26 July 2005
Big Bang Produced A "Perfect Fluid"
by Kate Melville
An unexpected discovery may see physicists heading back to the drawing board in order to update models representing the Universe immediately after the Big Bang. In an experiment not previously possible, physicists have created the state of matter thought to have filled the Universe just a few microseconds after the Big Bang. To their astonishment, physicists found that instead of a gas, the substance was more like a liquid. Understanding why it is a liquid should take physicists a step closer to explaining the earliest moments of our Universe.
The liquid is said to exhibit characteristics like nothing else physicists have observed before, and its collective movement is rather like the way a school of fish swims "as one". In fact, physicists' tentative calculations suggest that its extraordinarily low viscosity makes it the most perfect fluid ever created.
The new state of matter was forged in the Relativistic Heavy Ion Collider, situated at the Brookhaven National Laboratory. Colliding the central cores of gold atoms together, head-on at almost the speed of light, the researchers created a fleeting, microscopic version of the Universe a few microseconds after the Big Bang. This included achieving a temperature of several million million degrees (about 150,000 times the temperature at the center of the Sun). They then detected and analyzed the explosive rush of particles that this miniature Big Bang created. Researchers had confidently believed that they would observe something like "steam", made up of free quarks and gluons, but instead the researchers saw evidence of collective movement as the hot matter flowed out of the collision site. This indicated stronger interactions between the particles than expected, leading to the belief that the quark-gluon plasma is similar to a liquid.
This latest development is much more unusual than anyone expected. "No one predicted that it would be a liquid," said Professor John Nelson from the University of Birmingham, who heads the British involvement in the multinational experiment. "This aspect was totally unexpected and will lead to new scientific research regarding the properties of matter at extremes of temperature and density, previously inaccessible in a laboratory."
The liquid defies physicists' current understanding of how matter in the universe behaved microseconds after the Big Bang. According to previous models there should be no evidence of matter - as we know it - in existence mere microseconds after the big bang, because the extreme temperatures generated would have been far to high for any matter to exist. There is a suggestion that certain versions of string theory may be able to explain the liquid behavior of the quark-gluon plasma. Professor Nelson expects that progress will be made during the forthcoming Quark Matter 2005 conference in Budapest. "Although these findings did not fit with expectations, the theories are slowly coming into line. Hearing the theoretical developments is going to be the high point of the conference," said Nelson.
Pic courtesy of Brookhaven National Laboratory