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
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