Modern Physics – Introduction

Credits: XKCD

The following is adapted from a lecture by Dr. Sabieh Anwar cited at the end of this post:

Why Study Quantum Physics?

A common question that comes to our mind is: “Why are we studying Modern Physics?” After all, most of us want to become Electrical Engineers because that’s the way the wind is blowing these days. ‘Because that’s where the wind is blowing and we are trying to aimlessly follow the wind.So the question is, in a way, why exactly are non-Physics majors enrolled into this course?’ [translated] The reason for that is that Modern Physics … is one way to look at Nature. Modern Physics has transformed the way we look at Nature. [It] has transformed the way we invent technology. It has transformed our philosophical understanding of our surroundings. So it has transformed our outlook of life. And it’s a very embracing concept … If you look at electronic circuits, almost 75% of the revenue that comes these days in microelectronics is based on devices and inventions that are built on concepts learnt from Quantum Physics …

If we talk about lasers, ‘2010 marked the 50th anniversary of the laser. The first laser was made in 1960. So now we have lasers which are used in DVD-roms and CD players. How do lasers work?’ [translated] What is Silicon? Almost 25% of the Earth’s crust is made of Silicon. Such an abundant material. But why is Silicon so important in the electronic industry? What special features does silicon, or germanium, possess? What is the Big Bang experiment? What are X-Rays? How does diagnostic radiology work? We have a fractured bone. We visit the hospital, and an “X-ray” is performed. How do solar cells work? So all of these are concepts which are vital for an understanding of today’s technology, and an understanding of nature itself. A fundamental understanding of nature.

‘You took courses on Mechanics and Electricity & Magnetism in Freshman year. That was the classical way of looking at Nature.’ [translated] And it’s a very important perspective. With this perspective you can understand a large part of nature. You can understand and decipher how a large number of inventions work. The industrial revolution was based on Mechanics and Heat & Thermodynamics. The entire communications revolution that emerged with the discovery or the invention of radio waves by Heinrich Hertz in the 1890s, that uses concepts of electricity and magnetism. Every one of us carries a cell phone today. You need electricity and magnetism to understand how cell-phones work. Building new cell-phones or optimizing cell-phones. These courses will give you the basics of a large number of devices and concepts in Nature. But, there are certain gaps. The classical picture that was given to you in your first year was incomplete. …. It contains some gaps. There are some things that cannot be explained by it. And now when we’ll study Modern Physics, this will be your first curtain-raiser, your first introduction to non-classical Physics. And classical Physics is a subset of non-classical Physics. If I try to make a diagram:


So what we’ve learnt in the first year is classical Physics. … So now we enter the realm of non-classical Physics which is basically Quantum Mechanics or Quantum Physics. Now this Quantum Physics is a superset of classical Physics. When you look at classical physics, you’re actually looking at average non-classical behavior. So what’s really happening is you have this non-classical realm and you’re averaging this non-classical behavior to observe what is called classical behavior.


– Sabieh Anwar, Lecture 1-A, Modern Physics (2011), School of Science and Engineering, LUMS.

(For oppressed people in idiotic totalitarian countries where youtube is banned (like my country): )


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