This soup of quarks and gluons permeated the entire universe until a few fractions of a second after the Big Bang, when the universe cooled enough that quarks and gluons froze into protons and neutrons. In this plasma, the density and temperature are so high that protons and neutrons melt. The only way to separate these particles is to create a state of matter known as quark-gluon plasma. Because of this, quarks and gluons are bound inside composite particles. Because the strong nuclear force is so powerful, it makes it extremely difficult to separate quarks and gluons. It is much stronger than the three other fundamental forces: gravity, electromagnetism, and the weak nuclear forces.
This strong nuclear force is the most powerful force involved with holding matter together. The force that connects positive and negative color charges is called the strong nuclear force. These so-called color charges are just names-they are not related to actual colors. In addition to having a positive or negative electric-charge (like protons and neutrons), quarks and gluons can have three additional states of charge: positive and negative redness, greenness, and blueness. They are the only fundamental particles to have something called color-charge. Scientists’ current understanding is that quarks and gluons are indivisible-they cannot be broken down into smaller components. Quarks and gluons are the building blocks of protons and neutrons, which in turn are the building blocks of atomic nuclei.