Information Thermodynamics on Causal Networks and its Application to Biochemical Signal Transduction

Descripción

In physics, there are only a few fundamental laws that decide what is possible and what is not. Among them, the second law of thermodynamics is the most important law in physics which prohibits perpetual motion machines and distinguishes what is possible and impossible with regard to heat and energy. Around 1867, through a Gedankenexperiment (thought experiment), J.C. Maxwell demonstrated that the second law of thermodynamics can be violated by postulating an imaginary demon that can observe and operate microscopic states. The so-called Paradox of Maxwell’s Demon caused prolonged debates on information and thermodynamics. Nowadays, we are able to observe single-molecule dynamics and even manipulate them, thanks to development of modern technology. Thus, Maxwell’s demon comes closer to reality. Later, it was clarified that Maxwell’s demon does not contradict the second law of thermodynamics, implying that one can convert information to free energy in principle. Recent development of fluctuation theorems in non-equilibrium statistical mechanics moved us to the next stage for understanding well the relation between information and thermodynamics. The so-called information thermodynamics deals with the simplest Maxwell’s demon system, Szilard’s engine, which can extract work from an isothermal system by a feedback control. By separating Szilard’s engine into two subsystems, i.e., the demon that observes and performs feedback control and the system controlled by the demon and considering mutual information between two subsystems, our understanding of the relation between information and thermodynamics made great advances and finally the paradox was resolved.

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