www.nature.com/news/2005/050418/full/050418-5.html
RHIC/BN The Universe consisted of a perfect liquid in its first moments, accordin g to results from an atom-smashing experiment. Scientists at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven Na tional Laboratory on Long Island, New York, have spent five years search ing for the quark-gluon plasma that is thought to have filled our Univer se in the first microseconds of its existence. But, strangely, it seems to be a liquid rather than the expected hot gas. Quarks are the building blocks of protons and neutrons, and gluons carry the strong force that binds them together. It is thought that these part icles took some moments to condense into ordinary matter after the inten se heat of the Big Bang. To recreate this soup of unbound particles, the RHIC accelerates charged gold atoms close to the speed of light before smashing them together. Pr evious experiments have shown that these collisions create something the size of an atomic nucleus that reaches 2 trillion degrees Celsius, abou t 150,000 times hotter than the centre of the Sun. Dmitri Kharzeev Brookhaven National Laboratory "This stuff was last seen in the Universe 13 billion years ago," says Sam Aronson, a director of high energy research at Brookhaven. Now experiments have revealed that this hot blob is a liquid, which lives for just 10-23 seconds. "This was completely unexpected," says Wit Busz a of the Massachusetts Institute of Technology, one of the team of resea rchers who reported their discovery on 18 April at the American Physical Society conference in Tampa, Florida. Hot water "The surprising thing is that the interaction between the quarks and gluo ns is much stronger than people expected," says Dmitri Kharzeev, a theor etical physicist at Brookhaven. The strength of this binding keeps the m ixture liquefied despite its incredible temperature. "It's as much a flu id as the water in this glass," Kharzeev says, pointing to his drink. The researchers worked out the liquid's structure by tracking the particl es that spray out as the droplet falls apart and quarks team up to form normal matter.
The resulting liquid is almost 'perfect': it has a very low viscosity and is so uniform that it looks the same from any angle. This may help to explain why the deepest parts of the Universe seem simil ar wherever astronomers look, says Kharzeev. If the primordial liquid ha d been as viscous as honey, the Universe could have turned out much more lumpy, he explains. "We can be certain this will change our picture of the early Universe," he says. The researchers now hope to measure the heat capacity, viscosity and even the speed of sound in the quark liquid. But the RHIC has been hit by cu ts in the recent US budget, forcing it to reduce its operating time from 30 to 12 weeks next year. Further investigations will inevitably take y ears to complete, says Aronson.
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