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Absolute zero is a physical limit that will almost certainly remain beyond our grasp, although lately, physicists have been getting within a hair's breadth of that goal. What they've found is that in the ultimate cold, matter becomes truly bizarre.

Absolute zero: zero degrees on the Kelvin scale, or -273.15 °C is as cold as it gets. Nothing in nature gets this cold; the coldest known region of space, the Boomerang nebula in the constellation Centaurus, is a balmy one degree Kelvin.

It's a physical limit, theoretically impossible to reach. Attaining absolute zero would break the law of thermodynamics, which says that getting there would require an infinite amount of work. At absolute zero, there is no heat. All atomic motion ceases — atoms no longer move or vibrate; they have no thermal energy whatsoever.

Even getting close to the limit is problematic. Objects cooled to absolute zero must be kept as still as possible. Anything touching an object being cooled to absolute zero would pass on its thermal energy, so instead, physicists use lasers to trap the atoms and damp their movement to slow them down to near as near motionless as possible.

The technique – known as laser cooling – has taken atoms to within a few billionths of a degree of 273.15°C.

Nobel science

At this extreme cold, the quantum world takes over and some very strange and useful behaviour is observed.

For instance, certain materials may become superconductors, materials with zero electrical resistance and the ability to exclude their inner magnetic field. Superconducting magnets are used in particle accelerators and nuclear magnetic resonance (NMR) machines to image the brain, as well as in studies of the intrinsic properties of matter.

A number of institutions have recently formed with the common goal of taking atoms down to temperatures even closer to zero. And with good reason too: ultra-cold atoms have been the topic of two recent Nobel prizes in physics (in 1997 for the development of methods to cool and trap atoms with laser light; and in 2001 for studies of the properties of Bose-Eintsein condensates).

Scientists studying cold atoms are lining up to take the next prize, says quantum physicist Maciej Lewenstein, who leads the quantum optics theory group at the Institute of Photonic Sciences in Barcelona, Spain. "Concerning Nobel Prizes in this area, it's only a question of who's next," he adds.

In July, Lewenstein presented his theories on cold atom research along with some Europe's pre-eminent cold atom scientists at the European Science Foundation's Euroscience Open Forum (ESOF) in Barcelona.

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