Magazine article Science News

Violating a Not-So-Exclusive Exclusion Principle

Magazine article Science News

Violating a Not-So-Exclusive Exclusion Principle

Article excerpt

Violating a not-so-exclusive exclusion principle

The Pauli exclusion principle stands at the basis of the structure and stability of matter. It prevents, atoms, nuclei and larger structures, up to and including neutron stars, from collapsing on themselves. It does so by decreeing that no two particles of the class called fermions that have the same set of properties (the same quantum numbers) can be in the same place at the same time. The particles of physics are divided into fermions and bosons, and while any number of bosons can be in the same place, the exclusion principle maintains structures made of fermions (electrons, protons, neutrons) by restricing them.

Historically, physicists have believed the principle to be absolute. But now a few are asking, "Can it be violated?"

To explore that question, Oscar W. Greenberg and Rabindra N. Mohapatra of the University of Maryland at College Park have developed a theory that permits a slight violation of the exclusion principle. Experiments to test their theory are likely to follow.

According to Greenberg, the argument underpinning the absoluteness of the exclusion principle, using the statistical laws obeyed by fermions and bosons, makes a couple of false assumptions. As he said in a lecture last week at the National Bureau of Standards (NBS) in Gaithersburg, Md., those statistical principles are not general enough to support the argument. Greenberg and Mohapatra searched for a more generalized statistical law. When they found it, they discovered that it permits the existence of particles they call "parafermions" or "parons," which can violate the exclusion principle. The chance of violation is extremely small, about 1 in 100 million. However, this could produce unusual atomic states.

The experiment that may be closest to realization is one proposed by Daniel Kelleher of NBS, which would use helium atoms. …

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