Cosmological experiments in liquid He: status and prospects

A recent experiment, in which a small volume of liquid ⁴He is expanded rapidly through the lambda transition to model the mechanism of cosmic string creation in the early universe, is reviewed. New data are presented, suggesting that, although most of the quantized vortices generated in the expansion are created (like cosmic strings) by passage through the phase transition at a finite speed, a proportion of them are probably produced through more conventional processes. Possible ways of redesigning the experiment, so as to reduce the latter extraneous vortex creation processes, are discussed.