vendredi 11 mars 2016

CERN - In Theory: why bother with theoretical physics?

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March 11, 2016

“Children’s fiction books were boring so I read all the science books,” says John Ellis, a theoretical physicist who worked on the “Higgs-strahlung process” that helped discover the Higgs boson in 2012.

Boring. That word stands out when talking to the theoretical physicists at CERN about how they got to where they are now.

Boring and complicated are words often associated with people’s impression of physics in general. For some theoreticians working at CERN, physics wasn’t the career they saw for themselves – their own lessons in the subject were dull and off-putting. Instead they imagined themselves as mathematicians, doctors and engineers.

Image above: What makes a theoretical physicist pursue their career? Camille Bonvin is one of the fellows at CERN looking at theories of cosmology. (Image: Sophia Bennett/CERN).

It took teachers with a true passion for the subject – who saw beyond the mathematics to the fundamental questions it answers about nature – to show these future physicists their true calling. For others, while it would take them time to discover theoretical physics, their love of the subject was ignited by childhood pleasures long before anyone could make it seem boring.

“I liked physics, but I found it a bit dry, a bit boring, so I decided to study medicine,” explains Camille Bonvin, a fellow now at the beginning of her career in the CERN theory department.

Bonvin was at university studying medicine when something she learnt at the end of her school days began playing on her mind: “Right at the end of school we got this fantastic teacher that started to talk about cosmology, general relativity and quantum mechanics, not going into details as we didn’t have the background, but explaining the ideas behind these strange theories I hadn’t heard of before.”

This teacher was a trigger, and six weeks into her degree Bonvin switched to physics. Now, she is looking to begin her new role as an Assistant Professor at the University of Geneva – where she gained her PhD in 2008.

Image above: John Ellis, of Kings College London, in his office at CERN surrounded by science books. It was these books that drew him into physics as a child, when he found that he couldn't check out "good fiction" from the library until he was 14 years old (Image: Sophia Bennett/CERN).

“It wasn’t that I disliked medicine, it's just that I thought if I continue to study medicine I will never get to learn more about general relativity and quantum physics and so on,” she shrugs.

Similarly, Gian Giudice, the new Head of CERN’s Theory department, fell into physics after a substitute lecturer with a passion for the subject showed him that physics in school is often boring because it is taught without the tools of mathematics – it is the mathematics that makes physics so exciting.

“My high-school teacher was good at lecturing in mathematics but he was most boring when he was getting to physics. He was just stating some laws: the subject sounded totally dull,” Giudice explains. “One day he fell ill and this young substitute teacher came into class and showed us how, from the laws of mechanics applied to a system of colliding particles, one can derive the laws of thermodynamics. It opened my eyes to a completely new perspective on the power of logical deduction in physics. It was one of the most fascinating experiences of my life!”

But for Michelangelo Mangano, who has worked in the CERN theory department for 22 years, his goal was set as a child as he stared into the night skies, seeing the depth of the universe and wondering what he could learn.

“I’m from the Apollo generation – I was a kid when the Apollo missions were going to the moon, so that attracted me to the cosmos. I always planned to do astronomy and astrophysics,” Mangano grins.

Image above: Camille Bonvin, a fellow in CERN's Theory department was six weeks into a medical degree before she swapped to physics, when the thought of never learning about general relativity or cosmology made her change. (Image: Sophia Bennett/CERN).

“But when I got to university working on astrophysics meant going from the naive approach of a young person who looks at the sky into number crunching. That took away the fascination.”

To preserve his own pleasure in star-gazing, he started looking into particle physics instead.

It was at university that many of these theoretical physicists discovered that particle physics, like all other sciences, helps to answer questions of the universe. But unlike other sciences it’s about looking at nature to interpret the logic behind it and seeing which physical laws apply.

“Physics is not a descriptive science in which you just observe nature and make a catalogue of the facts. The goal is to understand the logic behind the facts and discover nature's inner workings,” says Giudice.

What is theory?

By university, each of these scientists had narrowed down their future career options, from a childlike love of general science and a natural aptitude for mathematics, to studying for a physics degree. But within physics there are many branches, and experimental physics often captures the public’s imagination more easily, with its huge machines that seem to mimic science fiction.

"At first I found particle physics very cold. But then when you look at it from the mathematical perspective and you realize the incredible connection there is between mathematics and the structure of the universe, well that gave it an incredible appeal.” –Michelangelo Mangano.

Experiments have been crucial to this decade’s greatest physics discoveries, despite the machines looking for something that theory had predicted many decades before.

The Large Hadron Collider dominated the particle physics news-reel since the huge discovery in 2012 of the Higgs boson – and as recently as last month, a large-scale experiment in the US, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves 100 years after Einstein’s theory predicted their existence.

With these two discoveries, two theories – Einstein’s Theory of General Relativity and the Standard model – have proved themselves to be the best description of our world, yet neither explain the complete picture.

Until now, these theories told the experiments where to look and what they were looking for. Theory was so crucial to experimental physics that CERN’s theory department, led by Niels Bohr, was set up two years before the rest of CERN.

Then, in 1952, a group of theorists, many under the age of thirty, met in Copenhagen and had three goals; scientific research on the fundamental problems in nuclear physics, training young theoretical physicists and developing active co-operation between laboratories – the original CERN theory department.

To this day, at CERN the theory department is working on numerous theories, from supersymmetry to string theory. But now, it’s possible these theories and ideas could be led by the experiments as opposed to vice-versa.

So what makes a newly fledged physicist follow the path of theory over experiments?

Why choose theory?

“I always wanted to become a theorist, I studied physics, I did physics while I was at school, my intention was always to become a theorist. In fact at university I studied mathematics and theoretical physics and did no experiments while I was at university at all.” – John Ellis.

“There are so many details involved in building an experiment. Checking all the magnets, or coiling 100 metres of wire, they’re not terribly exciting. Experimentalists have to have huge collaborations just to share out these boring repetitive tasks, but they also share the fun. In theory, we get to focus more on the conceptual side of things,” another CERN theorist, Slava Rychkov, explains why he chose this specific physics path – caveating that they also get to share the fun that comes with seeing a huge experiment being built.

Rychkov’s decision to become a theorist was easy, for him the choice was actually between mathematics and physics.

Where theoretical physicists say “ok, this is 99% true, lets move forward”, a mathematician could spend decades trying to complete that 1% to make it 100% true. That’s a big price to pay.”

Image above: “I was a double major at my university in Moscow. It just so happened I started doing research in pure mathematics, then much later I got the chance to try theoretical physics. I found I had all the fun I had in math, but in addition you have a feeling you’re really studying the fundamental questions of nature.” Slava Rychkov (Image: Sophia Bennett/CERN).

Like notable theorist Richard Feynman, who famously discussed his aptitude for electronics and tinkering with radios as a child, one thing many of the CERN theoreticians had in common was their complete lack of practical ability.

“I’m completely useless with my hands,” laughs John Ellis from in front of the mountains of papers and books that fill his office. “My wife finally got me doing some painting in the house for the first time in 30 years, just the day before yesterday!”

Giudice had the same problem, grinning, he explains that without his laboratory partners he never would have passed the practical lessons at university. “I was terrible. I was always a disaster in the lab, I had no clue what to do. Thankfully there were other people doing everything for me, because I’m not a practical man.”

While Mangano was useless with electronics, he disagrees this implies a lack of practicality, as he discusses his amateur carpentry, masonry and woodwork.

Wolfgang Lerche, in contrast, greatly enjoyed playing with electronics as a teenager, boasting that he could beat many of his experimental colleagues in terms of practical ability.

Image above: Wolfgang Lerche (right) works on the deeply mathematical aspects of string theory, despite his practical nature. Here, he is interviewed by Harriet Jarlett for this series of articles (Image: Sophia Bennett/CERN).

As a student in Germany his university didn’t teach particle physics. Instead he learnt about it in 1979 when, as a summer student at CERN, he found a whole new world of physics open up, and was lured into the realm of theoretical physics.

Lerche knows that, while the skills needed for both experimental and theoretical physics are different, there’s always some overlap.

“Much of any physicist’s time is spent trying to find out why something doesn’t work. The tolerance to deal with frustration, and the patience needed for solving “impossible” problems, belong to the basic skills that are needed by both groups.”

The next article in our In Theory series, on rival groups within the theory department, will be published next week. You can read the first article here:

CERN - In theory: Welcome to the Theory corridor:


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related links:

Higgs boson:

Gravitational waves:

Standard model:

Large Hadron Collider (LHC):

CERN's "Group of Theoretical Studies":

For more information about the European Organization for Nuclear Research (CERN), visit:

Images (mentioned), Text, Credits: CERN/Harriet Jarlett.


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