We love physics because physics helps us to understand the world around us and this universe and satisfy our curiosity. We are going to learn about 5th state of matter.
1. What is Bose-Einstein condensate?
92 electrons in a uranium atom can be compared to 92 residents of a high-rise apartment building, all of whom want to live as close as possible to street level.
If the landlord imposes on the residents an "exclusion principle" that limits every apartment to most one resident, the apartment will be occupied from the ground up apartment number 92 and all apartments above number 92 will be empty. The apartment, of course, correspond to states of motion.
If energy added to excite the atom, an electron can jump temporarily to a higher energy state. Despite a preference for lower floors, moves temporarily to one of the unoccupied apartment further up.
For electrons in a metal, the situation is similar, except that the number of electrons, even in a small bit of metal, is measured in the countless trillions and the spacing between energy levels is measured in nearly infinitesimal increments.
Yet, despite the vastly larger number of electrons and the vastly smaller spacing between energy levels, the exclusion principle works inexorable will in the same way. Electrons pile up in energy until the last one site at the highest occupied level, with all states below occupied and all states above empty.
At least, that's the way it would be at or near the absolute zero of temperature- a sharp dividing line between occupied and unoccupied states.
Then finite temperature, the thermal energy of the electrons near the top of the energy pile jiggle into higher states, leaving a few states unoccupied.
It's as if, in the apartment house, there is a kind of transition zone floors that are partially occupied. Above all apartments are empty. Below it all are fully occupied.
When a gas made up of bosons such as the rubidium-85 atoms. When bosons are cooled to near absolute zero, many atoms can in fact share of motion clustering into a completely overlapping, interpenetrating blob in which no atom can be distinguished from any other. It's as if the apartment house residents are not only all sharing the apartment are being transformed into murky clouds, each one of which spreads throughout the apartment.
Such a clustering is called a Bose-Einstein condensate.
Albert Einstein predicted this phenomenon in 1924, and it provided the explanation for the super fluidity of liquid helium, discovered in 1938. But many more years elapsed before researchers could realize a Bose-Einstein condensate in a gas of freely moving particles.
Will this condensate find practical application? It is dangerous to say no. More often than not, when scientists have gained understanding of and control over some new form of Matter, they have found a way to harness it for some practical purposes. But in this case it will be challenging.
Carl and Cornell in 1996 with justifiable smiles following their success the previous year in creating a Bose-Einstein condensate in a gas of rubidium atom.
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