In this grand universe, it is often that we carry around a barrage of questions with us in order to define our existence and intellect. Where are we? Who are we? Why do we exist? But the question often neglected is ‘What are we made of?’ This article is centred around this question with the main aim of trying to explain what elementary particles are and will briefly touch upon the foundations of quantum physics.
To begin, elementary particles are classified as either fermions or bosons. Fermions have a half-integer spin, while bosons have an integer spin. Spin is a property like mass and charge that every particle has, but what does spin mean? Basically, spin is a particle’s angular momentum and it could either be an integer or a non-integer. Fermions can then be divided into quarks and leptons. While quarks have a colour charge and interact with the strong force, leptons do not have a colour charge and can interact with either electromagnetic or weak force. Now, what does colour charge mean? In order to grasp what colour charge is, we must familiarize ourselves with the Pauli Exclusion principle – one of the founding pillars of quantum physics. According to the Pauli Exclusion principle, two fermions cannot exist in the same quantum state (just like its name, quantum state is the way a particle is in a quantum system and the quantum state consists of location, momentum, orbital angular momentum and spin) in a quantum system at the same time. Since a spin can either be spin up or spin down, doesn’t it contradict the Pauli Exclusion principle? Proton has two ‘up’ quarks together! To remove this discrepancy, scientists came up with the concept of colour. Hence, elementary particles like quarks that carry colour charge are required to have a colour. Like electrons carry a positive or negative charge, the charge that quarks carry due to their colours is colour charge and the force they feel between themselves is colour force. Additionally, quarks can be classified into six categories: ‘up’, ‘down’, ‘charm’, ‘strange’, ‘top’, ‘bottom. On the other hand, leptons do not have colour charges and are of six types: electron, electron neutrino, tuons, tau neutriono, muons, mu neutrino. In addition to the quarks and leptons that fall under fermions, each fermion has an antiparticle.
Any Star Trek enthusiast will quickly relate with the term ‘antimatter’ or ‘antiparticle’. Antiparticle is like an exact opposite of its corresponding ordinary particle. For example, a positron is an electron’s antiparticle since it is identical to an electron but carries a positive charge. Whenever a particle and its corresponding antiparticle meet, the result is mutual annihilation. The combined mass of the particles turns into energy (E =mc2). This process works in reverse as well. When conditions are right, pure energy turns into a particle-antiparticle pair.
The other elementary particles other than fermions are bosons that have an integer spin and are further divided into gauge bosons and Higgs Boson. Gauge boson has an integer and a non-zero spin. Gauge Bosons act as force carriers, but what are force carriers? According to the Standard Model of Physics, each force is transmitted by an exchanging particle that transfers momentum between two interacting particles. Just like photon is the force carrier for electromagnetic force, W and Z bosons are the force carriers for weak interaction while gluons are force carriers for strong force. The other type of boson is the Higgs Boson or the ‘God Particle’ which has an integer spin of 0. That is it for the division between elementary particles!
It is time to recall that we have already come across Pauli Exclusion Principle – one of the founding members of the quantum physics. It is time to meet the second pillar – the uncertainty principle. Till now, we have envisioned particles to be similar in shape to circular small tennis balls, but subatomic particles can act as waves too. This is known as the wave-particle duality. In the uncertainty principle, Werner Heisenberg stated that:
“The more we know about where a particle is located, the less we can know about its momentum and the more we know about its momentum, the less we can know about its position.”
Imagine as if you are observing an electron. We can detect an electron only if it manages to scatter some of the photons streaming by it, but photons are humongous compared to the diminutive electrons. If we use visible light with a wavelength of 500 nanometres, we measure its location only within 500 nanometres, which is the size of 5000 atoms. So if we flash a light at a row of 5000 atoms, we do not know where the electron is! Hence, if we try to use a shorter wavelength, the photon’s energy delivers a “kick” that disturbs the electron, changing the momentum that we are trying to measure. The higher the photon’s energy and the shorter the wavelength, more is the alteration in the electron’s momentum
This principle applies to all particles and it even applies to large particles such as baseballs, but the alteration is so small that it is unnoticeable. Hence there is little effect of the uncertainty principle in our macroscopic world. Since there is little effect in the macroscopic world, Newton’s laws work perfectly fine but the same laws fail to deliver in the microscopic quantum realm. The uncertainty principle runs further by implying that electrons does not even have a precise path.
The uncertainty principle can be summarized in the formula:
Uncertainty in location x Uncertainty in momentum = Planck’s constant
The second way of mathematically expressing the principle is to express it in terms of the amount of energy that a particle has and when it has this energy:
Uncertainty in energy x Uncertainty in time = Planck’s constant
So, we come to the end of this article. Remember that we have just stepped into the microscopic quantum realm and even though we may not be able to rescue Scott Lang (aka Ant-Man), we will fill our own quantum canisters with an abundance of knowledge. So, keep reading!!! And continue to speculate, innovate, till you constipate!