HOW CAN WE USE LOW-TEMPERATURE SYSTEMS TO SHED LIGHT ON QUESTIONS OF MORE GENERAL INTEREST

Low temperature physics is, almost by definition, that physical regime in which the complicating effects of the noise which is ubiquitous at room temperature has disappeared. How can we exploit this fact to ans wer questions of more general interest? In the first place, we can att empt to test same basic notions of quantum mechanics, e.g. the applica bility of the theory to ''macroscopic'' collective variables, or the i dea that ''relative phase'' is not defined until it is measured. Secon dly, we can use the strongly cooperative tendency of many low-temperat ure systems, in, particular those subject to some form of Bose condens ation, to amplify small effects which may be unobservable, or very dif ficult to observe, at the level of a single particle. Thirdly, we can, use low-temperature systems, which often have an extreme degree of pu rity and freedom from pre-existing defects, to test general notions ab out e.g. the mechanism of first-order phase transitions. I will discus s these and other possibilities, with particular emphasis on experimen ts in superfluid He-3-B and the BEC alkali gases which have either rec ently been done or may be possible in the future.