  The quantum tunnelling and nucleation theory of vortices in helium II is
reviewed. Arguments are given that the only reliable method to calculate
tunnelling probabilities in this highly correlated, strongly interacting
many-body system is the semiclassical, large scale approach for evaluation of
the tunnelling exponent, which does not make any assumptions about the unknown
dynamical behaviour of the fluid on microscopic scales. The geometric
implications of this semiclassical theory are represented in some detail and
its relevance for the interpretation of experimental data is discussed.
