Due to the spin-orbit interaction the energies of states of the same level but with different "j" will no longer be identical. This is because in the original quantum numbers, when formula_4 is parallel to formula_5, the interaction energy is positive; and in this case "j" = "ℓ" + "s" = "ℓ" + . When formula_4 is anti-parallel to formula_5 (i.e. aligned oppositely), the interaction energy is negative, and in this case . Furthermore, the strength of the interaction is roughly proportional to "ℓ".