Understanding Quantum Physics: An Advanced Guide for the Perplexed

quantum observer
there is still one physical observer whose brain state is definite at every
instant but undergoes random discontinuous change. There are three
possibilities for the conscious perception of such a quantum observer. The
first possibility is that the conscious perception of a quantum observer is
irrelevant to his superposed brain state. Obviously this possibility is inconsistent
with the above experience. The second possibility is that the conscious
perception of a quantum observer depends on his superposed brain state, and the
observer can instantaneously be conscious of his brain state. In this case, the
conscious perception of a quantum observer, parallel to his brain state, will
also undergo random and discontinuous change between the determinate conscious
perceptions corresponding to the brain states in the superposition [60] . This is not consistent with the above
experience either.
    The third
possibility is that the conscious perception of a quantum observer depends on
his superposed brain state, and the observer can be conscious of his brain
state only during a finite time interval. Then the conscious perception of the
quantum observer will not undergo random and discontinuous change between the
conscious perceptions corresponding to the brain states in the superposition,
as the time average of his brain state during a finite time interval contains
no randomness. In other words, his conscious perception will be not random but
fixed [61] . This is also inconsistent with the above experience.
    To sum up, the
above analysis shows that the de Broglie-Bohm theory and the many-worlds
interpretation are inconsistent with protective measurement and the resulting
interpretation of the wave function in terms of random discontinuous motion of
particles. If there are no hidden variables besides the wave function, then the
state of a quantum system including a measuring device will be represented only
by its wave function. If there are no many worlds either, then a definite
measurement result, which is usually denoted by a definite position of the
pointer of a measuring device, will be represented by a local wave packet of
the pointer, rather than by a superposition of local wave packets. As a result,
the transition from microscopic uncertainty to macroscopic certainty (e.g. the
emergence of definite measurement results) can only be achieved by the collapse
of the wave function. In other words, wavefunction collapse will be a real
physical process.
    As noted earlier,
however, the existing ontology of the dynamical collapse theories that admit
the reality of wavefunction collapse, such as mass density ontology and flash
ontology (Ghirardi, Grassi and Benatti 1995; Ghirardi 1997, 2008; Allori et al
2008), is inconsistent with the picture of random discontinuous motion of
particles. Especially, the existence of the effective mass and charge density
of a quantum system, which is measurable by protective measurement, seems to
already exclude the mass density ontology. In addition, the existing dynamical
collapse theories are still phenomenological models, and they are also plagued
by some serious problems such as energy non-conservation etc (Pearle 2007,
2009). In particular, the physical origin of the wavefunction collapse,
including the origin of the randomness of the collapse process, is still
unknown, though there are already some interesting conjectures (see, e.g.
Di´osi 1989; Penrose 1996). In the following sections, we will try to solve
these problems and propose a new dynamical collapse model in terms of the
random discontinuous motion of particles. A more detailed review of the
existing dynamical collapse theories will be given in the last section.
    4.2 The origin of wavefunction collapse
    It is well known
that a ‘chooser’ and a ‘choice’ are needed to bring the required dynamical
collapse of the wave function (Pearle 1999). The chooser is the noise source
that collapses the wave function, and the choices are the states toward which
the collapse tends. In this section, we will first analyze these two relatively
easier problems and then investigate the more difficult problem, the physical
origin of wavefunction collapse.
    4.2.1
The chooser in discrete time
    To begin with,
let’s analyze the chooser problem. In the existing dynamical collapse models,
the chooser is generally assumed to be an unknown classical noise field
independent of the collapsed wave function (Pearle 2007, 2009). If what