Landauer Floor.

The one-sentence version

The Landauer floor is the physical lower bound on the energetic cost of any irreversible discrimination: no system embedded in the universe can register a distinction without paying at least kT ln 2 joules per bit erased. Observation is never free.

Where the term comes from

Rolf Landauer’s 1961 result showed that logically irreversible operations — specifically the erasure of one bit — must dissipate a minimum quantity of free energy into the environment. Bennett’s later work on reversible computing clarified that the limit applies to erasure specifically, not computation in general. In ontogony the floor applies to every discriminating act in any finite observer at any register.

Why it matters

The Landauer floor closes Maxwell’s Demon: any demon that could exploit microscopic fluctuations must also maintain a memory register, and erasing that register costs exactly as much as the demon gained. More broadly, it establishes that the capacity to make distinctions — the foundation of every cognitive, biological, and institutional regime — is always already a thermodynamic commitment.