[Hermit: Notice that the emphasis and details of the source article are completely different from that presented by the BBC, despite this presumably being their source. The primary trouble I had with the BBC article was that the hype of their headline appeared to be completely inappropriate. The source article - still missing most of the information required to validate it - is announcing the alleged experimental validation of a well understood theoretical effect which modifies the applicability of the Second Law of Thermodynamics to nanoscale designs and presents some theoretical challenges to nanoscale engineering. It should be further noted that empirical evidence of this effect has previously been observed, the experiment is presumably significant due to the fact that it should have removed the influence of other potential sources of similar effects to that which would be demonstrated by the fluctuation theorem.]
Tiny details may affect nanomachine operation
Source: http://www.anu.edu.au/reporter/volume/32/17/conferences/nanomachine.html
Authors: David Salt (Communication Officer, Centre for Science and Engineering of Materials)
There is a lot of talk on how nanotechnology will soon be allowing us to build a wonderful array of nanomachines, from micron-sized motors to nanoscale train sets made from Teflon and cow’s brains.
But ground-breaking theoretical work led by Professor Denis Evans from the Research School of Chemistry shows that the very scale at which nanomachines operate will place limits on the work they’re capable of performing.
At a recent materials seminar run by the Centre for Science and Engineering of Materials, Prof. Evans demonstrated that things work quite differently at very small scales of time and space.
For example, as machines are made ever smaller, the probability that they will run in the reverse direction becomes ever greater until at a certain point, a machine is just as likely to run forwards as backwards.
This revelation arises from the work of Prof. Evans to resolve the paradox between the Second Law of Thermodynamics, which says that the disorder of the Universe can only increase in time, and the equations of classical and quantum mechanics, which are time reversible.
The solution was arrived at several years ago in the form of the Fluctuation Theorem. The Theorem states that the probability of the Second Law of Thermodynamics being violated decreases exponentially as the size of the system and/or the duration of the violation increases.
Therefore at human scales, the Second Law always applies and machines only ever run in one direction. However, when working at the nanoscale over extremely short periods of time, things can work in either direction.
As a result, nano-engines can either consume fuel to produce work, heat and waste or they can consume work, heat and waste to produce fuel. As the size of the engine gets smaller, the probabilities that the engine will run forwards or backwards become more nearly equal.
The full consequences of this are only just starting to be understood, but one practical outcome is that the Theorem sets a fundamental limit to the work available from nanomachines.
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