Einstein was never sure this moment would come.

But Thursday, in a remote corner of an MIT basement, physicists who followed in his footsteps marked a rare moment of validation. And it’s all because the world has finally heard a "chirp" from space.

That -- it turns out - is the sound two black holes make as they collide. A hundred years ago Einstein first described these pits of space that suck everything toward them, including light, with irresistible force. Their power, he theorized, would create ripples in the fabric of space-time.

But even Einstein wondered if anyone would ever be able to test his theory. When Nergis Mavalvala came to MIT and joined the team that decided to try, it was a risk.

“It had never been done before. Because the technology was not fully mature. And so there were all kinds of risks about -- were we right on the astrophysics? Would the technologies would work the way we thought they would?” she recalls. 

Over the next 25 years, Mavalvala helped create and fine tune instruments to detect gravitational waves. She’s now an MIT professor of physics.

“You know till the day came I never thought about what it would be like. It was sometimes a slog. Experiments always are," Mavalvala says.

And when they finally heard the sound that proved their theories, Mavalvala’s colleague. Matthew Evans. thought it was a mistake. He’s an assistant MIT physics professor.

“We knew about this event. We had looked about the data many months ago, Nergis and I. I think I told Nergis it was there back in September. And it was very exciting. We were all in a state of shock. I spent the month afterward combing through the instrument figuring out what had gone wrong -- because it had always in the past been something that needed to be fixed. And this was the first time where there was a signal that was unmistakably not just a bump in the detector because detectors don’t go 'chirp,'” he says. "At this point we’re maybe more on toward relief that we’ve checked everything out and are ready to announce it.”

Mavalvala says black holes and gravitational waves didn't sound the way she thought they would. 

"To be honest I had to work hard to hear it the first time," she says. "And then when you’ve heard it a few times you’re like this is the most natural sound in the world, how did I miss it.”

And this is just the beginning, Mavalvala says -- as scientific instruments improve, we’ll find the universe has many more rich and complex sounds for us to discover.