Perturbation of the evolution of a quantum system induced by its environment

We consider the effects of a massive homogeneous body on the state vector o f a molecule passing nearby. The interchange of virtual photons between bod y and molecule cause the latter to fail a proposed criterion of isolation e ven for molecules consisting of as little as 10(4) particles. The calculati on contains no free parameters but furnishes only a lower bound to the effe cts. The fact that matter consists of electrically charged particles is ess ential for a smooth transition from the quantum to the classical behavior a s the system grows larger. (C) 1999 Published by Elsevier Science B.V. All rights reserved.