Chapter 9: The Fundamental Forces and the Origin of Matter

To fully understand the origin of matter, we must consider four forces: the electromagnetic, weak, strong, and gravitational forces. These forces are essential to understanding the composition of matter and matter’s composition in the Universe.

Each force plays a role in different physical phenomena. For example, the electromagnetic force is responsible for the electron’s attraction to the nucleus to form neutral atoms, ultimately dictating chemical reactions. The weak force governs radioactive decay, and the transformations of particles like the neutron into other particles like the proton. The strong force forms the nucleus by binding neutrons and protons together. Lastly, we are familiar with the gravitational force.

What we have figured out from the electromagnetic forces is that the combination of the electrical and magnetic fields is what we conventionally call radiation. Radiation has a particle-wave duality; it can be a particle, such as a photon, or it can be a wave, which we know is part of the electromagnetic field.

When we talk about Schrodinger’s equation, we talk about the Uncertainty Principle. When we talk about the Uncertainty Principle, we must also consider what is called spin in quantum mechanics. Spin describes a particle’s rotation. Take the electron as an example, it can spin clockwise or counterclockwise. Each type of particle has a characteristic spin in multiples of a half. Fermions are a class of particles characterized by their half-integer spins. These are particles like electrons, protons, and neutrons. Bosons are particles characterized by their integer spins. Photons are an example of bosons with spin values of positive or negative one.

Fermions and bosons are very distinct and different in behaviour. In chemistry class, we learned about fermions because we studied the Pauli Exclusion Principle, which states, “Two fermions can never have the same energy, spin, position, or other property, which is necessary to classify each individual particle.” When the Pauli Exclusion Principle is applied to an atom, it details how electrons are organized around a nucleus, dictating the s, p, d and f orbitals. The Pauli Exclusion Principle and the organization of electrons in an atom is responsible for the atomic spectra that is observed.

In comparison to fermions, bosons are not subjected to restrictions like the Pauli Exclusion Principle. Instead, they are allowed to occupy and energy level.

British Physicist Paul Dirac constructed a quantum equation for the electron. In his research to explain the electron’s behaviousr, he rationalized the existence of another particle, the positron, with quantum properties opposite to the electron’s properties. Like the electron, it is a fermion, but it is positively charged. Basically, Dirac discovered that all particles have anti-particles.

The strong force is the force that holds protons and neutrons together in the nucleus. It is much stronger than the electromagnetic force, and overcomes the repulsion between electrons. However, once you go beyond the radius of an atom, the electromagnetic force is stronger than the strong force.

It turns out that protons and neutrons are made up of basic constituents called quarks. Quarks have a spin of one half, but their electrical charges are multiples of one-third. A proton is made up of three quarks. It’s charge is calculated by adding up the charges on the three quarks to give a value of positive one. A neutron is also made up of three different quarks. When you add up the charges to calculate a neutron’s charge, the resulting charge is zero. The strong force acts on quarks, allowing them to form protons and neutrons.

The weak force is responsible for radioactive beta decay of a neutron into a proton. The weak force changes the nature of interacting particles. The neutrino, the massless particle, only interacts with other particles through the weak force.

When we study matter, we must also study anti-matter. For example, the electron’s anti-matter is the positron, for every quark, there is an anti-quark, and for every proton, there is an anti-proton. Dirac’s discovery has now led scientists to the discovery of anti-particles for all matter particles. For every particle, there is an anti-particle.