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 Predicted by Albert Einstein nearly a century ago, the discovery
of the ripples, called gravitational waves, would be a crowning
achievement in one of the greatest triumphs of the human intellect:
an understanding of how the universe began and evolved into the
cornucopia of galaxies and stars, nebulae and vast stretches of
nearly empty space that constitute the known universe.
"This detection is cosmology's missing link," Marc Kamionkowski, a
physicist of Johns Hopkins University and one of the researchers on
the collaboration that made the finding, told reporters on Monday at
a press conference at the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts.
Gravitational waves are feeble, primordial undulations that
propagate across the cosmos at the speed of light. Astronomers have
sought them for decades because they are the missing evidence for
two theories.
One is Einstein's general theory of relativity, first published in
1915, which launched the modern era of research into the origins and
evolution of the cosmos. The general theory explains gravity as the
deformation of space by massive bodies. Einstein posited that space
is like a flimsy blanket, with embedded stars and planets causing it
to curve rather than remain flat.
Those curvatures of space are not stationary, Einstein said.
Instead, they propagate like water in a lake or seismic waves in
Earth's crust and so are "gravitational waves" that "alternately
squeeze space in one direction and stretch it in the other
direction," Jamie Bock, a physicist at the California Institute of
Technology in Pasadena and one of the lead scientists on the
collaboration, told Reuters.
The other, much more recent theory that predicted gravitational
waves is called cosmic inflation. Developed in the 1980s, it starts
with the well-accepted idea that the universe began in a Big Bang,
an explosion of space-time, 13.8 billion years ago.
An instant later, according to the theory, the infant cosmos
expanded exponentially, inflating in size by 100 trillion times.
That made the cosmos remarkably uniform across vast expanses of
space and also super-sized tiny fluctuations in gravity, producing
gravitational waves.
Although the theory of cosmic inflation received a great deal of
experimental support, the failure to find the gravitational waves it
predicted caused many cosmologists to hold off endorsing it.
That may change after the announcement on Monday.
"These results are not only a smoking gun for inflation, they also
tell us when inflation took place and how powerful the process was,"
Harvard University physicist Avi Loeb said in a statement. The
strength of the gravitational waves' signal is tied to how
powerfully the universe expanded during the brief era of inflation.
The measurements announced by the astronomers on Monday are nearly
twice as large as cosmologists predicted for gravitational waves,
suggesting a great deal more could be learned about how inflation
worked.
SOUTH POLE TELESCOPE
The gravitational waves were detected by a radio telescope called
BICEP2 (Background Imaging of Cosmic Extragalactic Polarization).
The instrument, which scans the sky from the South Pole, examines
what is called the cosmic microwave background, the extremely weak
radiation that pervades the universe. Its discovery in 1964 by
astronomers at Bell Labs in New Jersey was hailed as the best
evidence to date that the universe began in an immensely hot
explosion.
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The microwave background radiation, which has been bathing the
universe since 380,000 years after the Big Bang, is a mere 3 degrees
above absolute zero, having cooled to near non-existence from the
immeasurably hot plasma that was the universe in the first fractions
of a second of its existence.
The background radiation is not precisely uniform. And like light,
the relic radiation is polarized as the result of interacting with
electrons and atoms in space.
Computer models predicted a particular curl pattern in the
background radiation that would match what would be expected with
the universe's inflation after the Big Bang.
"It's mind-boggling to go looking for something like this and
actually find it," Clem Pryke, a physicist at the University of
Minnesota and another lead scientist on the collaboration, told
reporters. "Theorists are forever sending the experimentalists on
wild goose-chase missions. When we first saw hints of a signal we
totally didn't believe it."
It will be up to other teams of scientists, working with an array of
Earth-based, balloon-launched and space telescopes, to verify the
findings.
"This is the smoking gun for inflation," Kamionkowski said. But even
if the results hold up, "we've learned only that inflation has sent
us a telegram, encoded on gravitational waves and transcribed on the
cosmic microwave background sky."
It will be essential, he added, "to follow through with more
detailed and precise measurements to infer fully what this telegram
is telling us."
QUANTUM HINTS
The detection of gravitational waves may help physicists realize a
dream of Einstein's that he died before achieving: unifying all the
forces of nature.
Three of the four forces have been unified, which means that
physicists have shown that they are facets of the same basic force.
But the fourth, Einstein's beloved gravity, remains the odd man out:
it seems to be a property of space rather than a consequence of
subatomic, or quantum, particles as the other forces are.
The three quantum-based forces are electromagnetism, the weak
nuclear force (responsible for radioactivity) and the strong nuclear
force (which glues together the protons and neutrons in atomic
nuclei).
Because cosmic inflation was powered by quantum effects, with the
universe springing from a volume smaller than a subatomic particle,
primordial gravitational waves were also created by quantum
processes, cosmologists believe. If so, then by scrutinizing the
gravitational waves that pervade today's cosmos, scientists might
finally show that all four forces of nature arise from a single
uber-force, achieving Einstein's dream.
(Editing by Amanda Kwan and Leslie Adler)
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