Editing Fluctuation theorem (section)

== Implications ==

There are many important implications from the fluctuation theorem. One is that small machines (such as nanomachines or even [[mitochondria]] in a cell) will spend part of their time actually running in "reverse". What is meant by "reverse" is that it is possible to observe that these small [[molecular machine]]s are able to generate work by taking heat from the environment. This is possible because there exists a symmetry relation in the work fluctuations associated with the forward and reverse changes a system undergoes as it is driven away from thermal equilibrium by the action of an external perturbation, which is a result predicted by the [[Crooks fluctuation theorem]]. The environment itself continuously drives these molecular machines away from equilibrium and the fluctuations it generates over the system are very relevant because the probability of observing an apparent violation of the second law of thermodynamics becomes significant at this scale.

This is counterintuitive because, from a macroscopic point of view, it would describe complex processes running in reverse. For example, a jet engine running in reverse, taking in ambient heat and exhaust fumes to generate  [[kerosene]] and oxygen. Nevertheless, the size of such a system makes this observation almost impossible to occur. Such a process is possible to be observed microscopically because, as it has been stated above, the probability of observing a "reverse" trajectory depends on system size and is significant for molecular machines if an appropriate measurement instrument is available. This is the case with the development of new biophysical instruments such as the [[optical tweezers]] or the [[atomic force microscope]]. Crooks fluctuation theorem has been verified through RNA folding experiments.<ref>{{cite journal|last=Collin|first=D. |author2=Ritort, F. |author3=Jarzynski C. |author4=Smith, B. |author5=Tinoco Jr, I. |author6=Bustamante C. |title=Verification of Crooks fluctuation theorem and recovery of RNA folding free energies|journal=Nature|date=8 September 2005|volume=437|issue=7056|pages=231–4|doi=10.1038/nature04061|pmid=16148928|arxiv = cond-mat/0512266 |bibcode = 2005Natur.437..231C|pmc=1752236}}</ref>