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Physicists have been looking for a model that would unify quantum physics. It's difficult to test the predictions of candidate models. A small violation of the Pauli exclusion principle, which determines how electrons are arranged in atoms, is predicted by some models.
A project under the Gran Sasso mountains in Italy has been looking for signs of radiation produced by a violation of the Pauli exclusion principle.
The team reports that no evidence of violation has been found so far, ruling out some quantum-gravity models.
The Pauli exclusion principle helps explain why electrons can only arrange themselves in certain ways in atoms. There is a nucleus at the center of the atom. The firstorbital can only hold two electrons. Wolfang Pauli formulated the Pauli exclusion principle in 1925, which states that no two electrons can have the same state.
The result is that matter can't be passed through other matter. Catalina Curceanu is a member of the Foundational Questions Institute and the lead physicist on the experiments at INFN, Italy. It's a practical consequence that we can't cross walls.
The principle applies to all elementary particles belonging to the same family as electrons. It appears to hold for all fermions in tests. One of the core tenets of the model is the Pauli exclusion principle.
The principle is being violated.
The principle may be violated by some speculative models. Physicists have been looking for a fundamental theory of reality for a long time. Particles, interactions and quantum processes are explained in the standard model. It doesn't include gravity.
Physicists have been trying to develop a unifying theory of quantum gravity, some versions of which predict that certain properties of the standard model may be violated in extreme circumstances
"Many of these violations are naturally occurring in so-called 'noncommutative' quantum-gravity theories and models," says Curceanu. The string theory describes fundamental particles as tiny vibrating threads of energy in multidimensional spaces. A violation is predicted by some string theory models.
Some concrete realizations of quantum gravity were found to be unfavorable.
It's hard to test quantum gravity predictions because they only become relevant in arenas where there is a huge amount of gravity concentrated into a tiny space.
A signature that the exclusion principle and the spin-statistics theorem have been violated could be seen in lab experiments on Earth.
Curceanu's team is working on a project under the Gran Sasso mountains in Italy. A germanium detector is located near a thick block of Roman lead at the center of the apparatus.
The idea is that if the Pauli exclusion principle is violated, a forbidden atomic transition will occur within the Roman lead. The germanium detector can pick up X-rays.
The universe is silent.
The lab needs to be underground because the radiation signature from the process will be so faint that it will be lost in the background radiation. The Gran Sasso mountain reduces the amount of Cosmic rays by a million times. It is not enough.
The signal may have a rate of just one or two events a day. The materials used in the experiment must be "radio-pure" and the apparatus must be protected from radiation from the mountain rocks.
It's exciting that we can probe some quantum-gravity models with such high precision, which is impossible to do at present-day accelerators.
The team found no evidence that the Pauli principle had been violated. The data analysis techniques were developed with the help of FQXi- funding. The team was able to set limits on the size of any violation they might have.
The team analyzed the predictions of the so-called "theta-Poincaré" model and were able to rule out some versions of the model. Some concrete realizations of quantum gravity were found to be disfavored by the analysis.
The team is going to extend its research to other quantum-gravity models with the help of their theoretician colleagues. New target materials and new analysis methods will be used to find faint signals in spacetime.
It's exciting that we can probe some quantum-gravity models with such high precision, which is impossible to do at present-day accelerators. This is a big leap from both theoretical and experimental perspectives.
The strongest atomic physics bounds on noncommutative quantum gravity models are described in the Physical Review Letters. There is a book titled "PhysRevLett.129.131301."
The test of noncommutative quantum gravity was done by the team.
Journal information: Physical Review Letters , Physical Review D
The Foundational Questions Institute provided it.
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