Tag Archives: particle physics

Peter Higgs: The Life Scientific

Quantum physicist and broadcaster Jim Al-Khalili blogs on interviewing Peter Higgs for the new series of The Life Scientific on BBC Radio 4. Discover more about the LHC, particle physics and the search for the Higgs boson in our Collider exhibition

I love name dropping about some of the science superstars I’ve interviewed on The Life Scientific. ”Richard Dawkins was quite charming on the programme, you know”, or “James Lovelock is as sharp as ever”, and so on. So imagine my excitement when I heard I would be interviewing the ultimate science celebrity Peter Higgs.

When I discovered we had secured him for the first programme in the new 2014 series, I knew I had to get something more out of him than to simply regurgitate the popular account of the man as shy, modest and unassuming, and still awkward about having a fundamental particle named after him; or how the Nobel committee were unable to get hold of him on the day of the announcement because he had obliviously wandered off to have lunch with friends.

This was an opportunity for two theoretical physicists – OK, one who has a Nobel Prize to his name and one who doesn’t, but let’s not split hairs here – to chat about the thrill of discovery and to peek into the workings of nature, whilst the outside world listened in.

A couple of Bosons: Peter Higgs with Jim Al-Khalili

A couple of Bosons: Peter Higgs with Jim Al-Khalili. Credit: Charlie Chan

You can listen to the programme from 18 February, but here are a few extracts to whet your appetite.

Can you explain the Higgs mechanism in 30 seconds?

At some point in the programme, inevitably, I had to ask Peter to explain the Higgs mechanism and Higgs field (both more fundamental concepts than the Higgs boson). He gave a beautifully articulate and clear explanation, but I then thought I should ask him to give the ‘idiot’s guide to the Higgs’, just to cover all bases. Here’s how that went:

‘The Boson that Bears my Name’

Working alone in Edinburgh in the sixties, Peter Higgs was considered ‘a bit of a crank’. “No-one wanted to work with me”, he says. In 1964, he predicted the possible existence of a new kind of boson, but at the time there was little interest in this now much-celebrated insight. And in the years that followed, Peter Higgs himself failed to realise the full significance of his theory, which would later transform particle physics.

In July 2012, scientists at the Large Hadron Collider at CERN confirmed that the Higgs boson had indeed been found and Peter Higgs shot to fame. This ephemeral speck of elusive energy is now the subject of car adverts, countless jokes, museum exhibitions and even a song by Nick Cave called the Higgs Boson Blues. But Higgs has always called it the scalar boson or, jokingly, ‘the boson that bears my name’ and remains genuinely embarrassed that it is named after him alone.

In fact, three different research groups, working independently, published very similar papers in 1964 describing what’s now known as the Higgs mechanism. And Higgs told me he’s surprised that another British physicist, Tom Kibble from Imperial College, London didn’t share the 2013 Nobel Prize for Physics, along with him and Belgian physicist, Francois Englert.

On fame
When the 2013 Nobel Prize winners were announced, Peter was famously elusive (much to the frustration of the world’s media). Most people romanticised that he was blissfully unaware of all the fuss or just not that interested. These days, he’s constantly being stopped in the street and asked for autographs, so I asked him whether he enjoyed being famous:

Physics post-Higgs
With the discovery of the Higgs finally ticked off our to-do list, attention is turning to the next challenge: to find a new family of particles predicted by our current front-runner theory, called supersymmetry. Higgs would ‘like this theory to be right’ because it is the only way theorists have at the moment of incorporating the force of gravity into the grand scheme of things.

But what if the Large Hadron Collider doesn’t reveal any new particles? Will we have to build an even bigger machine that smashes subatomic particles together with ever-greater energy? In fact, Peter Higgs believes that the next big breakthrough may well come from a different direction altogether, for example by studying the behaviour of neutrinos, the elusive particles believed the be the most common in the Universe, which, as Higgs admits, “is not the sort of thing the Large Hadron Collider is good for”.

When it started up in 2008, physicists would not have dreamt of asking for anything bigger than the Large Hadron Colider. But today one hears serious talk of designing a machine that might one day succeed it. One candidate is the somewhat unimaginatively named Very Large Hadron Collider. Such a machine would dwarf the Large Hadron Collider. It would collide protons at seven times higher energy than the maximum the Large Hadron Collider is able to reach. And it would require a tunnel 100 km in circumference. Of course this is not the only proposal on the table and there are plenty of other ideas floating about – none of which come cheap, naturally.

There are certainly plenty more deep mysteries to solve, from the nature of dark matter and dark energy to where all the antimatter has gone, and we will undoubtedly find the answers (oh, the delicious arrogance of science). Let’s just hope we don’t have to wait as long as Peter Higgs did.

Keen to discover more? You can listen to Peter Higgs on BBC Radio 4′s The Life Scientific (first broadcast 9am on 18 February) and visit the Collider exhibition at the Science Museum until 5 May 2014. 

Anticipating Antimatter

Collider exhibition curator Dr. Harry Cliff blogs on Dirac’s discoveries and anticipating antimatter.

It was 86 years ago on Saturday (8 February) that one of the most important scientific papers of the 20th century appeared in the Proceedings of the Royal Society. Written by the young British physicist Paul Dirac, it was simply titled A Quantum Theory of the Electron, and was nothing short of a theoretical triumph.

Paul Dirac

Paul Dirac. Image: Nobel Foundation

In it, Dirac had set out to solve a problem that was occupying some of the greatest minds in physics. To date, quantum mechanics had failed to explain the fine detail of atomic spectra – the discrete wavelengths of light emitted and absorbed as electrons hop between different energy levels in atoms. In particular the electron had to be given a strange property known as “spin” to explain the number of different energy levels.

Spin itself was a rather mysterious quantity. It suggested that that the electron behaved as if it was rotating rapidly on its axis, but a quick calculation showed that this couldn’t be true – the electron would have to be spinning faster than the cosmic speed limit, the speed of light, something forbidden by Einstein’s theory. It also had to be bolted on to quantum mechanics like a clumsy afterthought, without any explanation for its origin.

Dirac, for whom mathematical beauty in the laws of physics was almost a religious cause, was deeply dissatisfied with this awkward situation. He believed that the problem lay in combining the two pillars of modern physics, quantum mechanics (the theory of the very small) and relativity (the theory of the very fast).

He was after an equation describing the behaviour of electron that was consistent with both theories, and also explained the known properties of the electron. Rather surprisingly perhaps, the approach he took was to guess.

An educated guess mind, based on some properties he knew the correct equation must possess and also on his aesthetic desire for simplicity and beauty. Working methodically, he tried equation after equation, discarding them one by one until in late November 1927 he came upon a solution.

Dirac's equation

Dirac’s equation

The equation was perfect. Not only did it accurately reproduce the known energy levels of the hydrogen atom, the property of spin naturally appeared in the equation, without the need to be stuck on by hand afterwards. Spin itself now seemed to be an inevitable consequence of combining relativity and quantum mechanics.

St. John’s College, Cambridge, where Dirac discovered his famous equation.

St. John’s College, Cambridge, where Dirac discovered his famous equation. Image: Andrew Dunn

Dirac, though famously reserved, must have been jumping for joy (though perhaps only in his head). He had pulled off a coup so impressive that his German competitors, Jordan and Heisenberg were left stunned and deflated.

As news spread of Dirac’s success, the man himself was growing increasingly nervous about an odd feature of his equation, one that he had brushed under the carpet in his Royal Society paper.

The equation itself had four solutions, and each solution represented a state that the electron could be in. Two of these corresponded to the garden-variety electron with negative electric charge, but the other two described an electron with positive electric charge and negative energy.

This made no sense whatsoever. No one had ever seen a positively charged electron, and worse still, if these negative energy states existed then ordinary electrons should be able to fall into them, causing an electron to spontaneously switch its charge from negative to positive.

For all the success of the Dirac equation, these negative energy electrons could well have spelt its doom, and no-one was more acutely aware of this than Dirac himself. In fact, this “problem” turned out to be Dirac’s greatest contribution to physics.

It would take Dirac more than three years to understand the true meaning of this extra set of solutions. He had first thought that these negative energy, positively charged electrons might in fact be protons – the positively charged particles inside the atomic nucleus – but he soon realised that this would imply that protons should have the same mass as electrons, when in fact they are roughly 2000 times heavier.

What Dirac eventually reasoned was that these odd solutions actually represented a completely new type of particle, a sort of mirror image of the electron that he dubbed the “anti-electron”. Anti-electrons would look completely identical to ordinary electrons, but positively charged. He also reasoned that other particles like protons should also have anti-versions, and that when a particle met its anti-particle they would annihilate each other.

This must have seemed far-fetched at the time; after all, no one had ever seen an anti-particle. But Dirac was convinced by the beauty of his equation, and in one of the most stunning episodes in modern physics, was proven right just a year later, as Carl Anderson spotted an anti-electron in cosmic ray experiments.

It’s hard to overstate what Dirac had achieved. Through the power of sheer thought, he had predicted the existence of a completely new type of stuff, a stuff never before imagined by scientists. This stuff, what we now call antimatter, is just as real as the stuff you and I are made from, but for some reason doesn’t exist in large quantities in our Universe. This is in fact one of the greatest unsolved mysteries in physics, and one that physicists at the Large Hadron Collider are trying to solve.

Find out more about antimatter by watching this short video or by visiting the Collider exhibition before the 5th May 2014.

Max and Tangle’s guide to particle physics

To celebrate our Collider exhibition, we worked with the BAFTA award-winning Brothers McLeod to bring particle physics to life in this short animation. Myles and Greg McLeod had a pretty tough brief to squeeze all of particle physics (the entire Standard Model) into a two minute animation, but we think they pulled it off.

Collider content developer Rupert Cole interviewed scriptwriter Myles McLeod to find out how they did it.

Is this your first animation to do with physics?

I think it is! Though we’ve done maths before. We won a BAFTA for our psychedelic preschool maths show ‘Quiff and Boot’. Yes, that’s right, psychedelic maths. We also once explained Calculus using zombies. We’ve also done a bit of biology – dinosaurs to be precise – which was fun. We had to summarise 165 million years in 3 minutes. That’s efficiency for you.

Was it a challenge to cram so much particle physics into a two-minute animation?

Well, the challenge is where the fun lies. We were lucky that Harry Cliff at the Science Museum provided us with a wonderful visual explanation. Since we understood it, and we’re definitely not physicists, we knew that others would too. It was a great starting place from where we could then construct the backbone of the narrative. The next thing was what kind of a story did we want to tell, and what kind of characters would be in it.

How did you find physics compared with other topics you have worked with?

I think physics is one of those subjects that does both frighten and fascinate people. Everyone seems to have a drop off point, a point where you go ‘yes I understand that, yes I understand that’ and then ‘no I have no idea what you just said’. It’s such a fundamental science and some of it seems so deep and complex that on the face of it almost seems like magic, especially when you start talking about time moving at different rates and space being curved. On the other hand, it’s all about stars and forces and time and looking to beyond and imagining what’s out there and how it all works, so it’s a beautiful science too.

Where did the names Max and Tangle come from?

Well we wanted to take some characters from the world of physics so the cat is supposed to be Schrödinger’s Cat. Schrödinger coined the term entanglement, and Tangle sounded like a good name for a cat. We just needed a second character and Maxwell’s Demon was mentioned to us, and hey presto we had Max.

How did you decide on what the personalities of Max and Tangle would be like?

A lot of it came out of the question, ‘why would someone explain in a conversation all this information about particle physics?’ It seemed logical that one was clued up and clever and the other not as smart. Then it seemed like this could be a game of one-upmanship. So the less smart one needed their own advantage to balance things out, for Max that had to be his slyness and gung-ho approach to experiments. Once you start writing the script and getting them talking to each other they really start to show their personalities to you. When the voices come and later the animation, then they become even more distinct.

Do you have a favourite between Max and Tangle?

Max is great because he’s up to no good and it’s fun to have a character like that. They create chaos. But if you were asking me who I’d rather have over to lunch, I think I’d go with Tangle to avoid Max’s life-threatening experiments.

Discover more about protons, quarks and particle physics in our Collider exhibition.

LHC: Lip Hair Champions

Content Developer Rupert Cole explores some famous moustaches in particle physics ahead of the opening of our new Collider exhibition on 13th November. 

It’s that time again: Movember – the eminently charitable moustache-growing month raising awareness for men’s health. But what, you might reasonably wonder, has facial hair got to do with particle physics? Well, I have a theory; one backed by hard pictorial and anecdotal evidence…

The Cavendish lab’s moustachioed students, 1897. Credit: Cavendish Laboratory

The Cavendish lab’s moustachioed students, 1897. Credit: Cavendish Laboratory

Consider the glory days of Cambridge’s Cavendish Laboratory, during which the first subatomic particle was identified, a revolutionary particle detector invented, and the atomic nucleus split by one of the first particle accelerators. Significantly, the great Cavendish leaders and pioneers of this period cannot be accurately described as clean shaven.

Joseph John Thomson

JJ Thomson has a “rather straggling moustache,” wrote a talented student called Ernest Rutherford in 1896, “but a very clever-looking face and a fine forehead”. In another letter to his fiancé, Rutherford made the additional comment that Thomson “shaves very badly”.

We may detect a hint of jealousy in Rutherford’s description of Professor “JJ”. As, according to one chronicler of the lab’s history, the young student Rutherford possessed only “a thinly sprouting moustache”.

JJ Thomson. Credit: Cavendish Laboratory

JJ Thomson. Credit: Cavendish Laboratory

Nevertheless, concealed in Thomson’s supposedly wayward bristles was a creative and audacious genius. At the time, the Cavendish’s director had been performing his groundbreaking experiments on cathode rays. The next year he shocked the scientific world when he announced the existence of a particle smaller than the smallest atom – later dubbed the “electron”.

Ernest Rutherford

Once the rambunctious New Zealander’s lip-hair had acquired its full bushy substance, he was well on the way to scientific stardom.

His first momentous contribution to physics came in 1902 at McGill University, Canada. Rutherford and his colleague Frederick Soddy explained what radioactivity actually is – the process of atomic decay.

Soddy described his co-discoverer simply as an “exuberant natural, young man with a moustache”. Biographers would later characterise Rutherford’s ever-growing asset as reminiscent of a “walrus”.

By the time he succeeded his old moustachioed mentor, JJ Thomson, as Professor of the Cavendish, Rutherford had already discovered the atomic nucleus (1911) and managed to split nitrogen atoms in half, causing them to transmute into two oxygen atoms (1917-19).

But it was at the Cavendish that he ushered in the era of accelerator physics. Contemporaries recall a particular accessory: a pipe, containing the world’s driest and instantly-flammable tobacco.

Ernest “The Walrus” Rutherford. Credit: Science Museum / SSPL

Ernest “The Walrus” Rutherford. Credit: Science Museum / SSPL

On one Spring day in 1932, Rutherford entered the lab in a famously foul mood. His pipe “went off like a volcano” – having pre-dried his tobacco on a radiator. Impatient at the progress his young researchers John Cockcroft and Ernest Walton had made with their 800,000-volt proton accelerator, he instructed them to “stop messing about… and arrange that these protons were put to good use”.

At Rutherford’s suggestion, they immediately installed a zinc-sulphide scintillation screen – a device which causes charged particles to sparkle when they hit – into their wooden observation hut. A few days later, Walton saw on this screen evidence that their machine was splitting the nucleus of lithium atoms!

Had the authority of the tache and pipe not intervened, the Cavendish men may have been pipped to the discovery by the clean-shaven American teams, who boasted the biggest and best of accelerators.

Charles Thomson Rees Wilson

CTR Wilson, one of Rutherford’s fellow students at the Cavendish, was a
“modest” personality with a similarly unassuming moustache. He spent 16 years assembling cloud chambers – a device he initially invented to study meteorological phenomena.

A keen mountaineer – an activity that always complements well-trimmed bristles – Wilson derived inspiration to build cloud chambers when he was atop Ben Nevis, observing beautiful optical effects.

His third and final chamber, completed in 1911, was later described by Rutherford as “the most original and wonderful instrument in scientific history”. Incredibly, it could capture with photographs the tracks of particles. Wilson had invented the first detector that could visualise and record the subatomic world.

CTR Wilson, 1927. Credit: AB Lagrelius and Westphal

CTR Wilson, 1927. Credit: AB Lagrelius and Westphal

It seems remarkable that the humble moustache may have had such a crucial role in the foundation particle physics. Never again would the Cavendish be led by lip-hair champions; and considering the lab’s unprecedented success in this golden period, we can reliably infer the cost of this absence.

I leave you with the words of Arthur Eddington: “An atom which has lost an electron is like a friend who has shaved-off his moustache.”

Next week you can see Thomson’s cathode-ray tube, Rutherford’s atomic models, the Cockcroft-Walton accelerator, CTR Wilson’s cloud chamber, and much more at the Science Museum’s new Collider exhibition. 

For more famous physics moustaches click here.

The Art of Boiling Beer: 60 years of the Bubble Chamber

Ahead of November’s opening of the Collider exhibition, Content Developer Rupert Cole explains how beer was used for cutting-edge particle physics research. 

Late one night in 1953, Donald Glaser smuggled a case of beer into his University lab. He wanted to test out the limitations of his revolutionary invention: the bubble chamber.

Previously, Glaser had only tried exotic chemical liquids in his device. But now his sense of experimental adventure had been galvanised by a recent victory over the great and famously infallible physicist Enrico Fermi.

Donald Glaser and his bubble chamber, 1953. Credit: Science Museum / Science and Society Picture Library

Donald Glaser and his bubble chamber, 1953. Credit: Science Museum / Science and Society Picture Library

Fermi, who had invited Glaser to Chicago to find out more about his invention, had already seemingly proved that a bubble chamber could not work. But when Glaser found a mistake in Fermi’s authoritative textbook, he dedicated himself to redoing the calculations.

Glaser found that, if he was correct, that the bubble chamber should work with water. To make absolutely certain he “wasn’t being stupid”, Glaser conducted this curious nocturnal experiment at his Michigan laboratory. He also discovered that the bubble chamber worked just as well when using lager as it had with other chemicals.

There was one practical issue however, the beer caused the whole physics department to smell like a brewery. “And this was a problem for two reasons,” Glaser recalled. “One is that it was illegal to have any alcoholic beverage within 500 yards of the university. The other problem was that the chairman was a very devout teetotaler, and he was furious. He almost fired me on the spot”.

On 1st August 1953, 60 years ago this Thursday, Glaser published his famous paper on the bubble chamber – strangely failing to mention the beer experiment.

Glaser’s device provided a very effective way to detect and visualise particles. It consisted of a tank of pressurised liquid, which was then superheated by reducing the pressure. Charged particles passing through the tank stripped electrons from atoms in the liquid and caused the liquid to boil. Bubbles created from the boiling liquid revealed the particle’s path through the liquid.

Particle tracks produced by Gargamelle indicating the discovery of the neutral currents, 1973. Credit: CERN

Particle tracks produced by Gargamelle indicating the discovery of the neutral currents, 1973. Credit: CERN

One of Glaser’s motivations for his invention was to avoid having to work with large groups of scientists at big particle accelerators. Instead, he hoped his device would enable him to study cosmic rays using cloud chambers in the traditional fashion; up a mountain, ski in the day, “and work in sort of splendid, beautiful surroundings. A very pleasant way of life – intellectual, aesthetic, and athletic”

Ironically, as the bubble chamber only worked with controlled sources of particles, it was inherently suited to accelerator research, not cosmic rays. Soon the large accelerator facilities built their own, massive bubble chambers.

Design drawings for CERN’s Gargamelle bubble chamber. Credit: CERN

Design drawings for CERN’s Gargamelle bubble chamber. Credit: CERN

Between 1965-1970 CERN built Gargamelle – a bubble chamber of such proportions that it was named after a giantess from the novels of Francois Rabelais (not the Smurfs’ villain). Gargamelle proved a huge success, enabling the discovery of neutral currents – a crucial step in understanding how some of the basic forces of nature were once unified.

This November you’ll have the chance to see up close the original design drawings for Gargamelle, and much more in the Collider exhibition.