Re: practical reasoning and strong SSA

From: <>
Date: Fri, 4 Jun 1999 12:30:34 -0700

Wei Dai, <>, writes:
> But where does P (I observe "N[Pi]=3.14159" | PI == 3.14159 AND I am
> here/now, doing this) come from (how is it defined) without the Strong
> SSA?

I don't see that the SSSA would play a role, because you are explicity
excluding the possibility that you are someone else in the specific
conditional probability under consideration. The strong SSA says that
you should consider yourself a random selection from among all observers.
But we are stipulating in the conditional probability that you are,
in fact, yourself, here and now. Whether you might have been someone
else is therefore irrelevant to the calculation and to the definition.

The way I have seen this calculation justified is to consider that you
are randomly chosen from among all possible observers who are consistent
with what you are experiencing here/now. This is more limited than
the SSA because the reference set is just those observers who share
identical mental states. Each person does his probability calculations
with regard to that reference set. From his perspective, he is in one
of many possible universes, constrained by what he observes and knows.
But there is no chance that he is a tentacled alien on alpha centauri.

Consider the "extra strong" SSA where the reference set is all subsystems
of all universes, not just conscious ones, so that you consider the
possibility that you might have been a rock in your calculations.
You will get the same answer for the probability above under this
assumption as well as the conventional SSSA, because in both cases we
exclude from consideration any other possibility than that you are you.
So this extra strong SSA should be just as good as the strong SSA in
terms of defining the conditional probability, so therefore the strong
SSA must not be a necessary philosophical underpinning.

Received on Fri Jun 04 1999 - 12:30:36 PDT

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