Kadanoff Prize: Many More is Different

In 1972 Phil Andersen articulated the motto of condensed matter physics as "More is different." However, for most condensed matter systems many more is quite similar to more--the behavior of a thousand Ising spins is nearly the same as that of a mole of them. Here I argue for a class of condensed matter, "adaptable matter," where the constituents have individually adjustable effective interactions, enabling the emergent collective behavior of many more to be very different from that of more. Such systems extend far beyond the long-recognized example of the brain, whose cognitive capabilities increase as size increases from 302 neurons (C. Elegans) to a million neurons (honeybees) to 100 billion neurons (humans). I propose that individually adjustable effective interactions are important for understanding the emergence of biological function in many cases, and that it is useful to develop a unifying conceptual framework to understand adaptable many-body systems ranging from physical systems capable of being trained to develop special collective behaviors to living systems to digital neural networks.