Saibal Mitra wrote:

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----- Original Message ----- From: "Quentin Anciaux" <[EMAIL PROTECTED]> To: <everything-list@eskimo.com> 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 observerfindthat > 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 findmyselfin > 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