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.

An A-level eye-opener

There is a general perception that A-levels ain't what they used to be. In my young day, when the world was right and the sun shone all summer and the streets were paved with orphans who were grateful for the work, that's when an education was a real education. You couldn't pass a physics exam by drawing a picture called "How I feel about electrons". The youth of today blah blah blah rant foam (to paraphrase the Daily Mail).

For those not conversant with the UK system, A-levels are "Advanced level" exams, usually taken at age 18, and required for entry into university. We university physics lecturers see the results of the school education system and, based on our impressions of each year's freshers, we too make assumptions and guesses about the state of the A-level system.

All the physics lecturers in the house say, "hey!"

I can't hear you! It's always important to have an idea of the audience for whom one is writing and, in my own experience of a normal working day, I've noticed that most adults are university physics lecturers, but I'm willing to entertain the possibility that my experience might not be entirely typical. Well, even if you happen to be one of those non-physics lecturers that I've heard about, the current standards of education are obviously important to you too because (a) you don't want your own hard-won qualifications to be devalued, and (b) today's schoolchildren will soon be building nuclear power stations, fighting world-hunger, and cleaning the dribble from our wrinkled chins.

So, you might be interested to know that, rather than continuing to speculate about A-level standards, last week I went to see for myself, spending a day sitting-in on science lessons at South Cheshire College, at the kind invitation of Head of Physics, Dr Phil Klein. It's a Further Education college teaching A-levels, vocational training and adult HE-access courses to a vast number and variety of learners. My first impression of the college's two-year-old £70M building was that it felt simultaneously light and spacious yet intimate and comfortable, and this was a triumph of design, considering that the institution was way bigger than any school or FE college I had previously visited. If its role-call of 300 doesn't sound huge, that's because it's just the number of teachers.

But there was no hint of the enormity of the place, or of the social deprivation in surrounding catchment area, as I attended the calm, orderly lessons in which the teachers had a friendly rapport with each of the dozen-or-so students. The first lesson, A-level physics, was closest to my heart and the main purpose of my fact-finding mission.

I had arrived with an open mind, but must admit that I expected to be horrified by a superficial syllabus, much diluted since my own sixth-form career in the late nineteen ahem-ties. (Excuse the frog in my throat; it's decrepit.) My smugness was instantly crushed, as I was confronted by a discussion of nuclear decay pathways that had me dredging dim memories of undergraduate lectures. Far from being watered-down, the syllabus has been extended to include serious stuff about subatomic particles and astrophysics. Meanwhile, I was delighted to discover that the vital foundations of the subject have not been abandoned; Newton's laws of motion, force balance and discharging capacitors are still covered in rock-solid fashion.

"It's all very well optimistically writing these topics into the national curriculum," I hear you say, "but do the bright young things actually understand any of it?" The exchanges that I witnessed, between teacher and pupils, convinced me that, within those Cheshire walls at least, there was no shortage of expertise. For instance, having worked though some algebra on the whiteboard, the teacher asked the class, "What's the best way of plotting a graph to demonstrate a power-law formula?" and I was impressed when several of the youngsters simultaneously replied,

"Log-log plot." In case that phrase is not redolent with meaning for you, I should point out that they were right, and that the log-log plot, while being one of the most useful weapons in a scientist's arsenal, is not at all straightforward to understand.

It would be misleading to claim that the future of sixth-form schooling is entirely rose-tinted. There are two blots on the exam boards' copy sheets, of which everyone who has followed their progress over the last twenty years is aware. The first is the well-known and undeniable phenomenon of grade inflation, that was an inevitable result of taking the exams business out of the hands of University boards, and into the mitts of profit-making companies, that tout for trade on the basis of their results.

The second is a subtle change in the nature of physics A-level exam papers that worries those of us who pick up the teachers' baton at university. The questions are still of the same standard and depth as ever and, as I say, of even greater breadth. But the answers, which used to be written on simple A4 lined paper, are now written into a pre-printed booklet, in which the appropriate diagrams, construction lines, and general shape of the answer have already been sketched out. This leaves the student with no opportunity to practise the crucial skill that we physics-types call "problem-solving". That is to say the spark of insight and invention required to take the cryptic description of a problem, choose how to approach it, and convert it into a sketch and subsequent calculation. The young people I met last week undoubtedly had the nous to find their own way to solve complex problems, but need to be given more practise at this skill during their formative years at school. In spite of this fly in the ointment, it filled me with relief and optimism to see such motivated, self-disciplined and well-informed A-levellers.

Black holes and the history game

When we’ve exhausted “I Spy” and “Twenty Questions”, my six-year-old son and I sometimes play a game that we invented. It’s a kind of quiz that exercises both our brains. I realise I’m in danger of coming across as one of those pushy, neurotic parents who forcibly over-educate their offspring to prove their superiority and give them a head start in the rat-race. But, cross my heart, we play purely for the fun of it.

Here’s how the game works (and, if you have sprogs of your own, you’re welcome). You, the grown-up, play the role of question-master. Think of three events, inventions or discoveries. Say them in a random order and, if necessary, explain what each one is. Then your diminutive descendant just has to put them into chronological order. Not convinced? Believe me, it’s a lot more fun than it sounds.

Let’s have a go. (Follow the links for clues to the answers.)

(1) Knights in shining armour; the Roman empire; Cavemen.

- This one won’t tax an adult, but it makes an interesting conversation point. Whether the apple of your eye gets it right or wrong, you’ll probably end up discussing dragons and castles until one of you falls asleep, and forget the rest of the game.

(2) Cars; boats; aeroplanes.

- Yes, they all still exist, but which was invented first? Again, this one’s not exactly challenging, but it might surprise your playmate, especially to learn how very long the first one was invented before the other two.

(3) Dinosaurs; fish; birds.

- Starting to work the grey-cells now?

(4) The wheel; the plough; fire.

(5) Digital radio; the first man on the Moon; the internet.

- This one will almost certainly surprise the younger player, for whom all three inventions belong to ancient history.

Did you get them all? Congratulations. Now, here comes the tricky one.

(6) Stars; galaxies; black-holes.

Until recently, physicists thought we knew the answer to this one. In the early universe, gravity made hydrogen clump together into big dense regions (proto-galaxies) where stars formed, fusing hydrogen nuclei into helium, and releasing energy. Once those stars had exhausted their hydrogen fuel, they collapsed and, if they were huge enough, kept on collapsing right down to zero size, forming a black hole, where gravity is so intense, it breaks space and swallows light.

That's how we thought it worked, but it was all just conjecture. In fact, we weren't even confident that black holes existed at all. A black hole was a possible solution to the “field equations” of General Relativity, Einstein’s theory of gravity, but there was no evidence of them until the discovery of active galaxies in the 1950s. It became clear that something at the heart of many distant galaxies was firing out incredibly energetic jets of matter and radiation and, because the intensity of the jets was observed to vary quite rapidly, the source had to be something tiny compared with the galaxy. A swirling vortex of gas around a black hole seemed like the only possible culprit. Still, this evidence wasn’t completely compelling. Finally, at the end of the twentieth century, detailed observations of the rapid orbits of stars at the centre of our own Milky Way galaxy settled the debate. Just watch the time-lapse movie of the observations collected between 1992 and 2005 to be convinced that an incredibly massive body is tugging those stars with huge gravitation force. Their motion tells us that the invisible object has a mass 3.7 million times that of the sun, but is much smaller than the orbit of the Earth.

More recently still, astronomers have discovered that most if not all galaxies possess such a super-massive black hole at their centre, and that these black holes could not have formed by the unpredictable chance collisions of stars within the galaxies, because there is a perfect correlation between the size of the galaxy and the size of the black hole. In other words, if you measure the size of the black hole, you can predict exactly the size of the galaxy surrounding it. This suggests the possibility that the black holes were there first, and actually caused the galaxies to form around them, by their gravitational pull.

To add to the mystery, data collected by the Hubble Space Telescope in 2011, to appear in Astrophysical Journal, reveal that supermassive black holes existed in dwarf galaxies in the early universe (as seen by observing very distant galaxies, in order to look back in time). So, perhaps supermassive black holes have always been there. They may be older than any galaxy and, if so, may well have been created at the dawn of time, in the big bang.

It seems such a straightforward question whether black holes, stars or galaxies came first, but the more we learn about the universe, the more it surprises us. The new evidence by no means settles the matter; it only proves that we have not yet understood how or when black holes and galaxies formed.

In case you’re wondering, my six-year-old’s answer was: stars then galaxies then black holes. At the moment, it’s as good a guess as any.

How the Aurora Borealis Saved the Civilized World

Don’t give up just yet. There is still hope for humanity. If you thought Mankind had descended into a baying horde of tax-dodging, Edexcel-colluding, The-Only-Way-Is-Essex-watching looters, bankers and phone-hackers, think again. Through the gloom shines a ray of hope that is green and fuzzy and arriving from the most unexpected direction.

It all began last week with a CME - a "coronal mass ejection". A massive solar storm flung an enormous lump of material out of the sun and into space, hurtling towards Earth at around a million miles per hour. This kind of event has long been expected, because the Sun gets restless every 11 years, and is due to do so again this year and next. In fact, the harbingers of doom have been wringing their hands in glee at the calamity promised by a large CME. When it hits the Earth, it threatens to overload power grids and burn out the electronic technology on which we have become so reliant.

On Sunday, after travelling through space for three days, the dreadful lump of solar plasma finally arrived but, guess what, civilization did not end. There was no calamity. In fact, it turned out to be a thing of beauty.

As anticipated, the myriad electrons and protons, arriving from the Sun, spiraled round and round the magnetic field lines that extend out of the Earth’s poles like iron filings on a bar magnet. And, as anticipated, the planet’s magnetic field flexed and wobbled under the assault, making it sweep past power lines, creating a makeshift dynamo. Electrical current surged through the grid but the four horsemen of the apocalypse failed to show up. The electrical surges were relatively small, and the marvellous people in charge of the world’s power supplies coped admirably.

So, did those subatomic particles from space go unnoticed by the general population? Not at all. Never has a solar flare caused such commotion here on Earth. Our magnetic field funnelled the swarm of high-energy particles toward the poles, where they smashed into the upper atmosphere, making its oxygen atoms shine with an unearthly green light: the aurora. It’s not uncommon for polar explorers and reindeer to see the northern and southern lights, but this week’s aurora were big - so big that they extended down all the way to parts of the UK, and mainland Europe.

But who cares about the aurora borealis? You and I do, but we’re special, aren’t we. For one thing, we love to marvel at the wonders of nature. Looking out into the clear night sky, and taking in the unbelievably vast majesty of it all gives us an overwhelming sense of exhilaration, that would only be increased by the excitement of witnessing the aurora. More than this, unlike the hoi polloi, we thoughtful types appreciate real beauty wherever it appears. Well...

Anyone tweeting during the last week knows that you and I are not alone in caring about the wonderful, mysterious, beautiful workings of the universe. On Sunday, and again on Tuesday when a second CME hit the Earth, Twitter was abuzz with excitement - not over the threatened electrical disaster - but over the impending aurora. People were re-tweeting the latest space weather predictions and everyone was hoping the lights would reach their local sky. First we got jealous of the Scandinavian tweeters, then Shetlanders reported miraculous skies, and soon even the coast of county Durham was alight. And across the world, we shared their joy and excitement. A surprising number of sky-watchers are expert photographers, who managed to capture some of the celestial awesomeness, even in the challenging low-light conditions, and they very swiftly uploaded their wonderful pictures for the rest of us to marvel at. Thank you aurora watchers, for sharing your anticipation, your excitement and your amazing pictures. You have restored my faith in humanity.

In the end, the dancing green light shone on many happy appreciative people, but didn’t quite reach my Yorkshire sky. I missed the live show, but I witnessed something equally beautiful and unexpected, on a social networking site.

The reliable musings of a Physics Bloke

Welcome to my blog. Come in, put your feet up and allow me to share with you some thoughts, anecdotes and news about my lifelong vocation. I am a fully qualified Physics Bloke, in possession of one PhD and one Y chromosome. My only goal, as we mull over the mysteries of this strange universe, is to be interesting. If it’s interesting, it goes in the blog, whether it’s the latest discovery, or was know by Aristotle. Of course, being interesting is easy if you make things up (consult the red-top newspaper of your choice) but, like any scientist, I promise to pursue only the truth. OK, so that’s two goals: to be interesting and accurate, and if I witter any longer, I’ll miss the first one. So have a look at this intriguing picture.




A living superfluid

http://www.dur.ac.uk/suzanne.fielding/interests.html

In this week’s PANDA meeting (that’s Pattern Formation, Nonlinear Dynamics and Applications) at Leeds University’s Department of Applied Mathematics, Dr Suzanne Fielding, a physicist from Durham University, presented the results of her theoretical research on "active fluids". The strange texture of folds and swirls, pictured above, is predicted by her mathematical model.

The symmetry-based theories of condensed matter physics are usually used to model inanimate materials like semiconductors, liquid crystals and magnets. But Fielding has applied them to understand the swarming behaviour of microscopic swimmers such as amoebae. These organisms are so numerous and tiny that, en masse, they form a fluid with liquid-crystalline properties, making shades of light and dark in polarized light (see picture), like a liquid crystal display (LCD).

This active fluid of living organisms flows in peculiar ways. A fluid’s viscosity is a measure of how “thick” it is – how hard you have to push to make it flow at a given rate. So water has a low viscosity, but treacle’s viscosity is high. Fielding has used her model to calculate the viscosity of a dense swarm of microbes.

“Even at zero stress, it can spontaneously flow with a finite shear rate,” she says. “So it has exactly zero viscosity. It’s a superfluid!”

This is a very strange result. Superfluids – liquids that flow without friction – are rare, and have previously only been encountered at extremely low temperatures, close to absolute zero. If Fielding’s predictions are correct, this would be the first example of superfluidity at room temperature. Whereas the “traditional” superfluid, liquid helium, relies on the weird quantum physics of ultra-low temperatures to achieve perfect frictionlessness, Fielding’s active fluid simply relies on the hard work of billions of microbes swimming furiously.

So what’s it going to be used for? The applications of a room-temperature superfluid have yet to be invented, since no-one ever anticipated such a discovery, but they will surely be impressive. Ideas anyone?

References:
“Nonlinear dynamics and rheology of active fluids: simulations in two dimensions”, S. M. Fielding, D. Marenduzzo and M. E. Cates, Physical Review E 83 (2011) 041910