Marcus Wilson

Dr Marcus Wilson is a lecturer in the Engineering Department at Waikato University and author of the Physics Stop blog. His current research involves modelling of the electrical behaviour of the human brain during natural sleep, focussing particularly on the transitions between sleep states. Previous research interests include infra-red physics and signature control (stealth) and quantum Monte Carlo methods. He graduated from Cambridge University in 1992 (BA Hons) and completed his PhD at Bristol University in 1995.

The problem with science communication - Physics Stop

Feb 24, 2016

Yesterday I was part of a very interesting workshop on Science in Society, in Auckland. There was a plethora of good examples of science communication discussed – including forest restoration on the East Coast, biological control of pests in vineyards in Canterbury and improvement of health outcomes for Native Americans in Montana. For me, it was clear that there were some resounding messages coming through about science communicaton. 1. It needs to be driven by the community. Here, community could mean a town or village, a marae, an industry group, a school – any group of people with an interest in achieving something. The participation of the scientist is as a partner, often as a junior partner. In other words, the community takes the lead. The scientist(s) doesn’t go out and say “Right, now I am going … Read More

Gravitational Waves - Physics Stop

Feb 12, 2016

The big breaking physics news is the detection of gravitational waves. These waves are distortions in space-time, caused by a large mass doing something spectacular (two colliding black holes in this case)  that propagate across the universe and create tiny changes in space when they reach us. The commentary here describes what goes on. Essentially, things change their length/width. When a gravitational wave passes through my office (say ceiling to floor) one can imagine the length of the office increasing slightly, coupled with a decrease in the width of the office, followed by the reverse – a decrease in the length and an increase in the width.  But its not just that the bricks that make up the room vibrate (e.g. as in a seismic wave) – its the whole of space that does it. These waves … Read More

Trusting your life to your own physics calculations - Physics Stop

Jan 30, 2016

Alison Campbell alerted me to the following: Physicist Andreas Wahl shoots himself with a gun underwater – and proves a point about drag force.  For the record – I won’t be repeating this. Physics or no physics, the guy is crazy. BUT, what I have done, is a quick post-hoc analysis from the safety of my own office. There’s a little bit of maths involved, but the gist of it is this. The drag force on an object (in turbulent conditions – which this most certainly is), is given by the equation c rho A v2 where c is the ‘drag coefficient’, rho is the density of the fluid in which the object moves, A its cross-sectional area and v its speed. If we equate this to the objects mass times acceleration (Newton’s second law) we get an expression … Read More

The world’s most beautiful equation - Physics Stop

Jan 25, 2016

Don’t miss the BBC poll on what is the world’s most beautiful equation. Are you a fan of Einstein’s field equation, or does the Riemann zeta-function hold you in raptures? There’s some great commentary on the twelve candidates here.  How did I vote? Well, that would be telling, but the fact that my very first publication is titled Auxiliary-field quantum Monte Carlo calculations for the relativistic electron gas [read it here! – at least if you have access to the Journal of Physics: Condensed Matter] might give the physicist readers a few clues.    … Read More

Don’t confuse accuracy with precision - Physics Stop

Jan 22, 2016

Going back to my last post, our fancy balance proclaims that it weighs objects from 0 to 200 g with a precision of 0.001 g (that’s one milligram).   And it does – put an object on and the balance gives you an attractive-looking number on its prominent display reading 184.139 g, or something similar. It is precise to 1 milligram. It’s not reading 184.138 g, neither is it reading 184.140 g, it is reading 184.139 g. So does that mean our test object has a mass of 184.139 g? Unfortunately not. Just because the balance gives us that number that precisely, it doesn’t mean that it is that accurate. University lecturers always have a good giggle when some poor unsuspecting first-year student records an answer to a wildly inappropriate number of significant figures – for example, … Read More

Weighing magnetic properties - Physics Stop

Jan 12, 2016

It’s a New Year and there are lots of things to do at work before the students get back in any numbers. There are still summer students and research students here, and in the last couple of days I’ve been working with a summer student on getting a new piece of equipment running for our Experimental Physics paper – the Gouy Balance for measuring magnetic susceptibility. Schematic of the Gouy Balance. Source: Wikimedia Magnetic susceptibility is a measure of how magnetically responsive a material is – how much it magnetizes when placed in a magnetic field. Materials can be categorized as diamagnetic, paramagnetic or ferromagnetic. Paramagnetism describes a material that magnetizes with the applied magnetic field – that is, it will be attracted to a region of high magnetic field. A ferromagnetic material goes beyond this … Read More

Tip or slide? - Physics Stop

Dec 18, 2015

We had our departmental Christmas lunch on Tuesday, outside in the campus grounds. We had some lovely sunshine, but the wind did rather spoil things. I’ve certainly got used now to living in a very wind-free place – a fresh breeze is something quite unsual here. We were hanging on to our paper plates, but didn’t expect to have to hang on to glass drink bottles as well. One particular gust was strong enough to take a newly opened individual-serving-sized glass bottle of lemonade and blow it over.  So, being a physicist I had a go at estimating just how strong the gust of wind needed to be to push over a lemonade bottle. As the wind hits the bottle it has to change direction, and this causes a change in its momentum. To do that requires a … Read More

On the track at the Avantidrome - Physics Stop

Dec 14, 2015

Yesterday I finally managed to achieve one of the things on my ‘to do’ list that’s been sitting there for about a year – attend a ‘Have a Go’ session at the velodrome in Cambridge. For those that don’t know it, it’s New Zealand’s new (which means about two years old) world-class velodrome and now ‘home’ to New Zealand cycling. It’s an impressive building – probably more so from the inside than the outside. Walking into the central area the first thing that greets you is a terrifying view of the banking on the corners. We were told it’s 43.5 degrees. It’s the kind of slope you’d find on a steep slide in a playground. And we’re meant to cycle on it. But our instructor built us up gradually to this. First off, was just getting used to … Read More

Is dark matter really dark? - Physics Stop

Dec 07, 2015

What is dark matter, or is there no such thing? Last week I attended a seminar by Ian Hawthorn of our Maths Department. He talked about some work which he’d done with a couple of students, Matt Ussher and William Crump. The title is a bit of a mouthful “The physics of sp(2,R)”  (what does that mean?) and I have to say that I didn’t follow most of it. But I did follow some of what Ian said, some of the time, in some places. Before I comment on what Ian said, first I need to say what dark matter is. Actually, that’s quite hard, because we really don’t know. It’s matter that we think is in the universe, but we can’t see. Why do we think it’s there? We can observe the structure of galaxies, and how … Read More

And the Nobel Prize in physics goes to… - Physics Stop

Nov 27, 2015

…the United States of America, of course. Hamish Johnston, editor of, has put together a neat little piece looking at where Nobel physics laureates start and end their days. There’s no surprise on the net migration front – a huge flow from everywhere to the US. What Johnston’s graphic doesn’t indicate is when the award winner migrated (e.g. was it before or after their prize?) and multiple migrations – he just shows where they were born, and where they died or are currently living. The biggest ‘loser’ is Germany – in fact a whopping 13 German-born laureates left Germany (11 of them for the US, including Albert Einstein, and 2 to Switzerland) although World War II accounted for many of the migrations here. While 30 laureates have immigrated to the US, only 2 have emigrated including the … Read More