Classical unified field theories since antisymmetry seemed essential for electromagnetism, the symmetry requirement was relaxed for one or both fields. Einstein's proposed unified-field equations (fundamental laws of physics) were generally derived from a variational principle expressed in terms of the Riemann curvature tensor for the presumed space-time manifold. In field theories of this kind, particles appear as limited regions in space-time in which the field strength or the energy density are particularly high. Einstein and coworker Leopold Infeld managed to demonstrate that, in Einstein's final theory of the unified field, true singularities of the field did have trajectories resembling point particles. However, singularities are
Unified primary Unified primary A unified primary is a proposed electoral system system for narrowing the field of candidates for a single-winner general election, similar to a nonpartisan blanket primary, but using approval voting for the first round. In the US, most primary elections are party-specific: voters select a political party, either as part of the voter registration process or at the ballot box, and may vote only for candidates sharing that same party affiliation. These primary systems use plurality voting, where each voter may express a preference for one candidate per office. The candidate in each party receiving the most votes