Maxwell's Demon / Szilard Engine

Information is physical: measuring a particle's position costs kT ln2 of free energy

Szilard Cycle

1. Insert partition → particle in L or R
2. Demon measures which side (1 bit)
3. Use knowledge → extract kT ln2 work
4. Erase demon's memory → pay kT ln2
Net: ΔS_total = 0 (Landauer 1961)

Statistics

Cycle count0
Work extracted (kT)0.000
Erasure cost (kT)0.000
Net gain0.000
Landauer limit: kT ln20.693 kT

Controls

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The Resolution

Landauer's principle:
Erasing 1 bit dissipates ≥ kT ln2
Demon's memory must be erased → 2nd law holds. Information has thermodynamic cost.