Just over 100 years after he published his
general theory of relativity, scientists have found what Albert
Einstein predicted as part of the theory: gravitational waves.
"We have detected gravitational waves. We did it," said David Reitze, executive director of
LIGO, the Laser Interferometer Gravitational-Wave Observatory, which was created to do just what Reitze announced.
Reitze
made the announcement Thursday at the National Press Club in Washington
surrounded by other LIGO researchers and National Science Foundation
head France Cordova.
The gravitational
waves -- ripples in space-time -- were created by the merging of two
black holes, Reitze said. One black hole had the mass of 29 suns; the
other was the equivalent of 36 suns. Each was perhaps 50 kilometers (30
miles) in diameter.
More
than a billion years ago -- LIGO estimates about 1.3 billion -- the two
collided at half the speed of light. Gravitational waves pass through
everything, so the result traveled through the universe for that time
before reaching Earth.
The 'chirp' of black holes colliding
The gravitational waves stretched and compressed space around Earth "like Jell-O," said Reitze.
However,
the waves are so small that it takes a detector like LIGO, capable of
measuring distortions one-thousandth the size of a proton, to observe
them. They were observed on September 14, 2015.
Scientists
heard the sound of the black holes colliding as a "chirp" lasting
one-fifth of a second. Though gravitational waves aren't sound waves,
the increase in frequency the collision exhibited in its last
milliseconds -- when the black holes were mere kilometers apart and
growing closer -- is a frequency we can hear, said Deirdre Shoemaker, a
Georgia Tech physicist who works on LIGO.
LIGO
is described as "a system of two identical detectors" -- one located in
Livingston, Louisiana, the other in Hanford, Washington -- "carefully
constructed to detect incredibly tiny vibrations from passing
gravitational waves." The project was created by scientists from Caltech
and MIT and funded by the National Science Foundation.
Szabolcs
Marka, a physicist at Columbia University who is leader of the LIGO
member Columbia Experimental Gravity Group, said you could think of it
as "a cosmic microphone."
Einstein's concepts
Gravitational
waves were predicted by Einstein in his general theory of relativity in
1915, the theory that proposed space-time as a concept. The waves are a
distortion of space-time.
However,
in order for us to detect them, they needed to be created by a mammoth
event -- for example, the collision of two black holes.
Black
holes are a holy grail of the gravitational wave concept. To date, we'd
been able only to see their aftereffects. Black holes themselves were a
conjecture.
"There's been a lot of
indirect evidence for their existence," says Shoemaker, an expert in
black holes. "But this is the first time we actually detect two black
holes merging and we know the only thing that predicts that (is)
gravitational radiation, (which) comes from a binary black hole merging.
There's no other way we could have seen that but gravitationally."
'Now we can listen to the universe'
But is LIGO correct? Have we really detected gravitational waves?
Scientists
have what they call a "five-sigma" standard of proof, and LIGO's
researchers say the gravitational wave discovery exceeds that.
"It
took six months of convincing ourselves that it was correct," says
Shoemaker. "It goes beyond that five-sigma to proving that nothing was
happening with the equipment that couldn't be understood."
She's thrilled with the possibilities.
"Imagine
having never been able to hear before and all you can do is see," she
says. "Now we can listen to the universe where we were deaf before. It's
a different spectrum (from the electromagnetic spectrum). It's unlike
anything we've ever detected before."
"What's
really exciting is what comes next," said Reitze at the announcement.
"I think we're opening a window on the universe -- a window of
gravitational wave astronomy."
Einstein would be surprised
Columbia
University physicist Marka, who's been working on the project for more
than a decade, said the discovery will open up new horizons, including
direct tests of Einstein's general theory. Those could further support
it -- or force physicists to come up with new ideas.
"A
physicist is always looking for a flaw in a theory. And the only way to
find a flaw is to test it," Marka told CNN. "Einstein's theory did not
present any flaws to us yet, and that is really scary. Physicists are
very (skeptical) of flawless theories because then we have nothing to
do."
Ironically, Einstein didn't think gravitational waves would be discovered.
"He
thought gravitational waves are a beautiful construct, but they are so
small nobody would ever be able to actually measure it," said Marka.
http://www.cnn.com/2016/02/11/us/gravitational-waves-feat/
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