Newton’s third law tells us that for every action, there’s an equal reaction going the opposite way. It’s been reassuring us for 400 years, explaining why we don’t fall through the floor (the floor pushes up on us too), and why paddling a boat makes it glide through water. When a system is in equilibrium, no energy goes in or out and such reciprocity is the rule. Mathematically, these systems are elegantly described with statistical mechanics, the branch of physics that explains how collections of objects behave. This allows researchers to fully model the conditions that give rise to phase transitions in matter, when one state of matter transforms into another, such as when water freezes.
But many systems exist and persist far from equilibrium. Perhaps the most glaring example is life itself. We’re kept out of equilibrium by our metabolism, which converts matter into energy. A human body that settles into equilibrium is a dead body.
To read more, click here.