# 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.

## Gravitational Waves - Physics Stop

Oct 20, 2009

One of my undergraduate students has been researching gravitational waves this year. Last Friday, he gave a nice presentation on the subject.

Gravitational waves are one of the many examples of waves in physics. We are perhaps more used to waves on the surface of water, or waves along a guitar string, or electromagnetic waves (such as radio waves and light), and, in many ways, gravitational waves aren't much different.

But they are a little strange. Whereas a radio wave travels through space and time, a gravitational wave (caused for example by a supernova)  travels 'on' space and time, rather like a water wave (caused by throwing a stone into a pond,) travels on the surface of water. This means that space-time distorts as the wave goes past. When a gravitational wave hits us front on, we will alternately squash in height and expand widthways, before squashing widthways and growing in height (the preferred option for most of us).

These changes in lengths are not some mathematical construction, they are real. At least, they are predicted to be real, but, to date, no-one has actually detected a gravitational wave. The problem is, that unless you are standing next to a supernova, the changes in length due to gravitational waves are very small indeed.  Imagine a rod the same length as the distance from the earth and the sun.  Now imagine it growing in length by about the width of an atom. That is the sort of distortion we are talking about. Not surprising that no-one has built a detector sensitive enough yet.

But that doesn't stop people trying. Detectors on earth are limited by, for example, seismic vibrations, and the constraints on how large an object you can build. But space doesn't have those problems. And so there is the LISA concept; three satellites in a large triangle 5 million kilometres apart, following the earth in its orbit around the sun, linked with laser beams. And you thought the Large Hadron Collider was ambitious.

If your internet link will cope with 40 MB, watch the movie

## The3is in Three - Physics Stop

Oct 19, 2009

I reckon that every scientist should be able to explain his or her work to any audience, in any situation. Whether it is a 30 second conversation with a six year old with the aid of a pencil and paper, an oral presentation to the general public (a la cafe scientifique), or a detailed effort using all the functionality of Microsoft Powerpoint at a specialist conference, it should be possible to convey meaning to your audience. In fact, if I'm feeling brave, I would go as far as to suggest that if a scientist is unable to do this, it is an indication that he or she does not understand the topic him- or herself.

## The physicist joke - Physics Stop

Oct 17, 2009

So, for those who want it in full, here is the joke I referred to earlier.

A geneticist, a physicist, and a statistician are all asked by a gambler to advise him on which horse to place his money in the Melbourne Cup.

## More chemistry-bashing - Physics Stop

Oct 15, 2009

There is nothing a physicist likes better than to get one up on a chemist. In a friendly way of course. Rather like New Zealand beating Australia at some sporting event.

So it is with great delight that I hear that the 2009 Nobel Prize in Chemistry has been awarded to a physicist. (See commentary by The Institute of Physics).

Venkatraman Ramakrishnan is not the only physicist with this distinction. Ernest Rutherford was awarded the Nobel Prize for Chemistry (not Physics) in 1908. Rather ironic for someone who said "All science is either physics or stamp-collecting."

## Large Hadron Collider activity - Physics Stop

Oct 14, 2009

Activity is really hotting up (should that be 'cooling down'?) at CERN as the Large Hadron Collider is prepared again for proton-proton collisions, hopefully in November. Most of the beam tunnel is now at operating temperature (1.9 K), with the rest expected to be ready very soon. I would expect to see the collider hitting mainstream media again shortly. The latest CERN bulletins can be found on their website.

## Everything’s relative - Physics Stop

Oct 13, 2009

What does 'big' mean? How big does something have to be in order to reasonably carry that adjective? The answer, of course, is 'it depends'.

For example, I am pretty tall. But after standing next to someone much taller than me on a tram last week, I realise that maybe I am not so tall after all. I got to see what it was like for many people looking at me.

## Miscellaneous thoughts on physics research - Physics Stop

Oct 09, 2009

Last year, according to the American Physical Society, there were over a hundred thousand articles published in physics journals

## Approximately speaking - Physics Stop

Oct 08, 2009

Physicists are notorious for making approximations.  This character trait is the subject of many jokes - for example, one rather rambling one involving a physicist advising a punter on which horse to put his money ends with the line "Oh, didn't I tell you - my calculations assumed a spherical horse rolling through a vacuum."

But approximations are useful things. The general idea is that a physicist will want to consider something in all necessary detail, but no more.  All necessary detail is obvious - for example it is very hard to adequately describe static electricity without talking about positive and negative charges. But physicists don't like going the other way either - for example the reason why the earth orbits the sun can be explained without invoking General Relativity. It just adds in extra complication that is not necessary.

## Brief pause - Physics Stop

Oct 02, 2009

I'm having an extra llllooonnnngggg weekend, so blogging may take a back seat for a few days, but I shall be back very soon.