Liquid Universe

The Universe consisted of a perfect liquid in its first moments, according to results from an atom-smashing experiment.

Scientists at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory on Long Island, New York, have spent five years searching for the quark-gluon plasma that is thought to have filled our Universe in the first microseconds of its existence. Most of them are now convinced they have found it. 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 particles took some moments to condense into ordinary matter after the intense 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. Previous experiments have shown that these collisions create something the size of an atomic nucleus that reaches 2 trillion degrees Celsius, about 150,000 times hotter than the centre of the Sun.

Now experiments have revealed that this hot blob is a liquid, which lives for just 10-23 seconds.

The surprising thing is that the interaction between the quarks and gluons is much stronger than people expected. The strength of this binding keeps the mixture liquefied despite its incredible temperature. It's as much a fluid as water in a glass.

The researchers worked out the liquid's structure by tracking the particles that spray out as the droplet falls apart and quarks team up to form normal matter. It's a very complicated thing says But it has been amazing at how simple the results are.

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 similar wherever astronomers look. If the primordial liquid had been as viscous as honey, the Universe could have turned out much more lumpy. It is certain this will change our picture of the early Universe.

The researchers now hope to measure the heat capacity, viscosity and even the speed of sound in the quark liquid. Further investigations will inevitably take years to complete.