A 62-day underground experiment has produced no evidence for the Foundational Questions Institute-supported Károlyházy gravity decoherence model, one of the oldest proposals for why quantum superpositions dissolve in the everyday world. The result, published in the New Journal of Physics in June 2026, does not close the book on gravity’s possible role in quantum decoherence, but it eliminates a prominent version of that idea and sets tighter constraints for whatever theory might replace it.
What the Károlyházy gravity decoherence model actually claims
The starting point is a puzzle physicists have lived with since quantum mechanics was formalised: particles can exist in superpositions, combinations of possible states, yet the large objects we encounter daily show no such behaviour. The transition between these two regimes, known as decoherence, lacks a fully agreed explanation.
In the 1960s, Frigyes Károlyházy, a Hungarian theoretical physicist, proposed one candidate mechanism. Building on Einstein’s general theory of relativity, which holds that massive objects curve spacetime, Károlyházy suggested that spacetime also undergoes tiny, unavoidable fluctuations. Those fluctuations, he argued, would progressively disrupt quantum superpositions, offering a reason why cats are either alive or dead rather than both simultaneously. The Károlyházy gravity decoherence model attracted sustained attention and was, according to the research team, recently revived and reformulated by FQxI member Angelo Bassi and colleagues.
The model cannot be tested directly, because no instrument can observe a spacetime fluctuation in isolation. However, the theory carries a detectable prediction: the fluctuations should cause electrically charged particles to move and accelerate randomly, producing extremely faint electromagnetic radiation. Find that radiation, and you have evidence for the model. Find nothing, and the model is in trouble.
Searching for a signal beneath 1.4 kilometres of rock
The experiment was conducted at the INFN Gran Sasso National Laboratory (INFN-LNGS), which sits beneath 1.4 kilometres of rock in the Italian Apennines. That rock acts as a radiation shield, blocking cosmic rays and other background interference that would otherwise swamp a signal as faint as the one the team was hunting.
‘The natural shielding provided by the rock creates one of the quietest environments on Earth for detecting extremely rare physical phenomena,’ says Catalina Curceanu, director of research and spokesperson for the VIP Collaboration at INFN-LNF.
The detector itself was built around a coffee-mug-sized piece of high-purity germanium crystal, wrapped in additional layers of copper and lead. Over 62 days, the team gathered data, subtracted the expected background radiation, and compared the remainder against the radiation signature the Károlyházy gravity decoherence model predicts. No signal appeared.
Kristian Piscicchia, a quantum physicist at the Enrico Fermi Research Centre/INFN/VIP and the experimental lead, described the absence as consistent with a broader pattern. ‘Every quantum gravity approach ends up with predicting the existence of a minimal length connected to the uncertainty in the measurement of spacetime,’ he says, placing the Károlyházy model within a family of related theoretical efforts.
What the null result does and does not establish
The team is careful about what the finding means. It rules out one version of gravity-induced decoherence; it does not demonstrate that gravity plays no role at all. Curceanu frames it as a narrowing of the search space: ‘By ruling out one of the oldest and most natural gravity-induced decoherence models, this work narrows the search for the theory describing the interplay between gravity and quantum mechanics.’
That framing is the right one. A null result in a well-designed experiment is genuine scientific information. The constraints it places on future theories are now tighter than they were before June 2026, which matters for attempts to unify gravity and quantum mechanics, including approaches such as string theory and loop quantum gravity that, the team notes, independently predict a minimal measurable length.
Quantum gravity has long been considered safely beyond experimental reach. This result, Curceanu argues, challenges that assumption: ‘Precision experiments are now reaching a level of sensitivity where they can test ideas that, until recently, belonged almost exclusively to the realm of theoretical speculation.’
The research was supported by FQxI through its Consciousness in the Physical World programme. The full paper, authored by Nicola Bortolotti, Piscicchia, Alessio Porcelli, Matthias Laubenstein, Simone Manti, Antonino Marcianò, Federico Nola and Curceanu, carries the DOI 10.1088/1367-2630/ae774c. The next step, implicitly, is a more sensitive detector, one that can probe the reformulated versions of the Károlyházy framework that Bassi and colleagues have since developed.
