Do we live in a multiverse?

MENAKA WILHELM: Hi, friends. We are so excited to be back with new episodes. But before we begin the episode today, we have a favor to ask of you. We're working on an episode right now about long journeys, and we want to hear from you.

If you were walking around the world, what is one place you definitely want to make sure you saw? Is it the pyramids in Egypt? Maybe the glow worm caves in New Zealand? Or perhaps, it's the lovely rolling hills of Western Wisconsin. Record your answer and submit it at brainson.org/contact. We'll include some of your answers in the show. Again, that's brainson.org/contact.

All right, on with the show.

EMOJA: You're listening to Brains On!, where we're serious about being curious.

CHILD: Brains On! is supported in part by a grant from the National Science Foundation.

MENAKA WILHELM: OK, Sanden. We just need to get this final string of holiday lights down.

SANDEN TOTTEN: Oh, can't we just leave the decorations up until next year? It's so cozy and bright.

MENAKA WILHELM: Yeah, I get that, but it's not as special if you do it all year long. Plus, these decorations have already been up for an extra month.

SANDEN TOTTEN: Ah, I guess you're right.

[NATURE SOUNDS]

MENAKA WILHELM: OK, I'm going to climb the ladder. Will you spot me?

SANDEN TOTTEN: Oh, shoot. My shoelace is loose again.

[CLIMBING LADDER]

[RAY BEAM]

MENAKA WILHELM: Sanden?

SANDEN TOTTEN: Dearest Menaka, I will be the spotter of thee.

MENAKA WILHELM: Thanks, Sanden. OK, almost got the lights down. And perfect. Coming down now.

SANDEN TOTTEN: What? Menaka, that's not me spotting you.

MENAKA WILHELM: Yeah, it is, but wait. When did you put on that fancy tuxedo and top hat?

FANCY SANDEN: Ha! I always sport my black and whites, me dear. 'Tis the only civilized way to dress.

MENAKA WILHELM: What is going on here?

[GASPS]

SANDEN TOTTEN: That's an impeccably dressed impostor!

[RAY BEAM]

SURFER SANDEN: Sup, everybody. Cha, bruh. What's going on? That bro ain't moi.

MENAKA WILHELM: Is that a Sanden with surfer shorts and a backwards baseball hat? There's three of you!

[RAY BEAM]

SANDEN TOTTEN: Menaka, there's another one right behind you.

GRANDPA SANDEN: Hello, young whippersnappers! You remind me of a younger version of myself back in my golden days. Ha!

SANDEN TOTTEN: Oh, jeez. It's Grandpa Sanden.

[GASPS]

MENAKA WILHELM: You're right.

GRANDPA SANDEN: I prefer Grampten or Sandy Pop Pops. Speaking of which, I've got a lollipop for you, kiddo.

SANDEN TOTTEN: I will begrudgingly take this lollipop from you, you fake old me.

[SLURP]

Dang it! it's delicious!

SURFER SANDEN: Cha! A lol? Right on, bruh. Can I get one, too, bruh.

GRANDPA SANDEN: Sure you can. Lollies for ollies.

SURFER SANDEN: Noice, bruh.

GRANDPA SANDEN: I can't eat them because they're bad for my Sand-dentures. Those are custom dentures I made that make my teeth look like tiny versions of my face. See?

SANDEN TOTTEN: Oh, wow. That's too much me face even for me.

FANCY SANDEN: Jeepers, that's quite a pretty pack of pearlies you're packing there, sir.

GRANDPA SANDEN: Huh! See, this guy gets it.

[RAY BEAM]

GIRL: Did somebody say lollipop?

MENAKA WILHELM: Is that girl Sanden?

GIRL SANDEN: No, I'm the regular Sanden, and all those are fake boy Sandens. You can tell I'm the real one because I know the sneakiest, most perfect place to hide my Halloween candy so Marc doesn't eat any.

SANDEN TOTTEN: Oh yeah, of course. If you want your candy to last all year round, you got to hide it well. That's why I always put it in a box that says, don't open. Live raptor inside.

GIRL SANDEN: Yes, in your closet?

SANDEN TOTTEN: No way. That's the first place Marc will look. You got to hide it in his closet.

[CHUCKLES]

GIRL SANDEN: Of course. That's what I do, too. How dare you steal my secrets?

MENAKA WILHELM: OK, original Sanden, quick huddle. (LOW VOICE) Sanden, what is going on here? This is Sandemonium!

SANDEN TOTTEN: I know. It's totally too many Tottens tomfoolery. Wait. Menaka, I think these are Sandens from other dimensions.

[GASPS]

MENAKA WILHELM: Parallel Sandens!

SANDEN TOTTEN: Sandens of the multiverse.

MENAKA WILHELM: Sanden, if that's true, this could be a huge discovery!

[RAY BEAM]

NOODLE OODLE SANDEN: What are we whispering about, noodle oodle?

SANDEN TOTTEN: Ah! Another Sanden!

NOODLE OODLE SANDEN: Yeah, I'm another Sanden, except every sentence I say ends in noodle oodle. So cool right, noodle oodle?

SANDEN TOTTEN: No, it's actually kind of annoying.

NOODLE OODLE SANDEN: You mean annoying noodle oodle, eh?

SANDEN TOTTEN: OK, I got to get on top of this situation before it gets even more out of hand. Menaka, can you tell Molly and our cohost Emoja about this mess of multiverse mes? And maybe you could help them figure out what's going on. I'll send a text to a friend who might be able to help you all out, too.

MENAKA WILHELM: On it. And in the meantime, you might want to check your candy stash. I'm pretty sure I saw Girl Sanden sneak off for it as soon as your back was turned.

SANDEN TOTTEN: Ah! She tricked me into revealing my secret candy hiding spot. That's so clever! I wish I thought of it. Oh, wait! I did. I'm so awesome. Oh wait, my candy! Ah! Get back here, you super cunning, clever, smart me!

[MUSIC PLAYING]

MOLLY BLOOM: You're listening to Brains On! from APM Studios. I'm Molly Bloom, and with me today is Emoja from Talleyville, Delaware. Hi Emoja.

EMOJA: Hey, Molly! Glad to be here to help out with this episode.

SANDEN TOTTEN: Today, we're looking for answers to these questions.

MIRA: Hi, my name is Mira. I live in Warrington, Pennsylvania. My question is what is the multiverse?

ZACH: I'm Zach from Florida. I'm 12, and my question is, how will we know if there are other universes out there?

MOLLY BLOOM: The multiverse is the idea that our universe isn't the only universe out there. What if there were other different universes existing alongside our own, ones with different laws of physics, different planets and stars, or maybe even different versions of us?

EMOJA: It's an idea that's so hot right now in books, TV shows, and movies. Who doesn't like thinking about a universe where things are just a little different?

MOLLY BLOOM: There's no evidence that multiverses actually exist.

EMOJA: Right now, all we really have are ideas about how multiple universes might exist.

MOLLY BLOOM: But the cool part is there's plenty of science that seems to back up the idea that a multiverse could exist, even if we can't prove it yet. So, Emoja, before this episode, have you heard of multiverses before?

EMOJA: Yeah, I have. And I've been thinking about it a lot. I sometimes go on YouTube and watch videos just of people just talking about it.

MOLLY BLOOM: So what do you ever think about what a parallel universe version of you would be like?

EMOJA: Sometimes I think about it.

MOLLY BLOOM: So what are those parallel versions like?

EMOJA: Some of them are opposite genders of me. Some of them like different things than me. Yeah.

MOLLY BLOOM: So what's one thing that you think all Emojas across all universes would have in common?

EMOJA: They'd definitely would love space and want to be an astrophysicist when they grow up.

MOLLY BLOOM: What about space is like so interesting to you and how did you first get interested in it?

EMOJA: Well, I always wanted to be an astronaut when I grew up. When I was younger, I would really get involved with space. I really liked to dress up as astronauts and pretend that I was an astronaut. But unfortunately, when I grew a little older, I realized, oh, astronauts, it's very unlikely to become an astronaut.

So I decided, OK, let's take that a little step less. And so I decided I wanted to be an astrophysicist. And I think I just love space because of all the possibilities there are to space and how wide and open it is, how pretty it is. Yeah, definitely how pretty it is.

ROBOT: Brains, brains, brains on.

MOLLY BLOOM: In lots of books and movies, people visit multiverses, and things are like our world but a little different.

EMOJA: Maybe people talk differently, or have different technology, or maybe they dress differently.

MOLLY BLOOM: We asked our listeners what they think people wear in a multiverse.

[MUSIC PLAYING]

MILES: I think people in a parallel dimension, like if they were us, every day, they'd were like the opposite color of what we were wearing.

CLARA: I think in a different universe, people would wear slime on their shirts with real butt arms. They would have snakes for hair and bumpy pits.

ELIZABETH: If we were in a different universe, I think we would wear technology clothes that we could change from the click of a button.

ARLO: I think people would wear cardboard.

DYLAN: And I think that clones in a different universe would wear clothes out of plastic, and instead of wearing shoes, they wear rollerblades.

QUINN: I think everything would be upside down. So it would look like your legs would be coming out of your shirt, and your head would be in one of your pant holes, and your arms would be through the other.

LAYLA: I think they would wear pants on their head, shoes on their hands, shirts on their legs and feet, and then a swimsuit for a top.

FINN: We are the clothes, and our clothes is human skin.

HANNAH: In a different universe, there might be too much garbage. So everyone would wear the same uniform we could recycle. So we don't make waste the clothes.

[MUSIC PLAYING]

MOLLY BLOOM: Thanks to Miles, Clara, Elizabeth, Arlo, Dylan, Quinn, Layla, Finn, and Hannah for sending in those multiverse ideas. They were truly out of this world. All right, let's get to it. Let's dig into the ideas behind the multiverse.

EMOJA: And hopefully help Sanden figure out where all those other Sandens are coming from.

[DOOR SLIDES OPEN]

MENAKA WILHELM: Hey, Molly. Hey, Emoja! I'm here to help. I've done a bunch of research about the multiverse, and I've got backup.

MOLLY BLOOM: Oh, hey, Menaka. Is this Sanden's friend who can help us understand the multiverse?

MENAKA WILHELM: Sure is. Everyone, meet Dr. Ronald Gamble, Jr. He's a theoretical astrophysicist with NASA Goddard Space Flight Center.

RONALD GAMBLE, JR.: Hey, Molly. Hey, Emoja. Sanden said you all need a crash course on the multiverse.

EMOJA: Oh, hi, Dr. Gamble.

MOLLY BLOOM: Yeah, hi. We could really use your help. There might be a portal to the multiverse in her building, and it's spitting out alternate Sandens. And also what is the multiverse? How many are there? Is it even real? And what is going on?

EMOJA: What she means is can you please help us make sense of the multiverse?

RONALD GAMBLE, JR.: Oh, yeah, I'm super excited about all of this stuff. I'd love to help.

MOLLY BLOOM: Oh, thank goodness.

MENAKA WILHELM: Well, let's get to it. Last I checked, there were seven Sandens, eight if you include that new houseplant that suddenly appeared and looked suspiciously like Sanden in ficus form.

RONALD GAMBLE, JR.: Cool. Let's go to Multi-university.

[MUSIC PLAYING]

Have a seat and get ready for some great ideas.

MOLLY BLOOM: OK, class. Let's start with the basics. When we talk about the multiverse, what are we talking about?

RONALD GAMBLE, JR.: There are many different theories right now, many different competing theories, I should say for the idea of a multiverse. But they all correspond to this overall idea that our universe is in a sea of many different other universes where different properties of science and physics change just slightly to create all of these other universes.

EMOJA: Science and physics might be different in these universes? What would that even look like?

RONALD GAMBLE, JR.: There could be a universe where gravity works backwards, and gravity is pushing everything away instead of pulling it together. Light could be dark in another universe, or dark things could be light things. There could be things like where the color red does not exist in a different universe. And other weird things, other possibilities that you can think of, there is probably a universe that may exist. That's the idea of a multiverse.

MOLLY BLOOM: Whoa.

EMOJA: Double whoa.

MOLLY BLOOM: Or maybe in the multiverse, it's a backwards whoa like aohw.

EMOJA: Double aohw.

MENAKA WILHELM: So like Dr. Gamble said, there are a lot of different ideas out there to explain how a multiverse might work. So these are theories. Right now, we can't really test if a multiverse exists, but these ideas have all come out of real science, which brings us to multiverse idea number one--

[DING]

--the Eternal Inflation Model.

MOLLY BLOOM: Eternal like forever and ever?

RONALD GAMBLE, JR.: Exactly.

EMOJA: And inflation like when I inflate a balloon by blowing it up?

MENAKA WILHELM: Sort of, more like how bread dough rises when it's full of yeast. But hold on to that thought. Let's rewind to long, long ago.

[REWINDING]

Before space was full of stuff, it was once just space.

[MUSIC PLAYING]

It was empty.

RONALD GAMBLE, JR.: We can think of an empty universe where there's no atoms, no protons, no planets, no suns, no people, no trees, no oxygen.

MENAKA WILHELM: And scientists think at some point, this emptiness started growing really fast, faster than anything we know of today.

MOLLY BLOOM: Ah, it was expanding like in the name Eternal Expansion.

RONALD GAMBLE, JR.: That's right.

MENAKA WILHELM: So space was expanding super fast in all directions. But some scientists think in some pockets of space, things just slowed down. Suddenly, those pockets weren't growing as fast as the rest of space. This is what happened in our corner of the cosmos, the place we call our universe. And when things slowed down, it led to the formation of cosmic dust and stars and eventually planets like ours.

MOLLY BLOOM: So when that expansion slowed down, our universe as we know it was born?

MENAKA WILHELM: Right, but here's where it gets really wild. Some scientists think that outside our universe, space kept expanding, and other universes in other pockets of that empty space may have formed there.

MOLLY BLOOM: So what does that mean?

MENAKA WILHELM: Well, to explain, let's get back to that ball of bread dough. Imagine space as a giant ball of rising dough.

EMOJA: I'm imagining it.

MENAKA WILHELM: It's slowly getting bigger and rounder in all directions.

EMOJA: Yep.

MENAKA WILHELM: Now, imagine if in one spot, it stopped rising as fast, so you had a little pocket of dough that slowed down. And that became a baby universe.

[BABY GIGGLING]

MOLLY BLOOM: I love thinking about a baby universe. So cute.

MENAKA WILHELM: Now, imagine that somewhere else on that dough, another little pocket slowed down, too, and made another little baby universe.

[BABY GIGGLING]

MOLLY BLOOM: Double baby universes means double the cute.

MENAKA WILHELM: But since the dough in between these two baby universes is still growing super fast, it's pushing them farther and farther apart from each other. And imagine that this happens all over the dough at different times. Little pockets of bready doughy materials stop expanding as fast, and then they form a baby universe in their little pocket of the dough. At the same time, the dough around them keeps rising super fast, pushing that universe away from all the other dough pockets that have formed.

MOLLY BLOOM: So sad. All those little universes will never know there are other little universes just like them.

MENAKA WILHELM: Exactly. So in this idea, there may be lots of little pocket universes like ours out there. So there would be multiple universes or a multiverse.

[MUSIC PLAYING]

But we can't find them because the space between us keeps growing and growing at a super duper extra ultra fast speed.

EMOJA: Totally cool idea.

MOLLY BLOOM: Yeah, and now, I'll think about the multiverse when I bake, which is awesome.

MENAKA WILHELM: That is awesome. OK, multiverse idea number two coming at you--

[DING]

--the Many Worlds Model. So this one has to do with the idea that for every event that happens, there could be a world where it didn't happen, right, Dr. Gamble?

RONALD GAMBLE, JR.: Absolutely, think of it as cause and effect, right. So you think of it as a timeline. If I put on a tie in this universe, there might be a universe where I don't put on a tie or I make the decision not to put on a tie. And that branches off and makes a different universe.

If we're thinking of branches on a tree, you can think of the trunk of the tree as a multiverse, and each individual branch on the tree is a separate universe itself. And of course, each branch itself can have many different branches, and you can branch off and branch off. And that's how you get a multiverse.

MENAKA WILHELM: And this idea stems from something called quantum mechanics or quantum theory.

MOLLY BLOOM: That has to do with how super tiny particles behave, right?

MENAKA WILHELM: Right. Quantum means kind of like the smallest amount you could have of something, and mechanics is all about motion and action.

EMOJA: So quantum mechanics is the action of the smallest things.

MENAKA WILHELM: You got it. So when we look at these very tiny particles, we notice something very weird. They seem to be in more than one place at the same time. But when they interact with something, they suddenly appear in just one place.

EMOJA: Wait. Hold up. So it's in two places at once and then just one place?

MENAKA WILHELM: Yeah, it would be like if I had two very tiny doors on a very tiny wall. Both doors are open, and somehow, a particle is standing in both of them at the same time. But when we send another particle along to interact with this weird double door standing particle, the particle suddenly appears in just the left door, and the right door is empty.

MOLLY BLOOM: That's some real weirdness right there.

MENAKA WILHELM: It really is, but based on our best evidence, this seems to be how particles behave on this teeny tiny ultra microscopic level. And so some people think every time this happens, our universe splits into two timelines like Ronald was mentioning, one, where the particle's in the left door and one where the particle's in the right door. And if you scale that up from particles to atoms to molecules to cells to eventually us animals, maybe every action we take also splits the universe into multiple realities like one where we put on a tie and one where we didn't.

MOLLY BLOOM: OK, I think I get it, but this idea is so bananas.

EMOJA: Yeah. It's twisting my brain.

RONALD GAMBLE, JR.: Here at Multi-university we love thinking those kind of thoughts.

MENAKA WILHELM: Indeed, and you all are not alone. A lot of scientists struggle with quantum theory. In fact, one famous scientist named Erwin Schrodinger came up with a thought experiment to show how totally bizarro it is.

MOLLY BLOOM: Oh, I think I've heard this. This is the Schrodinger's Cat Idea, right?

MENAKA WILHELM: Yeah, here's how it works. Imagine Schrodinger makes a box.

SCHRODINGER: A special box. Here it is! Tada!

MENAKA WILHELM: And in it, he puts a cat.

[MEOWS]

SCHRODINGER: There you go, kitty. No, down, kitty! Get in the box. Ow! No scratchies.

MENAKA WILHELM: And inside this box is also a vial of poisonous gas that will release if it's triggered.

SCHRODINGER: Ah, but here's the catch. The trigger is turned on by one of those teeny tiny quantum particles. If the particle is in one place, the vial stays closed. If it's in another place, the vial opens and adios cat.

MENAKA WILHELM: Right, but given what we know of quantum mechanics, the particle is in both places at once. It'll only pick one of those two options if we open the box to interact with it.

SCHRODINGER: So you catch my drift here, pals? If we leave the box closed, then this particle is both triggering the poison and not triggering it at the same time. So if you believe this quantum nonsense, that means the cat in this box is both alive and dead right now! How is that even possible? You can't be alive and dead at the same time. It's not a zombie ca--

[CAT GROWLING]

[GULPS]

Or is it?

MOLLY BLOOM: So the multiverse theory would say that there's one universe where the cat wound up living and one where the cat wound up dead?

RONALD GAMBLE, JR.: Right, and there might be a multiverse where Schrodinger himself was the cat, and the cat was doing the experiment.

SCHRODINGER: Wait, what? How'd I get in this box? Uh-oh, nice kitty. Let uncle Schrodi out and you get a num num.

RONALD GAMBLE, JR.: So it can branch off into almost anything you can think of.

MENAKA WILHELM: Also, just to be clear, this was a thought experiment. No actual cats were harmed.

[MEOWS]

MOLLY BLOOM: OK, this one gets a triple whoa.

MOLLY AND EMOJA: Whoa, whoa, whoa!

[MUSIC PLAYING]

MOLLY BLOOM: Yikes, what was that?

[DOOR SLIDES OPEN]

SANDEN TOTTEN: [CHUCKLES]

Hey, everybody. Sorry to interrupt. Do you know if we have a vacuum cleaner that works specifically on glitter and can reach the ceiling?

MOLLY BLOOM: Oh, dear. What happened?

SANDEN TOTTEN: Ugh, it's all those other Sandens. There are a dozen of them now, and they're getting into everything. One of them built a glitter cannon, and poof, ugh. Let's just say the kitchen is a lot sparklier right now.

MOLLY BLOOM: We better go see if we can help.

EMOJA: Yeah, and honestly, I could use a snack after all this big thinking.

MOLLY BLOOM: Good point. Why don't we all get snacks and see if we can help clean the kitchen? We'll be right back in a few minutes.

EMOJA: Stay tuned.

[MUSIC PLAYING]

MOLLY BLOOM: Hey, everyone, we've got some very exciting news. We wrote our very first ever picture book! It's called Earth Friend Forever, and it's full of beautiful illustrations, lots of science, and drawings of the moon wearing glasses.

EMOJA: That moon is so stylish.

MOLLY BLOOM: I know. We think you're going to love it. You can preorder it now and be the first to get it when it arrives in March 2022. Just go to brainson.org to find the link.

EMOJA: And you can send us a question there, too, like this one.

JULIAN: Hi, my name is Julian, and I'm from Ardmore, Pennsylvania. And my question is, how can liquid travel through a straw even going up?

MOLLY BLOOM: To hear the answer to that question and other head scratchers, head over to our brand new Moment of Um podcast. That's right. The same Moment of Um that you've come to know and love from Brains On now has its own show. New episodes come out every weekday to help you answer those little questions that make you go um. And it all happens in under 5 minutes. You can subscribe to the Moment of Um in your favorite podcast app. And don't forget to keep listening till the end of this episode when we'll shout out all the new members of the Brains Honor Roll.

EMOJA: So keep listening.

[MUSIC PLAYING]

MOLLY BLOOM: You're listening to Brains On. I'm Molly.

EMOJA: And I'm Emoja.

MOLLY BLOOM: And before we get back to pondering the mystery of the multiverse, let's ponder the--

[MUSIC PLAYING]

CHILD: (WHISPERING) Mystery sound.

MOLLY BLOOM: Here it is.

[MYSTERY SOUND]

EMOJA: I already know what it is.

MOLLY BLOOM: [LAUGHS] What do you think it is?

EMOJA: I think it's a basketball court like someone is like with their shoes, making that scrapey sound you get when you're running on a basketball court or like someone's basketball's hitting the basketball court because they have that eeky sound like eek.

MOLLY BLOOM: Mhm. Squeaky shoes on a basketball court, really good guess. Well, we'll listen to it again and give you another chance to guess a little bit later.

MEN: (SINGING) Ba ba ba ba ba ba ba ba ba ba ba ba brains on.

MOLLY BLOOM: OK, so we've heard two different ideas backed with some science about how multiverses could be real.

EMOJA: And we're ready for more. Menaka, Dr. Ronald Gamble, let us hear it.

MENAKA WILHELM: OK, we've got a few more. The next one has to do with something called String Theory.

PROFESSOR SANDEN: I can help with that. Professor Sanden at your service.

EMOJA: Oh no. This must be one of those alternate Sandens.

MOLLY BLOOM: Must be.

PROFESSOR SANDEN: I've written three books, none of which were published. I speak seven languages, six of which I made up myself, and I tied my own bow tie. So I must be smart.

EMOJA: That's clearly a clip-on tie.

MOLLY BLOOM: Hello, Professor.

PROFESSOR SANDEN: Now, the key to understanding string theory is to remember that our universe is made up of space and time. We call this the fabric of spacetime. And so it stands to reason that sometimes, like any fabric, that spacetime fabric will unravel just a little, creating a tiny spacetime thread or a string.

And if you pull that string, space and time itself will come undone, and then suddenly, our entire universe will be standing in a void completely naked, which is very embarrassing for our universe. And we don't want that to happen. So if you see a giant string in the sky, don't pull it. Thank you for coming to my talk.

RONALD GAMBLE, JR.: Yeah, sorry. That's not right.

MENAKA WILHELM: Not even close.

PROFESSOR SANDEN: Yeah, I didn't think that was it. Oh, well. Bye.

[DOOR SLIDES]

MENAKA WILHELM: Let's try this again. String Theory is an explanation for what the smallest particles in the universe are made of.

RONALD GAMBLE, JR.: String Theory in essence says that each particle in our universe, it exists as a string.

MENAKA WILHELM: But not like a shoestring or a kite string. We're talking about a string that is super tiny, the smallest possible thing in the whole entire universe, a fundamental string like a string that makes up all other things.

MOLLY BLOOM: OK, I need more info here.

MENAKA WILHELM: Totally got you. So we know that everything is made up of atoms, and atoms are made up of smaller particles like protons, and neutrons, and electrons. And even those particles are made up of smaller stuff. String Theory says what if the tiniest things in the universe, so the thing that all those other particles were made from was this special string that Dr. Gamble mentioned. So picture a string or better yet, a rubber band and stretch it out.

[STRETCHING]

RONALD GAMBLE, JR.: You stretch it out, and now, that string can vibrate kind of like a slinky.

MENAKA WILHELM: And depending on how you wiggle or vibrate that string, it can look different like either a big, long curve, or lots of tiny wobbles, or whatever.

RONALD GAMBLE, JR.: And the mode of vibration, right, or the frequency or the signature that it vibrates then determines what type of particle it is.

MENAKA WILHELM: So if it vibrates one way, it becomes one type of particle or another way, it becomes another particle.

RONALD GAMBLE, JR.: Exactly.

MENAKA WILHELM: But brace yourself for more weirdness. When scientists study these strings, it seems like they vibrate in lots of dimensions like 11 dimensions or even more. That's way more dimensions than we know of.

MOLLY BLOOM: Right, our universe only has four, length, height, width, and time.

MENAKA WILHELM: Exactly. We live in a four-dimensional universe. And some scientists think those other dimensions do exist, but they're tucked in or curled up in our universe in such a way that we can't find them. They're hidden like secret dimensions.

MOLLY BLOOM: OK, hard to imagine, but it kind of sounds like you're saying these other dimensions are hidden because they're curled up and cuddling our universe so tightly. And if that's the case, I'm totally here for it.

EMOJA: Me, too.

MENAKA WILHELM: Yeah. So here's where the multiverse enters the picture. some String Theory scientists think that there may be other universes where these hidden dimensions aren't hidden, and maybe our four dimensions are. And these scientists think that these different universes can have different particles and even different laws of physics.

MOLLY BLOOM: So these would be super extra strange universes if we could visit them.

MENAKA WILHELM: Totally. Our four-dimensional bodies might not even be able to exist in them. And these are just some of the ideas people have for how a multiverse could be possible. There are plenty more out there.

EMOJA: A multiverse of multiverse ideas.

MENAKA WILHELM: Yeah, and with that, our work here is done.

[MUSIC PLAYING]

RONALD GAMBLE, JR.: Congratulations, you are all now graduates of Multi-university.

[GASPS]

MOLLY BLOOM: Oh, gosh. I'm so proud.

EMOJA: I thought it would break my brain, but it didn't. Yay!

MOLLY BLOOM: Congrats, Emoja.

EMOJA: Back at you, Molly.

MOLLY BLOOM: But wait, do any of these ideas explain how all those Sandens got here?

MENAKA WILHELM: Well, no. None of these multiverse ideas are provable yet. And so even if they do exist, we would have no way of communicating with them or exploring them.

RONALD GAMBLE, JR.: Yeah, I have no idea where all those Sandens are coming from. Sorry.

[CHUCKLES]

SANDEN TOTTEN: OK, hi, everybody. It's me again. Hey, it's kind of an all hands on deck situation in the den. Menaka, Ronald, could you come help out?

MOLLY BLOOM: Oh, no. More glitter cannons?

SANDEN TOTTEN: What? Oh. Psh, nah. There's like 70 Sandens now, and we've got an epic game of Capture the Flag going. And we need like two more players. So you in?

MENAKA WILHELM: I'm totally in. Are you coming, Ronald?

RONALD GAMBLE, JR.: Yeah, sure. Thanks for having me, guys. See you in the multiverse.

SANDEN TOTTEN: Yes, all right. Come on. You could be on Team Sandy tots. Team Totty Sandies is kind of crushing it right now. And we could use a few more players on my team.

OPERA SINGER: (SINGING) Brains on!

[COUGHS]

MOLLY BLOOM: OK, Emoja. There may be multiple realities but only one answer to the mystery sound. Are you ready to hear it again?

EMOJA: Yep.

[MYSTERY SOUND]

MOLLY BLOOM: Emoja, what do you think?

EMOJA: I think it's-- I'm going to stick with the same idea I had last time, which is scraping shoes against a basketball court.

MOLLY BLOOM: Excellent guess. Here is the answer.

PASCAL: I'm Pascal from Bozeman in Montana, and that was the sound of basketball shoes squeaking on a basketball court.

MOLLY BLOOM: Oh my goodness, a hundred percent correct.

[SQUEALS]

EMOJA: I got it.

MOLLY BLOOM: Nice work. Oh my goodness, do you play basketball?

EMOJA: Like I didn't play it, but I have played around with it. I've never played basketball.

MOLLY BLOOM: It is a very distinctive sound though. So if you've seen basketball ever, there's a lot of squeaking.

EMOJA: Yeah, if you've been in a basketball court, and you're running with sneakers, that-- I like to just do it. Also, when I'm going shopping with my parents, if I rub my sneaker on the hard floor of the grocery store or anything, it will make a squeak. And so I know that sound. And my parents are like, don't make that sound.

[LAUGHS]

MOLLY BLOOM: That can be very satisfying, a little annoying. But it's a great sound. Nice work.

[MUSIC PLAYING]

ROBOT: Brains on, on, on.

SANDEN TOTTEN: Molly, Emoja, I figured it out. I know where all the Sandens are coming from.

MOLLY BLOOM: Is it a branch on the quantum timeline? Oh! Or a String Theory universe with other dimensions?

EMOJA: Or a holographic universe?

SANDEN TOTTEN: Actually, no.

FANCY SANDEN: Oh then please, do pray tell where is it?

SURFER SANDEN: Yah, bruh, don't keep us hanging, bruh.

NOODLE OODLE SANDEN: I'm quite curious myself, noodle oodle.

PROFESSOR SANDEN: My theory is that we're all a bad dream caused by eating some old string cheese. That's my String Cheese Theory.

[CHUCKLES]

SANDEN TOTTEN: Sandens, Sandens, shh. Let me explain.

[SIGHS]

It's all because of my Dial-and-era-time-o-vision-wonder-metronomatic!

MOLLY BLOOM: That 3D projector you made a while back that projects different time periods?

SANDEN TOTTEN: Yeah, yeah, yeah, the one I used when we were exploring the history of trash.

GRANDPA SANDEN: Back in my day, we called trash rubbish.

[RAY BEAM]

[CLATTERS]

TRASH SANDEN: I'm Trash Sanden. Where I come from, we eat trash and throw out new stuff. New stuff is gross. Ugh.

NOODLE OODLE SANDEN: Where I come from, we call it trash noodle oodle.

GIRL SANDEN: Speaking of trash, I may have left a giant pile of candy wrappers in your room, Boy Sanden. Sorry not sorry.

MOLLY BLOOM: Wait, so these are all projections?

SANDEN TOTTEN: Yeah, I forgot I made a mode that creates random Sanden projections, a Rando Sando setting, if you will, which I will because it's really clever. And I was going to make a bunch of them on Halloween and have them trick or treat in different neighborhoods, so I could get even more candy. But then I forgot about it and left it in my closet. And apparently, Marc accidentally turned it on looking for my candy stash.

[RAY BEAM]

[MUSIC PLAYING]

VAMPIRE SANDEN: You don't say. So even me, Vampire Sanden is a projection? Interesting.

[RAY BEAM]

[MUSIC PLAYING]

BASEBALL ANNOUNCER SANDEN: Baseball Announcer Sanden thinks that this explanation is a home run.

[BAT HITTING BALL]

GRANDPA SANDEN: Back in my day, we called home runs olioroundabouts.

GIRL SANDEN: Now, you're just making stuff up.

[RAY BEAM]

[MUSIC PLAYING]

PIRATE SANDEN: Arr! Pirate Sanden be mighty confused. Oh, what be a projection?

[SANDENS SPEAKING ALL AT ONCE]

SANDEN TOTTEN: And the best part is to make them all go away, I just hit this switch.

[POWERING DOWN]

EMOJA: They're gone just like that.

MOLLY BLOOM: Wow. Good thing you figured this out before the whole world was overrun by Sandens. But unfortunately, even though they weren't real, they left a real big mess.

EMOJA: Yeah, is there any version of you where you pick up after yourself?

SANDEN TOTTEN: Hey, Sandens are going to Sanden. What can I say? I'll do the cleaning though. My projections, my mess. So see you all later, and hey, thanks again for your help.

MOLLY BLOOM: Yeah, it was our pleasure. And we're glad to just have the real Sanden with us again.

SANDEN TOTTEN: Yeah, the real Sanden, noodle oodle.

[MANIACAL LAUGHTER]

[MUSIC PLAYING]

MOLLY BLOOM: The multiverse is the idea that our universe is just one of many possible realities.

EMOJA: These different realities might have different properties or even different dimensions.

MOLLY BLOOM: Some ideas of the multiverse involve big concepts in science like quantum mechanics and string theory.

EMOJA: Even though these ideas have some basis in science, they are still unproven. And we may never be able to prove or disprove them.

MOLLY BLOOM: So while multiverses are fun to think about. Don't expect to go exploring one in real life. Leave that to science fiction. That's it for this episode of Brains On!

EMOJA: Brains On! is produced by Molly Bloom, Ruby Guthrie, Marc Sanchez, Sanden Totten, and Menaka Wilhelm.

MOLLY BLOOM: We had production help from Anna Canny and engineering help from Johnny Vince Evans. Our intern is Catherine Sundquist, and our executive producer is Beth Pearlman. The executives in charge of APM Studios are Lily Kim, Alex Schaffert, and Joanne Griffith. Special thanks to Katie Mack, Adam Beckert, Phil Plate, Ronald Gamble, Jr., and Trey Livingston.

EMOJA: Brains On! is a nonprofit public radio program.

MOLLY BLOOM: You can support the show and help us keep making new episodes at brainson.org. There, you can donate to the show, join our free fan club, or check out our merch.

EMOJA: And don't forget to preorder the new Brains On! book.

MOLLY BLOOM: That's all at our website, brainson.org.

[MUSIC PLAYING]

Don't forget to head over to our new Moment of Um podcast. That's the only place you'll hear the answer to this question.

JULIAN: How can liquid travel through a straw even going up?

[MUSIC PLAYING]

PERSON: Um.

MOLLY BLOOM: I am ready to travel through this list of names. It's time for the Brains Honor Roll. These are the incredible kids who send us their questions, ideas, mystery sounds, drawings, and high fives.

[MUSIC PLAYING]

[LISTING HONOR ROLL]

ROBOT: Brains Honor Roll, high five.

MOLLY BLOOM: We'll be back soon with more answers to your questions.

EMOJA: Thanks for listening.