Hot stuff

It was the ultimate phase change. Two particle smashers are homing in on what caused the seething primordial soup of the early universe to evolve into the protons and neutrons that make up ordinary matter today. In the process one has set a new record: the hottest temperature ever created by humans.

Microseconds after the big bang, the hot universe consisted of a kind of soup in which quarks roamed free instead of being bound together in atoms as they are today. This almost frictionless quark-gluon plasma has been recreated at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, New York, by smashing gold ions together. Their plasma reached 4 trillion °C.

Now a team at the Large Hadron Collider at CERN, which smashes lead ions together, have made a plasma almost 40 per cent hotter. At the Quark Matter 2012 conference in Washington DC on 13 August, they reported that their quark-gluon plasma had reached over 5 trillion °C, the hottest temperature ever created in an experiment.


Boundary emerging

“In this field records are made to be broken,” says Jurgen Schukraft at CERN, near Geneva, Switzerland. The first hint of a record came in November 2010, when the LHC first collided lead ions, but it took two years to actually measure it, Schukraft says.

The RHIC researchers aren’t out of the game, though. What they really want to know is at what energies the quark-gluon plasma switches to normal matter.

At the Quark Matter conference, RHIC’s Steven Vigdor described how his team systematically varied the energy to create primordial plasma under a broad range of conditions.

He says initial measurements are delineating a boundary between ordinary matter and primordial stuff. “We are looking further back into the universe than ever before,” says Vigdor.