# Re: effective probability

From: Wei Dai <weidai.domain.name.hidden>
Date: Fri, 29 Jan 1999 19:59:03 -0800

On Fri, Jan 29, 1999 at 06:22:18PM -0500, Jacques M Mallah wrote:
> I don't see any difference how many universes exist. The DA is
> simple: considering yourself to be a random selection among humanity,
> the fraction of human lives that have passed, compared to the the amount
> over the lifetime of the species, can be assumed to have a uniform
> probability distribution on the interval (0,1). This is true whether or
> not there are other universes. So the median future lifetime of the human
> species can be expected to be fairly short. (Due to the recent population
> boom, most human lives have occurred in this century. So has yours.)

I'm not sure I understand this argument. What do you mean by "median
future lifetime of the human species"? Are you somehow sorting all
conscious experiences? On what basis?

However I'll try to explain why DA in its usual Bayesian form doesn't
work. With an "everything" theory, you have a prior probability of 1 that
all objects exist with a certain measure. Taking into account who/when
you are, you still have a posterior probability of 1 that all objects
exist with this measure. Therefore the knowledge of who/when you are
doesn't affect any statistic derived from the measure, such as the the sum
of measures of everyone who believes he has a birth rank > 10^100.

Now what isn't clear to me is a whether the following variant of DA will
work. Suppose I want to know the sum of measures of everyone who believes
he has a birth rank > 10^100. Since this number is not computable, I have
to be satisfied with an estimate. Knowing my own apparent birth rank
should help me with this estimate, and knowing that my own apparent birth
rank is < 10^100 should lower my estimate. I say "should" because it seems
intuitive but I don't know how to justify it formally. But note this
reasoning is not Bayesian, since it is dealing with computational
limitations and estimates, which Bayesianism ignores.
Received on Fri Jan 29 1999 - 20:00:17 PST

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