MOLLY WEBSTER: Hey, I'm Molly Webster.

LULU MILLER: I'm Lulu Miller, and this is Radiolab. And today we have two very different stories from two very different reporters, one of whom is you, Molly.

MOLLY: [laughs] Yeah.

LULU: Who each got pulled down into the same very strange and very dark place.

ANNIE MCEWEN: All right. Thank you for joining me.

LULU: And we're gonna begin with producer Annie McEwen.

ANNIE: Yeah. Yeah, yeah, yeah.

LULU: Well, where do you want to start?

ANNIE: Where do I want to start? I want to start in Siberia.

LULU: [laughs] Okay.

ANNIE: So the year is 1908. It is June. It is a bright, sunny morning. And in this remote part of Russia, it's mostly forest, swamp, bugs, reindeer. The few people in the area are waking up, stretching their legs, making breakfast, and everything's cool.

LULU: Okay.

ANNIE: It is promising to be just a beautiful day. But that is all about to change, because just after 7:00 am, something appears low in the sky, as bright as a second sun.

LULU: Hmm!

ANNIE: From oral histories gathered years later, people reported looking up and seeing this thing rocketing towards Earth, faster than a bullet. It quickly grows into a giant ball of fire, dragging behind it this tail of blue and white light.

LULU: Whoa!

ANNIE: It arcs across the sky, disappearing over the horizon. And then a shockwave pulses through the forest, flattening trees, shattering windows, throwing people to the ground. The earth shakes, boats are tossed from rivers. Some people reported a hot blast of wind. Others reported a colossal amount of smoke and fire. And luckily, because it's such a remote region, despite the fact that 800 square miles of forest were flattened, only somewhere between zero and three people are killed.

MOLLY: Huh. Wow!

ANNIE: And I don't know, have either of you heard of this before? It's called the Tunguska event?

LULU: No.

MOLLY: I've never heard of it.

LULU: Tunguska.

ANNIE: Tunguska.

LULU: Is that—that's the town?

ANNIE: That's the nearby river.

LULU: Okay.

ANNIE: And today, this is still considered the largest impact event in recorded human history. So an impact event ...

MOLLY: So there's a something that, like, hit us.

ANNIE: Yes. Well, maybe.

LULU: Hmm, okay!

ANNIE: So a bunch of scientists go plunging into the forest to try to figure out what the heck just happened. They scramble over fallen log after fallen log, through dense bog after dense bog for miles and miles until finally they realize they have no idea what happened out here.

LULU: [laughs] Okay. Really?

ANNIE: Yeah. They can't find any evidence of what caused this huge explosion.

LULU: Wait, what?

ANNIE: Like, they sort of figured this must have been an asteroid, so they thought they'd find debris from an asteroid. Like, space rock.

LULU: Yeah.

ANNIE: They don't find a single bit of space rock in this whole area.

LULU: Weird!

ANNIE: And not only that, an asteroid that would've caused this much destruction should've left probably something like a three-quarter-mile-long impact crater, and they don't find any crater whatsoever.

LULU: That's kind of spooky!

MOLLY: In 800 square miles of destruction, there was, like, nothing from space?

ANNIE: Yeah.

MOLLY: Not even a hole. This is why people think UFOs exist.

ANNIE: Yeah. And I think that, like, that's what the—the scientists were like, "Well, we have to—we have to find what obviously should be there." And so all kinds of ideas cropped up. Like, some people thought it was maybe like a natural gas bubble that burst from beneath Earth's crust. But that doesn't explain, like, the bright light in the sky. Some people thought maybe it was like a strange kind of volcanic eruption. But again, doesn't really explain the light moving through the sky.

LULU: Right.

ANNIE: One guy for a while thought that he had found the crater and it was a lake, but then the locals were like, "Yo, that lake was here. It's been here forever."

LULU: [laughs]

ANNIE: So they were trying for many, many years to figure out what the heck it was. But so the main theory, and the one that holds strongest today, is that it was an asteroid—a really big one.

LULU: Okay.

ANNIE: Estimates put it at 120 feet across, 220 million pounds.

MOLLY: Oh my gosh!

LULU: It's like an office building.

ANNIE: Yeah.

LULU: Or like an apartment building headed toward planet Earth.

ANNIE: Right. And the theory is that it came into Earth's atmosphere at kind of a weird angle, and so it stayed in the atmosphere and started to overheat. And it got so hot that it eventually just went boom!

LULU: Wait, but then are there some chunks? Or it's just dust and fire and energy?

ANNIE: So that's the thing. Like, that's a real question. Like, shouldn't there be some pieces of this, like, somewhere out there? Like, some sort of evidence?

LULU: Yeah!

ANNIE: And that's the part that is still a little weird.

ANNIE: What do you think of that?

MATT O'DOWD: That does seem strange, doesn't it?

ANNIE: I think it does.

MATT O'DOWD: Yeah. But, you know, it's pretty plausibly an atmospheric explosion, and I think, you know, most scientists have sort of dusted their hands off and moved on to the next question with regards to Tunguska.

ANNIE: It's not a cold case? It's not like, oh, on the shelf!

MATT O'DOWD: Well, I think in some people's minds it is.

ANNIE: Hmm.

MATT O'DOWD: Some still believe it wasn't an asteroid.

ANNIE: This is astrophysicist Matt O'Dowd.

MATT O'DOWD: Professor at the City University of New York, Lehman College.

ANNIE: And I reached out to Matt because I had recently seen him on his side gig ...

[ARCHIVE CLIP, PBS Spacetime: Have you ever asked what is beyond the edge of the universe?]

ANNIE: ... this really awesome physics YouTube show ...

[ARCHIVE CLIP, PBS Spacetime: What would it take to build a starship?]

MATT O'DOWD: ... which is called PBS Spacetime.

ANNIE: Talking about this really wild ...

MATT O'DOWD: Absolutely. [laughs]

ANNIE: ... alternate theory of what could have caused the Tunguska event of 1908.

MATT O'DOWD: Which is the black hole.

LULU: Wait ...

MOLLY: That's ...

LULU: What? [laughs]

MOLLY: That's different.

LULU: Like, a black hole, like a space black hole did this? Like, how? I don't know, radiated a death wave toward planet Earth?

MOLLY: [laughs]

ANNIE: No, Matt's talking about a black hole actually hitting Earth.

MATT O'DOWD: Exactly.

LULU: What?

ANNIE: Which sounds impossible, because usually when we're talking black holes ...

[ARCHIVE CLIP: My God, right out of Dante's Inferno!]

ANNIE: ... we're talking about these big, terrifying, churning places in space where gravity is just so strong that not even light can escape it.

[ARCHIVE CLIP: It's a monster, all right.]

ANNIE: They eat stars and planets and gas. And they have all these almost like supernatural qualities, like they ...

MATT O'DOWD: … warp the space around them, change the flow of time, and all of that awesome stuff that comes out of general relativity.

ANNIE: But if one of these black holes approached Earth, its gravitational pull would be so strong that ...

MATT O'DOWD: Earth would be, they call it spaghettified.

[ARCHIVE CLIP: The black hole is pulling us in!]

ANNIE: The entire planet would begin to stretch towards the black hole, and then as it punched in ...

MATT O'DOWD: Earth would essentially follow it through the hole that it made.

ANNIE: What?

MATT O'DOWD: So you can imagine Earth just folding in afterwards, and it would probably follow the black hole in this kind of stream of super hot stuff.

ANNIE: Until all of Earth, everything on it, everything in it is ripped apart into individual atoms and Earth is devoured.

MATT O'DOWD: Right, so ...

ANNIE: That's so awesome.

MATT O'DOWD: It's awesome.

ANNIE: Not what happened. [laughs]

MATT O'DOWD: But you would also notice, you know?

ANNIE: Right, right, right. We would all agree today, that was a black hole.

MATT O'DOWD: Exactly. Right.

ANNIE: Okay, so this obviously is not a very plausible explanation for the Tunguska event.

LULU: No.

MOLLY: No.

LULU: Certainly not.

ANNIE: But that's because there's one very important difference between these black holes and the one that potentially destroyed 800 square miles of Siberian forest, which is that rather than being this giant monster, the Tunguska black hole would have been a really, really ...

MATT O'DOWD: Teeny tiny ...

ANNIE: ... monster.

MATT O'DOWD: Very small.

LULU: Wait, black holes can be little?

ANNIE: Yeah, like, really small.

MOLLY: Like how small?

MATT O'DOWD: Like, very tiny. Like ...

ANNIE: Itty bitty.

MATT O'DOWD: ... so small.

ANNIE: I mean, could it fit on my hand?

MATT O'DOWD: Yeah, I mean ...

ANNIE: Are we talking like a peanut?

MATT O'DOWD: We're talking, like, the size of a hydrogen atom.

ANNIE: Oh, an atom!

MATT O'DOWD: Yeah.

LULU: Oh my goodness! That is very small for a black hole. Okay.

ANNIE: Now so these tiny little black holes are special black holes because typically, a black hole gets made after a star explodes.

LULU: Yeah.

ANNIE: But these tiny little black holes, they got made in this one particular explosion.

MATT O'DOWD: 13 and a half billion years ago, in the Big Bang.

ANNIE: Which was a very great day for existence.

MATT O'DOWD: Yeah, exactly. Awesome.

ANNIE: But a very upsetting day for gravity.

MOLLY: Because, like, the Big Bang was the explosion outward where things became free of gravity in a way?

ANNIE: Yes. Everything had been packed together in this really tight, dense ball, and then this little dense ball was this rapidly expanding ocean of ...

MATT O'DOWD: … hot hydrogen and helium.

ANNIE: ... these bright, swirling gasses.

MATT O'DOWD: Glowing.

ANNIE: And gravity was like, "Oh my God, I have to get all this back in that tiny little hole again!"

MATT O'DOWD: Exactly.

ANNIE: "For one minute I fell asleep!"

MATT O'DOWD: Seriously.

LULU: So gravity is stressed.

ANNIE: Gravity is stressed, and immediately begins ...

MATT O'DOWD: Trying to turn the whole universe into a black hole.

ANNIE: Trying to grab everything and pull it back together, which is not possible.

MATT O'DOWD: Mostly it fails, you know, happily.

ANNIE: Because the expansion of the Big Bang is just too powerful. But everything is still ...

MATT O'DOWD: ... so hot and so dense and so compacted together ...

ANNIE: ... that gravity is able to grab some of this stuff, crush it together to create ...

MATT O'DOWD: ... what we call primordial black holes.

ANNIE: Black holes from the beginning of time. And the idea is that these black holes have been just out there all this time, spinning through the universe, doing their thing, devouring stars and planets and other black holes, but over time, as the universe expands and things start to spread out more and more, space starts to get, well, pretty empty. And there's this weird thing about black holes, which is while they eat things up when they can, they are also very slowly spitting stuff out. Which means if they spend long enough moving around in empty space, they will, slowly over billions and billions of years, shrink—even down to the size of an atom.

MATT O'DOWD: Exactly.

ANNIE: So these primordial black holes, or PBHs. Which word do you prefer?

MATT O'DOWD: PBHs.

ANNIE: Really? It sounds like ...

MATT O'DOWD: No, no. Yeah, PBH. It sounds like PBS, but yeah.

ANNIE: No, it sounds like a condiment.

MATT O'DOWD: Yeah, exactly. PBH sauce, yeah. Primordial black hole is good. I'm happy to go with primordial black hole.

ANNIE: It's really good. Okay, I just didn't know if it was, like, too much every time. But okay, let's do it.

MATT O'DOWD: I'll try to say it fast.

ANNIE: Great.

MATT O'DOWD: All right, so ...

ANNIE: Matt explained that even though these primordial black holes could be as small as an atom ...

MATT O'DOWD: Still, they could be very massive.

ANNIE: ... there is still a huge amount of stuff packed into that small space.

MATT O'DOWD: So ...

ANNIE: ... it's an atom, but with the mass of ...

MATT O'DOWD: An asteroid, basically.

LULU: Oh!

ANNIE: And the other thing is that super big black holes, they usually sit in the middle of a galaxy with everything spinning around them. These little primordial black holes, they're kind of like untethered. And since everything in the universe is swirling and spinning and moving around ...

MATT O'DOWD: They do have to cross the orbits of other objects.

ANNIE: Other objects like planet Earth, for instance.

MATT O'DOWD: Exactly.

ANNIE: And it's possible, or so the theory goes, that on a beautiful June morning in 1908, one of these primordial black holes, a particularly small one about the size of a hydrogen atom, but with a mass equal to an office building-sized rock, zooming along at 62 miles a second, about to make a direct hit with a certain patch of Siberian forest.

LULU: Okay. We're back.

ANNIE: We're back. You ready for impact?

MOLLY: Oh my God, yeah!

ANNIE: All right, let's do it.

MATT O'DOWD: Mm-hmm. Okay. Now?

ANNIE: Now!

MATT O'DOWD: Okay. All right, so this primordial black hole punches through the atmosphere.

ANNIE: Like a tiny needle of gravity.

MATT O'DOWD: And stuff gets pulled towards that gravitational build.

ANNIE: Stuff like nitrogen molecules, carbon dioxide ...

MATT O'DOWD: Oxygen molecules.

ANNIE: And this tiny little black hole begins to eat. It devours molecule after molecule after molecule, and each one of those molecules ...

MATT O'DOWD: As it fell into the black hole ...

ANNIE: ... becomes hotter than the surface of a star, radiating ...

MATT O'DOWD: An enormous amount of heat and energy.

ANNIE: And with all that energy, around the black hole, this halo begins to form. And it's not very big, but it is shining ...

MATT O'DOWD: With the power of several Hiroshimas.

ANNIE: Several atomic bombs.

LULU: Oh my God!

ANNIE: And in that moment, if you'd been standing in the Siberian forest looking up at the sky, this would have looked exactly like a second sun rocketing through the sky, pulling behind it a tail of blue and white light. As it got closer and closer to the surface of the Earth, it would suck stuff from the atmosphere into it, and that would actually create enough heat and energy ...

MATT O'DOWD: ... to be equivalent in energy to an asteroid exploding.

ANNIE: Which meant this tiny primordial black hole was creating these enormous ...

MATT O'DOWD: Shockwaves.

ANNIE: And what did that sound like?

MATT O'DOWD: I imagine a ginormous kaboom.

ANNIE: Cool!

MATT O'DOWD: That would flatten forests ...

ANNIE: Knock people over, throw boats out of rivers, shatter windows.

MATT O'DOWD: And then it would hit the ground, and it should actually leave a crater.

LULU: Oh!

MATT O'DOWD: But ...

ANNIE: This one would be much smaller ...

MATT O'DOWD: Sort of a column.

ANNIE: ... thinner. Definitely not what the scientists had been looking for.

MATT O'DOWD: And it would have been harder to find.

ANNIE: It would also be very deep, because while an asteroid stops when it hits the Earth, the black hole doesn't even slow down.

LULU: What?

ANNIE: And as it plummets through the Earth ...

MATT O'DOWD: Through its whole passage ...

ANNIE: ... it would be generating these seismic waves.

MATT O'DOWD: These rings of earthquake expanding from around this bullet shooting through the Earth. And the earthquakes wouldn't be strong, but they would be global.

ANNIE: Meaning every single person, plant, animal on Earth ...

ANNIE: Everyone would just be like, [shaking sound] "What the heck?"

MATT O'DOWD: "Was that a little earthquake?"

ANNIE: Hmm.

MATT O'DOWD: Huh.

ANNIE: Anyway, as this little black hole rips through Earth, it would be eating or burning all the molecules of rock or dirt that it hit.

MATT O'DOWD: And some stuff does follow the black hole, but some stuff just gets super hot.

ANNIE: Leaving behind this trail that ...

MATT O'DOWD: It would at first be molten, and then it would solidify into this column of solid glass.

LULU: [gasps] Like a glass light saber all the way through Earth?

ANNIE: Yes!

MATT O'DOWD: Yeah.

LULU: Stop it!

MATT O'DOWD: This long tunnel of altered material.

LULU: Wow!

ANNIE: And then it comes out somewhere?

MATT O'DOWD: And then yeah, there would have to be an exit wound.

LULU: Wait, where would the exit wound be?

ANNIE: Well, it depends on what angle it came in at.

LULU: The angle?

ANNIE: Yeah. Like, if it had been a perfect shot directly through the middle of the Earth, it would be in Chile somewhere, but ...

MATT O'DOWD: Back in 1908, it could have easily been in the ocean somewhere, and we probably wouldn't have noticed.

ANNIE: If you were on a boat or standing nearby, would you be like, "Oh my goodness! That was—that was something that came up through the floor of the planet and it made a boom, and then there was a bright light."

MATT O'DOWD: It would be like a shooting star coming out of the ground.

ANNIE: That's so crazy!

MATT O'DOWD: Right?

ANNIE: That whole journey through the Earth would have taken this little black hole about two minutes, and then it would continue on making its way through the universe.

LULU: And as it goes forward on the rest of its journey, is there a little bit of 1908 forest floor Siberia inside it?

ANNIE: In some very altered form, yes.

LULU: But okay, I am wondering, like, how many people think—or how likely is it that this is what happened? Or is this, like, a pretty thought exercise?

ANNIE: Well, this is kind of a pretty thought exercise, but it doesn't mean that it's never happened or it's never going to happen. Tunguska just gives you kind of like a case study for, like, okay, well is it possible that it could have been? And these scientists found out yes, it is possible. And statistically, something like this either has happened in Earth's history or truly might happen in Earth's future.

LULU: Well, now that we know there are little black holes out there everywhere, when we come back from a short break we are gonna meet one up close, personal, intimately. Stick with us.

LULU: Lulu.

MOLLY: Molly.

LULU: Radiolab. B-holes. Black holes. So this next one comes to us from you, Molly.

MOLLY: Indeed.

LULU: So what have you got?

MOLLY: So when Annie came to our pitch meeting and she was like, "Have I got a story for you guys. It's about tiny black holes." I was like, "Whoa, Annie! Rolling up with your little black holes pitch? Like, I've got one, too."

LULU: [laughs]

MOLLY: And mine is a little black hole story that just took me in a completely different direction than the one that I or the show normally does.

LULU: Hmm.

MOLLY: And it came out of this conversation that I had with a physicist, Brian Greene, who's like a popular science dude. And we were just having a chat one day, and he told me about this mystery that consumed physicists for decades.

LULU: Okay.

MOLLY: Which is that when things fall into black holes, they seem to just vanish. No one's ever been inside a black hole, we don't know how to look inside of a black hole, so seemingly from our perspective, like, matter disappears.

LULU: Hmm.

MOLLY: But physicists were like, how can that be? Because the first law of thermodynamics says that nothing can be created or destroyed.

LULU: Mm-hmm.

MOLLY: So what happens to the stuff after it falls into the black hole?

LULU: Like, a star goes in ...

MOLLY: Star goes in.

LULU: ... and we don't know.

MOLLY: And you don't know, like, did the star get crushed?

LULU: Mm-hmm.

MOLLY: Is the star through a wormhole out somewhere else? Did the star burn up? Like, there are guesses, there are theories, but at the time no one knew. I mean, talk about a black box, you know? It was one of the biggest mysteries.

LULU: Hmm.

MOLLY: And then Stephen Hawking came along and proposed a solution, which is that even if we can't see what's happening inside of a black hole, the way that matter works is that, you know, occasionally particles are just shot out of things into the universe, right? A particle could come off of you, a particle could come off a chair, particle could be spit out of a black hole. And so he just—he came up with this, like, idea which we now call Hawking radiation, that—that is supported by math, which is a statement I don't fully understand.

LULU: [laughs]

MOLLY: But came up with this idea that if you got to the surface of a black hole, the black hole would be spitting out particles that contained information about, like, what was inside of it.

LULU: Oh, interes—so wait, so it's like the particles would come out, and they might have little clues about, like, the interiority of a black hole?

MOLLY: Yeah, they would be like, "Hey, I'm a particle and I'm telling you that there is a brown rock in here." Like, it would give you a hint of what the black hole has gobbled.

LULU: Oh!

MOLLY: Or what the black hole has seen or intersected with.

LULU: Ooh! Okay.

MOLLY: And the thought is is that all of these particles that are shot out of the black hole kind of gather on its surface and create a glow.

LULU: Hmm!

MOLLY: Yeah, which I just thought that was so beautiful, this, like, somewhat beastly object that none of us understands is revealing parts of itself to the rest of the universe.

LULU: Mmm.

MOLLY: So I learn about all this stuff and I'm like, "Oh, that would be a really cool story. And normally what I'd do is I'd do a lot of, like, reporting, and then I'd put a bunch of voices together and we'd put it on air.

LULU: Mm-hmm.

MOLLY: But—but the idea of a glowing black hole never stuck with me in kind of like a science report-y way. It more started just to remind me of people. And I just thought, "Oh, Little Black Hole would be a great children's book character."

LULU: Hmm.

MOLLY: And so I made it one. I wrote it into a kids' book.

LULU: Indeed you did. I have it right here in front of me.

MOLLY: Yay!

LULU: It is called Little Black Hole.

MOLLY: Yay!

LULU: Okay, and will you—will you flip to the first page of the story, and just read us the first couple pages of the story?

MOLLY: Okay. "There once was a little black hole who loved everything in the universe: the stars, the planets, the space rocks and the space fox, even the flying astronauts. The little black hole loved her friends.

MOLLY: "One day a star came by. The little black hole built a space castle with her. 'La la la,' they sang as they built and soared. The little black hole was having so much fun. She couldn't wait to show the star more of the galaxy. Maybe they could even watch one of the moons rise together."

MOLLY: Okay, so what happens is there's a little black hole, and she's at the center of her galaxy. And she has a bunch of friends—there's even a fox. But basically, there's like a repeated cycle of those friends leaving. Like, a star comes around, and she's excited and they're hanging out, and then the star goes away. And then she's, like, all alone. And this just keeps happening, and she just feels super sad.

MOLLY: And yes, she is eating her friends.

LULU: [laughs]

MOLLY: It's subtle but it's there.

LULU: We—we all eat our friends.

MOLLY: [laughs] And then the little black hole meets a big black hole, another black hole. And the big black hole tells the little black hole to take a deep breath and to close her eyes and to think about the things she loves. And what the little black hole sees is—essentially, she sees herself glowing. She sees her Hawking radiation.

LULU: Huh!

MOLLY: Like, she thought the star had left and the comet had left and the space fox and the space rocks and all these things from the millions of years that this little black hole is living, and she realizes that her friends are all with her. And that makes her feel a little more ready to, like, go on an adventure and play, or just to look out into the vastness and be okay.

LULU: Aww!

MOLLY: Yeah.

LULU: I know that this is based on, like, rigorous astrophysics, but the journey that this little black hole character is on, it does ring so true for loss in life. Like, when friends disappear, when people go away, when you look up blinking and no one's left, that's—that's a hard feeling. And I think everybody—and kids, for sure, but everybody, like, has.

MOLLY: Mm-hmm.

LULU: But I authentically, like, really, really just loved the realization that, like, the memories, the almost companionship in your mind, like, it doesn't have to go.

MOLLY: Yeah.

LULU: It can, but you—but it doesn't have to.

MOLLY: It's interesting that you say that because I had a lot of trouble with the ending.

LULU: Hmm.

MOLLY: Because I was like, I don't in any way want to imply to kids that just because you realize you have some memories inside of you, like, the world's a lot better.

LULU: Yeah.

MOLLY: Like, it's a little bit better.

LULU: Yeah.

MOLLY: And so that was interesting because I just dug from a space of, like, having this memory of a feeling of almost like left behind-ness.

LULU: Hmm.

MOLLY: Once I started to write the book, I'm like, "Oh, I'm the little black hole."

LULU: Hmm.

MOLLY: You know, I'm the youngest of—of four sisters.

LULU: Mm-hmm.

MOLLY: And growing up, I felt like they were constantly, like, leaving.

LULU: Hmm.

MOLLY: Especially as they each got older and, like, went off into the world and then, you know, it was just me. And then I was just like—I just wanted them to come back into my orbit again.

LULU: Yeah.

MOLLY: Did I say the word "orbit" when I was a kid? No, but I was always just like, "Why are you leaving? When are you coming back?" And, like, feeling this sense of, like, loss. And I've had that feeling again and again with other relationships as people come and go. And that kind of echoey solitude is like something that I've always contended with and has been like a daily part of my life.

LULU: Hmm.

MOLLY: And then at one point, I just had this feeling which was like, even if people aren't with me, these people are out there and they love me and they know me and they believe in me. And that somehow makes charging through the world, like, more doable.

LULU: Hmm.

MOLLY: And so for the little black hole, when she glows and sees her friends, she realizes, like, there is a support network somewhere around her, in her, with her, and that just helps her look to the next thing. Okay, so can I tell you one more thing really quickly?

LULU: Please.

MOLLY: Okay.

LULU: Yes!

MOLLY: So when I was fact-checking the book with Brian, he was saying that, you know, as black holes do this Hawking radiation thing, giving away bits and pieces of themselves, you know, they actually become smaller and smaller, which is what Annie talked about. That's how primordial black holes get so tiny. But the thing he told me was is that they give away so much of themselves that they end up evaporating.

LULU: Why?

MOLLY: And so, I don't know. They disappear in the end. They die. Brian was like, "Good luck making that into a kids' book.

LULU: [laughs]

MOLLY: So take that as you will.

ANNIE: Oh, I've got something for you.

LULU: Oh, whoa.

MOLLY: Oh, hey Annie!

ANNIE: Hello.

MOLLY: Where did you come from?

ANNIE: Oh, I've actually—I actually never left. I've just quietly been here.

MOLLY: Okay, cool. Very creepy but cool.

LULU: Anyway, so ...

ANNIE: So the reason I'm butting in is because of something that Matt told me.

MATT O'DOWD: So these are maybe my current favorite thing.

ANNIE: As we were wrapping up our interview.

MATT O'DOWD: Okay, so ...

ANNIE: We'd been talking about Hawking radiation, black holes evaporating, all that good stuff. But then he told me about some current thinking.

MATT O'DOWD: There is one theory. A number of very reasonable scientists think that once the black hole is very small ...

ANNIE: Like, when it evaporates basically all of itself away and is now ...

MATT O'DOWD: ... down to around the Planck scale ...

ANNIE: Which is so impossibly teeny tiny that a rough way of understanding it is, if the Earth was the size of an atom, then one of these small things, these Planck units, would be smaller than an atom on that atom-sized Earth.

LULU: Whoa!

ANNIE: And when the black hole has evaporated down to this inconceivably tiny size, the thought is that ...

MATT O'DOWD: There is no transition that lets it give up its last little bit of mass, so it's stuck.

MOLLY: Oh, whoa! so that means that it can't die, that it just won't.

ANNIE: Mm-hmm.

MOLLY: If that's true, then there are kajillions of skeletons of black holes all over the universe.

ANNIE: Yes.

LULU: What?

ANNIE: And the wildest part of all this is that there is this mystery in the universe you may have heard of, the question of dark matter.

MOLLY: Oh, yes. So that's the idea that there's 80 percent of matter in the universe, that we don't know what it is, but it is heavy, dark and impossible to detect.

ANNIE: Right, and the theory goes that if black holes actually can't totally disappear, but instead get locked at that last teeny tiny invisible size ...

MATT O'DOWD: That sounds exactly like dark matter.

ANNIE: Perfect!

MATT O'DOWD: Exactly. Perfect.

ANNIE: And Matt says if that's the case ...

MATT O'DOWD: Then there must be an unthinkably large number of them out there. And in fact, they must be passing through the Earth constantly if that's the case.

ANNIE: Really?

MATT O'DOWD: I mean, there probably aren't any in the room with you right now.

ANNIE: Okay.

MATT O'DOWD: But over the course of your life, you might be hit by one.

ANNIE: Okay.

MATT O'DOWD: They will, of course ...

ANNIE: Kill you?

MATT O'DOWD: ... pass straight through your body.

ANNIE: And what would happen?

MATT O'DOWD: And they are so small, it would leave absolutely no sign whatsoever.

ANNIE: Would you be like, "Ow!" No?

MATT O'DOWD: No, I don't think so. I'm sorry.

ANNIE: You wouldn't be like, "Uh?"

MATT O'DOWD: I mean, the thing is atoms are mostly empty space, so they would zip between your electrons.

ANNIE: Okay!

MATT O'DOWD: And I'm pretty sure even if they passed through the nucleus, they would just pass through the nucleus like it's empty space. I think they would need to have like a head-on with a quark or something, and then maybe. Then maybe.

ANNIE: [laughs] Then you may be like, "Ow!"

MATT O'DOWD: Yeah, and even—well, yeah. What? "Ah!" Exactly.

ANNIE: Collecting this trail of stuff it would be pulling behind it.

MATT O'DOWD: Yeah. Yeah, exactly. And—and that would be essentially what happens to most of the stuff, because …

LULU: A reminder that Molly's children's book is now out everywhere. You can find it online, you can find it in bookshops. It is called Little Black Hole. It's illustrated by Alex Willmore, and it is full of heart and beauty and darkness, and it's all based on science.

LATIF: Stay tuned. We got more black holes coming up after a quick break.

LATIF: Hey, I'm Latif Nasser. You're listening to Radiolab. Today we are falling very slowly into black holes. The next story comes from our spin off show for families, Terrestrials, hosted by our very own Lulu Miller. I'm gonna let Lulu take us away.

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

WANDA DÍAZ MERCED: Bending ...

LULU: Up and down.

WANDA DÍAZ MERCED: Like a—like a wave.

LULU: And you are ...

WANDA DÍAZ MERCED: Powerful!

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 ...

ANA GONZÁLEZ: Hola, Wanda. ¿Cómo estás?

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

WANDA DÍAZ MERCED: Ciao!

LULU: Ciao!

LULU: Dr. Wanda is an astrophysicist, and she's joining us today from her high security space observatory to tell us a 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 will 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.

WANDA DÍAZ MERCED: Yes. Sorry.

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 their 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?

WANDA DÍAZ MERCED: The eyes!

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 GOFFINSKI: 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.

STAVROS KATSANEVAS: Yes, yes.

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 ...

STAVROS KATSANEVAS: Lasers.

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 little girl was born in Puerto Rico.

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

LULU: [laughs]

WANDA DÍAZ MERCED: In 1974.

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 a just 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 ...

WANDA DÍAZ MERCED: Lost.

LULU: So, like many navigators before her, she turned to the stars for guidance. Though she couldn't see them anymore, she could still learn about them. So when she got to college she took a bunch of physics classes, though as she sat there in the lecture hall, giddy to listen to her professor explain how gravity and magnetism and electricity built our universe, 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?

WANDA DÍAZ MERCED: Yes.

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 she can hear the rumbles of star earthquakes, which I guess should be called 'starquakes.' And the whooshes of comets, and different planets. And when she first encounters the idea of gravitational waves, these invisible ripples that can rumble and rattle space even though we can't see them, she immediately believes in them.

LULU: Uh, speaking of which, regardless of how many people believed in them, those gravitational waves from the long-ago collision of black holes were, by the year 2011 after Wanda has earned her PhD and landed a job at Harvard's Smithsonian Center, are getting very, like, very, very, very, very close to planet Earth.

WANDA DÍAZ MERCED: Mm-hmm.

LULU: 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 ...

STAVROS KATSANEVAS: Lasers.

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. Searching and searching and searching. And then early in the morning on September 14, 2015, suddenly ...

[blip]

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

[blip]

LULU: Interference!

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

STAVROS KATSANEVAS: Exactly. Exactly.

LULU: Oh!

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 ...

WANDA DÍAZ MERCED: ¡Sí!

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 ...

[blip]

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: Huh.

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 near 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: Turns out with the right tools, you can hear not just the echoes from long-ago collisions, but the cries of baby stars being born, and the rattle of old stars dying, and the whooshes of comets, and all kinds of things you could never see through a telescope like interstellar turbulence. And wind.

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?

WANDA DÍAZ MERCED: Uh-huh.

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—get it? 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, 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 doesn't 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! 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?

WANDA DÍAZ MERCED: Sí.

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.

LULU: Ow!

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? But 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. Thanks so much for listening. If you liked that story, we have got a bunch more waiting in the Terrestrials feed. Great for kids, but also anyone who likes stories about nature and how it's weirder than you think. Just look up Terrestrials wherever you get podcasts. It's spelled T-E-R-R-E-S-T-R-I-A-L-S. It's an easy word for children that we picked. Thanks so much for listening.

 

-30-

 

Copyright © 2024 New York Public Radio. All rights reserved. Visit our website terms of use at www.wnyc.org for further information.

 

New York Public Radio transcripts are created on a rush deadline, often by contractors. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of programming is the audio record.