QED Book by Feynman

 

In the Quantum Optics course of the 5^th semester, Richard Feynman is being cited by the instructor as often as Sri Krishna in Bhagwad Gita recitation. Therefore, I decided to read QED: The Strange Theory of Light and Matter by the Sarathi, Richard Feynman, himself. I hereby present the Book description; I do not want to commit blasphemy by writing the word “review”.

Intro

As usual with any book by feyman, this book is also an editted transcript of lectures delivered by him. It is a four lecture series on Quantum Electrodynamics meant for general audience, as if, Quantum Mechanics was not weired enough already. For the background, one of the most confusing things which we encounter during our earlier studies of Optics (2^nd semester or high school) is, the question, whether light is particle or wave? Mostly, we are given vague statements like, it is both;  but what the heck does that even mean? While studying Quantum Mechanics, we come to undestand that it is the “wave like nature” that we mean by saying, it is both, and it is made up of particles; nothing is superficial here.  

                                                         Feynman has cleverly used particles to explain everything; no wave equations (2^nd semester) which makes it very confusing in later stages. Let me explain what do I mean by it. We have been taught from the very early on that light is made up of photons, afterwards, we are taught how to derive diffraction and interference pattern by treating it as a “real wave” just like “water wave” and we just forget about the particle nature. To add further to the confusion, QM is introduced by inferring the results of double slit experiment. QM uses the word “waves” in an abstract sense in Hilbert space not the physical space we live in, but alas, we are left utterly confused without any discussion on the above. Feynman is the solution (no waves have been used to describe interference pattern); just go through it and you will be saved from the easily avoidable confusions which I had during the 2^nd , and 3^rd Semester.

Photons: Particles of Light

The properties of light which I learned in my school were reflection and refraction. Both have been described using photons, yes just photons, without any “waves”; just particles.

Electrons and their ....

Do you want to understand the Feynman Diagrams? You can undestand it easily if you read this chapter. The ideas developed for photons have been used on electrons, furthermore, the interactions between electron and photon, have been discussed. It was totally new to me and quite surprising that whole QED can be summaried in three laws or rules (Newton would be pleased; rest in peace).

Loose Ends

The idea of QED was further expanded to neucleus, but things are not so simple there, it seems. Nuclear interactions (strong interaction) have been mentioned and is quite analogous to QED (electromagnetic interactions), but nucleus is very very messy. Did you know that there 400 fundamental particles? You can categorise them wisely to make sense of them but still it is messy. I do not know how much change has taken place in “Field Theory” since the publication of this book but it is obviously always a great idea to understand QED from the pioneer of the field himslef (He got a prize for it; he mentioned it too).

I recommed every physics student to go through the book (152 pages only) to get to know what thinking clearly means; we fool ourselves too much and too often by just using fancy terms without knowing what we are talking about.