Why is more different: the appearance of microscopic classical particles

Particles (electrons, atoms, molecules) in interaction with large ensembles of atoms, e.g. solids and surfaces, often display properties, which are unexpected, based on experimental and theoretical investigations of small ensembles. A frequently cited phrase has been coined by P.W. Anderson to focus on this problem: 'More is different'. Theoretical descriptions of the unexpected properties commonly use ad hoc assumptions, justified by referring to the vogue word 'emergence'. In this contribution some striking examples of behaviour changes are outlined with the transition from 'few' to 'more'. It is suggested that entanglement between the observable local system and unobservable continua of the environment (phonons, electron-hole pairs, gravitons) can contribute much to the understanding of the relationship between the behaviour of 'few' and 'more'. Solving the time dependent Schroedinger equation for coherent model worlds, comprising both the local system and the entangled continua of the environment, adsorbate motion at surfaces at low temperature is examined. In the time-dependent formalism the entanglement of the core movement of a gas atom to the high dimensional continuum of substrate environs leads to a qualitative behaviour as it is observed experimentally. The focus in the present article is the emergence of classical appearance of a local quantum system entangled with the excitations of the environment. The dynamical evolution of the quantum system is coherent and according to the time dependent Schroedinger equation. The environmental excitations can be phonons, tomonagons, gravitons, either observable or not observable in experiment.