The Strong Nuclear Force

Now let's actually look at one of the four fundamental forces.

The nucleus of an atom is made of protons and neutrons. Protons are electrically positive, and neutrons are electrically neutral. This means that there would be protons right next to protons. However, charges that are the same repel, so this shouldn't be possible unless there were some force overcoming the electromagnetic force. That force is the strong force.

This overcoming of the electromagnetic force is why elements after lead are unstable. At that point, the electromagnetic force is strong enough to resist the strong force.

The gauge boson for the strong force is the gluon.

1) Gluons are masses, and have a color charge as well as transmitting it. This means gluons can interact with other gluons.

2) Gluons are mixtures of two colors, such as green and anti-red

3)Quantum Chromodynamics is the gauge theory that describes the behavior of gluons and the strong force.

Here is an example of gluons in action. A red quark emits a gluon, and the gluon carries a red color charge and an anti-blue color charge. This gluon is absorbed by a blue quark and loses the blue color charge while gaining the red color charge. The initial red quark now has the green color charge. A gluon is then emitted from the new red quark and so on.

In this way, the quarks inside protons and neutrons are constantly interacting, which strains the color fields into string-like objects called flux tubes.

When a quark is pulled away from a nucleon with enough energy, the flux tube breaks. However, that energy used to pull the quark results in a quark being formed that replaces the missing quark, and an antiquark being formed that is paired with the pulled quark (this pair is a meson). With more energy, more mesons are formed. Because of this, you cannot permanently remove a quark in a phenomenon known as confinement. This is also why no free quarks have ever been detected.

It is also important to know that like how the electromagnetic force obeys U(1) symmetry, the strong force obeys SU(3) symmetry.