Erasa

Erasa wipes a bit clean and a puff of heat drifts off. Forgetting is never free.

The Physics

Erasing one bit of information, resetting a memory to a standard state no matter what it held, must on average release at least k_B T ln 2 of heat into the surroundings. At 300 K that is 2.87 × 10⁻²¹ J, about 0.018 eV. The cost comes from erasure; it does not apply to every logical step.

⟨Q⟩ ≥ k_B T ln 2

• Q: heat released per erased bit (J)
• k_B: Boltzmann constant, 1.380649 × 10⁻²³ J/K
• T: temperature (K)
• ln 2: ≈ 0.693 (dimensionless)

Rolf Landauer proposed it in 1961, and Bérut et al. measured it with a single trapped colloidal bead (Nature, 2012).

Honest caveat: It applies to logically irreversible erasure, not to every computation.

On the shirt

Front: Erasa, the pixel-art character, with the title. Back: the Landauer bound, its value at 300 K and the 1961 and 2012 sources. Printed on a unisex tee.