Traveling at 99.95% the
speed of light, the ions appear flat, instead of spherical, due to
the relativistic effects which occur at such speeds. In the second
image, the two ions collide, smashing into one another and then
passing through each other. Some of the energy they had before the
collision is transformed into intense heat and new particles.
If conditions are right, the collision "melts" the
protons and neutrons and, for a brief instant, liberates the
quarks and gluons (third image). Just after the collision,
thousands more particles form as the area cools off (fourth
image). Each of these particles provides a clue as to what occurred
inside the collision zone. Physicists will sift through those
clues for interesting information.
To understand why RHIC collisions are scientifically
interesting, it is important to know that scientists believe that
all protons and neutrons are made up of three quarks, along with
the gluons that bind them together. Theory
holds that for a brief time at the beginning of the universe there
were no protons and neutrons, only free quarks and gluons.
However, as the universe expanded and cooled, the quarks and
gluons bound together and, for the next 13 billion years, remained
virtually inseparable. RHIC is the first instrument humans have
built that can take us "back in time" to see how matter
behaved at the start of the universe.
Physicists around the world are interested in RHIC collisions.
The information found at RHIC can be applied in nuclear physics
(the study of the atom), particle physics (the study of the atom's
parts), astrophysics (the study of stars and planets), condensed
matter physics (the science of solid matter) and cosmology (the
study of the universe).
RHIC collisions occur thousands of times per second. Each
one acts as a microscopic pressure cooker, producing
temperatures and pressures more extreme than exist now even in the
cores of the hottest stars. In fact, the temperature inside a RHIC
collision can exceed 1,000,000,000,000 degrees above absolute
zero -- about ten thousand times the temperature of the sun.
But since the heavy ions in RHIC collisions are so small (see
physics primer), the actual impact of the speeding ions on each
other is about the same as the impact of a mosquito hitting a
screen door on a summer evening. And, RHIC collisions last only a
few billionths of a second.
In other words, RHIC collisions may be super-fast and
super-hot, which makes them interesting to physicists, but they're
too small and too brief to be dangerous.
On
to the quark-gluon plasma >