Are there new states of matter at ultrahigh temperatures and densities?
The theory of how protons and neutrons form the atomic nuclei of the chemical elements is well developed. At extremely high densities and temperatures, protons and neutrons may “dissolve” into an undifferentiated “soup” of quarks and gluons, which can be probed in heavy-ion accelerators. Still higher densities occur and can be probed in neutron stars and the early universe. The Relativistic Heavy Ion Collider (RHIC) is in operation at the DOE’s Brookhaven National Laboratory to study of extremely hot, dense nuclear matter. It collides beams of gold nuclei at energies sufficient to form brief microcosms of the hot, dense soup of elementary particles (quarks and gluons) that previously existed only for the first microseconds after the Big Bang origin of our universe. The experimental data to date have revealed unexpected characteristics and provide the first tantalizing clues of possible quark-gluon plasma formation. Physicists around the world are interested in the RHIC collisions, whic
