"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