Archive for October, 2014

Is anything truly impossible?

October 27, 2014

A recent Scientific American article highlighted the work of two Canadian engineers. Todd Reichert and Cameron Robertson, who built the world’s first (and only) human-powered helicopter.

After they had completed their brilliant and imaginative work, they learned of a recent paper which showed that what they had just done was impossible.

Their achievement put me in mind of Lord Kelvin’s misguided pronouncement:

Heavier-than-air flying machines are impossible.

This is a popular meme: illustrious expert says something is impossible: ingenue shows it is not.

But nonetheless, there are (presumably?) things which, even though they may be imagined, are still either truly or practically impossible.

But how can you distinguish between ideas which are truly or practically impossible, and those which are just hard to imagine?

This is not a merely an academic question

The UK  is currently committed to spending hundreds of millions of pounds on a nuclear fusion experiment called ITER which I am confident will never result in the construction of even a single power station.

Wikipedia tells me the build cost of the project is an astonishing $50 billion – ten times its original projected cost. Impossible projects have a way of going over budget.

I explained my reasons for considering the project to be impossible here

And on reading this Jonathan Butterworth, Head of Physics at UCL tweeted that he:

could write a similar post on why the LHC is impossible. IMHO

But I don’t think he could. Let me explain with some examples:

1. The large hadron collider (LHC) where Jonathan works is a machine called a synchrotron, which is itself a development of a cyclotron.

The first cyclotron was built in a single University physics department in 1932 (History). If, back then, you had told someone the specification of the LHC, would they have said it was impossible?

I don’t think so. Because although each parameter (size, energy etc.) has been stretched – through astonishing ingenuity and technically virtuosity  – the LHC is an extrapolation from something that they knew definitely worked.

2. A modern nuclear power station  is an engineering realisation of ‘a pile of graphite bricks‘ that was first constructed beneath the stand of a playing field of the University of Chicago in 1942.

Within this ‘pile’, the first controlled nuclear reaction took place and worked exactly as had been anticipated. Would the people who witnessed the reaction have said a nuclear power station was impossible?

Definitely not. Everyone in the room was aware of the significance (good and bad) of what had been achieved.

Controlled nuclear fusion, is in an entirely different category from either of these stories of engineering success.

  • It has never worked.

We have never created sustained nuclear fusion and the reasons for the failure of this achievement have always changed as we have understood the problem better.

The rationale for ITER is – cutting through a great deal of technical detail – that it is bigger than previous versions. This increases the volume of the plasma (where energy is released by fusion) in relation to the surface area (where it is lost).

I expect that ITER will meet its technical goals (or most of them). But even on this assumption, they would then have to solve the technical problems associated with confining a plasma at a temperature of 150 million ºC for 30 years rather  than 10 seconds.

As I explained previously, I just don’t think solutions to these problems exist that would allow reliable operation for 30 years with 90% availability required for power generation.

So I think controlled nuclear fusion as a means of generating power is – while perfectly conceivable – actually impossible.

What if – in 50 years time – we make it work? 

Then I will be proved wrong. If I am alive, I will apologise.

However, even in this optimistic scenario, it will be 50 years too late to affect climate change, which is a problem which needs solving now.

And we will have spent money and energy that  we could have spent on solving the problems that face us now using solutions which we know will definitely work.

The League of SI Superheroes

October 20, 2014

I have occasionally blogged about the International System of Units – the SI. I love the way this system helps people to measure stuff in all kinds of ways. I think it is one of humanity’s greatest achievements.

As a worker at the UK’s National Measurement Institute, NPL, I feel proud of what we do to solve measurement problems and encourage measurement best practice.

Despite occasional political misdirection, I think the UK is making good progress towards using measurement units rationally.

But my colleagues at the US National Institute for Standards and Techhnology, NIST, do not have it so easy.

They live in a country where the premier science magazine Scientific American, is more american than scientific when it comes to units.

However my NIST colleagues have expressed their love of the SI in a different way: through cartoon characterisations of the measurement units as superheroes.

The League of SI Superheroes’ work is never done. They toil tirelessly behind the scenes to make sure the measurements that interweave our lives are as accurate and precise as possible. 

It is very american approach, but I like it nonetheless.

In this particular story, the narrative is [PAUSE: delete previous text: insert modified text] contrived to put it mildly. But the characterisations are very strong.

The League of SI Superheroes are:

  • Meter Man: With his laser interferometer eyes, graduated arms and extendable body, no dimension is too big or too small for Meter Man to measure.
  • The Mole: Able to sniff out and count the atoms of every element, the Mole is a master of chemistry.
  • Professor Second: By reading the vibrations of her laser-cooled cesium atoms, Professor Second can synchronize any frequency and calibrate any clock.
  • Monsieur Kilogram: Monsieur Kilogram loves lifting weights, and it shows. With his balance scale arms, no mass is too big or too small for him measure.
  • Ms. Ampere: Ms. Ampere rules the flow of electrons—electrical current—and makes sure that the right amount gets where it needs to go.
  • Dr. Kelvin: Dr. Kelvin heats up or cools down objects by speeding up or slowing down the particles inside them. He can also measure the temperature of anything in the universe with his trusty thermometer.
  • Candela: Don’t let her small size fool you. Candela’s power over light helps to brighten the whole world.

Personally I would like to see The League to do battle against the endlessly variable Inchworm, and the evil Pound of Sprouts

But in fact a battle would be pointless because it has already been won. Since the 1960’s the inch and the pound have been defined as a given number of millimetres and kilograms respectively.

=============

By the way, 1337.15 K is equal to 1064 ºC which is close to the melting temperature of gold – so that would be quite some phone!

The experience of ignorance

October 15, 2014

Today I attended a meeting of the Royal Meteorological Society on the History of Climate Change Science .

It was an interesting meeting – and I will write about it another time.

But in the midst of the meeting, surrounded by experts, I was visited by an overwhelming sensation of personal and profound ignorance that filled me with despair.

  • It was the feeling of being ill-prepared for an exam – and knowing that it is too late to do anything about it.
  • It was the sickening feeling of looking over the edge into a deep, dark hole and feeling unsteady on my feet.
  • It was the feeling of looking back and realising I could have taken a different path some time ago, but now it was too late.

I felt awful. And I will not make it worse by letting you all know the particular trigger for this episode!

Of course this feeling was internal. But part of the sensation was the thought that my ignorance would be publicised and there would be some associated shame.

Why am I mentioning this?

Just remembering this feeling reminded me how powerfully destructive it is.

Reflecting on my own educational experiences. I generally ‘did well’ at school and university, and so I was rarely visited by this gut-wrenching feeling.

But I can nonetheless remember several occasions even from my early childhood when I was humiliated for not knowing something.

For example, I remember (age 10) failing to instantly the answer the multiplication question ‘6 x 7’* when asked by the head teacher.

I remember the way the numbers seemed jumbled and unclear in my head and I just didn’t know the answer. And I remember his ridiculous anger and my own public humiliation.

  • Why is it that I can remember that day so clearly all these years later? It must have made a powerful impression.
  • Why would anybody create that kind of negative feeling in the name of education? Did they think it would help?

And I guess that in many people’s educational experience this kind of maiming negative experience is commonplace.

Ignorance is inevitable

Ignorance is inevitable – no one can know everything! And in recent years I have been happy to accept my own ignorance and I have stopped beating myself up about the things I don’t know.

But the panic of re-visiting that feeling today reminded me that if one ever wants to engender a love of learning in students, then using ‘fear of failure’ as a tactic is unlikely to work.

———————

*For those troubled by such things, the answer is 42

Why measuring time accurately matters

October 5, 2014

Justin Rowlatt and Andrea Sella, have continued their fascinating trek through the elements of the periodic table with a podcast and a web page on caesium.

They focused their article on the role caesium plays in atomic clocks, and much of the article describes the astonishing regularity with which caesium clocks ‘tick’.

However somehow they didn’t mention the fundamental reason why measuring time accurately matters: time is at the base of the International System of Units – the SI.

This means that almost all physical measurements are referenced to a measurement of time. In short:

The accuracy of clocks represents a physical limit
to the accuracy with which we can measure anything!

And this importance is only going to increase in future.

Let me explain.

Measurement is simply the comparison of the thing you are measuring (such as a length or a mass, or a temperature) against a standard ‘unit’ amount of that quantity (length, or mass or temperature).

So no measurement can ever be more accurate than the standard of the quantity being measured.

For example, if ‘one metre’ in the UK is not the same as ‘one metre’ in other countries, then we limit the accuracy with which we can compare measurements made in the UK with those made in other countries.

Similarly, if one metre now is not the same as one metre in 10 years time, or 100 years time, then measurements made now could ‘become inaccurate’ over time.

So at the heart of the system of measurement we want units that are universal, and do not change over time.

The problem is that all physical artefacts – even the international prototype of the kilogram which is made of platinum-iridium and kept in a safe for most of its life – are perishable: they change.

For that reason metrologists frown upon the use of physical artefacts as measurement standards. Instead we are trying to create a system of units in which we separate the definition of the unit from its physical realisation.

We then look for definitions of the units of measurement that – to the best of our knowledge – can never change.

This approach offers the advantage that if technology improves, perhaps in ways we cannot imagine, then there is the possibility of improved realisations of measurement standards, without ever changing the definition – and hence the actual value.

The present system of units, the SI, is the result of many historical anomalies and so below I describe pictorially the ‘New SI’ that many metrologists hope will be in place in 2018.

I hope you can see the system more or less makes sense, and the fundamental role that Caesium atoms play at the root of almost all physical measurements.

We begin with an atom of caesium-133:

 fundamental constant Css is used to define what we mean by one second.

1. A particular natural frequency of vibration of an atom of  Caesium-133  is used to define what we mean by one second, the unit of time. One second is defined as the time taken for just over 9 billion of these oscillations  (9 192 631 770 to be precise)

2. Next the unit of the length, the metre, is defined in terms of the second and the universal constant, the speed of light in a vacuum.

2. Next the unit of the length, the metre, is defined in terms of the second and the universal constant, the speed of light in a vacuum.

3. The most significant change in the new SI is that the kilogram will be defined in terms of the second, the metre and the fundamental constant, the Planck constant.

3. The most significant change in the new SI is that the unit of mass, the kilogram, will be defined in terms of the second, the metre and the fundamental constant, the Planck constant.

Together these three definitions form the core of the SI. This is because with definitions of these three units we can define the unit of energy, the joule.

The unit of energy, the joule, is defined in terms of seconds, metres and kilograms.

The unit of energy, the joule, is defined in terms of seconds, metres and kilograms.

4. The candela - the unit of 'luminous efficacy' is defined in terms of the joule, and a constant that describes the sensitivity of he human eye to a particular wavelength of light.

4. The candela – the unit of ‘luminous efficacy’ – is defined in terms of the joule, and a constant that describes the sensitivity of the human eye to a particular wavelength of light. By the way, ‘luminous efficacy’ just means ‘How bright it seems’.

5. The unit of temperature, the kelvin (and also the degree Celsius) is defined in terms of the joule and a fundamental constant, the Boltzmann constant.

5. The units of temperature, the kelvin and the degree Celsius, are defined in terms of the joule and a fundamental constant, the Boltzmann constant. Colloquially this describes how many joules of energy a molecule must have to increase its temperature by one degree.

6. The unit of electric current, the ampere, is defined in terms of the fundamental constant the charge on the electron and the second.

6. The unit of electric current, the ampere, is defined in terms of the fundamental constant the charge on the electron and the second.

And finally we come to the odd-one-out – the mole – the unit of amount of substance. This is defined in terms of a standard (tremendously large) number of basic entities called the Avogadro constant.

7. The unit of the amount of substance, is the only unit not fundamentally linked to the second. Instead it is defined as a certain number - call the Avogadro constant - of basic entities, typically atoms or molecules.

7. The unit of the amount of substance, is the only unit not fundamentally linked to the second. Instead it is defined as a certain number – called the Avogadro constant – of basic entities, typically atoms or molecules.

You can download a pleasingly-animated version of these pictures in this PowerPoint file.


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