Scientists just announced the first ever detection of gravitational waves—ripples in space itself. Led by Caltech, MIT, and the LIGO Scientific Collaboration, the discovery takes place almost exactly 100 years after Einstein theorized their existence.

The scientists discovered the ripples from an event "1.3 billion years ago," says David Reitze, the executive director of the LIGO laboratory in today's press conference, "of two black holes spiraling into one another and merging." It's a sight that is impossible to see clearly with light or any other electromagnetic radiation. Only gravitational waves could detect it.

"Up until now we've been deaf to gravitational waves, that's just amazing to me."

"It's the first time this type of [binary black hole] system has ever been seen, and it's proof that binary black holes exist," Reitze says. "Up until now we've been deaf to gravitational waves, that's just amazing to me."

Today's discovery is "an unprecedented view into a regime of physics that was simply inaccessible to humanity thus far," says Stefan Ballmer—a physicist at Syracuse University and one of the researchers behind the gravitational-wave detection—who spoke with Popular Mechanics.

"It's a completely unprecedented way to observe the universe in a way no living being has ever been able to. It allows us to get as close as we conceivably can to extreme objects like black holes and neuron stars, and other things that are simply inaccessible in another way. "

What are gravitational waves?

Just like an ocean wave is a slosh of water and a sound wave is a movement of air, gravitational waves are likewise the motion of a medium. But with gravitational waves, it's space itself that's moving. If you imagine the world around you covered with 3D grid lines, the warping and stretching of those physical coordinates would be a gravitational wave going by.

So what causes them? Well, Einstein's general theory of relativity explained that when virtually any matter accelerates and moves about—like a planet, or your car, or even a mote of dust—it warps the physical coordinates of space around it, sending out these waves at light speed. But because space is so extraordinarily stiff, it takes a huge mass moving at an astonishing speed to produce a wave big enough for us to conceivably measure. (Sorry, dust mote.)

Now, gravitational waves have been indirectly detected before. In 1974, scientists found that a certain binary star system had to be producing gravitational waves—but only because the orbit of these stars decayed at the precise rate that energy had to be exiting in the form of gravitational waves. That's a bit like being told a never-before-heard sound was made somewhere, but not actually hearing it.

Today's detected waves were caused by two black holes spiraling in toward one another, and eventually crashing in to one another. "Because we have two detectors, which is like having two ears, we can tell it came from the southern sky, in the rough direction of the Magellanic Cloud," said Gabriela González, a physicist behind the detection.

"It's a completely unprecedented way to observe the universe in a way no living being has ever been able to."

How and why'd we find them now?

So how the heck did scientists detect the movement of a light-speed warp in space itself? Well, with light and mirrors at two massive detectors in Louisiana and Washington state. Together the instruments are called Advanced LIGO (the Laser Interferometer Gravitational-Wave Observatory).

To drastically oversimplify how the Advanced LIGO instruments work, each observatory splits a laser in two directions, bounces each half of the laser off two mirrors—each two and a half miles away—and, once they zoom back, measures if either half of the laser traveled farther than the other. If one laser takes a longer time to return, it could be because it had to travel through more space thanks to the slight stretching of space itself due gravity wave traveling through Earth. Each instrument tests for this possible stretching with an endless number of laser bursts, and compares any possible findings with the other instrument across the USA.

The tricky part: Gravitational waves are so achingly faint that to measure their slight stretch or compression of space, your observatory has to be incredibly still, and pretty much as noiseless as you can conceivably imagine.

Even ignoring the constant low-level hum of seismic jitters the Earth is constantly producing, just a pine-cone falling miles away from the observatory would mess up your reading. That's how faint these waves are. To adjust for this outside noise, in Advanced LIGO, the lasers travel through a highly insulated vacuum, and the entire L-shaped device is underground and suspended in a noise-canceling setup made of seven individually nested supports.

While LIGO itself has been up and running since 2002, last year it received a massive upgrade (becoming Advanced LIGO) which basically revamped the entire framework that keeps LIGO still an noise-less. "It's on the order of a thousand times better" at noise-canceling, says Ballmer. That upgrade is behind today's detection.

What does this mean?

Today's discovery is proof that detectors like Advanced LIGO really can allow astronomers to hear and measure the squishing and stretching of space by massive objects. "That opens up an entirely new regime of physics," says Ballmer. Because it takes such a massive force to create gravitational waves in the first place, it's also incredibly hard to deform these waves once they're made—they travel through galaxies and matter almost as if it were nothing. That means that today's discovery brings us unprecedented details of the physics underlying two colliding black holes.

Scientists hope that from now on, gravitational wave detections will be a cornerstone of a new way of conducting astronomy. In essence, opening a new window into the universe—not just to observe black holes in new ways, but to watch a world of other massive objects that would otherwise have been veiled to our eyes.

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