubt: Let’s say you get frozen by cryonics, and then revived a century later.

Self: Sure.

Doubt: Let’s say you know that you will be revived with exactly the same set of memories, preferences, thought patterns, etc, that you have currently. As you are beginning the process, what is your subjective credence that you will wake up a century later?

Self: Fairly close to 1.

Doubt: Now, let’s say they could recover all the information from your brain except your extreme love for chocolate, so when your brain is restored, they patch in a generic average inclination for chocolate. What is your subjective credence that you will wake up a century later?

Self: Fairly close to 1.

Doubt: Let’s say that all your inclinations and thought patterns and other stuff will be restored fully, but they can’t bring back memories. You will wake up with total amnesia. What is your… you get the idea.

Self: Oh crap. I… I really don’t know. 0.6??? But then again, this is the situation that several real-life people have found themselves in… Huh.

Doubt: For this one, inclinations and thought patterns and many of your memories are unrecoverable, so when your brain is restored, you only have a third of your memories, a strong belief that you are the same person that was cryopreserved, and a completely different set of… everything else except for the memories and the belief in personal continuity. P(I wake up a century later)?

Self: Quite low. ~0.1.

Self: But I see your point. For that whole personal identity/waking up as yourself thing, it isn’t a binary trait, it’s a sliding scale of belief that I’ll keep on existing which depends on the magnitude of the difference between myself and the being that wakes up. If upload!me were fed through a lossy compression algorithm and then reconstructed, my degree of belief in continuing to exist would depend on how lossy it was.

Doubt: Now you realize that the “thread of subjective experience” doesn’t actually exist. There are just observer-moments. What would it even mean for something to have a “thread of subjective experience”?

Self: (Taps into intuition) What about that big rock over there? Forget “subjective”, that rock has a “thread of existence”. That rock will still be the same rock if it is moved 3 feet to the left, that rock will still be the same rock if a piece of it is chipped off, that rock will still be the same rock if it gets covered in moss, but that rock will cease to be a rock if a nuke goes off, turning it into rock vapor! I don’t know what the hell the “thread of existence” is, but I know it has to work like that rock!!

Doubt: So you’re saying that personal identity over time works like the Ship of Theseus?

Self: Exactly! We’ve got a fuzzy category, like “this ship” or “this rock” or “me”, and there’s stuff that we know falls in the category, stuff that we know doesn’t fall in the category, and stuff for which we aren’t sure whether it falls in the category! And the thing changes over time, and as long as it stays within certain bounds, we will still lump it into the same category.

Doubt: Huh. So this “thread of existence” comes from the human tendency to assign things into fuzzy categories. So when a person goes to sleep at night, they know that in the morning, somebody extremely similar to themselves will be waking up, and that somebody falls into the fuzzy cluster that the person falling asleep labels “I”. As somebody continues through life, they know that two minutes from now, there will be a person that is similar enough to fall into the “I” cluster.

Doubt: But there’s still a problem. 30yearfuture!me will probably be different enough from present!me to fall outside the “I” category. If I went to sleep, and I knew that 30yearfuture!me woke up, I’d consider that to be tantamount to death. The two of us would share only a fraction of our memories, and he would probably have a different set of preferences, values, and thought patterns. How does this whole thing work when versions of yourself further out than a few years from your present self don’t fall in the “I” cluster in thingspace?

Self: That’s not too hard. The “I” cluster shifts over time as well. If you compare me at time t and me at time t+1, they would both fall within the “I” cluster at time t, but the “I” cluster of time t+1 is different enough to accommodate “me” at time t+2. It’s like this rock.

Doubt: Not the rock again.

Self: Quiet. If you had this rock, and 100yearfuture!thisrock side by side, they would probably not be recognizable as the same rock, but there is a continuous series of intermediates leading from one to the other, each of which would be recognizable as the same rock as its immediate ancestors and descendants.

 Self: If there is a continuous series of intermediates that doesn’t happen too fast, leading from me to something very nonhuman, I will anticipate eventually experiencing what the nonhuman thing does, while if there is a discontinuous jump, I won’t anticipate experiencing anything at all.

Doubt: Huh.

Self: So that’s where the feeling of the “thread of personal identity” comes from. We have a fuzzy category labeled “I”, anticipate experiencing the sorts of things that probable future beings who fall in that category will experience, and in everyday life, there aren’t fast jumps to spots outside of the “I” category, so it feels like you’ve stayed in the same category the whole time.

Doubt: You’ll have to unpack “anticipate experiencing the sorts of things that probable future beings who fall in that category will experience”. Why?

Self: Flippant answer: If we didn’t work that way, evolution would have killed us a long time ago. Actual answer: Me at time t+1 experiences the same sorts of things as me at time t anticipated, so when me at time t+1 anticipates that me at time t+2 will experience something, it will probably happen. Looking backwards, anticipations of past selves frequently match up with the experiences of slightly-less-past selves, so looking forwards, the anticipations of my current self are likely to match up with the experiences of the future being who falls in the “I” category.

Doubt: Makes sense.

Self: You’ll notice that this also defuses the anthropic trilemma (for humans, at least). There is a 1 in a billion chance of the quantum random number generator generating the winning lottery ticket. But then a trillion copies are made, but you at time (right after the generator returned the winning number) has a trillion expected near-future beings who fall within the “I” category, so the 1 in a billion probability is split up a trillion ways among all of them. P(loser) is about 1, P(specific winner clone) is 1 in a quintillion. All the specific winner clones are then merged, and since a trillion different hypotheses each with a 1 in a quintillion probability all predict the same series of observed future events from time(right after you merge) onwards, P(series of experiences following from winning the quantum lottery) is 1 in a billion.

Doubt: Doesn’t this imply that anthropic probabilities depend on how big a boundary the mind draws around stuff it considers “I”?

Self: Yes. Let’s say we make 2 copies of a mind, and a third “copy” produced by running the mind through a lossy compression algorithm, and uncompressing it. A blue screen will be shown to one of the perfect mind copies (which may try to destroy it). A mind that considered the crappy copy to fall in the “I” category would predict a 1/3 chance of seeing the blue screen, while a mind that only considers near-perfect copies of itself as “I” would predict a 1/2 chance of seeing the blue screen, because the mind with the broad definition of “I” seriously considers the possibility of waking up as the crappy copy, while the mind with the narrow definition of “I” doesn’t.

Doubt: This seems to render probability useless.


Self: It means that probabilities of the form (I will observe X) are mind-dependent. Different minds given the same data will disagree on the probability of that statement, because they have different reference classes for the word “I”. Probabilities of the form (reality works like X)… to be honest, I don’t know. Anthropics is still extremely aggravating. I haven’t figured out the human version of anthropics (using the personal continuity notion) yet, I especially haven’t figured out how it’s going to work if you have a AI which doesn’t assign versions of itself to a fuzzy category labeled “I”, and I’m distrustful of how UDT seems like it’s optimizing over the entire tegmark 4 multiverse when there’s a chance that our reality is the only one there is, in which case it seems like you’d need probabilities of the form (reality works like X) and some way to update far away from the Boltzmann Brain hypothesis. This above section may be confused or flat-out wrong.

Personal Blog