oh wait you're listening to radio lab from wnyc hey i'm molly webster i'm lulu miller and this is radio lab and today we have two very different stories from two very different reporters one of whom is you molly yeah who each got pulled down into the same very strange and very dark place all right thank you for joining me we're gonna begin yeah yeah yeah well where do you want to start where do i want to start i want to start in siberia okay okay 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 okay it is promising to be just a beautiful day but that is all about to change because just after 7 a.m something appears low in the sky as bright as a second sun 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 whoa 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 hot blast 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 huh wow and uh i don't know either of you heard of this before it's called the tungaska event no i never heard of it tungaska that's the town that's the nearby river okay and today this is still considered the largest impact event in recorded human history so there's something that like hit us yes well maybe okay so a bunch of scientists go plunging in the forest to try to figure out what the heck just happened they scramble over fallen log after fallen log through dense fog after dense fog for miles and miles until finally they realize they have no idea what happened here okay uh really yeah they can't find any evidence of what caused this huge explosion wait what like they sort of figured this must have been an asteroid so they thought they'd find debris from an asteroid like space rock yeah they don't find a single bit of space rock in this whole area weird and not only that an asteroid that would have caused this much destruction should have left probably something like a three-quarter mile long impact crater and they don't find any crater whatsoever that's kind of spooky in 800 square miles of destruction there was like nothing from space yeah not even a hole this is why people think ufos exist yeah and i think that's why the scientists were like well we have to we have to find what obviously should be there um and so all kinds of ideas cropped up like some people thought it was maybe like a natural gas bubble that burst from beneath their crust um that doesn't explain like the bright light in the sky some people thought maybe it was exchange kind of volcanic eruption but again it doesn't really explain the light moving through the sky 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 they were trying for many many years to figure out what the heck it was but uh so the main theory and the one that holds strongest today is that it was an asteroid a really big one okay sms put it at 120 feet across 220 million pounds oh my gosh it's like an office building yeah or like an apartment building headed toward planet earth 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 eventually it just went boom wait but then are there some chunks or just dust and fire and energy 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 yeah and that's the part that is still a little weird what do you think of that that does seem strange doesn't it i i think it does yeah but you know it's pretty plausibly an atmospheric explosion and i think um you know most scientists have sort of dusted their hands off and moved on to the next question with regards to tunguska it's not a cold case it's not like oh on the shelf well i think in some people's minds it is some still believe it wasn't an asteroid this is astrophysicist matt o'dowd professor at the city university of new york leemann college and i reached out to matt because i had recently seen him on his side gig have you ever asked what is beyond the edge of the universe this really awesome physics youtube show what would it take to build a station which is called pbs space time talking about this really wild absolutely alternate theory of what could have caused the tunguska event of 1908 which is the black hole wait that's what that's different like a black hole like a space black hole did this like how i don't know radiated a death wave toward planet earth no matt's talking about a black hole actually hitting earth exactly what which sounds impossible because usually when we're talking black holes my god i got these inferno we're talking about these big terrifying churning places in space where gravity is just so strong but not even light can escape it it's a monster all right they eat stars and planets and gas and they have all these almost supernatural qualities like they warp the space around them change the flow of time and all of that awesome stuff that comes out of general relativity but if one of these black holes approached earth its gravitational pull would be so strong that earth would be they call it spiketified the entire planet would begin to stretch towards the black hole and then as it punched in earth would essentially follow it through the hole that it made what so you can imagine just folding in afterwards and it would probably follow the black hole in this kind of stream of super hot stuff until all of earth everything on it everything in it is ripped apart into individual atoms and earth is devoured um all right so that's so awesome it's not what happened but you also notice you know okay so this obviously is not a very plausible explanation for the tunguska event no no certainly not 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 teeny tiny uh monster very small wait black holes can be little yeah like really small like how small like very tiny so small i mean could it fit on my hand yeah i mean are we talking like a peanut uh we're talking like the size of a hydrogen atom oh an atom yeah oh my goodness that is very small for black hole okay now so these tiny little black holes are special black holes because typically a black hole gets made after a star explodes yeah but these tiny little black holes they got made in this one particular explosion 13 and a half billion years ago the big bang which was a very great day for existence yeah exactly awesome but a very upsetting day for gravity because like the big bang was the explosion outward where things became free of gravity in a way yes everything had been packed together in this really tight dense ball and then this little dense ball was this rapidly expanding ocean of hot hydrogen and helium these bright swirling gases blowing gravity was like oh my god i'm just oh i think i was back in that tiny little hole again exactly for one minute i fell asleep seriously so gravity is stress gravity is stress and immunity begins trying to turn the whole universe into a black hole trying to grab everything and pull it back together which is not possible mostly it fails you know happily because the expansion of the big bang is just too powerful but everything is still so hot and so dense and so compacted together that gravity is able to grab some of this stuff crush it together to create what we call primordial black holes 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 exactly so these primordial black holes are pbhs which do you prefer pbhs really no no yeah pbh it's sounds like it's like pbs but no it's like a condiment yeah exactly yeah primordial black hole is good it's really good i'm happy to go with primordial black hole i don't know if it was like too much every time but no i'll try to say it fast great all right so matt explained that even though these primordial black holes could be as small as an atom still it could be very massive there is still a huge amount of stuff packed into that small space so it's an atom but with a mass of an asteroid basically oh 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 they do have to cross the orbits of other objects other objects like planet earth for instance exactly 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 size rock zooming along at 62 miles a second about to make a direct hit with a certain patch of siberian forest okay we're back we're back you ready for impact oh my god yeah all right let's do it okay now now okay all right so this primordial black hole punches through the atmosphere like a tiny needle of gravity and stuck its pool towards that gravitational field stuff like nitrogen molecules carbon dioxide oxygen molecules and this tiny little black hole begins to eat it devours molecule after molecule after molecule and each one of those molecules as it fell into the black hole becomes hotter than the surface of the star radiating enormous amount of heat and energy and with all that energy around the black hole this halo begins to form and it's not very big but it is shining with the power of several corrosioners several atomic bombs in that moment if you've 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 the equivalent in energy to an asteroid exploding which meant this tiny primordial black hole was creating these enormous shockwaves and what did that sound like um i i imagine a ginormous kaboom cool that would flatten the forest knock people over throw boats out of rivers shatter windows and then it would hit the ground and it should actually leave a crater oh but this one would be much smaller sort of a column thinner definitely not what the scientists had been looking for and we've been hard to find it would also be very deep because while an asteroid stops when it hits the earth the black hole doesn't even slow down what and as it plummets through the earth through its whole passage it would be generating these seismic waves these rings of earthquake expanding from around this bullet shooting through the earth and the earthquakes wouldn't be strong but that would be global meaning every single person plants animal on earth everyone would just be like what the heck until the earthquake hmm 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 and some stuff does follow the black hole but some stuff just gets super hot leaving behind this trail that would at first be molten and then it would solidify into this column of solid glass like a glass lightsaber all the way through earth yes yeah stop it this long tunnel of altered material wow and then it comes out somewhere and then yeah it would have to be an exit wound wait where would the exit wound be well it depends on what angle it came in at the angle yeah like if it had been a perfect shot directly through the middle of the earth it would be in chile somewhere but back in 1908 it could have easily been in the ocean somewhere and we probably wouldn't have noticed if you're 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 uh it would be like a shooting star coming out of the ground that's so crazy 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 and as it goes forward on the rest of its journey is there a little bit of 1908 forest floor siberia inside it in some very altered form yes 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 well this is a kind of a pretty thought exercise but it doesn't mean that it's never happened or it's never going to happen tangaska just gives you kind of like a case study for like okay well is it possible that it could have been and the scientists found out yes it is possible and statistically something like this either has happened in earth's history or truly might happen well now that we know there are little black holes out there everywhere when we come back for a short break we are going to be one up close personal intimately stick with us lulu molly radiolab b-holes black holes uh so this next one comes to us from you molly indeed um so what do you got um so when annie came to our pitch meeting and she was like 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 got one too 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 uh and it came out of this conversation that i had with a physicist brian green 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 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 a black hole um so seemingly from our perspective like matter disappears but physicists were like how can that be because the first law of thermodynamics says that nothing can be created or destroyed so what happens to the stuff after it falls into the black hole it's like a star goes in a star goes in And you don't know, like, did the star get crushed? Did the star threw a wormhole out somewhere else? Did the star burn up? 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. 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, a particle could be spit out of a black hole.
And so he came up with this idea, which we now call Hawking radiation, that is supported by math, which is a statement I don't fully understand, 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 what was inside of it. Oh, so wait, so it's like the particles would come out and they might have little clues about the interiority of a black hole? 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 or what the black hole has seen or intersected with.
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. Yeah, which I just thought was so beautiful. It's like somewhat beastly object that none of us understands is revealing parts of itself to the rest of the universe. So I learned about all this stuff.
I'm like, oh, that would be a really cool story. And normally what I do is I do a lot of like reporting and I put a bunch of voices together and we put it on air. But the idea of a glowing black hole never stuck with me in kind of like a science reporting way. It more started just to remind me of people.
And I just thought, oh, a little black hole would be a great children's book character. And so I made it one. I wrote it into a kid's book. Indeed you did.
I have it right here in front of me. Yay. It is called Little Black Hole. Okay.
And will you flip to the first page of the story and just read us the first couple pages of the story? Okay. There once was a little black hole who loved everything in the universe. The stars, the planets, the space rocks and the space box, even the flying astronauts.
The little black hole loved her friends. One day a star came by. The little black hole built a space castle with her. La la la, they sang as they built in sword.
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. 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. And yes, she is eating her friends. It's subtle, but it's there. We all eat our friends.
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.
Like she thought the star had left and the comet had left and the space box and space rocks and all these things from the millions of years of this little black hole 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. Oh, yeah. 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 a hard feeling. I think everybody and kids for sure, but everybody like has. 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. It can, but it doesn't have to.
It's interesting that you say that because I had a lot of trouble with the ending 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. Like it's a little bit better. And so that was interesting because I just dug from a space of like having this memory of a feeling of almost like left behindness. Once I started to write the book, I'm like, oh, I'm the little black hole.
You know, I'm the youngest of four sisters. And growing up, I felt like they were constantly like leaving, 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.
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. 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.
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? Please.
Okay, 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. What?
And so, I don't know, they disappear in the end, they die. Brian was like, good luck making that into a kid's book. So take that as you will. Oh, I've got something for you.
Oh, whoa. Hi. Hey, Annie. Hello.
Where did you come from? Oh, I've actually, I actually never left. I've just quietly been here. Okay, cool.
Very creepy, but cool. Anyway, so the reason I'm putting in is because of something that Matt told me. So these are maybe my current favorite thing. As we were wrapping up our interview.
Okay, so we've been talking about hawking radiation, black holes evaporating, all that good stuff. But then you told me about some current thinking. There is one theory. A number of very reasonable scientists think that once the black hole is very small, like when it evaporates basically all of itself away and is now down to around the Planck scale, 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.
Whoa. And when the black hole has evaporated down to this inconceivably tiny size, the thought is that there is no transition that lets it give up its last little bit of mass. So it's stuck. Oh, whoa.
So that means that it can't die, that it just won't. If that's true, then there are kajillions of skeletons of black holes all over the universe. Yes, what? 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. Oh, yeah, yes. So that's the idea that there's 80% of matter in the universe, that we don't know what it is, but it is heavy, dark, and impossible to detect. Right, and the theory goes that black holes actually can't totally disappear, but instead get locked at that last teeny tiny invisible size.
That sounds exactly like dark matter. Perfect. Exactly, perfect. And that says, if that's the case, 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. Really? I mean, there probably aren't any in the room with you right now. Okay.
But over the course of your life, you might be hit by one. Okay. They will, of course... Kill you.
...pass straight through your body. And what would happen? And they are so small, it would leave absolutely no sign whatsoever. Would you be like, ow?
No? No, I don't think so. I'm sorry. You wouldn't be like, oh.
I mean, the thing is, atoms are mostly empty space, so they would zip between your electrons. Oh, okay. And I'm pretty sure, even if they pass 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.
Okay. Then maybe. Then you'd be like, ow. Yeah, and even, well, yeah.
What? Ah! It's like a trail of stuff. It would pull you back.
Yeah, yeah, exactly. And that would be essentially what happens with most of the stuff, because it's so small, the amount that actually has a direct contact will be and it's all over the place. These are much more than ever. We're going to do whatever.
This episode was reported by Annie McKeown and Molly Webster. It was produced by Annie McKeown and Becca Bressler with help from Matt Kilty, fact-checked by Diane Kelly, and edited by Alex Neeson. Sound design by Matt Kilty and Annie McKeown, Jeremy Bloom, mixing by Jeremy Bloom, and dialogue mix by Ariane Wack. Special thanks to Matt Kaplan, a physicist at Illinois State University who worked on a team whose recent paper taught us what the impact creator left behind by a primordial black hole would actually look like.
We also want to thank Graham, but I'm not Rajen and Brian Green, and we dedicate this episode to our newest, favorite, littlest black hole, Annie McKeown's baby boy. 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. It's illustrated by Alex Wilmore and it is full of heart and beauty and darkness and it's all based on science. Before we go, Molls, do you have any last VHFs? Black hole facts?
VHFs? Black hole fun facts? For sure. I do.
I do always. Did you know, most black holes generally have a best friend? Who? A star.
Wait, what do you mean? It's just like always nearby? Like, what's his name? Flounder and the Little Mermaid?
Exactly. Exactly. Wait, in what way? For real?
The star orbits the black hole sort of floating in space together and then depending on how close they are, they may eat it all. At some point. My God, it's so wide right now. Or they may just, you know, grab up little bits of it and hug it pretty close.
That is wonderful. I am so happy to know that. All right, well, thanks so much for listening. Enjoy all the little black holes hitting you.
Bye. Radio Lab was created by Jada Abumrad and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our co-hosts. Bill and Keith is our director of sound design.
Our staff includes Simon Adler, Jeremy Bloom, Becca Bressler, Rachel Cusick, The Betty Foster-Keys, W. Harry Ford-Guner, David Nable, Maria Pascun-Thiades, Sindhu Yana Samman-Dung, Matt Kilti, Annie McEwan, Alex Neeson, Sarah Kari, Anna Vasco and Buzz, Sarah Sandback, Arian Webb, Pat Walters, and Molly Webster. With help, our fact checkers is provided by the Alfred P. Sloan Foundation.