Information is Physical
Landauer's principle: erasing information costs energy
LANDAUER'S PRINCIPLE (1961)
E ≥ kT ln(2) per bit erased
Erasing one bit of information dissipates at least kT ln(2) joules as heat, about 3 × 10−21 J at room temperature (k is Boltzmann's constant, T the temperature in kelvin)
BIT ERASURE DEMONSTRATION
Press "Erase Bit" to destroy information and watch the thermodynamic cost
REVERSIBLE vs IRREVERSIBLE COMPUTATION
IRREVERSIBLE (AND gate)
2 bits in → 1 bit out
Information destroyed.
Heat emitted: at least kT ln(2)
REVERSIBLE (Toffoli gate)
3 bits in → 3 bits out
Information preserved.
No minimum heat cost
IMPLICATIONS
- • Computation has thermodynamic cost — thinking requires energy
- • Information is not abstract — it has physical substrate and physical limits
- • Maxwell's demon is exorcised — the demon must erase its memory, paying the cost
- • Reversible computation is possible — but requires preserving all information
Information is physical. — Rolf Landauer
Minds — biological or digital — are thermodynamic engines. Thought has entropy.
core conceptinformationheat · erasure cost