Quantum chromodynamics

Quantum chromodynamics (QCD): describes the interaction between quarks, which involves the gluons, carrying the strong force. QCD involves the application of a "colour charge" ("red, "green" or "blue") to each quark with therefore three different colour types of each of the 6 quarks. So, each quark carries one colour charge (conventionally named red, blue or green although the names, like those of the quarks themselves, are not actually related to function)

Protons and neutrons contain 3 different colours of quarks and, because of the combination are thus "white".


* Complex numbers are numbers formed by multiplying a real number by i (where i= the imaginary number that is the square root of -1). Complex numbers can be useful in maths.

Image by Qashqaiilove via Wikimedia Commmons
Slowed by website author using ezgif.com

The above animation shows the colour interaction between quarks in a neutron. The gluons are the small circles with its colour charge in the centre and also an anti-colour charge around it. The three anti-colours are: cyan (anti-red), magenta (anti-green) and yellow (anti-blue). Each gluon can be seen to change the colour of the quark that receives it to the colour of the colour charge itself. In the slower version on the right, it can be seen that a quark emitting a magenta (anti-green) gluon, itself is changed to green. Similarly, a quark emitting a yellow (anti-blue) gluon, itself is changed to blue and a quark emitting a cyan (anti-red) gluon, itself is changed to red.

So, gluons transfer colour charge between two interacting particles (quarks), with one colour charge being transferred in each direction.  If a red quark emits a gluon that carries red/antigreen, then the red quark will change from red to green. That gluon will then interact with a green quark, and turn the green quark to red (as seen above).

As gluons carry two colour charges (one as a colour and one as an anti-colour), there are several gluon types.  In fact there are 8 different combinations. As each gluon can carry two colour charges, you might expect that there would be a total of 9 possible combinations (3x3)  (i.e. 6 with one colour and one different anti-colour as well as another 3 that carry a colour and anti-colour of the same colour).  In reality, only 8 exist in total, because one of the latter 3 is unable to exist. If all 3 existed then they would, in combination, eliminate each other.

Quantum electrodynamics (QED): describes the electromagnetic force between electrically charged particles and makes predictions that fit within quantum mechanics. Associated with the "U(1)" theory of electromagnetism

Quantum mechanics: describes how particles interact, particularly the photon and includes other fields of study.