Confinement — Gluing the Blocks Together

Why are quarks never alone? Counter to intuition, the force between them does not diminish when there is distance between the quarks. The force is so strong that we must expend an enormous amount of energy to try and pull the quarks apart. When the expended energy grows large enough, a quark/anti-quark pair is created rather than letting the original quarks separate (see illustration).

This property is called confinement. We observe this crucial phenomenon yet remain baffled by its underlying cause. Understanding confinement is one of the most fundamental questions in physics today. If quarks were not confined, the world would be a very different place.