After the many ramblings I made regarding Dark Matter previously, I want to turn around and think about Baryonic Matter again. Ordinary Matter is something that physicists know much more about than the mysterious Dark Matter and Dark Energy, even though in reality they do make up more than 95% of our known Universe. We are more knowledgeable about Baryonic Matter because of its presence all around us, after all, it is everything we can see and detect: from forms of life, elements in the Earth’s crust and mantle, buildings, cars, the Earth, the Sun, all of the stars… you get the idea.
Now, the stuff that makes up the matter. Firstly what comes to our mind may be elements, which are a table of 100 odd substances that are often called the “primary constituents of matter”. These elements can be identified through their chemical properties and are placed in the Periodic table in order of increasing atomic number (the number of protons in its atom’s nucleus).
Atoms are another level down from the elements of the periodic table, which distinguishes different types of atoms. Atoms themselves is another study on its own. In the early 20th Century, Rutherford and a couple other physicists discovered an awful lot that directly correlates to our modern understanding of the atom through an experiment – firing alpha particles at a piece of gold leaf.
Before then the popular theory was the so-called “plum pudding” model of the atom proposed by J J Thomson, the physicist who discovered the electron.
Rutherford’s experiment taught us that the atom was mostly made of empty space and that the central nucleus had mass and a positive charge. It was later identified that the nucleus was made out of two types of Baryon particles – the neutron and the proton, and the atom is thus comprised of these particles along with the orbiting leptons – electrons. The atoms are then held together by the Strong Nuclear and the Electromagnetic forces, exchanged through Gluons and Photons respectively.
You would’ve thought that protons and neutrons were the fundamental particles that couldn’t be broken down any further however physicists were curious to find if they were the true building blocks of our Universe.
To do this they smashed particles (and we still do by the way) through particle colliders like the LHC in CERN, by accelerating charged particles to very near light speed – like 0.99c or faster – using electric and magnetic fields to have them smash together and break into component parts, i.e. quarks! Quarks are really really strange, and cool – they have no size. There are 6 of them: Up, down, strange, charm, top and bottom, and they make up a fraction of the particles within the Standard Model of Particle Physics.
This theory also includes the electron and it’s second and third generation particles, plus their corresponding neutrinos – neutrinos are super cool too, but we can talk about them another day – and all of the force mediating particles (Bosons). Also, the Higgs Boson which is the story for another day as well. To this day, the Standard Model is one of the best-tested theories in physics, though a couple of decades ago, theoretical physicists brought in something called Quantum Field Theory which contributes more to our understanding of the interactions between the very small.
Quantum Mechanics and General Relativity, the two great pillars of Physics are known for their incompatibility with each other. Countless of theoretical and experimental work has been done at the very moment around the world to find a way to unify these two theories and find “the theory of everything” or a “theory of quantum gravity”. A good candidate for this is the popular “String Theory” however there are yet experimental proofs for the claims made by said theory. Nevertheless, Quantum Field Theory is an extremely successful theory and have been said to be “the best current theory to describe the nature of quantum interactions”, which is the only consistent reconciliation of Quantum Mechanics and Special Relativity. With General Relativity, we still have no idea…
Anyway, the underlying idea of Quantum Field Theory is that there are universally permeating “fields”. Fields for each and every one of the subatomic particles of the Standard Model: Up quark fields, Down quark fields, Electron fields, Muon fields….etc. So, essentially a Muon is just a localised vibration of the Muon field. Now, energy transformation is responsible for the interactions between the fields and what we perceive. Let’s say the Muon emits a Photon, the energy involved in this sets up a vibration in the Photon field which then moves away from the Muon vibration. The mathematics involved in QFT calculations is way beyond my knowledge right now as a Secondary School student, but despite this, the core ideas are not difficult to understand and are extremely intriguing to learn about.
Author – Susan Chen
Susan is a 5th year high school student currently studying three STEM subjects at Scottish Higher level-Mathematics, Physics and Chemistry (Crash Course). She particularly loves ideas in cosmology and hopes to embark on an academic journey in the area of theoretical physics.