An observer a1 at time t1 undergoes destructive scanning, and two exact
copies, observers a2 and a3, are created. If we ask a2 and a3, they will
each claim to remember "being" a1. We could say that as a result of the
duplication we have two people, a1a2 and a1a3, each with equal claim to have
been the original person a1.
Now, consider the use of the terms "observer" and "person" in the above
paragraph. In an old-fashioned linear world where a person is born, lives
his life, and dies, there is little point in making distinctions between the
two terms. When branchings and duplications start happening, however, the
concept of "person" becomes complicated and ambiguous. In the given example,
the observers a1, a2, a3 are unambiguous, separated from each other in time
and space; and it is this basic entity which I call an observer moment. A
person is then a complex entity extending along a certain path in the
multiverse, comprised of a concatenation of observer moments.
The observer moments a1, a2, a3 as defined above have duration and are
delimited by the duplication event at t1. There is no reason why the
duplication could not happen while a1 is in mid-thought. In that case, a2
and a3 may or may not continue and complete the thought, or they may
complete different thoughts (that start the same way) given that a2 and a3
may now be in different environments. It would then be a matter of
definition whether we say the thought cut short at t1 was half in a1 and
half in a2/a3, or whether we say it was completely in a2/a3 since, as I
think you are arguing, half a thought does not make a conscious experience.
It would be technically simpler if we allowed for part-thoughts, even though
this detracts somewhat from the intuitive appeal of the observer moment
concept. This would also allow for a continuum of instantaneous observer
moments, consistent with the continuous branching presumed to occur in the
Brent Meeker writes (quoting Stathis):
It is true that human cognition, memories etc. are not instantaneous.
There are two ways to keep the OM concept useful despite this. One is to
extend each "moment" so that it encompasses, for example, the minimum
period of awareness (probably a substantial fraction of a second), or any
interval of arbitrary length, such as the waking hours of a day. This
still allows one to think about questions involving continuity of personal
identity where multiple copies or near-copies of a given mind are running
simultaneously, the interval of the OMs under consideration being tailored
to the particular situation.
But giving OMs duration seems to invite other incoherence. It means that
time cannot be understood as a sequence of timeless OMs. On the other hand
it solves more than just the memory problem; if OMs have duration, then the
durations could overlap and thus define "worlds" and "personal identity" -
i.e. provide the accessiblity relation.
The other way is to bite the bullet and allow instantaneous
part-cognitions. A memory is then only associated with an OM during the
act of remembering, and each instantaneous OM covers only an instant of
that act, in the same way a frame in a film covers only an instant of the
action depicted by the series of frames.
I have difficultly with an "instant of cognition". A film records an
instant of spatial relations, but how is one to understand a non-extensive,
instant of cognition - certainly not by simple introspection. But it
seems that getting an explanation of the world via introspection is why OMs
were appealing in the first place.
On the road to retirement? Check out MSN Life Events for advice on how to
get there! http://lifeevents.msn.com/category.aspx?cid=Retirement