Matthew Donald wrote:
>Back in June, Nick Bostrom <N.Bostrom.domain.name.hidden> wrote
>> http://www.anthropic-principle.com/phd
>It took a while, but I finally managed to get round to reading it and
>I'm very glad I did. It is a clear and thoughtful exploration of an
>interesting topic.
Thanks!
>Bostrom leaves two crucial questions open:
>
>1) The reference class problem -- what counts as an observer?
>
>2) Why should the self-sampling assumption be true?
I place boundaries on the first, although it partly remains an open
question. The second question I think I answer, at least to the extent
of giving reasons for accepting SSA. I see it as a methodological
principle; hence I don't search for some kind of physical "cause" for
why it is true.
>For many years now, I have been developing a detailed version of
>the many-minds interpretation of quantum theory. In the papers on
>my web site
I'll have a look at that.
>The correct (objective) a priori probability of our observations is
>defined by whatever is the true physical theory.
Sounds like a contradiction! Objective probabilities aren't a priori -
they depend on what physics happens to be true in the actual world, and
that's something we only learn from experience.
>As a first approximation to the correct probabilities, however, it is
>not reasonable to guess that we are about as likely as most
>observers like us. This is the self-sampling assumption.
Not reasonable, or not unreasonable?
>One of the interesting problems that Bostrom raises for the
>self-sampling assumption is what an observer with an obviously
>expectional birth rank should believe. In particular, to what extent
>is the doomsday argument justified, and what should Adam and
>Eve have believed?
>
>My response is that most of our empirical testing of the objective
>probabilities which define our lives does not directly relate to our
>birth rank. If Eve has not studied quantum theory then it is hardly
>suprising if her ignorance leads her astray.
Quantum theory is irrelevant to the Adam&Eve example, because that is a
thought experiment, so I can simply postulate that quantum physics is
false in their world. It's important to distinguish between
methodological or epistemological rules (SSA), and empirical hypotheses
(quantum theory). The former can be applied to the latter, but mixing
them up can easily result in a category mistake.
>Nevertheless, Eve still must expect to be typical as an observer.
>Otherwise, she has no reason to believe her physical theories. Her
>birth rank puts her in the position of someone who has tossed a fair
>coin 1,000 times and it has always come up heads.
For all she knows, she may simply be one out of two humans - pretty
typical.
> But she is
>tossing a million other coins at the same time so it isn't really that
>surprising.
Let's assume the MWI is false.
P.S. There were one or two messages earlier in this thread that I never
got around to replying to (sorry!), because I was in the process of
moving to from U.K to the U.S. If those who sent them happen to still
have them handy, I'd be thankful if they could re-send them to me
privately, and I'll reply to the list.
Nick Bostrom
Department of Philosophy
Yale University
Personal Homepage:
http://www.nickbostrom.com
Email: nick.domain.name.hidden
Received on Fri Sep 22 2000 - 14:03:38 PDT