When an arbitrary system is isolated and left to itself, its property will in general change in time. ....after a sufficiently long time,the temperature will become the same at all points and then the system is in thermal equilibrium. - Sears and Salinger.
Now, if the system is isolated, how has it changed to bring the equilibrium?
It is an axiom of thermodynamics that when a body of material starts from a non-equilibrium,state of non-homogeneity or chemical non-equilibrium and by thermodymamic operation,is then isolated,it spontaneously towards its own internal state of equilibrium. - Wikipedia.
Now how does an isolated system attain thermodynamic equilibrium-thermal and mechanical especially in course of time?? Do each particle in the isolated system have same energy and no net force? No, each particle collide and there is force and energy of each particle changes. So,if force exists and energy changes,how can there be equilibrium?
And the wiki page also mentions :
In a macroscopic equilibrium,almost or exactly balanced microscopic exchanges occur.
What does this mean?