Contrary to popular belief about the grimness of "up North", Sussex has been host to the coldest place in the Universe over the last few weeks. They say Brighton is a chilled out place to be, but this has been taken to extremes by Dr Malcolm Boshier who, with his team, has managed to come within a few hundred billionths of a degree of reaching absolute zero - the coldest temperature possible in the entire Universe. Absolute zero (which is -273 C) has eluded British scientists until now, and has only been reached in a handful of labs around the world.
Malcolm Boshier, working with Aidan Arnold and Calum MacCormick, was proving a theory of Einstein's, developed with Satyendra Bose, that atoms cooled close to absolute zero would conglomerate into a 'superatom' with a condensed identity. This state, known as a Bose Einstein Condensate, or BEC, can be used for precise measurements of previously unknown quantities. Using the 'magnetic mirrors' developed by Professor Ed Hinds in the Sussex Centre for Optical and Atomic Physics, it could be possible to use BEC atoms to measure gravity. As Malcolm says: "BEC represents the tightest control you can have over atoms. We should be able to build devices that will be extremely sensitive to anything that affects an atom's energy levels, and that includes gravity." Such a device would illuminate the long-standing confusion over just how gravity works. According to Malcolm, "achieving BEC here at Sussex is going to do for atoms what lasers did for light."
Absolute zero is reached firstly by pre-cooling atoms through bouncing lasers off them. The atoms, which are held in a high quality vacuum, like a sophisticated thermos, are then trapped with a strong magnet so that only the hottest atoms can escape. Those that remain are completely immobile and have therefore reached BEC. Malcolm explains that this temperature can be imagined by visualising a thermometer as long as the UK, where the top mark stands for room temperature. Absolute zero represents 1% of the width of a hair right at the bottom of this scale. As John Murrell, Dean of CPES, points out: "It is a considerable achievement to be the first in the UK to have reached BEC. We also have the facilities for going a lot further in this subject."
 | This shows how the distribution of atoms in the magnetic trap changes as the temperature is lowered. Atoms joining the BEC collect right at the centre of the trap, eventually forming the sharp peak seen clearly in picture 2. |  |
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Friday October 16th 1998
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