Thus absorption and stimulated emission are reverse processes proceeding at somewhat different rates. Another way of viewing this is to look at the net stimulated emission or absorption viewing it as a single process. The net rate of transitions from E 2 to E 1 due to this combined process can be found by adding their respective rates, given above: ∂ ∂ N 1 net ∂ ∂ t = − − ∂ ∂ N 2 net ∂ ∂ t = B 21 ρ ρ ( ν ν ) ( N 2 − − N 1 ) = B 21 ρ ρ ( ν ν ) Δ Δ N .