In February 2010, scientists at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider on Long Island, New York, USA, announced that they had smashed together gold ions at nearly the speed of light, briefly forming an exotic state of matter known as a quark-gluon plasma.
This substance is believed to have filled the universe just a few microseconds after the Big Bang. During the experiments – which began in July 2001 and have taken a decade to authenticate – the plasma reached temperatures of around 4 trillionºC, some 250,000 times hotter than the centre of the Sun.

As of July 2012, even higher temperatures may have been achieved at Brookhaven, following the colliding of (heavier) uranium nuclei, but it will take a while to ascertain the temperatures reached; experiments using the Large Hadron Collider near Geneva, Switzerland, may have also achieved higher temperatures but are also yet to be determined.