>Landauer's principle defines a lower theoretical limit for energy consumption: kT ln 2 joules consumed per irreversible state change, where k is the Boltzmann

>Landauer's principle defines a lower theoretical limit for energy consumption: kT ln 2 joules consumed per irreversible state change, where k is the Boltzmann constant and T is the operating temperature of the computer.[2] Reversible computing is not subject to this lower bound. T cannot, even in theory, be made lower than 3 kelvins, the approximate temperature of the cosmic microwave background radiation, without spending more energy on cooling than is saved in computation. Well, technically, you just have to wait as the universe continues expanding if you want the temperature of the CMB to drop.