The origin of consciousness is one of the greatest mysteries of science. One
proposed solution, first suggested by Nobel Laureate and Oxford
mathematician Roger Penrose and anesthesiologist Stuart Hammeroff, at the
University of Arizona, in Tucson, attributes consciousness to quantum
computations in the brain. This in turn hinges on the notion that gravity
could play a role in how quantum effects disappear, or "collapse." But a
series of experiments in a lab deep under the Gran Sasso mountains, in
Italy, has failed to find evidence in support of a gravity-related quantum
collapse model, undermining the feasibility of this explanation for
consciousness. The result is reported in the journal Physics of Life
Reviews.
"How consciousness arises in the brain is a huge puzzle," says Catalina
Curceanu, a member of the physics think tank, the Foundational Questions
Institute, FQXi, and the lead physicist on the experiments at INFN in
Frascati, Italy. "There are many competing ideas, but very few can be
experimentally tested."
Quantum physics famously tells us that cats can be alive and dead at the
same time, at least in theory. Yet in practice we never see felines locked
in such an unfortunate limbo state. One popular explanation for why not is
because the "wavefunction" of a system–its quantum character allowing it to
be in two contradictory states simultaneously–is more likely to "collapse"
or be destroyed if it is more massive, leaving it in one defined state,
either dead or alive, say, but not both at the same time. This model of
collapse, related to gravity acting on heavy objects like cats, was invoked
by Penrose and Hammeroff when developing their model of consciousness, 'Orch
OR theory' (the Orchestrated Objective Reduction theory), in the 1990s.
Quantum computations in the brain
Curceanu first became interested in Orch OR theory when she met Penrose,
also an FQXi member, at a conference some years ago. Consciousness is not
usually associated with quantum properties because quantum effects are
fragile and difficult to maintain even under highly-controlled conditions
and cold temperatures in the lab. So it had long been assumed that the
brain's warm and wet environment would be too disruptive to allow quantum
effects to survive. But Penrose explained that he and Hammeroff have
identified tiny structures called microtubules within neurons in the brain
that could potentially sustain quantum effects for short periods—just long
enough to carry out quantum computations. Orch OR theory attributes
consciousness to quantum computations orchestrated ("Orch") by electrical
oscillations in these microtubules. "What I loved about this theory was that
it is in principle testable and I decided to search for evidence that might
help confirm or falsify it," says Curceanu.
"What I loved about this theory was that it is in principle testable and I
decided to search for evidence that might help confirm or falsify it."
At the heart of the theory is the idea that gravity is related to quantum
wavefunction collapse and that this collapse is faster in systems with more
mass. This concept was developed in a number of models by various physicists
in the 1980s. One of those was Lajos Diósi, at the Wigner Research Center
for Physics and at the Eötvös Loránd University in Budapest, Hungary, who
has co-authored the new paper with Curceanu, Maaneli Derakhshani of Rutgers
University in New Brunswick, New Jersey, Matthias Laubenstein also at INFN,
and Kristian Piscicchia of CREF and INFN. Penrose independently approached
this idea a few years later and it became the core of his consciousness
theory with Hammeroff.
The two theories are often referred to by the umbrella term, the
"Diósi-Penrose theory." But behind the joint name there is an important
difference, notes Curceanu. Diósi's approach predicts that collapse would be
accompanied by the spontaneous emission of a small amount of radiation, just
large enough to be detected by cutting edge experiments.
Going underground
Curceanu's underground lab is housed within the Gran Sasso National
Laboratory, 1.4 km under the Gran Sasso Italian mountains. The lab stands on
one side of the 10-km long highway tunnel which crosses the Gran Sasso
massif, connecting L'Aquila and Teramo. "The location was chosen because it
is basically free from cosmic-ray radiation sources above the ground, that
could interfere with the experiment," says Curceanu. The experiment uses an
extremely sensitive cylindrical detector, not much bigger than a mug, made
from highly pure germanium. It is surrounded by shielding, made of layers of
ultra-pure lead and copper, to shelter it from any background radiation
coming from the rocks. After running the experiment for two months the team
did not measure spontaneous radiation signals, constraining the feasibility
of gravity-related collapse. In 2020, the team reported in Nature Physics
that their negative result had helped them rule out the simplest version of
the Diósi-Penrose model.
In their new paper they have explicitly examined the repercussions of their
finding for Penrose and Hammeroff's Orch OR theory of consciousness. After
reanalyzing the most plausible scenarios set out by Hammeroff and Penrose,
in light of their recent experimental constraints on quantum collapse, they
were led to conclude that almost none of the scenarios are plausible. "This
is the first experimental investigation of the gravity-related quantum
collapse pillar of the Orch OR consciousness model, which we hope will be
followed by many others," says Curceanu. "I am very proud of our
achievement."
Interdisciplinary characteristics
The experiments and analysis are partially funded by a grant from the
Foundational Questions Institute, FQXi. "Without it, it would have not been
possible to achieve this outcome," says Curceanu. "It is hard to otherwise
get funding for projects such as this, based on its interdisciplinary
characteristics."
"It is really exciting to connect what you can do in the laboratory to
perhaps the biggest mystery in the universe—consciousness."
But all is not lost for Orch Or, adds Curceanu. "Actually, the real work is
just at the beginning." she says. In fact, Penrose's original collapse
model, unlike Diósi's, did not predict spontaneous radiation, so has not
been ruled out. The new paper also briefly discusses how a gravity-related
collapse model might realistically be modified. "Such a revised model, which
we are working on within the FQXi financed project, could leave the door
open for Orch OR theory," Curceanu says.
Meanwhile the team is preparing to test these refined new collapse models,
to further investigate their implications for the Orch OR model. "It is
really exciting to connect what you can do in the laboratory to perhaps the
biggest mystery in the universe—consciousness," says Curceanu.
Reference:
Maaneli Derakhshani et al, At the crossroad of the search for spontaneous
radiation and the Orch OR consciousness theory, Physics of Life Reviews
(2022). DOI: 10.1016/j.plrev.2022.05.004
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Physics