The field multivector, known as the Riemann–Silberstein vector, is F = E + I c B = E k σ σ k + I c B k σ σ k , and the four-current multivector is c ρ ρ − − J = c ρ ρ − − J k σ σ k using an orthonormal basis { σ σ k } . Similarly, the unit pseudoscalar is I = σ σ 1 σ σ 2 σ σ 3 , due to the fact that the basis used is orthonormal. These basis vectors share the algebra of the Pauli matrices, but are usually not equated with them, as they are different objects with different interpretations.