Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) demonstrated how particles, floating on top of a glycerin-water solution, synchronize in response to acoustic waves blasted from a computer speaker.

The study, published today in the journal Nature Materials, could help address fundamental questions about energy dissipation and how it allows living and nonliving systems to adapt to their environment when they are out of thermodynamic equilibrium.

“Dynamic self-assembly under non-equilibrium is not only important in physics, but also in our living world. However, the underlying principles governing this are only partially understood. This work provides a simple yet elegant platform to study and understand this kind of phenomena.

To hear some physicists describe it, this state of non-equilibrium, characterized by the ability to constantly change and evolve, is the essence of life. It applies to biological systems, from cells to ecosystems, as well as to certain nonbiological systems, such as weather or climate patterns. Studying non-equilibrium systems gets theorists a bit closer to understanding how life —particularly intelligent life—emerges.

However, it is complicated and hard to study because non-equilibrium systems are open systems.

Physicists believe individually ‘dumb’ particles can self-organize far from equilibrium by dissipating energy and emerge with a collective trait that is dynamically adaptive to and reflective of their environment. In testing, the particles followed the ‘beat’ of a sound wave generated from a computer speaker.”

Notably, after the researchers intentionally broke up the particle party, the pieces would reassemble, showing a capacity to self-heal.

Research like this could eventually lead to a wide variety of “smart” applications, like adaptive camouflage that responds to sound and light waves, or materials whose properties are written on demand by externally controlled drives.

While previous studies have shown that particles are capable of self-assembly in response to an external force, recent research presents a general framework that researchers can use to study the mechanisms of adaptation in non- equilibrium systems.

Physicists can now predict what happens and how the particles will behave.

In an experiment, the sound waves traveled at a frequency of 4 kilohertz, the scattering particles moved along at about 1 centimeter per minute. Within 10 minutes, the collective pattern of the particles emerged, where the distance between the particles was surprisingly non-uniform. The researchers found that the self-assembled particles exhibited a phononic bandgap – a frequency range in which acoustic waves cannot pass – whose edge was inextricably linked, or “enslaved,” to the 4 kHz input.

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This was a characteristic that was not present with the individual particles. It only appeared when the particles collectively organized.

The experimental design could hardly have been simpler. For the waveguide, the researchers used a 2-meter-long acrylic tube that contained a 5- millimeter-deep pool of a glycerin-water solution. The particles were made from straws floating on top of a flat piece of plastic, and the sound source came from off-the-shelf computer speakers that researchers directed into the tube via a plastic funnel. Measuring the sound waves proved to be the most technical part of the experiment.

This experiment can be replicated by anyone using parts that are available at your local hardware store.

The experiment focused on acoustic waves because soundproofing was easier to achieve, but the principles underlying the behavior they observed would be applicable to any wave system.

For better or for worse, this fundamental research could form the basis for developing intelligent networks that perform simple non-algorithmic computation, with a future toward systems that perform sentient-like decision making.