Here uµ ≡ dxµ/ds, Γ µ βγ is the usual 4D Christoffel symbol, and f µ is the fifth force (per unit inertial mass) which has been discussed for induced-matter theory [6] and membrane theory [7]. By (10), the motion in spacetime is only geodesic in the usual 4D sense if f µ = 0. This force may be split into a part(−gµα +uµuα)uβ(dl/ds)(∂gαβ/∂l) which by construction is normal to the 4-velocity uµ, and a part −(uµ/2)(uαuβ∂gαβ/∂l)(dl/ds) which is parallel to it. The latter has no analog in 4D general relativity or any field theory like it, including electromagnetism.