Hello, This is more a question about history of science in general. During my lectures on statistical physics, I noticed that some of the problems that Bolztmann faced lead to the introduction of: ##h/2\pi## (to introduce the unit of an action leading to a "unitless" partition function) which is nothing than the Plank's constant and the indistinguishability of atoms/molecules in a gaz introduced by Gibbs (in order to solve the Gibbs paradox). Also, introducing the density operator, leading to quantum statistical mechanics is very simple, smooth and elegant. Is it safe to say that the Boltzmann theory of gaz was be the first to introduce fundamental notions of quantum physics (the quanta, and the indistinguishability)? If so, do we know if these were helpful and used during the construction of quantum physics ? Is there anything to read about it (could not find anything yet) ? Thank you and have a great day.