Topological defects such as cosmic strings may have been formed at
early-universe phase transitions. Direct tests of this idea are impossible, but
the mechanism can be elucidated by studying analogous processes in
low-temperature condensed-matter systems. Experiments on vortex formation in
superfluid helium and in superconductors have so far yielded somewhat confusing
results. I shall discuss their possible interpretation.Comment: 10 pages. Text of an invited lecture, to be published in Proceedings
of the Second European Conference on Vortex Matter in Superconductors, Crete,
15-25 September 2001. Uses elsart.cls style fil