At some point between the tiny world of particles and atoms and the much larger world we experience every day, quantum behavior appears to fade away. Quantum mechanics allows particles to exist in combinations of possible states, a phenomenon known as superposition. That strange feature inspired Schrödinger's famous thought experiment involving a cat that is both alive and dead until it is observed.
Yet objects in the everyday world do not behave that way. Physicists call the loss of these distinctly quantum effects decoherence. Exactly why decoherence happens, and whether gravity plays a role, remains one of the major open questions in fundamental physics.
Now, a new experiment supported by FQxI has eliminated one prominent explanation involving gravity. The findings were published in the New Journal of Physics in June 2026. "One of the deepest questions in modern physics is why the strange quantum behavior that governs atoms and elementary particles seems to disappear in the macroscopic world we experience every day," says FQxI member Catalina Curceanu, director of research and spokesperson for the VIP Collaboration at the National Laboratory of Frascati of the National Institute for Nuclear Physics (INFN-LNF) in Italy.
Testing Gravity's Role in Quantum Decoherence The experiment was carried out at the INFN Gran Sasso National Laboratory (INFN-LNGS), the world's largest underground laboratory devoted to fundamental physics. Researchers focused on a model proposing that gravity itself could help destroy quantum superpositions. According to Einstein's general theory of relativity, massive objects curve the fabric of spacetime.
In the 1960s, Hungarian theoretical physicist Frigyes Károlyházy suggested that spacetime may also undergo tiny, unavoidable fluctuations. In his model, those fluctuations would gradually disrupt quantum superpositions. That process could help explain why large objects do not remain in the strange combinations of states allowed by quantum mechanics, such as the dead-and-alive situation imagined in Schrödinger's cat thought experiment.
Károlyházy's idea has continued to attract attention and was recently revived, refined and reformulated by FQxI's Angelo Bassi and colleagues. Searching for a Faint Radiation Signature The predicted spacetime fluctuations cannot be detected directly. But if they exist, they should have a measurable side effect.
Extract — continue reading at the source.
