Stathis Papaioannou writes:
> Hal,
> >I should add that I don't believe in QTI, I don't believe that we are
> >guaranteed to experience such outcomes.  I prefer the observer-moment
> >concept in which we are more likely to experience observer-moments where
> >we are young and living within a normal lifespan than ones where we are
> >at a very advanced age due to miraculous luck.
> Aren't the above two sentences contradictory? If it is guaranteed that 
> somewhere in the multiverse there will be a million year old Hal 
> observer-moment, doesn't that mean that you are guaranteed to experience 
> life as a million year old?

I don't think there are any guarantees in life!

I don't see a well defined meaning about anything I am guaranteed to

I am influenced by Wei Dai's approach to the fundamental problem of what
our expectations should be in the multiverse.  He focused not on knowledge
and belief, but on action.  That is, he did not ask what we expect, he asked
what we should do.

How should we behave?  What are the optimal and rational actions to take
in any given circumstances?  These questions are the domain of a field
which, like game theory, is a cross between mathematics, philosophy and
economics: decision theory.

Classical decision theory is uninformed by the AUP, but it does include
similar concepts.  You consider that you inhabit one of a virtually
infinite number of possible worlds, which in this theory are not real but
rather represent your uncertainty about your situtation.  For example,
in one possible world Bigfoot has sneaked up behind you but you don't
know it, and in other worlds he's not there.  You then use this world
concept to set up a probability distribution, and make your decision
based on optimal expected outcome over all possible worlds.

Incorporating the multiverse can be done in a couple of ways.  I think Wei
proposed just to add the entire multiverse as among the possible worlds.
Maybe we live in a multiverse, maybe we don't.  The hard part is then,
supposing that we do, how do we rank the expected outcomes of our actions?
Each action affects the multiverse in a complex way, being beneficial
in some branches and harmful in others.  How do we weight the different
branches?  Wei proposed to treat that weighting as an arbitrary part of
the user's utility function; in effect, making it a matter of taste and
personal preference how to weight the multiverse branches.

I would aim to get a little more guidance from the theory than that.
I would first try to incorporate the measure of the various branches
which my actions influence, and pay more attention to the branches with
higher measure.  Then, I think I would pay more attention to the effects
in those branches on observers (or observer-moments) which are relatively
similar to me.  However, that does not mean I would ignore the effects
of my actions on high-measure branches where there are no observers
similar to me (i.e. branches where I have died).  I might still take
measures such as buying life insurance for my children, because I care
about their welfare even in branches where I don't exist.  Similarly,
if I were a philanthropist, I might take care to donate my estate to
good causes if I die.

These considerations suggest to me an optimal course of action in a
multiverse, or even in a world where we are not sure if we live in a
single universe or a multiverse, which is arguably the situation we
all face.  It rejects the simplicity of the RSSA and QTI by recognizing
that our actions influence even multiverse branches where we die, and
taking into consideration the effects of what we do on such worlds.
There is still an element of personal preference in terms of how much we
care about observers who are very similar to ourselves vs those who are
more different, which gives room for various philosphical views along
these lines.

And in terms of your question, I would not act as though I expected to
be guaranteed a very long life span, because the measure of that universe
is so low compared to others where I don't survive.

Hal Finney

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