Physicists in the U.S. have achieved the highest temperature ever reached in a lab — four trillion C — hot enough to melt protons and neutrons into a "soup."

A computer simulation of the quark-gluon soup created after a collision between two gold ions in the Relativistic Heavy Ion Collider. (Brookhaven National Laboratory) Scientists at the Brookhaven National Laboratory in New York smashed gold ions together at nearly the speed of light to create matter at that temperature.

The researchers are trying to recreate the conditions of the early universe, a fraction of a second after the big bang 13.7 billion years ago.

The experiments were performed in the Relativistic Heavy Ion Collider at Brookhaven, a circular particle accelerator 3.8 kilometres long buried four metres below ground.

Before the construction of the Large Hadron Collider at the French-Swiss border, RHIC was considered the most powerful particle accelerator in the world.

Physicists believe that a substance called a quark-gluon plasma, a "soup" of subatomic particles, filled the universe within its first few microseconds.

The collisions at Brookhaven recreated that substance for less than a billionth of a trillionth of a second. Its existence was recorded by the collider's four detectors.

Data from those detectors was used to determine that the quark-gluon plasma created was 250,000 times hotter than the core of the sun.

The data also showed that the plasma behaved not as a super-hot gas, but as a near "perfect" liquid, that is, a fluid of quarks and gluons that flows with no frictional resistance.

"By matching theoretical models of the expanding plasma to the data, we can determine that the initial temperature of the 'perfect' liquid has reached about four trillion degrees Celsius," said Barbara Jacak of Stony Brook University in a statement.

The researchers are looking for irregularities in the plasma that might explain how matter formed out of the energy of the big bang.

In their research, reported this week in the journal Physical Review Letters, the researchers found that the normal interactions between the quarks and gluons broke down within "bubbles" inside the hot soup.

That break down of what physicists call "mirror symmetry" could point to a reason why matter predominated over anti-matter in the early universe.

This research into fundamental questions of physics also has practical applications. Researchers are hoping to apply the knowledge gains to the field of "spintronics," which could give rise to a new generation of more powerful solid-state computers and other devices.

RHIC physicists are planning upgrades to the collider's detectors and collaborations with research at the Large Hadron Collider to continue their research.