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CosmosUp | April 22, 2019

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Why Gravitational Wave Discovery Matter?

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Why Gravitational Wave Discovery Matter?

Last week, a teeny, tiny, unimaginably small little blip made headlines everywhere. That blip was humanity’s first direct evidence of gravitational waves, and the whole world freaked out about it.

The day of the announcement, we were just as excited as everyone else — probably a little bit more excited than average. There’s so much more to talk about this amazing discovery! Like: How can we be sure that the measurements are legit? Why, exactly, is this discovery so important? And… what’s next?

Around 1.3 billion years ago, two black holes collided. But we just found out about it this September, in a big way. On September 14, the whole planet was stretched and squeezed by just the tiniest bit — way too small for you or me to feel — but it was enough that some of the most advanced technology in the world could measure it.

According to Einstein’s theory of general relativity, mass curves spacetime. And when mass moves, it can compress and stretch spacetime, in the form of the ripples that we call gravitational waves. Using Einstein’s equations, physicists can look at certain scenarios and predict the patterns of the waves they’ll create. And in this case, the pattern matched what we’d expect to see if two black holes collided.

That signal was really hard to find, though, because the effects of gravitational waves are super tiny. Like, this whole discovery is based on some mirrors that moved by a few thousandths of the diameter of a proton! But even though the twitches were small, two state-of-the-art detectors were able to pick them up.

One is in Washington State, the other in Louisiana, and each of them is basically a giant L, with four-kilometer arms. The idea is that if a gravitational wave comes along, it’ll expand the space along one arm and squeeze it along the other.

Laser light travels along each arm of the detector, bouncing off of mirrors at either end. Eventually, the two beams of light recombine, and the waves of both beams should be traveling together, synchronously. But if one arm’s distance is suddenly longer than the other — because a gravitational wave stretched it — then one beam of light will have spent more time traveling, and the waves will be out of sync.

Using this awesome system, the detectors picked up on something that looked like a gravitational wave in the data. But that didn’t necessarily mean that’s what it was. There are all kinds of other factors that can affect the data, like if a distant earthquake made the mirrors jiggle a little. Plus, there are four people whose job it is to put in fake signals that look like gravitational waves — just to make sure that researchers are analyzing the data properly.

That’s why a team of about a thousand scientists spent months trying to figure out what really caused the signal on September 14. But they didn’t find any earthquakes. There was a lightning strike in Africa, but it wasn’t strong enough to affect the detectors. And nobody had stuck a fake signal in the data, either.

Eventually, the researchers realized that this had to be the real thing, that the odds of recording this signal and having it not be a gravitational wave were less than one in 3.5 million. So that’s it. And now that we know how to detect these waves, there are all sorts of new things we might discover.

Now we have proven that we have the technology to go after and detect gravitational waves, this opens up many possibilities,

Luis Lehner said during an interview soon after the conference’s announcement.

  Right now, we mainly observe the universe using the electromagnetic spectrum, searching for patterns in light waves that range from the lower-energy radio waves to high-energy X-rays. Those observations have taught us a lot, but there are some things — like black holes — that don’t produce electromagnetic radiation, but they do give off gravitational waves.

So all we need to do is measure the gravitational waves coming in, then use Einstein’s equations to work backward and figure out what caused any particular pattern. Eventually, we might be able to observe all kinds of things, like more black holes merging, or neutron stars crashing into each other, and other things that we could not otherwise detect.

Once we’ve collected data from pairs of black holes, they will be like lighthouses scattered through the universe,

said theoretical physicist Neil Turok.

We will be able to measure the rate the universe is expanding, or how much dark energy there is in the universe to extraordinary precision, far, far greater than what we can do today

He added:

Einstein developed his theory with some clues from Nature but made basically on the grounds of logical consistency. One hundred years later you’re seeing its predictions confirmed at exquisite precision.

According to the researchers in charge of the project, LIGO the pair of detectors that made the discovery has already detected more signals that look like they could be coming from gravitational waves. And bigger, better gravitational wave detectors are in the works.

The plan for the Einstein Telescope, for example, is to have three arms, each 10 kilometers long, arranged in a triangle. It’s still in the early stages of planning — they don’t yet know exactly where it’ll be built yet — but it could be online by the late 2020s.

Then there’s eLISA, an ESA mission planned for 2034, which would put three satellites in orbit around the Sun to look for gravitational waves in space. And its arms would be a million kilometers long. So, this might be the first event we’ve observed using gravitational waves. But it definitely will not be the last.

Similarly, when our descendants look back on this era, and they ask themselves, ‘What great things came to us?’ … I believe there will be an understanding of the fundamental laws of the universe and an understanding of what those laws do in the universe, and an exploration of the universe,

Kip Thorne said.

LIGO is a big part of that. The rest of astronomy is a big part of that. And I think that cultural gift to our future generations is really much bigger than any kind of technological spin-off, than the ultimate development of technology of any kind. I think we should be proud of what we give to our descendants culturally.

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