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Gravity's bias for left may be writ in the sky
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How to predict when a dictatorship is ready to fall NO ONE saw it coming. Three months ago the rulers of Tunisia and Egypt, Libya and Bahrain seemed firmly in control. Dissent of any kind, let alone revolutionary change, was nowhere on the horizon. Now it’s anybody’s guess which country will be next. This is not unusual. The US military tries to predict political instability, and the results, while secret, have apparently been poor. “We have never once gotten it right,” Robert Gates, US Secretary of Defense, said last week. Scientists who study mathematically complex systems claim we can do better. They are planning to study recent events to devise better ways to predict a fall. Complex systems with many interrelated variables, such as ecosystems or societies, can accumulate stresses while showing no obvious change – until they reach a point where a small stress can trigger a sudden shift to another stable state. For example, forests accumulate kindling until a spark ignites a fire. According to Yaneer Bar-Yam, who
Gravity’s bias for left may be writ in the sky IS GRAVITY left-handed? An answer could provide a clue to a long-sought theory of quantum gravity – and might be within our grasp by 2013. General relativity describes gravity’s actions at large scales. For tiny scales however, a theory of quantum gravity, incorporating quantum mechanics, is needed. But first physicists need to understand gravitons, hypothetical quantum particles that mediate the gravitational force. These likely come in left and right-handed varieties: in the former, the particle’s spin would 10 | NewScientist | 5 March 2011
heads the New England Complex Systems Institute in Cambridge, Massachusetts, the stresses of poverty, unemployment and an absence of government accountability built up in Middle Eastern countries with a large “youth bulge” of young adults without jobs, children or prospects. Then spiking food prices and the public suicide of one young Tunisian triggered revolution. The key to predicting regime shifts,
be aligned with the direction of its motion; in the latter, the spin would be the opposite. General relativity does not distinguish between right and left, so you might expect gravity to be transmitted by both varieties. But the quantum world may play favourites. When it comes to the ghostly particles known as neutrinos, for example, the weak force only interacts with the left-handed variety. To find out whether gravitons fall into the “ambidextrous” camp of general relativity or exhibit quantum asymmetry much like a neutrino, João Magueijo and Dionigi Benincasa of Imperial College London suggest looking to the cosmic microwave background, relic radiation from the big bang. During inflation, the faster-
says Marten Scheffer of the University of Wageningen in the Netherlands, is to look beyond individual behaviour to seek simple laws that describe a population’s collective behaviour. Bar-Yam has previously used mathematical models to predict violence between ethnic groups. Though the system’s mathematics was complex, it yielded a simple result: ethnic violence flares when enclaves are a certain size. This successfully modelled 90 per cent of recent ethnic Hidden instability left Tunisia ripe for revolution
than-light expansion of the nascent universe, powerful gravitational waves may have rippled through space-time, polarising the CMB’s photons in a telltale pattern. The pair calculate that if gravity depended on just left or right-handed gravitons, that would have skewed
“Are gravitons ambidextrous as per general relativity or do they exhibit quantum asymmetry like neutrinos?” the polarisation pattern in an obvious way. What’s more, inflation would have stretched these effects to astronomical proportions, making them easily visible to astronomers, write Magueijo and Benincasa in an analysis to appear in Physical Review
conflicts in India, Kenya, central Asia and former Yugoslavia (Science, DOI: 10:1126/science.1142734). With the right data we can model other social changes, he says – though good social data may be hard to find. Scheffer, however, believes such data may not be necessary. “All complex systems exhibit certain symptoms before a regime shift,” he says, including slower responses to small changes, and a tendency for all players to behave similarly. Bar-Yam has found this behaviour pattern in the lead-up to market crashes. Scheffer is launching research to look for such symptoms in social systems, including the Middle East. In the past, Scheffer says, analysts focused on the trigger that sparks change, rather than the underlying system. “We cannot predict the spark,” he says, “but we can say when a forest has accumulated dangerous levels of kindling.” Repressing revolution is not the way to achieve stability, he adds. It would be like preventing small forest fires, allowing kindling to accumulate until a big fire breaks out. But uncovering the symptoms of instability may warn societies to reform themselves before revolution happens. Debora MacKenzie n
Letters. The European Space Agency’s Planck telescope will image the CMB’s polarisation and will release the data in 2013. A theory called loop quantum gravity, an attempt to unite quantum mechanics and general relativity, already suggests that an asymmetry might be embedded deep into the laws of the universe and that this should render gravity left-handed. Evidence of left-handed gravitons in the CMB would be “a triple discovery”, says Lee Smolin of the Perimeter Institute in Waterloo, Ontario, Canada, who has worked with Magueijo and Benincasa on the subject. “It would confirm inflation, that gravity is quantum mechanical and that there is left-right asymmetry in quantum gravity.” Amanda Gefter n
FETHI BELAID/AFP/Getty Images
Insight
How to predict when a dictatorship is ready to fall NO ONE saw it coming. Three months ago the rulers of Tunisia and Egypt, Libya and Bahrain seemed firmly in control. Dissent of any kind, let alone revolutionary change, was nowhere on the horizon. Now it’s anybody’s guess which country will be next. This is not unusual. The US military tries to predict political instability, and the results, while secret, have apparently been poor. “We have never once gotten it right,” Robert Gates, US Secretary of Defense, said last week. Scientists who study mathematically complex systems claim we can do better. They are planning to study recent events to devise better ways to predict a fall. Complex systems with many interrelated variables, such as ecosystems or societies, can accumulate stresses while showing no obvious change – until they reach a point where a small stress can trigger a sudden shift to another stable state. For example, forests accumulate kindling until a spark ignites a fire. According to Yaneer Bar-Yam, who
Gravity’s bias for left may be writ in the sky IS GRAVITY left-handed? An answer could provide a clue to a long-sought theory of quantum gravity – and might be within our grasp by 2013. General relativity describes gravity’s actions at large scales. For tiny scales however, a theory of quantum gravity, incorporating quantum mechanics, is needed. But first physicists need to understand gravitons, hypothetical quantum particles that mediate the gravitational force. These likely come in left and right-handed varieties: in the former, the particle’s spin would 10 | NewScientist | 5 March 2011
heads the New England Complex Systems Institute in Cambridge, Massachusetts, the stresses of poverty, unemployment and an absence of government accountability built up in Middle Eastern countries with a large “youth bulge” of young adults without jobs, children or prospects. Then spiking food prices and the public suicide of one young Tunisian triggered revolution. The key to predicting regime shifts,
be aligned with the direction of its motion; in the latter, the spin would be the opposite. General relativity does not distinguish between right and left, so you might expect gravity to be transmitted by both varieties. But the quantum world may play favourites. When it comes to the ghostly particles known as neutrinos, for example, the weak force only interacts with the left-handed variety. To find out whether gravitons fall into the “ambidextrous” camp of general relativity or exhibit quantum asymmetry much like a neutrino, João Magueijo and Dionigi Benincasa of Imperial College London suggest looking to the cosmic microwave background, relic radiation from the big bang. During inflation, the faster-
says Marten Scheffer of the University of Wageningen in the Netherlands, is to look beyond individual behaviour to seek simple laws that describe a population’s collective behaviour. Bar-Yam has previously used mathematical models to predict violence between ethnic groups. Though the system’s mathematics was complex, it yielded a simple result: ethnic violence flares when enclaves are a certain size. This successfully modelled 90 per cent of recent ethnic Hidden instability left Tunisia ripe for revolution
than-light expansion of the nascent universe, powerful gravitational waves may have rippled through space-time, polarising the CMB’s photons in a telltale pattern. The pair calculate that if gravity depended on just left or right-handed gravitons, that would have skewed
“Are gravitons ambidextrous as per general relativity or do they exhibit quantum asymmetry like neutrinos?” the polarisation pattern in an obvious way. What’s more, inflation would have stretched these effects to astronomical proportions, making them easily visible to astronomers, write Magueijo and Benincasa in an analysis to appear in Physical Review
conflicts in India, Kenya, central Asia and former Yugoslavia (Science, DOI: 10:1126/science.1142734). With the right data we can model other social changes, he says – though good social data may be hard to find. Scheffer, however, believes such data may not be necessary. “All complex systems exhibit certain symptoms before a regime shift,” he says, including slower responses to small changes, and a tendency for all players to behave similarly. Bar-Yam has found this behaviour pattern in the lead-up to market crashes. Scheffer is launching research to look for such symptoms in social systems, including the Middle East. In the past, Scheffer says, analysts focused on the trigger that sparks change, rather than the underlying system. “We cannot predict the spark,” he says, “but we can say when a forest has accumulated dangerous levels of kindling.” Repressing revolution is not the way to achieve stability, he adds. It would be like preventing small forest fires, allowing kindling to accumulate until a big fire breaks out. But uncovering the symptoms of instability may warn societies to reform themselves before revolution happens. Debora MacKenzie n
Letters. The European Space Agency’s Planck telescope will image the CMB’s polarisation and will release the data in 2013. A theory called loop quantum gravity, an attempt to unite quantum mechanics and general relativity, already suggests that an asymmetry might be embedded deep into the laws of the universe and that this should render gravity left-handed. Evidence of left-handed gravitons in the CMB would be “a triple discovery”, says Lee Smolin of the Perimeter Institute in Waterloo, Ontario, Canada, who has worked with Magueijo and Benincasa on the subject. “It would confirm inflation, that gravity is quantum mechanical and that there is left-right asymmetry in quantum gravity.” Amanda Gefter n
FETHI BELAID/AFP/Getty Images
Insight