# RE: A calculus of personal identity (was:*THE* PUZZLE)

I should clarify, I have taken "amnesia in Moscow" as meaning that you arrive in Moscow with a proportion of your pre-teleportation memories missing, so that total amnesia would mean you are unconscious or in a vegetative state, as after a severe head injury. On re-reading, I see that you probably meant that you are fully conscious in Moscow, but then forget some or all of what happened in Moscow (but not in Brussels) at your next destination. Actually, analogous situations occur all the time with medical procedures involving the use of amnesia-inducing drugs such as midazolam. Faced with the prospect of a procedure which you know will ultimately be wiped from your memory, should you expect an unpleasant experience, or should you expect to just wake up post-operatively with a gap in your memory? If the latter, then if you expect to become demented when you are very old, shouldn't you stop worrying about anything that might happen between now and then?

Stathis Papaioannou

Bruno Marchal writes:

> The second question is related to your assessment (in older posts) that
> in a self-duplication W M, with annihilation of the "original" in
> Brussels, the probability are equal to 1/2. I don't disagree with this.

> But are you aware of the difficulty of composing such probabilities?
> What if in Moscow I am read and annihilated again, and duplicate into
> Sidney and Beijing? I mean what are in Brussels the (first person)
> probabilities to reach and stay in Washington, Sidney and Beijing
> respectively?
>
> The most common answers are "P(W) = 1/2 P(S) = P(B) = 1/4" and "P(W) =
> P(S) = P(B) = 1/3".
> The problem here is that you can have a continuum of thought
> experiments, where you introduce ranges of amnesia in Moscow going from
> a case where "clearly" it should be 1/2 1/4 1/4 and (in the case of a
> complete amnesia of anything happened in Moscow) 1/3 1/3 1/3.
>
> What would you say? I mention this problem because it has motivated me
> for going more technical. I think it shows that amnesia makes possible
> the relative fusion of comp histories ... like the one of the quantum
> (empirical) world. (I think George also assessed a relation between
> fusing and amnesia if I remember correctly (?)).

The problem hinges on an answer to the question, what criteria must be satisfied for two instantiations of a person to be the "same" person? In the world with which we are familiar, most people would agree that there is an objectively right or wrong answer. Our brains have evolved so that we are sure that we are the same person today as we remember being yesterday, and will remember having been tomorrow. I might add that this isn't a view that is subject to revision in the light of new information, like the belief that the world is flat; rather, it has been so fundamental to our evolution that it has a tenacity at the visceral level that is only otherwise seen in the delusions of the psychotic patient. But evolution has not had to cope with teleportation, mind duplication, duplication with partial amnesia in one copy, partial or complete mind merging, and all the other fantastic possibilities which may or may not one day be realised. If it had (or if it will, in the far future), we might be left with a view of personal identity something like that espoused by Lee Corbin, where each copy is regarded as "self" and the (selfish) aim of life is not to preserve a single linear temporal sequence of related copies, but to maximise the total number of copies, even at the cost of a single individual's death.

Returning to the question of teleportation and probabilities, I would say that objectively there is only one unequivocal answer: you don't survive the experiment at all, but people who look like you and believe they are you materialise in Washington, Sydney and Beijing with P=1. Subjectively, I would try to apply the (delusional, or may as well be delusional) belief that you are a single person persisting through time as best as I can to the unnatural situation. I think that the best answer in the two-step teleportation (Br..>W,M; M..>S,Be) is that you should expect P(W)=1/2, P(S)=P(Be)=1/4. I prefer this to an equal P of 1/3 for each destination city because (again, due to our evolved psychology, not because it is the "truth") we anticipate all possible candidates for the "next moment", but once this next moment arrives, all the other concurrent copies become irrelevant, and the only thing that matters is the *next* next moment. Consistent with this method, if there is complete amnesia for all that happens in Moscow, it is as if that stage has not occurred, and from Br you can anticipate arriving in W, S and Be with equal probability. In the case of intermediate levels of amnesia in Moscow, I suppose this would yield intermediate probabilities. However, I'm not very confident about this, because our minds are simply not made to deal with the situation. It would be like trying to define a subjective "up" and "down" in an environment where the direction of gravity is rapidly changing: you would probably just get very dizzy!

Stathis Papaioannou

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