RHIC — Stepping Back in Time

diagram of atomic structure

To understand why RHIC collisions are scientifically interesting it is important to know that all protons and neutrons, found in the nucleus of the atom, are made up of three quarks, along with the gluons that bind them.

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 built that takes us "back in time" to see how matter behaved at the start of the universe.

What researchers have discovered from the RHIC collisions was surprising -- the new state of hot, dense matter created out of the quarks and gluons was quite different than what had been predicted. Instead of behaving like a gas of free quarks and gluons, the matter appeared to be more like a “perfect” liquid with no resistance to flow. Scientists are now working to get a detailed understanding of the “quark-gluon plasma” produced at RHIC.

In 2005, RHIC physicists announced that the matter created in RHICs most energetic collisions behaves like a nearly perfect liquid in that it has extraordinarily low viscosity, or resistance to flow. Since then, the scientists have been taking a closer look at this remarkable form of matter, which last existed some 13 billion years ago, a mere fraction of a second after the Big Bang. Scientists have revelaed new findings, including the first measurement of temperature very early in the collision events, and their implications for the nature of this early-universe matter.

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