Universe with only "e+", "e-", photons, and gravitation? In theory could we have a universe with only electrically charged spin 1/2 particles and antiparticles of mass m and electrical charge e and that interacted only gravitationally and electromagnetically? If so could we fine tune things so that such a universe was long lived and closed? In the early phase of such a universe would there be roughly twice the energy density in the fields of the charged particles as in the electromagnetic field? Thanks for any help!