Jul 25 2005
Physicists have created the state of matter thought to have filled the Universe just a few microseconds after the big bang and found it to be different from what they were expecting. Instead of a gas, it is more like a liquid. Understanding why it is a liquid should take physicists a step closer to explaining the earliest moments of our Universe.
When two gold nuclei collide in the RHIC particle accelerator, Brookhaven, they produce a cascade of new particles. Each line on these images shows the path of one of those particles. The STAR detector captured these traces. By analysing the type and quantity of the particles produced, along with the direction in which the particles moved, physicists revealed that a new state of matter had been produced.
Not just any old liquid, either. Its collective movement is rather like the way a school of fish swims ‘as one’ and is a sign that the fluid possesses an extremely low viscosity, making it what physicists call a perfect fluid. In fact, tentative calculations suggest its extraordinarily low viscosity makes it the most perfect fluid ever created.
Researchers had confidently believed it would be something like ‘steam’, consisting of free quarks and gluons. “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 STAR Collaboration, a multinational experiment. “This aspect was totally unexpected,” said Professor Nelson, “and will lead to new scientific research regarding the properties of matter at extremes of temperature and density, previously inaccessible in a laboratory.”
The Birmingham contingent is funded entirely by the Engineering and Physical Sciences Research Council (EPSRC).
The new state of matter was forged in the Relativistic Heavy Ion Collider (RHIC), situated at the Brookhaven National Laboratory, Long Island, New York. By 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 centre of the Sun). They then detected the rush of particles that this miniature ‘big bang’ created. That was when things started to take an unexpected turn.
Instead of the ‘every-particle-for-itself, free-for-all’ that is expected from a gas, the researchers saw evidence of collective movement as the hot matter, formed at RHIC, 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 behaving like a liquid.
This type of experiment furthers our understanding of what happened in the instants immediately following the Big Bang, leading to a better understanding of the earliest moments of the Universe. However, the unexpected nature of this new state of matter is leaving physicists wondering if the current theoretical models can support these surprising new experimental results.
http://www.epsrc.ac.uk/