This "movie" consists of just six frames. To advance to the next frame, click on the displayed frame. Most browsers will retain some or all of the frames locally after your first run through. Thereafter, you can rapidly play the "movie" either forwards or backwards using the forward and back buttons on your browser. You may want to try the "single-panel movie" (see below) if your setup does not work well with the full-sized version.
The six frames show the simulated time-evolution of a collision between two gold nuclei at intervals of 2 fm/c (or one six hundred thousandth, billionth, billionth of a second). The graphs are akin to the weather radar pictures that are shown on local TV news, except that the colors (which show the intensity of precipitation on TV) show the intensity at that point of the quantity indicated in the caption. The quantity Px is related to the nuclear pressure generated at that point; it is this pressure that drives a supernova explosion - a violent ejection of matter from a collapsing star.
The initial nuclei are spherical in shape. However, they are converging at about 99.7% of the speed of light (186,000 miles per second), and are contracted along their direction of motion in accordance with Einstein's Special Theory of Relativity.
The simulations are derived from the ARC (A Relativistic Cascade) model developed by Dr. Sid Kahana and collaborators at Brookhaven National Lab. In the Px plots, a different color scale is used for nucleons from the projectile and target.