Landauer Principle

Every irreversible bit erasure dissipates at least kT ln 2 of heat — the fundamental thermodynamic cost of information

T = 300 K
N = 8 bits
2.0× limit

Rolf Landauer, 1961

Landauer proved that logically irreversible operations — specifically bit erasure (resetting to 0 regardless of previous value) — must dissipate a minimum heat of kT ln 2 per bit into the environment.

Q ≥ kT ln 2 ≈ 2.85 × 10−21 J per bit at 300 K

This is the absolute floor for computation. Modern chips dissipate ~106 × this minimum, but as circuits shrink toward molecular scale, Landauer's limit becomes physically real. Combined with Szilard, it completes Maxwell's demon's exorcism.