The end of 2015 coincided with the birth of Einstein’s general theory of relativity, which the great man presented to the Prussian Academy of Sciences in a series of four lectures in the midst of World War I. Widely regarded as the pinnacle of human intellectual achievement, "general relativity," as it came to be known, took many years to be well tested observationally. But today, after decades of thorough investigation, physicists have yet to find any flaw with the theory.
Nevertheless, one key test remains incomplete. Shortly after Einstein published his famous gravitational field equations, he came up with an intriguing solution of them. It describes ripples in the geometry of spacetime itself, representing waves that travel across the universe at the speed of light. The detection of these gravitational waves has been an outstanding challenge to experimental physics for several decades. Now, that long search seems to be nearing its culmination.
In the last few months, a laser system designed to pick up the passage of gravitational waves emanating from violent astronomical events has been upgraded, and rumors abound that it has already "seen something." The system concerned, called Advanced Ligo (for Laser Interferometer Gravitational Observatory), uses laser beams to spot almost inconceivably minute gravitational effects. In Europe, its counterpart, Advanced Virgo, is also limbering up. Advanced Ligo and Advanced Virgo are refinements of existing systems that have proved the technology but lack the sensitivity to detect bursts of gravitational waves from supernovas or colliding neutron stars on a routine basis. The stage is now set to move to that phase.
The detection of gravitational waves would not merely provide a definitive test of Einstein’s century-old theory, it would serve to open up a whole new window on the universe. Existing conventional telescopes range across the entire electromagnetic spectrum, from radio to gamma rays. Ligo and Virgo would open up an entirely new spectrum and with it an entirely new branch of astronomy, enabling observations of black hole collisions and other cosmic exotica.
Each time a new piece of technology has been used to study the universe, astronomers have been surprised. Once gravitational astronomy is finally born, the exploration of the universe through gravitational eyes will undoubtedly provide newsworthy discoveries for decades to come.