Bose-Einstein condensation is a phenomenon that occurs at low temperatures in systems
consisting of large numbers of bosons whose total number is conserved in collisions. Used
in the explanation of superfluidity, this phenomenon enables a significant fraction of the
particles to occupy a single quantum state. No analogous phenomenon occurs for two or more
fermions, which are prohibited by the Pauli exclusion principle from occupying the same
This property of making a group of bosons into the same quantum state so they act like a
single entity was done in 1995 by physicists at the Joint Institute of Laboratory
Astrophysics, in Boulder, Colorado. They succeed in cooling about 2000 atoms of rubidium
gas to 170 nanokelvin (170 billionths of a degree above absolute Kelvin), where they formed
a Bose-Einstein condensate less than 100 micrometers across. The condensate lasted for
about 15 seconds, and was cooled all the way down to 20 nanokelvin. If the technique can
be extended to large aggregates, it will make single 'quantum particles' visible.
Answered by: Dan Summons, Physics Undergrad Student, UOS, Souhampton
'If one wishes to obtain a definite answer from Nature one must attack the question from a more general and less selfish point of view.'