momentary and persistent minds

From: Wei Dai <weidai.domain.name.hidden>
Date: Thu, 28 May 1998 00:38:04 -0700

I found an especially interesting paragraph in David Albert and Barry
Loewer's paper on their many-minds interpretation of quantum mechanics.
The paper is "Interpreting the Many Worlds Interpretation" in Synthese 77
(1988) 195-213.

(begin quote)
One assumption, perhaps the most disturbing aspect of the dualism, is that
there is a matter of fact concerning whether or not a mind associated with
a brain at one time is the same mind as one associated with the brain at a
different time. This assumption violates the supervenience of the mental
on the physical since the evolution of the physical state of the universe
does not determine such identities. (On the other hand, as we previously
saw, the proportion of minds in various mental states associated with a
brain at a given time does supervene on the physical state of the brain,
or brain plus environment.) We could effect a partial retreat from this
dualism by postulating that associated with a brain at any one time is a
set of "momentary minds" while not postulating that there is a matter of
fact that a mind (associated with a particular brain) at one moment is
trans-temporal identical with a mind (associated with the same brain) at
another moment. However, the cost of surrendering the "trans-temporal
identy of minds" would seem to be that we can no longer make sense of
statements like "the probability that *I* will observe spin up on
measurement is p" since such statements seem to presuppose that it makes
sense to talk of a single mind persisting through time. Perhaps, however,
it could be argued (though we will not do so here) that the conception of
a mind persisting through time is an illusion; one that results from the
fact that "most" momentary minds will be associated with brain states
which record a "personal" history and so it will seem to such a mind that
it has existed as a persisting entity.
(p 210-211)

It seems to me the situation is worse than Albert and Loewer suppose. Not
only does the quantum mechanical formalism not determine trans-temporal
identity of minds (in the sense of the many-minds interpretation), it does
not even determine the trans-temporal identity of brains, because at
different moments a brain could be made of completely "different"
particles, thus one could not say (without some nonphysical theory of
brain identity) that two brain states at different times belong to the
same brain. This is obvious if for example the brain is implemented as
a computational process that migrates to a different computer after each
state evolution. Without trans-temporal identity of brains, we would need
an explicit theory of trans-temporal mind identity, which Albert and
Loewer do not give, instead of simply supposing that such identities
exist. But things are even worse than that. Even if we *did* have
a theory of trans-temporal brain/mind identity, we would still not be able
to consistently assign probabilities to statements like "I will observe
spin up" because of the possibility of death or brain duplication.

So perhaps we should take the "momentary minds" view more seriously. The
fact that we can't make sense of the probability of "I will observe X" on
this view should not count against it because we can't assign these
probabilities in any case. However all is not lost. Although we can't make
sense of predictive probabilities, probability theory can still be used
for explanation. The "momentary minds" view gives us a probability
distribution for current perception and memories, so we can talk about the
probability for "I observe X given that I remember perceiving Y." I
propose that we will have explained "why I observe X" if we understand the
process that generates the probability distribution and can show that the
probability for observing X is high compared to the probabilities for
other possible perceptions.
Received on Thu May 28 1998 - 00:38:34 PDT