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 final frontier - Physics Stop

Nov 24, 2009

New Zealand is, hopefully, just a few days away from becoming a space-nation. The private company Rocket Lab  (what a great name - I like names that describe what a business actually does) aims to put up its Atea-1 rocket from Great Mercury Island sometime around November 30th. The payload will reach an altitude of 120 km before returning to earth and being recovered.

But how high do you have to put something to get it into space?  The earth's atmosphere does not have a well-defined edge - atmospheric pressure decays roughly exponentially as altitude increases. At about 6 km altitude, the pressure is about half what it is on the earth's surface; and it approximately halves for every further 6 km you go up. So it doesn't take long for there to be little left. The lowest layer of the atmosphere is the troposphere (to about 10 km in altitude, but rather variable); here it gets colder as you go upwards. Passenger jets typically cruise at around 10 km in altitude.

Above the troposphere is the stratosphere; this goes to about 50 km in altitude and curiously temperature increases again as you go upwards. However, with so little air pressure, temperature starts to become somewhat less meaningful. With pressure so low at 50 km, the top of the stratosphere is not accessible to conventional aircraft (jet or propellor), but has been reached by rocket plane.

Beyond the stratosphere is the mesosphere (temperature decreases with height again), and beyond that is the thermosphere (temperature, for what it's worth, does a reverse again and now increases with height.) There's not much air left at all, and at 100 km the Karman line marks an arbitrary boundary as the 'edge of space'. Karman calculated that at about that altitude a place would have to travel so fast to gain enough lift from its wings it would be in orbit.  The Karman line is where the Federation Aeronautique Internationale sets the boundary for 'space', and it is where the Atea-1 rocket will have to reach before it is recognized as reaching space.

Prisoner’s Dilemma - Physics Stop

Nov 20, 2009

Writing my last post on public transport etiquette prompted me to recall William Poundstone's excellent book an game theory, 'Prisoner's Dilemma'.  Poundstone, in a very accessible manner, discusses the ideas behing game theory (a branch of mathematics developed by John Von Neuman), illustrating it terrifyingly with examples from the Cold War.

Deciding whether to get on the first bus, the crowded one that is already late, thus delaying it further, or waiting for the second, that is nearly empty and running ahead of time, is a dilemma. Do the former, and you'll get to work a little quicker than you would if you did the latter. Do the second, and your journey takes a bit longer, but it is to the benefit of everyone else on the first bus, who aren't delayed further by your boarding. The choice is yours. Our mathematician friends in Mexico are obviously going to try a publicity campaign for people to do the latter.

Bus problems - Physics Stop

Nov 18, 2009

There are a significant number of people who view scientists as boffins in white coats who lock themselves in their labs for twelve hours a day while they invent things that are entirely useless to anybody.  This view is somewhat stereotyped, and I hope my blog goes a small way to changing it. (Am I succeeding? - you tell me please).

So needless to say when I find scientific articles that basically support the boffin picture, I tend to put my head in my hands and wonder why I bother. 


Random use of the word ‘exponential’ - Physics Stop

Nov 15, 2009

One of the things I find mildly amusing is the way that physics and maths words get taken up into everyday vocabulary, where they take on a slightly different meaning from the original. The word 'random' seems to be a favourite in NZ at present, as in "I bumped into this random guy and he said this random thing". Others include 'infinite', which means merely very big "The All Blacks were infinitely better than the Wallabies"; and 'exponential', which means increasing rapidly "The NZ dollar is increasing exponentially".

What’s that buzzing? - Physics Stop

Nov 12, 2009

(Amended to correct major factual blunder - whoops - and more details added from original post of earlier today).

I was fascinated to read in the Herald this morning about the anti-teenager sounds that are being used to deter graffiti artists. High-pitched sounds that only the young can hear are being used to deter people away from places that tend to get subjected to vandalism. A quick bit of research shows that these systems have existed for a while. Whether they are ethical or not, I guess is a moot point. It makes some kind of implicit assumption that all children are criminals.

Group dynamics - Physics Stop

Nov 10, 2009

Well, I went down to Wellington last Thursday and presented at the Science Express event at Te Papa. It was the third time I've done a talk in that manner on the Large Hadron Collider, and it was for me intriguing how the audiences have picked up on different things each time.

The first time (Hamilton, late last year) the audience wanted to know about the structure of the nucleus - what's in a proton? (answer - three quarks, or at least we think so) - what's a quark made up of? how do they interact? and so on.  (If this sounds like you, have a read about the ALICE experiment at the LHC).

Bring on the computer - Physics Stop

Nov 09, 2009

To err is human, but to make a real mess requires a computer. Whether it is sending out a gas bill for ten million dollars, or sending a letter to the parents of a one-hundred-and-four year-old woman reminding them that she is due to start school, the rise of the computer has certainly opened up new avenues for getting things wrong in a big way.

But really it's not the computer that gets things wrong. It's the people that told it what to do. A computer is very good at obeying instructions. The trouble is, being just a collection of electronic circuits, it has no ability to independently check them for sanity first.