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Curated by RSF Research Staff

Study Reveals Mysterious Equality with which Grains Pack

How do grains of sand or rice pack together – and how does this effect their mechanical properties and behavior? For example, when sand is packed together it behaves like a solid, whereas when it is loose, it behaves like a fluid.

These were the questions that Mathematician Sam Edwards pondered upon and subsequently set about solving through the development of a statistical mechanical framework to describe their physical properties and behavior. Analogous to the energy of an ensemble of atoms, where all states (of same energy) occur with equal probability, Edwards conjectured that any possible arrangement of the grains within a certain volume will occur with the same probability.

However, although this framework allowed researchers to better understand the physical properties of granular materials, the basic premise was never proved. Now for the first time a team of researchers, led by Stefano Martiniani and no stranger to modelling complex systems, have shown that Edwards conjecture holds true – but only under certain conditions. Utilizing numerical simulations of 64 soft spheres - to allow for compression - the team found that if the system is at the critical transition point between: being a system and acting coherently and being individual grains and acting separately, then the conjecture held. However, beyond this critical point, at higher densities, the conjecture fails.

This is another great example of how the behavior of complex systems follows the same patterns and dynamics across scales which can essentially be explained by a fundamental framework. It will be very interesting to see how these studies develop – which could have huge implications for unified physics.



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