A look at Richard Feynman’s QED Lectures: Part 3

A Feynman diagram for what happens when an electrons and its antiparticle (the positron) annihilate.

This is part 3 of the four part summary of Richard Feynman’s lectures on Quantum Electrodynamics. This lecture focuses on describing the transmission and reflection of photons, as well as providing an introduction to his famous Feynman Diagrams which describe how subatomic particles (e.g. electrons, protons, neutrons) interact.

This lecture also includes a basic introduction to his famous Feynman diagrams and the underlying principles to understand them.

Lecture 3: Electrons and their interactions

In the last lecture, Feynman introduced us to calculating the probability of compound events, that is events with multiple steps. Following on from that, Feynman presents us with the following rules for our calculations:

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A Look at Richard Feynman’s QED Lectures: Part 2

Welcome back! This next lecture is focusing heavily on photons, the packets of light, and the how to calculate probabilities. Both of these were mentioned in Part 1, but in this lecture Feynman goes much more into depth as well as introducing interference.

Lecture 2: Fits of Reflection and Transmission- Quantum Behaviour

Feynman sets up this lecture with a diagram: a source, S, is pointed at an angle at a horizontal reflective surface. Horizontally across from the source is a photomultiplier, P, with a block between S and P to stop photons directly travelling to P without reflecting. Given I’ve described the situation correct, you should have a mental image something like this (minus the lines):

The lines represent the different paths a photon from S could take to get to P. While we might normally expect one line going to the middle of the reflective surface at G so as to obey the rule that the angle of incidence is equal to the angle of reflection, instead there are many different lines. And these lines seem counter-intuitive. Why would a photon go backwards to hit the reflective surface at A, meaning it has to travel even further to get to P?

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A Look at Richard Feynman’s QED Lectures: Part 1

A short introduction to QED

QED stands for Quantum Electrodynamics, the relativistic quantum field theory of electrodynamics- in short, it describes how light and matter interact.

Richard P Feynman, American theoretical physicist

QED was worked on by many scientists including British scientist Paul Dirac, Hans Bethe and Richard Feynman who ultimately came up with Feynman diagrams in 1948 to represent the behaviour of subatomic particles. Feynman, Julian Schwinger and Shin’ichirō Tomonaga, jointly received the Nobel Prize in Physics in 1965 for their work on QED.

In 1985, Feynman gave a series of four lectures on QED called “QED: The strange theory of light and matter”, the first of which I will be summarising below.

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How diamond’s properties can be used to differentiate it from fakes

Diamonds are a girl’s best friend.
Marilyn Monroe

Yep, someone probably said it before her. And however questionable you find it, diamonds find themselves among the most expensive gemstones in the world, and it’s obvious why. With a low critical angle, light is totally internally reflected inside a diamond many times which is what gives diamonds their super sparky appearance. But how are jewellers able to identify between the real deal and the fakes?

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How does non-melting chocolate work? A look the methods of creating non-melting chocolate and the use of cocoa butter alternatives.

I spent the majority of my childhood in Australia, so naturally I grew with Australian chocolate: the taste, texture, and most importantly its resistancy to melting in the hot climate.

When I was 8 years old I visited the UK and had my first taste of UK chocolate. While Australian chocolate is waxy and can form insoluble clumps in your mouth, UK chocolate has a thicker, richer consistency. While Australian chocolate refused to melt even in 40 degree heat, UK chocolate could melt in the palm of my hand.

I began to wonder: how could two products under the same brand name react so differently to the same conditions and what causes this?

cadbury comparison — An Australian/US Cadbury bar (left) and a UK Cadbury bar (right)

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