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This week 50 years ago
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This week– universe expands. Anything beyond this horizon is hidden because light from there has not had enough time to travel to us. The team calculated the energy generated when entangled particles are wrenched apart by this “event horizon”, and found that it matches the amount needed to explain the acceleration of the universe. “Dark energy is energy observed inside the spherical cosmological horizon,” says Lee (Journal of Cosmology and Astroparticle Physics, DOI: 10.1088/14757516/2007/08/005). Tomislav Prokopec, a –An eventful horizon– cosmologist at Utrecht University in the Netherlands, finds the idea appealing. “They’ve come up with an interesting physical mechanism for how [virtual particles] could lead to dark energy,” he notes. But he also points out that Lee’s model depends closely on the highest energy associated with the virtual particles that contribute to dark these virtual particles are ripped energy. “They have chosen a very apart from each other by the reasonable value for this, but if it expanding edge of our universe. According to quantum theory, turns out that this value is slightly even the perfect vacuum of space wrong, it could throw off all their predictions,” he says. isn’t empty: it is a sea of virtual Seth Lloyd, an expert on particles, created as entangled pairs of particles and antiparticles which exist only fleetingly and “Just as a black hole has an then annihilate each other. event horizon, our observable Calculations also show that funny things can happen to these universe has a boundary known as the ‘cosmological horizon’ ” entangled virtual particles when they are near a black hole’s event entanglement at the horizon – the boundary beyond Massachusetts Institute of which light cannot escape. If one Technology, is also impressed. member of a virtual pair crosses “I think they could really be onto the event horizon before it can something,” he says. Now he recombine, its partner will be would like to know whether the converted to a real particle. So model’s predictions match from the outside, the black hole would appear to radiate particles, detailed dark-energy measurements. a phenomenon known as That could soon be possible. Hawking radiation. Lee and his team are using their Lee’s team don’t seriously model to predict how dark energy suggest that we live inside a black hole, but say that the portion of the might affect imprints on the universe that we can observe can be cosmic microwave background. thought of in a similar way. Just as a This will be measured by the black hole has an event horizon, our Planck satellite, due to launch observable universe has a boundary next year. “Our model could be easily verified or ruled out soon,” known as the “cosmological Lee says. ● horizon”, which moves as the
Black hole universe makes dark energy ZEEYA MERALI
IMAGINE that we live inside a black hole. That could be the key to understanding the origin of dark energy, the mysterious force widely thought to be causing the expansion of the universe to accelerate. Some physicists have previously suggested that dark energy could arise from the quantum bubbling of virtual particles in empty space, but it wasn’t clear how. Now Jae-Weon Lee at the Korea Institute for Advanced Study in Seoul and his colleagues are proposing that dark energy is created as pairs of
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16 | NewScientist | 6 October 2007
THIS WEEK 50 YEARS AGO The space age begins At 15 minutes past midnight last Saturday morning, engineers at the BBC began checking for signals transmitted to Earth by the world’s first artificial satellite, called Sputnik. Every 90 minutes the signals came in on frequencies of 20,005 and 40,002 kilocycles as the satellite swung round the Earth in an elliptical polar orbit at speeds reaching 18,000 miles per hour. This is a great technical victory not only for the Russian engineers who built and launched this first of many satellites but for scientists the world over who have been predicting their characteristics and behaviour for several years – in the face of considerable scepticism – with what now turns out to be uncanny accuracy. To place a satellite in orbit requires a razor’s-edge balance between the speed of the satellite and the pull of gravity. Too fast and the satellite shoots into space, too slow and gravity pulls it to Earth. No one could know the exact nature of these forces until instruments had been carried into space. So it is a remarkable tribute to the accuracy of the scientists’ work that on our first step into outer space the vehicle should be travelling with all the predictability of a tram. This is, of course, only the first step. The Russian satellite fitted with radio transmitters – as the first American satellites will be – is a tram without passengers. Although the need to conserve their batteries means they may only transmit as they pass over their home receivers, the true purpose of satellites is to serve as a platform in space for instruments telemetering information down to Earth. This has yet to be achieved. All the same, while the satellite programme is not the most important part of this International Geophysical Year, it will stand as a landmark in progress long after the rest of the year has been forgotten. From The New Scientist, 10 October 1957
www.newscientist.com
This week– universe expands. Anything beyond this horizon is hidden because light from there has not had enough time to travel to us. The team calculated the energy generated when entangled particles are wrenched apart by this “event horizon”, and found that it matches the amount needed to explain the acceleration of the universe. “Dark energy is energy observed inside the spherical cosmological horizon,” says Lee (Journal of Cosmology and Astroparticle Physics, DOI: 10.1088/14757516/2007/08/005). Tomislav Prokopec, a –An eventful horizon– cosmologist at Utrecht University in the Netherlands, finds the idea appealing. “They’ve come up with an interesting physical mechanism for how [virtual particles] could lead to dark energy,” he notes. But he also points out that Lee’s model depends closely on the highest energy associated with the virtual particles that contribute to dark these virtual particles are ripped energy. “They have chosen a very apart from each other by the reasonable value for this, but if it expanding edge of our universe. According to quantum theory, turns out that this value is slightly even the perfect vacuum of space wrong, it could throw off all their predictions,” he says. isn’t empty: it is a sea of virtual Seth Lloyd, an expert on particles, created as entangled pairs of particles and antiparticles which exist only fleetingly and “Just as a black hole has an then annihilate each other. event horizon, our observable Calculations also show that funny things can happen to these universe has a boundary known as the ‘cosmological horizon’ ” entangled virtual particles when they are near a black hole’s event entanglement at the horizon – the boundary beyond Massachusetts Institute of which light cannot escape. If one Technology, is also impressed. member of a virtual pair crosses “I think they could really be onto the event horizon before it can something,” he says. Now he recombine, its partner will be would like to know whether the converted to a real particle. So model’s predictions match from the outside, the black hole would appear to radiate particles, detailed dark-energy measurements. a phenomenon known as That could soon be possible. Hawking radiation. Lee and his team are using their Lee’s team don’t seriously model to predict how dark energy suggest that we live inside a black hole, but say that the portion of the might affect imprints on the universe that we can observe can be cosmic microwave background. thought of in a similar way. Just as a This will be measured by the black hole has an event horizon, our Planck satellite, due to launch observable universe has a boundary next year. “Our model could be easily verified or ruled out soon,” known as the “cosmological Lee says. ● horizon”, which moves as the
Black hole universe makes dark energy ZEEYA MERALI
IMAGINE that we live inside a black hole. That could be the key to understanding the origin of dark energy, the mysterious force widely thought to be causing the expansion of the universe to accelerate. Some physicists have previously suggested that dark energy could arise from the quantum bubbling of virtual particles in empty space, but it wasn’t clear how. Now Jae-Weon Lee at the Korea Institute for Advanced Study in Seoul and his colleagues are proposing that dark energy is created as pairs of
NEW VERSION JUST RELEASED!
The essential tool for writing your research papers
www.endnote.co.uk T: 01462 480055 E: [email protected]
16 | NewScientist | 6 October 2007
THIS WEEK 50 YEARS AGO The space age begins At 15 minutes past midnight last Saturday morning, engineers at the BBC began checking for signals transmitted to Earth by the world’s first artificial satellite, called Sputnik. Every 90 minutes the signals came in on frequencies of 20,005 and 40,002 kilocycles as the satellite swung round the Earth in an elliptical polar orbit at speeds reaching 18,000 miles per hour. This is a great technical victory not only for the Russian engineers who built and launched this first of many satellites but for scientists the world over who have been predicting their characteristics and behaviour for several years – in the face of considerable scepticism – with what now turns out to be uncanny accuracy. To place a satellite in orbit requires a razor’s-edge balance between the speed of the satellite and the pull of gravity. Too fast and the satellite shoots into space, too slow and gravity pulls it to Earth. No one could know the exact nature of these forces until instruments had been carried into space. So it is a remarkable tribute to the accuracy of the scientists’ work that on our first step into outer space the vehicle should be travelling with all the predictability of a tram. This is, of course, only the first step. The Russian satellite fitted with radio transmitters – as the first American satellites will be – is a tram without passengers. Although the need to conserve their batteries means they may only transmit as they pass over their home receivers, the true purpose of satellites is to serve as a platform in space for instruments telemetering information down to Earth. This has yet to be achieved. All the same, while the satellite programme is not the most important part of this International Geophysical Year, it will stand as a landmark in progress long after the rest of the year has been forgotten. From The New Scientist, 10 October 1957
www.newscientist.com