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.

A small maths lesson for our prime minister - Physics Stop

Sep 03, 2015

This isn’t physics but I do feel strongly about it. John Key today is reported by the New Zealand Herald today as saying, with regard to the refugee crisis: :  It’s a global problem. I accept everyone needs to take their fair share of responsibility but actually as a government we have been doing quite a lot over recent years and I have every confidence we’ll do more in the future. Has Mr Key done his maths on what is New Zealand’s fair share of responsibility? Because it’s rather more than the yearly 750 quota that I’ve heard reported as being New Zealand’s current contribution. Just how many refugees have fled or are fleeing Syria alone. My understanding is that it’s the majority of the population. OK, so I’m not a demographer, but I think 10 … Read More

How to get entry into a physics degree (but not necessarily physics) - Physics Stop

Sep 03, 2015

So, I’m now back from a lovely holiday in the UK, following a not-so-lovely period of being sick. Quite possibly I can also get back to blogging. Among the great many emails awaiting for me yesterday were a few about school physics and university physics. They were coming from different sources for different reasons, but there was a co-incidental unifying theme which went along the lines of ‘how well does school physics prepare students for university physics?, and how well does university physics prepare students for a career in science?’.  First, the school-to-university transition. Here’s a quick little piece by Peter Coles in  Times Higher Education, drawing from an Institute of Physics report on the male-female balance in ‘A’-level physics. A key point he makes is that efforts by universities to recruit more women … Read More

Pluto as you’ve not seen it before - Physics Stop

Aug 03, 2015

Most of us have never seen Pluto. Most of us never will. Neptune is more plausible.I remember as a student looking for Neptune with the Northumberland Telescope in Cambridge. We were doing a 'planets' night - in which it was theoretically possible to tick off all the planets (save Pluto, which was still a planet back then) in one night. A hunt for Neptune had some historical significance - James Challis failed to find Nepturne with the same telescope in 1846. As I recall, we failed to find it too. We might have seen it, but without taking a photograph and coming back to the same area of the sky the next night, we weren't going to be certain. But I remember the view of Mercury just after sunset being spectacular - that's a planet that doesn't often show itself, being so close to the sun. 

Anyway, back to the 'Trans Neptunian Object known as Pluto'. The New Horizon's website has some fantastic pictures. Here's my favourite so far - a 'time-lapse' film of our view of Pluto through the years. The latest images are unimaginally detailed compared with what I remember seeing in the popular astronomy books when I was a child. 



Calculating pi with darts - Physics Stop

Jul 16, 2015

I love this one. Really, it's maths not physics, but there is a bit of experimental physics creeping in at the fringes when the experimenters realize that the first method is biased. The second method is much better designed. 

Regrettably, pi-day (March 14th, 2015, or 3.14.15) only works if you use the US system of recording dates.  But fear not,  e-day (2nd July 2018, or  February 7th, 2018 if you're American) isn't so far away...

A light puzzle - Physics Stop

Jul 13, 2015

Here's a puzzling photograph that Hans Bachor showed me at the end of the NZ Institute of Physics conference last week. It comes from his public lecture on lasers a week ago. And we don't have the answer to it, so maybe you can enlighten us (pun intended). 


The photo is of a demonstration of total internal reflection with a laser. Hans is holding a container of water, which has a small hole at the bottom. Consequently there is a jet of water emerging. A laser is held up to the container, and with careful orientation it can be made to shine down the stream of water. The light follows the water, due to total internal reflection at the boundary between the water and the air (rather like a fibre-optic). Actually, it's not TOTAL internal reflection - if it were we wouldn't see the light escaping from the stream of water, but a great proportion of it is contained within the water stream. 

Now, in this case, Hans didn't quite get the hole the right size and shape. Consequently the stream breaks up into discrete droplets, which you can see in the photograph. Now, here's the puzzle. Look at the droplets and you can see that a couple of them are shining green - i.e. they appear to have laser light in them. 

But how does that work? Light moves so much faster than water one can consider the water to be 'frozen' in space as far as the light is concerned. While the laser light will happily travel along the water stream, when the stream breaks up into drops there is no total internal reflection anymore. The drops should not be glowing. Perhaps the light is jumping from drop to drop to drop. Unlikely - each drop will scatter the light considerably so that very little will jump from one drop to the next - let alone across many drops. 

As you think about this, you should bear in mind the conditions the photograph is taken over. It's a flash photograph, but it's likely that the shutter is open for longer than the flash illuminates the scence. This might (or might not) be significant, since the flash will capture the position of the water stream, but the shutter will still be letting in light from the laser even after the flash has stopped. So the capturing of the 'green' laser light in the photograph is not completely synchronized with the capturing of the rest of the image. 

Our best hypothesis is that the light that is that drops are illuminated directly by light that is emerging from the end of the stream - that is, the light leaves the stream, travels though the air, and hits a drop. In the spirit of Eugenia Etkina's ISLE approach then, are there other hypotheses and what experiments can we formulate to test them?

NZIP2015 Highlights - Physics Stop

Jul 07, 2015

So the NZ Institute of Physics conference is in full swing. I have a bit of a break between the end of the last session and tonight's conference dinner, so there's time to give some highlights so far. 

Well, first, the low-light: Like the rest of my family and half of Hamilton I've had a horrible cold. On Sunday morning I was wondering whether I'd be able to make any of the conference. But I've managed to hold things together and now I've stopped sneezing I'm rather less infectious than I was at the weekend. So I've been able to get to some of the sessions. 

So what's been going on? We've heard from Hans Bachor that after decades of international scientific research into getting lasers to work, the world's first funding application for using lasers was for a 'death ray'. Fortunately, applications have grown well beyond this one (which is still, thankfully, not in place) and far beyond the ideas of the original researchers (i.e. 'blue sky' research can have real value). We've seen edible fibre-optics (basically jelly), and heard from Jenni Adams about the ICE CUBE detector at the South Pole for detecting high-energy neutrinos. 

The speed talk session last night gave us a rapid-fire mix-and-match bag of physics research from across the country - from Kannan Ridings' simulations of the melting of metal nanowire's through to Inga Smith's (unanswered) question of why do so few women do physics?  

But the real highlight for me has been Eugenia Etkina's inspiring talk yesterday and workshop this morning, on physics laboratory experiments. The basic idea here is that experimental science is done by experts in a particular way (and she has evidence for this), including a cycle of observation, hypothesis, experimental design, prediction-making, experimental testing, then judgement. Experiments  by experts are done for particular reasons - either to observe, to test, or to apply. Give a group of scientists a practical problem and they will tackle it in a very systematic way, that usually allows them to get to the bottom of what's happening. Give the same problem to first-year university students, and it's a mess of hypothesis, tesing, judgement, observation all rolled into one. So it then makes sense for us to give students opportunities to carry out the same scientific processes as real scientists. Too often we give them a series of instructions to follow. This isn't how real science works. It simply doesn't help them learn science. 

At the end of her talk, Eugenia asked a very simple but really telling question. "How do you know that Newton's third law is true?" My initial answer, to be honest, was: "because the text-books say so". Not the answer of a scientist.  Thinking about it a bit more, I can say "because that's what I experience...if I hit something hard it hurts...i.e. if I exert a large force on something it exerts a large force on me". But here's (roughly) what one of Eugenia's students said when given the same question:

"I have carried out many independent tests of this law and have not found a single case where it is violated." Now, that is the response of a real scientist. 






High-tech, Low-tech, planetary observations. - Physics Stop

Jul 01, 2015

First the low-tech:  The conjunction of Venus (the brighter one) and Jupiter as recorded by my very lousy cellphone camera  just after sunset yesterday. 


Now the high-tech: A day before that Pluto occulted a star. It moved in front of the star, rather like an eclipse. The significance of the event was that it allowed Pluto's atmosphere to be studied - by looking at the way the light moved through and around the atmosphere, various properties of the atmosphere can be inferred. The SOFIA project was in action, capturing the event, at the other end of the cost spectrum to my mobile phone.

There'll be more Pluto excitement coming as the New Horizons probe flies closeby in just a couple of weeks.  


P.S. I should add in the conversation I had with my son (just turned 3) yesterday, after showing him the planets outside. 

Benjamin: "I don't like planets"

Me: "Why not?"

Benjamin: "Because they're quite noisy"

Me: "How are they noisy?"

Benjamin: "Because Grandad says they're quite loud, actually."

Umm.... Work that one out!

Tips on organizing a conference - Physics Stop

Jun 23, 2015

With the NZ Institute of Physics conference rapidly approaching, I thought I'd share my thoughts and experiences on how to organize a good conference. Or maybe on how not to organize a good conference. Time will tell.

1. Don't try organizing a conference when you have 450 exam scripts to mark. 

2. Employ a professional conference organizer. They are worth their weight in free conference alcohol. 

3. Remember that participants at your conference will read 'deadline' as 'guideline'. Don't expect more than half your abstracts to come before the advertised deadline. While it's tempting to reject abstracts that are late, the reality is that we can't afford to do that. So it's a good idea to work out when the deadline really is, and advertise it for two weeks before then. One could say that exacerbates the problem, because your contributers will learn to take your deadline (whenever you set it for) and add two weeks to it. 

4. Remember, that any 'extended deadline' will be read as being 'extended guideline'. There will still be abstracts coming in well after the two-weeks extra that takes you up to where your deadline really should have been in the first place. And you can't afford to say no. And they'll be asking to be placed in premium oral slots, too. 

5. Inter- and intra-organizational politics is just as complex as parliamentary politics. 

6. Don't be treasurer of the organizing body (in this case NZ Institute of Physics), a key conference organizer, and an employee of the host institution (in this case University of Waikato) all at the same time. Way too many conflicts of interest to manage all at once. 

7. All the above notwithstanding, the conference will probably go very well and the average attendee will have no knowledge of points 1-6 above. So don't tell them. Whoops. 

And, finally, if you're a member of the physics community, remember it's not too late to register. And if you're not, we have two excellent public lectures lined up for you on the evenings of Sunday 5th July and Monday 6th July. See you there!


The equation of time strikes again - Physics Stop

Jun 17, 2015

Some of us are rather looking forward to getting to 22 June. That's when the days get longer again. Yes, the reality is that no-one's really going to notice much difference for a while, but it's encouraging to think that the days will be getting lighter again, if only by a little bit. Don't confuse that with temperatures getting warmer - the coldest day (on average, of course) lags the darkest day quite considerably. Here it's around the end of July

But there's an interesting effect going on with sunrise and sunset. We've already had the darkest evening (hooray!) yet the darkest morning is still to come. Look at the sunrise and sunset times (for Hamilton) on the MetService website: today we've had sunrise at 7.32am and with cloudless skies the sun may stay out all the way to sunset at 5.07pm. But tomorrow sunset is recorded at 5.08pm (later!) and on Saturday sunrise has shifted to 7.33am (also later!). How can that be?

The point here is that the length of a day, meaning now the time between when the sun is at its highest to the next time the sun is at its highest, is only 24 hours on average (for some periods of the year its greater, for some periods is less), and isn't equal to the time it takes for the earth to spin once on its axis. 

Let's take this last point first. It's solar midday, meaning that the sun is at its highest. Now, let the earth rotate exactly once on its axis. Do we get back to solar midday the next day? No. That's because, in the time taken for the earth to rotate once, it has also moved along its orbit (about 1/365th of the way around). That means it's got to spin a little bit more before the sun reaches its higherst point. The time to spin once (the siderial day) is about 23 hours 56 minutes - four minutes less than the mean solar day. Note that 4 minutes x 365 = 24 hours - which means one more revolution than you might expect  - the earth actually does 366 and a quarter revolutions each year. 

However, the movement along the earth's orbit in a day is only on average 1/365th of the orbit. When the earth is closest to the sun (called perihelion - 3 January at present) it moves faster. That's Kepler's second law. When it's further away (at this time of year) it moves slower. That would mean that in January, we should perceive that solar midday gets later every day by our watch (since the earth needs extra time to spin that extra bit more), but that in July, the solar midday should be getting earlier. However, that's not what is observed. Our prediction for January is true, but for July it's the other way around - solar midday actually gets later as measured by our watches. 

There's another effect going on.  This is because the earth is tilted on its axis. However, it's quite tricky to explain why that makes a difference.  Consider the transition from winter to summer, in the southern hemisphere. If we look at the position of the sun at sunrise and sunset, we see it move southward from one day to the next. What is significant is that at sunset the sun is further southward than for the previous sunrise. That gives us a shift in the measured time between solar midday and the next solar midday. A better explanation is given here.  This effect is 'zero' at the solstices and equinoxes, and does two cycles a year. Add this to the effect of Kepler's second law, and we get the odd-looking curve that is called 'the equation of time', and means that, at present, each solar day is slightly longer than 24 hours, giving both ligher evenings and darker mornings. 

You can see a net result displayed on the ground under the sundial in Hamilton Gardens. The elongated figure-of-eight is called an 'analemma'. It will show you the position of the tip of shadow of the pole at different times at different times of year.





Two great talks coming up in Hamilton - Physics Stop

Jun 11, 2015

As part of the forthcoming NZ Institute of Physics conference, and to celebrate the International Year of Light, we have arranged two fantastic and very different public talks for the evenings of Sunday 5th and Monday 6th July. 

First up we have Richard Easther, from the University of Auckland. In "Dawn's Early Light" he'll be talking about cosmology and the early universe. (Sunday 5th July, 7.30pm, Price Waterhouse Coopers Lecture Theatre, University of Waikato),

Then the following evening Hans Bachor, from the Australian National University will enlighten us (pun intended) on the everyday use of lasers. "Lasers are part of your life." This will include some exciting laser demonstrations, all done safely. (Monday 6th July, 7:30pm, Concert Chamber, Gallagher Academy of Performing Arts, University of Waikato). Note the different venues for the two talks. 

So if you're local to Hamilton, do come along and see (another pun) cutting-edge physics from those that do it. Both talks are free.