New Delhi, March 17: Astronomers using a telescope near the South Pole have detected the first ever signatures of gravitational waves — feeble ripples in space-time — lingering in the leftover heat from the Big Bang that gave birth to the universe 13.8 billion years ago.
The gravitational waves represent the first direct evidence for a theory that explains puzzling features of the universe by proposing that it experienced a burst of hyper-accelerated expansion called “inflation” in a tiny fraction of its first second of existence.
The astronomers, who had spent three years looking for these primordial gravitational waves, announced today that they had spotted these waves’ imprints on the cosmic microwave background, the relic radiation from the Big Bang that permeates the entire universe.
“This is mind blowing — this is direct insight into physics very close to the moment of creation,” said Clement Pryke, an associate professor and experimental cosmologist at the University of Minnesota who was one of the four principal investigators of the study.
“It’s amazing to go on a high-risk fishing expedition and actually find what we were looking for,” Pryke told The Telegraph.
The idea of cosmic inflation emerged in the early 1980s, first proposed by cosmologist Alan Guth at the Massachusetts Institute of Technology and refined independently by three other researchers: Andreas Albrecht, Andrei Linde and Paul Steinhardt.
Inflation explains two puzzling features of the universe: why, on a grand scale, the universe looks the same everywhere; and what Guth once called the “razor-sharp fine-tuning” of the mass density of the universe. But there has been no direct evidence to support the theory until now.
“Inflation is a nice idea, but it could be argued that it is a mere mathematical invention to explain these properties of the universe,” said Tarun Souradeep, a cosmologist at the Inter-University Centre for Astronomy and Astrophysics, Pune.
“We’ve all been eagerly awaiting this result. It provides direct evidence for inflation,” said Souradeep, who was not associated with the study but specialises in the early universe.
“If this holds up to scrutiny, this is a Nobel-worthy result.”
Researchers from several academic institutions across America, Canada and Britain collaborated to install the telescope, designed to capture signatures of the gravitational waves on the cosmic microwave background at a site only one kilometre from the South Pole.
Detecting these signals has been among the most important current goals of cosmology, said John Kovac, an astronomer at the Harvard Smithsonian Centre for Astrophysics in the US who led the research collaboration.
“The South Pole is the closest you can get to space and still be on the ground,” Kovac said in a media release issued by the Harvard Smithsonian.
“It is one of the driest, clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang.”
The astronomers detected the gravitational wave imprints in the polarisation —patterns of vibrations — of the cosmic microwave background.
“A gravitational wave background is a unique prediction of inflation,” James Bock, a principal investigator at the California Institute of Technology, said.
“The implication is that inflation not only happened, but that we can say more about the process.”
Inflation deals with only a tiny fraction of a second after the birth of the universe. The theory says that when the universe was only 10-raised-to-the-power-of-minus-35 seconds old, it underwent rapid hyper-acceleration that lasted a similarly small fraction of time. Then it slipped into the standard mode of expansion that continues today.
“This is a huge, huge discovery; it’s a rare occasion when a single result gives us insight about something that happened only 10 (to the power) minus 35 seconds after the birth of the universe,” Uros Seljak, a professor of physics at the University of California, Berkeley, said.
Seljak, who was not associated with the new result, had 18 years ago predicted that polarisation measurements of the cosmic microwave background could be used to reconstruct the details of the early universe.
A key architect of the theory of inflation today said he was excited about the new result, but cautioned that understanding inflation was still a work in progress that has generated significant controversy in cosmological circles.
“If upheld, this is an absolutely thrilling result,” Andreas Albrecht, professor of cosmology at the University of California, Davis, who had helped develop the theory, told this newspaper via email.
These signatures, he said, support the idea that inflation happened for a very brief period in the early universe.
“But the fundamental picture is about what happened before that, and what physics drove inflation,” said Albrecht, whose current research is tied to these questions.
“As the evidence for a brief period of inflation becomes stronger, the case for grappling with these fundamental aspects becomes all the more compelling.”
Over the past decade, cosmologists have pencilled multiple models of inflation.
“We’ll probably need more sophisticated experimental observations, perhaps space-based telescopes, to say which one is the correct model,” said Souradeep.