Monday, June 07, 2010

Fissioning in Prospect and Retrospect

Suppose that I need to endure some moderately unpleasant experience in order to protect my future self against an otherwise fatal disease. I don't at all resent filling my present with unpleasantness, because I value my future existence: I think of myself as a temporally-extended being, rather than a mere momentary existent (even though I don't think my present self literally endures into the future). So far so good. Moreover, suppose I take a temporary amnesia drug, so that afterwards I will not recall the details of the unpleasant experience (nor any plans or intentions, etc., that I make during this time). This seems unobjectionable -- if anything, it probably makes the overall situation better: no unpleasant memories!

But now consider an alternative situation. Suppose that I'm instead given the chance to fission, cell-like, into two future selves. Lefty would go on to live a long and flourishing life, whereas Righty would endure the moderately unpleasant experience before being swiftly vapourised. Is this significantly different?

Some might think so. On my understanding of the Lewisian 4-d worm view, we should think of Lefty and Righty as distinct people who share some temporal parts. As one of the overlapping parts, my present self should have 50% anticipation of ending up as (just) Lefty, and 50% anticipation of ending up as (just) Righty. But that's terrible: a 50% chance of swift death! Much better, on this view, to avoid fissioning, and just keep all the experiences in a single, long life.

But I think that's the wrong way to think of the situation. There's not really any "risk" here (it's not like I've got an enduring soul that'll go just one way or the other). We know exactly what will happen in the fission case: I'll have a continuant who goes on to live a flourishing life, and another continuant who experiences some mild unpleasantness. In other words, it's effectively the same prospect as I had before: some mild unpleasantness for some person-stages psychologically continuous with my present self (a future 'continuant' of me), plus a generally flourishing future for other continuant person-stages that are not psychologically unified with the suffering stages. I should fully identify with all of these future stages, and hence be happy to fission: it secures my full survival just as well as the original case.

So much for the prospective judgment. What should my post-fission continuants think about the situation? Intuitively, one feels, it'd suck to be Righty: at that stage, all that one has to look forward to is some unpleasantness followed by death. But I wonder if this intuition is simply a vestige of Cartesianism, or the assumption that there's some deep sense in which my amnesiac self would "survive" but Righty doesn't. In fact, no momentary stages literally endure into the future. So the real question is just whether there are future person-stages that are related to my present stage in the right kind of way. Now, it seems to me that Righty and my amnesiac stage are similarly related to my respective 'flourishing future' stages. In particular, for both there are future stages that share their long-standing memories and plans for the future, though in neither case will their present experiences or decisions impact upon the future stages. Is that enough to secure their "survival" (in the morally relevant sense)? I don't see why not.

What really matters in survival, it seems to me, is that a future stage continues on my general "life story". I don't need my present stage to be psychologically unified with the future stages (in the ongoing sense of laying down new memories, etc., for the future stages) in order for it to be narratively unified. Righty should continue to "identify with" Lefty's future. So, even retrospectively, I think I (in the form of each of my 'Lefty' and 'Righty' continuants) should find the fission scenario unobjectionable.

What do you think?


  1. "On my understanding of the Lewisian 4-d worm view, we should think of Lefty and Righty as distinct people who share some temporal parts. As one of the overlapping parts, my present self should have 50% anticipation of ending up as (just) Lefty, and 50% anticipation of ending up as (just) Righty."

    I don't think this is right. More specifically, I think the first sentence is, but the second sentence isn't. The Lewisian view doesn't leave room for your present self having a 50% anticipation of ending up as just Lefty, and a 50% anticipation of ending up as just Righty.

    I'd think the natural way of paraphrasing questions about "who you'll end up as" on the Lewisian view is to understand them as questions about which future time slices are part of the same 4d worm(s) as this (current) time slice. So "will I ever see Paris?" is understood as "is there some future person slice that sees Paris and which is part of a 4d person-worm that this (present) person-slice is also part of?"

    If that's how "who will I be" questions are understood, then there's no room for uncertainty in cases where you know that you will fission. Two person-worms contain your present person-slice, but there isn't some further question about which one "you" are, which we might be uncertain about. The Lewisian view, I think, can say what you want to.

    There are some variants of his view, however, that are committed to the idea that fission cases should be understood as involving uncertainty/risk (in fact, they embrace it). I'm thinking of Dilip Ninan's "Persistence and the First-Person Perspective." Ninan tries to keep the Lewisian ontology, while making sense of the idea that you can coherently worry whether you'll turn out to be lefty or righty. Personally, I'm with you in thinking that we shouldn't try to make room for coherent worries about whether you'll turn out to be lefty or righty.

  2. Ah, that makes sense. Thanks for the correction!


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