Demonic door operator

A thought experiment devised by the Scottish physicist James Clerk Maxwell in 1867 stumped scientists for 115 years. And even after a solution was found, physicists have continued to use “Maxwell’s demon” to push the laws of the universe to their limits.

~ Jonathan O’Callaghan from,

This is a fun, and well-done, description of what started out as a thought-experiment in 1867—that’s 154 years ago—and which after being solved in theory has subsequently been verified by doing literal experiments on lab benches. They’ve built several of the demons, put them to work and shown why entropy always increases. If you’ve heard of “entropy”, but have always scratched your head, then…

…well, to be honest, this cutesie article won’t explain it all. But it will get you a step in the right direction, so long as you don’t mind the demon working the door.