He realised that Maxwell had failed to consider the energy which the demon would require to decide whether a molecule was moving fast or slowly.

他恍然大悟，麦克斯韦没有考虑到这个小妖判定一个分子的速度是快还是慢也需要能量。

youdao

If it were not for this kick, the apparatus would be behaving just like Maxwell's Demon, a hypothetical creature (conceived of in the 19th century by James Clerk Maxwell) that could cause the spontaneous separation of hot and cold particles and thus do serious damage to some of the laws of physics.

ECONOMIST: Microrefrigeration