In free space, where ε = ε 0 and μ = μ 0 are constant everywhere, Maxwell's equations simplify considerably once the language of differential geometry and differential forms is used. The electric and magnetic fields are now jointly described by a 2-form F in a 4-dimensional spacetime manifold. The Faraday tensor F μ μ ν ν (electromagnetic tensor) can be written as a 2-form in Minkowski space with metric signature (− + + +) as F ≡ ≡ 1 2 F μ μ ν ν d x μ μ ∧ ∧ d x ν ν = B x d y ∧ ∧ d z + B y d z ∧ ∧ d x + B z d x ∧ ∧ d y + E x d x ∧ ∧ d t + E y d y ∧ ∧ d t + E z d z ∧ ∧ d t which is the exterior derivative of the electromagnetic four-potential A : A = − − ϕ ϕ d t + A x d x + A y d y + A z d z .