Physics of Information Yovav Kalifon Weizmann Inst. 18 Nov 2008 Szilard, L. (1929) `On the Decrease of Entropy in a Thermodynamic System by the Intervention of Intelligent Beings', Zeitschrift für Physik 53, 840 ¯ 856. Feynman, Feynman Lectures on Physics, Ratchet and Pawl, Volume 1, Chapter 46. Landauer, R. (1961) `Irreversibility and Heat Generation in the Computing Process', Advances in Chemical Physics 5, 183 ¯ 191.
Physics of Information Yovav Kalifon Weizmann Inst. 18 Nov 2008 Szilard, L. (1929) `On the Decrease of Entropy in a Thermodynamic System by the Intervention.
Dec 16, 2015
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Physics of Information
Yovav KalifonWeizmann Inst. 18 Nov 2008
Szilard, L. (1929) `On the Decrease of Entropy in a Thermodynamic System by the Intervention of Intelligent Beings', Zeitschrift für Physik 53, 840¯856.
Feynman, Feynman Lectures on Physics, Ratchet and Pawl, Volume 1, Chapter 46.
Landauer, R. (1961) `Irreversibility and Heat Generation in the Computing Process', Advances in Chemical Physics 5, 183¯191.
Physics of Information
•Making a measurement
Physics of Information
•What is information?
Physics of Information
•Information processing
• Exorcise Maxwell’s (mechanical) demon
• Consider intelligent beings as demons
• “Universal law” of measurements
Second Law of Thermodynamics
Second Law of Thermodynamics
Maxwell:
“The 2nd law is only statistically valid.
“Could statistical fluctuations be exploited to run a perpetual motion machine?”
Maxwell’s DemonExploiting fluctuations
Ratchet and pawl
Getting hit means Getting heat!
Forward Step
Stretchε
LiftLθ
FluctuationLθ+ε
Forward Step Rate
Stretchε
LiftLθ
FluctuationLθ+ε
Backward Step
Fluctuationε
DropLθ
ReleaseLθ+ε
Backward Step Rate
Fluctuationε
DropLθ
ReleaseLθ+ε
Reversible process
The engine keeps 2nd law
Trap door demon
Mechanical demons fluctuate
Ranque-Hilsch vortex tube (1933)
Szilard:
“Under what circumstances could we construct a perpetual motion machine, utilizing intelligent beings?”
Concerns of intelligent demons
Concerns of intelligent demons
Making measurements
Processing information
Erasing information
Szilard’s first machine
Intelligent being couples parameters
Szilard’s first machine
Work done at the expense of heat
ENTROPY BILL
• Ideal gas:
• Heat reservoir:
ENTROPY BILL
• The frequency of each outcome:
• Overall we get:
ENTROPY BILL
• Ansatz:
• Overall we get:
Szilard’s second machine
Szilard’s second machine
ENTROPY BILL
• If parameter (x) thermalizes reversibly:
• Ansatz:
ENTROPY BILL
• Overall we get:
• Szilard’s Universal Law:
The entropy of erasure
Landauer (1961) and Bennet (1982): • A measurement is essentially copying• Computation can be made reversible• Erasing memory means compressing the
phase space of possible physical states, inevitably heating up the environment
Szilard’s third machine
Szilard’s third machine
Szilard’s third machine
Szilard’s third machine
Szilard’s third machine
ENTROPY BILL
ENTROPY BILL
Summary• Simple demons fail due to Brownian motion
• Intelligent demons are a part of the system
• Demons make up for the missing entropy
• No perpetual motion machine is known
Summary
• Szilard assumes the 2nd law
• A “universal law” of measurements
Summary
• Szilard’s own work supports the claim that erasing memory is the only stage which necessarily raises the entropy of the system
• Inanimate automatic machines can measure parameters, store the information, process it, even print the result.
So what is intelligence?
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