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Question
Photons are Bosons, so why don't they make Bose-Einstein-Condensation?
Asked by: Sabine
Answer
Pretty technical question. So, we'll have to have a
pretty technical answer.
Bose-Einstein condensation occurs when matter is cooled
down, and there are just not enough many 'states' for
all the particles 'to fit'. So, being bosons, which can
squeeze into the same state, any excess bosons end up
squeezing into the same, ground state. This is what is
meant by 'Bose-Einstein condensation'.
So why doesn't it happen with photons? Because there
is no such law as 'conservation of photons', they can
be created and destroyed at will by interacting with
matter. So, when you try to cool down a photon gas to
achieve a B-E condensate, they just get absorbed by
the material they are in contact with. Therefore photons
can not go under B-E condensation.
Answered by: Yasar Safkan, Ph.D. M.I.T., Software Engineer, Istanbul, Turkey
They do, it's called a laser, where the photons
all have the same wave-function, except it's not
REAL Bose-Einstein condensation. The difference
is that no phase transition takes place in a laser.
A gas of rubidium-87 atoms say, can be made to condense
into a B-E condensate because as they are cooled
below the critical temperature, the chemical potential
goes through zero. Lasers on the other hand don't
'condense'.
Answered by: Edward Myall, B.S.
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