Abstract
In the context of the ECSK theory of gravitation we have obtained the solutions of the Einstein-Dirac equations in a Friedmann-Robertson-Walker spatially flat universe when spin has only one non-zero space-component. All solutions are singular: one of these is bounded and describes a universe whose lifetime is [(ℏ)/(mc2)], independently of initial conditions; the others describe a spatially flat open expanding or contracting universe, where spin increases the expansion rate or the contraction rate, respectively, of the universe for time intervals Δt ≈ [(hbar)/(mc2)] in a neighbourhood of the singularities.