Quantum Chromodynamics

Being a part of physics and music, I frequently will talk about how nature keeps harmony on every level, from the notes in music to the energy states that are being shaped by the fundamental forces and through them, until he comes to one such which he thinks very deeply about: Quantum Chromodynamics (QCD) — a theory that describes the strong interaction as one of the four fundamental forces of nature.

Naturally, while the electromagnetic force takes care of electric charge, QCD takes in a different "charge" yet, called colour charge.

The Language of Colour Charge

In QCD, quarks-the elementary constituents of protons and neutrons-carry colour charges: red, green, and blue. The carriers of the strong force are far more interesting: they carry both colour and anti-colour in different combinations.

Asymptotic Freedom — The Strength Weakens

One of the most beautiful aspects of QCD is asymptotic freedom. At extremely short distances (or high energies), quarks behave as if they are free:

This rare behaviour won Gross, Politzer, and Wilczek the Nobel Prize for Physics in 2004. Remarkably, the deeper we go within a nucleon, the weaker the force appears to be.

Confinement – The Indissoluble Link

The great irony is that in the average case, the very same forces that massively weaken at high energy become strengths at long distance, hence establishing confinement. Thus quarks will always exist confined within hadrons; they will never be seen by us in isolation.

Quarks, when attempted to separate, lead to an outpouring of energy into the system that forms anew respective pairs of quarks and antiquarks. This occurs with musical insymmetry.

QCD Beyond the Standard Model

QCD lives on not just in the static portion of the Standard Model but is, rather, intimately linked with contemporary open questions in physics — be it the quark-gluon plasma formed in heavy-ion collisions, the mass of the proton, or even beyond the Standard Model.

It also proposes one of the greatest unsolved problems:

Why does QCD preserve CP symmetry while it is, in principle, able to violate it?

The strong CP problem remains open to new physics, possibly foreshadowing the existence of axions.

Concluding Words

Quantum Chromodynamics, a perfect mix of disorder and beauty, is a symphony of colours holding together the universe as a whole. As a physicist and musician, I see no difference between the "harmony" within QCD equations and the harmony we seek in music.

There is a melody in the world of quarks and gluons — one that still has us all listening in — one that has yet to challenge, intrigue, and inspire us.