Today, scientists announced that, for the first time in history, gravitational waves have been detected.
Gravitational waves are ripples in spacetime throughout the universe. What’s truly remarkable about this discovery is that Albert Einstein predicted the existence of gravitational waves 100 years ago, but scientists have never been able to detect them, until now.
The discovery came out of the U.S. based Laser Interferometer Gravitational Wave Observatory (LIGO). The mission of LIGO was to directly measure gravitational waves. In order to do that, LIGO scientists needed to construct the most precise measuring device the world had ever seen.
The LIGO project, which began in 1992, was the largest scientific investment the National Science Foundation (NSF) has ever made.
At an NSF press conference this morning, LIGO Laboratory Executive Director, David Reitze, said “This was a scientific moon shot. And we did it – we landed on the moon.”
LIGO consists of two 4 kilometer (2.5 mile) tunnels located in Louisiana and the state of Washington. Because gravitational waves stretch space in one direction and compress space in the other, LIGO was designed to measure changes in length across large land distances.
Stretching of spacetime by a gravitational wave / Image courtesy of Wikicommons
If they could detect a stretch of land in the LIGO tunnels in one direction and compression in the other, they could theoretically detect a gravitational wave.
Northern leg (x-arm) of LIGO interferometer on Hanford Reservation in Washington / Image courtesy of Wikicommons
The “ruler” that scientists used to measure these tunnel lengths was the speed of light. The speed of light is constant, so LIGO can determine the length of the tunnels by measuring the time it takes for a laser to bounce from one end of the tunnel to the other.
Gravitational waves are created when masses accelerate. Measured back on September 14th, 2015, the gravitational wave signal that the LIGO scientists detected matches the exact signal they’d expect from two merging black holes accelerating at half the speed of light.
It took half a year to announce this discovery because the LIGO scientists needed time to rule out every other potential source of that signal. Today, they are confident that it was produced by a gravitational wave.
“What’s really amazing about this is this is the first time that this kind of a system has ever been seen – a binary black hole merger – and it’s proof that binary black holes exist in the universe.” David Reitze
Reitze explained that the black holes that created this gravitational wave merged 1.3 billion years ago. It took that long for the wave to travel to the Earth.
Each of the black holes were 30 times the mass of the sun and were accelerating at half the speed of light when they collided into each other.
The ability to measure gravitational waves will open up an entirely new window for astronomy. Reitze explained that this will enable scientists to look at the universe in a new way.
“This is the first time the universe has spoken to us through gravitational waves. Up until now we’ve been deaf to gravitational waves. Today, we’re able to hear them.” David Reitze
Today’s announcement is a milestone for the scientific community. LIGO proved that we now have the technology to detect gravitational waves. This capability, rather than the signal detected back in September, is the most important part of today. The LIGO scientists have created a new way to study the universe, which means the most exciting discoveries may lay ahead of us.