Scientists have cooled molecules of gas almost to the coldest temperature possible – absolute zero – and discovered something weird begins to happen.

Physicists at Massachusetts Institute of Technology used lasers to chill molecules of sodium potassium gas to a temperature of just 500 nanokelvins.

This is just a tiny fraction above absolute zero, the theoretical temperature at which all matter ceases to vibrate and the coldest possible.

Researchers at MIT used lasers and other cooling techniques to chill molecules of sodium potassium gas (shown in the illustration above) to a temperature of just 500 nanokelvins. At this temperature the movement of the molecule slowed so it moved centimetres each second - making it easier for scientists to stuy

Absolute zero is currently estimated to be -273.15°C (-459.67°F). It is thought to exist because heat is caused by the vibration of particles, so once they stop vibrating no more heat exists.

But the new research by scientists at MIT suggests ultracold molecules may start to form exotic states of matter as they get closer to absolute zero.

WHAT IS ABSOLUTE ZERO Absolute zero is a theoretical temperature at which all motion stop. Heat is the product of tiny atomic vibrations within a molecule - the hotter something is the more it moves around. When all of the enthalpy and entropy of an ideal gas reaches its minimum value - that is deemed to be absolute zero. However, at absolute zero not all motion is thought to stop as sub-atomic particles still move on the quantum level. According to international concusses, absolute zero is currently thought to occur at -273.15°C (-459.67°F). Measurements from cosmic background radiation have suggested the average temperature of the universe is approximately 2.73 kelvins (−270.42 °C; −454.76 °F). Advertisement

They found the ultracold molecules were stable and resisted collision with other molecules despite also having strong electric charges that should have acted like magnets pulling the molecules together.

Professor Martin Zwierlein, principal investigator at MIT’s Research Laboratory of Electronics who led the research, said: ‘We are very close to the temperature at which quantum mechanics plays a big role in the motion of molecules.

‘So these molecules would no longer run around like billiard balls, but move as quantum mechanical matter waves.

‘And with ultracold molecules, you can get a huge variety of different states of matter, like superfluid crystals, which are crystalline, yet feel no friction, which is totally bizarre.

‘This has not been observed so far, but predicted. We might not be far from seeing these effects, so we’re all excited.’

The researchers, whose study is published in the journal Physical Review Letters, used lasers and evaporative cooling to chill clouds of sodium and potassium atoms.

They then applied a magnetic field to prompt the atoms to bond together.

Ultracold molecules experience strong interactions over large distances in the presence of an electric field. The field polarizes the molecules, inducing a dipole moment (shown by the arrow in the illustration above). The MIT found their ultracold molecules had strong dipoles yet were remarkably stable and unreactive

These were then exposed to a pair of lasers – one with a frequency that matched the vibrating state of the molecule and the other with a lowest possible vibrational rate.

Using this superchilled method, the researchers were able to strip away 7,500 kelvins.

The kelvin temperature scale uses absolute zero as its starting point, meaning the boiling point of water, 100°C, is 373.15 kelvin.

Unlike in other experiments which have attempted to cool gas atoms, the scientists found their molecules had a relatively long lifetime of about 2.5 seconds.

Professor Zwierlein said: ‘In the case where molecules are chemically reactive, one simply doesn’t have time to study them in bulk samples.

‘They decay away before they can be cooled further to observe interesting states.

‘In our case, we hope our lifetime is long enough to see these novel states of matter.

‘Now we’re at 500 nanokelvins. A factor of 10 colder or so, and the music starts playing.’

However, their experiment is not the coldest temperature ever achieved in an experiment. In 2003 researchers at MIT and Nasa managed to cool sodium gas to a temperature of just 500 picokelvin, or 0.5 nanokelvin.