Quantum Chromodynamics 101

The Strong Force

Of all the forces, the most powerful force by far is the strong force.  Additionally, the strong force has one of the shortest interaction distances.  The strong force acts in two ways.  First, the strong force keeps protons in the nucleus, despite their repulsion force.  Secondly, the strong force connects quarks to form protons and neutrons.  These questions arise:  (1) How do particles of the same charge (protons) stay within the nucleus?  (2) What is it that “glues” quarks together?

To start answering these questions we start at the smallest particle and work our way outward.  As we know, baryons (protons and neutrons) are made up of quarks.  There are two up quarks and a down quark in a proton, and two down quarks and an up quark in a neutron.

These quarks are “glued” together by particles called gluons.  The attractive force of these gluons is very large.  Additionally, there are six different types of quarks (only two occur in nature).  These quarks are…

Quarks are affected by gluons.  A gluon has the ability to change the color (also called flavor) of a quark in order to keep the overall color charge of the baryon neutral (red light + blue light + green light = white light).

To answer the second question, the excess energy from the interaction between gluons and quarks in the proton provides excess color charge that overwhelms the electromagnetic repulsion produced by protons with like charges.

Similarly to the electromagnetic force, if the strong force were not to exist, matter would cease to exist.  More specifically, if the gluons that held quarks in the proton were to disappear, quarks would fall out of the proton.  Essentially the universe would contain nothing but up and down quarks.

QUESTION:  What would happen if quarks were controlled by the electromagnetic force, just like protons and electrons?

Click the link above to find out how scientists calculate these equations.

Gravity Weak Force Electromagnetic Force Strong force