Update: Months after researchers made the historic discovery of gravitational waves, physicists announced today they have detected waves for a second time — cementing gravity as a new lens for which astronomers can use to gaze upon the cosmos. Popular Science's Ryan F. Mandelbaum outlines the greater significance:

"Scientists think the second wave event is important for a lot of reasons. [David Shoemaker, Director of the Massachusetts Institute of Technology's LIGO lab] notes that, above all, this event showed that the first one wasn't a fluke, establishing that these experiments really can be used as observatories to detect crazy events in space. He also told us that since the black holes were smaller this time around (the first event's black holes were around 29 and 36 times the mass of our sun, but these two black holes were around 14 and 7.5 the mass of our sun), the signal was much quieter, and put LIGO's computers to the test. The tiny signal needed to be filtered out from all the natural jitters that happen in the background. Signals like this second one, called "GW151226," are much more like what LIGO scientists should expect to see moving forward.

[Popular Science]

​This past February, physicists announced that they discovered evidence of gravitational waves — a phenomenon that, a century ago, Einstein theorized existed but could not prove.

So, what exactly are gravitational waves and why are they so important? How did scientists detect them and why have they been so elusive? Here's what to read.

SPACETIME IS LIKE RUBBER, BLACK HOLES ARE BALLS

What Are They?

In the universe, things happen. Einstein posited that those events could be seen within fluctuations of the fabric of the universe, spacetime.

Confused? Just watch this:

Here's actual science journalists explaining that with even more clarity:

When Einstein announced his theory in 1915, he rewrote the rules for space and time that had prevailed for more than 200 years, since the time of Newton, stipulating a static and fixed framework for the universe. Instead, Einstein said, matter and energy distort the geometry of the universe in the way a heavy sleeper causes a mattress to sag, producing the effect we call gravity. A disturbance in the cosmos could cause space-time to stretch, collapse and even jiggle, like a mattress shaking when that sleeper rolls over, producing ripples of gravity: gravitational waves.

[The New York Times]





Gravitational waves are produced when two black holes, two neutron stars or a black hole and a neutron star collide, distorting the fabric of space-time around them in the process. Those ripples propagate out into the universe, distorting the space-time, around other objects, including Earth.

[Mashable]





ANOTHER WAY TO EXAMINE THE COSMOS

Why Do Scientists Care So Much About Them?

Like the electromagnetic spectrum, it's another avenue scientists can use to look into the previously unseen universe. Here's why that's so significant:

Apart from the fact that it would affirm a big piece of Einstein's theory of general relativity, gravitational waves can be used to probe some of the most mysterious phenomena in the cosmos. As LISA Pathfinder scientist Bill Weber told Gizmodo last month, they're "the most direct way of studying the large fraction of the universe which is dark."

[Gizmodo]





[G]ravitational waves could also help physicists understand the fundamental laws of the universe. They are, in fact, a crucial part of Einstein's general theory of relativity. Finding them would prove that theory—and could also help us figure out where it goes astray. Which could lead to a more accurate, more all-encompassing model, and perhaps point the way toward a theory of everything.

[Popular Science]





With LASERS, Basically

How Did They Detect Them?

The acronym you will likely hear thrown around is LIGO, Laser Interferometer Gravity Observatory. Here's how that works:

The technique being employed is laser interferometry.

Both Ligo labs work by splitting a light beam and sending the two halves down separate, 4km-long, evacuated tunnels.

The beams are bounced back and forth by mirrors before being recombined at their starting point and sent to detectors. If the delicate gravitational waves pass through the set-up, the laser light should show evidence of having been ever so slightly disturbed – either lengthened or shortened.

[BBC]





By listening for changes in the amplitude and frequency of gravitational waves, scientists like Hughes can literally hear the story the waves are telling. "I like to think of it in a linguistic way," said Hughes. "The vocabulary of the [event] is imprinted on the wave." For example, in the simplest kinds of collisions of two black holes, the sound you hear is a simple chirp; if the black holes are spinning rapidly, however, you get a warble on top. Hughes cautions that scientists are only just learning to understand this new language—the warbling that codes for spin could be inaudible if both black holes spin the same way.

[The Atlantic]





And here's what that gravitational wave sounds like

What's Next?

A very good question! This is the scientific equivalent of Christmas, so everyone is a little excited and not really sure exactly what the possibilities are. It's like granting sight to a blind person and then immediately asking them what their favorite color is. That said, Bad Astronomer Phil Plait certainly has high hopes:

Whenever we find a new window into the Universe — radio waves, gamma rays, even the invention of the telescope itself — immense wonders have been our reward. In the vast majority of cases we had no clue what was waiting for us once we peered outwards in a new way. Stars numbered beyond imagining, galaxies packed together clear across the cosmos, planets, nebulae, and even an eventual understanding of how the Universe came to be, how it changes, and how it will evolve in the future.

[Slate]





In the meantime, you should definitely watch the historic press conference and check out Gizmodo's live Q&A with one of the LIGO researchers.

Looking for more science news? Head on over to our Science Channel. And for more distillations like this one, check out our archive of roundups.