Einstein nailed it! Gravitational waves do exist

Scientists prove Einstein's theory after observing the collision of black holes.

Michelle Starr Science editor
Michelle Starr is CNET's science editor, and she hopes to get you as enthralled with the wonders of the universe as she is. When she's not daydreaming about flying through space, she's daydreaming about bats.
Michelle Starr
4 min read
Enlarge Image

Visualization of the gravitational waves caused by two black holes merging.


Scientists just discovered Einstein's ripples in the fabric of spacetime.

A century ago, Albert Einstein's General Theory of Relativity changed human understanding of space and time. From a fixed speed of light to the existence of gravitational waves, the modern era of theoretical physics was born in 1916.

On Thursday, researchers on the Laser Interferometer Gravitational-Wave Observatory project announced they have solid evidence for the existence of gravitational waves, disturbances in the fabric of spacetime.

Beyond proving Einstein's theory, the discovery brings us one step closer to a grand unified theory -- the holy grail of physics that provides an all-encompassing explanation for the universe as we know it.

A team of LIGO scientists said Thursday that they had observed gravitational waves, created 1.3 billion years ago by a collision between two black holes. These waves were detected on September 14, 2015, just three days after the facility was turned back on after a five-year upgrade.

The discovery marks not just the first time that gravitational waves have been confirmed, but the first time researchers have observed binary black holes. The first glimpse at gravitational waves also afforded an unprecedented look at a cosmic phenomenon that has otherwise been elusive, proving for the first time that the waves exist and suggesting that black hole mergers are both heavier and more common than previously thought. The research is published in the journal Physical Review Letters.

"This is a new kind of astronomy -- observing the universe using gravity itself," said Shane L. Larson, research associate professor at Northwestern University and an astronomer at the Adler Planetarium in Chicago. "We can't 'see' black holes with telescopes. This is the first time black holes have been directly detected by measuring them, through their gravity, as opposed to measuring the effect they have on other matter in the universe."

Animation of gravitational waves produced by a fast binary orbit.


How do you picture gravitational waves? Think of spacetime as a taut sheet. Rolling a ball across the sheet causes it to curve. As the ball moves, the sheet's curvature moves, and certain objects moving quickly cause ripples across the sheet.

Einstein's original theory proposed that as mass changes position, it causes a ripple in the universe's gravitational field, a wave traveling at the speed of light outward from the source. Gravitational waves are caused by objects like oddly shaped spinning planets and binary black holes and star systems. Theories also suggest that supernovae, and even the Big Bang itself, are a source of gravitational waves. You can read more about them on Einstein Online.

Now that LIGO has detected these waves, researchers have an entirely new way of studying these objects and events. In the case of black holes, which are very difficult to study since we cannot view them directly, it could blow research wide open. Researchers may even be able to peer back to just a split second after the Big Bang, something that is impossible with other methods.

'Suddenly we know how to listen'

Stop and think about that for a second. We may finally be able to see the beginning of time. The universe. Everything there is.

"Gravitational waves are akin to sound waves that traveled through space at the speed of light," said David Blair, a professor at the University of Western Australia. "

Up to now humanity has been deaf to the universe. Suddenly we know how to listen.
The universe has spoken and we have understood."

The LIGO facility uses two 4-kilometer (2.5-mile) arms in an L shape as "antennas" to track gravitational waves. Each arm contains an interferometer, an array of lasers and mirrors that detect the minute movements that gravitational waves would cause -- movements 10,000 times smaller than a proton.

But detecting gravitational waves is not easy to do. Gravity is, for something that binds the universe together, surprisingly weak. For almost a decade LIGO facilities failed to detect any gravitational waves. Five years of upgrades led to Advanced LIGO going live in September 2015, and it has identified gravitational waves in less than six months, even working out a rough location. The addition of a third facility will allow the team to triangulate the waves to accurately find their source. Two further detectors are planned later.

Robert Ward, an Australian National University scientist who installed the interferometers, explains how Advanced LIGO works.

Enlarge Image

LIGO Hanford Observatory.

Caltech/MIT/LIGO Laboratory

"The gravitational waves will affect masses that are free to move under the influence of gravity by changing the distance between them. This is often described at the wave 'stretching and squeezing the space between the masses'. We measure the distance between the two masses by attaching high-quality mirrors to them, and then by bouncing laser beams off those mirrors. We then effectively time how long it takes for the laser beam to return, and since we know the speed of light, that lets us measure the distance. Of course it's both more and less complicated than that, but that's the basic idea."

Now that the LIGO team has observed these waves, they will open up avenues not just to study obscure objects in greater depth, but also a new means to discover previously unknown objects, much like radio telescopy located objects undetectable by visible light telescopes.

In other words, gravitational wave astronomy will usher in an entirely new era of space discovery.

"Things we should never be entitled to see -- colliding black holes, merging neutron stars, gargantuan collisions of galaxies -- can now be routinely revealed to us. We are poised to discover whole new types of phenomena, and we will now receive entirely new insights on familiar objects," said astronomer Bryan Gaensler, director of Dunlap Institute for Astronomy and Astrophysics at the University of Toronto and the Canadian SKA science director, who has not worked on the LIGO project.

"There have been many scientific highlights of physics and astronomy in recent years: the Higgs Boson, landing a probe on a comet, and an amazing fly-by of Pluto," he said. "But all this is dwarfed by what has been announced this week.

A new era of science has begun."