Wei wrote:
> On Sat, Apr 18, 1998 at 02:56:18PM +0000, Nick Bostrom wrote:
> > I think that is wrong. It presupposes that I regard the name "Nick"
> > as being randomly choosen from the set of all possible names. When I
> > discover that I am called Nick, I would then get reason to believe
> > that many people are called Nick. --But "Nick" is not randomly
> > choosen from among all possible names. The only reason why "Nick" was
> > choosen as a sample was that there existed somebody with that name
> > who took his own name as a sample. And if you choose the name from
> > the set of all actual names (names of living persons), then you don't
> > get any information from finding that that name is instanciated.
>
> If you don't regard "Nick" as being randomly chosen, then why do you
> regard your birth rank as being randomly chosen?
Both are randomly choosen (according to the doomsdayer) but only from
the set of *actual* names and birth ranks.
> > Say that the percetage of B universes containing somebody called
> > "Nick" is twice that of A universes. But the same would hold for any
> > other name. Since I know that I have one name or another, then, if
> > the above reasoning were correct, I could infer that the B universe
> > was twice as likely as the A universe, even before I knew anything
> > about my name. This is equivalent to accepting the Self-Indication
> > Axiom. I show in my Doomsday-paper that there are serious problems
> > with accepting the SIA.
>
> Since "There is at least one person called Nick" and "There is at least
> one person called Sam" are not mutually exclusive, you can't sum over all
> possible names and conclude that the real universe is twice as likely to
> be type B before you learn your name.
But "There is at least one person called Nick." *is* incompatible
with "There is nobody called Nick.". So if the above reasoning were
correct, then you would say: "Suppose initially the A-universe
hypothesis is equally probable as the B-universe hypothesis.
Suppose my name is Mr. X. Since P(There exists someone called Mr.
X|A-universe hpothesis) is less than P(There exists someone called
Mr. X| B-universe hypothesis). Therefore the B-hypthesis is more
likely (even before you get to know what X stands for).
> > (The difference between finding your name and finding your position
> > in time is that you could have found that you position in time had
> > been incompatible with there being 100 people, but you couldn't find
> > a name that would have been incomplatible with either hypotesis.)
>
> "There is at least one person called Nick" is not incompatible with the
> "Real universe is type A" hypothesis, but it's less likely given that
> hypothesis.
I dispute that, for the reasons given above.
_____________________________________________________
Nick Bostrom
Department of Philosophy, Logic and Scientific Method
London School of Economics
n.bostrom.domain.name.hidden
http://www.hedweb.com/nickb
Received on Mon Apr 20 1998 - 19:11:40 PDT