Time, chaos, and memory: From physical objects to living beings

There are at least two sorts of memory devices: those which insert the trace to be memorized into their substrates by breaking existing symmetries, and those which infuse some hidden order into a randomly disorganized substrate. The latter kind is the more interesting from the point of view of time processes. Clearly, the memory of the cosmological history of the universe is quite an appropriate physical example. But in living beings, examples of "holographic" orders may also abound. With the living brain, evolution has given an example of a particularly complex system, whose structure is well adapted to store huge quantities of information. We suspect that memory traces in the brain involve subtle waves of modification of synaptic efficacies over the myriads of synapses scattered over the hundred of billions of neurons the skull shelters. Beyond the limits of the scientific certainties of the day, we can suspect that permanent memory traces consist of metabolic modifications of tiny neuron appendices, called spines, and that the retrieval of a memorized episode consists in reactivating in a holographic mode huge collections of such spines, scattered over the neocortex. Deciphering the mechanisms of such reactivation, however, would imply discovering their "implication parameter," whose kinship with time makes little doubt, but which may differ from time in important aspects.