Introduction to Quantum Theory ( or Quantum Mechanics )

Introduction to Quantum Theory ( or Quantum Mechanics )

One of the most misused words in the English language is the word QUANTUM. Most people, especially politicians love to promise their supporters that quantum leaps would be made to improve a certain aspect of their lives if the politicians were voted into power. Quantum is taken to mean unmeasurably large. This understanding is wrong on both counts. It is the smallest measurable unit. In fact, a quantum is the smallest possible unit of energy that can be given off or absorbed by an elementary particle when it moves from one orbit to the next. Politicians and other people use the word quantum probably because it sounds both sophisticated and scientifically miraculous.

The quantum concept was pioneered by the German scientist, Max Planck in 1900. Up to that particular point in time, scientists had been puzzled by a phenomenon they called the ultra-violet catastrophe in a situation known as' black body' radiation. First of all, the term black body is misleading because it is an object that need not be black. A black body object in the context of radiation simply means that it is an object that absorbs all incoming radiation so that it does not reflect any light. In this sense, it is black meaning it reflects no light which is a form of radiation. However, a black body object can emit radiation on its own if given enough energy. Common examples of black body objects are our sun and heavy metal like a bar of iron. The scientific puzzle facing the scientists is that classical theories ( as opposed to Quantum Theory ) such as Maxwell's equations predict that upon heating a bar of iron to higher and higher temperatures more ultra-violet rays will be emitted because higher temperature means higher energy level and this should in turn means more ultra-violet rays which have higher frequency on the thermo-electromagnetic spectrum. But in reality, this never occurs and the light rays emitted by the iron bar remain within the visible spectrum no matter how high the temperature the iron bar has attained as a result of the continuous heating. This is known as the ultra-violet catastrophy which had puzzled scientists since Maxwell whose equations unified the forces of heat, light, electricity and magnetism. These are collectively called the thermo-electromagnetic force because they had been proven to have the same origin- they are all different forms of electromagnetic waves ( within both the visible and invisible spectrum from the shortest microwaves to the longest radio waves ). Could Maxwell be wrong ? If so, why did his equations work perfectly in all other situations except black body radiation ?

In 1900, Max Planck invented his own set of equations which were able to predict the behaviour of black body radiation. He had discovered that if the traditional assumption of continuous and unrestricted emission of energy was scrapped and replaced by the rule that energy could only be emitted ( and absorbed ) in small but discrete ( measurable individual units ) packets, units or quanta then the puzzle of ultra-violet catastrophy in black body radiation could be explained. This was because the higher the temperature the more energy would have to be carried by the individual packets ( or quanta ) of energy carrying centres ( these should not be construed as solid entities ).

The higher level and more intensive energy packets are fewer in number ( these are more difficult to sustain because of the higher energy level required ) than the normal packets ( within the visible spectrum ) which carried less amount of energy per quantum so that they are more numerous in number. That is why the heated iron bar remains red hot or even white hot upon continuous heating without turning colourless as a result of emitting all heat energy in ultra-violet rays invisible to the human eye as predicted by classical theories. The photon was proven by Albert Einstein to be the quanta, carrier or energy packet for light and all electromagnetic radiation in his research on the Photo-Electric effect for which he was awarded the Nobel Prize in physics in 1921. His research had also placed him among the most prominent contributors to the Quantum Theory.

At first glance, Max Planck's discovery appears to be mundane rather than revolutionary. Who cares about the ultra-violet catastrophy and black body radiation except the nutty scientists ? In fact, it turns out that the Quantum view changed the whole philosophical outlook of the role played by human beings in the entire universe and the realm we call reality. You will appreciate this mystical nature of Quantum Mechanics when you come to learn about how atoms behave in some quantum experiments later on. To summarize at this preliminary look at Quantum Theory, it teaches us that the universe is not smooth or continuous all the way down to infinity. If it were, there would be a lot of impossibilities or paradox. To take the most famous paradox of all as an example, this is called the Zeno Paradox after a Greek philosopher. Zeno was able to prove logically that there could be no possibility of any movement in this world. His argument ran like this. He used the shooting of an arrow as a demonstration. In order for the arrow to fly through the air from point A to point B, it needed to pass the mid-point between A and B at each stage of the flight. Since there were supposed to be an infinite number of points along the straight line connecting A and B according to Euclid's postulates in geometry which described the space between A and B it would take an infinite amount of time to travel over an infinite number of mid-points along the straight line connecting A and B. Therefore, the arrow could never finish the flight from A to B. Therefore, there could be no movement of any sort. Of course, space cannot be divided into an infinite number of points or units according to Quantum Theory. Thus, the arrow had to complete its flight somehow. In fact, the smallest possible units of length and time are scientifically known as Planck length ( 1/10 to the 35 power of 1 metre ) and Planck time ( 1/10 to the 43 power of 1 second ). Nothing comes in any smaller size or shorter time span.
Most important of all, Quantum Theory explained why the electrons orbiting the nucleus of an atom do not smash into it as predicted by Classical or Newtonian Mechanics. Due to the fact that energy is quantized or comes in discrete packets there is a minimum value that can be assumed or emitted by an elementary particle. The lowest possible energy level is represented by the orbit closest to the atomic nucleus. Thus, the electrons cannot take on or reduce any level of energy they like but have to follow quantum rules. This makes it impossible for electrons orbiting at the orbit closest to the atomic nucleus to smash into it and destroy the atom itself because the electrons cannot reduce any more energy beyond a quantized minimum. Therefore, the quantization of energy by Nature has saved the world from destruction and has also revealed the intricate order in the universe.