 That is, it would take more thermodynamic work to gauge the speed of the molecules and selectively allow them to pass through the opening between "A" and "B" than the amount of energy gained by the difference of temperature caused by doing so.One of the most famous responses to this question was suggested in 1929 by Leó Szilárd, and later by Léon Brillouin.Szilárd pointed out that a real-life Maxwell's demon would need to have some means of measuring molecular speed, and that the act of acquiring information would require an expenditure of energy.