Chamseddine and Connes have argued that the action for Einstein gravity,
coupled to the SU(3)\times SU(2)\times U(1) standard model of particle physics,
may be elegantly recast as the "spectral action" on a certain "non-commutative
geometry." In this paper, we show how this formalism may be extended to
"non-associative geometries," and explain the motivations for doing so. As a
guiding illustration, we present the simplest non-associative geometry (based
on the octonions) and evaluate its spectral action: it describes Einstein
gravity coupled to a G_2 gauge theory, with 8 Dirac fermions (which transform
as a singlet and a septuplet under G_2). This is just the simplest example: in
a forthcoming paper we show how to construct more realistic models that include
Higgs fields, spontaneous symmetry breaking and fermion masses.Comment: 24 pages, no figures, matches JHEP versio