Astronomers announced on Monday that they had discovered what many consider the holy grail of their field: ripples in the fabric of space-time that are echoes of the massive expansion of the universe that took place just after the Big Bang.
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 Centre 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 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.
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