We have seen in the previous chapter that Bose dealt with photons which have no mass. Einstein extended the idea by treating quantum particles with mass as indistinguishable from one another for statistical purposes. "The quanta or molecules are NOT treated as structures statistically independent of one another" he wrote.
He applied this approach to a gas of quantum particles and was amazed to discover that they can condense into liquid state even without a force of attraction between them. On the other hand, a gas of classical particles will remain a gas unless the particles attract each other. This phenomenon is now called Bose-Einstein Condensation.
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