On Sun, Jun 15, 2008 at 01:40:09AM -0700, Greg Egan wrote:
> > My attributes (eg
> > height, weight and so on) are all drawn from distributions of such
> > attributes. Why not some hypothetical property like "observer class"
> > as set up in this toy problem?
> Why is your height and weight drawn from a certain distribution?  It's
> because you've been exposed to certain statistical influences on those
> attributes, and those influences are influences that you have in
> common with a certain subset of the human population. 

Of course. That was my point about it not being an actual sampling process.

> But it would be
> absurd to say that *your* height and weight is drawn from the
> distribution of heights and weights of all living creatures in the
> history of the universe.  Equally, it would be absurd to say that your
> observer class has been drawn from the distribution of all observers
> in the history of the universe.

It is absurd to say we're drawn from a distribution over all living
creatures. But it is not absurd to say we're drawn from a
distribution over all conscious things. That is the essence of
anthropic reasoning. It seems we're destined to disagree on this.

> > But we do this all the time. Why is it we reject crackpot claims that
> > the world will end on such and such a date for instance?
> We reject those claims because they flow from theories that we reason
> should have led to observable consequences in the past (e.g. theories
> of interventionist deities).  So what we have are prior probabilities
> that strongly disfavour those crackpot theories -- and given equal
> crackpot ratings, their predictions about the future are irrelevant.
> If crackpot A tells me that the world will end in 2012, and crackpot B
> tells me that the world will end in 20,012, then all else being equal
> I will (in 2008) give them both *equal* low credence.

I was actually thinking more of theories like "the law of gravity will
be suspended on the 25th of July, 2012, but otherwise everything else
is the same". Obviously it makes the same retrodictions as our usual
scientific theories (doing so by definition). The reason it is
rejected is because of the arbitrary nature of the date makes it a
more complex theory (in the Occam's razor sense).

> And given two (non-crackpot) cosmological theories with equal
> grounding in modern physics and which imply no observable differences
> up to the present epoch, but wildly different consequences in the very
> far future, we *cannot* use those far-future consequences to
> discriminate between them.  Specifically, we cannot use differences in
> the numbers of future observers in various classes that the different
> theories predict, in order to favour one theory over another, here and
> now.

Actually, I think this statement follows as a consequence of the RSSA
which Bruno mentioned earlier, in as far as we're discussing the
future of our universe (rather than all possible universes).

There is some discussion in my book "Theory of Nothing" about the RSSA
versus its main competitor the ASSA. Also



A/Prof Russell Standish                  Phone 0425 253119 (mobile)
UNSW SYDNEY 2052                         [EMAIL PROTECTED]
Australia                                http://www.hpcoders.com.au

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