A brief look at Quantum Mechanics

This article first appeared over at our affiliates site, mamak.com. The original piece can be found here.

Although I'd been a student of physics for the past two years (now I am in the second half of my third year), there are still so many aspects of physics that boggles my mind. A pioneer of modern physics, of which I have a long love-hate relationship with, where understanding of its quixotic nature renders me frustrated yet made me more deeply in love with its character, is Quantum Mechanics (or more fondly known as QM).

QM came about to explain the dual nature of light, how something that could radiate spectrums of electromagnetic waves (from where you get to listen to the radio, microwaves, your x-rays, your laser pointers, etc.) and have so much of the character of a tidal wave could have a corpuscular physique. Therefore the two men, Huygens (the man who founded the wave front theory) and Newton (of the Newton ring fame where you see alternating bands of shadows and light) who were so besotted by the fair characteristic of the Light that they became rivals for her hand. Several years down the century, we have dandy men by the name of de Broglie who found out by accident whilst conducting an experiment that our beloved electron (yes that little subatomic particle that makes up the one half of the electric current) propagates as a wave (if you want to know more, check out Britannica and look under de Broglie). Hence, the enigma of the dual-wave theory grew bigger until a smart fella by the name of Schroedinger decided to reconcile the ever-growing rift by his famous Schroedinger equations, making use of the previous discoveries by the likes of Hamilton (of the Hamiltonian Principle fame).

As foray into the physical subatomic world continues, Newtonian Physics could not explain more discrepancy that came about. One of them is the famous blackbody theory. Let's say a metal is heated up to 700 degree Celsius until it became red-hot. As the heating continues, it went from orange to white (at a very high temperature). A graph plotted of the intensity of light as oppose to its temperature would give you a curved (almost normal) graph. As the body of the metal continues to absorb heat, the body that is hotter than its surrounding would continuously beam out rays. A good reflector is also a good absorber. Therefore, a blackbody is a good absorber. Although a blackbody is not necessarily black, the term is coined by an experiment conducted with a metal box painted black on the inside and with a tiny hole poked through on ends of its side. Inside the box, spectrum of rays is reflected continuously, and we get a spectrum like the one of the abovementioned metal. Two important criteria observed: that the spectrum became continuous as the temperature increase and the position of the maximum peak from the spectrum moves towards a higher frequency. This is known as Wien's Law. According to the classical theory, a vibrating atom can reflect rays. Therefore the bigger the frequency, the more the rays produced. This is in accordance with the experiment conducted. Hence the Rayleigh-Jeans theory that provides the model to explain the experiments. But trouble is brewing ahead...

The blackbody could be said to be a harmonically vibrator. The atoms are akin to balls with springs. A vibrating particle gives out electromagnetic waves. At thermal equilibrium (when temperature is the same everywhere), the density of the energy in the matter is the same as the density of the energy of the vibrating atom.... therefore increase in temperature brings about higher vibration and ray density. It becomes that the ray increase indiscriminately in such a way that violates the aforesaid theory. Therefore we found classical physics insufficient when it comes to explaining such conditions. We need QM.

Another discovery made, that is little known by the non-enthusiast or non-hardcore fan, by Einstein that is another stepping stone to the QM theory is the photoelectric effect. To cut a long story short, it's basically taking a vacuum tube with a photosensitive detector that detects light rays coming from the sun. From the experiment, it was discovered that the light comes in little packages or quanta. Hence photons are produced from the metal detector. It was discovered that the characteristic of the photon violates the classical mechanics. Another case for QM. Notice the near similarity between quanta and quantum. Yes one is plural of the other. (:

From the reconciliation of the dual-function of light by Schroedinger's infamous equation and with the development of classical field theory and general relativity, we slowly moved towards what is today known as QM. If it is to be known, there are two aspects of QM, that is the relativistic and the non-relativistic. It shall not be explained here because it would serve to confuse the layman.

To highlight one important function of QM, is the tunneling effect. Let's take a simple example of a well. Let's say you are stuck in a deep well and could not seem to jump out no matter how hard you tried. To jump out, you have to overcome the potential barrier, which is the depth of the well. Suddenly, you remembered that you have small drill in your corduroy suit and you decide to drill your way out. Hence the tunneling effect. It's not a very good example but it serves to highlight an important aspect of QM as oppose to classical mechanics of CM. (not to be mistaken with central motion).

What we do know now is that QM provides explanations to the initially unknown characteristic of the physical world around us. But no one, not even the pioneers of this theory or the theoretical physicist studying it could yet understand WHY or HOW it works. By working at high-energy physics, we are slowly coming to understand how it works. But why does it work in this grand scheme of things? It's a big philosophical question mark.

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