Question in Bose-Einstein statistics

[patric44]

Homework Statement

why the number of ways to arrange ni particles in gi degenerate states is = (gi+ni-1) ?

Relevant Equations

(gi+ni-1)

iam not getting why in bose statistics the number of ways to arrange ni particles in gi degenerate states is = (gi+ni-1) ?
and why do we divide by ni factorial , and gi factorial .

 

[Abhishek11235]

The formula is wrong. The correct number of arrangements are:
$w_i= (N_i + g_i -1)!/(g_i !)(N_i-1)!$
This can be seen in number of ways. It is variant of Star and barn problem of combinatorics since bosons are indistinguishable. Wikipedia article explains it in detail and also it's variant. See https://en.wikipedia.org/wiki/Stars_and_bars_(combinatorics) .Alternatively,see the masterpiece book on probability: An introduction to Probability by William Feller,the person who devised this method. To answer why we multiply,it is because we are considering an ensemble of particles. A particular particle group can occupy any given state,another can occupy any given state(It may be same as 1st particle group since they are bosons).