Scientists create hottest substance on Earth

Events recorded by the ALICE experiment from the first lead ion collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair. (CERN LHC Alice Detector)

Scientists using the world's largest atom smasher have made some of the hottest and densest matter ever achieved on Earth.

The state of matter called a quark gluon plasma existed in the milliseconds after the big bang 13.7 billion years ago.

Physicists using the Large Hadron Collider (LHC) at CERN, the European Centre for Nuclear Research, smashed heavy lead ions together at close to the speed of light.

They generated temperatures of more than 1.6 trillion degrees Celsius, 100,000 times hotter than the centre of the Sun.

In the process they recreated the densest material ever observed - only black holes are denser.

The results - released at the Quark Matter Conference recently held in Annecy, France - allows scientists to understand the evolution of the early universe recreating the conditions that existed back then.

One of the fundamental building blocks of matter, called quarks, are bound together by gluons to form 'composite' subatomic particles such as protons and neutrons.

But in its infancy, just microseconds after the Big Bang, the universe was so hot and dense these quarks and gluons existed freely and unbound.

The new results confirm that quark gluon plasma acts almost like a fluid, with minimal viscosity.

The results are based on analysis of data collected during the last two weeks of the 2010 LHC run, when the atom smasher switched from colliding hydrogen protons to lead-ions.

The LHC heavy-ion program builds on experiments conducted more than a decade earlier at CERN's Super Proton Synchrotron accelerator, which saw hints that a quark gluon plasma could be created and studied in the laboratory.

Then, in 1999, the US Brookhaven National Laboratory's Relativistic Heavy-Ion Collider established that a quark gluon plasma could be created on a miniscule scale.

Professor Geoffrey Taylor, from the University of Melbourne and part of the scientific team involved with the Large Hadron Collider's Atlas Detector, describes the work as an amazing achievement.

"This state of matter doesn't exist anywhere naturally on Earth and is thought to only now occur during the collision of two neutron stars," he said.

"This will help our understanding of the dynamics of the astrophysical processes taking place as a star collapses.

"Looking at how particle jets and subatomic particles like W and Z bosons are created in heavy lead ion collisions compared to lighter hydrogen proton collisions gives us an insight into the conditions that existed in a quark gluon plasma when the universe was just milliseconds old."

Professor Taylor says the results were accomplished in just two weeks of atom smashing.

"These collisions are also generating antimatter, which will help us try to understand why we live in a stable universe of matter when equal amounts of matter and antimatter were created in the big bang," he said.

"It takes our understanding of things that are happening in the cosmos one step further."

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