# Blog index

## What is a quantum field? qft

As a mathematician trying to learn QFT, a question that always bothered me was "what is a quantum field?". This blog post explains one point of view (the Schrödinger picture) on the answer to this question which I find satisfying.

## Pre-QFT 1: the quantum harmonic oscillator qft quantum

The archetypal physical system is the simple harmonic oscillator: a ball on a spring following Hooke's law follows periodic motion along a circle in phase space (its displacement and momentum oscillate sinusoidally between two extremes and out of phase like sin and cos). Understanding the corresponding quantum system is fundamental to understanding quantum field theory: indeed, quantising a free (bosonic) field turns out to be equivalent to quantising an infinite collection of simple harmonic oscillators.

## Quantum field theory reading group qft ucl

Like many people, I got into maths because I was interested in quantum field theory and didn't understand what was going on. I have spent a lot of time idly browsing QFT textbooks over the years in an effort to rectify this, but stuff always got in the way.

Ed Segal and I are planning to run a QFT reading group at UCL to improve our understanding. I will post my own notes from the reading group to this blog, as well as some foundational "pre-QFT" material which I always forget and have to re-read whenever I start looking into this stuff after a long break.

If you are interested in attending the reading group, please let Ed or me know.

## Equivalence relations revision mathm205

Equivalence relations are an important concept in mathematics, but sometimes they are not given the emphasis they deserve in an undergraduate course. Having a good grasp of equivalence relations is very important in the course MATHM205 (Topology and Groups) which I'm teaching this term, so I have written this blog post to remind you what you need to know about them. I will kick off with a few examples, then give a more formal definition.

## Theorem and proof environments in CSS blog org

Here is a nice idea from Dr Z.ac, the blog of Zachary Harmany. You can use CSS to create LaTeX-style theorem/proof environments on a website.

## Connecting to wifi from command line linux wifi

I so rarely need to connect to a new wifi network that, when I do, I always forget how I managed to do it the previous time. For future reference, here's how I did it this time (using "NetworkManager Command Line Interface" or "nmcli"):

$ nmcli dev wifi list $ nmcli dev wifi connect NETWORKNAME password NETWORKPASSWORD

## New blog blog org emacs

I've decided that I don't like my old blog and I'm setting up a new blog using org-mode.