vrijdag 17 augustus 2012

Anthropic Water

Water, plain and simple water, is an intriguing substance. Its chemical formula is H2O. A water molecule is composed of one oxygen atom and two hydrogen atoms. A simple chemical structure indeed. But the spatial structure of water is not as simple as we might imagine. The most ‘straightforward’ structure is the most symmetrical one, with the two hydrogen atoms opposite of each other and the oxygen atom in the middle, the three atoms nicely on a straight line. Like the three atoms in carbon dioxide, CO2, for example. No, in water the three atoms form a triangle. The angle at the vertex where the oxygen sits is 104.5 degrees. And this is of vital importance. Literally.

It makes water a polar molecule, with the negative charge (the electrons) closer to the oxygen than to the hydrogen. Its bent structure and the charge distribution determine the properties of water as a solvent. They also make water a liquid at standard temperature and pressure, which is quite exceptional for such a light molecule. (Even H2S, which has a similar structure but a smaller dipole moment, is a gas, even if it is heavier than water.) Without water and its properties, largely determined by its bent shape, there would be no life.

The structure of water can be understood by describing its electron orbits as determined by quantum mechanics. The radii of these orbits (the distance from the relatively heavy and immobile oxygen and hydrogen nuclei) and the velocity of the electrons are such that their product is of the order of one (in so called ‘natural units’). Through the ‘uncertainty relations’ we know that in this case we enter the ‘quantum domain’ and quantum mechanics is the theory we need to describe the physical reality.

It would go too far to call quantum mechanics a straightforward theory. It is quite an amazing theory, but once you have accepted it, its use is straightforward. This does not mean it is easy: water consists of three nuclei and ten electrons and even if you simplify the nuclei to pointlike particles it is impossible, for now and always, to exactly solve the quantum mechanical equation (the Schrödinger equation) for this many body system. It is, however, possible to make acceptable approximations and to resort to the use of computers and the result is that the structure of water, vital for life, follows compellingly from quantum mechanics, a perhaps counter-intuitive but profound construct of the human mind and an accurate description of the physical world.

All this was known when I went to university in 1967 and it was exciting, very exciting, to ‘rediscover’ this during the initial years of university training. There was more to be discovered and personally I was (and I am) attracted by the challenges of elementary particle physics. In recent years a connection between particle physics and another field really catching the imagination, cosmology, has been made. In the beginning there was particle physics... Our understanding of the beginning of the universe, of the very initial phases of the Big Bang, is hampered by our lack of understanding of gravity. It must have played an important role at the quantum level, initially, when the energies involved were very high. A lack of understanding of quantum-gravity does not mean a lack of candidate theories for including gravity in the description of the elementary world. Based on the principles of the theories of relativity and quantum mechanics (a ‘minimal’ condition for candidate theories) and with the notion of ‘elementary particle’ replaced by ‘elementary string’ in fact a practically infinite number of theories can be chosen from. Even if we assume, perhaps somewhat naively, that the right ‘theory of everything’ has been found in principle, no one is capable of singling it out from the huge number of possible theories.

I will now tread on slippery ground. Cosmologists have invoked the ‘anthropic principle’ to explain, or rather to be absolved of explaining why the universe and the laws that govern it are as they are. According to the ‘anthropic principle’, the universe we observe and the laws we find must be consistent with ‘us’, with conscious life – if not, we would not be there to make observations and find explanations in the first place. So only universes compatible with conscious life (is this well-defined?) can ‘exist’. The ‘anthropic principle’ may be interesting philosophically, but, as far as I can see, it is not useful to help us find the right ‘theory of everything’ amidst the huge number of possible theories. Neither is it able to explain the structure of water, but quantum mechanics is, and was so long before anyone felt the need for an anthropic principle!

Jos Engelen
August 17, 2012

maandag 13 augustus 2012

Nature, an open book?

Open Access (OA) to scientific publications is generally considered to be the desirable standard. In particular publications resulting from publicly funded research should not be obstructed by a (pay)wall and should be accessible easily by researchers, cross-disciplinary, by researchers in the private sector, including SME’s, and by the general public. Sharing scientific information widely is clearly beneficial for science itself, for facilitating applications and for involving and informing the public.

The transition to OA publishing is rather straightforward in principle but the practical implementation requires certain obstacles to be overcome. Publishing is a professional activity concerned with standards of quality control and editorial policies that have led to a body of scientific journals that has an important and recognized role in scholarly communication. This, or such a body of qualified scientific journals should be preserved under the transition to OA. Ideally the important publishers should stay on board by adapting their business models.

The highest standard of excellence is implied when reference is made to articles published in ‘Nature or Science’.  Or in a few other similarly highly ranked journals. Nature and Science are not OA journals, but they have a very strong position and researchers are keen to get their results published in them. So, in a sense, ‘Nature and Science’ are an obstacle to reaching the desired OA standard.

Let us look in somewhat more detail at Nature, as an example. Let me stress from the outset: my purpose is not to question the high quality that is attributed to Nature, my purpose is to understand whether it is possible to make it part of the ‘OA world’.

Nature’s Editor in Chief repeated recently, during a panel discussion at the European Science Open Forum conference in Dublin, that Nature has adhered to the same editorial policy ever since its foundation in 1869. Namely: in order to qualify for acceptance by Nature an article should report on new results, present ‘a first’, not reported on before. I do not find this very helpful, because every research article published in the scientific literature should satisfy such criteria. So what makes Nature so unique? What has changed since 1869 is the intensity and diversity of scientific research: the volume of excellent research has increased by orders of magnitude. The role of research has also changed: from a rather esoteric activity of a rather small elite to a societal necessity for competitiveness and sustainability. The number of manuscripts submitted to Nature for publication has increased enormously during its existence and the fraction of manuscripts actually accepted for publication has plummeted dramatically. This fact alone has contributed considerably to Nature’s almost mythical status. It is not Nature’s fault. Nature employs a staff of full time, professional editors, who, helped by reviewers (scientists, ‘peers’ of the authors submitting articles) do the utmost to select the best manuscripts for publication. But how do you define ‘the best’? There is a danger here of getting caught in a tautological illusion. To find clues I invite you to have a look at a number of recent issues of Nature. A first observation is that only about half of the published pages is dedicated to original scientific results (a small fraction of that half to fully fledged articles, the rest to ‘letters’). The remaining half is filled with news, views, advertisements, announcements, recruitment pages. I now ask myself again: how are ‘the best’ scientific articles defined. ‘The best’ for attracting the right audience for ‘the rest’?

Let us return to the scientific articles, 50% of Nature’s business. It remains a problem that the overly prolific submission of manuscripts to Nature puts a very heavy burden on the editorial staff. It comes at a cost that makes a transition to an Open Access business model for Nature prohibitive. At least, that is what Nature says. But why would that be so? The relatively few articles that are published in Nature can easily be paid for once the ‘author pays’ (means: research funding organization pays) model would be generally accepted. It is perfectly possible to maintain the highest scientific quality standards whilst adopting Open Access publishing as the new standard. This is true in general, this is true for Nature. It requires a critical attitude of the scientists, of the research funders and of those ‘measuring’ the quality of research and its practitioners. Nature should follow the scientific community, not the other way around.

(This 'blog' appeared, translated in Dutch and slightly edited, in 'NRC Handelsblad' of July 31, 2012)

Jos Engelen
July 28, 2012

maandag 9 juli 2012

Brown Sugar

On the 4th of July 2012 the world knew: the Higgs-particle had been discovered by two experiments, ATLAS and CMS, at the Large Hadron Collider of the European Laboratory for Particle Physics near Geneva. Two wonderful seminars at CERN summarized many years of innovative experimentation and data analysis, culminating in the highlight for now: the observation of the Higgs boson through its decay into two photons. A peak is observed in the two photon spectrum, the evidence being corroborated by other for the time being somewhat less populated channels.

There was relief and excitement, euphoria even, among those who had been involved in this long and risky project. Understandably so: the stakes had been very high, many had invested more than a decade and some more than two, of their scientific careers in this endeavour: the search for ‘the Higgs’. But the excitement was by no means limited to the ‘small’ circle of insiders: through the interest of the media in this news an audience of many, many millions was reached. Heart-warming for all the physicists and engineers who had been one way or another involved in this adventure, but also an opportunity for explaining and sharing the excitement with ‘the public’. ‘The Higgs’ is public property, the research has been entirely publicly funded by the Member States of CERN, by the associate members, by other bilateral agreements and by the various national research organisations (in the Netherlands this is NWO).

What ìs the Higgs particle? Why is this discovery so important? What is the use of it? I would love to address these questions and I would do so along the lines I have done many times before. I will not do that here. I would also love to answer questions like: how was the discovery made? Why was it so hard, why did it take so long? I will not do that here either. I use this space to challenge the ‘experts (without credentials)’ to properly think about answers to these questions before making statements and appearances in the mass media. If you are not passionate about the subject, either explain that or stay away from it. If you are not knowledgeable: stay away from it.

In a Dutch TV show the Higgs field was modelled as brown sugar. ‘Ah brown sugar how come you taste so good’.

Jos Engelen
July 9, 2012

vrijdag 15 juni 2012

Science and Significance

Science can only flourish in freedom: scientists should be allowed to choose their subjects freely, they should be trusted to find the most challenging frontiers of knowledge to be pushed back. Scientific breakthroughs cannot be forced, cannot be achieved ‘on command’. One counter-example sometimes quoted is the development of the atomic bomb. It is true that forces had to be joined at an unprecedented level in order to collect and develop all the knowledge and technology needed for such a gigantic project. But the basic knowledge had been obtained in research purely driven by curiosity, by the desire to push back frontiers. I refer to the discovery of radioactivity, of the atomic nucleus, of fission. Based on the understanding of neutron induced fission the idea of a chain reaction was born. This fundamental knowledge was the basis for the Manhattan project. On a more peaceful note: joining forces on a global level to achieve controlled fusion is a challenge that has been taken up by the ITER project. Also here most of the underlying physics is known, but the technological challenges for achieving energy production on a ‘routine’ basis are still enormous.

Scientific freedom does not mean that funding for scientific projects comes easy. Scientists apply for funding of their favorite projects and only the most excellent of these win grants. It may sound straightforward, but it is at the heart of all successful scientific research systems worldwide. In May 2012 a large gathering of national research organisations (‘councils’)  took place in Washington, hosted by the National Science Foundation, NSF: the North American research funding organisation. During this meeting, where 40 nations, including the Netherlands were represented the Global Research Council was founded. In a careful first step as a ‘virtual organisation’, i.e. an organisation free of overhead (‘bureaucracy’) without a ‘boss’ and with collective ownership. As a first topic of common interest the GRC discussed  ‘merit review’ or ‘peer review’  as the basis for selecting the best research proposals in the granting process. It may not sound very exciting but it is very important to share common values and principles as the basis for (international) cooperation. Because scientific research is, increasingly, a global endeavor. And it is fantastic to see how science is able to transcend political differences. Nations that still have some distance to go before a truly democratic political system is in place, adhere to ‘merit review’ – intrinsically democratic -  as the basis for their national research funding system. Science brings nations together.

Science brings those nations together that have a thriving scientific community. The Netherlands have such a community, strong and excellent but threatened by undernourishment. To the vision of the necessity of a well organised and properly funded scientific  community for addressing scientifically, economically and societally relevant topics I would like to add the vision that such a community adds to our international standing. And to our national pride. A country without significant science will cease to exist.

The Global Research Council will convene again in May 2013, in Berlin. The topics to be addressed, the ‘common values’ to be established are ‘scientific integrity’ and Open Access (to scientific publications and data).  This summit will be commonly organised by the German research council (DFG) and the Brazilian research council (CNPq).

The Netherlands are not automatically invited to the G20, the economic summit, but they are a natural guest and participant in ‘scientific summits’  like the GRC. I will make every effort to keep it that way. What the Euro has a hard time to do, science can achieve easily: science brings nations together!

Jos Engelen
June 15, 2012

zondag 29 april 2012

On quarks, viruses and melting ice.

The introduction of ‘quarks’ as fundamental constituents of matter marked a revolutionary step forward in our understanding of the physical world. As revolutionary as the introduction of atoms, about five decades earlier.

Quarks and electrons and the forces between them: that is all that is needed to build up the material world.

As an example let us look at the proton, the simplest of all atomic nuclei, the nucleus of the hydrogen atom. It consists of three quarks ‘swimming’ in the force field that binds them together. As in taxonomy we label the quarks with (trivial) names for ease of description. Two of the three quarks in the proton are ‘u’ quarks and one is a ‘d’ quark. So a proton can be labeled ‘uud’. Quarks have a property that initially was impeding their acceptance as real, physical objects: their electrical charge is not equal to an integer multiple of the electron charge, the fundamental charge e. The u quark has positive charge 2/3 |e| and the d quark negative charge -1/3 |e|. A neutron is then ‘udd’. A third quark was required to ‘build’ the particles that were known at the time of the construction of the quark model: the s quark, with the same charge as the d quark. Using all three quark species for making combinations of three quarks it is possible to make ten combinations that form the so called baryon decuplet – baryon is the generic name for ‘proton like particles’, consisting of three quarks.

A spectacular confirmation of this quark picture was the discovery of the Ω- (Omega-minus) particle (in 1964): the ‘sss’ state that completes the baryon decuplet.

‘Baryon spectroscopy’ has revealed the existence of many hundreds of three quark states, including ‘excitations’ of the ground states. Although the underlying quark picture is very simple, the reality built on it, is very complex. What purpose this complexity serves is unknown. Perhaps this is what Steven Weinberg meant when he wrote: The more the universe seems comprehensible, the more it seems pointless.

The story does not end here. Three more quark species were discovered, the ‘c’, ‘b’ and ‘t’ quarks: charm, beauty and truth, or, somewhat more down to earth: charm, bottom and top. There are six quarks species, or, as the more commonly used nomenclature says: six quark flavors. (Why six? Nobody knows, but a lot can be said about it. I will not do that here.) So we can now build baryons by combinations of three quarks where each quark has one of six flavors. The ‘decuplet’ referred to above, thereby turns into a ’56-plet’.  (Please verify!).

The CMS collaboration at the Large Hadron Collider published this week the first ever detection of an excited state of the three quark combination ‘usb’. This particle is called ‘xi-star sub b’. It belongs to the ’56-plet’ I suspect. It is the good old ‘decuplet’ xi-star (‘uss’) with one ‘s’ quark replaced by a ‘b’ quark. For CMS this result is a by-product: the real aim is to find the Higgs boson and other ‘new physics’. But the measurement of this new baryon is an achievement that would have been deemed impossible a few years ago – it is possible thanks to superbly functioning state of the art technology of both the CMS setup and the LHC accelerator. Frontiers of technology were pushed back to achieve this result and new knowledge was added in a wonderful contribution to scientific culture. The article is freely available on arXiv.org prior to publication in an ‘official’ journal. Enjoy!

There was more news this week. The Dutch scientist Fouchier and his group have created a mutation of the virus (H5N1) causing bird flu that can be transferred to humans. This finding has been publicized by the scientists months ago, but they were not allowed to publish, because of the possible abuse of their results by terrorists. Good sense has finally prevailed and the arguments in favor of publication put forward by the authors have won (increased knowledge of the influenza virus, the subsequent development of vaccines, etc.) The publication is yet to appear and will, I understand, be published in Science. The main author, Fouchier, is relieved that finally the work can be published, and rightly so. He is quoted to have said: ‘together with the editors of Science we will now write the text in such a way that it is understandable for a broad audience, also in view of all the commotion that has surrounded our work’. Bravo! But... Science is not accessible to the general public. It is not Open Access, but published behind a pay-wall. I urge Fouchier and his co-workers to publish the article in a place that is freely accessible for everybody interested, as soon as it is written. I am almost sure that Science will not allow this...

Yet more news this week. Nature published an article co-authored by a leading Dutch scientist, Van den Broeke, entitled: ‘Antarctic ice sheet loss driven by basal melting of ice shelves’. A dramatic thinning is observed of the floating Antarctic ice sheet by warming up ‘from below’ by streams of warmed up seawater. If I understood correctly. The result was highlighted on Dutch national television and possible dramatic consequences for sea level rise were explicitly mentioned. This article has to appear in the public domain. The work has been publicly funded and it is not reasonable that the public should pay 32 dollars to Nature to be allowed to familiarize itself with these important findings!

All rich scientific results referred to above should be freely available for all of us – general public, politicians and scientists alike!

Jos Engelen
April 29, 2012

zondag 8 april 2012


An idea can be captured in a formula.

This has been successfully demonstrated in science. The idea comes first, it marks the most important moment in scientific research: the moment of creativity.

A famous example of such an idea is the one that led Einstein to the theory of relativity.

The idea is that it is impossible to measure ‘absolute motion’.

Close your eyes and imagine yourself drifting through empty space. There is nothing but you. According to Einstein’s idea it is impossible for you to know whether you are in motion or at rest. You were clever enough to bring a flashlight. You send flash of light into the direction ahead of you. The light will travel with a speed that equals the speed of light with respect to the flashlight plus the speed of the flashlight itself - your speed. So by measuring the speed of the light your flashlight emitted you can then determine whether you are in motion or not. No, Einstein says. He holds on to his idea and asserts: the speed of light is constant and independent of the state of motion of the source that emits it and independent of the state of motion of the observer that detects it. He extended this idea with a further assertion, somewhat more subtle. If ‘absolute motion’ is a meaningless concept, the state of motion of a particular observer, say a physicist conducting experiments, is irrelevant for the laws of nature this observer discovers. In other words: the laws of nature are invariant under transformations of one frame of reference to another. These two ideas have far reaching consequences. The most dramatic is that ‘time’ is not absolute, but relative. Relative to the state of motion of the observer with respect to the clock that is used for clocking the time. ‘Moving clocks run slower’ is the brief summary of this result of Einstein’s theory of relativity.

In a formula: t’=t/sqrt(1-v*v/c*c)

Imagine an elementary particle, like a muon (abundantly present in cosmic rays), that is unstable and has a characteristic natural lifetime. (Two millionth of a second in this particular case). If we observe this particle flashing by with a speed v then we see it decay after t’ seconds according to this formula. c is the speed of light, 300 000 km/sec. For speeds v approaching the speed of light, to 90 or even 99 percent or more, t’ can become much bigger than t and the particle can travel much further than one would expect according to its natural lifetime t. This is exactly what is observed in experiments. There is something else the formula tells us: v can never become bigger than c, no object can travel faster than the speed of light. In that case we would have to take the square root of a negative number and the formula becomes meaningless.

Physics stops at the speed of light.

When the OPERA experiment, employing a neutrino beam generated at CERN and a detector located at the Gran Sasso laboratory in Italy, announced the observation of neutrino’s travelling faster than light the theory of relativity was challenged. Before publicizing such an earthshaking result you better be very sure that your measurement is right. The measurement was wrong. Who should take responsibility for publicizing this erroneous measurement prematurely? The ‘spokesperson’ of the Opera team, Antonio Ereditato, has resigned over it. So be it. He took his responsibility even if he is no more guilty than many of his senior colleagues; that is the way it goes.

The publicity on superluminal neutrinos and the subsequent withdrawal of this claim has done considerable harm to CERN’s reputation as a center of excellence. Those responsible for its governance and management should speak up. They should explain themselves.

Jos Engelen

maandag 26 maart 2012

Meritocratic or mediocre?

ATLAS and CMS are the names given to two large experimental setups at the Large Hadron Collider (LHC), the world’s biggest accelerator for high energy physics (elementary particle physics) at the European CERN laboratory near Geneva. The setups are huge and heavy – 10,000 tons – and technologically very advanced and innovative: from superconducting magnets to highly integrated ‘deep sub-micron’ electronics. The detectors deal with tens of proton-proton collisions every 50 nanoseconds, producing thousands of particles at this high rate. In order words: the proton bunches in the beams meet and collide at the center of these detectors two hundred million times per second. Powerful and smartly programmed computer systems filter out about one hundred of the most interesting collision ‘events’ per second for recording them on a mass storage medium for further ‘off line’ analysis. In total the experiments record approximately 15 million gigabytes per year. The worldwide LHC computing grid – a distributed infrastructure – was developed for storing and analyzing these data.

The teams of scientists involved in each of these experiments (ATLAS, CMS) number two and a half, maybe three thousand persons. The period over which ATLAS/CMS were designed, constructed, built, commissioned up to ‘data taking’ and data analysis (‘physics’) is about 15 years, longer for the hand full of pioneers involved from the very early days of audacious planning. Audacious because they had to plan for technological advances that were by no means sure to happen. They had to work hard to make them happen!

ATLAS/CMS fully live up to the expectations. They collect their data very efficiently from the collisions provided prolifically by the Large Hadron Collider, also working wonderfully well. Prolific is also the production of scientific papers by ATLAS/CMS. I read them with great interest. It is exciting, breathtaking, to follow the hunt for the Higgs boson (its ‘hiding place’ has been localized quite accurately; before the end of 2012 we will have captured it!).

But there is one thing that disturbs me about the scientific publications of ATLAS/CMS. And that is the author list, in particular the length of it. You can find all 3000 authors on every paper. That is ridiculous. It brings high energy physics into a cultural crisis. It prevents the young and brilliant to manifest themselves through a distinctive publication record. It allows mediocrity to creep in.

I call on ATLAS/CMS to do something about this. In these days of web-based publishing it should be technically easy to distinguish, say, five categories of authors. 1: those who really did the innovative analysis published in a particular paper; 2: those, usually more senior, who were closely involved in inspiring, supervising, checking, improving the work; 3: those who made distinctive, but more generic contributions to the technical infrastructure of particular importance for the paper under consideration; 4: the present leadership of the collaboration; 5: the long retired who once made a contribution to the collaboration.

I know, my categories are not perfect, but they are a start. If high energy physics is to survive it has to very quickly re-emphasize scientific excellence again as the most important criterion for leadership.

Jos Engelen, March 26, 2012

woensdag 21 maart 2012

Het Anthropoceen

Op vrijdag 16 maart staat op de publieke website van de Volkskrant een artikel dat de aandacht vestigt op nieuwe wetenschappelijke inzichten die vragen om een totaal nieuw milieubeleid. Het staat er zo: ‘Wetenschappers van de Vrije Universiteit Amsterdam pleiten met een groep toonaangevende wetenschappers in het tijdschrift Science voor een dringende fundamentele verandering van het wereldwijde milieubeleid. Zo'n verandering is nodig om het toenemende aantal milieurampen, zoals overstromingen, voedsel- en waterschaarste en afname van biodiversiteit, het hoofd te kunnen bieden.’ Dat liegt er niet om!

Zo’n artikel moet onmiddellijk onder de aandacht gebracht worden van de politici die het beleid bepalen. Ik zoek het artikel op, op de website van Science. En ik weet al wat er vervolgens gebeurt. Ik mag er niet bij. Het artikel zit achter slot en grendel en alleen abonnees of betalende bezoekers van de website hebben toegang. Welke meerwaarde heeft de redactie van Science opgeleverd voor dit uiterst belangrijke artikel, zodat Science Magazine het eigendom ervan mag opeisen? Geen enkele. Het omgekeerde is het geval: Sciende ontleent gewicht aan de artikelen die er in staan. En de auteurs van die artikelen weer gezag aan het feit dat ze in Science publiceren. Een gesloten systeem, bevredigend voor degenen binnen het systeem. Maar het deugt niet: het staat de disseminatie van wetenschappelijke inzichten, van kennis en daarmee de ontwikkeling van de wetenschap zelf in de weg. Ik roep F. Biermann van de Vrije Universiteit en mede-auteurs op hun artikel ‘Navigating the Anthropocene: Improving Earth System Governance’ publiek toegankelijk te maken, al was het maar door het gewoon op hun website te zetten. Of mag dat niet van Science? Van mij moet het!

Jos Engelen
21 maart 2012
(ook verschenen als ingezonden brief in de Volkskrant van 21 maart)

woensdag 14 maart 2012

Zonnepanelen, maar dan anders

De bundelpijp van een ‘opslagring’ als de LHC versneller van CERN moet aan hoge vacuümeisen voldoen. De rondcirkelende protonbundels blijven ‘opgeslagen’ gedurende pakweg 10 uur en draaien elke seconde zo’n 11.000 rondjes van 27 km. De residuele gasdruk moet dus erg laag zijn (‘beter dan op de maan’), anders zou de protonbundel door botsingen met de gasmoleculen snel verloren gaan.

De bundelpijp van de LHC loopt voor een groot deel van de omtrek door supergeleidende
magneten die tot lager dan 2700 onder nul worden afgekoeld. Daar is het relatief
eenvoudig om een goed vacuüm te handhaven: restgas vriest eenvoudigweg vast aan de wand. Maar er zijn ook lange, rechte stukken rond de experimentele opstellingen waar de bundelpijp niet door magneten omgeven en ‘warm’ is. Om daar goede vacuümcondities
te handhaven zijn extra maatregelen nodig. En die extra maatregelen zijn mogelijk dank
zij een technologische innovatie. De bundelpijp wordt van de binnenkant bedekt met een
dun laagje materiaal, een ‘coating’ van TiZrV (titanium, zirconium, vanadium). Na
verhitting tot 1800   (eenmalig) wordt dit materiaal geactiveerd als ‘getter’: een molecuul dat er
tegenaan botst wordt geadsorbeerd. Deze ‘coating’ verbetert en handhaaft het vacuüm op deze manier aanzienlijk. Voor de LHC niet alleen aanzienlijk maar ook essentieel: de in totaal 5 km lange ‘warme’ bundelpijp zou anders niet op het gewenste vacuüm te brengen zijn. Toen de LHC ontworpen werd waren ‘getter’ materialen al bekend, maar twee wezenlijke innovaties maakten toepassing ervan in de warme bundelpijp mogelijk. Het materiaal (TiZrV) kon opgebracht worden dank zij ‘sputter’ technieken die eerder en voor andere toepassingen (supergeleidende radio-frequente trilholtes voor de LEP-versneller) ontwikkeld waren en, de tweede innovatie, de nieuw gevonden coating hoefde maar tot 1800 en niet tot de gebruikelijke 6000 verhit te worden.

De onderzoeker die deze vondsten deed is Cristoforo Benvenuti. Hij bedacht ook een toepassing buiten de versnellertechniek. Een even eenvoudige als adembenemende. Vacuüm is een ideale isolator. Dus hij stelde zich een doorzichtig doosje voor, vacuüm, met daarin ‘zwevend’ een zwart plaatje. Straling (licht) die op dat plaatje invalt zal het verwarmen, omdat de straling door het zwarte plaatje geabsorbeerd wordt. (Dat is de definitie van zwart...) En vervolgens kan het plaatje die warmte niet afgeven, omdat het zich in vacuüm bevindt. Het wordt dus steeds warmer. Het wordt heet. Het vacuüm in de doosjes wordt gehandhaafd dank zij de fameuze nieuwe coating. De ‘levensduur’ ervan is 25 jaar!

Met deze technologie heeft een Spaans bedrijf nu een grote zonnepaneel-installatie gebouwd die geplaatst wordt op het dak van de gebouwen van het vliegveld van Genève, groot genoeg om dit te verwarmen in de winter en te koelen in de zomer. Een prachtige ‘demonstrator’. Een mooi voorbeeld van onverwachte ‘transfer’  van technologie die werd ontwikkeld ten behoeve van fundamenteel onderzoek naar een toepassing met potentieel grote economische en maatschappelijke waarde. Een toepassing die naar alle waarschijnlijkheid nooit was gevonden zonder de nieuwsgierigheid naar het gedrag van elementaire deeltjes...

Jos Engelen
14 maart 2012

vrijdag 2 maart 2012


Electrons, the ubiquitous constituents of matter, are very interesting objects of study. The electron was the first elementary particle to be discovered (by J.J. Thomson in 1897)  and today it belongs to the rather exclusive group of the fundamental particles of the Standard Model.

In 1927 Paul Dirac discovered the equation that describes the propagation (in space and time) of electrons. This was a great achievement: his equation incorporated Einstein’s theory of relativity and the principles of quantum mechanics (Bohr, Heisenberg, Schrödinger) at the same time. The Dirac equation had a very remarkable feature. It predicted, in fact it required, that if electrons exist, which is obviously the case, also the anti-particle of the electron should exist, but no such particle was known. Initially this was a problem for Dirac but when the positron was discovered (Anderson, 1933) this problem was solved.

The electron and the positron are distinctly different particles as they have opposite charge. Neutrinos are fundamental particles in many respects similar to electrons and positrons, with one distinct difference: they carry no electrical charge, they are neutral. And this opens the possibility that neutrinos and their
anti-particles, the anti-neutrino’s, are in fact the same particles. This possibility was suggested by Majorana (in a publication of 1937).  In somewhat technical terms, Majorana found a representation of the Dirac equation with real (as opposed to complex) wave functions as a solution. For a particle described by a real wave function the distinction between particle and anti-particle vanishes.

Both electrons and neutrinos carry a quantity called ‘spin’, angular momentum. They carry a spin of ½ unit. Such particles are called fermions. (All fundamental constituents of matter are fermions.) Their quantum-mechanical properties are very different from particles with ‘integer’ spin (bosons). This difference is expressed by the Pauli exclusion principle, it leads for example to electron orbits in atoms and explains the structure and stability of matter.

Whether neutrinos are ‘Dirac particles’ or ‘Majorana particles’ is a valid physics question that has not been answered to date. It is experimentally very difficult to answer this question, but experiments are ongoing. If neutrinos are Majorana particles this has profound consequences for our understanding of the nature of fundamental particles as encoded in the Standard Model.

Whether Majorana particles exist or not in nature remains an open question. Apart from neutrinos, so called neutralinos are candidates as well. Neutralinos appear in extensions of the Standard Model (invoking ‘super symmetry’ between fermions and bosons) but whether Supersymmetry is realized in nature is not at all sure. This is one of the questions the Large Hadron Collider at CERN is trying to answer.

Nature News of February 28, 2012 announces:  Quest for quirky quantum particles may have struck gold’ , Evidence for elusive Majorana fermions raises possibilities for quantum computers. The scientific quality of this news article is rather poor. Although it is published by Nature. But it is a news article. Sensational, that sells. The achievement it describes is impressive, however. Leo Kouwenhoven and his group of Delft University have created a setup to demonstrate, for the first time, the existence of quantum states in a nano-device that are mathematically equivalent to Majorana ferminos as described above. Moreover such devices may be used as ‘quantum bits’ of futuristic quantum computers. Leo Kouwenhoven has produced a scientific result that ranks in a rare category: that of breakthroughs. We will hear more from him!

The question whether neutrinos are Majorana particles or Dirac particles continues to need an answer. Elementary particle physicists will have to continue their experiments to find out. The question whether neutralinos are realized in nature: high energy physics experiments will have to tell.

Meanwhile I will find out more about Majorana states in condensed matter and as soon as Kouwenhoven’s results are available in the Open Access literature I will read more about them with great interest!

Jos Engelen
March 2, 2012

zondag 26 februari 2012

Vallende neutrino's

Afgelopen week publiceerde CERN het persbericht dat er een losse kabel en een niet goed functionerend elektronisch circuit waren gevonden in de apparatuur van het OPERA experiment. OPERA is opgesteld in Gran Sasso en vangt neutrino’s op die op CERN, 730 km ‘stroomopwaarts’ worden weggeschoten. Een aantal maanden geleden publiceerde OPERA een voorlopig resultaat dat de wereld op zijn kop zette: de neutrino’s legden de weg van CERN naar Gran Sasso af met een snelheid groter dan die van het licht. ‘Meten is weten’ zei Kamerlingh Onnes ooit. Het is een waardig adagium voor de experimentele natuurkunde. Maar ‘meten’ is pas ‘weten’ als de meting correct is. Toen Sam Ting en zijn groep in 1974, toevallig het J/psi deeltje vonden en daarmee een nieuwe quark (‘charm’ of ‘tover’) publiceerden ze dat pas na een hele serie, ook gepubliceerde, tests om zich ervan te overtuigen dat het waargenomen signaal geen instrumentele artefact was.

Als er een wereld is aan gene zijde van de lichtsnelheid dan moet er voor die wereld een nieuwe natuurkunde worden uitgevonden. En moet er een verband tussen de veilige wereld die Einstein voor ons ontdekt heeft en die nieuwe wereld zijn. Pas als de lichtsnelheid niet de ultieme snelheid in de natuur blijkt te zijn is er een dwingende reden naar die nieuwe natuurkunde op zoek te gaan. OPERA heeft daarom een grote verantwoordelijkheid op zich geladen door een voorlopig resultaat te publiceren dat nu prematuur lijkt te zijn. Ondanks het feit dat er open is gecommuniceerd en er voortdurend gewaarschuwd is dat er onafhankelijke bevestiging van de meting nodig was, overheerst toch het beeld van ‘knulligheid’. Vanwaar de haast? Het achtuurjournaal van de NOS meldde dat CERN een eerder aangekondigd spectaculair resultaat had ingetrokken. Daarbij werden beelden getoond van de Large Hadron Collider en de experimenten die op zoek zijn naar het Higgs boson! Het neutrino-experiment lijkt daardoor de reputatie te beschadigen van de top-experimentatoren die met grote competentie en creativiteit het net om het Higgs-boson proberen te sluiten. Ook hier heeft CERN veel te vroeg de publiciteit gezocht door speculaties te voeden over wat er eventueel al in het net zit. Komend jaar wordt het net opgehaald. En dan zullen we het weten. Want meten is weten.

Jos Engelen
26 februari 2012

maandag 23 januari 2012

Fraude in de wetenschap

Het artikel ‘Op zoek naar zonden’ in de NRC van 14 januari presenteert een statistische inventarisatie van wetenschappelijke misstappen door in Nederland werkzame wetenschappers. Het artikel is gebaseerd op de journalistieke methode. Noodzakelijk anekdotisch, maar feitelijk correct. Anekdotisch zijn ook de commentaren van wetenschappers en bestuurders die in het artikel aan het woord komen. In aanvulling op die commentaren wil ik hier mijn rotsvaste vertrouwen in de kracht van de wetenschap zelf uitspreken: door geknoei tot stand gekomen ‘resultaten’ zullen nooit en te nimmer standhouden. Om misverstanden te voorkomen: ik bagatelliseer het geknoei niet en ik verdedig de knoeiers niet. Maar dat we met zijn allen, misleid door knoeiers ten prooi zouden vallen aan pseudo-wetenschap: het kan niet, letterlijk niet.

Wetenschap gaat om het vinden van feiten en verbanden, het presenteren van vernieuwende inzichten; het trekken van conclusies gebaseerd op de wetenschappelijke methode. Objectiviteit, verifieerbaarheid en reproduceerbaarheid zijn wezenlijke kenmerken van die methode. Het verzinnen van data, bijvoorbeeld, kan daarom niet. Letterlijk niet.

In dezelfde krant van 14 januari staat een recensie van ‘Ik was altijd heel slecht in wiskunde’, een boek van Jeanine Daens en Ionica Smeets. Daarin wordt verteld over het bewijs van het vermoeden van Kepler. Het vermoeden beschrijft de meest efficiënte wijze om bollen (‘sinaasappelen’) te stapelen. Hoe stapel je de sinaasappelen zo dat de ruimte zo efficiënt mogelijk benut wordt? Het ‘vermoeden’ is intuïtief heel aannemelijk, het bewijs werd pas eeuwen later geleverd na een enorme inspanning. En de onafhankelijke verificatie van het bewijs vergde weer een enorme inspanning. Dit is voor mij een prachtige illustratie van hoe wetenschap werkt. Van creatief idee, via een briljant en in elk geval degelijk onderzoek, via onafhankelijke verificatie (‘reproduceerbaarheid’) tot een resultaat. Het is niet altijd zo ‘gemakkelijk’ als in de wiskunde, maar de wetenschappelijke methode is generiek. Het begrijpen van de opwarming van de aarde, het wetenschappelijk onderzoek naar duurzame energievoorziening, naar het wezen van de zwaartekracht of het bestaan van het Higgs boson, etc.: het is niet af, er zijn debatten mogelijk over de tussenstand, verhitte debatten; maar uiteindelijk staat de wetenschappelijke methode garant voor het vinden van de objectieve waarheid en niet voor het promoten van een opvatting en al helemaal niet voor frauduleuze misleiding.

Jos Engelen
23 januari 2012