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The matter surrounding us consists of atoms that obey the laws of quantum mechanics. At normal temperatures these often agree with classical conceptions, and a gas under these conditions behaves rather like a swarm of billiard balls bouncing against one another and the containing walls. When the temperature is lowered and the speed of the atoms is reduced, however, their properties will be increasingly dominated by the principles of quantum mechanics.
As early as 1924 the Indian physicist S. N. Bose carried out a statistical calculation for the kind of particles which have since come to bear his name, bosons, and more specifically light particles later termed photons. Bose presented an alternative derivation for the radiation law earlier found by Planck. Bose sent his work to A. Einstein, who realised its importance. He translated it to German and had it published. Einstein rapidly extended the theory to cover Bose particles with mass and he himself published two articles in quick succession, predicting that when a given number of particles approach each other sufficiently closely and move sufficiently slowly they will together convert to the lowest energy state: what we now term Bose-Einstein condensation (BEC) occurs.
Ever since publication of this pioneering work, physicists have wished to be able to achieve this new fundamental state of matter, which was expected to have many interesting and useful properties. Seventy years were to pass before this year's laureates, Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman, using very advanced methods, finally managed to do this in 1995. The state was achieved in alkali atom gases, in which the phenomenon can be studied in a very pure manner. Nowhere else in the universe can one find the extreme conditions which BEC in dilute gases represents. Manifestations of Bose-Einstein condensation have earlier been observed in more complicated systems: condensation of paired electrons in superconductors (loss of all electrical resistance) and suprafluidity (loss of internal friction in fluids). Here, too, low temperatures are required. Research in these areas has been rewarded with several Nobel Prizes. As opposed to alkali-atom vapours these quantum-mechanical systems are not simple since the condensation phenomenon concerns only a part of the systems and the strong interactions involved tend to hide the BEC phenomenon.
According to the laws of quantum mechanics that govern conditions in the microcosmos, what we normally term a particle can sometimes behave like a wave. This is well known and is used in e.g. the electron microscope. As early as 1924 L. de Broglie postulated the existence of matter waves and expressed their wavelength in terms of the of momentum of the particles p:
where h is Planck's constant. The more slowly the particle moves the less its momentum and the longer the de Broglie wavelength. According to the kinetic theory of gases low particle velocities correspond to low temperatures. If a sufficiently dense gas of cold atoms can be produced, the matter wavelengths of the particles will be of the same order of magnitude as the distance between them. It is at that point that the different waves of matter can 'sense' one another and co-ordinate their state, and this is Bose-Einstein condensation. It is sometimes said that a "superatom" arises since the whole complex is described by one single wave function exactly as in a single atom. We can also speak of coherent matter in the same way as of coherent light in the case of a laser.
Originally posted by Amorymeltzer
The obvious problem is that the only way to see if you're there is to measure it, and in order to measure it you've gotta add something external into the system, something above absolute zero. And then you don't have absolutle zero anymore.