The English Patient

(As published on iopblog)

I’m writing this post from Room 7 of the paediatric emergency ward of l’Hopitale Sud in Rennes, France. It’s my fifth day spent in the room, distantly separated from my holiday luggage. It might seem like a strange priority, writing a piece for physicsfocus at this juncture, but there’s not a lot to do in the evenings, other than watch a cathode ray tube plotting graphs of the electrical signals emanating from my four year old son in the bed next to mine. I’m fine. He will be too, thanks to several dozen outstanding French doctors and the miracles of medical physics.

It has been a week that we’ll never forget; a week that has tested our emotional stamina and my O-level French to the limit. I could write about the turmoil caused by the cruel and dangerous condition that suddenly afflicted my son, or about the sheer brilliance of the French doctors who managed to diagnose an illness that only affects one person in a hundred thousand, with unique symptoms each time. But in view of this blog’s remit, I’ll tell you about a physical phenomenon that helped to preserve my sanity by providing a distraction from an otherwise bleak day.

Some of the vital diagnostic clues were provided by an MRI machine. You might know that MRI (Magnetic Resonance Imaging) uses an incredibly strong magnetic field, only realisable by modern superconducting electromagnets that can carry high electric currents without the resistance that would make ordinary metal wires heat up to melting point. Consequently, I was told, before approaching the machine, to remove any metal objects including my belt, phone, etc, that might fly towards the magnet, causing injury. Surprisingly, I was allowed to keep my gold wedding ring.

Entering the MRI room, I noticed the heavy door was edged with copper contacts that meshed with similar contacts in the door frame, to complete a Faraday cage: a metal enclosure completely surrounding the machine, screening its sensitive magnetic probes from stray radio noise in the outside world, and also preventing its own radio signals spilling out into the hospital.

My little one lay in the machine’s central tunnel, and the compassionate technician in charge let me lean in to hold his hand. The technician was ad-libbing, since this was an adult hospital, to which we had been diverted due to a broken MRI in the local children’s hospital. So perhaps she had overlooked the fact that my left hand – complete with wedding ring – would be inside the high-field region. In the event, the ring remained obediently on my finger and caused no problems, but I was treated to the distracting sensation of the gold band dancing and vibrating on my ring finger as the magnetic field was switched back and forth to elicit informative radio broadcasts from all the atomic nuclei in my son’s brain.

By tugging magnetically on the tiny bar magnet that is an atomic nucleus, then nudging it with a radio wave, the machine makes it precess exactly like a wobbling spinning top. That wobbling nucleus makes its own magnetic field wobble, generating radio waves that are picked up by the machine. As a side effect, the switching magnetic field made electric currents flow around my gold ring, turning it into an electromagnet that pushed and pulled against the field. Understanding the process made it seem no less magical when an invisible force shook my hand.

I’m very glad to be living in an age when this incredible technology, which would have been science fiction only a few years ago, has developed out of the curiosity-driven research of academic physicists. The non-invasive MRI scan was able to rule out all the common ailments, leading to a swift diagnosis and treatment.

They tell me he’s going to be OK; we just have to wait. The French medical staff have been excellent and the medical physics has been state-of-the-art. Call me a harsh critic, but I’m afraid, all in all, the holiday still gets a thumbs down.

Image: Kondor83/Shutterstock.com

"What do you do?"

(As published on iopblog)

Physics has always been my vocation. Perhaps it’s because my dad is an engineer, so my earliest memories are of soldering irons, microscopes and torque gauges. For whatever reason, I have always cared very deeply about trying to understand how the world works, and have never lost the childish impulse to ask “why” on every possible occasion. I pursued physics, and am now lucky enough to do it for a living. So when someone asks me “What do you do?” you might expect me to have a good answer at the ready.

It’s a question we all get asked whenever we meet someone, whether at a party, a bus-stop or (so we are led to believe) an audience with the Queen. Unless your life conforms to some standard set of labels, you probably find the question as tricky to answer as I do. You could just give your job title, but that doesn’t really summarise you, does it?

“I’m a university lecturer,” I’ll say.

I could have told them I’m a physicist, teaching and researching at Leeds University Department of Applied Maths, or that I’m a proud father – the activities that occupy most of my time. But I usually go with the job title. This prompts the response,

“What’s your subject?”

As any physicists out there will know, the traditional course of this conversation goes as follows:

“Physics.”

“Oh, I wasn’t any good at physics at school,” …followed by an uncomfortable silence.

I never know how to respond to that. “Oh dear” just sounds patronising, and “I was” would be worse. I would be grateful to hear your suggestions for diverting this social train-crash.

But ever since physics celebs Brian Cox and (fellow physicsfocus blogger) Jim Al-Khalili have captured the public imagination, I am pleased to report that the conversation these days tends to run more like this:

“Physics”

“Oh, that’s really interesting. What do you work on? Is it astronomy or subatomic particles?”

Of course, like anyone with properly functioning goose-pimples, I am filled with fascinated awe by both the vast and tiny extremes of our universe. But my own research is in a less well-publicised area of fundamental physics: statistical mechanics.

Statistical mechanics is the third pillar which, together with General Relativity and Quantum Mechanics, underpins our understanding of the physical world. Stat mech, as it’s known to its friends, lies between the realms of the very large and the very small, linking the two. It is the theory that explains why ice is hard and water is runny and liquid-crystals are weird.

Often the next question I am asked is:

“So, what substance are you working on at the moment?”

This is the point at which my interlocutor might reasonably begin to lose patience. I would love to be able to give a straight answer to that question, as a chemist or an engineer or even many physicists could.

“It’s not like that,” I have to say.

You see, some types of research apply to specific substances or specific gadgets. Some scientists study graphene, for instance, and some technologists design solar cells. But often, it’s more useful to classify research by the ideas that it addresses, rather than its applications.

Stat mech describes what happens when vast numbers of tiny particles interact with each other to form large-scale materials. Its principles can be applied equally well to water molecules, electrons in a metal, or the neutrons in a pulsar, to predict their behaviour en masse. The only proviso is that the collection of particles must be at equilibrium, meaning that they are not flowing.

Image: This artist’s concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way. Credit: NASA, ESA, and A. Schaller (for STScI)

In my research, I am working to extend the well-established theory, to find the principles governing non-equilibrium systems, ie collections of objects that are in a state of flux, whether they are molecules of molten plastic flowing into a mould, or stars swirling round a black hole. I study the universal principles behind these types of collective motion, rather than focussing on a particular case. Any progress that can be made in this area will have countless applications that haven’t been imagined yet, so it’s a worthwhile thing to do, as well as being fascinating.

I believe that we need both types of research – ideas-based and applications-based – in order to achieve a really broad, deep and productive understanding of the physical world. I know which type I personally find more interesting. Unfortunately, it’s the one that’s hardest to explain at parties. It’s probably a blessing that I’ve never met the queen – I’m not sure she’s got the stamina for it.

In Focus

This week, the Institute of Physics launched physicsfocus, a new forum for discussion on all aspects of physics, from education to research to whimsy. The nine regular bloggers contributing to physicsfocus include a bloke with whom you may be familiar. It's a pleasure to rub shoulders (electronically) with such informed, provocative and erudite writers. I recommend you have a look at physicsfocus, and join the discussions. Meanwhile, just for completeness, I'll be reproducing my own physicsfocus posts here at PhysicsBloke.com, as well as posting other articles that don't appear on the IoP's site.

Gravitons

Since beginning my occasional series “The Big Questions” in Sky At Night Magazine, I have been contacted by people asking me to explain other enigmas of physics. Many of them are already extremely well informed, so it’s a real challenge to give an accurate and satisfying answer – a challenge that I find myself enjoying. Writing for the magazine has been an elevating and refreshing experience in many ways.

It would be wrong to mention Sky at Night this week without paying tribute to Sir Patrick Moore, whose inspirational life came to an end on Sunday. I won't attempt an obituary, as many have been published this week, far better than I could manage. Brian May, writing in The Guardian, put it particularly well: "the world has lost a priceless treasure that can never be replaced". But I will just add my ha'peth, as one of the legion of scientists who owe their earliest interest in astronomy to Sir P. I would like to express my gratitude for his enormous enthusiasm and thought-provoking presentation. Unfortunately, unlike the presenters of the TV programme, contributors to the magazine do not tend to meet, working instead by email and telephone. Nevertheless I feel fortunate to have my name appearing in a few of the same issues as his.

Returning to the point, one of the readers recently e-mailed me with a really deep question. It's a bit more technical than my usual blog entries, but I know it's something that a lot of physicists wonder about. So, with my correspondent's permission, I’ll reproduce his question and my answer here in full.

Subject: Gravitons

Dear Dr Evans

As a Sky at Night reader I have seen and enjoyed your first two articles, so look forward to the others.

Separately, in the last year or so, I have make making an effort to understand, or at least, get a better feel for Einstein’s relativity.

I have been able to (sort of) follow the steps that lead to Special Relativity and the how the problem of gravity (instantaneous action at a distance and so on) was resolved by the development of General Relativity simplistically as a geometric description – curved space-time.

What still does confuse me however is that elsewhere gravity continues to be described as a force with attempts being made to combine it with the electromagnetic, strong and weak forces into a theory of everything. In this context  the graviton is described as the force carrier for gravity (analogous to the photon, W & Z bosons, and the gluons for the other forces) on the way to the development of a quantum theory of gravity.

I suppose the question is whether gravitons are reconcilable with general relativity, or whether this means that the latter in itself is still not a complete description. I have looked at various websites to try and get some light thrown on this but without much success – references to stress energy tensors, and so on don’t mean anything to me, and I doubt are ever likely to!

It would be useful to know from someone working is this field what the current thinking is – definitely not in terms of any technical description, but just a summary that could be understood by the interested non specialist as to the status of the various theories.

If you are able to find time to respond, that would be useful, but quite understand if not.

Regards

Brian Radesk             

---

Dear Brian,

Thanks for your message. I'm glad you've been enjoying my articles.

It's a very interesting question that you ask. The short answer is that General Relativity hasn't been overturned. It has been built upon. Or, more accurately, it is being built upon, since there isn't yet a complete quantum version of it.

First, I should say, gravity is a force. I mentioned in my last article that "in a sense" there is no force, only geometry, but that's really just a way of understanding the nature of this particular force. Look in detail at any type of force, and you'll find an alternative way of describing it. So there is no contradiction between General Relativity and descriptions of the "force" of gravity.

Gravitons, like photons and the other "gauge bosons" (force carriers) are very confusing, and almost universally misunderstood. They are called "particles", but things that are called "particles" in quantum field theory (the "standard model") are not really particles at all in any sense that we would normally use the word. You might have heard of the idea of wave-particle duality in quantum mechanics, where an object like an electron sometimes seems to behave like a particle, and sometimes like a wave. In fact, all quantum mechanical "particles" behave almost entirely like waves. The only thing that they have in common with classical particles is that, under certain very specific conditions, they can be countable.

Take the theory of electromagnetism, for instance. This was all worked out by the Victorians, culminating in James Clerk Maxwell's theory that unified electricity and magnetism by describing them both with four elegant equations. That theory predicted the existence of electromagnetic waves, including light. 

Subsequently, those waves were found to exist with only a discrete set of possible amplitudes (or energies). So you can count the amount of energy possessed by those waves in discrete steps. One of these countable increments in the energy of an electromagnetic wave is called a photon. You see, it's not really much like a particle. And the existence of photons doesn't over-throw Maxwell's theory of electromagnetism.

Similarly, Einstein's field equations of General Relativity have solutions describing gravitational waves. Applying the principles of quantum mechanics, people expect those waves only to be allowed to exist with a discrete set of possible energies. These countable excitations of gravitational waves are called gravitons, but we don't yet have a full self-consistent mathematical description of them. Whatever the correct theory of quantum gravity turns out to be, you can bet it will incorporate the field equations of General Relativity.

I hope this helps.

Best wishes.

Mike Evans.

_______________

Dr R Mike L Evans

Lecturer

Department of Applied Mathematics

University of Leeds, LS2 9JT, UK

@PhysicsBloke

The Sky's the limit

Breaking News: The biggest name in popular astronomy publishing, Sky At Night Magazine, has a new writer. It's me! 

Over the next three issues (November 2012 – January 2013), I'll have a series of four-page feature articles about the physics of space – what it is, how it works and where it comes from. The series is called “The Big Questions” and, in each article, I’ll tackle one of the enduring questions about the Universe, and try to convince the readers that they don’t need to be Albert Einstein to understand the answers. 

The first article will be called “What is spacetime?”. I guess everyone has heard of “spacetime” and felt curious about what it really means, but most people assume that you need to be good at maths or have a degree in physics to have any chance of really knowing about it. I believe that no topic is too advanced to be explained in an entertaining way. 

So my articles are aimed at everyone. Curiosity is the only qualification that my readers need. The style is going to be irreverent, but never at the expense of accuracy. I expect to answer more "Big Questions" later in the year, as well as more news-based features on areas of applied maths and theoretical physics.

I enjoy writing, and I think that helping to make science more accessible is one of the most worthwhile things I can do. So I'm very excited to be embarking on this new project. Sky At Night Magazine has a great reputation, and it turns out that the editorial staff are really friendly and easy to work with. It's been great to see my scribblings being turned into polished and visually stunning articles.

As a theoretical physicist, I regularly talk about my research in academic circles - in seminars and at conferences. So I often rub shoulders with the great and the good - I've met a few Nobel laureates, and am no longer easily star-struck. But I have to admit that writing for the partner publication to the world-renowned television programme, founded and presented by Patrick Moore, does give me a frisson of pride and excitement. Or, to put it another way, Woohoo!

The November issue will be in the shops from 16th October.

Fireball

I was out in town on Friday night, having a drink or two with friends. This, in itself, is worthy of note, as my party-animal days are long gone, and my evenings are usually spent reading bed-time stories (no, not to myself), putting the rubbish out, and generally up to my elbows in domestic bliss.

But I’m not writing to inform you of my newly rediscovered social life, but of an even more fortuitous turn of events. Having drunk ourselves close to penury (have you seen the prices recently?), my companions and I were meandering homeward and, coming to the parting of our ways, we paused to put the world to rights and bid each other a hearty farewell.

As we stood face to face, my attention was caught by movement at the upper edge of my vision. In the heat of the moment, I failed to suppress an involuntary Anglo-Saxon word escaping my lips as I glanced skyward and beheld a spectacle for which I was utterly unprepared.

Above the high-rise rooftops of central Leeds, a dazzling fireball was racing across the sky. It was obviously not a firework, because the scale was all wrong, and it was clearly traveling extremely fast on a nearly straight trajectory, heading very slightly downward of horizontal.

My first thought was that it was a stricken aircraft - an international airliner judging by its height and speed. My second thought was that it could just possibly be a meteor - a rock from outer space burning up due to friction with the atmosphere. But I’ve seen a lot of meteors, and it wasn’t the first thing that came to mind, because meteors don’t normally look like that.

It’s a by-product of being an amateur astronomer - spending hours outside in the dark, trying to align a telescope with some almost-invisible marvel of deep space - that I often happen to be looking the right way when a meteor, an extraterrestrial sand-grain, hits the atmosphere and burns up. It typically happens once or twice during each observing session, and it’s a nice experience to witness the brief flashes corriscating across the heavens. They are colloquially known as shooting stars because, like the stars, they appear as points; zero-size dots (although that’s all they have in common, since the true stars are each really millions of times the volume of the whole world, while a typical meteor is a trillion trillion trillion times smaller). And, as the name suggests, it shoots across the field of view so rapidly that you don’t get a chance to point it out to a friend.

The most spectacular meteor I had previously seen had broken into several widely-spread fragments, so that their dimly glowing uneven rank stalked silently across the sky like the broad wings of some spectral vulture.
The startling phenomenon at 10.55pm on Friday was quite different.

For one thing, it moved more slowly. It was faster, I soon realized, than most commercial aeroplanes, but didn't streak across the sky like a normal meteor. And it was no dim little dot. This was a blazing white ball shooting out sparks just like a super-sized sparkler on Guy Fawkes Night. It was accompanied by host of smaller fragments, and trailed a glowing orange tail. A short distance behind followed some smaller shining orange pieces, but also much bigger than a normal shooting star.

I was relieved to notice that none of the pieces was the shape of a wing or fuselage or jet engine. So the biggest, most spectacular meteor I had ever seen seemed to be the most likely explanation.

On arriving home, I tweeted my strange experience, and soon saw others’ tweets and news stories about the fireball, from right across the north of Britain. A few people even had their cameras handy at just the right moment:


Photo: Ian Bolton. Click on image to follow link to original.

Photo: Adam Badrick. Click on image to follow link to original.

Early the next morning, after the hubbub of questions, misconceptions and emergency calls had finished flying about the ether, Jodrell Bank posted a message on Twitter, saying, "No real consensus on whether last night's spectacular fireball was a space rock burning up or space junk (bit of spacecraft)".
I hadn’t thought of space junk up to that point, but it seemed to fit with what I saw. It would explain the relatively low speed of the mystery object, as material in terrestrial orbit is not quite as fast as rocks orbiting the sun. Also, something intangible about its shape and the way it tumbled suggested an artificial, un-rock-like object to me. If it was indeed space junk, it was the prettiest, most spectacular junk I’ve ever seen.

I have since heard various second-hand news reports of the event, some even seeming to imply that the whole sky was ablaze with shooting stars like a scene from Day of the Trifids. It wasn't, but the sight was nonetheless impressive, and one that I will remember for a long time. As one of the lucky few who witnessed it first-hand, I thought it would be worthwhile recording my account. And now that I've done so, I must return to the domestic bliss of putting out my incomparably less spectacular rubbish.

Lord Kelvin's Thunderstorm

This week, I wholeheartedly embraced the physicist’s stereotype, and set to work constructing a twenty-thousand-volt spark generator out of an ice-cream tub, two plastic taps, some metal cans and a few bits of wire. And I mustn’t forget the most important ingredient: a pint of water. I am happy to say that it worked a treat. It’s fun to mix electricity and water. Forget I said that. What I meant, of course, was, “Never mix electricity and water, kids!” ...unless you follow in the footsteps of William Thomson, a.k.a. the First Baron Kelvin, because this collection of bits and bobs comprises the near-miraculous invention known as Lord Kelvin’s Thunderstorm.

The finished article, looking like Heath Robinson’s offering to a Blue Peter junk-art competition, is a strange and tantalizing thing to watch. It has no battery or electrical supply and only the most basic constituent parts. Yet, as water pours from one vessel into another, the metal hoops and wires that surround them spontaneously spring into life, and begin to crackle and flicker with the blue light of high-voltage electrical discharges. As with any contraption, there was a fair amount of anguished troubleshooting before it agreed to play, so, when the first blue arcs finally illuminated my sweat-drenched forehead, I was tempted to run from my workshop shrieking, “It’s alive!”

The weird spectacle and sheer sense of achievement that the machine generated were well worth the effort. So, this blog entry takes the form of an instruction manual. You too can safely create high-voltage electricity from soggy junk.

You’ll see from the photo that I made a wooden stand to support the whole thing. Although wood is normally regarded as a good electrical insulator, surprisingly, at the very high voltages and low currents involved in this particular escapade, wood conducts electricity too well, and will short-circuit the electrics unless all of the metal parts are mounted on plastic supports. At the bottom of the contrivance are two tin cans (actually one of mine was a stainless steel cup) for catching drips, which I stood on plastic trays intended for house plants. Above them are two metal cylinders (which I made by cutting up a hairspray can - white in the photo) held by a plastic bar (hacked off a kitchen cutting board). Two pieces of wire connect the right-hand cylinder to the left-hand tin can and vice versa and a further two pieces almost connect the cylinders to each other, but are separated by a small gap across which the sparks jump. Above all this stands a tub of water, from which emerge two plastic taps (the only parts I had to buy: £5 including delivery from Ebay) designed for kegs of home-brew. That’s really all there is to it.

Now, switch on the taps just a fraction, so that thin streams of water fall though the metal cylinders without touching the sides. The continuous streams must break up into drops whilst within those cylinders. Then stand back and watch the sparks fly.

“But how does it work?” I hear you say.

I thought you would never ask. Well, there are only two pieces of physics that you need to know: opposite charges attract, and all matter contains positive and negative charges in equal amounts.

Now, the water, as you know, is made of negatively charged electrons and positively charged nuclei of hydrogen and oxygen. Let’s suppose that, as those countless trillions of charged particles drip out of the left-hand tap, just one electron too many ends up in the left-hand tin, without a positive hydrogen nucleus to balance its charge. So the left-hand tin now has a tiny overall negative charge, and the water left in the ice-cream tub has a tiny net positive charge. The extra electron in the tin can easily travel up the copper wire to the right-hand cylinder, attracted by the nearby positively charged tub of water. Now the positive charges in that tub of water feel the pull of that negatively charged cylinder, and get attracted towards the right-hand tap, while the negative charges are predominantly repelled towards the left-hand tap. So we get positively charged drips falling from the right-hand tap, and negative from the left. The right-hand tin collects those positive charges, and the left tin collects negative, making the cylinders more strongly charged, which in turn pull more strongly on the charges in the tub.

The tins keep on getting more and more highly charged until the voltage across the spark gap is high enough (around 20 000 volts in this case) to push an electrical current through thin air. Like Evel Knievel, the electrons jump the gap, crashing into air molecules on the way, making them shine with the blue light so familiar to Doctors Thomson and Frankenstein alike. Only by performing this dare-devil stunt can the electrons be re-united with the surfeit of positive nuclei in the right-hand tin. Neat, isn’t it?

This is similar to the way in which large amounts of opposite charge get separated by water droplets moving around a thundercloud (hence the device’s name), though the finer details of cloud electrification are still up for debate, and I’m fairly sure there are no hairspray cans involved.

At first, this spontaneous self-charging mechanism seems too simple to be true. You might even worry that it seems to violate the principle of conservation of energy, creating electrical power for free, but not so. Can you spot where the machine got its energy from? Whoever lifted the tub of water onto the wooden stand had to expend some energy to overcome gravity. That stored gravitational energy is used by the machine when the charged drips fall into a tin that has a like charge. Without gravity, those drips would be repelled from the tin.

In fact, as the voltage rises, the electrical repulsion competes noticeably against gravity. As a prelude to each spark, the splashing sound actually gets quieter as the drops hit the surface more slowly, and the smallest droplets don’t even make it into the tin, instead fleeing the high charge by spraying out sideways, drenching the operator in what should logically be called “Lord Kelvin’s Drizzle”. This repeated diminuendo culminating in a tiny crack and flash makes quite a striking rhythm. Not only are the electrical forces felt by the water; the copper electrodes of the spark gap (being long and bendy in my particular construction) become pulled slightly together due to their opposite polarities, then suddenly released when discharged by the spark, causing them noticeably to spring apart, in synchrony with the rhythmic son-et-lumière.

Even knowing in advance that the design was feasible, it took me several hours to get the thing working, and gave me a huge sense of achievement when I finally did. You have to admire its inventor’s remarkable cleverness, particularly considering that he and his Victorian contemporaries didn’t know of the existence of electrons or atoms.

If you’re sufficiently intrigued to build your own weird and wonderful spark generator, I recommend a look at Bill Beaty's electrostatics website http://amasci.com/emotor/kelvin.html for some helpful troubleshooting tips and other design ideas.

Having generated electrical arcs that lasted only a few microseconds, it was quite another task to photograph them for your delectation, dear reader. But I won’t bore you with the details. Suffice to say, I spent a disagreeable half hour hunched over a camera in the pitch dark, stoically enduring his lordship’s drizzle. But I can bear him no grudge. Not only did he invent a wonderfully entertaining curio, he also earned me the highest praise from my six-year-old son who, on witnessing my ramshackle handywork in action, declared it to be “cooo-el”. Thanks Lord K.