# Brownian motion and equilibrium

I would like to know if when you consider a system in which you have Brownian motion if it is considered a system in equilibrium or far from equilibrium and why. i.e., is Brownian motion considered as something in equilibrium?

• Are you interested in a system of particles who are all individually undergoing Brownian motion? Or are you asking about a system whose parameters undergo Brownian motion? Only under the first of these is equilibrium a well-defined concept. – probably_someone Dec 11 '17 at 15:51
• I am interested in this case: [link] (en.wikipedia.org/wiki/Brownian_motion#/media/…) Here we have one particle (the yellow one) performing a Brownian motion. The smaller particles (in black) are also performing Brownian motion due to the collisions with each others but I am interest in studying the yellow particle. – pipita Dec 11 '17 at 16:01