Here's a simple way to understand the situation. Imagine you have a room of uniform pressure. Air particles are bouncing around at random speeds but its chaot

Here's a simple way to understand the situation. Imagine you have a room of uniform pressure. Air particles are bouncing around at random speeds but its chaotic and uniform. The randomness means that there will be moments where the rooms pressure is not EXACTLY uniform. Now image you have a demon that can divide the room at one of those times. The demon does not work on the particles in the room. It simply divides the room. ...But now you have two rooms with a pressure differential. You can use that difference to do work and it will only return the rooms to uniform pressure again. You get work for free. How can this be? This is the paradox.