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 multiverse.

Stathis Papaioannou

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.

Brent Meeker

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