21 March 2011

Fundamental Particle Spin As Emergent

Professor Chris Regan and graduate student Matthew Mecklenburg, in a March 18 article in the journal Physical Review Letters, drawing on their discoveries in graphene properties, suggest note that a particle acquires apparent spin in a medium of light and dark tiles where the tiles are so close that their separation cannot be detected. They reason from there that:

"An electron's spin might arise because space at very small distances is not smooth, but rather segmented, like a chessboard," Regan said. . . .

In 1928, British physicist Paul Dirac showed that the spin of the electron is intimately related to the structure of space-time. His elegant argument combined quantum mechanics with special relativity, Einstein's theory of space-time (famously represented by the equation E=mc2).

Dirac's equation, far from merely accommodating spin, actually demands it. But while showing that relativistic quantum mechanics requires spin, the equation does not give a mechanical picture explaining how a point particle manages to carry angular momentum, nor why this spin is two-valued.

Unveiling a concept that is at once novel and deceptively simple, Regan and Mecklenburg found that electrons' two-valued spin can arise from having two types of tiles -- light and dark -- in a chessboard-like space.

The implication would seem to favor the program of loop quantum gravity, which attempts to derive general relativity and other fundamental properties of physics, such as the number of space-time dimensions from a simple model which has as a core premise, the notion that space-time is discrete rather than continuous.

If fundamental particle spin could be shown to be emergent from this model, this would be a major breakthrough in developing a quantum theory of gravity.

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