Causal loops and time travel
I've been working through Lewis' "The Paradoxes of Time Travel." He mentions the phenomenal short story "—All You Zombies—" by R.A. Heinlein, who is, I think, the best sci-fi author to date. The story itself can be hard to get a grip on. There's a graphical representation of the causal loops in the story available; ignore the paragraph immediately above the picture, it's confusing and wrong.
Now, here's a summary of the story. One day, a man walks in to a bar. The narrator is the bartender. In his internal narration, the bartender refers to the man as the Unmarried Mother. The bartender and the UM get to talking, and the latter tells the former his story. The UM's story is this: he was originally a woman, and an orphan. She was raised in an orphanage, and was never adopted. Eventually, she was turned out on her ear, and went out into the world. She encountered a mysterious drifter, who seduced her and left her pregnant. However, here we learn that she was something of a freak of nature. Her reproductive organs were up to the task of producing a child, but she couldn't give birth without a Cesarean. Further, after the surgery, the organs wouldn't work anymore. Luckily, with some hormone treatments, she could become a fully-functioning man. Please suspend your disbelief here; I'm eliding some matters that make it slightly more sensible, and it's just a story.
So, she becomes a man. Then, tragedy strikes again, and her child vanishes from the hospital. She, now he, embarks on a career as a writer, penning penny-dreadfuls about fallen women under a pseudonym. The bartender, having heard this story, offers to show the UM something special in the back room - a time machine. They flash back several years; the bartender gives the UM some cash, and points him towards a girl walking in the park. The UM seduces the girl, and then the bartender takes him to the future to receive training in time travel. Meanwhile, the girl is pregnant. Nine months later, she gives birth by C-section. The bartender goes back in time again and steals the baby from the hospital. Then he goes back further and leaves the baby, a young girl, at an orphanage. The girl had to give birth by C-section, and as a matter of fact is something of a freak of nature. The story resolves as you might imagine; the bartender (who wears a Ouroboros as a ring) takes off his shirt, revealing a scar from a C-section. And so the loop is complete.
The story is notable not only for its treatment of time travel and causal loops, but also its use of the idea of zombies. The story closes with this line from the bartender: "Then I glanced at the ring on my finger. The Snake That Eats Its Own Tail, Forever and Ever. I know where I came from - but where did all you zombies come from? I felt a headache coming on, but a headache powder is one thing I do not take. I did once - and you all went away. So I crawled into bed and whistled out the light. You aren't really there at all. There isn't anybody but me - Jane - here alone in the dark. I miss you dreadfully!"
The zombies he's talking about are phenomenal (philosophical) zombies, not the regular shambling, brain-eating kind. That's interesting, but not what I'm going to talk about. No, what's interesting is time travel.
Lewis cites this story as an example of sensible time travel, along with another Heinlein tale, "By His Bootstraps." I haven't read that one. What follows are my thoughts on Lewis' defense of this sort of story. These are notes, and I haven't taken the time to go over my language, meaning I'm probably ambiguous or unclear in many places. I apologize.
In “The Paradoxes of Time Travel” David Lewis argues that while causal loops may be inexplicable and uncaused, they are not paradoxical. He makes an analogy to God and the Big Bang, both of which he claims are inexplicable, uncaused, and widely accepted. This doesn’t seem right. Certainly, God and the Big Bang are uncaused, but they don’t seem to be inexplicable. With regards to God, it seems fair to think that if God exists, he exists necessarily; similarly, one might imagine that necessarily, something exists. Now, neither of these accounts are causal stories. Nor are they entirely convincing. But they are explanations, although they might not be exhaustive. One might grant that necessarily, something exists, but then ask why the Big Bang brought it into existence. However, we have plenty of evidence for the Big Bang (or something like that) which serves as an explanation for our belief that the Big Bang happened.
It doesn’t seem like any similar story can be given for causal loops like the one in Heinlein’s “—All You Zombies—.” Here’s why. We’re more-or-less comfortable thinking of God, or the universe, as necessary. Humans, on the other hand, are contingent beings. Being necessary seems to be a sufficient explanation for a thing’s existence, but a defender of causal loops has no such recourse. Further, we typically want our explanations of contingent events to be causal stories, or at least include them. Consider this scenario: I spy a unicorn in a meadow. When I try to explain this to a society of biologists and taxonomists, I’d probably be asked to offer a hypothesis as to how the unicorn got there, and why no one else has seen a unicorn before. My interlocutors wouldn’t find it acceptable for me to say that the unicorn was created ex nihilo. The fact that we generally want causal stories when we seek explanations of contingent events suggests that we might find paradox in the idea of events which are contingent but uncaused.
It seems that we can even give causal explanations of contingent a priori events. For example, let’s assume Kripke is right, and the length of the standard meter bar is contingent, but known a priori. We ask for an explanation: why is the standard meter bar as long as it is? The story would probably have to invoke performatives. We’d say that by declaring that this is the standard meter bar, we make it so. This is a causal story, albeit not a story of physical causation. It doesn’t seem that you can give a similar story for causal loops.
One very important thing missing from my discussion is why uncaused contingent events are paradoxical. I think this discussion is suggestive, but I might be pointing at an irrelevant disanalogy. I've got to think about it some more.
Now, here's a summary of the story. One day, a man walks in to a bar. The narrator is the bartender. In his internal narration, the bartender refers to the man as the Unmarried Mother. The bartender and the UM get to talking, and the latter tells the former his story. The UM's story is this: he was originally a woman, and an orphan. She was raised in an orphanage, and was never adopted. Eventually, she was turned out on her ear, and went out into the world. She encountered a mysterious drifter, who seduced her and left her pregnant. However, here we learn that she was something of a freak of nature. Her reproductive organs were up to the task of producing a child, but she couldn't give birth without a Cesarean. Further, after the surgery, the organs wouldn't work anymore. Luckily, with some hormone treatments, she could become a fully-functioning man. Please suspend your disbelief here; I'm eliding some matters that make it slightly more sensible, and it's just a story.
So, she becomes a man. Then, tragedy strikes again, and her child vanishes from the hospital. She, now he, embarks on a career as a writer, penning penny-dreadfuls about fallen women under a pseudonym. The bartender, having heard this story, offers to show the UM something special in the back room - a time machine. They flash back several years; the bartender gives the UM some cash, and points him towards a girl walking in the park. The UM seduces the girl, and then the bartender takes him to the future to receive training in time travel. Meanwhile, the girl is pregnant. Nine months later, she gives birth by C-section. The bartender goes back in time again and steals the baby from the hospital. Then he goes back further and leaves the baby, a young girl, at an orphanage. The girl had to give birth by C-section, and as a matter of fact is something of a freak of nature. The story resolves as you might imagine; the bartender (who wears a Ouroboros as a ring) takes off his shirt, revealing a scar from a C-section. And so the loop is complete.
The story is notable not only for its treatment of time travel and causal loops, but also its use of the idea of zombies. The story closes with this line from the bartender: "Then I glanced at the ring on my finger. The Snake That Eats Its Own Tail, Forever and Ever. I know where I came from - but where did all you zombies come from? I felt a headache coming on, but a headache powder is one thing I do not take. I did once - and you all went away. So I crawled into bed and whistled out the light. You aren't really there at all. There isn't anybody but me - Jane - here alone in the dark. I miss you dreadfully!"
The zombies he's talking about are phenomenal (philosophical) zombies, not the regular shambling, brain-eating kind. That's interesting, but not what I'm going to talk about. No, what's interesting is time travel.
Lewis cites this story as an example of sensible time travel, along with another Heinlein tale, "By His Bootstraps." I haven't read that one. What follows are my thoughts on Lewis' defense of this sort of story. These are notes, and I haven't taken the time to go over my language, meaning I'm probably ambiguous or unclear in many places. I apologize.
In “The Paradoxes of Time Travel” David Lewis argues that while causal loops may be inexplicable and uncaused, they are not paradoxical. He makes an analogy to God and the Big Bang, both of which he claims are inexplicable, uncaused, and widely accepted. This doesn’t seem right. Certainly, God and the Big Bang are uncaused, but they don’t seem to be inexplicable. With regards to God, it seems fair to think that if God exists, he exists necessarily; similarly, one might imagine that necessarily, something exists. Now, neither of these accounts are causal stories. Nor are they entirely convincing. But they are explanations, although they might not be exhaustive. One might grant that necessarily, something exists, but then ask why the Big Bang brought it into existence. However, we have plenty of evidence for the Big Bang (or something like that) which serves as an explanation for our belief that the Big Bang happened.
It doesn’t seem like any similar story can be given for causal loops like the one in Heinlein’s “—All You Zombies—.” Here’s why. We’re more-or-less comfortable thinking of God, or the universe, as necessary. Humans, on the other hand, are contingent beings. Being necessary seems to be a sufficient explanation for a thing’s existence, but a defender of causal loops has no such recourse. Further, we typically want our explanations of contingent events to be causal stories, or at least include them. Consider this scenario: I spy a unicorn in a meadow. When I try to explain this to a society of biologists and taxonomists, I’d probably be asked to offer a hypothesis as to how the unicorn got there, and why no one else has seen a unicorn before. My interlocutors wouldn’t find it acceptable for me to say that the unicorn was created ex nihilo. The fact that we generally want causal stories when we seek explanations of contingent events suggests that we might find paradox in the idea of events which are contingent but uncaused.
It seems that we can even give causal explanations of contingent a priori events. For example, let’s assume Kripke is right, and the length of the standard meter bar is contingent, but known a priori. We ask for an explanation: why is the standard meter bar as long as it is? The story would probably have to invoke performatives. We’d say that by declaring that this is the standard meter bar, we make it so. This is a causal story, albeit not a story of physical causation. It doesn’t seem that you can give a similar story for causal loops.
One very important thing missing from my discussion is why uncaused contingent events are paradoxical. I think this discussion is suggestive, but I might be pointing at an irrelevant disanalogy. I've got to think about it some more.
posted by Dan @ 1:00 AM
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