Understanding Quantum Physics: An Advanced Guide for the Perplexed

measurement problem, e.g. the
many-worlds interpretation, before experiments give the last verdict.
    In the following,
we will further show that the existence of many worlds is not consistent with
the picture of random discontinuous motion of particles either. In order to
examine the many-worlds interpretation, it is necessary to know exactly what a
quantum superposition is. No matter how to define the many worlds, they
correspond to some components of a quantum superposition after all (e.g. the
components where measuring devices obtain definite results, and in particular,
observers have definite conscious experience). According to the picture of
random discontinuous motion of particles, a quantum superposition exists in a
form of time division. For a superposition of two positions A and B of a
quantum system (e.g. the pointer of a measuring device), the system randomly
and discontinuously jumps between these two positions. At some random and
discontinuous instants the system is in position A, and at other instants it is
in position B. In this picture of quantum superposition, it is obvious that
there is only one system all along, which randomly and discontinuously moves
throughout all components of the superposition, no matter the system is a
microscopic particle or a measuring device or an observer. In other words,
there is only one world whose instantaneous state is constantly changing in a
random and discontinuous way.
    This conclusion is
also supported by a comparison between discontinuous motion and continuous
motion. For a quantum particle undergoing discontinuous motion, the position of
the particle changes discontinuously. For a classical particle, its position
changes continuously. There is no essential difference between these two kinds
of changes. For both cases the position of the particle is always definite at
each instant, and the positions of the particle at different instants may be
different. Moreover, the discontinuous change, like the continuous change, does
not create the many worlds, because, among other reasons, the change happens
all the while but the creating process only happens once. Therefore, if there
is only one world in classical mechanics, then there is also one world in
quantum mechanics according to the picture of random discontinuous motion of
particles, no matter how the many worlds are precisely defined.
    We have argued
that there are no many (physical) worlds as claimed by the many-worlds
interpretation, and in particular, even if the physical state or brain state of
an observer is in a quantum superposition, there is still one physical
observer. However, the argument does not exclude the variants of the
many-worlds interpretation that assume a distinct dynamics for the evolution of
an observer's mental state, e.g. the many-minds theory (Albert and Loewer 1988) [59] . For example, although the superposed
brain state of an observer does not correspond to many physical observers, each
of which has a definite measurement record, it may correspond to many minds of
a unique observer, each of which has the experience of a definite measurement
record, as assumed by the many-minds theory. Since what we can immediately
access is not the position of the pointer of a measuring device, but our
immediate conscious experience, it is indeed necessary to analyze the conscious
experience of an observer during a conventional impulse measurement. In the
final analysis, the measurement problem is the problem of explaining the
apparent incompatibility of our determinate experience and the existence of
indeterminate quantum superpositions.
    According to our
existing experience, when an observer makes an impulse measurement (by or not
by a measuring device) on a quantum superposition of two states of a measured
system, each of which can lead to a determinate conscious perception of the
observer, his conscious perception is randomly one of the determinate
perceptions corresponding to the two states (with probability being equal to
the objective probability of the respective state in the superposition). The
question is whether an observer in a quantum superposition of definite brain
states, which may be called a quantum observer, can have a determinate
conscious perception corresponding to one of these brain states in a
probabilistic way consistent with the above experience. We will argue below
that the answer is negative.
    According to the
picture of random discontinuous motion of particles, for a