Lorraine Ford
I should add that, in the Maxwell’s demon thought experiment, Maxwell’s demon is looking at the speed, direction, and 3D position relative to the 3D position of the plane of a door between the chambers, of a gas molecule that he is focussing on.
In order to open the door for the faster molecules, and close the door for the slower molecules, the demon needs to change his own 3D position (e.g. the position of his arm) in order to physically manipulate the door, or to press a button to open and close the door.
Also, light particles coming from both the molecules and the door, would have to interact with Maxwell’s demon’s eyes and be analysed by the demon in order for him to consciously distinguish the door from the background, and distinguish the gas molecule from the background, and in order for him to estimate the speed, direction and position of the gas molecule that he has previously distinguished from the background.
All this brainpower would take time and use Maxwell’s demon’s energy. Also, the demon’s arm movements, in order to open or close the door, would also take time and use the demon’s energy.
Obviously, the Maxwell’s demon thought experiment is an idealisation, and nothing like what happens in the real world.