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Archive for February, 2013

Doomed Universe?

Wednesday, February 27th, 2013

Gian Giudice is a rather smiling and relaxed person for someone who has just shown the Universe might be doomed. This rather shaking discovery did not induce any lack of sleep to this CERN theorist whom I met yesterday. He and his colleagues showed in their latest calculations that if the Standard Model holds beyond all what we have seen so far, the Higgs field will change its value and all matter as we know it will simply cease to exist.

But rest assured, nothing is due to happen for roughly another 10100 years, that is 1 followed-by-100-zeros years. As Gian put it, we should not stop paying our taxes. Given that the Universe is only about 13.77 billion years old, it still gives us plenty of time. One billion is “only” nine zero, a very small number in comparison with the time estimated for this change to happen.

What he and his colleagues found is that we live in a Universe having parameters sitting just on the edge. Their calculations established that the stability of our Universe depends on the specific values assumed by various entities such as the masses of some fundamental particles. Assuming the new boson found last July is the Higgs boson and has a mass of 126 GeV, and injecting the known value of the top quark mass (roughly 173 ± 1 GeV), implies the Universe sits in a meta-stable region. This means the Universe is doomed to undergo some sort of “phase transition” at some distant time in the future.

The left plot, extracted from their paper, shows three types of regions depending on the value of these two masses: the red ones indicate that the Universe would have been unstable and would not have formed. The green region corresponds to a set of values leading to eternal stability, where the Higgs field would remain unchanged forever. The yellow region describes a meta-stable region. The right plot shows that, with the assumed mass values, we fall in the meta-stable region, where eventually the Higgs field value will change, leading to a complete collapse of all atoms.

The Higgs field is a physical entity, just like a magnetic field around a magnet. And the Higgs boson is simply an excitation of this field, just like a wave is an excitation of the surface of the ocean.

This change of the Higgs field value would be just a phase transition similar to what happens when a liquid starts to boil. Bubbles form and eventually, the liquid evaporates and disappears. Since the value of the Higgs field has a direct impact on the mass of quarks and electrons, it also determines the size of atoms. If the field value changes sufficiently, the atoms equilibrium is at risk and all matter could collapse.

What is puzzling Gian Giudice the most is why are these parameters such as to put us right on the edge between the meta-stable and stable region. Why has Nature chosen such unlikely values out of all possibilities? Could it be that all values are possible and we simply happen to live in a Universe having these specific ones? This would then mean there would be zillions of other Universes out there, each one having its own set of parameters, some of them being completely unstable and undergoing rapid phase transitions, others simply never being born. Our Universe would be part of a multiverse.

Much food for thoughts! The easiest way out is still for the Large Hadron Collider (LHC) to lead to the discoveries of new particles, revealing that the Standard Model does not provide the full picture. This in turn would mean all these calculations would just be good for the garbage, as Gian Giudice is the first to point out laughingly.

Pauline Gagnon

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L’Univers va-t-il disparaître ?

Wednesday, February 27th, 2013

Gian Giudice est plutôt souriant et tranquille pour quelqu’un qui vient tout juste de démontrer que l’Univers est peut-être voué à disparaître. Cette découverte pour le moins renversante n’a pas fait perdre le sommeil à ce théoricien du CERN que j’ai rencontré hier. Lui et ses collègues ont démontré que si le Modèle Standard tient bien au-delà de ce que nous avons vu à ce jour, le champ de Higgs changera de valeur et toute la matière cessera d’exister sous sa forme actuelle.

Mais il n’y a rien à craindre : cela ne devrait pas se passer avant dix puissance cent années (10100), soit 1 suivi de cent zéros. Comme le dit Gian, inutile de ne pas payer ses impôts. Sachant que l’âge de l’Univers se chiffre à 13,77 milliards d’années, on a encore bien le temps, un milliard n’étant qu’un suivi de neuf zéros, rien en comparaison du temps estimé avant cette transition.

Ce que lui et ses collègues ont trouvé, c’est que nous vivons dans un Univers se situant juste à la limite. Leurs calculs ont établi que la stabilité de l’Univers dépend des valeurs spécifiques de différentes quantités comme les masses de particules fondamentales. En supposant que le boson découvert l’an dernier est bien le boson de Higgs ayant une masse de 126 GeV, et en incluant la valeur de la masse du quark top (environ 173 ± 1 GeV), ils ont déduit que l’Univers se trouve dans une région métastable. Cela signifie qu’éventuellement l’Univers passera par une sorte de « transition de phase ».

Le graphe de gauche, tiré de leur article, montre qu’il existe trois types de régions dépendant des valeurs de ces deux masses: en rouge,  les zones d’instabilité où l’Univers ne pourrait exister ; en vert, les zones de stabilité éternelle où le champs de Higgs ne changera jamais de valeur, et enfin en jaune, une région métastable. Le graphe de droite montre que pour les valeurs de masse en question, on tombe en zone métastable où éventuellement la valeur du champ de Higgs changera, causant la disparition de tous les atomes.

Le champ de Higgs est une entité physique, tout comme le champ magnétique qui entoure un aimant. Le boson de Higgs quant à lui n’est qu’une excitation de ce champ, comme une vague est une excitation de la surface de l’océan.

Un changement de valeur du champ de Higgs s’apparentera à une transition de phase, comme lorsqu’un liquide se met à bouillir. Des bulles se forment, puis peu à peu le liquide s’évapore et disparaît. Puisque la valeur du champ de Higgs a un impact direct sur la masse des quarks et des électrons, elle détermine aussi la taille des atomes. Si cette valeur change suffisamment, tout l’équilibre des atomes sera menacé.

Ce qui étonne le plus Gian Giudice, c’est le fait que les valeurs de ces paramètres soient à la limite entre les zones de stabilité et de métastabilité. Pourquoi la Nature en a-t-elle décidé ainsi parmi toutes les valeurs possibles ? Se pourrait-il que toutes les valeurs soient permises et qu’on s’adonne simplement à vivre dans un Univers ayant un ensemble particulier de valeurs ? Ceci signifierait qu’il existe en parallèle une multitude d’autres univers, chacun ayant son propre ensemble de paramètres. Certains seraient donc instables et n’auraient pu se former, tandis que d’autres passeraient par des transitions de phase rapides. L’Univers ferait alors partie d’un multivers.

Cela donne matière à réflexion. Le plus simple serait encore si le Grand collisionneur de hadrons ou LHC conduisait à de nouvelles découvertes, révélant ainsi que le Modèle Standard n’est pas l’ultime théorie. Cela impliquerait du coup que tous ces calculs, qui assument l’infaillibilité du Modèle Standard, ne seraient bons que pour la poubelle, me lance en riant Gian Giudice.

Pauline Gagnon

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Expérience de taille à Dubna !

Wednesday, February 20th, 2013

Les 15 et 16 janvier derniers nous fêtions le 40ème anniversaire des accords bilatéraux de l’IN2P3 et du JINR de Dubna, l’occasion pour nous d’évoquer un épisode de cette longue collaboration.

Les physiciens savent se montrer pragmatiques lorsqu’ils font face à un problème inattendu, particulièrement en URSS dans les années 1970… Catherine Thibault, chercheuse au CSNSM d’Orsay (Centre de spectrométrie nucléaire et de spectrométrie de masse), nous raconte un épisode de recherche qui le démontre brillamment !

Départ du CSNSM - ©CSNSM

Départ du CSNSM - ©CSNSM

En 1974, dans le cadre de l’étude de la fission nucléaire, une équipe du CSNSM dirigée par Robert Klapisch (le papa de Cédric oui !) voulait mesurer la production des différents isotopes de rubidium et césium produits lors de la fission de l’uranium 238 par des ions lourds. Les expériences eurent lieu à Dubna, au JINR, l’équivalent du Cern pour les pays de l’Est. Dans un premier temps, il a fallu acheminer tout le matériel, dont un ordinateur américain (PDP), ce qui nécessitait une autorisation d’exportation temporaire en URSS (pour seulement 8 ko de mémoire !), que nous avons pu obtenir.

La partie principale était un spectromètre de masse permettant de séparer en quelques centaines de millisecondes les différents isotopes de rubidium ou de césium produits par la fission d’une cible. Ceci permettait de mesurer leurs différents taux de production.

Arrivée à Dubna -

Arrivée à Dubna - ©CSNSM

Bien que le spectromètre contenant la cible ait été positionné avec le plus grand soin, aucun signal n’était observé… jusqu’à ce qu’une cible de rechange placée quelques centimètres au-dessous de la cible-source ait été trouvée détruite par le faisceau ! Nous devions donc baisser le spectromètre de quelques centimètres ce qui posait un problème de taille puisque ce dernier était déjà réglé à son minimum de hauteur. « Qu’à cela ne tienne, ont alors dit les collaborateurs russes, nous allons abaisser le sol ! ». Chose dite, chose faite avec une remarquable efficacité… C’est au marteau piqueur que l’on a attaqué le sol de béton !

L’expérience a ensuite très bien fonctionné… Et les données obtenues analysées puis publiées, ont servi de base à une thèse. Qui a dit que les chercheurs étaient de doux rêveurs ?

— anecdote fournie par le Centre de spectrométrie nucléaire et de spectrométrie de masse (CSNSM), unité mixte de recherche du CNRS/IN2P3 et de l’Université Paris Sud, dans le cadre des 40 ans du CNRS/IN2P3.

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Using Physics to Find More Physics

Thursday, February 14th, 2013

The best kind of physics is the new kind. How do you find new physics? By using physics of course!

Hi All,

A maxim in particle physics says to

use physics to find more physics!

I forget from where or whom I first heard this saying but the idea goes something like this: When a new particle is discovered, in principle, our knowledge of the particle only consists of what we have directly measured and what the theory that lead us to its discovery tells us. The theory, of course, is most likely incorrect but that is the point. As far as we know, any newly discovered particle might have some hereto unknown quantum number. But if this is the case, then by scrutinizing a new particle we might get lucky, very luck and discover something completely unexpected. One perfect example comes from neutrino physics. After finally discovering them, physicists learned eventually how to make beams of neutrinos only to find out (1) that there are several types of neutrinos and (2) they have mass. Another example involves the W boson and brief history of modern particle colliders.

The purpose of particle colliders like the Super Proton Synchrotron (SPS), the Large Electron-Positron collider (LEP), the Tevatron, or the Large Hadron Collider (LHC) is to test physical theories in order to ultimately figure out what works and doesn’t work. Sometimes all the time we get disappointing results (technicolor, extra dimensions, additional vector bosons), and sometimes rarely we score big (top quark, Higgs boson). It’s all a part of the business. The utility of colliders is that, with them, there are multiple ways hypotheses can be tested. One particularly powerful method to test models like the Standard Model of Particle Physics (SM) is to look for processes that are both (a) relatively rare and (b) relatively unique. For example: in the theory that governs how light and matter interact, also known as Quantum Electrodynamics (QED), we can take an electron (e-) and its antiparticle, a positron, (e+), and use them to produce two photons, the particles of light (γ). Figure 1 below shows how this can happen diagrammatically. In short, either the electron or the positron first radiate a photon (γ), and then the electron and positron annihilate forming the second photon (γ).

Figure 1. A Feynman diagram representing the production of two photons from electron (e-) and positron (e+) annihilation.

In the 1990s, back when the Large Hadron Collider (LHC) was just a dream on paper, another accelerator called the Large Electron-Positron collider (LEP) existed in the same tunnel the LHC currently occupies. The goal of LEP was to study the very fine details (“precision work”) of the theory we now call the Standard Model of Particle Physics (SM). At the time, this was particularly concerning because the W and Z bosons had only been discovered ten years prior at the Super Proton Synchrotron collider (SPS), and establishing the SM hinged on knowing their properties. LEP, along with the Tevatron, did just this. In fact, some of the most precisely measured results of the SM bosons still come from LEP.

At LEP, physicists decided to pursue an idea that made many of the same people who discovered the W and Z bosons pause for just a moment. LEP experimentalists set out to produce two W bosons and two Z bosons at the same time. Just like the diagram for producing two photons in QED (Fig. 1), there is diagram depicting how two W bosons can be produced from an electron (e-) and positron (e+). See Figure 2 below. The diagram for producing two Z bosons is identical to Fig. 1, just replace “γ” with “Z“. In the case of W+W- production, either an electron or a positron first radiates a W boson; an e- will radiate a negatively charged W boson, W-, and an e+ will radiate an positively charge W boson, W+. After radiating the boson, the electron (or positron!) is converted into a neutrino (or anti-neutrino!), and annihilates with the positron (or electron!) to produce the second W boson.

Figure 2: A Feynman digram representing how the neutrino contributes to W+W- pair production from electron (e-) and positron (e+) annihilation.

However, unlike producing two photons, there is another process that can contribute to producing two W bosons. Figure 3 below shows that an electron (e-) and positron (e+) can also annihilate into a photon (or a Z boson), and then the photon (or Z boson) can split into a W+ and W- boson.

Figure 3: A Feynman digram representing how the photon and Z boson contribute to W+W- pair production from electron (e-) and positron (e+) annihilation.

In the 2000s, physicists at the Tevatron took this a step further. It starts by recognizing that since electrons and positrons can produce two W bosons, and since physics going forward in time behaves identical to physics operating backward in time (time-reversal symmetry), then two W bosons can be used to produce an electron and positron. Figure 4 below shows how this can happen diagrammatically.

Figure 4: A Feynman diagram representing how to produce an electron (e-) and positron (e+) pair from a W+ and W- boson pair.

Here is physicists got clever. The diagram in Figure 3 and the left diagram in Figure 4 have the same intermediate particle: a photon or Z boson. The rules of quantum field theory allow us to then take the second half of Fig. 3 and the first half of the left diagram in Fig. 4, and attach them! As a result, two bosons can be used to produce two more bosons! A few examples: a W+ boson and a W- boson can annihilate or exchange a photon (or Z boson) and produce another two W bosons (Figure 5 below); two W bosons can also go in and produce two photons, two Z bosons, or a photon and Z boson; in fact, two photons can go in and even produce two W bosons! This sort of phenomena is generically called “Weak Boson Scattering,” “Vector Boson Scattering,” or “Vector Boson Fusion,” and in 2006, the Tevatron‘s DZero detector experiment provided the proof of this process when it measured the rate of two Z bosons being produced simultaneously (press release).

Figure 5: A Feynman diagram representing how the photon and Z boson contribute to W+W- scattering.

Warning: Technical Detail. Abandon hope all ye who… I mean, Weak Boson Scattering at the Tevatron differs from producing two bosons at LEP in a subtle way. At LEP, both the electron (e-) and positron (e+) ultimately annihilated and ceased to exist. At the Tevatron, each initial W and Z boson came from a quark (or antiquark) that radiated the boson but did not ultimately annihilate (Figure 6 below.). The analogous process that occurred at LEP did occur at the Tevatron (and vice versa), but the two processes can be to some extent distinguished from each other.

Figure 6: Diagram depicting the process known as WW Scattering, where two quarks from two protons each radiate a W boson that then elastically interact with one another.

However, we have to be careful here. Much like how we needed to include an additional diagram when progressing from producing two photons to W+W- production with electrons and positrons, we need to include additional diagrams for W+W- production when starting with two W bosons. A hugely important process that warranted the Higgs boson’s existence long before it was found is when we replace the intermediate photon and Z in Fig. 5 (above)  with a Higgs boson. See Figure 7 below. By measuring the rate of weak boson scattering, one can in principle infer the mass of the Higgs boson. This is precisely how physicists at the Tevatron and the LHC were able to rule out the existence of a very massive Higgs boson.

Figure 7: A Feynman diagram representing how the Higgs boson contributes to W+W- scattering.

In fewer than 30 years, physicists have gone from discovering the W and Z bosons (SPS),  to producing two of them simultaneously (LEP), to creating a proof-of-principle vector boson collider (Tevatron), to using a new vector boson collider as a probe for new physics (LHC)! We have already discovered the Higgs boson using this method and we are definitely hoping to find something more. If there are more vector bosons in the universe, then it is certainly possible that they may contribute to vector boson scattering by replacing any of the lines in Fig. 5; see Figure 8 below.

Figure 8: A Feynman diagram representing how a new vector boson (?) can contribute to W+W- scattering.

It is also certainly possible that there are additional Higgs bosons. Those can contribute to vector boson scattering by replacing the Higgs boson in Fig. 7; see Figure 9 below.

Figure 9: A Feynman diagram representing how a new scalar (?) can contribute to W+W- scattering.

This is how research in high energy physics progresses: discover something new, turning it around, and throwing it back at itself. You can be certain that there is already research into scattering Higgs bosons and how this next iteration of collisions could be excellent tests of theories like technicolor, extra dimensions, or the existence of additional vector bosons. Until next time!

 

Happy Colliding

– richard (@bravelittlemuon)

 

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Au revoir, faisceaux!

Wednesday, February 13th, 2013

Cette fois, c’est vrai. Le Grand Collisionneur de Hadrons (LHC) cessera pour deux ans de produire des collisions dès demain, 14 février à 6:00 du matin, après une brève extension de trois jours visant à fournir suffisamment de données pour les études d’ions lourds. En un rien de temps, à l’annonce de cette extension, des dizaines de personnes se sont portées volontaires pour opérer les salles de contrôle des expériences et des accélérateurs à la veille de cette longue pause.

J’étais parmi ces personnes, heureuse de pouvoir travailler une dernière fois dans la salle de contrôle d’ATLAS. L’ambiance y est toujours spéciale: c’est là qu’on prend part à la prise des données et par la même occasion, on y rencontre ou apprend à connaître nos collègues qui travaillent ailleurs qu’au  CERN, souvent sur d’autres continents.

Alors nous voilà, neuf personnes venant d’autant de pays différents, chargées d’opérer le détecteur, en plus des expert-e-s qui vont et viennent tout au long de cette avant-dernière période de garde.

Stephanie Zimmermann, une des deux personnes en charge de l’opération du détecteur, admet qu’elle se serait réjouie s’il s’agissait d’une pause de quelques  mois, mais deux années, ce sera long dit-elle. Cependant, Anna Sfyrla, une des expertes sur le système qui décide quels évènements conserver, est ravie de ne plus avoir à assister aux meetings quotidiens six jours sur sept. Par contre, tout le plaisir de la salle de contrôle va lui manquer.

Une autre personne qui a évidemment une opinion sur le sujet, c’est Kerstin Lantzsch. Comme elle vit pratiquement dans la salle de contrôle, on sait toujours où la trouver. Depuis sept mois, elle coordonne les opérations des pixels, le détecteur situé au plus près des faisceaux, et donc le plus vulnérable. Pratiquement chaque fois que le LHC amène de nouveaux faisceaux en collision, c’est-à-dire plusieurs fois par jour,  elle vient à la salle de contrôle pour décider quand il est sécuritaire d’activer ce détecteur. Pas étonnant qu’elle ait hâte de retourner à une vie normale mais elle sait tout de même que l’action va lui manquer.

Giovanna Lehman, une des expertes du système central d’acquisition des données, partage cet avis. Elle doit pouvoir répondre à une variété de questions pointues à toutes heures du jour et de la nuit dès que ça accroche et que la personne de garde ne peut gérer.  Elle aussi rêve déjà de nuits ininterrompues et se réjouie de travailler sur les améliorations prévues au système.

Et puis il y a les occasionnels de la salle de contrôle,  ceux et celles qui comme moi ne viennent que pour prendre leurs quarts de travail. Des gens comme Aungshuman Zaman, étudiant à Stony Brook à New York et Nedaa Asbah, étudiante à l’université de Montréal. Les deux ont déjà pleins de projets : lui, s’impliquer dans les améliorations au détecteur de pixels, elle écrire sa thèse de maîtrise.

Cyril Bécot, étudiant à Orsay près de Paris, utilisera cette pause pour compléter sa thèse de doctorat. Puisqu’il travaille sur les désintégrations du boson de Higgs en deux photons, il a dû travailler sous haute tension durant les derniers six mois. Loin d’être triste, il est tout heureux d’avoir enfin le temps d’approfondir un peu plus son analyse au lieu de constamment courir contre la montre, étant donné la haute priorité de son sujet de recherche.

Même son de cloche chez Anna Lipniacka, professeure à Bergen en Norvège. Bien sur, elle est un peu triste mais tout comme Cyril, elle est bien heureuse d’avoir un peu plus de temps pour bien observer les données et améliorer ses méthodes d’analyse.

Quant à Mansoora Shamim, post-doc à l’université de l’Oregon, elle dit être modérément triste de voir partir les faisceaux pour les mêmes raisons. Elle est bien heureuse d’avoir un peu plus de temps pour se concentrer à sa recherche sur les trous noirs.

Et moi aussi,  je suis triste bien qu’à long terme cela signifie de meilleures chances de faire de nouvelles découvertes. Entre temps, grâce à la dernière bordée de neige, le champagne est au frais afin qu’on puisse porter un toast au LHC à la fin de notre tour de garde.

Pauline Gagnon

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Bye bye beams!

Wednesday, February 13th, 2013

This time, it’s true. The Large Hadron Collider (LHC), will stop making collisions for about two years tomorrow, 14 February at 6:00 am, after postponing the date by three days to give the heavy ion community enough data. Shortly after this extension was announced,  dozens of volunteers signed up to staff the experiments and accelerators control rooms.

I was one of them, happy for the opportunity to say goodbye to the ATLAS control room where I have had lots of great moments on shifts. The ambiance is always special: this is where you meet or get to know better many collaborators who normally work outside  CERN, and often, on different continents. Many come to CERN to take their share of the operation load and participate in the data taking.

So here we are, nine people staffing the control room from as many different nationalities plus a few experts on call, coming and going during the one before last shift.

Stephanie Zimmermann, one of the two people in charge of running the detector, confides she would welcome a short break, a few months would be great. But two years will be long. But Anna Sfyrla, one of the trigger experts who has to attend the run meetings six days a week says she won’t miss those meetings and is looking forward to have a breather. Nevertheless, she will miss the fun of the control room.

One other obvious person to ask is Kerstin Lantzsch. Easy to catch her since she practically lives in the control room. She is run coordinator for the pixels, which means she is responsible for the sub-detector placed closest to the beam, the one most likely to be damaged when beams are injected inside the accelerator. She has been coming to the control room every time for the past seven months when the LHC brings fresh beams into collisions, which means a few times a day. No wonder she is looking forward to having a more normal life but nevertheless, she knows she will miss the action.

Similar thoughts for Giovanna Lehman who is one of the experts working on the central data acquisition system. This entails answering all sorts of tough questions at all times of day or night when there is a hiccup in the system that the shifter cannot handle. She looks forward to sleeping more regular hours and getting involved in the many improvements they are planning for this system.

Then some only come occasionally to the control room to take a few shifts. People like two students, Aungshuman Zaman from Stony Brook in New York and Nedaa Asbah from Université de Montréal. They will both have plenty to do. Aungshuman has his work cut out on a detector upgrade and Nedaa will write her masters thesis.

Cyril Bécot, a student at Orsay near Paris will use the time afforded by the long shutdown to complete his PhD thesis. Since he studies Higgs boson decays to two photons, he had to work under great pressure over the last six months given the high profile of the Higgs search. Far from being sad to see the beams go, he looks forward to taking his time to improve his analysis and go more in depth instead of constantly racing against the clock.

Same thing for Anna Lipniacka, a professor at Bergen University in Norway. Sure, she feels a bit sad, but just like Cyril, hopes it will give us time to think a bit more deeply on how to look into the data and develop new analysis techniques.

Mansoora Shamim agrees. She is a post-doc at University of Oregon and admits being moderately sad for the same reasons. She is happy to have more time to work on her analysis, searching for black holes. But she will miss the ambiance of the control room.

And so will I, even if it means more chances for greater discoveries later on. In the meantime, thanks to fresh snow outside, the champagne is cooling off as we plan to toast the LHC at the end of our shift.

Pauline Gagnon

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Hangout with CERN, anyone?

Tuesday, February 12th, 2013

I’m helping organize the ongoing Hangout with CERN series of events, and this Thursday I get to host. To make the event a success, I need your help! Interested? Read on…

Hangout with CERN happens each week at 17:00 CET, 11 AM EST, or whatever you want to call that time. It’s an informal Google+ hangout in which physicists, engineers, IT experts, and other folks from CERN connect to tell you about what we do here. In our latest format, we devote two weeks to each topic. The first week introduces the topic and lets you hear experts describe their work, along with a quiz and a few questions from the public. (We monitor comments on Twitter and YouTube the whole time.) The second week – which is the part I work on – is even more informal: we try to have a few guest members of the public, get to more questions, and so on.

Here’s last week’s video, entitled “LHC and the Grid – The world is our calculator,” which discusses the worldwide computing system we use to analyze all the data from the LHC:

Next week’s event on Google+ is here. We’ll be discussing the same topic, and we want to hear your questions about it. Do you have a question? Might you want to participate live in the hangout and ask your question directly? Let me know in the comments!

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Is science merely fiction?

Friday, February 8th, 2013

Hans Vaihinger (1852 – 1933) was a German philosopher who introduced the idea of “as if” into philosophy. His book, Die Philosophie des Als Ob (The Philosophy of ‘As If’), was published in 1911, but written more than thirty years earlier. He seems to have survived the publish or perish paradigm for thirty years.

In his book, Vaihinger argued that we can never know the true underlying reality of the world but only construct systems which we assume match the underlying reality. We proceed as if they were true.  A prime example is Newtonian mechanics. We know that the underlying assumptions are false—the fixed Euclidean geometry for example—but proceed as if they were true and use them to do calculations. The standard model of particle physics also falls into this category. We know that at some level it is false but we use it anyway since it is useful. Vaihinger himself used the example of electrons and protons as things not directly observed but assumed to exist. They are, in short, useful fictions.

Vaihinger’s approach is a good response to Ernst Mach’s (1838 – 1916) refusal to believe in atoms because they could not be seen.  In the end, Mach lost that fight but not without casualties.  His positivism had a negative effect on physics in many ways was a contributing factor in Ludwig Boltzmann’s (1844 – 1906) suicide.  The philosophy of ‘as if’ is the antithesis of positivism, which holds closely to observation and rejects things like atoms which cannot be directly seen. Even as late as the early twentieth century, some respectable physics journals insisted that atoms be referred to as mathematical fictions.  Vaihinger would say to proceed as if they were true and not worry about their actual existence. Indeed, calling them mathematical fictions is not far from the philosophy of ‘as if’.

The ideas of Vaihinger had precursors. Vaihinger drew on Jeremy Bentham’s (1748 – 1832) work  Theory of Fictions. Bentham was the founder of modern utilitarianism and a major influence on John Stuart Mill (1806 – 1873) among others.  ‘As if’ is very much a form of utilitarianism: If a concept is useful, use it.

The idea of ‘as if’ was further developed in what is known as factionalism. According to fictionalism, statements that appear to be descriptions of the world should be understood as cases of ‘make believe,’ or pretending to treat something as literally true (a ‘useful fiction’ or ‘as if’).  Possible worlds or concepts, regardless of whether they really exist or not, may be usefully discussed. In the extreme case, science is only a useful discussion of fictions; ie science is fiction.

The core problem goes back at least to Plato (424/423 BCE – 348/347 BCE) with the parable of the cave (from The Republic). There, he talks about prisoners who are chained in a cave and can only see the wall of the cave.  A fire behind them casts shadows on the wall and the prisoners perceive these shadows as reality since this is all they know. Plato then argues that philosophers are like a prisoner who is freed from the cave and comes to understand that the shadows on the wall are not reality at all. Unfortunately, Plato (and many philosophers after him) then goes off in the wrong direction. They take ideas in the mind (Plato’s ideals) as the true reality. Instead of studying reality, they study the ideals which are reflections of a reflection. While there is more to idealism than this, it is the chasing after a mirage or, rather, the image reflected in a mirage.

Science takes the other tack and says we may only be studying reflections on a wall or a mirage but let us do the best job we can of studying those reflections. What we see is indeed, at best, a pale reflection of reality. The colours we perceive are as much a property of our eyes as of any underlying reality. Even the number of dimensions we perceive may be wrong. String theory seems to have settled on eleven as the correct number of dimensions but that is still in doubt. Thus, science can be thought of as ‘as if’ or fictionalism.

But that is far too pessimistic, even for a cynic like me. The correct metaphor for science is the model. What we build in science are not fictions but models. Like fictions and ‘as if,’ these are not reality and should never be mistaken for such, but models are much more than fictions. They capture a definite aspect of reality and portray how the universe functions. So while we scientists may be studying reflections on a wall, let us do so with the confidence that we are learning real but limited knowledge of how the universe works.

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Heat: Adventures in the World's Fiery Places (Little Brown, 2013). If you haven't already fallen in love with the groundbreaking science that's taking place at RHIC, this book about all things hot is sure to ignite your passion.

Bill Streever, a biologist and best-selling author of Cold: Adventures in the World’s Frozen Places, has just published his second scientific survey, which takes place at the opposite end of the temperature spectrum. Heat: Adventures in the World’s Fiery Places features flames, firewalking, and notably, a journey into the heart of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.

I accompanied Streever for a full-day visit in July 2011 with physicist Barbara Jacak of Stony Brook University, then spokesperson of the PHENIX Collaboration at RHIC. The intrepid reporter (who’d already tagged along with woodland firefighters and walked across newly formed, still-hot volcanic lava—among other adventures described in the book) met with RHIC physicists at STAR and PHENIX, descended into the accelerator tunnel, and toured the refrigeration system that keeps RHIC’s magnets supercold. He also interviewed staff at the RHIC/ATLAS Computing Facility—who face the challenge of dissipating unwanted heat while accumulating and processing reams of RHIC data—as well as theorists and even climate scientists, all in a quest for understanding the ultrawarm.

The result is an enormously engaging, entertaining, and informative portrayal of heat in a wide range of settings, including the 7-trillion-degree “perfect” liquid quark-gluon plasma created at RHIC, and physicists’ pursuit of new knowledge about the fundamental forces and interactions of matter. But Streever’s book does more: It presents the compelling story of creating and measuring the world’s hottest temperature within the broader context of the Lab’s history, including its role as an induction center during both World Wars, and the breadth and depth of our current research—from atoms to energy and climate research, and even the Long Island Solar Farm.

“Brookhaven has become an IQ magnet, where smart people congregate to work on things that excite geniuses,” he writes.

Streever’s own passion for science comes across clearly throughout the book. But being at “the top of the thermometer” (the title of his final chapter, dedicated in part to describing RHIC) has its privileges. RHIC’s innermost beam pipes—at the hearts of its detectors, inside which head-on ion collisions create the highest temperature ever measured in a laboratory—have clearly left an impression:

“… I am forever enthralled by Brookhaven’s pipes. At the top of the thermometer, beyond any temperature that I could possibly imagine, those pipes explore conditions near the beginning of the universe … In my day-to-day life, bundled in a thick coat or standing before my woodstove or moving along a snow-covered trail, I find myself thinking of those pipes. And when I think of them, I remember that at the top of the thermometer lies matter with the audacity to behave as though it were absolutely cold, flowing like a perfect liquid…”

There’s more, a wonderful bit more that conveys the pure essence of science. But I don’t want to spoil it. Please read and share this book. The final word is awe.

The book is available for purchase through major online retailers and in stores.

-Karen McNulty Walsh, BNL Media & Communications Office

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A Change of Pace

Monday, February 4th, 2013

Some physicists and engineers from Purdue and DESY, and me, at the beamline we used to test new pixel designs

Every so often, a physicist needs a vacation from doing data analysis for the Higgs boson search. A working vacation, something that gets you a little closer to the actual detector you work on. So last week, I was at the DESY laboratory in Hamburg, Germany, helping a group of physicists and engineers study possible changes to the design of individual pixels in the CMS Pixel Detector. (I’ve written before about how a pixel detector works.) We were at DESY because they had an electron beam we could use, and we wanted to study how the new designs performed with actual particles passing through them. Of course, the new designs can’t be produced in large scale for a few years — but we do plan to run CMS for many, many years to come, and eventually we will need to upgrade and replace its pixel detector.

What do you actually do at a testbeam? You sit there as close to 24 hours a day as you can — in shifts, of course. You take data. You change which new design is in the beam, or you change the angle, or you change the conditions under which it’s running. Then you take more data. And you repeat for the entire week.

So do any of the new designs work better? We don’t know yet. It’s my job to install the software to analyze the data we took, and to help study the results, and I haven’t finished yet. And yes, even “working on the detector” involves analyzing data — so maybe it wasn’t so much of a vacation after all!

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