NASHVILLE, Tenn. – Research reported April 20 at a meeting of the
American Physical Society reveals that the early universe may have
behaved like a liquid in the first few microseconds after the Big Bang.
Physicists from Vanderbilt University were part of a prestigious
international team that made the surprising findings. The experiments
were done using the Relativistic Heavy Ion Collider (RHIC, pronounced
“Rick”) at the U.S. Department of Energy‘s Brookhaven National
Laboratory in Upton, N.Y.
“We have been trying to produce a new state of matter, a soup of
subatomic particles called quarks and gluons. The universe could have
existed in this state just microseconds after the Big Bang,” Vicki
Greene, Vanderbilt University associate professor of physics and chair
of an internal committee that reviewed the paper for one of the
experiments, said. “These new results may mean that the very early
universe was a nearly perfect liquid.”
Greene and her Vanderbilt colleagues, Professor of Physics Charles
Maguire and Assistant Professor of Physics Julia Velkovska, use the
PHENIX detector at RHIC. RHIC operates by accelerating two beams of
heavy ions, such as gold nuclei, to nearly the speed of light in
opposite directions around a ring 2.4 miles in circumference. At four
different places around the collider‘s path, the two beams are brought
together so that the ions will crash into one another. At each of these
“interaction points,” different teams of scientists have designed and
built elaborate detectors that track the showers of subatomic particles
that are produced in these collisions.
PHENIX is the largest of the four instruments that make up RHIC. It
weighs 2,000 tons, is 40 feet wide and four stories tall. By analyzing
the information produced by PHENIX, the Vanderbilt physicists and their
colleagues have been able to bring the nuclei of the gold atoms
together at such force that their energy briefly generated
trillion-degree temperatures, temperatures that are 300 times that of
the solar surface and that last existed at the birth of the universe.
The results from PHENIX and the other experiments over the past three
years were compiled into four papers, which have been accepted for
publication in the journal Nuclear Physics A.
In the papers, the researchers report that quarks and gluons –
subatomic particles which are usually only found bound into larger
particles like protons and neutrons – behaved like a liquid at the
extreme temperatures produced in the experiments. The findings are
contrary to expectations that the particles would produce a gas.
Unlike ordinary liquids in which individual molecules move about
randomly, the hot matter formed at RHIC seems to move in a pattern that
exhibits a high degree of coordination among the particles – somewhat
like a school of fish that responds as one entity while moving through
a changing environment.
“This is fluid motion that is nearly ‘perfect,‘” Sam Aronson,
Brookhaven‘s associate laboratory director for high energy and nuclear
physics, said. By “perfect,” Aronson means that the fluid has extremely
low viscosity and the ability to reach thermal equilibrium very rapidly
due to the high degree of interaction among the particles.
“The finding of a nearly perfect liquid in a laboratory experiment
recreating the conditions believed to have existed a few microseconds
after the birth of the universe is truly astonishing,” Praveen
Chaudhari, director of Brookhaven Laboratory, said. “The four RHIC
collaborations are now collecting and analyzing very large new data
sets from the fourth and fifth years of operation, and I expect more
exciting and intriguing revelations in the near future.”
One area that has captured the attention of physicists is the potential
that these results have to validate string theory, which approaches
fundamental physics using 10 dimensions rather than the usual three
spatial dimensions plus time.
“The possibility of a connection between string theory and RHIC
collisions is unexpected and exhilarating,” Raymond Orbach, director of
the DOE Office of Science, said. “String theory seeks to unify the two
great intellectual achievements of 20th century physics, general
relativity and quantum mechanics, and it may well have a profound
impact on the physics of the 21st century.”
For Greene and her colleagues, the findings are just one step – though
a very large one – along the path to understanding matter at both the
smallest and the largest scales.
“These findings give us a picture of how matter behaves when it is
heated to unimaginable extremes, a picture that we didn‘t have before,”
Greene said. “We will now have to take this information and try to fit
it into the picture of the early universe. Until we do that, we don‘t
know what we‘ll find. It really is an exploration.”
The Vanderbilt researchers‘ work at RHIC is supported by funding from the Department of Energy.
Media contact: Melanie Catania, (615) 322-NEWS
melanie.moran@vanderbilt.edu