I googled ”relaxation to equilibrium” and found these pictures:

Figure 1: Meditation: Relaxation to equilibrium

What is the meaning of “relaxation to equilibrium” in meditation? By meditation, we recreate an inner space that allows us to relax our mind from the external circumstances. That helps us develop the mental equilibrium.

But, are we discussing about meditation in this chapter? No.

However, similar to human beings, excited atoms also relax to equilibrium as time evolves i.e. the excited atoms density function converges to an equilibrium distribution as tends to infinity. Let us recall the equation of from Chapter 1:

where the interaction operator is defined as

By the H-Theorem, Equation (1) has a family of equilibria: where is the Boltzmann’s constant and the temperature of the quasiparticles whose distribution is . is approximated by the same form with Chapter 1.

In this joint work with Miguel Escobedo (Bilbao), we only study, instead, the relaxation process of the equation linearised around one equilibrium. Let us then write: Plugging this expression in the equation and keeping only the linear terms in we obtain an equation of the form:

then, we can prove that in which

In the next Chapter, we will discuss the analog between chemical reaction networks and quantum kinetic equations.