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On the front line
In this section n Species doomed to extinction by conflict in Libya and Syria, page 11 n We gave Neanderthals our genes, too, page 12 n Shocking alternative to Viagra, page 14
Caltech/Ligo
be combined to help understand the nature of dark energy, which is causing the universe’s expansion to accelerate. From the “shape” of the signal – how the waves’ frequency and volume rise and fall – we can discern the sizes of the black holes involved, and determine how loud the event was at its source. Comparing how powerful it really was to the faint vibrations LIGO detected tells us how far away it occurred. Combined with observations from standard telescopes, this can tell us how space has expanded during the time the waves took to reach us, providing a measure of dark energy’s effect on space. This measure should be stronger and more reliable than anything we have used so far. Spotting just a few black hole mergers would change everything, Loeb says. “If you have tens of them, it will be a new branch in cosmology.” Other researchers are hoping to use gravitational wave signals to put Einstein’s general theory of relativity to even more stringent tests. One way is through the equivalence principle, an assumption that gravity affects all masses in the same way. “In the age of GPS and space travel, where even minute deviations from the assumed theory of gravity would have major consequences, it is of enormous importance,” says
Xue-Feng Wu of Purple Mountain Observatory in Nanjing, China. Erminia Calabrese, an astronomer at the University of Oxford, sees gravitational waves as a way to check whether gravity behaves as relativity predicts it should over large distances. “If their strength fell off with distance in a surprising way we could detect this with the upcoming LIGO data,” she says.
a huge, space-based detector. A preparatory experiment, LISA Pathfinder, is in orbit and will begin tests next month. NASA pulled out of the project in 2011, but has now formed a committee to look into how it might rejoin. Further ahead, we might see more sensitive gravitational wave detectors, working at shorter wavelengths than LIGO. These may allow us to sense primordial gravitational waves from the very More detectors young universe. These waves LIGO’s success could see an should have been produced in explosion in gravitational wave the period of inflation – the detection. India, for example, tremendous growth spurt in has long been slated to host a the first instants after the big third LIGO detector. Funding bang. Unlike photons and other has yet to materialise, but after electromagnetic radiation, they last Thursday’s announcement, would have travelled freely Indian prime minister Narendra through the newborn universe. Modi tweeted that he hopes At the moment we can only see “to move forward to make as far back as 380,000 years after even bigger contribution with the big bang, when the universe an advanced gravitational wave became transparent to light. detector in the country”. Gravitational waves may even Other types of detectors point the way toward a grand could come on the scene, too. unified theory of the universe. “Now that we know gravitational Theory suggests that at some waves exist, it will be much easier point in the universe’s history, to convince people to invest all four fundamental forces were money and make all kinds of united into a single force. As the gravitational wave detectors,” universe expanded and cooled, Stojkovic says. the forces split off from one New designs are already in the another in a series of as-yet poorly pipeline. The European Space understood events. “Gravitational Agency is about to start tests of wave observatories that can detect equipment for the Evolved Laser much shorter wavelengths could Interferometer Antenna (eLISA), probe those,” Stojkovic says. For now, physicists already have a mystery to solve: a faint gammaray burst that seems to be related to LIGO’s signal. No one expected merging black holes to give off gamma rays. “Everything lines up except the physics,” says Valerie Connaughton of NASA’s Marshall Spaceflight Center. LIGO team member Daniel Holz at the University of Chicago reckons this surprise is just the beginning. “Every time we’ve opened a window to the universe, we’ve found all sorts of unexpected things,” Holz says. “I’d be surprised if I wasn’t –LIGO has a big reach– surprised.” n
on the front line
“It’s hard to describe; after years of dreaming about this, writing all these papers saying, ‘Maybe we could even see two big black holes collide, it would be phenomenal!’ And here it is.” Daniel Holz, LIGO team member
“It’s been a very long road, but this is just the beginning. Now that we have detectors able to detect these systems, now that we know that binary black holes are out there, we can begin listening to the universe.” Gabriela Gonzalez, LIGO spokesperson, at the press conference on 11 February
“What we’ve learned today: LIGO works, black holes exist, black holes collide, new black holes are born, general relativity works. Need I keep going?” Nergis Mavalvala, LIGO team member, at the press conference on 11 February
“The era of gravitational wave astronomy is under way.” Avi Loeb of Harvard University
“This is truly marvellous! It opens a whole new window onto observing the universe, as well as further confirming Einstein’s general theory of relativity.” Russell Hulse, co-recipient of the 1993 Nobel prize in physics for indirect evidence of gravitational waves
“It’s a fabulous discovery. It will be a rich source of information.” Alan Guth at MIT, one of the authors of the theory of inflation
20 February 2016 | NewScientist | 9
Caltech/Ligo
be combined to help understand the nature of dark energy, which is causing the universe’s expansion to accelerate. From the “shape” of the signal – how the waves’ frequency and volume rise and fall – we can discern the sizes of the black holes involved, and determine how loud the event was at its source. Comparing how powerful it really was to the faint vibrations LIGO detected tells us how far away it occurred. Combined with observations from standard telescopes, this can tell us how space has expanded during the time the waves took to reach us, providing a measure of dark energy’s effect on space. This measure should be stronger and more reliable than anything we have used so far. Spotting just a few black hole mergers would change everything, Loeb says. “If you have tens of them, it will be a new branch in cosmology.” Other researchers are hoping to use gravitational wave signals to put Einstein’s general theory of relativity to even more stringent tests. One way is through the equivalence principle, an assumption that gravity affects all masses in the same way. “In the age of GPS and space travel, where even minute deviations from the assumed theory of gravity would have major consequences, it is of enormous importance,” says
Xue-Feng Wu of Purple Mountain Observatory in Nanjing, China. Erminia Calabrese, an astronomer at the University of Oxford, sees gravitational waves as a way to check whether gravity behaves as relativity predicts it should over large distances. “If their strength fell off with distance in a surprising way we could detect this with the upcoming LIGO data,” she says.
a huge, space-based detector. A preparatory experiment, LISA Pathfinder, is in orbit and will begin tests next month. NASA pulled out of the project in 2011, but has now formed a committee to look into how it might rejoin. Further ahead, we might see more sensitive gravitational wave detectors, working at shorter wavelengths than LIGO. These may allow us to sense primordial gravitational waves from the very More detectors young universe. These waves LIGO’s success could see an should have been produced in explosion in gravitational wave the period of inflation – the detection. India, for example, tremendous growth spurt in has long been slated to host a the first instants after the big third LIGO detector. Funding bang. Unlike photons and other has yet to materialise, but after electromagnetic radiation, they last Thursday’s announcement, would have travelled freely Indian prime minister Narendra through the newborn universe. Modi tweeted that he hopes At the moment we can only see “to move forward to make as far back as 380,000 years after even bigger contribution with the big bang, when the universe an advanced gravitational wave became transparent to light. detector in the country”. Gravitational waves may even Other types of detectors point the way toward a grand could come on the scene, too. unified theory of the universe. “Now that we know gravitational Theory suggests that at some waves exist, it will be much easier point in the universe’s history, to convince people to invest all four fundamental forces were money and make all kinds of united into a single force. As the gravitational wave detectors,” universe expanded and cooled, Stojkovic says. the forces split off from one New designs are already in the another in a series of as-yet poorly pipeline. The European Space understood events. “Gravitational Agency is about to start tests of wave observatories that can detect equipment for the Evolved Laser much shorter wavelengths could Interferometer Antenna (eLISA), probe those,” Stojkovic says. For now, physicists already have a mystery to solve: a faint gammaray burst that seems to be related to LIGO’s signal. No one expected merging black holes to give off gamma rays. “Everything lines up except the physics,” says Valerie Connaughton of NASA’s Marshall Spaceflight Center. LIGO team member Daniel Holz at the University of Chicago reckons this surprise is just the beginning. “Every time we’ve opened a window to the universe, we’ve found all sorts of unexpected things,” Holz says. “I’d be surprised if I wasn’t –LIGO has a big reach– surprised.” n
on the front line
“It’s hard to describe; after years of dreaming about this, writing all these papers saying, ‘Maybe we could even see two big black holes collide, it would be phenomenal!’ And here it is.” Daniel Holz, LIGO team member
“It’s been a very long road, but this is just the beginning. Now that we have detectors able to detect these systems, now that we know that binary black holes are out there, we can begin listening to the universe.” Gabriela Gonzalez, LIGO spokesperson, at the press conference on 11 February
“What we’ve learned today: LIGO works, black holes exist, black holes collide, new black holes are born, general relativity works. Need I keep going?” Nergis Mavalvala, LIGO team member, at the press conference on 11 February
“The era of gravitational wave astronomy is under way.” Avi Loeb of Harvard University
“This is truly marvellous! It opens a whole new window onto observing the universe, as well as further confirming Einstein’s general theory of relativity.” Russell Hulse, co-recipient of the 1993 Nobel prize in physics for indirect evidence of gravitational waves
“It’s a fabulous discovery. It will be a rich source of information.” Alan Guth at MIT, one of the authors of the theory of inflation
20 February 2016 | NewScientist | 9