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*Henry P. Stapp
Abstract
Orthodox Copenhagen
quantum theory renounces the quest to understand the reality in which we are
imbedded, and settles for practical rules that describe connections between our
observations.
Many physicists have
believed that this renunciation of the attempt describe nature herself was
premature, and John von Neumann, in a major work, reformulated quantum theory
as a theory of the evolving objective universe. In the course of his work he
converted to a benefit what had appeared to be a severe deficiency of the
Copenhagen interpretation, namely its introduction into physical theory of the
human observers.
He used this
subjective element of quantum theory to achieve a significant advance on the
main problem in philosophy, which is to understand the relationship between
mind and matter. That problem had been tied closely to physical theory by the
works of Newton and Descartes. The present work examines the major problems
that have appeared to block the development of von Neumann’s theory into a fully
satisfactory theory of Nature, and proposes solutions to these problems.
The Nonlocality
Controversy
“Nonlocality gets more
real”. This is the provocative title of a recent report in Physics Today. Three
experiments are cited. All three confirm to high accuracy the predictions of
quantum theory in experiments that suggest the occurrence of an instantaneous
action over a large distance. The most spectacular of the three experiments
begins with the production of pairs of photons in a lab in downtown Geneva. For
some of these pairs, one member is sent by optical fiber to the village of
Bellevue, while the other is sent to the town of Bernex. The two towns lie more
than 10 kilometers apart. Experiments on the arriving photons are performed in
both villages at essentially the same time.
What is found is this:
The observed connections between the outcomes of these experiments defy
explanation in terms of ordinary ideas about the nature of the physical world
on the scale of directly observable objects. This conclusion is announced in
opening sentence of the
Physical-Review-Letters
report that describes the experiment: “Quantum theory is nonlocal”. This
observed effect is not just an academic matter. A possible application of
interest to the Swiss is this: The effect can be used in principle to transfer
banking records over large distances in a secure way.
But of far greater
importance to physicists is its relevance to two fundamental questions: What is
the nature of physical reality ? What is the form of basic physical theory ?
The answers to these
questions depend crucially on the nature of physical causation. Isaac Newton
erected his theory of gravity on the idea of instant action at a distance.
According to Newton’s theory, if a person were to suddenly kick a stone, and
send it flying off in some direction, every particle in the entire universe
would immediately begin to feel the effect of that kick.
Thus, in Newton’s
theory, every part of the universe is instantly linked, causally, to every
other part. To even think about such an instantaneous action one needs the idea
of the instant of time “now”, and a sequence of such instants each extending
over the entire universe.
This idea that what a
person does in one place could act instantly affect physical reality in a
faraway place is a mind-boggling notion, and it was banished from classical
physics by Einstein’s theory of relativity.
But the idea
resurfaced at the quantum level in the debate between Einstein and Bohr.
Einstein objected to the “mysterious action at a distance”, which quantum
theory seemed to entail, but Bohr defended “the necessity of a final renunciation
of the classical ideal of causality and a radical revision of our attitude
towards the problem of physical reality”.
The essence of this
radical revision was explained by Dirac at the 1927 Solvay conference. He
insisted on the restriction of the application of quantum theory to our
knowledge of a system, rather than to the system itself. Thus physical theory
became converted from a theory about ‘physically reality’, as it had formerly
been understood, into a theory about human knowledge.
This view is
encapsulated in Heisenberg’s famous statement: “The conception of the objective
reality of the elementary particles has thus evaporated not into the cloud of
some obscure new reality concept, but into the transparent clarity of a
mathematics that represents no longer the behaviour of the particle but rather
our knowledge of this behaviour.”
This conception of
quantum theory, espoused by Bohr, Dirac, and Heisenberg, is called the
Copenhagen interpretation. It is essentially subjective and epistemological,
because the basic reality of the theory is ‘our knowledge’.
This way of dodging
the action-at-a-distance problem was challenged by Einstein, Podolsky, and
Rosen in a famous paper entitled: “Can quantum mechanical description of
physical reality be considered complete?” The issue was whether a theory that
is specified to be merely a set of rules about connections between human experiences
can be considered to be a complete description of physical reality. Einstein
and his colleagues gave a reasonable definition of “physical reality”, and then
argued, directly from some basic precepts of quantum theory itself, that the
answer to this question is ‘No’.
Bohr disagreed.
Given the enormity of
what must exist in the universe as a whole, and the relative smallness human
knowledge, it is astonishing that, in the minds of most physicists, Bohr
prevailed over Einstein in this debate: the majority of quantum physicists
acquiesced to Bohr’s claim that quantum theory, regarded as a theory about
human knowledge, is a complete description of physical reality. This majority
opinion stems, I believe, more from the lack of a promising alternative
candidate than from any decisive logical argument. Einstein, commenting on the
orthodox Copenhagen position, said: “What I dislike about this kind of argument
is the basic positivistic attitude, which from my view is untenable, and seems
to me to come to the same thing as Berkeley’s principle, ‘esse est percipi’,
“to be is to be perceived”. Several other scientists also reject the majority
opinion. For example, Murray Gell-Mann asserts: “Niels Bohr brainwashed a whole
generation into believing that the problem was solved fifty years ago”.
Gell-mann believes that
in order to integrate quantum theory coherently into cosmology, and to understand
the evolutionary process that has produced creatures that can have knowledge,
one needs to have a coherent theory of the evolving quantum mechanical reality
in which these creatures are imbedded. It is in the context of such efforts to
construct a more complete theory that the significance of the experiments
pertaining to quantum nonlocality lies.
The point is this: If
nature really is nonlocal, as these experiments suggest, then the way is open
to the development of a rationally coherent theory of nature that integrates
the subjective knowings introduced by Copenhagen quantum theory into an
objectively existing and evolving physical reality.
(…)
The Passive and Active
Roles of Mind
The founders of
quantum theory recognized that the mathematical structure of quantum theory is
naturally suited for, and seems to require, bringing into the dynamical
equations two separate aspects of the interaction between the physical universe
and the minds of the experimenter/observers.
The first of these two
aspects is the role of the experimenter in choosing what to attend to; which
aspect of nature he wants to probe; which question he wants to ask about the
physical world. This is the active role of mind.
The second aspect is
the recognition, or coming to know, the answer that nature returns.
This is the passive
role of mind.
The Active Physical
Counterpart to the Passive Mental Event
I have mentioned the Schrödinger
evolution of the state S(t) of the universe. The second part of the orthodox
quantum dynamics consists of an event that discards from the ensemble of
quasi-classical elements mentioned above those elements that are incompatible
with the answer that nature returns. This reduction of the prior ensemble of
elements, which constitute the quantum mechanical representation of the brain, to
the sub ensemble compatible with the “outcome of the query” is analogous to
what happens in classical statistical mechanics when new information about the
physical system is obtained.
However, in the
quantum case one must in principle regard the entire ensemble of classically
described brains as real, because interference between the different elements
are in principle possible.
Each quantum event
consists, then of a pair of events, one physical, the other mental. The
physical event reduces the initial ensemble that constitutes the brain prior to
the event to the sub ensemble consisting of those branches that are compatible
with the informational content of the associated mental event.
This dynamical
connection means that, during an interval of conscious thinking, the brain
changes by an alternation between two processes.
The first is the
generation, by a local deterministic mechanical rule, of an expanding profusion
of alternative possible branches, with each branch corresponding to an entire
classically describable brain embodying some specific possible course of
action. The quantum brain is the entire ensemble of these separate, but equally
real, quasi-classical branches.
The second process
involves an event that has both physical and mental aspects. The physical
aspect, or event, chops off all branches that are incompatible with the
associated mental aspect, or event. For example, if the mental event is the
experiencing of some feature of the physical world, then the associated
physical event would be the updating of the brain’s representation of that
aspect of the physical world. This updating of the (quantum) brain is achieved
by discarding from the ensemble of quasi-classical brain states all those
branches in which the brain’s representation of the physical world is
incompatible with the information content of the mental event.
This connection is
similar to a functionalist account of consciousness. But here it is expressed
in terms of a dynamical interaction that is demanded by the requirement that
the objective formulation of the theory yield the same predictions about
connections between our conscious experiences that the empirically validated
Copenhagen quantum theory gives. The interaction is the exact expression of the
basic dynamical rule of quantum theory, which is the stipulation that each
increment in knowledge is associated with a reduction of the quantum state to
one that is compatible with the new knowledge.
The quantum brain is
an ensemble of quasi-classical components. As just noted, this structure is
similar to something that occurs in classical statistical mechanics, namely a
“classical statistical ensemble.” But a classical statistical ensemble, though
structurally similar to a quantum brain, is fundamentally a different kind of
thing. It is a representation of a set of truly distinct possibilities, only
one of which is real.
A classical
statistical ensemble is used when a person does not know which of the
conceivable possibilities is real, but can assign a ‘probability’ to each
possibility. In contrast, all of the elements of the ensemble that constitute a
quantum brain are equally real: no choice has yet been made among them,
Consequently, and this is the key point, entire ensemble acts as a whole in the
determination of the upcoming mind-brain event.
Each thought is
associated with the actualization of some macroscopic quasi-stable features of
the brain. Thus the reduction event is a macroscopic happening. Moreover, this
event involves, dynamically, the entire ensemble of quasi-classical brain
states. In the corresponding classical model each element of the ensemble
evolves independently, in accordance with a micro local law of motion that
involves just that one branch alone. Thus there are basic dynamical differences
between the quantum and classical models, and the consequences of these
dynamical differences need to be studied in order to exhibit the quantum
effects.
The only freedom in
the theory—insofar as we leave Nature’s choices alone—is the choice made by the
individual about which question it will ask next, and when it will ask it.
These are the only inputs of mind to the dynamics of the brain. This severe
restriction on the role of mind is what gives the theory its predictive power.
Without this restriction mind could be free to do anything, and the theory
would have no consequences.
Asking a question
about something is closely connected to focussing one’s attention on it.
Attending to something is the act of directing one’s mental power to some task.
This task might be to update one’s representation of some feature of the
surrounding world, or to plan or execute some other sort of mental or physical
action.
The key question is
then: Can this freedom merely to choose which question is asked, and when it is
asked, lead to any statistical influence of mind on the behaviour of the brain,
where a ‘statistical’ influence is an influence on values obtained by averaging
over the properly weighted possibilities.
The answer is Yes !
The Quantum Zeno
Effect
There is an important
and well-studied effect in quantum theory that depends on the timings of the
reduction events arising from the queries put to nature. It is called the
Quantum Zeno Effect. It is not diminished by interaction with the environment.
The effect is simple.
If the same question is put to nature sufficiently rapidly and the initial
answer is Yes, then any noise-induced diffusion, or force-induced motion, of
the system away from the sub ensemble where the answer is ‘Yes’ will be
suppressed: the system will tend to be confined to the sub ensemble where the
answer is ‘Yes’. The effect is sometimes called the “watched pot” effect:
according to the old adage “A watched pot never boils”; just looking at it
keeps it from changing.
Also, a state can be
pulled along in some direction by posing a rapid sequence of questions that
change sufficiently slowly over time. In short, according to the dynamical laws
of quantum mechanics, the freedom to choose which questions are put to nature,
and when they are asked, allows mind to influence the behaviour of the brain.
A person is aware of
almost none of the processing that is going on in his brain: unconscious brain
action does almost everything. So it would be both unrealistic and
theoretically unfeasible to give mind unbridled freedom: the questions posed by
mind ought to be determined in large measure by brain.
What freedom is given
to man ?
According to this
theory, the freedom given to Nature is simply to provide a Yes or No answer to
a question posed by a subsystem. It seems reasonable to restrict in a similar way,
the choice given to a human mind.
* original design of T. Gleitzer
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