I was reading Blundell and I came with the topic of the Canonical Ensemble.
And as long as I did understand, the system when is in contact with the large reservoir and it’s left in this condition for a sufficiently amount of time so they both come into thermal equilibrium, the temperature is fixed (and the temperature of the reservoir is equal to the temperature of the system).
Although, in thermal equilibrium we expect the energy content of the system to remains constant, but the the the canonical ensemble says we rather have some probability distributuion of the different (but possible) values of energy the system can have.
This is given by the Boltzmann Distribution.
But why is the energy not fixed? That is a requirement for being in the thermal equilibrium state, right?
(I think I might be missing something in the middle of this but I’m not sure of what. Thank you for your time)