A century after Einstein proposed it, scientists may be close to confirming the existence of gravitational waves. Katie Sargent reports
GRAVITATIONAL waves have been detected confirming Albert Einstein’s famous theory of General Relativity, according to scientists at Washington’s National Science Foundation.
The breakthrough, possibly the biggest in physics in a century, could be the key to new understanding of the universe.
The discovery has been made with the use of the Laser Interferometer Gravitational-wave Observatory (LIGO) — a system of two detectors constructed to spot tiny vibrations from passing gravitational waves.
The announcement has electrified the world of physics and astronomy. Scientists say the finding opens a new way of observing the cosmos.
“We discovered gravitational waves from black holes. This is just the beginning, the first of many to come,” said Gabriela Gonzalez, the spokeswoman for the LIGO Scientific Collaboration.
“Now that we know there are binary black holes out there we will begin listening to the universe.”
Are you excited about #gravitationalwaves like @LKrauss1? #showusyourwave – get creative (video or pics) & tag us! pic.twitter.com/T9Td82rsKk
— RiAus (@RiAus) February 11, 2016
The LIGO Scientific Collaboration is comprised of more than 1000 people from over 90 institutions in 15 countries, including Australia.
The Australian Consortium for Interferometric Gravitational Astronomy, Australian National University, Charles Sturt University, Monash University, University of Adelaide, University of Melbourne and the University of Western Australia were involved in the scientific breakthrough.
Some scientists likened the breakthrough to the moment Galileo took up a telescope to look at the planets.
“Until this moment we had our eyes on the sky and we couldn’t hear the music,” said Columbia University astrophysicist Szabolcs Marka, a member of the discovery team. “The skies will never be the same.”
For many years, scientists have had indirect evidence of the existence of gravitational waves rippling across the universe.
In 1974, student Russell Hulse and his supervisor Joseph Taylor calculated that a pair of burnt-out stars spiralling towards one another were radiating gravitational waves at exactly the rate predicted by Einstein. This earned both researchers a Nobel prize around twenty years later.
But now, an all-star international team of astrophysicists using an excruciatingly sensitive, $US1.1 billion instrument have not only detected one of these waves but they have been able to localise the signal.
The signals seen by LIGO Hanford and Livingston! pic.twitter.com/MHDNxG15mO
— Lawrence M. Krauss (@LKrauss1) February 11, 2016
“Not only did we detect gravitional waves, we can localise the signal. It came from the southern sky,” said Gonzalez.
According to Einstein’s theory, published in 1916, the universe is made up of a “fabric of space-time”: massive accelerating objects in the universe are believed to bend this fabric, causing ripples known as gravitational waves. The colliding of two black holes or merging of two pulsars are among the presumable causes of such waves’ formation.
Being able to observe ripples of space-time as they move across our skies could open up a whole new realm of astronomy. We could ‘see’ invisible objects such as black holes and events such as colliding neutron stars, and perhaps peer back to the dawn of time itself.
To make sense of the raw data, the scientists translated the wave into sound. At a news conference, they played what they called a “chirp” — the signal they heard on September 14. It was barely perceptible even when enhanced.
Detecting gravitational waves is so difficult that when Einstein first theorised about them, he figured scientists would never be able to hear them. Einstein later doubted himself and even questioned in the 1930s whether they really do exist, but by the 1960s scientists had concluded they probably do, Ashtekar said. In 1979, the National Science Foundation decided to give money to the California Institute of Technology and the Massachusetts Institute of Technology to come up with a way to detect the waves.
Twenty years later, they started building two LIGO detectors in Hanford, Washington, and Livingston, Louisiana, and they were turned on in 2001. But after years with no luck, scientists realised they had to build a more advanced detection system, which was turned on last September.
“This is truly a scientific moonshot and we did it. We landed on the moon,” said David Reitze, LIGO’s executive director.
EINSTEIN’S INSPIRED IDEA
Einstein’s famous Theory of General Relativity turned our understanding of space and time on its head. He argued that neither is fixed. Instead, they are dependent upon each other — and the state of one changes with the condition of the other.
Space and time for a single object sitting stationary remains static. But put two objects together, and the matter and energy within them interacts to distort space-time — causing the objects to accelerate and spiral towards each other. This acceleration emits gravitational waves. Their behaviour is thought to be similar to that of light and radio waves, except that they move through space and time itself. They ‘warp’ the very fabric of the universe — shrinking and expanding the distance between two points in the same way a flag billows in the wind.
But gravity is also the weakest force. Gravitational waves cause such a tiny wiggle in space-time that Einstein thought they would never be detected.
Einstein inferred the energy of an exploding star — a supernova — would be dissipated by relatively huge gravitational waves rushing outward at the speed of light.
He also calculated that two immensely dense neutron stars orbiting each other very closely would also ripple-out immense energy as gravitational waves.
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But it has long appeared that his idea that the titanic fallout from the collision of two black holes would blast across the cosmos like a rock crashing into a still pond was the most likely to bare fruit.
So what’s the problem with seeing gravitational waves produced by such a colossal collision?
On an intergalactic scale, even the incomprehensible energy of colliding black holes translates to the barest vibration of atoms inside our bodies — or a flutter of photons between two lasers.
One of the most advanced (and expensive) efforts to catch gravitational waves in the act began in 2002: The Laser Interferometer Gravitational-Wave Observatory (LIGO). As the complicated name infers, this experiment has been attempting to measure the infinitesimal vibration of perpendicular laser beams reflected along a 4km vacuum tube in a tunnel.
Two such enormous L-shaped tunnels are positioned some 3000km apart — one on either side of the United States.
The theory goes that any true gravitational wave would cause a ripple in the lasers at both locations. Any nearby slamming doors would therefore be cancelled out.
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