A
team of physicists who can now count themselves as astronomers
announced on Thursday that they had heard and recorded the sound of two
black holes colliding a billion light-years away, a fleeting chirp that
fulfilled the last prophecy of Einstein’s general theory of relativity.
That
faint rising tone, physicists say, is the first direct evidence of
gravitational waves, the ripples in the fabric of space-time that
Einstein predicted a century ago. And it is a ringing (pun intended)
confirmation of the nature of black holes, the bottomless gravitational
pits from which not even light can escape, which were the most
foreboding (and unwelcome) part of his theory.
More
generally, it means that scientists have finally tapped into the
deepest register of physical reality, where the weirdest and wildest
implications of Einstein’s universe become manifest.
Conveyed
by these gravitational waves, an energy 50 times greater than that of
all the stars in the universe put together vibrated a pair of L-shaped
antennas in Washington State and Louisiana known as LIGO on Sept. 14.
If
replicated by future experiments, that simple chirp, which rose to the
note of middle C before abruptly stopping, seems destined to take its
place among the great sound bites of science, ranking with Alexander Graham Bell’s “Mr. Watson — come here” and Sputnik’s first beeps from orbit.
“We
are all over the moon and back,” said Gabriela González of Louisiana
State University, a spokeswoman for the LIGO Scientific Collaboration,
short for Laser Interferometer Gravitational-Wave Observatory. “Einstein
would be very happy, I think.”
Members
of the LIGO group, a worldwide team of scientists, along with
scientists from a European team known as the Virgo Collaboration,
published a report in Physical Review Letters on Thursday with more than
1,000 authors.
“I
think this will be one of the major breakthroughs in physics for a long
time,” said Szabolcs Marka, a Columbia University professor who is one
of the LIGO scientists.
“Everything
else in astronomy is like the eye,” he said, referring to the panoply
of telescopes that have given stargazers access to more and more of the
electromagnetic spectrum and the ability to peer deeper and deeper into
space and time. “Finally, astronomy grew ears. We never had ears
before.”
Long-Awaited Triumph
The
discovery is a great triumph for three physicists — Kip Thorne of the
California Institute of Technology, Rainer Weiss of the Massachusetts
Institute of Technology and Ronald Drever, formerly of Caltech and now
retired in Scotland — who bet their careers on the dream of measuring
the most ineffable of Einstein’s notions.
“Until
now, we scientists have only seen warped space-time when it’s calm,”
Dr. Thorne said in an email. “It’s as though we had only seen the
ocean’s surface on a calm day but had never seen it roiled in a storm,
with crashing waves.”
The
black holes that LIGO observed created a storm “in which the flow of
time speeded, then slowed, then speeded,” he said. “A storm with space
bending this way, then that.”
The chirp is also sweet vindication for the National Science Foundation,
which spent about $1.1 billion over more than 40 years to build a new
hotline to nature, facing down criticism that sources of gravitational
waves were not plentiful or loud enough to justify the cost.
“It’s
been decades, through a lot of different technological innovations,”
France Córdova, the foundation’s director, said in an interview,
recalling how, in the early years, the foundation’s advisory board had
“really scratched their heads on this one.”
Word
of LIGO’s success was met by hosannas in the scientific community,
albeit with the requisite admonishments of the need for confirmation or
replication.
“I
was freaking out,” said Janna Levin, a theorist at Barnard College at
Columbia who was not part of LIGO but was granted an early look at the
results for her warts-and-all book about the project, “Black Hole
Blues,” to be published this spring.
Robert Garisto, the editor of Physical Review Letters, said he had gotten goose bumps while reading the LIGO paper.
Elusive Disturbances
When
Einstein announced his theory in 1915, he rewrote the rules for space
and time that had prevailed for more than 200 years, since the time of
Newton, stipulating a static and fixed framework for the universe.
Instead, Einstein said, matter and energy distort the geometry of the
universe in the way a heavy sleeper causes a mattress to sag, producing
the effect we call gravity.
A
disturbance in the cosmos could cause space-time to stretch, collapse
and even jiggle, like a mattress shaking when that sleeper rolls over,
producing ripples of gravity: gravitational waves.
Einstein
was not quite sure about these waves. In 1916, he told Karl
Schwarzschild, the discoverer of black holes, that gravitational waves
did not exist, then said they did. In 1936, he and his assistant Nathan
Rosen set out to publish a paper debunking the idea before doing the
same flip-flop again.
According
to the equations physicists have settled on, gravitational waves would
compress space in one direction and stretch it in another as they
traveled outward.
In 1969, Joseph Weber,
a physicist at the University of Maryland, made headlines when he
claimed to have detected gravitational waves using a six-foot-long
aluminum cylinder as an antenna. Waves of the right frequency would make
the cylinder ring like a tuning fork, he said.
Others
could not duplicate his result, but few doubted that gravitational
waves were real. Dr. Weber’s experiment inspired a generation of
scientists to look harder for Einsteinian marks on the universe.
In
1978, the radio astronomers Joseph H. Taylor Jr. and Russell A. Hulse,
then at the University of Massachusetts Amherst, discovered a pair of
neutron stars, superdense remnants of dead stars, orbiting each other.
One of them was a pulsar, emitting a periodic beam of electromagnetic
radiation. By timing its pulses, the astronomers determined that the
stars were losing energy and falling closer together at precisely the
rate that would be expected if they were radiating gravitational waves.
Dr. Hulse and Dr. Taylor won the Nobel Prize in Physics in 1993.
Another group of astronomers who go by the name Bicep made headlines in 2014
when they claimed to have detected gravitational waves from the
beginning of the Big Bang, using a telescope at the South Pole. They
later acknowledged that their observations had probably been contaminated by interstellar stardust.
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