GENERATION OF DEFECTS IN SUPERFLUID HE-4 AS AN ANALOG OF THE FORMATION OF COSMIC STRINGS

ALTHOUGH the birth of the Universe is inaccessible to experimental stu dy, aspects of cosmological theories can nonetheless be explored in th e laboratory. Tiny inhomogeneities in the mix of particles and radiati on produced in the Big Bang grew into the clusters of galaxies that,ve see today, but how those inhomogeneities arose and grew is still uncl ear. Cosmologies based on grand unified theories suggest that a symmet ry-breaking phase transition occurred via the Higgs mechanism about 10 (-34) s after the Big Bang as the Universe cooled through a critical t emperature of 10(27) K. It has been proposed by Kibble(1) that this tr ansition may have generated defects in the geometry of space-time (suc h as cosmic strings), which provided the inhomogeneities on which gala xies subsequently condensed. Zurek(2-4) has suggested that it might be possible to model this cosmological phase transition by a laboratory analogue, the superfluid transition of liquid He-4 induced by fast adi abatic expansion through the critical density. Here we report the resu lts of such an experiment. We observe copious production of quantized vortices(5), the superfluid analogue of cosmic strings. These results support Kibble's contention that such defects were available in the ea rly Universe to seed galaxy formation.