Multiplicity of a two state system

AI Thread Summary
The discussion centers on the definition of multiplicity in a two-state system, questioning the validity of two expressions: Ω=2^N and Ω(N,n) = \binom{N}{n}. The first expression represents the total multiplicity of a system with N independent states, while the second expression calculates the number of ways to choose n states from N. It is noted that 2^N does not equal \frac{N!}{2!\cdot(N-2)!}, leading to confusion about the applicability of the second formula. However, summing the second expression over all possible n values yields the first expression, indicating that the second formula is not incorrect but rather a specific case. Ultimately, both expressions can be related through summation, clarifying their roles in defining multiplicity.
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I only have a doubt about which definition to use for the multiplicity of a two state system. Clearly the total multiplicity of a two state system is given by:

Ω=2^N,

but what about the definition:

Ω(N,n) = \binom{N}{n} = \frac{N!}{n!\cdot(N-n)!}.

Clearly:
2^N ≠ \frac{N!}{2!\cdot(N-2)!}.

What is the difference between these two expressions for multiplicity? Is the second one incorrect for a two state system of N things?
Thanks.
 
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If you sum the second one over n you get the first one.
 
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