Quantum mechanics
Rohan Agarwal
It is common knowledge that matter is comprised of particles. Or is it? We all think that light consists of waves. How true are these claims? Although it may seem counterintuitive on the surface, various experiments and supporting theories have proved that the line between what is particulate and what is wavelike is finer than we imagine. At a fundamental, sub-atomic level, matter and light are both wavelike and particulate; it is only on the macroscopic scale that the divisions become better defined.
The study of the physical laws that govern the realm of the very small, such as atoms, protons, and the like; developed from Planck’s quantum principle and Heisenberg’s uncertainty principle are termed as quantum mechanics. The principles of quantum mechanics revolve around two major theories- the wave-particle duality, and, in extension to this, the theory that it is possible for absolutely small particles to be in two different states at the same time. Theoretical physicists have arrived at these conclusions after powerful observations of experiments, and these will be discussed in due course. Before doing so, it is imperative to understand that this quantum strangeness does not transfer to the macroscopic world, and so some claims in this article will seem absurd. In order to demonstrate this, Erwin Schrodinger published a paper in 1935, containing a thought experiment, now popularly known as Schrodinger’s cat.
A cat is put in a steel chamber that contains radioactive atoms, and a mechanism that causes a hammer to break open a flask of poison if an energetic particle is released. If the flask breaks, the cat dies. The steel chamber is closed; therefore the whole system remains unobserved. The radioactive particle is then in a state in which it has both emitted and not emitted the particle (with equal probability). The flask is both broken and not broken, so the steel chamber would have, in the words of Schrodinger, “in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts”. The problem arises when we try to observe the system. The opening of the chamber and the very act of observation, forces the entire system into one of the two states, i.e. the cat is either dead or alive. When unobserved, the cat is both dead and alive, when the chamber is opened; it is only one of the two. The experiment may seem absurd, but it was meant to demonstrate that quantum strangeness is unique to the microscopic world, not applicable to the macroscopic.
Similar to the both dead and alive cat is the electron. Electrons can be both wavelike and particulate. The wavelike behavior of electrons can be demonstrated by placing an electron gun behind two thin slits and a photographic plate in front of the slits. One would expect two narrow lines of electrons directly in front of the slit, but experiments found that an interference pattern, similar to the pattern formed by light is formed. This is only possible if electrons display a wavelike behavior. If devices, such as Geiger counters, are placed near the slits to sense which slit the electron passes through, two thin lines are formed directly in front of the slits. Thus, when unobserved, electrons are in two different states at the same time. However, when one tries to observe one of the properties, the electron obeys the laws of the property that we want to observe. The electron must then be in either one state or the other. This absurd nature of the electron is known by physicists as the wave-particle duality. Werner Heisenberg set out to address this absurdity by asking two very simple questions- 1. Where is the electron in an atom? (Related to the particle nature- the position), and 2. Where is the electron going? (Related to the wave nature of the electron- the velocity). He conducted various experiments, observations and measurements, and concluded that it is not possible to know the answer to both of these questions at the same time. In all its simplicity, this statement is Heisenberg’s Uncertainty Principle.
Similarly, light has both, wavelike and particulate properties. The double slit interference pattern formed by light demonstrates the wavelike nature of light. The explanation behind the particulate nature is a bit more complex and was discovered much later. This property is demonstrated by the photoelectric effect, first observed by Heinrich Rudolf Hertz in 1887 while studying the effect of light on electrolytic cells. It was explained later by Einstein and Max Planck. When light is incident on particular metals, the metals begin to emit electrons. As per Maxwell’s wave model of light, the energy of each emitted electron should depend on the intensity of incident light. However, it was found that the energy of the emitted electrons did not depend on the intensity of light but on the frequency of incident light. Furthermore, no electrons were emitted, at any intensity if the frequency of light used was below a certain “threshold frequency”. After this “threshold frequency”, light of even a low intensity would cause the emission of electrons. This is only possible if light was being transmitted in discrete quanta or ‘packets’ of energy. Planck had paved the way for Einstein years earlier by theorizing that heat waves travel in discrete quanta. Einstein explained the photoelectric effect the same way theorizing that light too travels in discrete quanta. Each packet is called a photon, and the energy of each photon is its frequency times Planck’s constant.
Quantum theory has many different interpretations; however each interpretation gives the same result, so it remains a matter of belief. One of the more famous interpretations is the Many Worlds Interpretation, first theorized by Hugh Everett III in 1957. The many worlds interpretation proposes that when an observation is made, there is a split in the universe, i.e. all the possible outcomes occur, but in various realms of reality. Thus, there must be a multitude of parallel universes created where the other outcomes are observed. This interpretation has been said to transfer to the macroscopic world as well. If there are various realms of reality, the single narrative of our life that we take for granted, is actually only an illusion. It decimates our notion of individuality, for the coherent and discrete trip that we are making through ‘space and time’ is really just an expanding set of instances that branch off into various possibilities at different moments in time.
Quantum mechanics explains many phenomena that were previously unaccounted for, hence it has immense support. However, it has been disparaged by Albert Einstein, who criticized it because of its random, unpredictable element, saying “God does not play dice.” In the words of John Polkinghorne, “quantum theory has proved to be fantastically fruitful during the more than 75 years of its exploitation following the originating discoveries.” It has baffled some of the world’s greatest scientists; from Erwin Schrodinger to Max Planck, and even now, continues to remain an enigma.

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[ 2 ]. Encyclopedia Britannica,. "Photoelectric Effect | Physics". N.p., 2015. Web. 4 Mar. 2016.
[ 3 ]. Byrne, Peter. "The Many Worlds Of Hugh Everett". Scientific American. N.p., 2016. Web. 4 Mar. 2016.