The signal detected with LIGO, an observatory with sites on both sides of the United States, was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics.
The signal detected with LIGO, an observatory with sites on both sides of the United States, was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics. EPA - JULIAN STRATENSCHULTE

Historic first: Scientists finally detect gravity waves

Gravitational ripples in the fabric of spacetime, first predicted by Albert Einstein 100 years ago, have now been detected by scientists who believe the discovery opens new vistas into the "dark" side of the Universe.

Physicists around the world confirmed that they had detected unambiguous signals of gravitational waves emanating from the collision of two massive black holes 1.5 billion light years away in deep space.

As the two black holes spiralled into one another in a violent collision that was over in a second, immense amounts of matter were instantly converted into energy, which sent shock waves travelling through space for 1.5 billion years until they were picked up by gravitational-wave instruments on Earth.

Massachusetts Institute of Technology astrophysics professor Nergis Mavalvala, center, takes questions from members of the media as MIT physics professor Matthew Evans, left, and MIT research scientist Erik Katsavounidis, right, look on during a presentation on the discovery of gravitational waves, Thursday, Feb. 11, 2016, on the school's campus, in Cambridge, Mass.
Massachusetts Institute of Technology astrophysics professor Nergis Mavalvala, center, takes questions from members of the media as MIT physics professor Matthew Evans, left, and MIT research scientist Erik Katsavounidis, right, look on during a presentation on the discovery of gravitational waves, Thursday, Feb. 11, 2016, on the school's campus, in Cambridge, Mass. AP Photo - Steven Senne

The detection of  gravitational waves not only confirms Einstein's general theory of relativity, it amounts to the first direct detection of a pair of colliding black holes, the mysterious structures in space that are so dense they exert a gravitational force from which nothing -not even light - can escape.

One senior British physicist described the breakthrough as the greatest scientific discovery so far this century. It is, he said, bigger than the discovery of the Higgs boson because of its ramifications for our basic understanding of the Universe and the possibility it creates for new ways of observing the hidden regions of space.

Two sets of super-sensitive instruments in two American observatories both detected the same sub-atomic movements in the spacetime continuum - the mathematical model that weaves space and time into a single entity - caused by the gravitational waves as they passed through the Earth.

  The direct detection of gravitational waves will now enable astronomers to see the Universe in a different light, giving them an unprecedented opportunity to observe the "dark" side of the cosmos, almost back to the beginning of time itself.

It will enable scientists to build a network of gravitational-wave observatories both on Earth and in space that can see through billions of light years of the cosmic void. It will give astronomers the ability to witness collisions between black holes and the interactions of massive stellar objects, even providing them with a time-machine to look back almost to the time of the Big Bang 13.7bn years ago when the super-heated Universe began to cool down to form the the first atoms.

"This detection marks not only a confirmation of Einstein's theories but most exciting is that it is marks the birth of gravitational astronomy. This expands hugely the way we can observe the cosmos, and the kinds of physics and astrophysics we can do," said Professor Sheila Rowan, director of the University of Glasgow's Institute for Gravitational Research.

* Filmed before today's announcement

Gravitational waves were first predicted in 1916 as a result of Einstein's general theory of relativity, the most commonly accepted description of gravity, published a year earlier. However, despite decades of searching, gravitational waves remained theoretical as they were too elusive for the most sensitive of gravity-detecting instruments - until now.

Scientists from the US Laser Interferometer Gravitational Wave Observatory (Ligo) confirmed in Washington [today/yesterday] what had been rumour for several weeks. They had witnessed changes in their laser measurements at Ligo's two observatories that could only be due to gravitational waves stretching and contracting space-time as they passed by the Earth.

The observation of the gravitational waves produced by the collision of the two back holes is officially known as GW150914. Scientists said it marks a new era in the scientific exploration of the Universe and the laws of physics that control it.

"The observation of GW150914 marks three milestones for physics: the direct detection of gravitational waves, the first observation of a binary black hole, and the most convincing evidence to-date that nature's black holes are the objects predicted by Einstein's theory," said Professor Alberto Vecchio of the University of Birmingham's School of Physics and Astronomy.

Ed Daw, a physicist at University of Sheffield, said: "A measure of its significance is that even the source of the wave, two black holes in close orbit, each tens of times heavier than the Sun which then collide violently, has never been observed before, and could not have been observed by any other method. This is just the beginning."

* Filmed before today's announcement

If the spacetime continuum is like a taught trampoline, then massive objects are like heavy bowling bowls distorting the trampoline's fabric. When massive objects interact - such as colliding black holes - they send ripples known as gravitational waves travelling at the speed of light through spacetime.

These ripples were too weak and difficult to detect by the previous generation of laser instruments used by Ligo, but an upgrade completed last year made the Advanced Ligo several times more sensitive, enabling it to detect distortions or movements of just one thousandth of the diameter of a sub-atomic proton over a distance of 1 kilometre.

Britain and Germany both contributed key element to the upgrade, and Russian scientists provided critical input. Britain's Science and Technology Facilities Council built the sensitive technology of suspending the instrument's delicate mirrors while Germany provided state-of-the-art laser equipment.

Ligo's 4km-long laser beams has now detected the minute stretching and contraction caused by a passing gravitational wave. It was the definitive proof that the scientist had long been waiting for - they had directly witnessed gravitational waves for the first time, and precisely 100 years after Einstein's general theory had predicted them.

The signal detected with LIGO, an observatory with sites on both sides of the United States, was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics.
The signal detected with LIGO, an observatory with sites on both sides of the United States, was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics. EPA - JULIAN STRATENSCHULTE

Both of Ligo's two observatories, one in Hanford, Washington, and the other in Livingston, Louisiana, detected the same gravitational waves simultaneously which provided the definitive proof the scientists need to confirm the find a statically significant level of "sigma 5" - virtually ruling out a chance effect.

The discovery also confirms the general theory by direct observation, again for the first time since it was published in 1915. Although astronomers had indirectly inferred the existence of gravitational waves in 1974 when they had observed the movements of two stars orbiting one another in a binary pulsar, [today's/yesterday's] announcement seals their existence - and the veracity of the general theory of relativity - with direct proof.

"I began looking for evidence of gravitational waves in 1971, and I've spent my career since then involved in projects aiming to discover experimental proof of their existence," said Professor Jim Hough, associate director of Glasgow's Institute for Gravitational Waves.

"My immediate reaction when we heard about the first detection was a certain amount of delighted surprise, followed by great excitement when it became clear that the evidence was solid….This is the biggest scientific discovery so far this century - even bigger than the Higgs," Professor Hough said.



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