Quantum Mechanics is the physics of subatomic particles and their interactions at a particulate level. Intrinsically, it constitutes the study of light and matter at the most fundamental level. Strangely, Quantum Mechanics is not compatible with Einstein’s theories of relativity, which opens up the infinite quest for unification, within which physicists aspire to find an equation to sum up all of our branches of physics, which seem incompatible at the moment.

The most basic and classical element of quantum physics is the definition of a “quanta”. A quanta is a packet of energy, with a minimum value. A light wave carries energy as photons, and any photon with the frequency of the above would have that energy, which cannot be further broken down. Quantum physics also revolutionised the visualisation of atoms. Hitherto, atoms were understood to have orbitals containing a set of electrons, however, quantum revealed that we can only analyse the probability of the electron being at a certain position and that they may move through the orbitals however they may move from one shell to another. In some cases, they may even be in multiple locations at one point in time. We cannot with full confidence ascertain the position and momentum of an electron.

To comprehend this better, we need to understand the concept of wave-particle duality. De Broglie, in 1924 realised that both waves and particles can be observed behaving like each other, so for this he developed the equation Particleλ = h/(mv), which is known as the equation for the DeBroglie wavelength. Now the essence of this equation lies in the fact that observing a particle acting like a wave brings rise to the need for understanding this relation. It defines the wavelength of a particle as Planck’s constant divided by the particle’s momentum. One must note that the DeBroglie wavelengths are extremely small, which is why nobody was able to comprehend them. If we attempt to use this on large macroscopic objects, we might get incessantly small values, with exponents like -34. This is over three times smaller than an atom. If we apply this formula to a smaller particle, like an electron, we may find that the de Broglie wavelength comes out in the range of a few Å, (an Å is the diameter of one atom, it is called an angstrom.) which is a significantly larger and more measurable wavelength. This means that the wave correspondence of subatomic particles can be observed.

This concept is extremely fundamental, as it demonstrates Heisenberg’s Uncertainty Principle. The principle states that one cannot decipher with complete accuracy the position and momentum of a particle at any given point in time. The equation demonstrates this principle: ∆x∆p ≥ h/(4π). This formula demonstrates that to find the position (x) you must compromise on momentum (p), and vice versa. It is imperative to note that in a macroscopic universe, this formula is fairly irrelevant. Now this principle mainly focuses on the wavelike nature of particles and hence we can envision the particle’s wave correspondent with an ability to diffract, spread, or condense in a plane. This is what gives us the uncertainty in the space plain, considering its uncertain state. A wave at a fixed point would represent an infinitesimally small wavelength, hence undefined and unmeasurable, whereas a measurable momentum would mean a wavelength tending towards infinite; also immeasurable. 

Now, coming to superpositions. Schrödinger demonstrated an experiment in which he put a cat inside a box. He then linked a Geiger counter to a gun and then placed a uranium piece next to the counter. When the uranium decays, the Geiger counter would cause the bullet to fire, in theory killing the cat. Schrödinger’s theory, however, states that we don’t know whether the cat survived the gunshot without taking a definitive look within, or whether the Geiger counter received the radiation, we can say the cat is in a superposition. until the box is opened the cat is both dead and alive simultaneously. This shows that when an event is in the question of an atomic event until checked or confirmed, the subject is in a superposition. Much like the age-old question, is a tree falls in a forest where no one can see or observe it, did it ever fall?

Photons too, tend to obey Quantum Mechanics. If you cut two vertical slits parallel to each other in a board, and fire a photon through, it should logically go through one of the slits, right? Well not quite. Somehow the photon travels through both of them, and instead of forming a point or dot on the wall behind it, it forms ripples. Much like ripples formed when two rocks are thrown into a pond. This demonstrates superpositions too.