Caltech colleagues across the country and in a campus auditorium in Pasadena heard reason to burst into applause as they watched a colleague step to the lectern Thursday during a webcast from Washington.
"We have detected gravitational waves. We did it!" proclaimed David Reitze, PhD, The Caltech physicist who has served as executive director of the collaboration that led to the epic discovery.
It's been almost exactly a century since Albert Einstein -- who later spent three winters as a visiting professor at the California Institute of Technology -- realized a consequence of his general theory of relativity: disturbances involving massive objects must generate waves that momentarily warp space and time as they travel through the universe at the speed of light.
Predicting gravitational waves was one thing -- finding them was another.
Unlike garden-variety gravity waves that occur in the earth's atmosphere and in bodies of water,
the amount of motion to be detected from gravitational waves is infinitesimally small -- orders of magnitude less than the diameter or an atom, far smaller even than a proton.
Ideas for how to do it began to be sketched out in the early 1970's. In 1983, Caltech and the Massachusetts Institute of Technology (MIT) developed a plan that the National Science Foundation (NSF) agreed to fund.
It relies on devising extremely sensitive laser interferometers. On the Caltech campus, a device built with perpendicular 40-meter-long arms became the test bed and prototype for the twin 4,000 meter Laser Interferometer Gravitational-wave Observatory (LIGO) detectors built in Hanford, Washington and Livingston, Louisiana.
As originally devised, the LIGO observatories proved unable to separate gravity waves from background noise. They were upgraded and enhanced to become "Advanced Ligo," and last September 14 at 5:51am EDT -- days before the designated official beginning of the experiment -- both observatories detected a signal determined to be a gravitational wave.
The conclusion is reinforced by the close similarity of the wave profile to what was generated by a supercomputer crunching numbers through Einstein's field equations, Reitze said.
Other researchers had made previous claims of gravitational wave discovery that could not be verified. The LIGO team spent more than four months analyzing and vetting its data before submitting a paper for publication.
From the data, the team concluded the gravitational wave had been generated more than a billion years ago by twin, rotating black moles holes that spiraled together in a merger that released an intense burst of energy.
That conclusion represented a second breakthrough: collisions of black holes had been predicted but never before observed.
Scientists believe gravitational wave detectors will also enable the discovery of other astronomical phenomena that have been invisible to traditional observatories. In the centuries since Galileo focused a telescope on the heavens, astronomers have relied on the data that can be extracted from examining portions of the electromagnetic spectrum, first visible light, and later x-rays and microwave radiation.
"We are here today with a great triumph, a whole new way to observe the universe," said Kip Thorne, PhD, the Caltech-based LIGO co-founder.
It comes at a price: by its count, NSF has invested $1.1 billion.
Gravitational waves do not appear to be an everyday occurrence. The LIGO team expects to detect them perhaps 3-4 times a year. Since September, the detection of a second possible gravitational wave has also been investigated. It was smaller and there is a 2 percent chance it could have been caused by something else, said Caltech Physics Prof. and LIGO team member Alan Weinstein, PhD.
There are data from months of observations that the team has yet to analyze thoroughly for evidence of possible additional gravitational wave events, Weinstein said.
But he sees no doubt the Sept. 14 event was in fact a gravitational wave.
"What we just observed is going into textbooks," Weinstein said.
Back in Washington, after hearing the LIGO team's presentation, the National Science Foundation director France Cordova returned to the lectern.
"Einstein would be beaming, wouldn't he," Cordova said.
