Archive for January, 2016

Critical Opalescence in Carbon Dioxide

January 27, 2016

One feature of the teaching at Dalhousie University’s Physics Department is a laudable emphasis on demonstrations.

Visiting Professor Tom Duck there, I was delighted to be shown a demonstration I had heard of, but never seen: the phenomenon of critical opalescence in carbon dioxide.

I have written about critical opalescence previously on this blog (here) and with more pictures (here), so I won’t repeat most of that.

In my previous articles I described the phenomenon in two immiscible liquids which is an exact analogy for the physics of critical opalescence in a pure substance. But it’s not what physics students read about in text books.

Michael: What are you going on about?

The phenomenon occurs when one heats a liquid in a container with a small amount of free space.

  • As the liquid heats up, it expands causing its density to fall.
  • The liquid also evaporates causing the vapour (gas) pressure to increase.
  • The critical point is where the density of the liquid matches that of the vapour.

Above this ‘critical’ temperature and pressure, the substance forms a single fluid with no distinct liquid state. In the movie you can see that the meniscus at the top of the liquid just gradually disappears – there is now no ‘surface tension’.

At the critical point, the density of the fluid is typically one third of the liquid density at atmospheric pressure. Because there is no difference between liquid and gas, the latent heat associated with evaporation (when molecules move from the liquid to the gas) and condensation (when molecules move from the gas to the liquid) falls to zero.

Critical Opalescence can be seen when cooling just below the critical temperature.

The random motion of the molecules in the fluid causes some regions to transiently have densities that are slightly greater than the average (more typical of the liquid) – and others to have densities more typical of the gas.

Because the latent heat and the surface tension are very close to zero, these microscopic fluctuations can grow dramatically. Spontaneous fluctuations can cause regions as large as a thousandth of a millimetre – containing thousands of billions of molecules -to fluctuate into and out of the liquid state – forming droplets.

Although the difference in density (and hence refractive index) between the liquid droplets and the gas is tiny – it is just enough to scatter light – like a fog – a phenomenon which someone poetically named ‘opalescence’ rather than fog.

Critical Opalescence is mentioned in Physics course, but  it is rarely seen. The high pressures involved (more than 73 atmospheres in this case) present a hazard that few people are prepared to tackle. I suspect that students at Dalhousie may not appreciate how lucky they are!

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P.S. It turns out that carbon dioxide above its critical point is an excellent non-toxic solvent for caffeine and so when you sip your de-caff latte tomorrow – you can now imagine the physics that describes the fluid which took away the caffeine.

Thanks MAW

January 27, 2016
Professor Mary Anne White from Dalhousie University Halifax, Nova Scotia

Professor Mary Anne White from Dalhousie University Halifax, Nova Scotia

Last week I allowed my enthusiasm for adventure to overcome my anxiety, and what a good decision that was.

The main purpose of my visit to Canada was to visit Professor Mary Anne White (MAW) at Dalhousie University, Halifax.

While there I gave a couple of talks, and met an inspiring group of people doing amazing work. I’ll say more in the next couple of posts.

Here I just wanted to say ‘Thank You’ to Mary Anne. Firstly, for her kind invitation, but more importantly for her positivity. I found this really inspiring.

Clearly someone else found her inspiring too because on January 1st 2016 Mary Anne was awarded the Order of Canada – sort of equivalent to an OBE – for her scientific and outreach work.

Mary Anne and her team were looking at a wide range of materials problems: some very specific, some highly technical, and others which were profoundly fundamental.

Their approach to solving problems was to make precision measurements with real attention to detail, measurement uncertainty and reproducibility. Hearing her describe the approach was a heartwarming affirmation of the importance of measurement science.

One of the problems she was addressing concerned the equilibrium crystal structure of Boron – the fifth element in the periodic table. I can’t remember the name of the structure which appeared to win out – but I was shocked to find that there were still questions like this to be resolved about such apparently ‘simple’ materials.

Another problem concerned materials with negative thermal expansion – they get smaller when heated. This group of materials even includes – in one temperature range – silicon. Understanding these materials is both a matter of curiosity and of great practical value – they could allow the development of materials with zero thermal expansion which would be useful in a large number of applications.

So my task for the coming months is to allow myself to be inspired by Mary Anne’s positivity, and to incorporate a little of it into my day-to-day activities. As I face the daunting tasks ahead of me, this possibility feels like a real gift: Thanks MAW.

Anxiety and Adventure

January 17, 2016

MdeP in Canada

I’m in Canada!

And thank you for asking, I am not suffering from gut-wrenching anxiety.

Now I am anxious, but I think that is rational. I am in a strange place and I have three talks to give in the next four days: two seminars (at Canada’s NRC and Dalhousie University) and a public lecture!

I have brought demonstration equipment with me and there are quite a few things that can go wrong. So I think a certain level of anxiety is appropriate.

However, I feel determined not to let anxiety spoil the sheer enjoyment of being in this new place.

Today (Sunday) a colleague from NRC called and we went for a walk near a lake. The scene was like a picture postcard caricature of Canada: It was breathtakingly beautiful and -11 °C (I brought a thermometer: obviously) .

P1110494

We saw a council worker on a snow mobile creating ski tracks; I wore snow shoes (!); and there were families who had cleared the snow from an area of lake to play ice hockey!

It would be insane to spoil the pleasure and surprise of such experiences as wearing snow shoes by being overly anxious.

As I have been writing this, an analogy has dawned on me:

I feel as if I live in an ocean of anxiety and I need remind myself to swim in it. Occasionally I will go under and swallow a mouthful, but if I don’t panic, I won’t drown! And if I can relax a bit, it might even support me.

 

Is Physics fundamental?

January 15, 2016

This is a re-written version of a piece I wrote some 26 years ago. I was irritated reading the old version by how I didn’t stick to the point. So this version is hopefully more focussed and uses approximately half the number of words of the original.

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Fundamental adj. 1. of, involving, or comprising a foundation; basic 2. of, involving or comprising a source; primary [New Collins Dictionary

 Is Physics fundamental? As a student I certainly thought that it was, but now – outside of a very narrow domain – I really don’t think it is.

I used to imagine a hierarchy of knowledge with physics underpinning the entire structure. For example, I used to consider that molecular biology was less fundamental than chemistry, and that chemistry was less fundamental than physics. The reason for this is that chemistry, uses concepts like wave-functions and electrons, whereas physics examines these concepts in detail.

My student self would have had a hard time writing down the chain that linked psychology to physics, but he would have believed that chain did existed. And he would certainly not have regarded psychology as fundamental in any sense. I think many physicists still think this way.

But there is another way to look at things. Consider the question “What is Physics?”.

Physicists typically answer the question along the lines of: ‘Physics is the study of the (non-living?) structures in the Universe’. The precise terms of the definition are irrelevant here. What is relevant is that this definition fails to include the fact that physics is an activity performed only by human beings.

Another answer might bePhysics is a cultural tradition whose adherents study the (non-living?) structures in the Universe’. In this definition physics lines up with all our other cultural traditions, for example, chemistry, sociology, psychology, English, and even astrology! This definition does not detract from what physics is, but it does allow us to place it in a human context.

I believe that the distinction between these two answers is more than important. because it affects the way that physicists as a community think about ourselves. And it affects the way we try to communicate to students and colleagues, the special skills and ways of looking at the world that are at the heart of our tradition.

For exampleconsider the physicist’s bête noire: sociology, a subject which is obviously far more fundamental than physics. You disagree? Well ask question ‘What is physics?’ Surely physics is a social activity undertaken by specially trained groups of (mainly) men.

From this sociological viewpoint one can ask questions like ‘Why have structures arisen in society which allow people to study topic X?’ or ‘Which groups dominate the study of of topic X?’. These questions are clearly more fundamental questions than anything to do with the mere content of topic, even X where X = Physics.

One can construct similar questions involving just about any study. For example, since we communicate our thoughts using languages, it is particularly striking that linguistics and neurophysiology are ‘more fundamental’ than anything which is merely the content of thoughts or languages.

The key point here is that ‘What is fundamental?’ depends on context.

In short, it is my belief that it is important to acknowledge that Physics is an activity performed only by human beings and so human beings are central, and not peripheral, to the description physics gives of the world.

SI Superheroes

January 12, 2016

Somehow this episode of SI Superheroes came out last May (2015) and I didn’t notice!

If anything, this is even better than the first episode – perhaps because it’s more focussed on a single theme without the need to introduce all the characters.

In case you are unfamiliar with the work of NIST, the US National Institute for Standards and Technology, they are basically the US version of NPL and are a very serious organisation. In my recollection, this is only the second output from NIST that has featured laugh-out-loud moments (which I will not reveal!).

I can foresee great things for these characters.

Remember that Superman, Batman and their friends and foes inhabited a (DC) universe of paper comics for decades.

Then they became TV cartoon characters.

And only relatively recently have they become the stars of the current genre of all action, computer-graphic laden movies.

I wonder if they will be recruiting for a male with slightly older looks to play Dr. Kelvin…

9192631770

Incidentally, the number 9,192,631,770 displayed on the side of the cartoon satellite is the number of oscillations a Caesium atom that defines what we mean by the passage of one second.

At places like NPL and NIST we can make clocks based on Caesium atoms that very perfectly realise this definition.

The atoms in these super-clocks vibrate at  9,192,631,770.000 000 ± 0.000 001 oscillations per second and form the basis of Universal Coordinated Time (UTC)  that is used throughout the world.

One of the difficulties which Major Uncertainty may have tried to exploit is that the number of oscillations per second changes very slightly with changes in the physical environment of the atom.

Some of the environmental parameters that matter for clocks mounted in space are:

  • the strength of the gravitational field,
  • any accelerations that the atom experiences,
  • the  speed of the clock with respect to the person (often on the ground)  counting the oscillations,
  • the temperature of the walls surrounding the atoms.

Anyway – all is well now that the League of SI Superheroes has done their job again.

Physics is not fundamental

January 8, 2016

 

This article was written in 1990 when I looked like this. This was before the invention of colour, or children, and before I needed glasses.

This article was written in 1990 when I looked like this. This was before the invention of colour, or children, and before I needed glasses.

While searching on the internet, I came across an article I wrote in 1990 called Physics is not fundamental.

I wouldn’t quite agree with everything my 30 year-old self wrote, but I don’t disagree with much of it.

Anyway, for good or bad, here it is: all 1350 words – more than twice as long as  normal blog post: sorry.

October 1990

In between lectures, I was discussing with one of my students the reasons why he was studying physics. The student pointed to the cost of attending the course, and the extra costs involved in terms of time, books and travel, and said that if he considered it in terms of the cost of the course and the likely financial rewards, then he wouldn’t bother. He then said that the key thing about physics that made it all worthwhile was that it was fundamental. And that set me thinking . . .

I had in fact been thinking about this particular question for a long time: ‘Is physics fundamental?’. I recalled that as a student I had certainly thought that it was, but I realised that now I didn’t really believe that anymore. What had happened?

As a physics student I believed that physics was the most fundamental study one could undertake. I recall that I looked down on engineers with their apparently endless parametrisation. I recall being mystified at how someone could study English for three years! I could not conceive of how anyone could really want to study something other than physics.

My attraction to physics had grown from my teenage interest in answering the questions we all ask. ‘What is going on here?’, and ‘Why is it going on?’. I side-stepped the philosophers’ stumbling block of trying to find out whether or not I existed, and physics (or natural philosophy, as I still like to call it) was where I ended up. With the minimal assumption that both oneself and the world existed, physics seemed to supply very solid answers to my questions. However, the type of questions I asked then differ from those I ask now.

Now I have learned to ask directly solvable questions such as ‘What voltage should I expect at my pick-up coil?’. And slowly (very slowly) I have learned to answer these questions. This process is still a joy to me. However, aside from learning about these technical matters, my questioning has gone on, and I have come to think that physics doesn’t really supply very solid answers after all. In particular, I have come to the view that only in a very limited sense can physics be considered fundamental. My dictionary describes fundamental as:

Fundamental adj. 1. of, involving, or comprising a foundation; basic 2. of, involving or comprising a source; primary [New Collins Dictionary]

and it is in the sense of referring to a foundation that I use the word. I think the image that my student had in mind when he used the word fundamental was of a hierarchy of knowledge with physics underpinning the entire structure.

For example, molecular biology would be seen as less fundamental than chemistry, and chemistry would be seen as less fundamental than physics. The reason for this chain is that chemistry, for example, uses concepts like wavefunctions and electrons, whereas physics examines these concepts in some detail. Physics then in some sense underlies chemistry and thus molecular biology. My student would have had a hard time writing down the chain that linked psychology to physics, but he would have believed it existed, and would certainly not have regarded psychology as fundamental. This reductionist approach may be aptly referred to as Lego philosophy. It is my belief that a number of physicists subscribe to some version of this philosophy, and it is my aim in this article to show that there is another way to look at things.

This other way to look at things starts with the question ‘What is physics?’. The Lego philosophers answer this question with something along the lines of: ‘Physics is an attempt to study/describe the (non-living?) structure/matter in the Universe’. The precise terms of the definition are irrelevant in this argument. What is relevant is that this definition fails to include the fact that physics is an activity performed only by human beings. The physics found in books is just a part of a cultural heritage that is held in the minds of people like you and me. We are it! I would put forward another definition of physics which would start: ‘Physics is a cultural tradition whose adherents attempt to study /describe . . .’.In this definition physics lines up with all our other cultural traditions, for example, chemistry, sociology, psychology, astrology, and even English! It is a valuable tradition. No more. No less. This definition does not detract from what physics is, it merely allows us to place it in its proper context.

I believe that the distinction between these two definitions is more than pedantry. It affects the way that as a community we think of ourselves. It affects the kind of people who might want to become physicists. And it affects the way we try to communicate to students and colleagues, the special skills and ways of looking at the world that are at the heart our tradition.

Let me give a couple of examples of what I’m trying to get at.

First, consider sociology, a subject which is obviously far more fundamental than physics. You disagree? Well think about it for a while: take a look around and gather some data: What is physics? I think there are two types of answers corresponding to the two definitions I gave above. One might say physics is the keystone of a pyramid of ‘knowledge’, or that physics is an activity undertaken by specially trained groups of (mainly) men. Both answers are equally valid in their own terms.

If one takes the first view then nothing can be more fundamental than physics: ‘Everything else is stamp collecting‘.

But if one takes the second view, one is able to appreciate that different things are fundamental in different contexts. From this viewpoint one can see that questions like ‘Why have structures arisen in society which allow people to study topic X?’, are more fundamental questions than anything to do with the mere content of topic X, even where X = physics. One can construct similar questions involving just about any study. For example, since we communicate our thoughts using languages, it is particularly striking that linguistics and neurophysiology are ‘more fundamental’ than anything which is merely the content of thoughts or languages.

Secondly, let me highlight what a shift of emphasis in our definition of ‘What physics is‘ might achieve by considering my own area of work as a university lecturer. I believe that the standard of physics education at universities is appalling. One of the reasons it is so bad is that physics lecturers have failed to appreciate what it is they are doing when they give a lecture. They have failed to appreciate that physics is not a syllabus and is not contained in the ‘content’ of a lecture. It is an activity, and students are learning the social norms of that activity. Such norms include the asking of questions if you understand what is being taught, and not asking questions if you don’t! Is it really possible that rational human beings could have established such norms in an educational establishment?

If physicists could recognise that what we have is a valuable cultural tradition, then maybe we could get around to realising that the most fundamental thing about a lecture is not its ‘content’, but the establishment of norms that allow and indeed encourage students to discuss what they don’t understand. In this context psychology is more fundamental than physics.

To summarise, it is my belief that it is important to acknowledge that physics is an activity performed only by human beings and so human beings are central, and not peripheral, to the description physics gives of the world. The prize to be won by such a collective change of mindset is a reinvigoration of the community of physicists, making it a more welcoming group for people to want to belong to.

 

‘Clean Coal’ is a fantasy

January 4, 2016
The Kemper Coal Plant under construction in Mississippi USA. This is the most expensive coal plant ever construction and will release more than 10 times as much CO2 as conventional coal fired station would .

The Kemper Coal Plant under construction in Mississippi USA. This is the most expensive coal plant ever constructed and when operational will release more than 10 times as much CO2 as conventional coal fired station would . Image from Wikipedia.

Someone once put the words ‘Clean’ and ‘Coal’ together and thus created the phrase ‘Clean Coal’.

However the idea that this phrase represents does not have a counterpart in physical reality, and will not form part of a sustainable energy future.

In case you are unfamiliar with this fantasy, the idea is that by using some unspecified ‘Clean Coal’ technology, we will be able to burn Earth’s vast abundance of coal while releasing only minimal amounts of carbon dioxide.

It is important to understand that ‘Clean Coal’ technology, like ‘Flying Cars’, can be built.

Scientific American (SA) this month (January 2016) covers the technology – sometimes called ‘Carbon Capture and Storage‘. The article is a litany of expensive failure after expensive failure.

SA look in detail at the 582 MWe Kemper coal plant currently under construction. SA tells us that this is ‘the most advanced coal plant in the US‘.

When it starts working – it’s about 2 years late – it will have cost 6.3 billion dollars (3.9 billion dollars over-budget) – a price tag more normally associated with nuclear power stations – and rather defeating the whole point of the exercise.

However the real craziness comes when SA describe the plans to put Kemper’s CO2 into the Tinsley Oil Field.

This will be done to to force more oil out of the ground which will then be refined and burned and so release more CO2!

However SA do not explicitly calculate the ratio of the amount of CO2 that will be buried in the Oil Field, to the amount of CO2 that will be released when the oil produced is subsequently burned.

SA states that currently 770 million cubic feet of CO2 are used in the Tinsley field annually, “boosting oil production from 50 barrels a day to more than 5000 barrels a day”.

Readers, I know you are busy and the units are confusing, so on your behalf I have done the sums for you:

  • The mass of 770 million cubic feet of CO2 is approximately 42 million kilograms.
  • The CO2 released by burning 4950 barrels of oil every day for a year is about 777 million kilograms of CO2

In other words, for every kilogram of CO2 buried, 18.5 kilograms of CO2 will  eventually be released to the atmosphere.

Of course, it would be possible to bury the CO2 without extracting any oil. But that would make the plant even more expensive to run than it currently is.

Overall, the Kemper plant is useless for sequestering CO2. It would be cleaner to just burn the coal directly.

After thought

Now that I think about it, comparing ‘clean coal’ with ‘flying cars’ is an insult to flying car builders.

A better comparison would be with ‘flying toasters’: an utterly pointless distraction from reality.

"After Dark Flying Toasters" by Source. Licensed under Fair use via Wikipedia -

Flying toasters: something as pointless as carbon capture and storage. “After Dark Flying Toasters” by Source. Licensed under Fair use via Wikipedia

The calculation (skip if you don’t like this kind of thing)

Calculation 1

770 million cubic feet of CO2 corresponds to a volume of 21.8 million cubic metres

Using the ideal gas law PV = nRT I calculate that at STP, this corresponds to about 960 million moles of CO2

Each mole of CO2 weighs 0.044 kg and so the mass of this gas is 960 x 0.044 =42.3 million kilogrammes

Calculation 2

The EPA tell me that 1 barrel of oil is equivalent to 0.43 tonnes of CO2: This is 430 kilogrammes

The Tinsley Well produces an additional 4950 barrels of oil per day which corresponds to 365 x 4950 = 2.12 million barrels of oil per year.

So this corresponds to 2.12 million barrels  x 430 kg = 777 million kilograms of CO2

Clever Daffodils

January 2, 2016

  

Above is a photograph taken today
2nd January 2016 showing daffodils blooming in my brother’s garden in Leicester. 

In a previous post I explained how anomalous the weather was in December 2015. 

To do that I had to record the temperature every 10 minutes through the month, calculate the averages of the daily maxima and minima, and then compare the results with local climate normals. 

These daffodils worked it all out by themselves.

Clever daffodils. 

My New Year’s Resolution 2016

January 1, 2016
A picture of me taken this summer.

A picture of me taken this summer. If I remember correctly, I wasn’t feeling gut-wrenchingly anxious as this picture was taken. In the coming year I would like to experience more such moments.

My resolution for 2016 is simple:

  • I want to stop feeling gut-wrenchingly anxious.

I am not anxious all the time. But in the latter part of 2015 I felt sick with anxiety most days!

My aim for 2016  is to replace this feeling of dread with a feeling of positive curiosity about the future. And a sense that failure at any specific activity will not be terminal.

Predictably, I don’t expect it to be easy.

To Care or Not to Care

As suggested by a Guardian article, one answer is simply to stop caring about things.

And indeed I have done just that for a large number of worry-able activities.

But the problem is that I still care about a wide range of things: my wife, my children, my friends and family, my work – and it is often work which forms the proximate focus of my anxiety. And I also care about the wider communities of Teddington, the UK, the World, and the World of Science.

And I care about myself too. And it is balancing caring for myself with my responsibilities that is perhaps at the heart of my feelings.

I am aware that no part of my life – at work or at home – is enhanced by approaching it with a feeling of gut-wrenching anxiety.

And the task as I see it: to keep going doing pretty much the things I would do anyway, but at each moment – and with each breath – to resist the feeling of imminent ‘failure’, ‘death’, or some variety of ‘social death’.

The year ahead

At work, the first half of the 2016 looks busy. And the fact that I have said ‘Yes’ to many of these activities is testament to the fact that I have been able to face up to the demon who whispered to me that if I would just stop caring, I could just say ‘No’.

Two things which often precipitate anxiety are talks and foreign travel. The first 6 months of 2016 involves trips and talks in Canada, India, London, Poland and possibly Italy. And in between these trips and talks I need to do the work and write the scientific papers that justify the trips.

My day-to-day work is in someways like anyone else’s work, except that it typically this involves doing things I have never done before, better than anyone else has ever done them.

For example at the minute I am trying to mix two isotopes of argon gas in precisely known amounts and if I get it wrong the £12,000 worth of gas will instantly become worth approximately a penny. Or less.

Two Bottles containing isotopes of argon gas. The bottle on the left contains 2-g of argon-36 and cost £6000. The bottle n the right is much better value. It contains 80 grams of argon-40 and also cost £6000

Two bottles containing isotopes of argon gas. The bottle on the left contains 2 grams of argon-36 and cost £6000. The bottle on the right contains argon-40 and represents much better value: it also cost £6000, but it contains 80 grams of gas!

At home, my wife has similar trips and challenges, and my youngest son has his A level exams. So the year ahead is filled with busy-ness in many spheres. And filled with activities whose outcomes I care about.

What I would like is to feel able to approach events at home and at work with a sense of positivity and adventure rather than negativity and dread. Please wish me luck.

In any case, every best wish to you, dear reader, in whatever struggles you face in the year to come.


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