Saibal Mitra wrote:
>
>----- Original Message -----
>From: "Quentin Anciaux" <quentin.anciaux.domain.name.hidden>
>To: <everything-list.domain.name.hidden>
>Sent: Monday, June 20, 2005 11:37 PM
>Subject: Measure, Doomsday argument
>
>
> > Hi everyone,
> >
> > I have some questions about measure...
> >
> > As I understand the DA, it is based on conditionnal probabilities. To
>somehow
> > calculate the "chance" on doom soon or doom late. An observer should
>reason
> > as if he is a random observer from the "class" of observer.
> >
> > The conditionnal probabilities come from the fact, that the observer
>find
>that
> > he is the sixty billions and something observer to be "born". Discover
>this
> > fact, this increase the probability of doom soon. The probability is
> > increased because if doom late is the case, the probability to find
>myself
>in
> > a universe where billions of billions of observer are present is greater
>but
> > I know that I'm the sixty billions and something observer.
>
>
>This is a false argument see here:
>
>http://arxiv.org/abs/gr-qc/0009081
>
>
>To calculate the conditional probability given the birthrank you have you
>must use Bayes' theorem. You then have to take into account the a priori
>probability for a given birthrank. If you could have been anyone of all the
>people that will ever live, then you must include this informaton in the
>a-priori probability, and as a result of that the Doomsday Paradox is
>canceled.
I don't think the cancellation argument in that paper works, unless you
already *know* the final measure of one type of civilization vs. another
from the perspective of the multiverse as a whole. For example, if I know
for sure that 50% of civilizations end after 200 billion people have been
born while 50% end after 200 trillion have been born, then it's true that
observing my current birthrank to be the 100 billionth person born, I should
not expect my civilization is any more likely to end soon, since 50% of all
observers who find themselves to have the same birthrank are part of
200-billion-person civilizations and 50% of all observers who find
themselves to have the same birthrank are part of 200-trillion person
civilizations. But if I don't know for sure what the measure of different
civilizations is, suppose I am considering two alternate hypotheses: one
which says 50% of all civilizations end after 200 billion people and 50% end
after 200 trillion, vs. a second hypothesis which says 99% of all
civilizations end after 200 billion people and 1% end after 200 trillion. In
that case, observing myself to have a birthrank of 100 million should lead
me, by Bayesian reasoning, to increase my subjective estimate that the 99/1
hypothesis is correct, and decrease my subjective estimate that the 50/50
hypothesis is correct.
Jesse
Received on Mon Jun 20 2005 - 19:50:43 PDT