Volume 1 No 1 (2003)
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Conscious Events as Orchestrated Space-Time Selections
Stuart Hameroff and Roger Penrose
Abstract
What is consciousness? Some philosophers have contended that "qualia," or an experiential
medium from which consciousness is derived, exists as a fundamental component of reality.
Whitehead, for example, described the universe as being comprised of "occasions of
experience." To examine this possibility scientifically, the very nature of physical reality must
be re-examined. We must come to terms with the physics of space-time--as is described by
Einstein's general theory of relativity--and its relation to the fundamental theory of
matter--as described by quantum theory. This leads us to employ a new physics of objective
reduction: " OR" which appeals to a form of quantum gravity to provide a useful description
of fundamental processes at the quantum/classical borderline. Within the OR scheme, we
consider that consciousness occurs if an appropriately organized system is able to develop
and maintain quantum coherent superposition until a specific "objective" criterion (a
threshold related to quantum gravity) is reached; the coherent system then self-reduces
(objective reduction: OR). We contend that this type of objective self-collapse introduces
non-computability, an essential feature of consciousness. OR is taken as an instantaneous
event--the climax of a self-organizing process in fundamental space-time--and a candidate
for a conscious Whitehead "occasion" of experience. How could an OR process occur in
the brain, be coupled to neural activities, and account for other features of consciousness?
We nominate an OR process with the requisite characteristics to be occurring in
cytoskeletal microtubules within the brain's neurons. In this model, quantum-superposed
states develop in microtubule subunit proteins ("tubulins"), remain coherent and recruit
more superposed tubulins until a mass-time-energy threshold (related to quantum gravity)
is reached. At that point, self-collapse, or objective reduction (OR) abruptly occurs. We
equate the pre-reduction, coherent superposition ("quantum computing") phase with
pre-conscious processes, and each instantaneous (and non-computable) OR, or self-collapse,
with a discrete conscious event. Sequences of OR events give rise to a "stream" of
consciousness. Microtubule-associated-proteins can "tune" the quantum oscillations of the
coherent superposed states; the OR is thus self-organized, or "orchestrated" ("Orch OR").
Each Orch OR event selects (non-computably) microtubule subunit states which regulate
synaptic/neural functions using classical signaling. The quantum gravity threshold for
self-collapse is relevant to consciousness, according to our arguments, because macroscopic
superposed quantum states each have their own space-time geometries. These geometries
are also superposed, and in some way "separated," but when sufficiently separated, the
superposition of space-time geometries becomes significantly unstable, and reduce to a
single universe state. Quantum gravity determines the limits of the instability; we contend
that the actual choice of state made by Nature is non-computable. Thus each Orch OR
event is a self-selection of space-time geometry, coupled to the brain through microtubules
and other biomolecules.
If conscious experience is intimately connected with the very physics underlying
space-time structure, then Orch OR in microtubules indeed provides us with a completely
new and uniquely promising perspective on the hard problem of consciousness
Keywords
consciousness, quantum theory, quantum gravity, space-time, collapse, objective reduction, microtubules
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