The origin of consciousness is one of the greatest mysteries of science. A proposed solution, first suggested by Nobel laureate and Oxford mathematician Roger Penrose and anesthesiologist Stuart Hammeroff, of Arizona State University, Tucson, attributes consciousness to quantum computations in the brain. This in turn rests on the notion that gravity might play a role in how quantum effects fade away, or “collapse”. But a series of experiments in a lab deep in Italy’s Gran Sasso mountains failed to find evidence to support a gravity-bound quantum collapse model, compromising the feasibility of this explanation of consciousness. The result is reported in the journal Opinion on the physics of life.
“How consciousness arises in the brain is a huge puzzle,” says Catalina Curceanu, member of the physics think tank, Foundational Questions Institute, FQXi, and chief experiment physicist at INFN in Frascati. , in Italy. “There are many competing ideas, but very few can be tested experimentally.”
Quantum physics 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 state of limbo. A popular explanation for why not is that a system’s “wave function” – 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 a defined state. state, either dead Where alive, let’s 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, the “Orch OR theory” (orchestrated objective reduction theory ), in the 1990s.
Quantum calculations in the brain
Curceanu first became interested in Orch OR theory when she met Penrose, also a member of FQXi, at a conference a few 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 laboratory temperatures. It was therefore long assumed that the warm, humid environment of the brain would be too disruptive for quantum effects to survive. But Penrose explained that he and Hammeroff identified tiny structures called microtubules in brain neurons that could potentially sustain quantum effects for short periods of time, just long enough to perform quantum calculations. The Orch OR theory attributes consciousness to quantum computations orchestrated (“Orch”) by electrical oscillations in these microtubules. “What I liked about this theory is that it is in principle testable and I decided to look for evidence that could help confirm or refute it,” says Curceanu.
“What I liked about this theory is that it is in principle testable and I decided to look for evidence that could help confirm or refute it.”
At the heart of the theory is the idea that gravity is related to the collapse of the quantum wave function and that this collapse is faster in systems with more mass. This concept was developed into a number of models by various physicists in the 1980s. One of them was Lajos Diósi, from the Wigner Research Center for Physics and Eötvös Loránd University in Budapest, Hungary , who 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 approached this idea independently a few years later and it became the core of his theory of consciousness with Hammeroff.
Both theories are often referred to by the umbrella term, the “Diósi-Penrose theory”. But behind the common name, there is an important difference, notes Curceanu. Diósi’s approach predicts that the collapse would be accompanied by the spontaneous emission of a small amount of radiation, just large enough to be detected by state-of-the-art experiments.
The Curceanu underground laboratory is housed in the Gran Sasso National Laboratory, 1.4 km below the Italian Gran Sasso mountains. The laboratory is on one side of the 10 km long road tunnel that crosses the Gran Sasso massif, connecting L’Aquila and Teramo. “The location was chosen because it is basically free of above-ground cosmic radiation sources, which could interfere with the experiment,” says Curceanu. The experiment uses an extremely sensitive cylindrical detector, not much bigger than a cup, made from very pure germanium. It is surrounded by shielding, made up of layers of ultra-pure lead and copper, to shield it from any background radiation from the rocks. After running the experiment for two months, the team did not measure spontaneous radiation signals, limiting the feasibility of gravity-driven collapse. In 2020, the team reported in Natural Physics that their negative result had helped them eliminate the simplest version of the Diósi-Penrose model.
In their new paper, they explicitly examined the implications of their discovery for Penrose and Hammeroff’s Orch OR theory of consciousness. After re-analyzing the most plausible scenarios stated 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-bound quantum collapse pillar of the Orch OR model of consciousness, which we hope will be followed by many more,” says Curceanu. “I am very proud of our achievement.”
The experiments and analysis are partially supported by a grant from the Foundational Questions Institute, FQXi. “Without that, it would not have been possible to achieve this result,” says Curceanu. “It is difficult to obtain funding for projects like this otherwise, due to its interdisciplinary characteristics.”
“It’s really exciting to connect what you can do in the lab to perhaps the greatest mystery in the universe: consciousness.”
But all is not lost for Orch Or, adds Curceanu. “In fact, the real work is only at the beginning.” she says. In fact, Penrose’s original collapse model, unlike Diósi’s, did not predict spontaneous radiation, so it was not ruled out. The new paper also briefly discusses how a gravity-driven collapse model could be realistically modified. “Such a revised model, which we are working on in the FQXi-funded project, could leave the door open for Orch OR theory,” Curceanu says.
Meanwhile, the team is preparing to test these new refined collapse models, to further investigate their implications for the Orch OR model. “It’s really exciting to connect what you can do in the lab to perhaps the biggest mystery in the universe: consciousness,” Curceanu says.
Deconstructing Schrödinger’s Cat
Maaneli Derakhshani et al, At the crossroads of spontaneous radiation research and Orch OR theory of consciousness, Opinion on the physics of life (2022). DOI: 10.1016/j.plrev.2022.05.004
Provided by the Fundamental Issues Institute
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