In a landmark study published in the June 2026 issue of the New Journal of Physics, an international team of researchers has successfully tested and eliminated a long-standing theory that sought to explain the boundary between the quantum realm and the classical world through the lens of gravity. The experiment, conducted deep beneath the Italian Apennines at the Gran Sasso National Laboratory, represents a significant step forward in solving the "measurement problem"—the enduring mystery of why the strange, probabilistic behavior of atoms and subatomic particles does not manifest in the solid, predictable world of everyday objects.
For over a century, quantum mechanics has provided an incredibly accurate framework for understanding the universe at its smallest scales. Central to this framework is the principle of superposition, which allows particles to exist in multiple states simultaneously. This phenomenon is famously illustrated by Erwin Schrödinger’s 1935 thought experiment involving a cat that is both dead and alive until observed. However, as objects increase in size and complexity, these quantum effects seem to evaporate, a process known as decoherence. While various theories have been proposed to explain this transition, the new findings from the VIP (Violation of the Pauli Exclusion Principle) Collaboration suggest that one of the most prominent gravity-based models may no longer be viable.
The Quantum-Classical Divide and the Mystery of Decoherence
The discrepancy between the quantum and classical worlds remains one of the deepest philosophical and technical challenges in modern science. In the quantum world, an electron does not occupy a single point in space but exists as a "wave function" of probabilities. When a measurement is made, the wave function is said to "collapse" into a single state. The question that has haunted physicists since the days of Einstein and Bohr is: what causes this collapse?
Decoherence occurs when a quantum system interacts with its environment—such as air molecules or photons—causing the delicate superposition of states to break down. Yet, many physicists suspect that even in a perfect vacuum, there might be a fundamental mechanism that prevents large objects from existing in superpositions. One leading hypothesis suggests that gravity, the force that governs the macroscopic universe, is the ultimate "observer" that forces quantum systems to choose a single state.
"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," explains Catalina Curceanu, a member of the Foundational Questions Institute (FQxI) and director of research at the National Laboratory of Frascati of the National Institute for Nuclear Physics (INFN-LNF) in Italy. Curceanu, who serves as the spokesperson for the VIP Collaboration, has spent years searching for the precise point where quantum mechanics might break down.
The Károlyházy Model: Gravity as a Disruptor
The specific theory under investigation was first proposed in the mid-1960s by the Hungarian physicist Frigyes Károlyházy. He suggested that the fabric of spacetime is not smooth, as Einstein’s General Theory of Relativity describes, but is instead subject to tiny, inherent fluctuations at the Planck scale. Károlyházy hypothesized that these fluctuations would exert a "smearing" effect on the position of massive objects.
According to this model, while a single atom is small enough to remain unaffected by these spacetime ripples, a larger object composed of trillions of atoms would experience enough gravitational interference to cause its quantum wave function to collapse almost instantly. This would provide a natural explanation for why we never see chairs or planets in two places at once. Recently, this model was refined and reformulated by FQxI member Angelo Bassi and his colleagues, providing specific, testable predictions that the VIP Collaboration could finally put to the test.
Searching for the "Glow" of Spacetime Fluctuations
The challenge in testing Károlyházy’s theory lies in the fact that spacetime fluctuations themselves are far too small to be observed directly with current technology. However, the model predicts a detectable side effect: the spontaneous emission of radiation.
If spacetime is indeed fluctuating, these fluctuations should interact with electrically charged particles, such as the protons and electrons within an atom. This interaction would cause the particles to "jiggle" or accelerate randomly. According to the laws of electromagnetism, any accelerated charged particle must emit electromagnetic radiation. Therefore, if Károlyházy’s theory were correct, all matter should be emitting an extremely faint, constant glow of X-rays and gamma rays.
Detecting this signal requires an environment of near-absolute silence. On the Earth’s surface, cosmic rays and natural radioactivity create a cacophony of background noise that would easily drown out the faint signature of gravity-induced decoherence. To overcome this, the researchers turned to the INFN Gran Sasso National Laboratory (INFN-LNGS), the largest underground laboratory in the world.
The Experiment at Gran Sasso
Located 1.4 kilometers (nearly one mile) beneath the rock of the Gran Sasso massif, the laboratory is shielded from the relentless rain of cosmic muons by a factor of one million. "The natural shielding provided by the rock creates one of the quietest environments on Earth for detecting extremely rare physical phenomena," says Curceanu.
The experimental setup centered on a high-purity germanium (HPGe) crystal, roughly the size of a coffee mug. Germanium detectors are renowned in particle physics for their extreme sensitivity and ability to measure the energy of incoming photons with incredible precision. To further isolate the crystal, the team surrounded it with additional layers of high-density shielding made of ultrapure copper and lead, designed to block any stray radiation from the surrounding laboratory walls.
The researchers collected data for a period of 62 days. During this time, the detector monitored for any excess photons that could not be attributed to known sources of background radiation. Using sophisticated statistical models, the team subtracted the expected signals from trace amounts of natural isotopes and thermal noise.
Results: The Silence of Gravity
When the final analysis was completed, the results were definitive: no signal was found. The radiation pattern predicted by the Károlyházy model was entirely absent from the data.
"The result was simple: no signal appeared," the researchers noted in their report. While a "null result" might seem disappointing to a layperson, in the world of fundamental physics, it is a major discovery. By failing to find the predicted radiation, the team has effectively ruled out the original and most prominent version of the Károlyházy model.
"This absence of a signal is itself a major scientific result," Curceanu says. "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, bringing us one step closer to understanding one of the deepest mysteries in fundamental physics."
Implications for Quantum Gravity and String Theory
The experiment’s impact extends beyond the specific model proposed by Károlyházy. It touches upon the broader quest for a "Theory of Everything"—a single mathematical framework that unites gravity (General Relativity) with the other three fundamental forces (Quantum Mechanics).
Most modern attempts to reconcile these two theories, such as String Theory and Loop Quantum Gravity, suggest that there is a "minimal length" in nature—a pixelation of space below which distances cannot be measured. This concept is intrinsically linked to the uncertainty in spacetime measurements that Károlyházy explored.
"Every quantum gravity approach ends up with predicting the existence of a minimal length connected to the uncertainty in the measurement of spacetime," says Kristian Piscicchia, a quantum physicist at the Enrico Fermi Research Center and the experimental lead on the study. By setting tighter boundaries on how gravity interacts with quantum systems, this experiment provides crucial data for theorists working on these complex models. It suggests that if gravity does cause quantum collapse, it must do so through a much more subtle mechanism than previously thought.
A Timeline of Quantum Foundations Research
The journey to the June 2026 announcement has been decades in the making. The following timeline highlights the key milestones leading to this discovery:
- 1927: The Solvay Conference establishes the Copenhagen Interpretation, suggesting that "observation" collapses the wave function, but leaves the mechanism of collapse undefined.
- 1935: Erwin Schrödinger publishes his "Cat" thought experiment to highlight the absurdity of macroscopic superposition.
- 1966: Frigyes Károlyházy proposes that gravitational fluctuations limit the precision of spacetime and cause the collapse of the wave function in macroscopic bodies.
- 1980s-1990s: Roger Penrose and Lajos Diósi independently develop the Penrose-Diósi model, another gravity-related collapse theory based on gravitational energy differences.
- 2010s: The VIP Collaboration at Gran Sasso begins using high-purity germanium detectors to test various "non-standard" quantum effects, including potential violations of the Pauli Exclusion Principle.
- 2020-2024: Angelo Bassi and collaborators reformulate the Károlyházy model into a modern mathematical framework, providing the specific radiation signatures needed for experimental testing.
- 2025: The 62-day data collection run at Gran Sasso is completed.
- June 2026: Results are published in the New Journal of Physics, ruling out the Károlyházy model.
The Role of FQxI and Future Outlook
The research was made possible through support from the Foundational Questions Institute (FQxI) as part of its "Consciousness in the Physical World" program. FQxI specializes in funding high-risk, high-reward research that traditional agencies might overlook—specifically research that addresses the fundamental nature of reality.
"The type of research that FQxI is encouraging brings teams together across generations, across boundaries, across disciplines," says Curceanu. "It really can act as an incubator of new ideas."
While the Károlyházy model has been sidelined, the search for gravity’s role in quantum mechanics is far from over. Other models, such as the aforementioned Penrose-Diósi theory, remain on the table, though they too are facing increasingly stringent experimental tests. As detector technology continues to improve, physicists are moving closer to the "standard quantum limit," where they may eventually observe the actual moment of wave function collapse.
"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," Curceanu concludes. "As sensitivity improves, the boundary between theory and measurement continues to move, opening new possibilities for discovering the fundamental principles that govern our universe."
The findings at Gran Sasso serve as a reminder that in science, knowing where the truth is not is often just as important as knowing where it is. By clearing away the Károlyházy model, the VIP Collaboration has cleared the path for the next generation of theories that will eventually bridge the gap between the atom and the everyday world.
