A Traffic Control System For Molecules

Roland Piquepaille writes "Our cells contain small protein factories which have to deliver materials inside the cell via a network of microtubules. And the transportation is carried out by biomolecular motors. Now, researchers from Delft University of Technology in the Netherlands have built a traffic control system able to force individual molecules to choose between 'roads' by applying strong electrical fields locally at Y-junctions. This traffic control system can potentially lead to new nano-fabrication techniques. Read more for additional references and pictures showing how this traffic system works."

Re:Maxwell's Demon now a possibility?

[wsherman]

Broadly speaking, the Fluctuation Theorem [wikipedia.org] makes it unlikely that you can get more energy out of the sorting than you will have to expend to accomplish the sorting. To put it another way, any sorting process that is not driven by an external energy input will be just as likely to run in reverse. In the classic Maxwell's demon example, a sorting process that can put hot molecules in a specific place will be just as likely to run in reverse and remove hot molecules from that place.

It is interesting to note that the Fluctuation Theorem depends on microscopic reversability (time symmetry of interactions at the atomic level). On the scale that we humans experience things (the macroscopic level), our experience of time is closely correlated with increases in entropy: a person can look at a movie of a drop of ink dissolving in a glass of water and know whether or not the movie is being played in reverse. Essentially, time asymmetry at the macroscopic level (ie. the human scale) depends on time symmetry at the microscopic (atomic) level.

Getting into the realm of very wild and crazy speculation, for classical Newtonian mechanics (charged particles in non-relativistic electric fields), time symmetry holds even when the system experiences external forces (static electric fields). Once we add relativity, however, we get magnetism (magnetism is relativistic contraction of electric fields) and time symmetry does not hold for a system (of charged particles) experiencing an external (static) magnetic field.

To the extent that the Second Law of Thermodynamics still holds in external magnetic fields then it may be possible to prove a version of the Fluctuation Theorem that depends on an even weaker assumption than microscopic reversability. On the other hand, magnetic fields induce spontaneous currents (ordered atomic motion) in diamagnetic materials (superconductors, bismuth, water, etc.) and if it was ever possible to tap into these currents (or any aspect of the ordered atomic motion) then that would show that the Second Law doesn't hold under relativistic conditions (ie. external magnetic fields).