Matter of Memory

Coordinators: Sidney Nagel

We are all familiar with the memories that are stored in the connections of neurons within our brains. Certain experiences are indelible even if experienced only once while others need many repetitions in order to be reliably recalled. We are likewise familiar with memories stored on a sheet of paper (by pencil marks) or with digitized information in a computer stored in the form of bits. Memories are stored in physical as well as biological matter.

Both in biology and in materials science, memory formation takes many forms. Not only do we remember facts and feelings but we are also able to remember how to do certain activities by constant and frequent repetition. It seems unlikely that we store such “muscle memory” in our brains in the same fashion that we store our home address or cell-phone number. In materials, we can read out information that has been stored in a digital fashion; magnets store information of the largest field to which they have been subjected. A less common example occurs in the aging and rejuvenation of glasses. A glass can remember its cooling history: it has a memory of the temperature at which the cooling was halted before it was cooled to much lower temperature. The memory is retrieved upon reheating.

Systems render information about their formation and training, information which is erased after they relax to equilibrium. In other words, a system that has not fully relaxed has the potential to retain memories of its creation. Out-of-equilibrium systems may form memories by falling into a recognizable set of states in a vast, rugged energy landscape. This Teachers’ Conference will look at what is common in these diverse systems, and will perhaps point the way forward for novel ways for information to be encoded in matter.