A Day at CERN. Gautier Depambour
into the SPS, leave for the antimatter factory, which we will visit later; others leave for a lead target, producing high-energy neutrons studied by the n-ToF experiment, with applications in both astrophysics and medicine. The same is true for the SPS: some protons, if not injected into the LHC, are directed to the AWAKE experiment, which employs another plasma-based particle acceleration technique; others leave for the COMPASS experiment, which studies quarks and gluons within the atomic nucleus. So, even if we focus today on the ATLAS experiment, there are many others.
Follow me as I move to the other side of this room in the Globe. I would like to show you a little curiosity — which might even be raised to the status of an object of worship. Look into that sphere.
The first Web server
This is the first Web server, which was developed by Tim Berners-Lee in 1989. Take in what I’m about to tell you: the World Wide Web and the HTTP transfer protocol were invented at CERN! If you still had doubts about the usefulness of CERN, keep repeating to yourself: without CERN, no Facebook, no Google, no YouTube, no Wikipedia, no Amazon, no Twitter... Imagine your life today without the Web. Well, that would be a life without CERN.
Next to this server, you can see a document: it is the article that Tim Berners-Lee submitted to his superior in presenting his project. The reaction of the superior: “Vague... but exciting!” Initially, the Web project was intended to allow data sharing between physicists: we know what it is today.
The article at the origin of the Web (Copyright: CERN)
But the Web is not the only contribution of CERN to IT! It is also at CERN that the idea of the touch screen was invented. So, once again, imagine a world without a touch screen: it’s a world without CERN. Last but not least, it is at CERN that the prototype of what can be considered as the ancestor of the computer mouse was developed. That was in 1972, a certain Bent Stumpe had to design a system for the SPS control room — which I was telling you about a moment ago — to move a cursor on a control screen. He then ordered 12 bowling balls and developed the precursor of the ball mouse. The bowling ball was chosen for reasons of stability and fluidity of movement, but fortunately, all this could be miniaturized.
To anyone who would tell you that CERN has never been used for anything and that it is expensive, I now count on you to tell him or her that without CERN there would be no Web, no touch screen, no computer mouse. And if this person persists in his scepticism, sincerely, it is because he or she is acting in bad faith.
Before leaving the Globe, I have two more little surprises. Come on...
The first particle accelerator
Equations which describe the infinitely small
In this sphere, you can contemplate the very first circular particle accelerator, a few centimetres in diameter. Don’t you find the experience moving? And in this other sphere, here, you can admire the beauty of the equations that rule particle physics today. There’s no rule against getting a little bit ecstatic!
Let’s leave the Globe. Now you’re ready for the discussion we’re going to have with Arnaud Marsollier. Arnaud is part of the communication department, and I made an appointment with him to talk about money issues: how much did the LHC cost? And the detectors? What are the various economic and societal benefits? I think it is useful to understand from the beginning of the visit that the money invested in CERN is not lost money, far from it. But first, on the way to his office, let me tell you a little bit about the history of CERN, so that you can feel the weight of history as you walk through its corridors...
A brief history of CERN
If there is one place in the world devoted to science that beats records, it is CERN! Imagine: an international collaboration with 22 Member States in 2016 has built a ring of 27 km in circumference, at an average depth of 100 m, to cause tiny constituents of matter (such as protons) to collide at a vertiginous speed almost equals to that of light. When you work at CERN and repeat this description almost mechanically, you tend to get used to it and forget that... it’s just amazing! But behind such exploits lies a whole history, whose story deserves to be told.
As you may know, the first half of the 20th century deeply changed our view of physics: first with Einstein, who formulated his theories of special relativity and general relativity in 1905 and 1915 respectively, and then with the rise of quantum mechanics, which developed considerably from the 1920s onwards. However, all these conceptual revolutions did not take place just anywhere: they took place in Europe. Heisenberg, Pauli, Dirac, Schrödinger, de Broglie, Born, Bohr, Einstein: almost all the great physicists who founded quantum physics were European.
But the Second World War, which led to a brain drain to America, put an end to this golden age, and fundamental research in Europe came to a standstill. To remedy this, Louis de Broglie — among other personalities such as the Italian Eduardo Amaldi and Pierre Auger and Raoul Dautry of France — proposed in 1949 the creation of a European laboratory for high-energy physics, with UNESCO’s support, which encouraged the creation of scientific collaborations without a military aspect. The idea was to bring together young researchers from all over Europe, to put them in contact with each other, then to send them back to their home universities with a high level of excellence and thus restore the reputation of basic science in Europe. Eleven countries agreed on the principle, but it was still necessary to decide where the new laboratory would be located.
One group of theorists made a strong argument for Copenhagen. This is where the iconic Niels Bohr Institute of Theoretical Physics was (and still is) located, an essential place in the advent of quantum mechanics, which witnessed an intense intellectual ferment in the 1920s and 1930s. Niels Bohr himself, still alive at the time, was involved in the creation of CERN.
There were other possible choices: France, Italy... But Switzerland, with its central position in Europe and its tradition of peace, was the ideal candidate. The question of location was settled in Amsterdam in 1952, at a conference where it was decided that the Laboratory would be located in Meyrin, in the open countryside near Geneva — a decision endorsed by a referendum in 1953 by which the local population accepted the project. And the following year, 12 countries signed the CERN Convention, officially recording its birth: Belgium, Denmark, France, Germany (in fact, the FRG), Greece, Italy, Norway, the Netherlands, the United Kingdom, Sweden, Switzerland and Yugoslavia. In parallel, the theoretical section of CERN, of which Niels Bohr was a member, was initially established in Copenhagen, but this did not last long, given the distance from Switzerland.
The first objective of the collaboration was to build particle accelerators to unlock the secrets of matter. Several circular accelerators thus emerged one after the other, each larger than the one before. In the 1950s, the Proton Synchrotron was built, which, among other things, allowed the study of very strange particles that we will have the opportunity to discuss again: neutrinos. About twenty years later, the Super Proton Synchrotron was born — from then on, the PS was converted into an SPS injector, so that the protons arriving in the SPS had already acquired a certain energy, as I explained earlier.
The SPS, which sent protons against antiprotons, had its moment of glory in 1983 by allowing the discovery of the Z0, W+ and W- bosons, which earned Carlo Rubbia and Simon van der Meer the Nobel Prize in 1984. These are the mediating particles of one of the four fundamental forces of nature: the weak nuclear force, involved in beta radioactivity processes. Today, the mass of the boson Z0 is known with great precision, and for this reason it acts as a standard when calibrating the detectors.
Proton collisions are conducive to the discovery of new particles; indeed, because they have a composite structure, they can produce a wide variety of collisions, allowing a wide range of energy to