Supercomputers can simulate the types of fluctuations you would expect for the wide range of temperatures and densities at RHIC. They start by mathematically modeling all the possible interactions of subatomic quarks and gluons as governed by the theory of Quantum Chromodynamics, or QCD, which includes variables such as temperature and density in the equations. Because the number of values for these and many other variables in the equations of QCD is very large, only supercomputers can handle the complex calculations. To simplify the problem, the computers look at interactions of quarks and gluons placed at discreet points on an imaginary four-dimensional “lattice” that accounts for three spatial dimensions plus time. The lattice consists of about 300,000 grid points, and on each point the values of 48 variables need to be adjusted to characterize a specific configuration of the interacting quarks and gluons. Supercomputers use Monte Carlo sampling—more or less trying random numbers, like rolling a pair of dice—to find the most probable configuration of these values.
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