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Sporting knowledge

“Skateboarders know some righteous physics, dude.”

That lead sentence of an article in Science News a few months ago summarized an experimental result by the Arizona State University psychologist Michael McBeath. McBeath and collaborators had asked subjects to say which inclined path a rolling ball would complete faster: a shorter one with a constant slope, or a longer one with two steep slopes separated by a flat section. Most subjects guessed the shorter, gentler path. Skateboarders, however, were more likely to say, correctly, that the ball would complete the longer path with steeper sections faster. The suggestion of the Science News article was that the skateboarders thereby knew physics.

I would say the remark is light-hearted – except that I regularly encounter similar comments when reading about athletes, dancers and performers. I once read a blog by an athletics coach that said “many of us already know physics but don’t know that we know physics”, and to confirm this cited examples involving levers and vectors. A gymnast who once tried to instruct me in trapeze moves (in vain, for I’m not much of an athlete) meaning to be encouraging rather than provocative, said “You know it already – it’s just physics!”

Such remarks are often protected by implicit or explicit quotation marks – athletes “know” the laws of physics – to inoculate against obsessive literalists like me by suggesting that what is involved is not really knowing. So why do I still find that maddening?

Bodily coping

Athletes are certainly movement experts. Anyone competing in basketball, football, javelin, shot-put, archery, pole-vault or tennis will seek to send themselves or various objects into carefully anticipated trajectories. Rowers and swimmers, meanwhile, will strive to move as swiftly and efficiently as possible through a liquid medium.

Athletes’ grasp of movement is even sometimes quantitative. The US basketball superstar Bill Bradley – later a US senator and presidential candidate – once found himself having to practise in an unfamiliar high-school gymnasium and started out badly, missing six baskets in a row. “He stopped, looking discomfited, and seemed to be making an adjustment in his mind,” recounted writer John McPhee. “Then he went up for another jump shot from the same spot and hit it cleanly. Four more shots went in without a miss.” Bradley turned to McPhee and announced “That basket is about an inch and a half low.” Weeks later, the fastidious McPhee returned to the same gymnasium with a stepladder and steel tape, climbed up and measured the basket. It was indeed one and one-eighth of an inch below the required 12 feet.

Kenneth Laws, emeritus professor of physics at Dickinson College in Pennsylvania, has written books about the physics of dance, analysing the often surprisingly complex and unexpected physics principles of classical ballet. “The dance studio is a physics laboratory,” he declares. Even the movement of non-dancers can be used to illustrate physics principles, he says, pointing out that when we jog, we don’t let our arms dangle but cock them at the elbows, reflecting simple laws of pendulum motion. Laws, however, carefully avoids implying that this means we know such principles, and explicitly denies that his research provides a “how to” for dancers.

But performing trajectories is not ballistics, swimming is not hydrodynamics and dancing is not mechanics. One discipline – the art – involves knowing the kinetic possibilities of one’s own body in the world. This knowledge is largely self-instructive (aided by coaches) and impossible without first-person experience. We don’t learn to move by studying anatomy. The other discipline the science – involves knowing how abstract bodies move in abstract space and time.

Movement and motion, in short, involve knowledge of different phenomena and are two entirely separate expertises. It would be wrong to say that what is involved is implicit and explicit knowledge of the same thing, or that an athlete or physicist knows what the other knows plus something else.

The critical point

What troubles me is the urge to conflate the two expertises in a way that implies that the one has priority over the other. It is yet another manifestation of the problem, discussed by philosophers since ancient times, of the relationship between theoretical and practical knowledge. The French are wise in having two words for “to know”: connaître, to know concretely in one’s bones and in practice; and savoir, propositional knowledge, theoretical knowledge or know-how. The French philosopher Maurice Merleau-Ponty notably refers to the ordinary – not just athletic – human body as a corps connaissant, or “knowing body”.

Conflating the senses of knowing – and giving priority to the theoretical sense over the practical – simply reflects our adherence to the ancient myth that true knowledge is theoretical. We feel that knowledge is formulated in rules and concepts, and that it can be codified in fully linguistic, situation-independent terms; practical knowledge is merely the conscious, instrumental application of theoretical knowledge. The result is to give a bias to theoretical knowledge, a bias often manifested by the need to give dignity to practical knowledge – putting a stamp of academic respectability on it – by asserting, even in a light-hearted way, that it is really theoretical knowledge, whether implicitly or in disguise.

I consider McBeath’s experiment – which approached its subjects in an abstract, third-person way – to simply illustrate how counterintuitive physics can be. If he and his co-workers had put physicists and others on skateboards to see who could make it to the bottom quickest, would there be anything interesting to report?

The right way to express the results lightheartedly is not to say that athletes “know” the laws of physics, with the quotation marks implying that real knowing is not involved. The right way would be to say that athletes know the laws of “physics”.

It’s a boson, but what sort?

We have found it – now we have to work out exactly what “it” is. That neatly sums up the thoughts of many physicists at CERN yesterday as they began to absorb the announcement that the Large Hadron Collider (LHC) had discovered a Higgs boson – or at least something like a Higgs. CERN’s director general Rolf-Dieter Heuer was very careful to describe the new particle, which has a mass of about 125 GeV/c2, as a “fundamental scalar boson”. However, even the scalar part of that description – which indicates that the particle has zero spin – has not been completely nailed down.

To learn more about the particle they have found, CERN physicists need more data and more time. Heuer therefore announced yesterday that the LHC will run for an extra three months beyond its scheduled December 2012 maintenance shutdown to allow physicists to do just that. According to CERN’s Bill Murray, the performance of an accelerator and its associated experiments usually improves toward the end of the run, which suggests that physicists can expect many more quality data before the LHC is temporarily switched off in early 2013.

Precision measurements

The LHC creates the Higgs in proton–proton collisions, with the giant ATLAS and CMS experiments detecting the particles created when the Higgs decays. This occurs in a number of different ways – or “channels” – and by studying how these decays take place, physicists should get a better picture of exactly what they have discovered.

Most of the data contributing to the new discovery come from the so-called precision measurements, whereby the Higgs decays either into two photons (the diphoton channel) or into two Z bosons (ZZ). Since all of the decay products in both of these channels can be detected, physicists can therefore calculate the mass of the Higgs very precisely.

But there are also a number of different channels in which not all the decay products can be detected. These channels are trickier to deal with because some information about the decay is missing and therefore the mass that calculations based on these channels give is not as precise.

Yesterday, both the ATLAS and CMS teams reported that their precision diphoton and ZZ results were enough to push both experiments over the magic 5σ level that is generally considered a discovery in particle physics. ATLAS chose not to present results from other, less-precise channels, although CMS did – something that brought the statistical significance of its finding down to 4.9σ.

Beyond the Standard Model?

The Standard Model of particle physics describes how the Higgs should decay through various channels; so by comparing these predictions with how the decays actually appear to proceed in the LHC, physicists can tell if what they are dealing with is a Standard Model Higgs. So far the results are consistent with a Standard Model particle, with all channels lining up to the Standard Model to within the error bars.

Intriguingly, however, the number of events in the diphoton channel of both CMS and ATLAS continues to be greater than expected as more data are gathered. This excess could therefore be the result of “new physics” that goes beyond the Standard Model, such as a new charged particle, the existence of a multitude of Higgs, or perhaps the effects of “supersymmetry” – the idea that all particles have “superpartners” with very different spin properties.

Deficit of evidence

Whereas there is a surfeit of diphoton events in the LHC data, it is a different story for the decay of the Higgs into two W bosons – the WW channel. Conventional theories about the Higgs predict that this channel should be seen by the LHC, but to date far fewer events than expected are being reported. Indeed, if this channel does not exist, a major shake-up of particle-physics theory could be on the cards, which could be why many physicists at CERN believe that the WW deficit is not real but simply the result of the fact that the WW channel is tricky to measure.

But if there really is a deficit in the WW channel, it could suggest that the new particle might not be a scalar boson with zero spin. “The WW search is designed to look for a spin-0 [scalar] particle,” admits Bill Murray, who is a member of the ATLAS collaboration. “They have not considered the possibility that it might be spin-2.” Although experiments at the Tevatron at Fermilab seem to rule out spin-2 (and spin-1 is ruled out by the diphoton data), physicists are therefore left with the remote – but exciting – possibility that this new particle is not a scalar boson.

Daniela Bortoletto of Purdue University in the US, who is a member of the CMS team, points out that the channels in which the Higgs decays to a pair of tau leptons or a pair of b-particles also appear to have deficits of events. Given that tau and b-particles are both fermions, Bortoletto says that if this deficit endures as more data are collected, then it might mean that the Higgs interacts differently with fermions and bosons.

Murray, though, says that the deficit could point to a “mixed model” of fermion versus boson coupling to the Higgs, adding that the tau–tau and b–b channels will definitely benefit from the three-month run extension. Indeed, most physicists at CERN who were digesting yesterday’s big announcements believe that by the end of the extended run they should have a much better idea of whether they have a Standard Model Higgs.

Future prospects

But one important measurement that the LHC will not be able to make until it is upgraded to collide protons at 14 TeV – rather than 8 TeV today – is the “self-interaction” of the Higgs boson. That is how two Higgs behave when they encounter each other – something that should only be seen at higher collision energies in which two Higgs could be produced. “An important question is whether you need to measure the self-interaction before you can say you really have a Higgs?,” says Murray. As the LHC’s 14 TeV upgrade is not likely to be completed before the end of 2014 at the earliest, it looks like the debate is set to continue.

Before then, all eyes will surely be on who, if anyone, should win a Nobel prize for the new discovery. Peter Higgs – after whom the boson is named – appeared reluctant at yesterday’s press conference to be drawn on the matter, having always maintained that he was not alone in devising the core ideas that led to the prediction of the Higgs boson in the early 1960s. Speaking recently to Physics World, he said at least five other theorists – include the late Robert Brout, François Englert, Gerald Guralnik, Carl Hagen and Tom Kibble – deserve credit too. But given that the Nobel committee can award the physics prize to no more than three physicists each year, it will have a tricky job on its hands.

Spread the praise
Spread the praise

 

The smiles say it all at CERN

Higgs excitement

By Hamish Johnston in Geneva

To me, this photo of CMS physicists Yves Sirois of École Polytechnique in Paris and Daniela Bortoletto of Purdue University in the US sums up the day nicely. Both spent every waking hour of the last two weeks analysing data – yet were so full of energy and excitement that it even rubbed off on a curmudgeon like me!

Introducing the higgson

Now that a fundamental scalar boson has finally turned up and become real, it is time to give it a better name. We advocate calling it the "higgson".

"Higgs boson" or "Higgs particle" is a real mouthful; it's too long and awkward. No wonder physicists trim it down to "the Higgs". But that just invites questions: the Higgs what? field? mechanism? mass? It's too ambiguous. Something seems seriously amiss with the existing nomenclature.

And why do we want to keep highlighting one physicist's formal surname, when at least five others were involved in conceiving the core ideas underlying this particle? Some have suggested we resolve the problem by calling it the BEH boson or EBH particle, but both fall flat phonetically and leave us cold. To continue following that logic, we could perhaps call it the BEHGHK boson. Or how about the ANGBEHGHK particle? You get our point.

As Frank Close recently detailed in The Infinity Puzzle, Peter Higgs made the clearest statement that the symmetry-breaking mechanism involved would have observable consequences: a scalar boson corresponding to oscillations in the underlying field. Thus it makes sense to associate his name with this boson, at least informally. But that doesn't mean we have to capitalize it explicitly.

We can just call this particle the higgson.

Such a label can then take its rightful place alongside other classic particle names, such as the electron, proton, neutron, neutrino, quark and gluon. That includes the labels used for entire classes of particles such as leptons, hadrons, mesons, baryons, fermions and bosons – for still other higgsons may well exist.

The names electron and proton established a distinguished trend that has lasted a century. When competition arose for the neutron label, between Rutherford's neutral nuclear inhabitant and Pauli's beta-decay product, it eventually was settled in favour of the former, while the latter became Fermi's "neutrino". All great names.

With the advent of particle accelerators during the 1950s and 1960s, two whole alphabets – Greek and Roman – had to be mobilized as the list of putatively elementary particles burgeoned. One particle stood out, borrowing its name from both: the famous J/Ψ that we've lived with now for almost 40 years.

It took the genius of Murray Gell-Mann – who possesses a real naming gift – to recognize that the list was becoming unmanageable and establish a different way to label particles found at the next lower level of matter. Reaching into James Joyce's Finnegan's Wake, he lifted the word "quark" from the drunken dream of Humphrey Chimpden Earwicker to name the odd, fractionally charged fundaments that had cropped up as a result of his SU(3) theory. Happily, it stuck.

Soon we had humdrum up and down quarks, but intriguing strange and charm quarks. After a third family of elementary particles turned up, the elegant names truth and beauty gradually succumbed to the more commonplace top and bottom. All these fanciful quarks stuck to one another by swapping rather prosaic gluons.

After Gell-Mann, particle physics seemed to be running out of imagination. With all the appeal of an intellectual cold shower, the emerging paradigm was labelled the Standard Model. Scientifically it was ambitious, but this phrase was not very useful in cocktail-party conversations with colleagues from other fields. Electromagnetism became wedded to the weak force in the electroweak force, a good name, but it was carried by vapid "intermediate vector bosons" called W and Z.

And at the heart of the new theory, shrouded in mystery, was a symmetry-breaking mechanism that preserved gauge invariance (which has served electromagnetism well) but allowed elementary particles to gain heft. It had been assembled bit by bit during the early 1960s through the concerted efforts of more than a dozen theorists. You have to fill the bathtub before you can shout "Eureka!" But despite this great communion of minds, it eventually came to be known as the Higgs mechanism after just one of its principal proponents.

Along with this mechanism came the need for a new scalar boson (or bosons), similarly dubbed. Leon Lederman used an entire book to try to rename it the "God particle". But that was a little too much for agnostic particle physicists, who clung stubbornly to the "Higgs particle". And after looking in almost every accessible nook and cranny for the past four decades, they have at long last discovered this elusive, quintessential quarry.

Photo of Peter Higgs
Peter Higgs

One episode in this century-long naming saga strikes us as particularly relevant in giving the scalar boson an appropriate moniker. With the 1920s rise of quantum mechanics, physicists recognized that wave functions could be symmetric or antisymmetric. As with the symmetry-breaking mechanism of the early 1960s, many physicists contributed, but symmetric wave functions came to have Bose–Einstein statistics and antisymmetric ones Fermi–Dirac statistics. Soon the corresponding particles became known as "Fermi particles" and "Bose particles", dropping two eminent physicists' names but saving speakers several syllables.

Then in December 1945 Dirac gave a public lecture on atomic theory in war-ravaged Paris. The audience was hoping to hear about the atomic bomb, but he spoke instead about arcane topics in quantum mechanics that few understood. In the process he introduced two new words into our lexicon. Instead of Fermi particles he talked about "fermions", and he called Bose particles "bosons". Dirac's new names eluded most of the audience, but they caught on among physicists, to our great benefit.

In the same vein, it's time we stop calling the scalar boson the Higgs boson or the Higgs particle and start calling it something better. Physicists have lower-case names for important measurement units such as newton, coulomb, ampere, volt, ohm, watt and kelvin. Why can't we do something similar for this fascinating new particle?

Let's call it the higgson.

Picture of a new particle

event data

By Michael Banks

This is what a new boson looks like.

Presenting the latest results in the search for the Higgs boson at CERN this morning, Joe Incandela of the CMS experiment displayed a plot showing a clear bump in the data centred at around 125 GeV.

Incandela reported that CMS has indeed seen a new particle – that looks at the moment to be the Higgs boson – with a mass of 125 GeV. The result was given with a statistical significance of 5σ – a level that physicists call a "discovery".

Shortly after Incandela's talk, ATLAS spokesperson Fabiola Gianotti also reported that its detector has seen something at 126 GeV with a statistical significance of 5σ.

So we have a new particle, but more effort will be needed to work out the details.

Look out for more news and analysis on the latest results on physicsworld.com in the coming days.

CERN discovers Higgs-like boson

Physicists working at the Large Hadron Collider (LHC) have announced the discovery of the Higgs boson – or at least a particle that resembles the Higgs. In two special seminars this morning at the CERN particle-physics lab in Geneva, spokespeople for the LHC's two main experiments – ATLAS and CMS – both reported measurements of the Higgs' mass at confidence levels of 5σ. Any finding that passes this statistical threshold is generally, but not always, considered a "discovery" among the particle-physics community.

However, today's announcement of a discovery of a particle that looks like the Higgs is by no means the end of the story, as physicists have yet to understand its complete nature.

Physicists have had the Higgs boson in their sights for nearly 50 years because its discovery would complete the Standard Model of particle physics. The particle and its associated field explain how electroweak symmetry broke just after the Big Bang, which gave certain elementary particles the property of mass. The Standard Model does not, however, predict the mass of the Higgs, and successive experimental programmes at CERN's Large Electron–Positron Collider (LEP), Fermilab's Tevatron and now the LHC have tried to measure the particle's mass.

Presenting the latest results from the CMS experiment, spokesperson Joe Incandela announced that his experiment has discovered the Higgs boson at a mass of 125 GeV/c2 and a statistical significance of 5σ.

Incandela described the result as "A phenomenal effort considering that we stopped taking data two weeks ago."

Incandela was followed by ATLAS spokesperson Fabiola Gianotti, who says that ATLAS has measured the mass of the Higgs as 126 GeV/c2, which agrees with preliminary results released by CERN in December 2011. The statistical significance of the measurement is 5σ.

"The search is more advanced today than we imagined possible," says Gianotti. However, she cautioned that "a little more time is needed to finalize these results, and more data and more study will be needed to determine the new particle's properties".

Measurements with 5σ from both detectors – combined with previous searches by Tevatron and LEP – leave no doubt that a "Higgs-like" particle has been discovered by the LHC.

"We have reached a milestone in our understanding of nature," says CERN director general Rolf-Dieter Heuer, who described the new particle as being "consistent with the Higgs boson".

Speaking in the CERN auditorium immediately after the results had been presented, Edinburgh University particle theorist Peter Higgs congratulated researchers on their finding. "For me, it's a really incredible thing that it's happened in my lifetime," he said.

More to follow.

Brace yourself for the Higgs endgame

By James Dacey

Hamish Johnston, editor of physicsworld.com, has just left the building and is winging his way to Geneva. Hamish will be on the ground at CERN tomorrow reporting on developments as the two primary experiment teams at the LHC searching for the Higgs boson – ATLAS and CMS – will be presenting new results. Strong speculation suggests that an official discovery of this long-sought particle is now tantalizingly close, though whether or not the particle complies with the Standard Model of particle physics remains to be seen.

To whet your appetite ahead of the big day tomorrow, take a look at this video, which gives you an insight into how scientists at ATLAS and CMS are trying to find the Higgs. I produced this video report at CERN last year and it's interesting to hear scientists from both experiments saying they were confident that by the end of 2012 they would know whether or not the Higgs exists. I was given a tour of the CMS control room by the experiment's then-spokesperson, Guido Tonelli, who talked me through the collision images on a big screen and the particle trails they expect to see for a Higgs boson.

Since this film was made we have undoubtedly entered the endgame in this hunt. But will tomorrow bring a decisive capture? Stay tuned to physicsworld.com and our Twitter feed for updates.

Space–time crystals on the horizon

Exotic structures known as "space–time crystals" could soon become reality, thanks to research carried out by a collaboration of physicists in the US and China. The researchers, developing an idea put forward by theoretical physicist Frank Wilczek, of the Massachusetts Institute of Technology in the US, have shown how a crystal made of trapped ions could rotate persistently, even when in its lowest energy state, enabling it to break temporal as well as spatial symmetry.

Normal crystals consist of atoms or molecules arranged in ordered 3D structures, which form below a certain temperature in order to minimize the potential energy within the material. The carbon atoms in diamond, for example, experience an attractive force at longer distances but a repulsive force at smaller scales, meaning that their energy is at a minimum when they are separated from one another by approximately the same intermediate distance. Contrastingly, at higher temperatures, the atoms in a crystal can exist in many more disordered states than ordered states and if the former tends to prevail, it causes the material to melt. "Crystals are a victory of energy over entropy," says Wilczek.

Timely symmetry breaking

Wilczek came up with the idea of a "time crystal" after asking himself whether a material at low temperatures could be structured in time, rather than space or in addition to it. A normal crystal is said to break spatial symmetry because its constituent particles line up in specific directions, rather than being regularly spaced (as they are at higher temperatures). Breaking temporal symmetry, analogously, simply means that an object or a collection of particles experiences some kind of systematic change in time. As Wilczek points out, this is true of planets in the solar system as well as clocks, for example. But these are systems that were set in motion by some kind of external energy source and will eventually run down. Wilczek wondered whether motion might also be possible in isolated systems that exist in their ground states.

He concedes that this idea is "perilously close" to that of a perpetual motion machine. He points out that, being in their ground states, such systems could not be employed to produce useful work. They would, however, require energy to be stopped. "They would generate a form of perpetual motion", he says, "which is a little scary to say for someone with a reputation in physics."

Reservations aside, Wilczek realized that superconductors come close to acting in this way, since they exist in their lowest state but transmit an electrical current. However, they fall short because the current does not change in time. To turn a superconductor into a time crystal, Wilczek proposed varying a supercurrent to give it a temporal peak, which, when travelling around a superconducting ring, would resemble "a mouse moving inside a snake". He found mathematically that such a scheme is in fact possible, and that the system's finite kinetic energy is allowed because it results from a larger drop in the system’s potential energy.

Ion trapping

Xiang Zhang and Tongcang Li of the University of California, Berkeley and colleagues, however, think that this particular scheme would be difficult to realize in practice because it would require particles with like-charge to attract one another in order to create the lump in the current. Their proposal instead involves trapping ions at very low temperatures and exploiting their mutual repulsion so that they arrange themselves into a ring shape. This ring, explains Li, would be similar to a conventional crystal. By then setting up a magnetic field with certain values across the ring, the ring could be made to rotate continuously in its lowest energy state – in other words, he says, it would become a space–time crystal.

Li says that the main challenge in actually building such a device will be cooling ions in small enough traps down to sufficiently low temperatures. He and his colleagues calculate that to form a space–time crystal one tenth of a millimetre across, 100 beryllium ions would need to be cooled down to just one billionth of a kelvin, with larger rings requiring even lower temperatures. But he is confident that this technical demand can be met, either by his own group or other groups. "It can be overcome in the near future with the development of ion trap technologies", he says, adding that exactly when this happens "depends on funding and many other factors".

Zhang believes, that, once built, such a device could "provide a new dimension for exploring many-body physics and emerging properties of matter" and may also improve our understanding of symmetry breaking, such as that which is believed to have given particles their mass as the universe expanded and cooled.

Wilczek, who describes the trapped-ion proposal as "much more spelled out and professional" than his own scheme, also argues that space–time crystals could have practical applications, even if it is not clear at this stage what those applications are. "This work is exploring new states of matter", he says, "and could lead in unexpected directions."

The paper is available on the arXiv pre-print server (arXiv:1206.4772v1).

Tiny pressure sensor takes off

Researchers in Japan have built a tiny sensor that can measure the pressure differences on a butterfly's wing, helping to better understand the dynamics of insect flight. The team hopes to study the different pressures acting on the wing during take-off, something that has never been measured before. The work will help in building robotic insect-sized flyers or to develop artificial wings.

The seemingly impossible manoeuvres that insects can perform during flight – such as hovering and sudden turns that are very difficult for birds – have long interested researchers. Among the many winged insects, butterflies, and more specifically the Papilionidae family of butterflies (commonly known as swallowtail butterflies) possess a unique wing design that allows them to ascend in a zigzagging path, with low flapping frequency. Hidetoshi Takahashi from Tokyo University, who is lead author and part of the team conducting the research, points out that, according to conventional aerodynamics, the estimated force generated by a flapping insect wing should be insufficient to support its body weight. This means that the actual aerodynamic force of an insect wing exceeds that observed under steady aerodynamics, – where there are equally distributed forces acting across a surface – making it more likely that some "unsteady aerodynamic phenomena" come into play. That is why many researchers have been trying to reveal the mechanism behind this unsteady force, explains Takahashi.

Unsteady aerodynamics

To find out more about these unsteady phenomena, the team has tried to measure the differential pressure distribution – responsible for the aerodynamic force – across an insect's wing. The work had two main aims – first, to develop a microelectromechanical system (MEMS) differential-pressure sensor that is light enough to let the butterfly achieve flight and that also has high sensitivity to detect minute pressure differences. The second was to measure the force on the wing, mainly during take-off, as the actual aerodynamic force generated by real insect wings during free flight has never been measured directly. "Previous research has been limited to large-scale, tethered conditions using robotic flappers. This makes it difficult to duplicate the actual interaction of the aerodynamic forces with the body motion and wing deformation of insects," explains Takahashi.

Tiny sensor

The researchers built a piezoresistive cantilever, measuring 125 µm × 100 µm × 0.3 µm. The differential pressure between the upper and lower surfaces of the cantilever causes it to bend and this deformation, in turn, registers as a resistance change in the sensor. "The resolution of the differential pressure is 0.02 Pa from –20 Pa to 20 Pa. Also, the structure is very simple so that the sensor chip can be subminiaturized easily" says Takahashi.

The sensor was then attached to a butterfly wing and the output was measured through a copper-polyimide electrode and gold wires. The total weight of the attachment, including the sensor chip, electrode and wires is 35 mg – lighter than the amount of food that the butterfly consumes at a given time, which is about 100 mg.

"We measured the differential-pressure distribution of four points on the wings of eight butterflies during take-off. "Our measurements show that the differential pressure simply rises and falls periodically and symmetrically in accordance with wing motion. The magnitude of the differential pressure increases as the position shifts from the wing root to the tip during take-off," explains Takahashi. The researchers also found the instantaneous pressure at the forewing tip reaches a maximum of 10 Pa, which is 10 times larger than the wing loading of the butterfly.

The team points out that understanding the varying aerodynamic forces acting on flying insects using this direct measurement method could help in developing artificial insect-sized flyers in the future. Such robotic insects could be built specifically to easily get into restricted or dangerous spaces, such as disaster sites, to help assess the situation. Also, the studies could help in building artificial wings for aerodynamic experiments or real-time flight control.

The work is reported in Bioinspir. Biomim. 7 036020.

Mind your Zs and Ws

By Hamish Johnston

On Wednesday I will be at CERN in Geneva to hear about the latest in the quest for the Higgs boson – and if the rumours are to be believed, I won't be disappointed.

As the big day approaches, physicists have moved away from gossiping about whether a discovery will be announced (no, if you consider individual experiments, which are both expected to report evidence at the 4-sigma level...yes if you "unofficially" combine these results to get a statistical significance greater than the magical 5-sigma) and on to the nitty-gritty of what has been seen in the various detection channels.

Once the Higgs is created in the LHC, it can be detected in a number of different ways – or "channels" to use the jargon – several of which are being scrutinized by the LHC's experiments. Two important channels involve the Higgs decaying to a pair of W bosons (WW) or a pair of Z bosons (ZZ). Conventional theories say that the physics behind these decays is similar, so the assumption is that evidence of both should be seen in the LHC data. However, rumours coming out of CERN suggest that this is not the case – the WW signal doesn't appear to be there.

However, the Higgs can also decay creating two photons (what's known as the diphoton channel) and the word on the street is that many more events than expected have been seen in this channel. This also contradicts the absence of WW events because conventional theory predicts that a large diphoton signal should also be accompanied by a large WW signal.

Meanwhile, researchers at Fermilab in the US have been rifling through their data from the now switched-off Tevatron collider and have announced further analysis of their own Higgs search today. The Tevatron results seem to suggest that the LHC should be seeing WW events.

So why isn't the LHC seeing WW decays? One possibility is that there's something wrong with how the LHC is looking for these events – a rather boring situation that can be fixed. More tantalizing is that the LHC is right about the WW deficit – which could mean that the particle glimpsed so far is not the "real Higgs", but rather an "imposter"!

The unexpectedly high diphoton signal is also interesting in itself. It could point to the existence of a new charged particle not described by the Standard Model of particle physics, or it could mean that there are a multitude of Higgs particles – or something completely different.

Indeed, the only certainty is that much more work will be needed before physicists get a handle on the Higgs. So Wednesday will likely be remembered as the beginning of a new era in particle physics – as well as the end of a long search for the Higgs boson.

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