Oct 13, 2022

Terrestrials: The Unimaginable

Over a billion lightyears ago, in the darkness of outer space, a collision of black holes sent out a fleet of invisible waves that were headed right toward planet Earth. The waves were so powerful they could ripple spacetime but most people on Earth didn't believe the waves were real. SPOILER ALERT: The waves are called gravitational waves and…they are real! Astrophysicist Dr. Wanda Díaz Merced tells the story of what happened when they hit Earth in 2015 and how scientists came to learn to use senses beyond eyesight to detect the waves. We also learn from Dr. Stavros Katsanevas about the building of a giant gravitational wave catcher called “The Interferometer.” This episode also explores how to persist in the face of doubt as we learn Wanda's tale of going blind and learning how to listen to the stars.

Learn about the storytellers, listen to music, and dig deeper into the stories you hear on Terrestrials with activities you can do at home or in the classroom on our website, Terrestrialspodcast.org

Watch the interferometer come to life, disco style, and find even MORE original Terrestrials fun on our Youtube.

Badger us on Social Media: @radiolab and #TerrestrialsPodcast 

More from Terrestrials 

The Shovels: Dig Deeper

For each episode of Terrestrials, we provide a selection of activity sheets, drawing prompts, musical lessons, and more. We call them “shovels” because we hope they will help you (and your friends, family, students, neighbors, etc) dig more deeply into the world! You can do them at home, in the classroom, outside, or in the privacy of your own mind. We hope you enjoy!
If you want to share what you’ve made, ask an adult share it on social media using #TerrestrialsPodcast and make sure to tag @Radiolab

Draw -  Use your ears to draw! In this very special drawing prompt, Wendy Mac and the DrawTogether team pull in an actual rockstar to play you various favorite sounds to draw. It's a feast for the mind, ears, and hands. Grab a pencil, pen, crayon, marker, anything, and check it out here!

Play 🎶 - Learn how to play the chords to the song “UNIMAGINABLE

Do - Get crafty with a fun activity sheet!  

This week’s storyteller is Dr. Wanda Díaz Merced.

Want to keep learning? Check out these resources to learn about the time-bending power that is the gravitational wave:

Get to Wanda a little better; watch her TED talk!
Take a tour of the world’s first interferometer! (Free monthly tours in person in Richland, WA)
Train yourself to use sound for signal detection in astronomy. 
Learn more about asteroseismology with the wonderful Hank Green!
Spooked by the idea of the infinite universe? Listen to John Green’s “Against Nihilism” (probably best for 13 and up)!

Terrestrials is a production of WNYC Studios, created by Lulu Miller. This episode is produced by Ana González, Alan Goffinski and Lulu Miller. Original Music by Alan Goffinski. Help from Suzie Lechtenberg, Sarah Sandbach, Natalia Ramirez, and Sarita Bhatt. Fact-check by Natalie Meade. Sound design by Phoebe Wang with additional engineering by Joe Plourde. Our storytellers this week are Dr. Wanda Díaz Merced and Dr. Stavros Katsanevas. Transcription by Caleb Codding.

Our advisors are Theanne Griffith, Aliyah Elijah, Dominique Shabazz, John Green, Liza Steinberg-Demby, Alice Wong, and Tara Welty.

Terrestrials is supported in part by Science Sandbox, an initiative of the Simons Foundation.

Have questions for us, badgers? Badger us away! Your parent/guardian should write to us along with you, so we know you have their permission, and for maybe even having your ideas mentioned on the show. Email terrestrials@wnyc.org

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LULU MILLER: Three, two, one.

WANDA DÍAZ MERCED: Let's imagine that you are invisible.

LULU: And you're soaring through outer space.

WANDA DÍAZ MERCED: Moving at the speed of light.

LULU: And you fly, you dip up and down ...


LULU: Up and down.

WANDA DÍAZ MERCED: Like a—like a wave.

LULU: And you are ...


LULU: When you hit nearby planets, you stretch and squeeze them like play-doh, sending ripples through space and even ...

WANDA DÍAZ MERCED: Having an effect on time. Mm-hmm.

LULU: And as rocks and stars and time itself apparently, tremble in your wake ...

WANDA DÍAZ MERCED: You became a gravitational wave.

LULU: How do you say that in Spanish, by the way, gravitational wave?

WANDA DÍAZ MERCED: Onda gravitacional.

LULU: Onda. Onda gravitacional?

WANDA DÍAZ MERCED: Very good! Perfecto!

LULU: [laughs] Gracias! All right, well now is the time when I try to make you sing the theme song with me.

WANDA DÍAZ MERCED: Sí, cómo es—how is the song?

LULU: Okay. "Terrestrials. Terrestrials. We are not the worst, we are the ..."

WANDA DÍAZ MERCED: And what do I say?

LULU: [sings] "Bestrials!"


LULU: Terrestrials is a show where we uncover the strangeness waiting right here on Earth, and sometimes break out into song.

[Theme song: There's so much to discover when you listen close. Terrestrials. Terrestrials. This time we get celestial.]

ALAN GOFFINSKI: Meaning the stuff up there in the sky, like stars, moons, suns and, you know, outer space stuff.

[Theme song: Terrestrials. Terrestrials!]

LULU: Good voices not required. I am your host, Lulu Miller, joined as always by my Songbud ...

ALAN: Hello, hello!

LULU: Alan.

ALAN: Y hola a todos!

LULU: And ...

ANA GONZÁLEZ: Hola, Wanda. ¿Cómo estás?

LULU: Producer Ana, here to help me occasionally translate our very special guest, Dr. Wanda Díaz Merced.


LULU: Ciao!

LULU: Dr. Wanda is an astrophysicist, and she's joining us today from her high security space observatory to tell us this story about a pack of gravitational waves that were headed right for planet Earth, only very few people on Earth believed the waves were actually coming because we couldn't see them.

WANDA DÍAZ MERCED: So let's—let's do this. I'm ready.

LULU: Okay. So our story begins in the dark—the darkness of outer space, 1.3 billion light years ago, when suddenly ...

[crash sound]

LULU: ... there's a crash!

WANDA DÍAZ MERCED: Oof! It was very powerful.

LULU: Two giant black holes collided. And out of that collision came gravitational waves. Picture them like the ripples that come after you drop a pebble in a pond, only these waves can ripple space-time, meaning they stretch and squeeze anything in their path be it stars, planets or even time itself. And some of these incredibly powerful and fast waves were headed right for planet Earth.


LULU: [laughs] Uh oh!

LULU: Now no one on Earth knew the waves were coming for them because there was no one on Earth yet. But even once humans appeared, they still had no idea that even a single wave was headed our way because ...

WANDA DÍAZ MERCED: It doesn't fall into what we can perceive with—como se dice—with the thing I have on my face. Como ...

ANA: Eye?


ANA: [laughs]

LULU: Thanks, Ana.

WANDA DÍAZ MERCED: The human eyes, sí. Forgive me!

LULU: And so we all walked around with our human eyes not seeing these waves headed our way, until one dude, instead of using his eyes to look for what was out there, used ...

WANDA DÍAZ MERCED: His imagination.

ALAN: Hmm ...

LULU: This guy's name, by the way, was ...

WANDA DÍAZ MERCED: Albert Einstein.

LULU: Maybe you've heard of him? Big hair, a little bowtie. He conjured up this idea of spooky, invisible waves that could bend both space and time.

ALAN: [imitating Einstein] What should I call them?

WANDA DÍAZ MERCED: Gravitational waves!

LULU: But very few people believed the waves were actually real. And then his time on Earth ran out. But in his wake, every so often someone would read his work and believe.


LULU: Like this guy, Dr. Stavros Katsanevas ...

STAVROS KATSANEVAS: Because I've seen the equations.

LULU: ... a scientist from Greece who believed in Einstein's idea so deeply, he began standing up in front of meetings of fancy government officials ...

STAVROS KATSANEVAS: In front of the unbelievers.

LULU: ... saying that he could prove the waves were out there if they would just give him millions of dollars to build a machine that was the size of a shopping mall and filled with ...


LULU: And while Stavros joined the frontlines of scientists saying that with the right machine they could prove the waves were real ...

STAVROS KATSANEVAS: For 40 years, we were fighting.

LULU: ... a girl was born in Puerto Rico.

WANDA DÍAZ MERCED: I was born long, long after Albert Einstein.

LULU: [laughs]


LULU: In a little town called Gurabo, that was alive with things she couldn't see.

WANDA DÍAZ MERCED: During the nighttime, we would hear the coquís making the sound [coquí, coquí].

LULU: Little tree frogs.

[coquí, coquí]

LULU: And she began to wonder about the things that existed beyond the coquís.

WANDA DÍAZ MERCED: I do remember we went to the island of Culebra.

LULU: The things above the coquís.

WANDA DÍAZ MERCED: There is no light pollution at all.

LULU: And one night on the beach ...

WANDA DÍAZ MERCED: I looked up, and I saw so many stars. So many! It was—it was like someone took a brush, dipped it in white paint, and then just splashed the brush on dark.

LULU: Huh.

WANDA DÍAZ MERCED: On a very black background.

LULU: Like, just a big splatter all across the night sky? Like, it was just more stars than you'd ever seen?

WANDA DÍAZ MERCED: Sí! And for some reason, I felt closer to them.

LULU: But as Wanda was looking at those bright stars, dark spots were closing in. She didn't tell anyone at first that she was going blind. And the less she could see the world around her, the more she felt ...


LULU: But she didn't want to give up on those stars and thinking about the questions they brought alive inside her, so when she got to college she took physics classes. And while she couldn't see the words in her textbooks anymore, she figured could record audio of her professors teaching. Only when she got home to play the tapes back and study, she just heard ...

WANDA DÍAZ MERCED: Today we are discussing ... [sound of chalk on a blackboard] ... Gauss's equation.

[sound of chalk on a blackboard]

LULU: She could hear the chalk writing on the blackboard, but had no way of knowing what the writing said.

WANDA DÍAZ MERCED: Like, I'm thinking "What equation?" Because Gauss had a number of equations. And then you hear the chalk circling, "Shhhh."

LULU: Was there ever a moment where you started to worry you would not be able to do science?

WANDA DÍAZ MERCED: Sí. That feeling of impossibility really kept me—kept me searching and searching and searching and trying and trying and trying and repeating class after class after class, regardless how much my lecturers would laugh at me.

LULU: Hmm. They'd laugh?

WANDA DÍAZ MERCED: Yes, they did.

LULU: "You should change your major," they'd say. "You'll never be a blind astrophysicist."

WANDA DÍAZ MERCED: But I remember that my mentor, Dr. Daisaku Ikeda, that he said, "Let them say what they will. Whatever they're saying, it tells more about them than about you."

LULU: So Wanda kept ...

WANDA DÍAZ MERCED: Searching and searching and searching. And searching and searching and searching. Trying and trying and trying.

LULU: And then one day, she meets up with her really good friend.

WANDA DÍAZ MERCED: Emilio, who knew that I was losing my sight.

LULU: And he was holding in his hand this really old device that he wanted to give to her called a radio.

WANDA DÍAZ MERCED: It's a radio receiver that receives the waves that are emitted by an antenna, like the radio station.

LULU: Only this radio wasn't picking up the hottest Puerto Rican tracks of the '90s coming from radio stations. It was able to hear things beyond the Earth.

WANDA DÍAZ MERCED: It was capable of detecting things like, for example, emissions from the sun, and also the galactic background.

LULU: Wait. So like, you're hearing that in real time?


LULU: [gasps]

WANDA DÍAZ MERCED: I was hearing it!

LULU: Wanda played us the sound of a bit of energy leaving Jupiter.

WANDA DÍAZ MERCED: And when I heard that, I thought there is a space for me in this science.

LULU: So Wanda keeps listening to the night sky. She learns that she can hear the swooshes of comets and bangs of faraway collisions and rumbles of star earthquakes.

LULU: Which are a thing, and I guess should be called starquakes?


LULU: And while other astronomers are straining through telescopes and computer screens to make out little pinpricks of light, Wanda is grooving out in her headphones, listening to the chorus of information coming from space, earning her PhD, landing at a lab at Harvard's Smithsonian Center.


LULU: And at some point, she comes across the idea of gravitational waves. And the thought that there might be invisible ripples whooshing through space affecting reality even if we can't see them immediately made sense to her.


LULU: Uh, speaking of which, those gravitational waves from the long ago collision were by this point—the year 2011—getting very—like, very, very, very, very, very close to our planet. What was going to happen when they hit? Find out after this short break!


LULU: Terrestrials is back. A fleet of invisible gravitational waves are headed toward our planet, where finally believers like Stavros and Wanda and a bunch of folks at MIT, Caltech and beyond, have convinced governments to let them build this massive machine with two arms that are each over a mile long and filled with ...


LULU: That should, using a complicated set of physics and mirrors, be able detect if a gravitational wave actually passes through.

STAVROS KATSANEVAS: That was my glory. [laughs]

LULU: And since the machine detects the presence of gravitational waves by picking up interference in space-time, the machine is obviously called the inf ...

WANDA DÍAZ MERCED: Interferometer.

LULU: Interferometer.

[ALAN: [singing] What's that new machine with those funky laser beams? (It's the interferometer.) Right on! And how will these astronomers detect data from the universe? (The interferometer.) That's right! Laser beams so strong, shoot three kilometers long, oh yeah! (Interferometer.) That's 1.86 miles, my friend. These beams of light are gonna expand our understanding of the universe. (We hope! We think!] It's a complicated machine, but nobody believes in it like Stavros. (And Wanda) Maybe everyone will believe something no one ever could see when an invisible wave riding through space hits the Earth.]

LULU: So ...

[ALAN: [singing] Let's fire this machine up, see if this thing works!]

LULU: ... one day in 2015, scientists set the interferometer in motion, and the lasers start searching.

WANDA DÍAZ MERCED: Searching and searching and searching. And searching and searching and searching. Trying and trying and trying.]

LULU: And then early in the morning on September 14, 2015, suddenly ...


LULU: Did you hear it? Okay, one more time.


LULU: Interference!

LULU: And that little bloop is actually a gravitational wave hitting the Earth in real time?



STAVROS KATSANEVAS: That's how we've heard the universe.

LULU: You have a big smile on your face.

STAVROS KATSANEVAS: Yeah, of course.

LULU: Do you remember where you were that day?

WANDA DÍAZ MERCED: Sí claro. Of course I remember!

LULU: Wanda's working in the Harvard lab at the time.

WANDA DÍAZ MERCED: We heard the news. Everyone is in their office. Everyone is excited. But also everyone is—everybody's working.

LULU: So, like, you're whispering? Like, "A gravitational wave has been detected!"

WANDA DÍAZ MERCED: [laughs] Oh, we've been waiting—[whispers] we've been waiting for decades for this to happen! Oh, my God! Finally! You get excited.

LULU: And as for those waves, they didn’t hurt anyone or anything, but they did knock things around a little bit. They jiggled buildings, they shook the lasers and mirrors of the interferometer, which is how we knew they hit. They changed the distance between cities. For just a moment, they messed with time.

[ALAN: [singing] Which I still don't really understand, but I gotta keep moving on with the story.]

WANDA DÍAZ MERCED: Even in our bodies we didn't notice, right? But our bodies may have vibrated.

LULU: Like a little ripple? Like, as it passed through, we all kind of jiggled ...


LULU: ... a tiny bit?

WANDA DÍAZ MERCED: Like a wiggle. Like a wiggle.

LULU: [laughs]

WANDA DÍAZ MERCED: But we didn't—we didn't notice, right?

LULU: Wow!

LULU: We couldn't feel it. We couldn't see the waves, but the reason the scientists knew they had hit was again because of ...


LULU: ... sound.

WANDA DÍAZ MERCED: There is much more than what the eye alone can perceive.

LULU: Space, Wanda says, is noisy with information that we can use our sense of hearing to understand.

WANDA DÍAZ MERCED: But we are trained not to use it. So what I want to bring is that we kind of detach ourselves from using all my senses in the process of learning.

LULU: She worries in particular about astronomers and astrophysicists.

WANDA DÍAZ MERCED: Their training is strictly visual.

LULU: Hmm.

WANDA DÍAZ MERCED: They are fine men and women, right?

LULU: Mm-hmm.

WANDA DÍAZ MERCED: Great researchers. But what is visible is just an itty bitty tiny region, tiny region of the electromagnetic—so limited.

LULU: Are you saying that by only focusing on the tiny region of light that we can see, astronomers ...

WANDA DÍAZ MERCED: They may be—they may be missing discoveries.

LULU: Hmm.

WANDA DÍAZ MERCED: Yes. That is what I'm saying.

STAVROS KATSANEVAS: We have passed all these years in light and shadow. We did not use sound as a discovery instrument. We did not use all the senses.

LULU: When Stavros heard about Wanda's work, he reached out to her. And now they work together at the interferometer in Pisa, Italy, where she's teaching him to recognize more and more sounds coming from space.

STAVROS KATSANEVAS: Each one of them is a cosmic piano.

LULU: Wanda is training him and other scientists how to recognize the rattling of space dust in the tail of a comet, and the sound of shooting stars and dying stars and stars being born, and even the sounds of things we'll never be able to see like Martian wind, interstellar turbulence, and the echoes from long ago explosions.

STAVROS KATSANEVAS: Each one of them has its own frequencies.

LULU: And the symphony of all those different frequencies raining down from space can give humanoid scientists new clues about the evolution of the universe, and even the potential for life on faraway planets.

WANDA DÍAZ MERCED: We did experiments simulating astronomy information. When professional astronomers used audio, their sensitivity to events that were hidden in the data increased.

LULU: Wait. Meaning they could understand more about what was happening in space when they used their ears?


STAVROS KATSANEVAS: Exactly. That's the fantastic thing.

LULU: Wild!

LULU: Now as for the end of the story of what happened to those gravitational waves from those two black holes that collided long ago? Well, after they literally rocked our world—[laughs] because they, like, rocked the planet when they hit—well, they just kept rippling out into the universe, passing by stars and moons.

WANDA DÍAZ MERCED: What I imagine is the amount of unimaginable—unimaginable things those ripples may find on their way as they are traveling to—into infinity, right? The wonderful things that they will find.

LULU: Like what? Like planets and comets and suns?

WANDA DÍAZ MERCED: Beyond! Unimaginable.

[ALAN: [singing] A collision sends a shockwave. I will shake anything that's in my way. And as I rattle space and time I leave it all behind. Everything we've ever known, unimaginable. Wandering the dark night sky, towards infinity I fly. Beyond the planets and the stars, the asteroids and meteors. Beyond the galaxies we've named and all the ones we've yet to tame, I go, I go and go and go. Unimaginable.]

WANDA DÍAZ MERCED: They remain a mystery because we do not know about it. And the fact that we do not know about it, doesn't mean they do not exist. And the fact that we do not know about it, doesn't mean they do not exist. It does not mean that they do not exist.

[ALAN: [singing] And I don't care if I'm alone in this and nobody believes. I will swim this sky forever. I will always feel the breeze. When everything that is familiar fades to black and turns to cold, I will listen on in wonder, unimaginable.]

WANDA DÍAZ MERCED: Unimaginable.

LULU: Songbud! Bringing the ballad this week. Putting his heart on the line. Where's your heart? Is it on the line? Or is it in a cage? Terrestrials was created by me, Lulu Miller, with WNYC Studios. It is produced by the time- and mind-bendingly amazing Ana Gonzalez and Alan Goffinski—along with me. With help from Suzie Lechtenberg, Sarah Sandbach, Natalia Ramiez, Miriam Bernard, Natalie Meade, Joe Plourde and Sarita Bhatt. With sound design this episode by Phoebe Wang!

LULU: Our advisors are: Theanne Griffith, Aliyah Elijah, Tare Welty, Liza Steinberg Demby, Dominique Shabazz and Alice Wong.

LULU: Terrestrials is supported in part by Science Sandbox, an initiative of the Simons Foundation. Special thanks this episode to Bryn Bliska for original cosmic keyboard, and to J.D. Voyek, Sam Schultz, Vincenzo Napolitano, Emilio and Jeremy Bloom. Now you should stop listening to this wonky collection of sound waves because there is nothing else cool about to happen.

LULU: Huh. What's that?

BADGER: Excuse me, I have a question.

BADGER: Me too.

BADGER: Me three.

BADGER: Me four.

LULU: The badgers!

LULU: Listeners with badgering questions for the expert. Are you ready?


BERIT: Hi. My name is Berit, and I'm eight years old. I was wondering, would the gravitational pull of a black hole stretch you as thin as a piece of spaghetti if you got sucked into it?

WANDA DÍAZ MERCED: [laughs] Sí! If I'm approaching the black hole head first, my head will be pulled towards the black hole.


WANDA DÍAZ MERCED: As my feet are being pulled away from me. I'm becoming a piece of spaghetti, yes. Yes.

LULU: Pasta luego!

REX: Hi, I'm Rex. I'm eight years old. My question is: once a star dies, can it come back to life?

WANDA DÍAZ MERCED: Ah, que pregunta. What a beautiful question. Hmm, as far as we know, once that object dies, elements that are vital for the generation of life as we know it here on Earth, are spreaded all over the universe.

LULU: Hmm, so the star doesn't come back to life, but we do?

WANDA DÍAZ MERCED: Yes. The star corpses is the seeds of life.

EMILY: My name is Emily Silverman, and I'm 34 years old. My question is: could we ever use gravitational waves to propel ourselves through space at faster than the speed of light?

WANDA DÍAZ MERCED: I do not believe in impossibles, right? Very, way unlikely. Way unlikely.

RUSE: Hello. My name is Ruse Nichols. I'm 10, and my question is: is there an end to the universe?

WANDA DÍAZ MERCED: I don't know. I don't think so. No.

LULU: All right. We'll leave it there. Infinite possibility ahead—and behind—and I definitely won't tell you the thing that Wanda told me that's still bothering me at night, which is that apparently we are all on our way to turning into black holes. I'm nice, so I won't curse you with that knowledge. Don't worry. It's not gonna happen for, like, millions of years. If you would like to badger an expert or suggest a topic for the show, head on over to our website, TerrestrialsPodcast.org. There, we also have special drawing prompts that were made for every episode by the incredible Wendy Mac of the DrawTogether podcast. For this one, she has you draw different sounds. And it's just this neat podcast that you can listen to, so she's like, encouraging you and coaching you in your ear while you draw. It's so much fun. You can find that again, along with other activities and videos on our website, TerrestrialsPodcast.org.

LULU: If you are liking the show, please rate and review us. It helps our chance of continuing on. Thanks much you for listening. Catch you in a couple spins of this star-dusted old planet of ours. Bye!

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