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| 'Update' due on gravitational waves | |
| (about 20 hours later) | |
| An international effort to detect ripples in space itself has scheduled a "status report" for Thursday. | An international effort to detect ripples in space itself has scheduled a "status report" for Thursday. |
| These gravitational waves were first proposed 100 years ago by Albert Einstein, as a key prediction of his Theory of General Relativity. | These gravitational waves were first proposed 100 years ago by Albert Einstein, as a key prediction of his Theory of General Relativity. |
| But in decades of searching they have never been detected, despite several years of operation from two huge laser instruments in the US and one in Italy. | But in decades of searching they have never been detected, despite several years of operation from two huge laser instruments in the US and one in Italy. |
| Teams from the US detectors will speak in Washington DC at 15:30 GMT Thursday. | Teams from the US detectors will speak in Washington DC at 15:30 GMT Thursday. |
| Speculation is rife that they will announce the detection of gravitational waves by both the US instruments, which together make up the Laser Interferometer Gravitational Wave Observatory (Ligo). | Speculation is rife that they will announce the detection of gravitational waves by both the US instruments, which together make up the Laser Interferometer Gravitational Wave Observatory (Ligo). |
| Radiating rumours | Radiating rumours |
| Gravitational waves are concentric ripples that squeeze and stretch the fabric of space-time. They are caused by the movement of mass, but most are so weak that they have no measurable effect. | Gravitational waves are concentric ripples that squeeze and stretch the fabric of space-time. They are caused by the movement of mass, but most are so weak that they have no measurable effect. |
| For current technology to glimpse them, we need to find the waves - still incredibly subtle - that are radiating across the cosmos from extremely violent events, like explosions or collisions involving stars or black holes. | For current technology to glimpse them, we need to find the waves - still incredibly subtle - that are radiating across the cosmos from extremely violent events, like explosions or collisions involving stars or black holes. |
| At each Ligo detector, a laser beam is split in two and sent down identical, perpendicular 4km tunnels - then reflected back again. The two arms work like rulers, at right angles, made of light. | At each Ligo detector, a laser beam is split in two and sent down identical, perpendicular 4km tunnels - then reflected back again. The two arms work like rulers, at right angles, made of light. |
| If a gravitational wave throbs past, light in one of those beams will travel further than light in the other - by a tiny, tiny fraction of the width of an atom. | If a gravitational wave throbs past, light in one of those beams will travel further than light in the other - by a tiny, tiny fraction of the width of an atom. |
| Ligo's two stations are 3,000km apart in the states of Louisiana and Washington - allowing them to compare notes on the timing and apparent direction of any such disturbance. | Ligo's two stations are 3,000km apart in the states of Louisiana and Washington - allowing them to compare notes on the timing and apparent direction of any such disturbance. |
| Rumours have been circulating for weeks that both instruments had indeed picked up a signal, and that researchers were working on a paper about the discovery. | Rumours have been circulating for weeks that both instruments had indeed picked up a signal, and that researchers were working on a paper about the discovery. |
| It was only in September 2015 that these detectors went back into operation, after a $200m upgrade that saw the facility redubbed Advanced Ligo and dramatically boosted its sensitivity. | It was only in September 2015 that these detectors went back into operation, after a $200m upgrade that saw the facility redubbed Advanced Ligo and dramatically boosted its sensitivity. |
| Its first run, from 2002-2010, had drawn a blank. | Its first run, from 2002-2010, had drawn a blank. |
| Similarly, the Virgo instrument in Italy - built according to the same design - closed in 2011 after an empty-handed four years of "listening". | Similarly, the Virgo instrument in Italy - built according to the same design - closed in 2011 after an empty-handed four years of "listening". |
| That project's next incarnation, Advanced Virgo, is due to start work later in 2016. | That project's next incarnation, Advanced Virgo, is due to start work later in 2016. |
| If detection of these waves is now a reality, we are at the beginning of a new era in astronomy - especially once three detectors are online, allowing the source of the ripples to be triangulated. | If detection of these waves is now a reality, we are at the beginning of a new era in astronomy - especially once three detectors are online, allowing the source of the ripples to be triangulated. |
| Gravitational waves will join the myriad types of light, plus some particles like neutrinos, that scientists already use to probe the far reaches of the universe. | Gravitational waves will join the myriad types of light, plus some particles like neutrinos, that scientists already use to probe the far reaches of the universe. |
| Crucially, because they travel straight through matter, nothing can obscure the source of these waves - there are no shadows. And they could offer an unparalleled "view" of objects that don't emit light, like black holes. | Crucially, because they travel straight through matter, nothing can obscure the source of these waves - there are no shadows. And they could offer an unparalleled "view" of objects that don't emit light, like black holes. |
| This is why gravitational astronomy has been described as listening to, rather than looking at, the cosmos. | This is why gravitational astronomy has been described as listening to, rather than looking at, the cosmos. |
| Tuck Stebbins, from Nasa's Goddard Space Flight Center, told the AFP news agency that gravitational waves could even be a window - in fact, the only possible window - on the origin of the universe. | Tuck Stebbins, from Nasa's Goddard Space Flight Center, told the AFP news agency that gravitational waves could even be a window - in fact, the only possible window - on the origin of the universe. |
| "These waves are streaming to you all the time and if you could see them, you could see back to the first one trillionth of a second of the Big Bang," he said. | "These waves are streaming to you all the time and if you could see them, you could see back to the first one trillionth of a second of the Big Bang," he said. |
| Ripples in the fabric of space-time | Ripples in the fabric of space-time |