Re: predictions

From: Nick Bostrom <>
Date: Mon, 6 Apr 1998 23:38:08 +0000

 Wei Dai wrote:

> This operationalization allows you to make explanations, but not
> predictions.
> At time 1, it doesn't help me to know that "If I'm at time 2 and I
> remember observing coin landing heads at time 1, then the probability of
> observing x is p." I mean it is not helpful in the sense of helping me
> make decisions at time 1, because the probability is conditional on my
> state of knowledge at time 2. According to decision theory, I can only use
> probabilities that are conditional on my current state of knowledge.

When you make your decision at time 1 you don't need any
probabilities, since you already know with certainty what's going to
happen given that you take a certain proposed action (and provided
you have the conputational ability to derive this). You know that if
you take such and such an action, then there will be n copies of
yourself at some later time. In my opinion there is no further fact
as to which one of these copies you will "really" turn out to be;
you'll be all of them.

> It is helpful to me at time 2, but only in the sense that it explains why
> I am observing x, namely that I remember observing heads at time 1 and
> therefore now have a probability p of observing x.

Also, it helps you make predictions at time 2, provided that you
haven't yet opened your eyes and seen how the coin landed. (If you
already know how it landed, then the issue is of course settled
and the probability is 1 or 0).

Nick Bostrom
Department of Philosophy, Logic and Scientific Method
London School of Economics
Received on Mon Apr 06 1998 - 15:45:41 PDT

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