Gravitational waves detected, providing the final piece of the puzzle for general relativity

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Two black holes colliding far out in space have produced gravity waves that have been detected by super-sensitive equipment on Earth for the very first time(Credit: Caltech)

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An international team of scientists today announced what could be the biggest breakthrough in physics in a hundred years. Specifically, they claim to have at last detected gravitational waves, the enigmatic and elusive ripples in the fabric of spacetime that Albert Einstein first predicted in 1916, in his theory of general relativity.

Reported today by the Advanced Laser Interferometer Gravitational-Wave Observatory (Advanced LIGO) team, astronomers say the detection of gravitational waves reveals an entirely new way to observe the universe, revealing distant events that aren't able to be observed using optical telescopes, but whose faint tremors can be felt across the cosmos.

"This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality," said Gabriela González, LSC spokesperson and professor of physics and astronomy at Louisiana State University.

First detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC), the gravitational waves were recorded by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington.

The event detected was the arrival of gravitational waves on Earth produced by two massive black holes colliding around 1.3 billion years ago. In the collision, some three times the mass of our sun was turned into gravitational waves in microseconds creating a power output at the height of the collision about 50 times that of the entire visible universe.

The LIGO device reflected laser beams repeatedly along two L-shaped detectors in its 4-km (2.5-mile)-long arms onto mirrors equipped with exceptionally sensitive movement sensors, to search for coincident expansions and contractions caused by gravitational waves as they passed by the Earth. As a result of the black holes colliding, the scientists measured minuscule changes in the length of the arms, as tiny as one thousandth the width of a proton.

A previously impossibly small perturbation to measure, LIGO has finally achieved its purpose some 50 years after it was originally proposed as a possible means of detecting gravitational waves by scientists from Caltech and MIT.

"Our observation of gravitational waves accomplishes an ambitious goal set out over five decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein's legacy on the 100th anniversary of his general theory of relativity," said Caltech's David H. Reitze, executive director of the LIGO Laboratory.

When Einstein's theory of general relativity turned Newton's understanding of gravity on its head by showing that matter and time were inextricably linked, the theory of space-time was born and the four-dimensional structure of the universe in which matter, energy and gravity are all interlinked elements of that structure, gravitational waves became an inevitable conclusion from this theory.


Undetectable in Einstein's time, these tiny ripples in the fabric of space-time are so weak that it took the eventual production of the most sensitive detectors ever made and the incredible force of two black holes crashing into each other to make their presence known.

"The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation," said Rainer Weiss, Emeritus Professor at MIT, and one of the original proponents of gravitational wave detection. "It would have been wonderful to watch Einstein's face had we been able to tell him."

LIGO research is performed by the LIGO Scientific Collaboration (LSC), a collective of more than 1,000 scientists from universities around the United States and 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data, and around 250 students are contributing members to the collaboration.

Source: Caltech

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