tell you a little bit about its history.
“... Only CERN has carried and continues to carry this message of peace with the same strength. For example, the SESAME project (supported by CERN and UNESCO) for a new synchrotron accelerator in Jordan brings together Israelis and Palestinians, but also Egyptians, Iranians, Pakistanis, Turks, Cypriots, Bahrainis and of course Jordanians. Symbolically, it is extraordinary: I am firmly convinced that we can unite countries through science. CERN is a model of international collaboration, which promotes respect for cultures and origins, and which, through its ability to bring together very different people, provides an answer to the question: how can we live well together? In my opinion, this aspect is very important.
So we will leave each other with this cry from the heart! Thank you, Bernard, for sharing your knowledge of CERN with us.
- You’re welcome; if you have any further questions, feel free to come back to my office.”
After this warm and informative nice introduction offered by Bernard, I have only one desire: to take you to the Globe! Let’s go out the way we entered — it’s the fastest. You will tell me that we have not discussed economic issues with Bernard: don’t worry, we will have another interview very soon that will be specifically devoted to that question.
As we walk along the impressive line of flags, you may wonder what languages are spoken at CERN. There are two official languages here, English and French; yet, against all odds, neither is the majority language. Don’t be surprised: you can rest assured that no one here speaks Shakespeare’s language, or even like Shakespeare; no, here the unofficial but nevertheless the most common language is globish. For French people like me, it is, if you will, a generalization of “Frenglish” to the whole world, with a rather limited vocabulary. So, what you need to understand is that here we do not speak all the languages, but that we speak one — globish — with all possible accents.
There is one word in particular that you should know in globish, plot. Here, when you see what looks like a histogram, a graph, a diagram or something similar, you don’t look for the precisely appropriate word, you just say: plot. This can save you from tricky situations, such as when you start an emphatic sentence with: “Oh! Very nice, your... your uh...” And then, since you don’t know the exact word, you let the worst escape: “...your drawing.” So if you have any doubts about what is represented, do as everyone else does; don’t take any risks and say “plot.”
With plot, you already reach the semi-pro grade, but if you want to appear immediately as a true professional, I have a trick to suggest: season all your sentences with basically. “Basically” is a word that, in English as in globish, is meaningless but very effective in making you shine. If you are asked a question, especially if it concerns particle physics, assume a very inspired look, and start by saying in your most beautiful globish “Basically, I think that....” You will give considerable weight in advance to your words, I assure you.
We’re arriving at the entrance of the Globe — after you.
The exhibition “Universe of Particles”
As you will see, the effect is quite striking when you discover the exhibition room.
Impressive, isn’t it? I am always amazed by the beauty of this room. I particularly appreciate its cosmic aspect: in the middle of these big luminous spheres, one feels projected into interstellar space.
The exhibition “Universe of Particles”
This room thus sends to everyone an essential subliminal message, which Bernard has already mentioned earlier and which I find magnificent: it is by observing the smallest things that we can understand the biggest. What a beautiful idea! Perhaps we will find answers to astrophysical mysteries, such as dark matter or dark energy, by studying the smallest components of matter. At CERN, therefore, we do not limit ourselves to understanding the infinitely small: we try to understand the universe on every scale.
The spheres you see in this room — at least those close to the ground — each contains a curiosity relating to CERN’s history, to accelerators or particle detectors, or to a point of theoretical physics. We’re going to discover some of them, but just before that, I have to take out my secret weapon: My beautiful drawing of CERN’s accelerator chain! With this visual aid, I will be able to describe the path of the protons: after being accelerated, some of them will frontally meet other protons coming from the opposite direction. The energy released during such a collision will allow, by virtue of the equivalence between mass and energy formalized by Einstein, the production of new particles that can be studied using particle detectors.
But let’s not go too fast, and let’s start at the beginning: where do these protons come from? Don’t expect a staggering answer, because the protons simply come from a hydrogen bottle. This is an opportunity to show you the first sphere — come closer.
A hydrogen bottle
Hydrogen is the simplest atom that can be found: its nucleus consists of only one proton of positive electrical charge +1, around which gravitates an electron of negative electrical charge −1. More precisely, if we do not want to stick to this classical image, which dates back more than a century, it is better to imagine the electron as an electronic cloud which represents its probability of presence around the nucleus. However, there is no need to discuss the electrons, since they are separated from their respective protons as soon as they leave the hydrogen bottle, thanks to an electric field.
The protons thus obtained are first injected into a straight-line accelerator: LINAC 2, which stands for LINear ACcelerator 2. Its cousin, LINAC 3, which you can also spot on the diagram, accelerates not protons but Pb29+ lead ions, i.e., lead atoms that have been stripped off some of their electrons. However, most of the time, accelerated particles are protons — let’s focus on them for now. They will go through a succession of increasingly powerful accelerators, which will make them go faster and faster, giving them more and more energy.
Why do we need several accelerators in a chain, and why don’t we send the protons directly into the largest accelerator? For a simple reason: because you don’t immediately switch from a local road to the highway. It is as if you were asked to arrive on the highway at 40 km/h, then accelerate to 130 km/h: this is not possible; cars that are already there are going too fast. The protons therefore pass through successive insertion ramps. In the life of an accelerator, there is no retirement: when you are supplanted by a bigger one, you become the insertion ramp of the newcomer.
First, in LINAC 2 — note this! — protons are grouped in packets. Then these packets of protons are sent to the Booster, which accelerates them and sends them to the PS — the Proton Synchrotron with its 628 m of circumference. The PS (which is located on the surface) accelerates them and then sends them 40 m underground to the SPS, the Super Proton Synchrotron, with its 7 km of circumference. The SPS accelerates them and then sends them to the LHC, the Large Hadron Collider, with its 27 km of circumference. But here there is a subtlety: the SPS sends half of the proton packets clockwise into the LHC, and the other half counterclockwise for the purpose of producing collisions!
The tunnel of the LHC
As
