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 s → → is parallel to l → → , the interaction energy is positive, and in this case j = ℓ + s = ℓ + 1 ⁄ 2. When s → → is anti-parallel to l → → (i.e. aligned oppositely), the interaction energy is negative, and in this case j = ℓ − s = ℓ − 1 ⁄ 2. Furthermore, the strength of the interaction is roughly proportional to ℓ.