Wiggling carbon nanotube bugs evolve

The second law of thermodynamics tells us that a closed system will  always move towards thermodynamic equilibrium, a state of maximum  "disorder" or entropy. But, there is some wiggle room, according to US research.

Alexey Bezryadin and colleagues at the University of Illinois have  demonstrated that the emergence of apparent order in self-organized  structures, actually drives a non-equilibrium system to maximum entropy production. As the maximum is achieved, the phase characterized by re-occurring avalanches gives way to a much more stable phase without avalanches or extinction events. The finding has implications for how the archetype of self-organizing systems, living things, may have emerged and evolved [A. Belkin, A. Hubler and A. Bezryadin, 2015 Scientific Reports; DOI: 10.1038/srep08323]

To demonstrate the principle at the fundamental level, the Illinois team suspended carbon nanotubes in a non-conducting non-polar fluid and pushed the system away from equilibrium using a strong electric field. The system then reconvened to a maximal entropy through two distinct intermediate stages, with spontaneous formation of self-assembled conducting nanotube chains along the way. Of course, the maximum entropy cannot be achieved in this experiment since it would correspond to a complete discharge of the battery running the experiment.

In the first stage, conductive chains align themselves according to the polarity of the applied field. This allows the system to carry a current and so lose energy through resistive heating and so produce entropy. But, the nanotubes also sprout appendages connecting them, again increasing entropy production. Excessive heat causes destructive cascades or "avalanches" that tear them apart, but the appendages sometimes retract before this happens and regrow once the energy is shed. "The avalanches were apparent in the changes of the electric current over time," explains Bezryadin.

In the second intermediate there are no destructive avalanches and the system is much more stable hinting at how a system might evolve past a critical point, all the while generating entropy. This stable phase occurs after the systems evolves to the point that it is able to consume and convert into heat the maximum possible power provided by the battery and limited by a fixed resistor. Interestingly, such a tendency to approach the maximum power consumption and the subsequent stabilization of the system resembles a philosophical concept the so-called "Dyson sphere" Such a sphere might be constructed by a technologically advanced civilization in order to consume all power supplied by the sun.

The team now needs to scale-up its systems to confirm that the principle holds more widely and to show that their self-organizing and self-connecting nanotube systems could somehow self-replicate. Self-replication can be expected on general grounds, since it would allow the system to further increase the entropy production. "The general trend of the evolution of biological systems seems to be this: more advanced life forms tend to dissipate more energy by broadening their access to various forms of stored energy," Bezryadin explains. "Thus a common underlying principle can be suggested between our self-organized clouds of nanotubes, which generate more and more heat by reducing their electrical resistance and thus allow more current to flow, and the biological systems which look for new means to find food, either through biological adaptation or by inventing more technologies."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".