Wei Dai wrote:
> On Tue, May 18, 1999 at 09:37:03AM -0700, hal.domain.name.hidden wrote:
> > I think that Nick Bostrom, who (as far as I know) conceived of and named
> > the SSA, was not thinking in terms of the Strong SSA. When he discusses
> > "my" birth rank, he is implicitly assuming that I am the same observer
> > today that I was when I was born. I think it is best, therefore, to
> > distinguish the two assumptions by giving them names in this form.
>
> I think what you call "Strong SSA", Nick calls "SSA with observer-moments
> as the reference class". One of his papers is supposed to have a
> discussion of whether the reference class should consist of observers or
> observer-moments, but I am unable to find it. (Nick, if you're reading
> this please point us to the paper.)
It is there, in our future light cone ;-)
I think it is a good idea to call the "SSA with observer-moments as
the reference class" the Strong SSA, as Hal suggests. Using a uniform
distribution over observer-moments involves using the SSA with each
observer given a weight proportional to her longevity (and the number
of instanciations, if running on multiple processors or existing in
many worlds?). In addition it permits one to draw conclusions
about one's own life expectancy, but only in principle. In practice,
that is not possible, since the no-outsider requirement is not
satisfied. (All those observer-moments of other observers!) The fact
that this observer-moment belongs to Nick Bostrom indicates that he
is a person containing many observer-moments. This counterbalances a
Doomsday argument applied to one's own lifespan, in the same way as
the existence of lots of extraterrestrials would cancel the effect of
the original Doomsday argument. (See e.g. my "The DA is alive and
kicking" paper for details, at
http://www.anthropic-principle.com).
I'd like to make a couple of brief comments on two messeges that
appeared earlier:
Russell Standish wrote:
> "Self-Sampling Assumption". It is a generalisation (or
> specialisation?) of the totalitarian, or Copernican principle, in
> that you are saying there is nothing special about you. For example,
> SSA is often applied to birth order - that there are as many people
> born before you as are born afterwards - implying some sort of
> population crash in the near future.
That there is as many people before as after you is actually not a
consequence of SSA. You need to make other assumptions (empirical or
a priori) to get that result. Relative to not applying the SSA, the
SSA always argues in favour of as few extra people as possible, over
and above those people you already know will have existed.
Gale wrote:
>The example given is commonly called the "Doomsday Argument" and is
>an incomplete application of SSA. The principle needs to be applied
>not only to birth order conditional on some particular number of
>humans ever living, but also to the number of humans ever living.
>When SSA is fully applied, there is no longer an implication of some
>sort of population crash in the near future.
What Gale is referring to is the Self-Indication Assumption, stating:
(SIA) The fact that one is an observer gives one some reason to
believe that the world contains many observers.
It is true that this cancels the DA, but the SIA is very problematic.
There is a discussion of the SIA in my "Investigations into the DA"
(about half way down in the document).
Nick Bostrom
http://www.hedweb.com/nickb n.bostrom.domain.name.hidden
Department of Philosophy, Logic and Scientific Method
London School of Economics
Received on Mon May 24 1999 - 17:02:45 PDT