Abstract:
The possibility that experiments at high-energy accelerators could create new forms of matter that would ultimately destroy the Earth has been considered several times in the past quarter century. One consequence of the earliest of these disaster scenarios was that the authors of a 1993 article in "Physics Today" who reviewed the experiments that had been carried out at the Bevalac at Lawrence Berkeley Laboratory were placed on the FBI's Unabomber watch list. Later, concerns that experiments at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory might create mini black holes or nuggets of stable strange quark matter resulted in a flurry of articles in the popular press. I discuss this history, as well as Richard A. Posner's provocative analysis and recommendations on how to deal with such scientific risks. I conclude that better communication between scientists and nonscientists would serve to assuage unreasonable fears and focus attention on truly serious potential threats to humankind.

Abstract:
Substantial collective flow is observed in collisions between large nuclei at high energy, as evidenced by single-particle transverse momentum distributions and by azimuthal correlations among the produced particles. The data are well-reproduced by perfect fluid dynamics. In a separate development, calculation of the dimensionless ratio of shear viscosity eta to entropy density s by Kovtun, Son and Starinets within AdS/CFT yields eta/s = 1/4pi, and they conjectured that this is a lower bound for any physical system. It is shown that the transition from hadrons to quarks and gluons has behavior similar to helium, nitrogen, and water at and near their phase transitions in the ratio eta/s. Therefore it is possible that experimental measurements can pinpoint the location of this transition or rapid crossover in QCD via the viscosity to entropy ratio in addition to and independently of the equation of state.

Abstract:
Substantial collective flow is observed in collisions between large nuclei at high energy, and the data are well-reproduced by perfect fluid dynamics. In a separate development, calculation of the dimensionless ratio of shear viscosity $\eta$ to entropy density within AdS/CFT yields $\eta/s = 1/4\pi$, which has been conjectured to be a lower bound for any physical system. It is shown that the transition from hadrons to quarks and gluons has behavior similar to helium, nitrogen, and water at and near their phase transitions in the ratio $\eta/s$. Conversely, there are indications that the ratio of bulk viscosity $\zeta$ to entropy density may have a maximum in the vicinity of the phase transition. Therefore it is possible that experimental measurements can pinpoint the location of the transition or rapid crossover in QCD via the ratios $\eta/s$ and $\zeta/s$ in addition to and independently of the equation of state.

Abstract:
Five groups have made predictions involving the production of strange hadrons and entered them in a competition set up by Barbara Jacak, Xin-Nian Wang and myself in the spring of 1998 for the purpose of comparing to first year physics results from RHIC. These predictions are summarized and evaluated.

Abstract:
A QCD phase transition in the early universe could have left inhomogeneities in the baryon to photon ratio and in isospin that might have affected nucleosynthesis later on. At very high temperature QCD plasma can be described by perturbation theory because of asymptotic freedom, but a possible phase transition requires a nonperturbative approach like lattice gauge theory. Assuming that a first order transition did occur, a dynamical set of equations can be solved to evolve the universe through it and to quantify the scale of inhomogeneity. Unfortunately this scale appears to be too small by two orders of magnitude to affect nucleosynthesis.

Abstract:
Microscopic black holes explode with their temperature varying inversely as their mass. Such explosions would lead to the highest temperatures in the present universe, all the way to the Planck energy. The possibility that a quasi-stationary shell of hot matter surrounds these black holes has recently been proposed and studied with relativistic Boltzmann transport equations and with relativistic viscous fluid dynamics. For example, a black hole with a mass of 10$^{10}$ g has a Hawking temperature of 1 TeV, a Schwarszchild radius of 1.6$\times10^{-5}$ fm, a luminosity of 7$\times10^{27}$ erg/s, and has less than 8 minutes to live. It is an outstanding theoretical challenge to describe the conditions exterior to such microscopic black holes and a great challenge to finally detect them in the new millennium.

Abstract:
Enhancement of omega and antiomega baryon production in Pb+Pb collisions at a c.m. energy of 17 A GeV can be explained by the formation of many small disoriented chiral condensate regions. This explanation implies that neutral and charged kaons as well as pions must exhibit novel isospin fluctuations. We compute the distribution of the fraction of neutral pions and kaons from such regions. We then propose robust statistical observables that can be used to extract the novel fluctuations from background contributions in pion and kaon measurements at RHIC and LHC.

Abstract:
We estimate the probability that a hard nucleon-nucleon collision is able to nucleate a seed of quark--gluon plasma in the surrounding hot and dense hadronic matter formed during a central collision of two large nuclei at AGS energies. The probability of producing at least one such seed is on the order of 1-100\%. We investigate the influence of quark--gluon plasma formation on the observed multiplicity distribution and find that it may lead to noticable structure in the form of a bump or shoulder.

Abstract:
We consider the form of the chiral symmetry breaking piece of the effective potential in the linear sigma model. Surprisingly, it allows for a second local minimum at both zero and finite temperature. Even though chiral symmetry is not exact, and therefore is not restored in a true phase transition at finite temperature, this second minimum can nevertheless mimic many of the effects of a first order phase transition. We derive a lower limit on the height of the second minimum relative to the global minimum based on cosmological considerations; this limit is so weak as to be practically nonexistent. In high energy nuclear collisions, it may lead to observable effects in Bose-Einstein interferometry due to domain walls and to coherent pion emission.

Abstract:
We investigate the production of baryons and antibaryons in the central rapidity region of high energy nuclear collisions within the framework of the Skyrme model taking into account the effects of explicit chiral symmetry breaking. We argue that the formation of disordered chiral condensates may lead to enhanced baryon-antibaryon production at low transverse momentum.