**3. The Bohm Approach.**

The Copenhagen and von Neumann formulations of quantum theory are
non-deterministic. Both specify that human choices enter into the
dynamics, but neither specifies the causal origins of these choices. The
question thus arises: what determines these choices?

One possibility is that these choices arise in some yet-to-be-specified
way from what we conceive to be the *idealike aspect of reality*. That
option was pursued by Penrose, with his suggestion that our thoughts are
linked to Plato's world of ideal forms. Another -- seemingly different
-- possibility is that there is a *more complete* *physical description*
that involves physically described entities that are different from the
smeared out structures of the orthodox formulations, and that these
*other physical elements* determine the features left undetermined by
the orthodox formulations.

This second approach was developed by David Bohm (1952, 1993). His
formulation of quantum theory postulates, in effect, the existence of
the old-fashioned world of classical physical theory. This
classical-type world is supposed to exist in *addition to the wave
function of quantum theory* and, like that wave function, it evolves in
a way completely determined by what precedes it in time. This theory
reinstates determinism in a way compatible with the predictions of
quantum theory, but at the expense of abandoning locality: Bohm's theory
entails strong, long-range, instantaneous action-at-a-distance.

One serious failing of Bohm's approach is that it was originally
formulated in a non-relativistic context, and it has -- after half a
century and great effort -- not been extended to cover the most
important domain in physics, namely the realm of quantum
electrodynamics, which is the theory that covers the atoms that make up
our bodies and brains, along with the tables, chairs, automobiles, and
computers that populate our daily lives. This deficiency means that
Bohm's theory is, at present, primarily a philosophically interesting
curiosity, not a practically useful physical theory.

Also, Bohm's theory, at least in its original form, is not really
germane to the issue of consciousness. For Bohm's theory *successfully
achieved its aim,* which was precisely to get rid of consciousness:
i.e., to eliminate consciousness from the basic dynamical equations,
just as classical physics had done.

Bohm recognized, later on, that some understanding of consciousness was
needed, but he was led instead, to the notion of an infinite tower of
mechanical levels, each controlling the one below, with consciousness
somehow tied to the mystery of the infinite limit. (Bohm, 1986, 1990)
This infinite-tower idea tends to negate the great achievement of the
original theory, which was to reinstate physical determinism in a simple
way. To examine this conceivable option of a *complete physical
determinism compatible with the empirical predictions of quantum theory*
it is instructive to examine Bohm's original deterministic model in
order to see how, within that deterministic consciousness-free
framework, consciousness nevertheless enters effectively, at the level
of scientific practice.

As explained in the introductory section, scientific practice involves
setting up experimental conditions that fill consciously experienced
objectives. In von Neumann's theory these consciously chosen actions
influence the subsequent course of events in The Observed System, which,
according to von Neumann's re-construction of quantum theory, is
primarily the brain of the human participant. A key point is that these
choices, made by the experimenter about how he or she will act, are
treated in von Neumann's theory, and also by Copenhagen quantum theory,
as *input data*, to be fixed by the experimenter. These choices are
*treated* as free, controllable, input boundary conditions.

In Bohm's theory these choices are not actually free: freedom is an
illusion. The apparently free choice is, at a deeper dynamical level,
completely determined by *physical* conditions, just as it was in
classical physics. However, the putative existence of this deeper
dynamical underpinning does not subvert or displace the quantum
dynamics. The analysis of Heisenberg shows that, even within the context
of Bohmian mechanics, the human observers can never determine, or
*know*, which of the conceivable logically possible classical Bohmiam
worlds their experiences belong to. The Heisenberg Uncertainty Principle
cannot be evaded: the most that experiencers can ever actually
***know*** about the Bohmian classical world of which they are a
putative part is represented by a quantum wave function.

This limitation *in human knowledge* is acknowledged by Bohm. Indeed,
Bohm's theory leaves scientific practice the same as it is in the
Copenhagen approach. This *equivalence at the practical level* of Bohm's
model to the Copenhagen formulation means that in actual practice the
unfillable gap in human knowledge mandated by the uncertainty principle
is bridged by using quantum dynamics to replace the
*in-principle-unknowable information about the microscopic physical
conditions* by *in-practice-controllable and knowable realities*, our
conscious choices about how to act. That is, although the details of the
Bohmian microstructure can, as a matter of principle, never be known to
us, and hence cannot be directly used to make predictions, we can and do
experience the immediate consequences of our conscious choices about how
to act, *and these experiences place conditions on the putative Bohmian
microstructure*. These knowable input conditions entail *statistical*
consequences in the realm of subsequent human experiences, which can be
computed on the basis of the quantum mechanical equations. Thus these
equations allow us to evade the need to know anything about the
unknowable Bohmian micro-substructure beyond what is specified by
quantum mechanical states.

The bottom line is that, *even within the context of the deterministic
Bohmian theory, it is the quantum rules that constitute the useful
scientific tools,* because they allow us, without needing to know
anything about the in-principle-unknowable classical idealizations, to
make predictions pertaining to what we can know. This conclusion will
continue to be true in the context of *any* deterministic theory that is
*compatible with* the statistical rules of quantum theory.

When solving a problem in physics there is always a question about which
variables to use. At the level of practical science it is advantageous
to use variables that are controllable and knowable in actual practice
rather than unknowable in principle. Why bring unknowable parameters
into science, instead of knowable ones that we can *in practice*
control, when we have equations that bring these controllable parameters
directly into the description of dynamical process, leaving out the
unknowable ones, and that, according to the unchallenged arguments of
Heisenberg and Bohr, tell us all that we can ever learn (within the
framework of the principles of physics) about the effects of our
conscious choices upon our future conscious experiences?

The advantages of using equations involving controllable and knowable
parameters rather than unknowable ones are just as real in neuroscience
as they are in atomic physics. Of what use are (highly nonlocal)
deterministic equations that depend on the in-principle-unknowable
motions of classically conceived calcium ions inside nerve terminals, in
place of our knowledge about our controllable actions and their
experienced feedbacks?

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Bohm, D. (1952). A suggested interpretation of quantum theory in terms
of hidden variables. *Physical Review,* 85, 166-179.

Bohm, D. J. (1986). A new theory of the relationship of mind to matter.
*The Journal of the American Society for Psychical Research,*

80, 113-135.

Bohm, D. J. (1986). A new theory of the relationship of mind to matter.
*Philosophical Psychology*, 3, 271-286.

Bohm, D, & Hiley, D.J. (1993). *The Undivided Universe.* London and New
York: Routledge.