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Scientists Detect Gravitational Waves As Black Holes Collide

Far from our galaxy, in the vast darkness of space, two massive black holes merged into a single, larger hole.

And now researchers say they have detected rumblings from that cataclysmic collision as ripples in the very fabric of space-time itself. The discovery comes a century after Albert Einstein first predicted such ripples should exist.

"It's a really big event," says Saul Teukolsky, a theoretical astrophysicist at Cornell University. "This is probably the most exciting episode of my professional career."

Einstein predicted the existence of such ripples, known officially as gravitational waves, in 1916, as part of his general theory of relativity. General relativity re-imagines the gravitational pull between heavy objects like Earth and the sun as a "warping" of space and time. When very heavy objects such as black holes are involved, the theory predicts that gravitational waves will emerge and ripple across the entire universe.

That's the idea. But in practice, seeing such gravitational waves has been nearly impossible. To make detectable waves, massive objects must be moving quickly. Researchers predicted a collision between two black holes would do the trick. But nobody knew how often that might happen.

Nevertheless, scientists built two massive detectors to take a look. Known collectively as the Laser Interferometer Gravity-Wave Observatory (LIGO), the detectors are located in Washington state and Louisiana. They are separated by thousands of miles in order to detect ripples coming in from deep space as they pass through Earth.

Each detector looks like a big L, made up of two tunnels 2.5 miles long. It's designed so that if a gravitational wave passes by, it will stretch space along one direction of the tunnel and squish space along the direction of the other. The stretching and squishing changes the tunnels' lengths by a tiny amount, and that change can be detected by lasers.

Although LIGO was completed in 1999, it took more than a decade for it to see anything. The detectors had to be made incredibly sensitive to pick up the tiny waves. But they were so touchy, they were set off by everything from minute shifts in Earth's core to traffic entering the parking lot. And even after researchers got rid of all the terrestrial jiggles, LIGO still wasn't quite good enough to see gravitational waves.

All that changed after a major upgrade in 2014. Better vibrational isolation and upgrades to lasers and mirrors dramatically boosted the instrument's power.

And the black hole collision was seen almost as soon as the team began observing again in the fall of 2015. On Sept. 14 at 5:51 a.m., the waves passed through both of the detectors.

According to a paper published in the journal Physical Review Letters, the two black holes were each roughly 30 times the mass of the sun. They merged some 1.3 billion light years from Earth. The waves were generated in the final moments before the black holes merged. The signal was brief but definitive.

The measurements are dramatic proof that gravitational waves exist. The signal in the detector matches well with what's predicted by Einstein's original theory, according to Teukolsky, who was briefed on the results. It matches predictions of the ripples produced by two large black holes, in the final moments before they merge, swirling together at an enormous speed.

This is, arguably, the most direct observation of black holes ever made. Because black holes are (as their name implies) "black", they can't be seen with ordinary telescopes. Up until now, their existence has been inferred by looking at the stars and gas swirling around them. This gravitational signal comes directly from the holes, and it is virtually incontrovertible proof that the holes are out there. "If black holes didn't really exist, you couldn't explain these waves," he says.

Other researchers believe that the gravitational waves could tell us even more about our cosmos. "It's like looking at the universe with new eyes — the amount of information that's there is going to be amazing," says Mina Arvanitaki, a theorist at the Perimeter Institute of Physics in Waterloo, Ontario. Arvanitaki will use LIGO's data to probe for undiscovered fundamental particles that might only exist in the warped space around black holes.

Teukolsky says the discovery shows just how extraordinary the natural world can be. "The universe is stranger than any kind of fiction we could imagine," he says. "I mean, it's preposterous." npr

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Does America Really Need The National Mall?

Just a few weeks ago, the nonprofit Trust for the National Mall staged a music festival — featuring Drake and the Strokes — to benefit the remarkable public space in Washington, D.C., that includes some of America's most recognizable landmarks, including the Jefferson Memorial, Lincoln Memorial, Martin Luther King Jr. Memorial and Washington Monument.

The Trust reports that the festival drew an estimated 50,000 people and raised some $570,000 to be used for improving, preserving and restoring the Mall, which is sometimes known as "America's front yard."

Indeed. The National Mall, says Nancy Levinson, editor of Places Journal, "is a remarkable space — one of the greatest public spaces in modern times — and it deserves to be repaired, restored and honored. Just think of its history, of the activism that it's been the setting for, from suffrage marches to the Bonus Army to Marian Anderson to Martin Luther King to the AIDS Quilt to Stewart & Colbert's 'Rally to Restore Sanity and/or Fear' ... and those are just some of the most famous events."

The bad news, though, is that in many ways the National Mall is a mess. People who know it well — even those who love it — point out its problems. According to the Trust, the Mall is currently up against a maintenance backlog of $400 million and requires an estimated $350 million in necessary upgrades and sustainable improvements.

In the face of such staggering financial needs, the obvious question arises: Does America really need a National Mall anymore?

Cracked And Crumbling

"Frankly, people think of the National Mall as they see it on TV — lush grounds dotted with perfectly polished memorials," the Trust's MacKenzie Babb tells NPR. "Unfortunately, the reality is a far cry from that ideal."

She cites several examples of deliquescence and disrepair:

• In April 2014, a 5-by-3-foot stone toppled from the portico roof of the Jefferson Memorial. "Thankfully," Babb says, "this took place in the early morning hours and no visitors were injured. That said, the stone has yet to be replaced; still today, portions of the memorial remain cordoned off to the public. What could speak more clearly to the need to restore our National Mall than one of our temples to democracy literally crumbling?"

• In Constitution Gardens — the 38-acre area connecting the Vietnam Veterans, World War II and Lincoln memorials — "a large gravel plaza sits empty," Babb says. "Dedicated in 1976 for the nation's bicentennial, the plaza was meant to become home to a building that would offer food, restrooms and recreation to visitors, but before construction could begin, federal funds ran out and the site remains today unused and unknown. Some of the granite walls surrounding the lake have begun to collapse. The concrete-bottomed pond is covered in algae and is responsible for annual fish kills. Many of the trees meant to buffer city noise and create a contemplative atmosphere are instead severely stunted and struggling to survive because of poor soil quality and inadequate drainage. And at the north end of Constitution Gardens, the historic Lockkeeper's House — which oversaw the last lock on the canal that once ran down the center of Washington and remains the oldest building still standing on the National Mall — now sits boarded up and abandoned."

• The U.S. Park Police Horse Stables constructed in 1976 as a temporary structure just south of the Lincoln Memorial Reflecting Pool have never been converted to permanence because of budget restraints. "These stables are the home to the horses used daily by our U.S. Park Police Horse Mounted Unit to patrol the National Mall and keep us all safe," Babb says. "Yet the horses that serve to protect our nation's capital are living in stables marked by outdated machinery, rusted and unsafe doorways, poor ventilation, flood-inducing drainage, and insufficient turnout space."

• Throughout the park, she says, "basic visitor amenities such as restrooms and food options are hard to find — making it difficult for families with young children to spend a day in the park. Cracked and flooded sidewalks are impassable to some of our visitors in wheelchairs."

Too Much Love

How did the Mall reach this sad state of affairs?

Imagined in the 1790s by urban planner Pierre L'Enfant — as a gigundo public gathering point for a new nation — the National Mall today attracts an estimated 29 million visits each year. That's more than the Grand Canyon, Yellowstone and Yosemite national parks and the Statue of Liberty combined.

Factor in stagnated federal funding, which has not kept pace with the needs of the Mall, according to MacKenzie Babb, "and you're left with a park that has quite simply been loved to death. Moreover, unlike many of America's other national parks, the National Mall charges no admission fee — rather, it is a uniquely inclusive and open space that welcomes all to learn, pay tribute to and participate in the American story."

The Trust for the National Mall wants to keep it free. And for years now, the group has been seeking funds.

Common Ground

But in this age of social media and virtual meetings and online protests, why do we need a large public space for people to physically gather?

"The National Mall is a uniquely American space where we are invited to speak truth to power without fear of persecution," says Babb. "It's where women fought for the right to vote, protesters marched to end the Vietnam War, and Dr. Martin Luther King Jr. shared a dream that sparked a new American reality."

She adds: "As much value as online platforms can provide, there are few things so powerful as coming together on our country's common ground to make your voice heard. That's probably why even in today's Digital Age, roughly 3,000 events are permitted to take place on the National Mall each year. People travel from across the country and around the world to the National Mall, using the grounds where American history is remembered to make history of their own."

Nancy Levinson of Places Journal agrees. "Digital media," she says, "aren't in any important ways replacing physical public spaces. We know that all the rallies listed above happened not just because their organizers were passionate about a cause but also because the Mall exists as an actual, physical, photographable place — the ultimate place — to bring a cause to national attention. With the Mall as a destination, you can mobilize thousands for an event that might make history."

Perhaps we do need such a public arena, but can we afford it? "At urban design conferences it's become the familiar cry: There's no money for public works," Levinson says. "But the U.S. is a very rich country, and the money's there; we just need — once again — to tax for it. ...   npr

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A Day After His Death, Frei Otto Awarded Pritzker Architecture Prize

Architect Frei Otto is known for the large-scale roofs on the sports facilities for the 1972 Munich Olympics.

German architect Frei Otto is this year's winner of the Pritzker Architecture Prize, a day after his death at age 89.

The prize's jury, in its citation, said Otto had developed "a most sensitive architecture that has influenced countless others throughout the world."

"The lessons of his pioneering work in the field of lightweight structures that are adaptable, changeable and carefully use limited resources are as relevant today as when they were first proposed over 60 years ago," the jurors said. "He has embraced a definition of architect to include researcher, inventor, form-finder, engineer, builder, teacher, collaborator, environmentalist, humanist, and creator of memorable buildings and spaces."

Otto's works are often designed in collaboration with others. His most notable projects include the cable net structure at German Pavilion at Expo 67 in Montreal, the large-scale roofs for the 1972 Munich Olympics and the Mannheim Multihalle in 1974. npr

Police Fire Tear Gas On Kenyan Kids Protecting A Soccer Field

Hundreds of elementary schools were protesting the illegal seizure of their playground by a private developer in Nairobi, Kenya, when police fired tear gas into the crowd.

The incident sparked outrage across the city — and on social media, where Kenyans tweeted with the hashtag #OccupyPlayGround.

But the shocking images and videos of the ordeal provoked a surprisingly proactive response. In the end, these Kenyan kids did what ordinary Kenyans are rarely able to do: Defend disappearing public space.

The process is known as "land-grabbing." A fence suddenly appears overnight around a parcel of government property. Those who protest are warded off — sometimes violently — by police. In time, a new high-rise or hotel or parking lot appears, owned by a politically connected magnate.

But this time, the land in question was next to an elementary school, Langata Road Primary School. And the protesters were kids as young as 8, who used the land to play soccer.

When developers set up a fence separating the school from the playground over the winter break, several hundred kids showed up on Monday to protest. They ended up breaking down the new fence. In response, heavily armed police fired tear gas on the kids.

"The tear gas was so bad!" Kevin Sande, 10, said Tuesday.

The gas made their eyes red and caused them to cough, other kids said.

In full disclosure, I can't be sure that Sande and his classmates I interviewed at Langata Road Primary School were the ones that got tear-gassed. In the disturbing photos from that day, it's hard to make out the faces on the green uniforms engulfed in white smoke.

"I didn't understand whether we are in Kenya or the Gaza Strip," says Rahab Mwikali, an activist, who came to the school to express sympathy. "I thought what could this be?" npr