What Kind of Fluid is a Quark-Gluon Plasma?

The hot soup of free quarks and gluons that existed in the very early universe, and a state of matter that physicists have been trying to re-create amid high-energy nuclear collisions, QGP is actually not a superfluid, as the original version of Update 681 erroneously suggested.

According to University of Washington physicist Laurence Yaffe (206-543-3902, lgy@phys.washington.edu), QGP is actually a normal, conducting fluid. It has viscosity, eliminating it from the list of superfluids. It is somewhat electrically resistive, precluding it from being a superconductor. Yaffe and coworkers recently performed calculations of several QGP fluid properties from first principles (P. Arnold, G. D. Moore and L. G. Yaffe, Journal of High Energy Physics, 17 June 2003 and 14 February 2003).

Still, observations of high-density quark matter produced thus far at Brookhaven's RHIC accelerator suggest that QGP might prove to be the most ideal regular fluid observed in nature, according to Ohio State nuclear theorist Ulrich Heinz (614-688-5363, heinz@mps.ohio-state.edu). The viscosity of the RHIC matter appears to be exceedingly low, and it redistributes its heat ("rethermalizes") extremely quickly. This near-ideal regular fluid behavior should greatly facilitate comparisons between theory and experimental observations of QGP, once its presence is confirmed at RHIC.