Sortex

Sortex is a clerk at a trapdoor, and his trouble is paperwork.

In 1871 James Clerk Maxwell imagined a tiny being guarding a hole in a wall between two boxes of gas. It lets fast molecules through one way and slow ones the other, and without doing any work it makes one side hot and the other cold, against the second law of thermodynamics.

Sortex runs that door. He watches each molecule, decides, and logs the decision in his ledger as a 1 or a 0. For decades the usual exorcism was that looking must cost energy. In 1961 Rolf Landauer at IBM argued instead that the unavoidable cost lies in erasing information: wiping one bit releases at least kT ln 2 of heat, the first line on this page, about 2.87×10⁻²¹ J at 300 K. In 1982 Charles Bennett applied this to the demon. Measuring can in principle be done without dissipation; resetting the memory cannot. Sortex’s ledger fills, and to keep working he feeds pages to a shredder that blows out warm air.

The bound itself has been measured. In 2012 Antoine Bérut and colleagues in Lyon erased a bit stored in a single silica bead held in a laser trap and approached kT ln 2 as the erasure slowed; in 2014 Yonggun Jun, Momčilo Gavrilov and John Bechhoefer confirmed it with high precision in a feedback trap.

What remains open is the exorcism. Bennett’s account is one standard resolution, and whether Landauer’s principle is really what defeats the demon is still debated. John Earman and John Norton argued in 1998–99, and Norton again in 2005 and 2011, that the principle is either circular or unproven; James Ladyman and colleagues defended it in 2007.

Sorting can be free. Forgetting isn’t.