Matt Evans

An interesting blog about interesting things.

# physics

• Anatomy of a Particle Physics Experiment Feb 19, 2014 - 9 min read

Recently I returned from a particle physics experiment at the Paul Scherrer Institut, a nuclear research lab in Switzerland. I was one of ten students from the University of Heidelberg and ETH, Zürich who had two weeks of (nearly) free reign to carry out an experiment on the PSI’s proton beam line. To put into perspective how crazy that is, ordinarily the going rate for such a privilege is €10,000s per day!

Our goal was to measure a mysterious number called the “Panofsky ratio”. The ratio is named after Wolfgang Panofsky, first to attempt to measure it, and corresponds is the relative likelihood of two events involving particles called protons and pions occurring. It is important, because historically its value strongly contradicted the expectation of theoretical physicists.

• Solving the Schrödinger Equation with Numerov's Algorithm Jul 10, 2013 - 3 min read

The Schrödinger equation describes the energy and time-evolution of a particle or system of particles, and is one of the fundamental building blocks of modern physics. In it’s general form, the (time-independent) Schrödinger equation for a one-dimensional harmonic oscillator reads thus:1

$$\label{eq:sch} \frac{-\hbar^2}{2m} \frac{\partial^2}{\partial z^2}\psi(z) + \frac{mz^2}{2} \psi(z) = E\psi(z)$$

There are relatively few situations in which the Schrödinger equation can be solved analytically, and numerical methods and approximations are one way around that analytical limitation. To demonstrate how this is possible and how a numerical solution works, what better way than to solve a system which can be solved analytically and comparing the results.

• Fourth Order Runge Kutta Algorithm in Javascript With Demo May 2, 2013 - 3 min read

The general Runge-Kutta algorithm is one of a few algorithms for solving first order ordinary differential equations. Below is a specific implementation for solving equations of motion and other second order ordinary differential equations (ODEs) for Physics simulations, amongst other things.

• Physics Bungee Rope Cursor Trailer Apr 13, 2013 - 1 min read

I’m getting ready for starting a course in computational physics, and so, ignoring the fact I’m meant to be revising for an exam this Monday, I thought I’d prepare for the more exciting of the two. I’ve always wanted to code this little physics model ever since I saw it on one of those JavaScript snippet websites back when dial-up was fast and people downloaded mp3s one at a time. Those were the days.

• Physics Problems and Related Stuff Dec 2, 2012 - 1 min read

Just a quick one here. It’s pushing a month since I last checked in, and not for want of desire. I’ve not been entirely negligent though: I’ve been busy putting together a few typed up solutions to both foundational and pretty challenging/rare problems in statistical physics. My motivation is two-fold: a) to get extremely familiar with the material, what with exams just around the corner and b) for a few of the problems, the solutions are nearly impossible to do or to find help online for if you can’t do them.