 I don't really understand why everyone makes such a big deal about the transporter and personal identity. Isn't it just when Jason Statham hits you on the head and you wake up somewhere else? One of the oldest and most pervasive themes in western philosophy is something that I touched on in episode 93. How is it that something can change and yet still remain the same thing? The question requires paying close attention to the difference between qualitative identity and numeric identity. I can have two pencils that are according to any measurement identical, in size, in shape, in color, in functionality, but there's always some distinction that can be made between them, like one is over here and the other one's over here. That's qualitative identity. In any conceivable situation, you could replace one pencil with the other one and nothing would change. On the other hand, numeric identity is something that we take for granted in conversation and thought, but is actually much, much weirder. Like, say I have a pencil, then I use that pencil to make a mark on a piece of paper. Now, you'd probably say that that's the same pencil. But there are measurable differences between this thing and the thing that I started with. It's a little bit duller. It has lower total mass. My fingerprints are on it in different places. If I were to compare it to its past self with certain tools, I'd be able to tell the difference in a way that I might not be able to with a qualitatively identical pencil. But we still say it's the same pencil. I could do any number of other things to change it, like maybe painting it or even breaking it in half. And we'd still probably agree that it persists, that there's some relation that this has to the original pencil, which is somehow more incident than the qualitative relationship that this one has to it. After all, I wouldn't say that this is the original pencil, even though it's much more like it than this is. Your first impulse is probably to think of some material connection. After all, most of the atoms that were in the original pencil are here in this one. But what about things that are a little more dynamic than pencils, like rivers, or software, or people? Human beings are living organisms, which are constantly absorbing nutrients from their environment and using those nutrients to rebuild themselves. If you're in perfect health, your body will have replaced almost every single cell in it in about seven years. Then what is it that makes me the same individual that I was seven years ago? If I were to replace 99% of the particles in my pencil with different particles, I'm not sure that's the same thing anymore. What makes me numerically identical with that guy? Am I that guy? It seems a little absurd to suggest that the last time I went to the bathroom, I severed all ties of identity with that other person named Josh from 2010. That now, those are two different people, just because I don't share any of those atoms anymore. We certainly don't act like they're separate people. I mean, I still have the same name. Relatives who haven't seen me in seven years still recognize and talk to me, and it's not like I have to write a will bequeathing my books to me in seven years when I cease to be. Also, if you'll indulge a little bit of sci-fi, what if I were to clone my body and then transplant my brain into that clone? It seems a little weird to suggest that that new organism with all new parts wouldn't be me anymore, or that the empty-headed body that I left behind is somehow still me. Well, maybe that indicates where we should be focusing, the brain. After all, there's some aspect of past Josh's psychology that still persists in me, right? It seems like there should be some relationship between my mind and his mind that makes us the same person as I used to be him, although it would probably have to be something that's pretty general. I mean, I used to be really into Settlers of Catan, but my copy's gotten a little, shall we say, played out. I just prefer other games now, and it seems a little silly to suggest that just because we don't share a deep, unabiding love for Catan, that we're not the same person. There's an important distinction here, that qualitative numeric identity thing again. We sometimes say things like, Sally is a totally different person since she took up swing dancing, but we don't mean that Sally is dead and some alien creature is now possessing her body. She's still Sally. She's just different than what we're used to. With that being said, let's take a couple of stabs at this supposed psychological relationship, which allows people to persist. Maybe it's continuity of consciousness. I have a continuous experience of existing and being the same person, so maybe that's what makes me persist over time. Unless I go under anesthesia, or fall asleep, or space out for a few seconds. Now, on second thought, let's skip that one. Maybe it's something more like continuity of memory. I have memories of being Josh in 2010. Maybe what makes me numerically identical with that person is that I remember being him. That sounds plausible, but there are some problems. As anyone who knows me can tell you, my memory isn't all that stellar. If I can't remember some part of my past, that would imply that it wasn't me who bought all of these steam games. The longest journey? What even is this? Worse yet, at least for the enterprise of trying to establish a criteria by which we could judge whether someone is numerically identical with their past selves, memory is a really finicky thing. It's very easy to convince eyewitnesses that they saw something that they didn't, or any number of other things about their past selves. If I managed to convince someone that they also bought this game during the summer sale, that would mean that we're somehow both the same person at that time. You might say that doesn't count because it's not an accurate memory, but you can only say it's inaccurate if you're using some other criteria to answer the question we were trying to answer in the first place. So if it's not about sharing a memory with someone in the past, we've got more work to do. Okay, what about some combination of memory and causality? A chain of memory. Like, I might not specifically remember buying those games, but I do remember surfing steam during the summer sale. I remember a past version of myself, and he remembers buying those games. That sounds pretty feasible, and we get to dodge that memory duplication problem because only one of us has an unbroken chain of memory that goes back to that event. I might be able to convince you that you also bought those games, but there's no past version of you who remembers that. It's also got some interesting and potentially useful implications. Like, if you ever sever that chain of memory, you are a different person. If you accidentally get blackout drunk one night and then look at the pictures afterward, it definitely feels like that was someone else. One of the ways that we can test this theory of persistent personal identity is to invent weird but logically possible scenarios to see if we can break it. Star Trek is unfortunately not a documentary of the real world, but it does contain a neat little thought experiment that we can use to apply pressure to that chain of memory idea. It's time for the transporter, obligatory CGP gray and philosophy tube shout out. One of the most important technologies in Star Trek is a machine which scans people down to the subatomic level, then disassembles them into their component atoms, and reassembles atoms somewhere else into an identical structure. It's called the transporter, and it's used as a teleportation device. If you were dedicated to some of those previous criteria of persistent personal identity, like having all the same atoms, or a continuity of consciousness, then being disassembled into your component atoms is probably terrifying because it's synonymous with death, even if there's a copy of you reassembled somewhere else. But then again, you were also dying every seven years or every time you fell asleep, so meh. Other psychological criteria kind of seem like they don't have a problem with the transporter. The copy of you that shows up at the destination shares all the same psychology with the you that stepped into the machine. So, it's you. Well, let's tweak the thought experiment a scosh. Let's say that instead of disintegrating you, the transporter just knocks you unconscious, then duplicates you, then drops both bodies in sickbay, without any indication of which one is the original. When they wake up, there are now two people who share psychological continuity with your past self, but they're in different beds. They'll have different memories and different experiences from this point forward. They might develop different characters or even disagree with each other. They're very clearly different people now. So, which one is you? Which one counts as you persisting into the future? Which one should get your stuff or sleep with your partner? We've kind of got the two-pencil situation here. They may be qualitatively identical, but unless one can somehow equal two, they can't be numerically identical with the person that you were before you stepped into the transporter. Now, obviously, this is a fantastic scenario, and there's a lot of physics in between you and a quirk-perfect copy of yourself. But even if it couldn't happen, except in some fictional universe where someone's invented Heisenberg compensators, if it's logically possible for two people to be psychologically continuous with the same past person, then psychological continuity of any form isn't a sufficient criteria to establish persistent numeric identity. So, where does that leave us? Well, there's a reason that the problem of persistent identity has plagued Western philosophy since Heraclitus. He pointed out, you could not step twice into the same river. It's really, really hard. We have an intuition that things, like pencils, persist in time, that gets a little uncomfortable when we really put the screws to it. It's even more uncomfortable to realize that the things that we're most intimately familiar with in the entire universe ourselves are subject to the same uncertainty. Even people who believe in eternal supernatural entities like souls or gods are faced with the same problem. I mean, the transporter problem wasn't first imagined in the context of Star Trek, but almost 200 years earlier in the context of the apocalypse and resurrection. As such, there isn't really a wrong answer to these sorts of questions, just different kinds of answers with more or less intuitive implications. Some philosophers think that it's really important to establish what makes us continue to be us. While other philosophers think that the entire idea of a persistent personal identity is some sort of cognitive or linguistic mistake. But personally, if you've got a transporter trip to Mars or a nice shiny robot body for me to slip into, I'm not going to lose a lot of sleep wondering if it's still technically me afterward. One to beam up. Do you think that there's a meaningful criterion to establish persistent personal identity? Please leave a comment below and let me know what you think. Thank you very much for watching. Don't forget to subscribe, Blasher, and don't stop thunking. Engage.