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The stuff of legend
We seek it here, we seek it there. Will we ever find the elusive magnetic monopole, asks Richard Webb
The stuff of legend J
IM PINFOLD hurries me through the low-lit corridors of the theory department at the CERN laboratory near Geneva in Switzerland. Posters announcing conferences of yesteryear plaster the walls. On one door, an A4 poster adorned with a Nike swoosh announces “Physics: Just Do It”. Through another door, a group of physicists stand in pensive silence around a blackboard covered in chalk hieroglyphics as they sip sparkling wine from plastic cups. It is barely midday. “Walk quickly through here,” he says. “In case you get any funny ideas.” For Pinfold, theory has always been a means to an end; in this case, a shortcut to the car park from which he will drive me over the Swiss-French border to his latest experiment. The ultimate end, he hopes, will be proving an idea that has been burning in the minds of theorists for decades: that magnetic monopoles exist. A monopole is a magnetic north pole without its accompanying south, or a south without its north. No one has ever seen one. And if our present understanding of particles and forces is correct, we don’t have the remotest chance of snaring one. Pinfold, a silver-haired, fast-talking Londoner who works at the University of Alberta in Edmonton, Canada, begs to differ. “I’d give us about the same chance of finding a monopole as we would have given of finding the Higgs boson 10 years ago,” he says. “It’s a bullish answer, but it’s my answer.” Magnetic monopoles’ no-show has long been a bugbear to the sort of physicist that sees truth in the beauty of mathematical 34 | NewScientist | 16 August 2014
formulae, and among the most beautiful are the four equations collated by James Clerk Maxwell in the 1860s. These encapsulate the idea that electricity and magnetism are two manifestations of the same thing: the fundamental force of electromagnetism. Maxwell’s equations predicted the existence of individual, freely moving electric charges – things nature supplies in abundance in the form of particles such as electrons and protons. To achieve an aesthetically pleasing symmetry in the equations, similar freewheeling magnetic charges had to exist, too. This was less obvious. North and south magnetic poles that attract and repel each other do exist, just as positive and negative electric charges do. But from the humblest bar magnet to Earth’s mighty interior dynamo, magnetic poles only ever crop up tied together in pairs. Chop a magnet in half and, like Walt Disney’s sorcerer’s apprentice with his magic broom, you forge two new complete magnets, each with a north and south pole. Faced with a brute fact of nature, Maxwell eschewed beauty and wrote the freely moving monopole out of his equations – and out of history. However, monopoles made a comeback thanks to Paul Dirac, a British theorist who was notoriously word-shy and obsessed with mathematical beauty. Quantum theory was all the rage in 1931, and Dirac began applying its ideas to Maxwell’s classical electromagnetism. Dirac’s calculations showed that even if there was just one magnetic monopole in the entire universe, its existence would explain why all the electric charge we see comes in the same bite-sized chunks of +1 or -1. >
kolchoz
16 August 2014 | NewScientist | 35
“Quite plausibly, there is just one monopole in the entire visible universe” This time, the idea stuck. Forty years on, physicists discovered that the electromagnetic force and the weak nuclear force that controls radioactive decay could be rolled into one, and were seeking ways to unify this force with a third, the strong nuclear force. Gerard ’t Hooft and Alexander Polyakov independently showed that monopoles were essential if such a “grand unified theory” were to make predictions in accordance with reality. “Without monopoles, you would have to expect electrically charged particles to have all sorts of charges,” says ’t Hooft, who is at Utrecht University in the Netherlands and who won a share of the 1999 Nobel prize in physics for his work on unifying weak and electromagnetic interactions.
Particle zoo Fellow theorist Joseph Polchinski of the University of California, Santa Barbara, also has no doubt about the reality of monopoles. “Of all the new things we have predicted – supersymmetry, strings and so on – I would still put the very highest confidence in monopoles,” he says. So where are they? Researchers have looked for monopoles everywhere, from Antarctic ice to moon rocks. Things acting like monopoles have even been created in various supercooled materials in the lab (see “Mission impossible?”, right). But the closest we’ve come to the real thing was on Valentine’s night in 1982. That was when physicist Blas Cabrera saw a promising event in a monopole detector he had set up in
a basement at Stanford University in California. It proved to be a one-night stand, prompting some wag to post Cabrera this loving note exactly a year later: “Roses are red/Violets are blue/The time has now come/For monopole two”. These days Cabrera’s monopole and a couple of other even more ambiguous sightings are regarded as experimental blips. But Dirac’s calculations provide a ready-made excuse for the monopole’s absence. They show that the smaller the unit of electric charge is, the larger the unit of magnetic charge must be. Because the basic electric charge is incredibly small – you need around 1000 billion electrons to power a hearing aid for just 1 second – the basic magnetic charge is so large that it would take an implausible amount of energy to make a particle carrying it. Precisely how much energy depends on the variant of force unification that you choose – theorists have come up with several ways of performing this feat over the years. If you follow the variant that underlies our current best theory of particles and forces, the standard model, then the only time that enough energy was around to make monopoles in any abundance was in the first infinitesimal fraction of a second after the big bang. About the same time, a period of rip-roaring cosmic expansion known as inflation is thought to have occurred that would have scattered monopoles to the four winds. “Quite plausibly what was an overabundance of monopoles would be diluted to one in the entire volume of the visible universe,” says Polchinski.
Hello, Mrs Chips Teacher Becky Parker is about to lead her pupils to a first: full membership of an international particle physics collaboration. “It’s barmy, isn’t it?” she says. Parker is director of the Langton Star Centre, a research lab she set up at Simon Langton Grammar School in Canterbury, UK. Her pupils have been using semiconductor chips, developed at CERN near Geneva, to measure the characteristics of highly energetic particles. Their chips have already been incorporated into a cosmic-ray detector, which was one of eight scientific payloads that blasted off from Baikonur Cosmodrome in Kazakhstan last month. 36 | NewScientist | 16 August 2014
From 2015, however, they will be monitoring their chips from CERN, as part of the detectors that the MoEDAL (Monopole and Exotics Detector at the LHC) collaboration hopes will capture monopoles (see main story). Katherine Evans, the final-year pupil who headed the student contingent this year, will have moved on by the time the detectors are switched on in 2015, but she is happy to lay the groundwork for future pupils. “It’s nice to think they’ll be the ones to see it,” she says. Parker, meanwhile, is in no doubt of the value of the project. “All the best science is done by the youngest people,” she says. “Why not give them a chance to get stuck in?”
MoEDAL’s detectors are trying to snare a monopole
Or, says Pinfold, we might just find one down a tunnel in Geneva. A narrow, rattly lift just vacated by a technician and his wheelbarrow carries us down 100 or so metres to a cavernous underground hall that is home to one of the giant experiments of the Large Hadron Collider (LHC) – and to Pinfold’s venture. Now is a good time to visit the bowels of the LHC: the accelerator is switched off until early 2015 while it undergoes an upgrade. We climb a series of metal stairways back up from the cavern floor and reach a platform where a thin metal pipe emerges from the middle of a whitewashed door. Next year protons will once again zip along this pipe at 99.9999991 per cent of the speed of light and collide head-on up to 600 million times a second with other protons travelling at the same speed in the opposite direction. The innards of these high-energy protons provide the raw material for the LHC’s investigations of material reality, as all manner of exotic and unfamiliar particles are fleetingly created in the resulting mini fireballs. Pinfold’s experiment is small by LHC standards, and its feel seems to be almost a rebuke of the LHC’s expensive cutting-edge technology. It is called MoEDAL (short for the Monopole and Exotics Detector at the LHC), and its principal component is a series of metal cases attached to the walls around the platform. Neatly outlined in yellow masking tape, each trails a curl of wires to the floor. By the time protons start colliding again,
mission IMPOSSIBLE? The hunt for magnetic monopoles has been far-reaching. Here’s where we have looked and failed to find them:
TRAPPED IN... < Moon rocks from the Apollo 11 mission < Antarctic meteorites < Volcanic rocks
PASSING THROUGH... < Experiments looking for high-energy neutrinos and cosmic rays < Dedicated monopole detectors < Cosmic microwave background radiation
MADE IN...
Richard Webb
< Various particle colliders < Magnetic materials
these cases will entirely surround the crash the LHC are the most energetic ever made in a site. “Mind out,” says Pinfold from beneath particle accelerator, they fall far short of what his hard hat as he invites me to crane my neck is needed to make a monopole if you take the into a pit immediately below the beam pipe. standard model at face value. “If you bang your head there, it’s hard.” But Pinfold’s experiment is far from a Within each of the metal boxes are detectors fool’s errand. Fundamental physics is in consisting of a series of stacked layers of a funk. While the discovery of the Higgs plastic that act as a form of photographic boson slotted the final piece into the jigsaw plate. Because a monopole must carry a huge of the standard model, the theory is clearly magnetic charge, it would rip through the incomplete. It manages to describe polymer bonds of the plastic, etching a trail electromagnetism and the weak and strong whose size, shape and alignment would reveal forces in a broadly satisfying way. Yet it the particle’s character. Once produced, remains silent on the fourth, gravity, and monopoles are expected to be highly stable – so the experimental set-up also includes “If monopoles are light, it trapping detectors in which any passing monopole might be bottled and kept boosts the chances of for further tests: a true exotic from the producing one at the LHC” particle zoo. There is an improvisatory spirit about MoEDAL. Although the powers that be at it doesn’t give any clues as to the identity of CERN gave the go-ahead for the experiment dark matter and dark energy, which seem to in 2010, the 60-strong collaboration must make up 96 per cent of what is out there. raise its own funding. With money from These are far from the only question official sources tight, the team is looking to marks hanging over the standard model, and crowdsource some of it. Meanwhile, part of scepticism about it is further fuelled by that the monitoring of the experiment’s output nagging question of aesthetics. Although its will be done by pupils at a school in the UK predictions, as far as they go, agree peerlessly (see “Hello, Mrs Chips”, left). The uncertainty well with experiments, mathematically about what, if anything, the experiment will the standard model is a bit of a kludge, a see is part of its charm, says Richard Soluk, pasting together of different bits of theory MoEDAL’s technical coordinator. “You don’t with the occasional safety pin and sticking make a breakthrough looking for things plaster to cover the gaps. “It would be very, people expect you to find,” he adds. very surprising if it were the end of things,” Even though the mini fireballs produced at says Polchinski.
Many attempts to improve on the standard model have emerged in recent years. Some of these exotic theories, such as ones that predict the existence of extra dimensions, predict a significantly lighter monopole too, says ’t Hooft. This dramatically boosts the LHC’s chances of producing a monopole and MoEDAL’s chances of bagging one. “Their energy would be much closer to where the LHC or its future descendants can reach, so the prospects look brighter,” adds ’t Hooft. All that means Polchinski is crossing his fingers for an upset. “Any kind of new physics would turn the field upside down,” he says. “For monopoles to be within the reach of the LHC will require us to be lucky, but I think we have to look everywhere.” At the end of a long day, the CERN cafeteria is a good place to muse over monopoles. Stickers by the buttons on the water fountain offer three choices, “Order”, “Chaos” and “Self-destruct”. I opt for a beer instead, and rejoin Pinfold in the bustle of physicists and technicians. He is also a member of the ATLAS collaboration, one of the teams that found the Higgs boson, but it is clear that his heart beats for monopoles – as perhaps do those of many a soul in the yellowing corridors of CERN’s theory department. “All we need is one,” says Pinfold. “Everyone was expecting the Higgs. But no one is expecting this.” n Richard Webb is New Scientist’s deputy features editor 16 August 2014 | NewScientist | 37
The stuff of legend J
IM PINFOLD hurries me through the low-lit corridors of the theory department at the CERN laboratory near Geneva in Switzerland. Posters announcing conferences of yesteryear plaster the walls. On one door, an A4 poster adorned with a Nike swoosh announces “Physics: Just Do It”. Through another door, a group of physicists stand in pensive silence around a blackboard covered in chalk hieroglyphics as they sip sparkling wine from plastic cups. It is barely midday. “Walk quickly through here,” he says. “In case you get any funny ideas.” For Pinfold, theory has always been a means to an end; in this case, a shortcut to the car park from which he will drive me over the Swiss-French border to his latest experiment. The ultimate end, he hopes, will be proving an idea that has been burning in the minds of theorists for decades: that magnetic monopoles exist. A monopole is a magnetic north pole without its accompanying south, or a south without its north. No one has ever seen one. And if our present understanding of particles and forces is correct, we don’t have the remotest chance of snaring one. Pinfold, a silver-haired, fast-talking Londoner who works at the University of Alberta in Edmonton, Canada, begs to differ. “I’d give us about the same chance of finding a monopole as we would have given of finding the Higgs boson 10 years ago,” he says. “It’s a bullish answer, but it’s my answer.” Magnetic monopoles’ no-show has long been a bugbear to the sort of physicist that sees truth in the beauty of mathematical 34 | NewScientist | 16 August 2014
formulae, and among the most beautiful are the four equations collated by James Clerk Maxwell in the 1860s. These encapsulate the idea that electricity and magnetism are two manifestations of the same thing: the fundamental force of electromagnetism. Maxwell’s equations predicted the existence of individual, freely moving electric charges – things nature supplies in abundance in the form of particles such as electrons and protons. To achieve an aesthetically pleasing symmetry in the equations, similar freewheeling magnetic charges had to exist, too. This was less obvious. North and south magnetic poles that attract and repel each other do exist, just as positive and negative electric charges do. But from the humblest bar magnet to Earth’s mighty interior dynamo, magnetic poles only ever crop up tied together in pairs. Chop a magnet in half and, like Walt Disney’s sorcerer’s apprentice with his magic broom, you forge two new complete magnets, each with a north and south pole. Faced with a brute fact of nature, Maxwell eschewed beauty and wrote the freely moving monopole out of his equations – and out of history. However, monopoles made a comeback thanks to Paul Dirac, a British theorist who was notoriously word-shy and obsessed with mathematical beauty. Quantum theory was all the rage in 1931, and Dirac began applying its ideas to Maxwell’s classical electromagnetism. Dirac’s calculations showed that even if there was just one magnetic monopole in the entire universe, its existence would explain why all the electric charge we see comes in the same bite-sized chunks of +1 or -1. >
kolchoz
16 August 2014 | NewScientist | 35
“Quite plausibly, there is just one monopole in the entire visible universe” This time, the idea stuck. Forty years on, physicists discovered that the electromagnetic force and the weak nuclear force that controls radioactive decay could be rolled into one, and were seeking ways to unify this force with a third, the strong nuclear force. Gerard ’t Hooft and Alexander Polyakov independently showed that monopoles were essential if such a “grand unified theory” were to make predictions in accordance with reality. “Without monopoles, you would have to expect electrically charged particles to have all sorts of charges,” says ’t Hooft, who is at Utrecht University in the Netherlands and who won a share of the 1999 Nobel prize in physics for his work on unifying weak and electromagnetic interactions.
Particle zoo Fellow theorist Joseph Polchinski of the University of California, Santa Barbara, also has no doubt about the reality of monopoles. “Of all the new things we have predicted – supersymmetry, strings and so on – I would still put the very highest confidence in monopoles,” he says. So where are they? Researchers have looked for monopoles everywhere, from Antarctic ice to moon rocks. Things acting like monopoles have even been created in various supercooled materials in the lab (see “Mission impossible?”, right). But the closest we’ve come to the real thing was on Valentine’s night in 1982. That was when physicist Blas Cabrera saw a promising event in a monopole detector he had set up in
a basement at Stanford University in California. It proved to be a one-night stand, prompting some wag to post Cabrera this loving note exactly a year later: “Roses are red/Violets are blue/The time has now come/For monopole two”. These days Cabrera’s monopole and a couple of other even more ambiguous sightings are regarded as experimental blips. But Dirac’s calculations provide a ready-made excuse for the monopole’s absence. They show that the smaller the unit of electric charge is, the larger the unit of magnetic charge must be. Because the basic electric charge is incredibly small – you need around 1000 billion electrons to power a hearing aid for just 1 second – the basic magnetic charge is so large that it would take an implausible amount of energy to make a particle carrying it. Precisely how much energy depends on the variant of force unification that you choose – theorists have come up with several ways of performing this feat over the years. If you follow the variant that underlies our current best theory of particles and forces, the standard model, then the only time that enough energy was around to make monopoles in any abundance was in the first infinitesimal fraction of a second after the big bang. About the same time, a period of rip-roaring cosmic expansion known as inflation is thought to have occurred that would have scattered monopoles to the four winds. “Quite plausibly what was an overabundance of monopoles would be diluted to one in the entire volume of the visible universe,” says Polchinski.
Hello, Mrs Chips Teacher Becky Parker is about to lead her pupils to a first: full membership of an international particle physics collaboration. “It’s barmy, isn’t it?” she says. Parker is director of the Langton Star Centre, a research lab she set up at Simon Langton Grammar School in Canterbury, UK. Her pupils have been using semiconductor chips, developed at CERN near Geneva, to measure the characteristics of highly energetic particles. Their chips have already been incorporated into a cosmic-ray detector, which was one of eight scientific payloads that blasted off from Baikonur Cosmodrome in Kazakhstan last month. 36 | NewScientist | 16 August 2014
From 2015, however, they will be monitoring their chips from CERN, as part of the detectors that the MoEDAL (Monopole and Exotics Detector at the LHC) collaboration hopes will capture monopoles (see main story). Katherine Evans, the final-year pupil who headed the student contingent this year, will have moved on by the time the detectors are switched on in 2015, but she is happy to lay the groundwork for future pupils. “It’s nice to think they’ll be the ones to see it,” she says. Parker, meanwhile, is in no doubt of the value of the project. “All the best science is done by the youngest people,” she says. “Why not give them a chance to get stuck in?”
MoEDAL’s detectors are trying to snare a monopole
Or, says Pinfold, we might just find one down a tunnel in Geneva. A narrow, rattly lift just vacated by a technician and his wheelbarrow carries us down 100 or so metres to a cavernous underground hall that is home to one of the giant experiments of the Large Hadron Collider (LHC) – and to Pinfold’s venture. Now is a good time to visit the bowels of the LHC: the accelerator is switched off until early 2015 while it undergoes an upgrade. We climb a series of metal stairways back up from the cavern floor and reach a platform where a thin metal pipe emerges from the middle of a whitewashed door. Next year protons will once again zip along this pipe at 99.9999991 per cent of the speed of light and collide head-on up to 600 million times a second with other protons travelling at the same speed in the opposite direction. The innards of these high-energy protons provide the raw material for the LHC’s investigations of material reality, as all manner of exotic and unfamiliar particles are fleetingly created in the resulting mini fireballs. Pinfold’s experiment is small by LHC standards, and its feel seems to be almost a rebuke of the LHC’s expensive cutting-edge technology. It is called MoEDAL (short for the Monopole and Exotics Detector at the LHC), and its principal component is a series of metal cases attached to the walls around the platform. Neatly outlined in yellow masking tape, each trails a curl of wires to the floor. By the time protons start colliding again,
mission IMPOSSIBLE? The hunt for magnetic monopoles has been far-reaching. Here’s where we have looked and failed to find them:
TRAPPED IN... < Moon rocks from the Apollo 11 mission < Antarctic meteorites < Volcanic rocks
PASSING THROUGH... < Experiments looking for high-energy neutrinos and cosmic rays < Dedicated monopole detectors < Cosmic microwave background radiation
MADE IN...
Richard Webb
< Various particle colliders < Magnetic materials
these cases will entirely surround the crash the LHC are the most energetic ever made in a site. “Mind out,” says Pinfold from beneath particle accelerator, they fall far short of what his hard hat as he invites me to crane my neck is needed to make a monopole if you take the into a pit immediately below the beam pipe. standard model at face value. “If you bang your head there, it’s hard.” But Pinfold’s experiment is far from a Within each of the metal boxes are detectors fool’s errand. Fundamental physics is in consisting of a series of stacked layers of a funk. While the discovery of the Higgs plastic that act as a form of photographic boson slotted the final piece into the jigsaw plate. Because a monopole must carry a huge of the standard model, the theory is clearly magnetic charge, it would rip through the incomplete. It manages to describe polymer bonds of the plastic, etching a trail electromagnetism and the weak and strong whose size, shape and alignment would reveal forces in a broadly satisfying way. Yet it the particle’s character. Once produced, remains silent on the fourth, gravity, and monopoles are expected to be highly stable – so the experimental set-up also includes “If monopoles are light, it trapping detectors in which any passing monopole might be bottled and kept boosts the chances of for further tests: a true exotic from the producing one at the LHC” particle zoo. There is an improvisatory spirit about MoEDAL. Although the powers that be at it doesn’t give any clues as to the identity of CERN gave the go-ahead for the experiment dark matter and dark energy, which seem to in 2010, the 60-strong collaboration must make up 96 per cent of what is out there. raise its own funding. With money from These are far from the only question official sources tight, the team is looking to marks hanging over the standard model, and crowdsource some of it. Meanwhile, part of scepticism about it is further fuelled by that the monitoring of the experiment’s output nagging question of aesthetics. Although its will be done by pupils at a school in the UK predictions, as far as they go, agree peerlessly (see “Hello, Mrs Chips”, left). The uncertainty well with experiments, mathematically about what, if anything, the experiment will the standard model is a bit of a kludge, a see is part of its charm, says Richard Soluk, pasting together of different bits of theory MoEDAL’s technical coordinator. “You don’t with the occasional safety pin and sticking make a breakthrough looking for things plaster to cover the gaps. “It would be very, people expect you to find,” he adds. very surprising if it were the end of things,” Even though the mini fireballs produced at says Polchinski.
Many attempts to improve on the standard model have emerged in recent years. Some of these exotic theories, such as ones that predict the existence of extra dimensions, predict a significantly lighter monopole too, says ’t Hooft. This dramatically boosts the LHC’s chances of producing a monopole and MoEDAL’s chances of bagging one. “Their energy would be much closer to where the LHC or its future descendants can reach, so the prospects look brighter,” adds ’t Hooft. All that means Polchinski is crossing his fingers for an upset. “Any kind of new physics would turn the field upside down,” he says. “For monopoles to be within the reach of the LHC will require us to be lucky, but I think we have to look everywhere.” At the end of a long day, the CERN cafeteria is a good place to muse over monopoles. Stickers by the buttons on the water fountain offer three choices, “Order”, “Chaos” and “Self-destruct”. I opt for a beer instead, and rejoin Pinfold in the bustle of physicists and technicians. He is also a member of the ATLAS collaboration, one of the teams that found the Higgs boson, but it is clear that his heart beats for monopoles – as perhaps do those of many a soul in the yellowing corridors of CERN’s theory department. “All we need is one,” says Pinfold. “Everyone was expecting the Higgs. But no one is expecting this.” n Richard Webb is New Scientist’s deputy features editor 16 August 2014 | NewScientist | 37