Generally, if there’s some amount of particles in a container, and force is applied to the container, then the bonds between the particles become weaker and weaker until the structure of the container gives way. This reaction is not universally true though. Much in the same way that a clinch knot gets tighter as more strain is applied to it, the wild and crazy physics of our universe allow a similar effect to occur with particles; certain shapes of particles can cause their accumulation to actually gain stiffness as force is applied. It’s strange, I know, and I don’t fully understand it, but graduate student Marc Miskin and the William J. Friedman & Alicia Townsend Professor in Physics, Heinrich Jaeger, have a pretty good grasp of the concept.
It’s called jamming, and researchers at the physics lab of the University of Chicago are utilizing modern technology to study the phenomenon. Miskin and Jaeger first developed a computer program that starts with a certain shape, like a sphere, and runs it through a jamming simulation to test its response; then the program creates iterations of the shape in a process called “evolutionary optimization,” running every variation of the shape through the simulation. Finally, the program outputs the shapes that were calculated to have the most desirable jamming response, like stiffness. To test the program’s predictions, the researchers 3D printed the shapes and physically tested them with a precise force meter. Not surprisingly, the program output shapes that do indeed gain stiffness under pressure, and the shapes were not ones that physicists would have come up with on their own, as they’re quite asymmetrical. This is easier to understand with the video: