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Time cloak conceals chunks of history
earth observatory/nasa
THIS WEEK
The green flip side of carbon emissions Fred Pearce
THE planet is getting lusher, and we are responsible. Carbon dioxide generated by human activity is stimulating photosynthesis and causing a beneficial greening of the Earth’s surface. For the first time, researchers claim to have shown that the increase in plant cover is due to this “CO2 fertilisation effect” rather than other causes. However, it remains unclear whether the effect can counter
Time cloak deletes chunks of history ERASING the past is now easier thanks to the latest “time cloak”, which conceals events instead of objects. The device can’t cloak large-scale events such as a bank robbery but it can hide data flowing through an optical fibre, which could allow secret messages to be sent without a trace. “In a sense we’re erasing this data from history,” says Joseph Lukens at 14 | NewScientist | 8 June 2013
any negative consequences of global warming, such as the spread of deserts. Recent satellite studies have shown that the planet is harbouring more vegetation overall, but pinning down the cause has been difficult. Factors such as higher temperatures, extra rainfall, and an increase in atmospheric CO2 – which helps plants use water more efficiently – could all be boosting vegetation. To home in on the effect of CO2, Randall Donohue of Australia’s
Purdue University in Lafayette, Indiana. Time cloaks work by slowing down light in an optical fibre, creating a gap in the beam. Any outside light that enters the hole becomes cloaked when the original beam is sped up. It’s as if the original beam has been stitched back together like a spliced movie, hiding any record that the extra scene ever happened. Last year researchers at Cornell University in Ithaca, New York, demonstrated the first working time cloak via a gap lasting 40 trillionths of a second. But that could only hide a small blip of information. Now Lukens
lends “strong support” to the idea that CO2 fertilisation drove the greening. Climate change studies have predicted that many dry areas will get drier and that some deserts will expand. Donohue’s findings make this less certain. However, the greening effect may not apply to the world’s driest regions. Beth Newingham of the University of Idaho, Moscow, recently published the result of a 10-year experiment involving a greenhouse set up in the Mojave desert of Nevada. She found “no sustained increase in biomass” –More verdant at the margins– when extra CO2 was pumped into the greenhouse. “You cannot assume that all these deserts national research institute, the respond the same,” she says. CSIRO in Canberra, monitored “Enough water needs to be present vegetation at the edges of deserts for the plants to respond at all.” in Australia, southern Africa, the The extra plant growth could US Southwest, North Africa, the have knock-on effects on climate, Middle East and central Asia. Donohue says, by increasing These are regions where there rainfall, affecting river flows is ample warmth and sunlight, and changing the likelihood of but only just enough rainfall for vegetation to grow, so any change wildfires. It will also absorb more CO2 from the air, potentially in plant cover must be the result damping down global warming of a change in rainfall patterns or but also limiting the CO2 CO2 levels, or both. If CO2 levels were constant, then fertilisation effect itself. the amount of vegetation per unit Donohue cannot yet say to of rainfall ought to be constant, what extent CO2 fertilisation will affect vegetation in the too. However, the team found coming decades. But if it proves that this figure rose by 11 per cent to be significant, the future in these areas between 1982 and may be much greener and more 2010, mirroring the rise in CO2 (Geophysical Research Letters, benevolent than many climate doi.org/mqx). Donohue says this modellers predict. n
and colleagues have created a series of time cloaks in quick succession, allowing much more information to be cloaked. A diffraction grating stretches out a laser beam, producing a series of gaps. Pulses of light sent along the fibre at the same time slot into these. A second grating then closes the holes, hiding the pulses from the intended receiver. There is now no record that the pulses ever
“The ‘time cloak’ can hide up to 1.5 gigabytes per second, enough to cloak real-world data”
traversed the fibre (Nature, DOI: 10.1038/nature12224). This string of cloaks can hide up to 1.5 gigabytes per second. “We’re able to actually cloak real-world data,” says Lukens. That might be useful for securing communications, but only once the data can be uncloaked at the other end to read the message. Until then, the cloaks could be used to block nefarious messages. Paul Kinsler of Imperial College London, who helped dream up the idea of a time cloak in 2010, says a stream of cloaks is an interesting twist on the notion of concealing one event. Jacob Aron n
THIS WEEK
The green flip side of carbon emissions Fred Pearce
THE planet is getting lusher, and we are responsible. Carbon dioxide generated by human activity is stimulating photosynthesis and causing a beneficial greening of the Earth’s surface. For the first time, researchers claim to have shown that the increase in plant cover is due to this “CO2 fertilisation effect” rather than other causes. However, it remains unclear whether the effect can counter
Time cloak deletes chunks of history ERASING the past is now easier thanks to the latest “time cloak”, which conceals events instead of objects. The device can’t cloak large-scale events such as a bank robbery but it can hide data flowing through an optical fibre, which could allow secret messages to be sent without a trace. “In a sense we’re erasing this data from history,” says Joseph Lukens at 14 | NewScientist | 8 June 2013
any negative consequences of global warming, such as the spread of deserts. Recent satellite studies have shown that the planet is harbouring more vegetation overall, but pinning down the cause has been difficult. Factors such as higher temperatures, extra rainfall, and an increase in atmospheric CO2 – which helps plants use water more efficiently – could all be boosting vegetation. To home in on the effect of CO2, Randall Donohue of Australia’s
Purdue University in Lafayette, Indiana. Time cloaks work by slowing down light in an optical fibre, creating a gap in the beam. Any outside light that enters the hole becomes cloaked when the original beam is sped up. It’s as if the original beam has been stitched back together like a spliced movie, hiding any record that the extra scene ever happened. Last year researchers at Cornell University in Ithaca, New York, demonstrated the first working time cloak via a gap lasting 40 trillionths of a second. But that could only hide a small blip of information. Now Lukens
lends “strong support” to the idea that CO2 fertilisation drove the greening. Climate change studies have predicted that many dry areas will get drier and that some deserts will expand. Donohue’s findings make this less certain. However, the greening effect may not apply to the world’s driest regions. Beth Newingham of the University of Idaho, Moscow, recently published the result of a 10-year experiment involving a greenhouse set up in the Mojave desert of Nevada. She found “no sustained increase in biomass” –More verdant at the margins– when extra CO2 was pumped into the greenhouse. “You cannot assume that all these deserts national research institute, the respond the same,” she says. CSIRO in Canberra, monitored “Enough water needs to be present vegetation at the edges of deserts for the plants to respond at all.” in Australia, southern Africa, the The extra plant growth could US Southwest, North Africa, the have knock-on effects on climate, Middle East and central Asia. Donohue says, by increasing These are regions where there rainfall, affecting river flows is ample warmth and sunlight, and changing the likelihood of but only just enough rainfall for vegetation to grow, so any change wildfires. It will also absorb more CO2 from the air, potentially in plant cover must be the result damping down global warming of a change in rainfall patterns or but also limiting the CO2 CO2 levels, or both. If CO2 levels were constant, then fertilisation effect itself. the amount of vegetation per unit Donohue cannot yet say to of rainfall ought to be constant, what extent CO2 fertilisation will affect vegetation in the too. However, the team found coming decades. But if it proves that this figure rose by 11 per cent to be significant, the future in these areas between 1982 and may be much greener and more 2010, mirroring the rise in CO2 (Geophysical Research Letters, benevolent than many climate doi.org/mqx). Donohue says this modellers predict. n
and colleagues have created a series of time cloaks in quick succession, allowing much more information to be cloaked. A diffraction grating stretches out a laser beam, producing a series of gaps. Pulses of light sent along the fibre at the same time slot into these. A second grating then closes the holes, hiding the pulses from the intended receiver. There is now no record that the pulses ever
“The ‘time cloak’ can hide up to 1.5 gigabytes per second, enough to cloak real-world data”
traversed the fibre (Nature, DOI: 10.1038/nature12224). This string of cloaks can hide up to 1.5 gigabytes per second. “We’re able to actually cloak real-world data,” says Lukens. That might be useful for securing communications, but only once the data can be uncloaked at the other end to read the message. Until then, the cloaks could be used to block nefarious messages. Paul Kinsler of Imperial College London, who helped dream up the idea of a time cloak in 2010, says a stream of cloaks is an interesting twist on the notion of concealing one event. Jacob Aron n