Bien sûr, si vous demandez ce que le boson de Higgs mettra dans l’assiette de l’humanité, la réponse est simple: personne ne le sait. Quand le ministre des Finances a questionné Michael Faraday sur la valeur pratique de l’électricité en 1850, il n’en avait aucune idée mais a répondu  «Un jour, monsieur, vous trouverez un moyen de la taxer.”

La découverte du boson de Higgs signifie que nous avons désormais une théorie complète qui explique ce qu’est la matière visible. L’humanité peut donc aller se coucher ce soir en en sachant un peu plus sur l’univers dans lequel nous vivons.

Par contre, les retombées indirectes sont nombreuses et découlent de l’ensemble des activités de recherche en physique des particules. Plusieurs viennent d’être résumées dans une nouvelle brochure intitulée «Accélérer la science et l’innovation – Les avantages sociétaux de la recherche européenne en physique des particules” (en anglais).

Cette brochure a été présentée par le CERN aux ministres des sciences et de la technologie d’Europe la dernière semaine de mai à Bruxelles à l’occasion d’une réunion spéciale du Conseil du CERN organisée par la Commission européenne.

Le World Wide Web, inventé au CERN il y a plus de 20 ans, est estimé avoir stimulé € 1,5 billion en trafic commercial annuel. C’est 1500 fois plus que le milliard de francs suisses consacrés à la recherche au CERN chaque année.

Environ 10.000 accélérateurs servent en médecine à travers le monde, tous utilisant la technologie développée en physique des particules.

Grâce à la physique, la radiothérapie et les rayons X sont utilisés tous les jours pour le traitement du cancer et l’imagerie médicale. La thérapie hadronique, où des protons ou des ions de carbone sont utilisés au lieu des photons comme en radiothérapie conventionnelle, est la dernière technique prometteuse développée récemment et devrait améliorer considérablement le traitement de certains types de cancer. De tels accélérateurs développés en collaboration avec le CERN sont déjà utilisés par MedAustron  en Autriche et CNAO en Italie.

L’accélérateur développé pour la thérapie hadronique par CNAO en collaboration avec le CERN pour détruire plus efficacement les tuneurs cancérigènes (photo gracieuseté de CNAO)

Même les recherches sur l’antimatière sont mises à contribution. L’expérience ACE effectuée à « l’usine » d’antimatière du CERN a montré que les antiprotons pourraient être efficaces pour détruire les tumeurs.

La physique des particules au CERN a aidé à produire des panneaux solaires plus efficaces et contribue maintenant au développement d’accélérateurs de poche qui permettront aux hôpitaux de produire localement leurs propres doses d’isotopes radioactifs suivant la demande.

Des ingénieurs du CERN testent des câbles supraconducteurs à haute température faits de diborure de magnésium. Ce type de recherche pourrait signifier éventuellement le transport de l’électricité sur de grandes distances sans perte d’énergie.

Panneaux solaires nouvelles génération de l’aéroport de Genève utilisant la technologie du vide développée pour les accélérateurs du CERN

Les technologies des accélérateurs sont également utilisées dans divers projets de nettoyage industriels. Dans des essais effectués au Texas, des faisceaux d’électrons ont converti les boues d’épuration hautement infectieuses en engrais agricole sécuritaire. Des efforts sont également en cours sur l’installation n-TOF du CERN pour transmuter les déchets nucléaires hautement radioactifs en matériaux inoffensifs.

Ce ne sont là que quelques-unes des nombreuses applications découlant de la recherche menée dans les laboratoires de physique des particules. Et c’est encore sans compter la formation d’une main d’oeuvre hautement qualifiée prête à relever d’autres défis technologiques ainsi que l’enthousiasme suscité parmi les jeunes, les professeur-e-s et le grand public.

C’était donc une excellente nouvelle fin mai quand le Conseil du CERN a adopté la Stratégie européenne pour la physique des particules lors de sa réunion spéciale organisée par la Commission européenne. Les bénéfices sociétaux sont multiplés quand les nations unissent leurs efforts et leurs ressources pour l’approfondissement de la connaissance fondamentale.

Pauline Gagnon

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Of course, if you are asking what will the Higgs boson put on humanity’s plate, the answer is easy: nobody knows. When the finance minister asked Michael Faraday about the practical value of electricity in 1850, he had an idea, but he replied: “One day sir, you may tax it.”

At least, the discovery of the Higgs boson means that we now have a complete theory to explain how visible matter works. Hence, humanity can go to bed knowing a little more about the Universe we live in.

But there are plenty of indirect returns stemming from all the research activities in particle physics. Many of them have just been summarised in a new brochure called “Accelerating science and innovation – Societal benefits of European research in particle physics”.

The brochure was presented by CERN to European science and technology ministers last week of May in Brussels on the occasion of a special meeting of the CERN Council hosted by the European Commission.

The World Wide Web, invented at CERN more than 20 years ago, is estimated to have stimulated €1.5 trillion in annual commercial traffic. This is 1500 times larger than the billion CHF spent on research annually at CERN.

Around 10,000 accelerators using technology developed for particle physics are now in operation for medical use in hospitals worldwide.

Thanks to physics, X-rays and radiotherapy are used everyday for cancer treatment and medical imaging. Hadron therapy, where protons or carbon ions are used instead of photons as in conventional radiotherapy, is the latest promising technique developed recently and is set to greatly improve therapy for certain types of cancer. Such accelerators developed in collaboration with CERN are already in used by MedAustron in Austria and CNAO in Italy.

The CNAO accelerator used for hadron therapy developed in partnership with CERN provides a more efficient way to kill cancerous cells.

Even antimatter research is put to good use. The ACE experiment performed at CERN’s antimatter facility showed that antiprotons could be powerful in destroying tumours.

Particle physics at CERN has helped produce more efficient solar energy panels and is now developing desk-top accelerators to enable hospitals to produce locally their own single doses of radioactive isotopes as needed.

CERN engineers are testing high temperature superconducting cables of magnesium diboride. This kind of research could lead to electricity being carried over large distances without energy loss.

The solar panels used by the Geneva airport for heating use a technology created to improve the vacuum in CERN accelerators beam pipes.

Accelerator technology is also used for various industrial clean-up projects. In trials in Texas, electron beams have converted highly infectious sewage sludge into safe-to-handle agricultural fertiliser. Efforts are also underway with the n-TOF facility at CERN to transmute highly radioactive nuclear waste into safe materials.

These are but a few of the many applications stemming from research conducted in particle physics facilities. Not to mention training a supply of people ready for technological challenges, stimulating students and teachers interest and igniting enthusiasm for physics all over the world.

So it was great news last week that CERN Council adopted the European Strategy for Particle Physics at its special meeting hosted by the European Commission. The benefits are multiplied when nations pool their efforts and resources in the pursuit of fundamental knowledge.

Pauline Gagnon

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Let us start with a simple question: What does it mean when we say a tree exists? The evidence for the existence of trees falls into two categories: direct and indirect. Every autumn, I rake the leaves in my backyard. From this I deduce that the neighbour has a tree. This is indirect evidence. I develop a model that the leaves in my backyard come from a tree in the neighbour’s yard. This model is tested by checking the prediction that the leaves are coming from the direction of the neighbour’s yard. Observations have confirmed this prediction.  Can I then conclude that a tree exists? Probably, but it would be useful to have direct evidence. To obtain this, I look into my neighbour’s yard. Yup, there is a tree. But not so fast–what my eye perceives is a series of impressions of light. The brain then uses that input to construct a model of reality and that model includes the tree. The tree we see is so obvious that we frequently forget that it is the result of model construction, subconscious model construction, but model construction none-the-less. The model is tested when I walk into the tree and hurt myself.

Now consider a slightly more sophisticated example: atoms. The idea of atoms, in some form or other, dates back to ancient India and Greece but the modern idea of atoms dates to John Dalton (1766 – 1844). He used the concept of atoms to explain why elements always interact in the ratios of small whole numbers. This is indirect evidence for the existence of atoms and was enough to convince the chemists but not the physicists of that time. Some like Ernst Mach (1838 – 1916) refused to believe in what they could not see up until the beginning of the last century[1]. But then Albert Einstein’s (1879 – 1955) famous 1905 paper[2] on Brownian motion (the motion of small particles suspended in a liquid) convinced even the most recalcitrant physicists that atoms exist.  Einstein showed that Brownian motion could be easily understood as the result of the motion of discrete atoms. This was still indirect evidence but convincing to almost everyone. Atoms were only directly seen after the invention of the scanning electron microscope and even then there was model dependence in interpreting the scanning electron microscope results. As with the tree, we claim that atoms exist because, as a shown by Dalton, Einstein and others, they form an essential part of models that have strong track record of successful predictions.

Now on to the God particle. What a name! The God particle has little in common with God but the name does sound good in the title of this essay. Then again, calling it the Higgs boson is not without problems as people other than Peter Higgs[3] (1920 – ) have claimed to have been the first to predict its existence. Back to the main point, why do we say the God particle exists? First there is the indirect evidence. The standard model of particle physics has an enviable record of successful predictions. Indeed, many (most?) particle physicists would be happier if it had had some incorrect predictions. We could replicate most of the successful predictions of the standard model without the God particle but only at the expense of making the model much more complicated. Like the recalcitrant physicists of old who rejected the atom, the indirect evidence for the God particle was not good enough for most modern-day particle physicists. Although few actually doubted its existence, like doubting Thomas, they had to see it for themselves. Thus, the Large Hadron Collider (LHC) and its detectors were built and direct evidence was found. Or was it? Would lines on a computer screen have convinced the logical positivists like Ernst Mach? Probably not, but the standard model predicted bumps in the cross-sections and the bumps were found. Given the accumulated evidence and its starring role in the standard model of particle physics, we confidently proclaim that the God particle, like the tree and the atom, exists. But remember, that even for the tree our arguments were model dependent.

Having discussed the God particle what about God? I would apply the same criteria to His/Her/Its existence as for the tree, the atom, or the God particle. As in those cases, the evidence can be direct or indirect.  Indirect evidence for God’s existence would be, for example, the argument from design attributed to William Paley (1743 – 1805). This argument makes an analogy between the design in nature and the design of a watch. The question is then is this a good analogy? If we adopt the approach of science this reduces to the question: Can the analogy be used to make correct predictions for observations? If it can, the analogy is useful, otherwise it should be discarded. There is also the possibility of direct evidence: Has God or His messengers ever been seen or heard? But as the previous examples show, nothing is ever really seen directly but depends on model construction. As optical illusions illustrate, what is seen is not always what is there. Even doubting Thomas may have been too ready to accept what he had seen. As with the tree, the atom or the God particle, the question comes back to: Does God form an essential part of a model with a track record of successful predictions?

So does God exist? I have outlined the method for answering this question and given examples of the method for trees, atoms and the God particle. Following the accepted pedagogical practice in nuclear physics, I leave the task of answering the question of God’s existence as an exercise for you, the reader.

La visite s’accélère !
Jeudi 08 novembre 2012

Un élément d’un accélérateur (je ne sais plus lequel).

La journée commence par une citation de notre collègue Joseph : « si tu veux pas entendre parler de protons, va à Conforama ! » Notre guide ce matin s’appelle François. Il est belge et ingénieur en informatique. Il nous présente le site LINAC-LEIR où l’on trouve tous ce qu’il faut pour préparer les noyaux que l’on va injecter ensuite dans les différents accélérateurs. Il porte un détecteur de radioactivité pour mesurer les doses qu’il reçoit dans une journée. D’ailleurs, il y a des détecteurs de radioactivité à l’entrée et à la sortie du CERN, et gare à celui qui a subi une injection de radio-isotopes pour une analyse médicale, il va sonner aux portiques pendant une semaine (c’est déjà arrivé). Sinon, en cas de problème, faire le 74444 (les pompiers).

Mario Campanelli et sa  tablette tactile géante.

Mario Campanelli est un physicien italien qui travaille sur le projet ATLAS (après le Tevatron aux USA, Gran Sasso en Italie…), ce n’est pas une tablette tactile même géante qui va lui faire peur.

Il nous montre une représentation quasiment en temps réel des informations qui circulent  sur le réseau de calcul du CERN à travers le monde. Il s’agit du GRID, sorte de WEB des logiciels, un partage réseau mondial dont on voit un bout à droite, nécessaire pour traiter les milliards de données qu’engendrent les collisions de particules dans le LHC (sous linux toujours).

On appelle ce lieu le CCC : le Centre de Contrôle du CERN. On voit les personnels à travers une vitre mais la plupart ne contrôle rien à l’instant car un apéro est organisé pour fêter les objectifs de puissance atteints. Tout est prétexte pour faire la fête hein ?!

A 11h, petite pause conférence (Solène Chevalier-Théry de Sciences à l’école puis Morgan Piezel professeur, pour l’exploitation de ce stage dans nos lycées) dans la salle où a été annoncée la découverte du Higgs, ou en tout cas, quelque chose qui s’en rapproche. Les physiciens que nous rencontrons espèrent d’ailleurs que ce n’est pas exactement le boson prévu par le Modèle Standard, car alors… ça serait trop simple.

La soirée se termine avec une partie de quarks poker, un jeu inventé par le physicien retraité Patrick Roudeau. En comprendre les règles fut un des exercices les plus difficiles de la semaine.

À suivre…

Jocelyn Etienne est enseignant au lycée Feuillade de la ville de Lunel.

Pour soumettre sa candidature pour la prochaine session du stage au CERN, c’est par ici.

Hi All,

This post is long overdue but nonetheless I am thrilled to finally write it. We have discovered the a some  ??? Higgs boson, and it is precisely my trouble writing this very sentence that inspires a new post. CERN‘s press office has keenly presented a new question in particle physics known as the Definite Article Problem:

Have we discovered “a” Higgs boson or “the” Higgs boson?

We can express the Article problem in another way:

Are there more Higgs bosons?

Before I touch upon that problem, I want to explain about why the Higgs boson is important. In particular, I want to talk about the Sun! Yes, the Sun.

The Higgs Boson and Electroweak Symmetry Breaking is Important because the Sun Shines.

Okay, there is no way to avoid this: I really like the sun.

Slide Credit: Mine. Image Credit: GOES Collaboration

It shines. It keeps the planet warm. There is liquid water on Earth, and some very tasty plants too.

Slide Credit: Mine. Image Credit: NobelPrize.org

At the heart of the Sun is a ranging nuclear furnace and involves two types of processes: (1) those that involve the Strong nuclear force and (2) those that involve the Weak nuclear force (look for the neutrinos!). The two types of processes work together in a solar relay race to complete a circuit, only to do it over and over again for billions of years. And just like a real relay race, the speed at which the circuit is finished is set by the slowest member. In this case, the Weak force is the limiting factor and considerably slows down the rate at which the sun could theoretically operate. If we make the Weak force stronger, then the Sun would shine more brightly. Conversely, if we make the Weak force even weaker, the Sun would be dimmer.

Slide Credit: Mine. Image Credit: NobelPrize.org

From studying the decays of radioactive substances, we have learned that the rate of Weak nuclear processes is set by a physical constant called Fermi’s Constant. Fermi’s Constant is represented by symbol GF. From study the Higgs boson and the Higgs Mechanism, we have learned that Fermi’s Constant is literally just another constant, v, in disguise. This second physical constant (v) is called the Higgs “vacuum expectation value” , or “vev” for short, and is the amount of energy the Higgs field has at all times relative to the vacuum.

The point I want to make is this: If we increase the Higgs vev, Fermi’s Constant gets smaller, which reduces the rate of Weak nuclear interactions. In other words, a larger Higgs vev would make the sun shine less brightly. Going the other way, a smaller Higgs vev would make the sun shine more brightly. (This is really cool!)

Slide Credit: Mine. Image Credit: Jacky-Boi

The Higgs vev is responsible for some other things, too. It is a source of energy from which all elementary particles can draw. Through the Higgs Mechanism, the Higgs field provides mass to all elementary particles and massive bosons. One would think that for such an important particle we would have a firm theoretical understanding it, but we do not.

Credit: Mine

We have a very poor theoretical understanding of the Higgs boson. Among other things, according to our current understanding of the Higgs boson, the particle should be much heavier than what we have measured.

Credit: Mine

The Definite Article Problem

There are lots of possible solutions to the problems and theoretical inconsistencies we have discovered relating to the Standard Model Higgs boson. Many of these ideas hypothesize the existence of other Higgs bosons or particles that would interact like the Higgs boson. There are also scenarios where Higgses have identity crises: the Higgs boson we have observed could be a quantum mechanical combination (superposition) of several Higgs bosons.

I do not know if there are additional Higgses. Truthfully, there are many attractive proposals that require upping the number Higgs bosons. What I do know is that our Higgs boson is interesting and merits much further studying.

Credit: Mine

Happy Colliding

- richard (@bravelittlemuon)

PS In case anyone is wondering, yes, I did take screen shots from previous talks and turn them into a DQ post.

This is why the Diversity office was recently created and has already started shaking some old beliefs by organizing a series of special seminars.

This week, CERN welcomed Dr Tom Shakespeare, an outstanding speaker who overcame many barriers. Bearing his surname, he said laughing, was more challenging than suffering from a growth-impairing disease and being paraplegic. But just like his unproven but most likely famous ancestor, Tom has a knack with language and captivated his audience with a lecture on how working places would benefit from being more welcoming to people having all sorts of disabilities, be they physical or mental. His key message was that people are more disabled by society than by their own minds or bodies.

“Disability is an issue of human rights and equality”, he said, “not disease”.  He went on talking about several famous physicists who made great contributions to physics despite having some form of disability. Isaac Newton was a highly anxious and insecure person probably suffering from either autism, Asperger or Tourette syndrome. Albert Einstein’s difficulties in school may have stemmed from dyslexia while Paul Dirac had some form of neurological difference giving him an eccentric and peculiar personality. In particular, he showed a compelling video where Stephen Hawking, one of the most celebrated astrophysicists, talks about his life, explaining how he was able to become so successful despite his disease, and where he gives his full support to the World Report on Disability.

This World Health Organisation report shows that one billion people in the world have some form of disabilities. This means just about 15% of all people have some level of impairment affecting the way they move, talk, hear, see, behave or think. “You might not have any disability now but most of you are at risk of developing one as you age”, Tom told the audience.

He insisted on the importance for a work place to adapt to people’s handicaps, and not the other way around, such as to enable every individual to contribute to their full potential. Neurodiversity can in fact be seen as an opportunity instead of a challenge. People with attention deficit disorder, Asperger syndrome or autism for example can contribute in their own unique ways.

He gave very valuable and simple tips on proper etiquette on how to treat disabled people with respect and dignity: don’t stare; don’t make assumption, just ask; treat the person as a human being and not a disease (like talk about a person who is blind rather than “the blind” or “the quadriplegic”); address the person directly not their parent or carer, and give them a chance to speak for themselves. Finally, ask questions about things you need to know and not just because you are curious.

Pauline Gagnon

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C’est pourquoi le Bureau de la diversité, créé récemment, a déjà commencé à secouer certains anciens préjugés en organisant une série spéciale de séminaires.

Cette semaine, le CERN a accueilli le Dr Tom Shakespeare, un orateur hors pair qui fait a dû surmonter plusieurs barrières. Assumer son nom de famille a-t-il dit en riant a été plus difficile que de souffrir d’une maladie affectant le développement et d’être paraplégique. Mais tout comme son fort probable mais non établi célèbre ancêtre, Tom a un talent exceptionnel et a captivé son audience en élaborant sur la façon dont les lieux de travail gagneraient à être plus accueillants pour les personnes souffrant de handicaps, qu’ils soient physiques ou mentaux. Son message clé est que les gens sont plus handicapés par la société que par leur corps ou leur esprit.

«Le handicap est une question de droits humains et d’égalité”, a-t-il dit, “pas de maladie”. Il a nommé plusieurs physiciens célèbres qui ont grandement contribué à la physique en dépit de diverses formes de handicap. Isaac Newton par exemple était une personne terriblement anxieuse et incertaine, souffrant probablement soit d’autisme, soit du syndrome d’Asperger ou de Tourette. Les difficultés d’Albert Einstein à l’école ont pu venir de dyslexie alors que Paul Dirac avait une certaine forme de différence neurologique lui conférant une personnalité excentrique et singulière. En particulier, Tom Shakespeare a montré une vidéo saisissante où Stephen Hawking, l’un des plus célèbres astrophysiciens, parle de sa vie, en expliquant comment il a pu réussir à développer pleinement son potentiel en dépit de sa maladie et où il donne son appui total au Rapport mondial sur le handicap.

Ce rapport de l’Organisation mondiale de la Santé montre qu’un milliard de personnes dans le monde souffrent d’une certaine forme de handicap. Cela signifie qu’à peu près 15% de la population doit surmonter des difficultés particulières affectant la façon dont ils se déplacent, parlent, entendent, voient, se comportent ou pensent. “Vous n’avez peut-être pas d’handicap aujourd’hui, mais la plupart d’entre vous risquent d’en développer un durant votre vieillesse”, a-t-il lancé à l’auditoire.

Il a insisté sur l’importance d’avoir des lieux de travail qui s’adaptent aux personnes handicapées, et non l’inverse. Il faut permettre à chacun et chacune de contribuer à son plein potentiel. La neuro-diversité peut en fait être considérée comme une opportunité plutôt qu’un défi. Les personnes atteintes de troubles du déficit de l’attention, du syndrome d’Asperger ou d’autisme par exemple peuvent toutes contribuer de leur propre façon.
Il a donné quelques conseils simples mais précieux sur comment traiter les personnes handicapées avec respect et dignité: ne pas fixer la personne du regard, ne rien supposer mais plutôt demander, traiter la personne comme un être humain et non comme une maladie (parler d’une personne qui est aveugle plutôt que «d’un aveugle» ou «d’un tétraplégique»); adresser à la personne directement et non pas leur parent ou assistant-e, et leur donner une chance de s’exprimer. Enfin, ne posez des questions que sur les choses que vous devez savoir et pas par simple curiosité.

Pauline Gagnon

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Since I’m new on Quantum Diaries, let me first introduce myself. I’m Rob, a Belgian Ph.D. student at CERN. Unlike most other physicists here, I am doing purely theoretical work, the kind of work for which one doesn’t need CERN’s Large Hadron Collider or any other equipment, except perhaps for its blackboards. 

See you next year at the caves ouvertes!

Rob

Website (in French)

Mainly cernies here

Here as well.

Dans les cavernes des géants
Mercredi 07 novembre 2012

La matinée est animée par un physicien autrichien guide alpin hyperactif dont je n’ai pas saisi le nom mais que je devrais pouvoir retrouver avant la fin du séjour dans un lieu où même le boson de Higgs est détectable (edit : Michael Hoch en fait). Il nous amène voir les sites où se trouvent deux gigantesques détecteurs de particules, CMS et ATLAS, placés à l’endroit où les faisceaux de protons du LHC se rencontrent.

Avant cela, rapide visite dans un site où un bout du LHC est exposé. On y voit les deux conduits dans lesquels les faisceaux de protons circulent quasiment à la vitesse de la lumière, et dans des sens opposés.

Quatre fois sur les 27 km, ces 2 tuyaux se croisent pour causer les collisions qui sont analysées par CMS et ATLAS (mais aussi LHCb et ALICE). Le module sur lequel je m’appuie sur la photo comporte aussi des électroaimants supraconducteurs refroidis à -271°C par de l’hélium liquide. Les aimants servent plus ou moins à diriger et comprimer le faisceau, son accélération se faisant en d’autres points à l’aide de champ électrique haute fréquence. Mais tout ça ne peut-être vu en fonctionnement car cela se situe à 100 m sous terre et de plus, les radiations émises pourraient nuire à mon cuir chevelu.

À CMS, c’est le physicien Jean Fay qui nous fait visiter les locaux avec grandes compétence et gentillesse. Bien que l’on ne puisse pas approcher le détecteur (mais l’affiche de la photo donne une idée de sa taille), une salle de contrôle de la bestiole nous est accessible.

Le système d’exploitation est linux car les pannes windows sont à proscrire… C’est le monsieur qui me l’a dit. Je résume sa pensée : « Vindoze, c’est bon pour les présentations poveurpoïnt, et encore… »

Attends, je dois vérifier un truc… non, c’est bon en fait !

Vite, il nous faut retourner vers ATLAS. Il se situe en fait vers le CERN, alors que CMS est diamétralement opposé, et en France si j’ai bien tout compris.

C’est un physicien retraité à l’esprit vif comme un neutrino qui nous guide : Klaus Bätzner. Le site ATLAS est plus orienté vers le public car il est proche du CERN et sans doute plus accessible. Une salle de projection 3D est mise à notre disposition. Équipés de lunettes et d’un casque, la vidéo qu’on nous présente est impressionnante.

La salle de contrôle est pleine de grands écrans, de petits écrans, de claviers, et de gens qui regardent des écrans tout en pianotant sur les claviers. Ils sont comme dans un aquarium et on peut les observer sans trop interférer avec leur comportement.

Après le déjeuner avalé en vitesse, direction la salle du conseil pour écouter l’excellent Fabrice Piquemal du CNRS nous parler des neutrinos. Ça tombe bien, les détecteurs précédents ne font qu’extrapoler la présence de neutrinos lors d’une collision, par calcul de l’énergie manquante. Les neutrinos ont la fâcheuse tendance à traverser la matière comme qui rigole, et ne vont pas plus vite que la lumière contrairement à une idée faussement répandue.

Le soir, nous nous retrouvons à Genève après avoir sagement suivi la ligne 14. Le dîner se déroule dans un restaurant où des musiciens jouent avec tout ce qui leur passe sous la main : scie, cuillère, cloche, parfois même des instruments de musique à condition qu’ils fassent plus de 3 mètres. Exténué, retour vers 23 h au CERN.

À suivre…

Jocelyn Etienne est enseignant au lycée Feuillade de la ville de Lunel.

Pour soumettre sa candidature pour la prochaine session du stage au CERN, c’est par ici.

Fermilab’s new Run Like A Proton accelerator path at the Lederman Science Center is now open. Photo: Reidar Hahn

It’s one thing for kids to try to envision particles zipping around underground when learning about the science at Fermilab. It’s another thing entirely for them to pretend to be particles charging along an accelerator path, revealing new physics as they fly by.

This week the Fermilab Education Office celebrated the completion of its new Run Like A Proton accelerator path for middle- and high-school-age visitors to the laboratory.

Located at the Lederman Science Center, the path is an aboveground, scaled-down version of the routes a particle can take through Fermilab’s accelerator complex. While running along the path, kids can act like they are the particles of the lab’s physics program zipping through underground tunnels.

“Kids have different modes of learning,” said Spencer Pasero of Fermilab’s Education Office. “They can learn about the work of the lab with our indoor exhibits, but now they can also learn about it through our new outdoor playground.”

It’s a playground with a physics lesson. Kids playing the parts of protons and antiprotons “collide” by high-fiving each other as they run along the accelerator path. Signs along the path guide them in the right direction, whether they want to follow the path a proton would take as it circles the Main Injector or assume the flight of a neutrino headed toward Minnesota.

Kids won’t be limited to playing the part of particle. If they want a role as someone who sets the particles in motion, they can learn about how an operator interacts with the accelerator complex as she works with her controls on the playground.

At more than 100 feet across – longer than a basketball court – the path gives kids plenty of space to let loose in their particle impressions.

The accelerator path is the first stage in the laboratory’s long-term plan to build a larger physics playground.

The Fermilab Education Office has already taken the Run Like A Proton accelerator path for a test drive with a few student groups, and the new outdoor feature has been a hit.

“Students run like a proton around the accelerator path, and afterward when they go on a tour of Fermilab, the docents ask them, ‘Remember when you were running like a proton?’” said Marge Bardeen, head of the Education Office. “And they remember! What a great way to learn.”

The Run Like A Proton accelerator path is made possible by a grant from the Kane County Riverboat Fund and a contribution from an anonymous donor, both through the Fermilab Friends for Science Education, which supports innovative programs at Fermilab. A ribbon-cutting ceremony for the playground was held on Tuesday, May 21, at the Lederman Science Center.

The Lederman Science Center is open to the public Monday to Friday, 8:30 a.m. to 4:30 p.m. and on Saturdays from 9 a.m. to 3 p.m.

“We hope this playground will activate kids’ imaginations and that they immerse themselves in the physics we’ve been doing at the lab for 30 years,” Pasero said.

The operators of the Large Hadron Collider seek to collide as many protons as possible. The experimenters who study these collisions seek to observe as many proton collisions as possible. Everyone can agree on the goal of maximizing the number of collisions that can be used to make discoveries. But where the accelerator physicists and particle physicists might part ways over just how those collisions might best be delivered.

Let’s remember that the proton beams that circulate in the LHC are not a continuous current like you might imagine running through your electric appliances. Instead, the beam is bunched — about 10¹¹ protons are gathered in a formation that is about as long as a sewing needle, and each proton beam is made up of 1380 such bunches. As the bunches travel around the LHC ring, they are separated by 50 nanoseconds in time. This bunching is necessary for the operation of the experiments — it ensures that collisions occur only at certain spots along the ring (where the detectors are) and the experiments can know exactly when the collisions are occurring and synchronize the response of the detector to that time. Note that because there are so many protons in each beam, there can be multiple collisions each time two bunches pass by each other. At the end of the last LHC run, there were typically 30 collisions that occurred per bunch crossing.

There are several ways to maximize the number of collisions that occur. Increasing the number of protons in each bunch crossing will certainly increase the number of collisions. Or, one could imagine increasing the total number of bunches per beam, and thus the number of bunch crossings. The collision rate increases like the square of the number of particles per bunch, but only linearly with the number of bunches. On the face of it, then, it would make more sense to add more particles to each bunch rather than to increase the number of bunches if one wanted to maximize the total number of collisions.

But the issue is slightly more subtle than that. The more collisions that occur per beam crossing, the harder the collisions are to interpret. With 30 collisions happening at the same time, one must contend with hundreds, if not thousands, of charged particle tracks that cross each other and are harder to reconstruct, which means more computing time to process the event. With more stuff going on each event, the most important parts of the event are increasingly obscured by everything else that is going on, degrading the energy and momentum resolution that are needed to help identify the decay products of particles like the Higgs boson. So from the perspective of an experimenter at the LHC, one wants to maximize the number of collisions while having as few collisions per bunch crossing as possible, to keep the interpretation of each bunch crossing simple. This argument favors increasing the number of bunches, even if this might ultimately mean having fewer total collisions than could be obtained by increasing the number of protons per bunch. It’s not very useful to record collisions that you can’t interpret because the events are just too busy.

This is the dilemma that the LHC and the experiments will face as we get ready to run in 2015. In the current jargon, the question is whether to run with 50 ns between collisions, as we did in 2010-12, or 25 ns between collisions. For the reasons given above, the experiments generally prefer to run with a 25 ns spacing. At peak collision rates, the number of collisions per crossing is expected to be about 25, a number that we know we can handle on the basis of previous experience. In contrast, the LHC operators generally to prefer the 50 ns spacing, for a variety of operational reasons, including being able to focus the beams better. The total number of collisions delivered per year could be about twice as large with 50 ns spacing…but with many more collisions per bunch crossing, perhaps by a factor of three. This is possibly more than the experiments could handle, and it could well be necessary to limit the peak beam intensities, and thus the total number of collisions, to allow the experiment to operate.

So how will the LHC operate in 2015 — at 25 ns or 50 ns spacing? One factor in this is that the machine has only done test runs at 25 ns spacing, to understand what issues might be faced. The LHC operators will re-commission the machine with 50 ns spacing, with the intention of switching to 25 ns spacing later, as soon as a couple of months later if all goes well. But then imagine that 50 ns running works very well outset. Would the collision pileup issues motivate the LHC to change the bunch spacing? Or would the machine operators just like to keep going with a machine that is operating well?

In ancient history I worked on the CDF experiment at the Tevatron, which was preparing to start running again in 2001 after some major reconfigurations. It was anticipated that the Tevatron was going to start out with a 396 ns bunch spacing and then eventually switch over to 132 ns, just like we’re imagining for the LHC in 2015. We designed all of the experiment’s electronics to be able to function in either mode. But in the end, 132 ns running never happened; increases in collision rates were achieved by increasing beam currents. This was less of an issue at the Tevatron, as the overall collision rate was much smaller, but the detectors still ended up operating with numbers of collisions per bunch crossing much larger than they were designed for.

In light of that, I find myself asking — will the LHC ever operate in 25 ns mode? What do you think? If anyone would like to make an informal wager (as much as is permitted by law) on the matter, let me know. We’ll pay out at the start of the next long shutdown at the end of 2017.

We often think of the roots of science starting with the ancient Greeks, or even further back to the Babylonians.   The canonical history is a marriage of mathematics and logic coupled with empirical observation.  The story stretches through the Arab translations of works like Euclid’s Elements during the Dark and Middle Ages, through the emergence of the scientific revolution, and culminating in the dizzying heights of modern works like quantum field theory.   This is not to say that there weren’t hiccups.   Although most scientists would dismiss astrology as quackery, astronomy and astrology were once deeply intertwined from their Western birth in Babylon through the time of Kepler.

I invite you to take a big step back and ponder the following conjecture – that Homo sapiens has always been intrinsically disposed toward scientific thinking.   This is perhaps not ‘science’ in the way we view Western science, but it still has the existence of conceptual framework on which to hang and connect observations.

In the process of doing research for the book, I interacted with a number of anthropologists who are studying the navigational schemes of Pacific Islanders.   Their work demonstrates the existence of an exceedingly sophisticated ‘toolkit’ of navigational schema that allowed them to travel huge distances across the ocean to find small target islands successfully.   Three anthropologists in particular have uncovered some amazing findings:  Cathy Pyrek, Rick Feinberg, and Joe Genz.

Most archaeological evidence points to the emergence of long-distance voyaging by a group called the Lapita people, circa 1600 BC from the Bismarck Archipelago, near New Guinea.   They built craft capable of sailing into the wind, making jumps of hundreds of miles eastward to locations like Fiji, Tonga, Tahiti and the Marquesas.   Even more astonishing was the rapid explosion of voyages of thousands of miles around AD 1000 to Hawaii and the north island of New Zealand.

In order to sail against the wind, one needs to create a sail capable of lift, like a wing and use it in combination with a hull that ‘grabs’ the water as it slices through.    The Lapita figured how to harness the complex fluid dynamics involved in lift and used it to their advantage.  In the 18^th century, Captain James Cook marveled at sophisticated design of the Polynesian voyaging canoes that allowed them to travel at speeds far in excess of Western European vessels.  It wasn’t until 1904 that physicist Ludwig Prandtl laid out the theoretical basis for lift in wings, and wasn’t until the 1970’s that this theory was applied to sails.

The clever design of voyaging canoes was only part of the innovations the Pacific Islanders.   In order to sail across vast stretches of ocean, they needed viable navigational schema.    We don’t have written records from the height of the voyaging period for Polynesians (circa AD 1000), but we do have interviews with modern day practitioners of indigenous navigational techniques that hint at the ways their ancestors crossed large stretches of ocean accurately.

Anthropologists Rick Feinberg and Cathy Pyrek from Kent State have shown how indigenous navigators in eastern Solomon Islands use a ‘navigational tool-kit’, that consists of multiple signs.   Stars that are rising or setting close to the horizon form a natural star-compass.  Their rising and setting positions allow navigators to find the ‘azimuth’ or compass heading toward a destination island.   This requires the navigator to memorize a large number of stars and become familiar with their paths across the sky at different times of the year.

While a star compass may be useful, what does a navigator do during the day or in overcast weather?   Another helpful construct is a wind-compass.  Winds blowing from different directions have different characteristics.    In the eastern Solomons, the trade winds blow from the southeast, and are marked by characteristic ‘trade wind cumulus’ clouds that only grow to heights of roughly 15,000 feet and are then truncated.   These winds mark the direction ‘tonga’, or the southeast, which corresponds to the direction of the island cluster of Tonga.   Winds from the north arrive during the winter months and are associated with variable, stormy weather.

Steady winds and storm systems can also create ocean swells that act as reliable direction indicators.  Often, multiple swells can arise – for example, the Southern Ocean produces a long swell from the south, while trade winds can create shorter wavelength swells from the east.   Even if the wind shifts, the swells retain some ‘memory’ of the winds that created them allowing the navigator to maintain a steady heading.

The above tools are useful in maintaining direction under different conditions, but there’s an inherent uncertainty in the position of a vessel, and this uncertainty grows with time.   A navigator completing a 200-mile journey may only be able to establish a position to within 20 or 30 miles.   Another trick then comes into play:  birds.   Certain birds, like pelicans and frigate birds will fly some distance out to sea to feed, and then will return to their home islands in the evening.   A sailor only has to get to within 30 miles of a target island and then observe land-based birds.   The sail is dropped and when the birds fly home in the evening, a course is set.

The navigational toolkit allows for a kind of successive approximation, where the stars, wind, and swells form a rough guide, and the presence and behavior of birds provides the final precision.

A somewhat related but unique tradition is that of wave-piloting in the Marshall Islands.  Most of us are familiar with refraction and reflection of waves, whether they’re light or sound waves.   Waves on the oceans’ surface are similar, but have some notable differences.   First waves in deep-water have a speed that is proportional to the square root of the wavelength.   Second, waves in shallow water have a speed that’s proportional to the square root of the depth.   This latter relation causes waves to refract in shallow water.   When waves get into very shallow water, they’ll often break, losing much, if not all of their energy.   On the other hand, waves impinging on a steep cliff that extends underwater will reflect with very little energy lost.   Depending on the bathymetry surrounding an island, one can get very different wave patterns produced by the interaction of an incident swell with the island.

Joe Genz from the University of Hawaii studied the tradition of Marshall Island wave piloting for his doctoral thesis.   Navigators in the Marshalls have their own language for describing characteristic wave patterns around islands. Nit in kōt is the name given to a crossing pattern of waves on the lee side of an island.   If a uniform swell impinges in the eastern shore of an island, the waves passing the north shore will be refracted inside the swell-shadow toward the south and the waves passing the south shore will be refracted into the swell-shadow toward the north.   The resulting pattern of crossing waves creates a disturbed region that’s easy to identify at distances beyond which the islands are visible.

In principle, reflected ways should also give clues to the presence of an island.  Joe made the acquaintance of one Captain Korent Joel, a native Marshall Islander who was trying to revive the tradition of wave piloting.   Joe persuaded Captain Korent to demonstrate his wave piloting technique to a group of oceanographers who deployed a set of sensitive wave buoys.  As Captain Korent left the atoll of Arno, he first pointed out the incoming swell from the east, and then the reflected swell off of Arno.

There was only one problem.   No one on the boat with Captain Korent could notice the reflections, although the dominant eastern swell was clearly visible.   Even the sensitive wave buoys couldn’t detect the presence of the reflected swell.    What was going on?    Joe wondered whether Captain Korent just thought he should be seeing a reflected swell and was making this up.

In order to put Captain Korent to a sterner test, Joe waited until he (Captain Korent) was taking a nap on in the cabin.   Joe instructed the crew to motor some 30 miles to the southwest of Arno to get to a new location.   When Captain Korent woke up, Joe told him that he had taken the boat to an undisclosed location and asked him if he could identify the direction to Arno, and the kind of wave patterns he was seeing.   Captain Korent was quite certain the Arno was to the northwest, and he was also quite correct!   So, he was reading the waves properly after all!

I met Joe in person at a conference of the Association for Social Anthropology in Oceania (ASAO) in Portland Oregon in February 2012.    Joe had some videos on his laptop of Captain Korent and shared them with me.   I downloaded them to my computer.   That evening, I watched the video where Captain Korent was pointing out the reflected swell to Joe on the boat.   This was the reflected swell that Joe couldn’t see, and the oceanographer’s buoys couldn’t detect.   Joe told me what Captain Korent was saying in Marshallese about the waves.   I do some sea kayaking, and I’m often close to the water, and am a bit of an amateur wave-watcher myself.

In my first viewing of the video, I could definitely see the incoming dominant swell from the east.   But, by the third or fourth viewing, I could see a weaker reflected swell moving at slight angle against the larger incoming swell.   When I compared my observations to what Captain Korent was saying in Marshallese, they agreed completely!  By the tenth viewing, I became 100% convinced that Captain Korent was pointing out the reflected swell correctly.

The next day, I called Joe over, along with Cathy Pyrek, who was also attending the ASAO conference.   I pulled up the video on my laptop and showed what I saw as the reflected swell.   Joe said, “Oh yeah, now I see it”.    I turned to Cathy and asked if she really saw it, or I was just convincing them of it, but she said,“It’s definitely there, it’s strange that everyone missed it.”

We still have much to learn about how the human mind operates, but it struck me that Captain Korent’s talents show how we’re capable of picking up very weak signals in the presence of noise.   Evidently there is more information on the surface of the ocean than the oceanographer’s buoys were capable of recording.   This is perhaps not surprising, but it’s evidence that there are different frameworks of knowledge out there that are effective and are based on empiricism.   It may not be Western, but it is a kind of science.

For further reading:

Joeseph Genz, et al., “Wave Navigation in the Marshall Islands,” Oceanography, 22, June 2009, 234-245.

Joseph Genz, “Marshallese Navigation and Voyaging: Re-learning and Reviving Indigenous Knowledge of the Ocean,” (PhD diss., University of Hawaii, 2008)

John Huth, The Lost Art of Finding Our Way, (Belknap Press, Cambridge MA, 2013).

Twitter:  @JohnHuth1

One of the over 5000 DOMs (Digital Optical Modules) which make up the IceCube Observatory being deployed into the ice.

There’s a nice Gizmodo article with interesting comments.

University of Wisconsin news item.

Phys.org coverage of the news item.

The BBC news article.

Nature blog entry.

New Scientist entry written by our friend Anil who got to visit IceCube during construction.

Since the middle of last week, the news are spread around and there are Russian, Spanish, and French language versions (at a minimum!) of the news. Previously, only the neutrinos from Supernova 1987A had been seen from beyond the sun and the Earth’s atmosphere. Analysis is still ongoing, so this isn’t a final result by any means, but it is a proof-of-functionality of the IceCube detector and of neutrino astronomy.

Addition:

Scientific American’s article includes good quotes from the three Wisconsin-Madison postdocs who led the analysis, Nathan, Claudio, and Naoko.

This essay makes a point that is only implicit in most of my other essays–namely that scientists are arro—oops that is for another post. The point here is that science is defined not by how it goes about acquiring knowledge but rather by how it defines knowledge. The underlying claim is that the definitions of knowledge as used, for example, in philosophy are not useful and that science has the one definition that has so far proven fruitful. No, not arrogant at all.

The classical concept of knowledge was described by Plato (428/427 BCE – 348/347 BCE) as having to meet three criteria: it must be justified, true, and believed. That description does seem reasonable. After all, can something be considered knowledge if it is false? Similarly, would we consider a correct guess knowledge? Guess right three times in a row and you are considered an expert –but do you have knowledge? Believed, I have more trouble with that: believed by whom? Certainly, something that no one believes is not knowledge even if true and justified.

The above criteria for knowledge seem like common sense and the ancient Greek philosophers had a real knack for encapsulating the common sense view of the world in their philosophy. But common sense is frequently wrong, so let us look at those criteria with a more jaundiced eye. Let us start with the first criteria: it must be justified. How do we justify a belief? From the sophists of ancient Greece, to the post-modernists and the-anything-goes hippies of the 1960s, and all their ilk in between it has been demonstrated that what can be known for certain is vanishingly small.

Renee Descartes (1596 – 1960) argues in the beginning of his Discourse on the Method that all knowledge is subject to doubt: a process called methodological skepticism. To a large extend, he is correct. Then to get to something that is certain he came up with his famous statement: I think, therefore I am.  For a long time this seemed to me like a sure argument. Hence, “I exist” seemed an incontrovertible fact. I then made the mistake of reading Nietzsche[1] (1844—1900). He criticizes the argument as presupposing the existence of “I” and “thinking” among other things. It has also been criticized by a number of other philosophers including Bertrand Russell (1872 – 1970). To quote the latter: Some care is needed in using Descartes’ argument. “I think, therefore I am” says rather more than is strictly certain. It might seem as though we are quite sure of being the same person to-day as we were yesterday, and this is no doubt true in some sense. But the real Self is as hard to arrive at as the real table, and does not seem to have that absolute, convincing certainty that belongs to particular experiences. Oh, well back to the drawing board.  

The criteria for knowledge, as postulated by Plato, lead to knowledge either not existing or being of the most trivial kind. No belief can be absolutely justified and there is no way to tell for certain if any proposed truth is an incontrovertible fact.  So where are we? If there are no incontrovertible facts we must deal with uncertainty. In science we make a virtue of this necessity. We start with observations, but unlike the logical positivists we do not assume they are reality or correspond to any ultimate reality. Thus following Immanuel Kant (1724 – 1804) we distinguish the thing-in-itself from its appearances. All we have access to are the appearances. The thing-in-itself is forever hidden.

But all is not lost. We make models to describe past observations. This is relatively easy to do. We then test our models by making testable predictions for future observations. Models are judged by their track record in making correct predictions–the more striking the prediction the better. The standard model of particle physics prediction of the Higgs[2] boson is a prime example of science at its best. The standard model did not become a fact when the Higgs was discovered, rather its standing as a useful model was enhanced.  It is the reliance on the track record of successful predictions that is the demarcation criteria for science and I would suggest the hallmark for defining knowledge. The scientific models and the observations they are based on are our only true knowledge. However, to mistake them for descriptions of the ultimate reality or the thing-in-itself would be folly, not knowledge.