[RADIOLAB INTRO]

MOLLY WEBSTER: Hey, I'm Molly Webster.

LULU MILLER: I'm Lulu Miller.

MOLLY: And this is Radiolab.

LULU: 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 was 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 it seem—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's been 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: Wait!

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 of the stuff, because ...

LULU: This episode was reported by Annie McEwen and Molly Webster. It was produced by Annie McEwen and Becca Bressler, with help from Matt Kielty. Fact-checked by Diane Kelly, and edited by Alex Neason. Sound design by Matt Kielty and Annie McEwen, Jeremy Bloom. Mixing by Jeremy Bloom, and dialogue mixed by Arianne Wack.

LULU: Special thanks to Matt Caplan, a physicist at Illinois State University who worked on a team whose recent paper taught us what the impact crater left behind by a primordial black hole would actually look like.

MOLLY: We also want to thank Priyamvada Natarajan and Brian Greene. And we dedicate this episode to our newest, favoritest, littlest black hole, Annie McEwen's baby boy.

LULU: And then finally 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. Illustrated by Alex Willmore, and it is full of heart and beauty and darkness. And it's all based on science.

LULU: Before we go, Molls, do you have any last BHFs? Black hole facts? BHFFs? Black hole fun facts to share?

MOLLY: [laughs] I do. I do, always. Did you know most black holes generally have a best friend?

LULU: Who?

MOLLY: A star.

LULU: Wait, what do you mean? That's just like always nearby?

MOLLY: Yeah.

LULU: Like—like what's his name? Flounder in the Little Mermaid?

MOLLY: Exactly. Exactly.

LULU: Wait, but, like—wait, in what way, for real?

MOLLY: The star orbits the black hole. They're sort of floating in space together, and then depending on how close they are, they may eat it all.

LULU: [laughs] At some point. My jaw is so wide right now. I never knew that!

MOLLY: Or they may just, you know, grab up little bits of it and hug it pretty close.

LULU: That is wonderful. I am—I'm so happy to know that. All right, well thanks so much for listening. Enjoy all the little black holes hitting you. Bye!

[LISTENER: Radiolab was created by Jad Abumrad, and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our co-hosts. Dylan Keefe is our director of sound design. Our staff includes: Simon Adler, Jeremy Bloom, Becca Bressler, Rachael Cusick, Ekedi Fausther-Keeys, W. Harry Fortuna, David Gebel, Maria Paz Gutiérrez, Sindhu Gnanasambandan, Matt Kielty, Annie McEwen, Alex Neason, Sarah Qari, Anna Rascouët-Paz, Sarah Sandbach, Arianne Wack, Pat Walters and Molly Webster. With help from Sachi Kitajima Mulkey. Our fact-checkers are Diane Kelly, Emily Krieger and Natalie Middleton.]

[LISTENER: Hi. My name's Michael Smith. I'm calling from Pennington, New Jersey. Leadership support for Radiolab's science programming is provided by the Gordon and Betty Moore Foundation, Science Sandbox, a Simons Foundation initiative, and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.]

 

-30-

 

Copyright © 2023 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.