  We discuss speculative disaster scenarios inspired by hypothetical new
fundamental processes that might occur in high energy relativistic heavy ion
collisions. We estimate the parameters relevant to black hole production; we
find that they are absurdly small. We show that other accelerator and
(especially) cosmic ray environments have already provided far more auspicious
opportunities for transition to a new vacuum state, so that existing
observations provide stringent bounds. We discuss in most detail the
possibility of producing a dangerous strangelet. We argue that four separate
requirements are necessary for this to occur: existence of large stable
strangelets, metastability of intermediate size strangelets, negative charge
for strangelets along the stability line, and production of intermediate size
strangelets in the heavy ion environment. We discuss both theoretical and
experimental reasons why each of these appears unlikely; in particular, we know
of no plausible suggestion for why the third or especially the fourth might be
true. Given minimal physical assumptions the continued existence of the Moon,
in the form we know it, despite billions of years of cosmic ray exposure,
provides powerful empirical evidence against the possibility of dangerous
strangelet production.
