2010/1/13 Nick Prince <m...@dtech.fsnet.co.uk>:
> I’ve read through a good deal of previous posts on the ASSA/RSSA
> debate but I keep reaching a stumbling block regarding how successive
> observer moments (OM) are to be expected in terms of their
> continuity.  I think Youness Ayaita  queried the same thing as I am
> here but articulated it much better - this post was "a question
> concerning the ASSA/RSSA debate (Sept 18 2007).  Stathis gave an
> answer which was very helpful  (as usual) but he still referred to a
> uniform? distribution which I find difficult to understand.  Russell
> called it global!
> From the everything wiki I have looked up the relevant definitions for
> the two contentious sampling assumptions which are quote :
> "The Relative Self Sampling Assumption (RSSA) is a form of anthropic
> reasoning that assumes our present observer moment is selected
> according to a measure that depends on another given observer moment
> (the prior observer moment). As such it implicitly relies on a notion
> of time that gives rise to a succession of observer moments.
> In one interpretation of quantum mechanics, observer moments are
> identified with the quantum state |psi>. The measure used with the
> RSSA is just given by the Born rule
> The Absolute Self Sampling Assumption, (ASSA) is a form of anthropic
> reasoning that assumes our present observer moment is selected from
> the set of all observer moments according to some absolute measure. To
> be contrasted with the Relative Self Sampling Assumption."
> Where I have difficulty with understanding the ASSA is in terms of its
> implications for our next observer moment.  Is the absolute measure,
> referred to in the ASSA definition really intended to be a uniform
> distribution in the sense that my next OM could be equally any one
> from the multiverse?  This would be strange indeed and would result in
> me experiencing all sorts of discontinuous happenings – even if the
> reference class was restricted to OM’s which I experience. On the
> other hand, am I to understand that the ASSA does not carry with it
> any implicit assumption about the probability distribution (absolute
> measure) that OM’s are selected from?  Instead must we assume the
> nature of this distribution for picking out our next OM is to be
> determined by some other considerations like: “it is the laws of
> physics which glue OM’s together” as an example)?  (I know that a
> computationalist might come up with another solution as to how the
> OM’s are stitched together, but that is not my point).  Is it assumed
> (as a given for now anyway), that there is some additional mechanism
> or explanation as to why observer moments are stitched together in the
> way they are?  Or, if a uniform distribution is implied, then how can
> this be reasonable?
> The RSSA, as I understand it would use the Born rule to indicate which
> successive OM’s are possible and likely.
> Why the ASSA is applicable to determine our birth OM I am also not
> sure of either.  I would be very grateful to anyone who can clarify
> this for me.

The ASSA/RSSA distinction on this list came, as I understand it, from
debate on the validity of the idea of "quantum immortality". This is
the theory that in a multiverse you can never die, because at every
juncture where you could die there is always a version of you that
continues living. The ASSA proponents say that even though there are
thousand year old versions of you in the multiverse they are of very
low measure and you are therefore very unlikely to find yourself one
of them, as unlikely as you are to end up living to a thousand through
pure good luck in a single universe. This paper by Jacques Mallah
outlines the position: http://arxiv.org/abs/0902.0187. A point of
disagreement when we discussed this paper on the list about a year ago
is that Jacques thinks it would be a bad thing if there were many
copies of a person in lockstep and some of the copies were destroyed,
whereas if I were one of the copies it wouldn't worry me at all.

The problem with the ASSA is that it assumes that each OM is sampled
randomly from the set of all OM's. In fact, this is not how life
works. Today is Wednesday. I'm pretty sure that when I wake up
tomorrow morning it will be Thursday, and not Friday, even though
(absent some disaster) the measure of my Friday OM's in the multiverse
is about the same as the measure of my Thursday OM's. Even if there
were a billion copies of me on Friday and only one copy on Thursday, I
can still expect to go through the Thursday copy before ending up a
Friday copy. Once embedded in the multiverse, it puts constraints on
my possible successor OM.

If I'm not already embedded in the multiverse then I could be anyone,
and I am therefore more likely to be someone from a high probability
group or era. So I am more likely to be a modern human than an early
human, for example, because there are more modern humans. I think
that's what Russell means by the ASSA being aplicable in birth order.
This is a tricky concept to get your mind around and leads to
semi-weirdness such as the Doomsday Argument. But that I'll experience
Thursday before Friday even if there are lots of me on Friday is, I
think, relatively straightforward.

Stathis Papaioannou
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