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 Arizona State University, 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.