Yahoo – AFP,
Jean-Louis Santini , and Pascale Mollard Chenebenoit in Paris, 11 February 2016
 |
This image,
taken December 14, 2015, shows a Laser Interferometer Gravitational
Wave
Observatory (LIGO) optics technician inspecting one of LIGO's core optics
(mirrors) (AFP Photo)
|
Washington
(AFP) - In a landmark discovery for physics and astronomy, scientists said
Thursday they have glimpsed the first direct evidence of gravitational waves,
ripples in the fabric of space-time that Albert Einstein predicted a century
ago.
When two
black holes collided some 1.3 billion years ago, the joining of those two great
masses sent forth a wobble that hurtled through space and reached Earth on
September 14, 2015, when it was picked up by sophisticated instruments,
researchers announced.
"Up
until now we have been deaf to gravitational waves, but today, we are able to
hear them," said David Reitze, executive director of the LIGO Laboratory,
at a packed press conference in the US capital.
 |
A woman
photographs a statue of Albert
Einstein on February 11, 2016 in
Washington (AFP
Photo/Brendan
Smialowski)
|
"I
think we are doing something equally important here today. I think we are opening
a window on the universe," Reitze said.
The
phenomenon was observed by two US-based underground detectors, designed to pick
up tiny vibrations from passing gravitational waves, a project known as the
Laser Interferometer Gravitational-wave Observatory, or LIGO.
It took
scientists months to verify their data and put it through a process of
peer-review before announcing it on Thursday, marking the culmination of
decades of efforts by teams around the world including some 1,000 scientists
from 16 countries, according to the National Science Foundation, which funded
the research.
Strain in
space
Gravitational
waves are a measure of strain in space, an effect of the motion of large masses
that stretches the fabric of space-time -- a way of viewing space and time as a
single, interweaved continuum.
They travel
at the speed of light and cannot be stopped or blocked by anything.
As part of
his theory of general relativity, Einstein said space-time could be compared to
a net, bowing under the weight of an object. Gravitational waves would be like
ripples that emanate from a pebble thrown in a pond.
While
scientists have previously been able to calculate gravitational waves, they had
never before seen one directly.
According
to the Massachusetts Institute of Technology's (MIT) David Shoemaker, the
leader of the Advanced LIGO team, it looked just like physicists thought it
would.
 |
David
Reitze, executive director of LIGO, speaks during an announcement that
scientists have observed gravitational waves for the first time at the National
Press Club in Washington, DC, February 11, 2016 (AFP Photo/Saul Loeb)
|
Wobbling
like jelly
"The
waveform that we can calculate based on Einstein's theory of 1916 matches
exactly what we observed in 2015," he told AFP.
"It
looked like a chirp, it looked at something that started at low frequencies --
for us low frequencies means 20 or 30 hertz, that's like the lowest note on a
bass guitar, sweeping very rapidly up over just a fraction of a second... up to
150 hertz or so, sort of near middle C on a piano."
The chirp
"corresponded to the orbit of these two black holes getting smaller and
smaller, and the speed of the two objects going faster and faster until the two
became a single object," he explained.
"And
then right at the end of this waveform, we see the wobbling of the final black
hole as if it were made of jelly as it settled into a static state."
Underground detectors
The
L-shaped LIGO detectors -- each about 2.5 miles (four kilometers) long -- were
conceived and built by researchers at MIT and Caltech.
One is
located in Hanford, Washington, and the other is in Livingston, Louisiana. A
third advanced detector, called VIRGO, is scheduled to open in Italy later this
year.
Tuck
Stebbins, head of the gravitational astrophysics laboratory at NASA's Goddard
Spaceflight Center, described the detector as the "one of the most complex
machines built by humans."
Physicists
said the gravitational wave detected at 1651 GMT on September 14 originated in
the last fraction of a second before the fusion of two black holes somewhere in
the southern sky, though they can't say precisely where.
Physicist
Benoit Mours of France's National Center for Scientific Research (CNRS), which
is leading the VIRGO team along with Italian colleagues, described the
discovery as "historic" because it "allows us to directly verify
one of the predictions of the theory of general relativity."
 |
LIGO
co-founders Kip Thorne (R), and Rainer Weiss (L), speak about
confirming a
prediction of Albert Einstein's theory of relativity, during a press
conference
at the National Press Club in Washington, DC, February 11, 2016
(AFP Photo/Saul
Loeb)
|
New
discoveries ahead
Einstein
had predicted such a phenomenon would occur when two black holes collided, but
it had never before been observed.
An analysis
by the MIT and Caltech found that the two black holes joined about 1.3 billion
years ago, and their mass was 29-36 times greater than the Sun.
The wave
arrived first at the Louisiana detector, then at the Washington instrument 7.1 milliseconds
later.
The two
instruments are 1,800 miles (3,000 kilometers) apart, and since both made the
same reading, scientists consider their discovery confirmed.
Accolades
poured in from across the science world, as experts hailed a discovery that will
help mankind better understand the universe.
"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.
Abhay
Ashtekar, director of the Institute for Gravitation and the Cosmos at Penn
State University, described the discovery as "breathtaking" and said
it "will stand out among the major achievements of the 21st-century
science."
"We
can now listen to the universe rather than just look at it," said
Professor B S Sathyaprakash of Cardiff University. "This window
turns on the soundtrack for the universe."
Indirect
proof of gravitational waves was found in 1974 through the study of a pulsar
and a neutron star. Scientists Russell Hulse and Joseph Taylor won the Nobel
Prize for physics for that work in 1993.
Scientists glimpse Einstein's gravitational waves https://t.co/7Ioy62sRQA pic.twitter.com/fSYkPE7gKs— AFP news agency (@AFP) February 11, 2016
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