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Equation 13 · Part 12 · From Origins to Frontier: A History of Stochastic Thermodynamics and Complex Systems

Denominator: P_R(-W)

PF(W)PR(−W)=e(W−ΔF)/kBT\frac{P_F(W)}{P_R(-W)} = e^{(W-\Delta F)/k_B T}
PR(−W)P_R(-W)

What this part means

The complete quantity below the fraction bar; it must be nonzero for this division.

Its job in the formula

PR(−W)P_R(-W) occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

The passage around this formula

This is a striking claim on its face: it says a quantity defined only for reversible, quasistatic processes — a free energy difference — can be computed from measurements of an irreversible process, no matter how fast or violent the driving, provided enough repetitions are averaged. Two years later, Gavin Crooks derived a closely related and in some respects more general result, the Crooks fluctuation theorem, in “Entropy Production Fluctuation Theorem and the Nonequilibrium Work Relation for Free Energy Differences,” published in Physical Review E in 1999 [ 4 ] . Crooks’s relation compares the probability of observing work W in a forward protocol to the probability of observing -W in the…

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Learn the underlying idea

A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.

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Sources cited in the surrounding passage

These citations provide research context; check each source for the exact claim it supports.