Listener Questions #28

Daniel and Kelly answer questions about black holes, duplicate organs and bubble Universes! See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

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• 1:42Daniel Whiteson?

  How can massless photons add to a black hole's might? Can you really make a singularity out of light?

• 1:50Kelly Weinersmith?

  Organs that come in tubes include the lung, hand, kidney, foot, and eye. But why do I only have one of some things? And what's the plural of anus? Ain't I?

• 2:02Daniel Whiteson?

  Could drifting bubble universes collide to end our cosmic show? Might gravity in other dimensions ever let us know?

• 2:11Kelly Weinersmith?

  Whatever questions keep you up at night, Daniel and Kelly's answers will make it right.

• 2:16Daniel Whiteson?

  Welcome to Daniel and Kelly's Extraordinary Universe.

• 2:20Kelly Weinersmith?

  We've done 28 of these.

• 2:34Kelly Weinersmith?

  Hello, I'm Kelly Wiener-Smith. I study parasites and space and whatever it is that y'all ask me when you send us emails.

• 2:42Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist and I've answered a lot of questions from listeners, but never any about anay.

• 2:49Kelly Weinersmith?

  Oh, no, that's well, Daniel, you'd be taking my questions. I am the anay expert in this group. Thank you very much. You stick to the black holes and I stick to the biology black holes.

• 3:00Daniel Whiteson?

  Isn't there an obvious connection? Exactly. Aren't black holes a sort of physics anus?

• 3:05Kelly Weinersmith?

  Yeah, yes, yes.

• 3:07Daniel Whiteson?

  Anay of the universe?

• 3:09Kelly Weinersmith?

  You stick to the anay of the cosmos. I stick to the anay of the Earth.

• 3:14Daniel Whiteson?

  But wait, now I'm realizing that we have it all wrong, don't we? Black holes are more like mouths and white holes would be more like anuses.

• 3:21Kelly Weinersmith?

  Why?

• 3:21Daniel Whiteson?

  Because things don't come out of black holes.

• 3:24Kelly Weinersmith?

  Oh, they go in and things go out of white holes. Well, you know, yet another instance where the physicist did a poor job of naming things. That's

• 3:31Daniel Whiteson?

  Yes.

• 3:32Kelly Weinersmith?

  There you go again.

• 3:33Daniel Whiteson?

  It is hard to keep the ins and the outs straight sometimes.

• 3:36Kelly Weinersmith?

  Yes. Okay. Well, we have started by going off track, so let's work on getting back on track. So we are very lucky to have an audience that has so many absolutely fascinating questions and you all send them to us. You send them to us at questions at danielandkelly.org.

• 3:53Daniel Whiteson?

  And it's our job to break down the ins and the outs of the universe, to explain to you how it all works, to inject the whole universe into your brain. And that's what we're going to do on today's episode. We have three wonderful questions from listeners, people who are curious about the universe, people who have been listening and thinking and there's something that doesn't quite click in their minds. We want to make that click happen for you. So if you are sitting on a question, something you've never really had satisfactorily explained, please don't be shy. Write to us, [email protected]. We really do write back to everybody.

• 4:29Kelly Weinersmith?

  Daniel writes back to everybody within a day. I am not quite as punctual as Daniel. You'll get an answer from me in less than a week, for sure. But yeah, we write back to everybody. Some of the questions even end up on the show.

• 4:43Daniel Whiteson?

  I promise you that email address is not a black hole. It's more like a white hole because answers come out of it.

• 4:48Kelly Weinersmith?

  That's right. That's right. And we are going to stretch this metaphor as far as we can. And so stick with us till the end of the show to see where we go with it. So let's start with our first question with Stephen from British Columbia.

• 5:01Speaker 06

  Hi, Daniel and Kelly. It's Stephen from B C, Canada, again with another question about our universe. In one of your past episodes, you glaze over a fact that photons can collapse into tiny black holes. My question today is about those tiny black holes. What is really going on inside a tiny black hole? How can something with no mass be able to collapse, never mind collapse into one of the most densest objects known in the universe? How can a black hole be tiny? Is there a singularity in them? How can a photon become a singularity inside a tiny black hole? I look forward to your answers.

• 5:38Daniel Whiteson?

  All right, I love this question because he's really thinking about the extremes. You know, we talk on this show about general relativity and energy density and stuff. And he's pushing it to the edge, which is what you have to do to really understand physics to say, does this really connect in my brain? Do I understand every scenario? What about this? What about that? What about this other thing? What about this thing I heard? So Stephen is out there doing physics in his mind. Congrats, Stephen. And I'm very excited to answer this question for you.

• 6:06Kelly Weinersmith?

  And usually when we need to answer a physics question, it makes sense to go way back to the beginning to terms that you've heard since you were in kindergarten because there's probably something basic about them that you don't quite understand. So Daniel, let's start with gravity. What, what, remind us, what is gravity?

• 6:25Daniel Whiteson?

  Yeah, so Newton told us that gravity was a force between masses. But then Einstein revealed that it's actually the curvature of spacetime, that what we think of as gravity is actually a pseudo force because we can't see the curvature of spacetime and its effect on the motion of objects. And because we can't see its effect, we attribute some mysterious force to doing that. Sort of like if you're on a merry-go-round and you throw a ball at somebody across the merry- Go around from you, it won't reach them. It'll curl to the side and you'll think, why is that? I didn't throw it to the side. So you'll come up with some pseudo force that accounts for the motion of that object, the acceleration of that object. In the same way, if you're standing on the surface of the earth and you let go of an apple,

• 7:10Daniel Whiteson?

  it seems like something accelerates it towards the earth. Really, the apple is just following the curvature of spacetime. You're the one accelerating against spacetime. So general relativity reformulates gravity as the curvature of spacetime that affects the motion of objects in a way that makes us think there's a force we would call gravity.

• 7:30Kelly Weinersmith?

  Feels like that doesn't make any sense, but if Newton got it wrong, I don't feel so bad about getting it wrong, too.

• 7:38Daniel Whiteson?

  And the crucial thing to understand in the context of this question is that the curvature of spacetime comes from energy density. We often think about it as mass tells spacetime how to bend, but it's not just mass. General relativity generalizes from beyond just mass to any kind of energy density. So, for example, if you have a bunch of photons that contributes to the energy density and it can make it easier to have a black hole because photons have energy, of course.

• 8:08Kelly Weinersmith?

  Okay, photons have energy. That is not a controversial statement, right?

• 8:13Daniel Whiteson?

  Yeah, exactly. And so like the canonical way to make a black hole is to take a big bunch of mass and squeeze it down into a tiny area. Like if you took the mass of the earth and you squeezed it down to the volume of about a peanut, then it would become a black hole. So black holes are about energy density. Or if you took the sun and you squeezed it down to a few kilometers, it would become a black hole. But you can also do that with just energy. If you took enough light, if you focused a lot of photons in a tiny region, like you had a bunch of lasers overlapping or you had a big spherical mirror, so all the photons were in the same place. If you got enough energy density in one location at the same moment, it would curve spacetime enough to give you a black hole.

• 8:58Kelly Weinersmith?

  Oh, all right. So isn't there that, uh, there's a facility in California that's working on fusion and they're shooting a bunch of lasers at a little bit of fusion fuel. Are they going to kill us all with a black hole?

• 9:11Daniel Whiteson?

  That's the National Ignition Facility and they're working on inertial confinement fusion. They take little pellets of fuel and they zap them with like 196 lasers, I think they are, in order to implode it. Like the explosion of the shell creates an implosion, which compresses the core and then ignites fusion for that little pellet. Super awesome, really cool project, but not nearly enough energy to create a black hole. In order to create this kind of energy, you'd need very high energy density, something like 10 to the 35 joules in a region like 10 to the negative 15 meters across. You need like more energy than is put out by the sun every second, concentrated into a tiny little

• 9:56Daniel Whiteson?

  region. So it's a pretty big engineering problem. In principle, it's possible, which I think is the source of Stephen's question. In practice, you don't have to worry about black holes being made on the earth by tiny little dinky man-made lasers.

• 10:10Kelly Weinersmith?

  That's comforting.

• 10:14Daniel Whiteson?

  And so Stephen's asking, how can something with no mass collapse into one of the densest objects in the universe? So remember, it's energy density that's collapsing here, that's creating that surface. And when you think about like, well, what is that black hole made out of? Is there a singularity inside of it? Remember that the black hole is not made of the original matter that you put into it. Like if you drop a bunch of electrons into a tiny region to make a black hole, you don't know what the form of the matter is inside the black hole. It's not like there are a bunch of electrons still in there. The only thing you can know about the black hole is its total mass, which represents the energy that's captured inside of it, its total charge, and its spin. No original

• 10:57Daniel Whiteson?

  nature of the objects is preserved as far as we know. So if you make a black hole out of photons, it looks exactly the same as a black hole made out of neutrons or anything else that has the same total energy, charge, and spin.

• 11:11Kelly Weinersmith?

  So what happened to the electrons? Did they just get like smooshed into something unrecognizable?

• 11:15Daniel Whiteson?

  We don't know, right? Like general relativity tells us that they form a singularity, but that ignores all All the quantum mechanical stuff we know about electrons and how they don't like to be on top of each other. And who knows what happens when you squish them down. Maybe there's things inside the electrons. Maybe the electron is a composite particle. When you smoosh them together that tightly, they break open and form some sort of plasma of their intermediate states. Who knows, right?

• 11:37Kelly Weinersmith?

  We might finally know.

• 11:39Daniel Whiteson?

  We might finally know, but it would be hidden behind the event horizon. So the point is that like, yes, general relativity predicts a singularity at the heart of a black hole made out of pure photons, but you can't really know. And the singularity itself is a prediction of general relativity, which ignores quantum mechanics anyway. So we think it's probably wrong. So the answer is, we have no idea what's going on inside that black hole. But in principle, that black hole is no different from a black hole you made out of electrons, or cheese, or you know, the anuses of your lab rats, or whatever.

• 12:13Kelly Weinersmith?

  Oh, great. Would you pick lab rats? I feel like blue whales. Like there's got, if you're gonna make a black hole out of something, you gotta go, go big, or go home.

• 12:21Daniel Whiteson?

  Well, I mean, if you add up the biomass of the anuses of rats on Earth versus blue whales, what do you think is larger?

• 12:27Kelly Weinersmith?

  Oh, probably rats. Yeah. But what do you think the greatest anus biomass on the planet is? I bet it's, could it be humans? Might be humans.

• 12:37Daniel Whiteson?

  I can't believe you're a biologist and you don't know the answer to this question off the top of your head.

• 12:41Kelly Weinersmith?

  I'm a little embarrassed. I'm a little embarrassed.

• 12:45Daniel Whiteson?

  And you know, while it's out of the reach of our technology to create black holes out of photons currently, in the future, you know, maybe if we become like a Kardashev type two civilization or whatever, we build a Dyson sphere that captures all of the energy of the sun. It is possible in the future, we might be able to do it, or maybe aliens are out there doing it right now, and we could watch them doing it from afar. That could be the way that we discover the existence of aliens. Amazing. Awesome. Would be super cool. Please don't point those beams at us. But there's another way. It's possible that we could create these black holes. It's possible they could also exist naturally. Now, there's no like natural huge laser focusing light beams, but in the very early

• 13:30Daniel Whiteson?

  Universe, things were very hot and very dense. And there's the theory that black holes could have formed even before like protons formed and electrons formed. In that primordial soup, there was great energy density. Now, the whole universe didn't collapse quickly into a black hole because to get a black hole, you need relative energy density. You need one region to be denser than another. So if the whole universe is like filled with energy density, you don't get a black hole. But we also know there were little quantum fluctuations, some pockets that were more dense than others. And so this is the theory of primordial black holes, that maybe there were some regions

• 14:10Daniel Whiteson?

  that fluctuated enough to have enough energy density to create black holes before there was even particles made. Now, we've never seen any of these, but in principle, back in the early universe, when it was radiation dominated, when most of the energy in the universe was in things like photons, then it's possible you had a pocket of space that had enough energy density just in photons to make a primordial black hole out of light. So it's possible it does exist in the universe.

• 14:40Kelly Weinersmith?

  Oh, you're looking at me because it's my turn to say something, but I am still trying to figure out the anus thing. I'm so sorry. I mostly was listening, but I can't. Oh, boy.

• 14:52Daniel Whiteson?

  All right. Well, then, since Kelly's, since Kelly's been distracted, let's see if Steven's been paying attention. Steven, let us know if that answered your question, or if you're just gonna file it away in the white hole in your mind.

• 15:06Daniel Whiteson?

  I don't know if that made any sense.

• 15:07Kelly Weinersmith?

  I don't think so.

• 15:10Speaker 06

  Hi, Daniel and Kelly. It's Steven from British Columbia again. Thanks again for answering my question about what is going on inside tiny black holes. That explanation was super helpful.

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• 17:30Daniel Whiteson?

  Okay, we're back and we're answering questions from listeners about black holes, about white holes, about ins and outs, about everything in the universe. We want to answer your questions because science is for everybody and the universe deserves to be understood. Up next, we have an amazing question about the human body and its symmetry and asymmetry from Jerry.

• 17:52Speaker 06

  Hey, Daniel and Kelly. Love the show. My left brain learns so much, but then my right brain has a question. How come there are two parts to a lot of our body? We have two eyes, we have two ears, we have two lungs, we have two kidneys, but those kidneys only lead to one bladder, and there's only one stomach, and there's only one spleen. You probably could live with one lung or one kidney, and maybe you could live with half a brain and be a politician, but why are we built this way? We have two of some things and only one of another. Love the show. Thanks.

• 18:29Kelly Weinersmith?

  Well, I gotta be honest with you. I have had this question sitting on my stack for a few months because I just kind of wasn't really sure how to answer this one. Like, what is the answer? Why? Sometimes a human body just is the way it is. And so, all right, so here's what I came up with because it is a good question. It's a great question.

• 18:50Daniel Whiteson?

  Well, let's start with the meta-answer. Like, is there always an answer? What kind of answer do you think Jerry is looking for? Is he looking for an answer where it's like, this works better than the opposite? Like, there's a reason we don't have two brains, and there's a reason we don't have two mouths because it would be better? Or is it satisfying just to say, we don't know, this seems to work, and we can't ever trace back all the details of our evolutionary history to understand why?

• 19:16Kelly Weinersmith?

  Yeah, so I tried to find an evolutionary answer, and I tried to find a mechanistic answer, and I tried to find a like... Stories that kind of make this make sense sort of answer.

• 19:27Daniel Whiteson?

  You didn't go for an Aristotelian answer? It isn't the way of humanity to have one mouth.

• 19:32Kelly Weinersmith?

  To have one butt.

• 19:35Kelly Weinersmith?

  One butt, but with two cheeks.

• 19:36Daniel Whiteson?

  What was Aristotle's theory of the anus? Was he the first one to think about the anus?

• 19:40Kelly Weinersmith?

  You know, I didn't get as far back as Aristotle, actually.

• 19:43Daniel Whiteson?

  You always got to go back to Aristotle, Kelly.

• 19:45Kelly Weinersmith?

  I know.

• 19:46Daniel Whiteson?

  He's like the original, you know, paper out of the Soviet Union that you didn't read and that came out in the 1970s that totally scoops your thesis. He was the original dude to do that.

• 19:55Kelly Weinersmith?

  Whoa, yes, yes. Well, I'm really, I hope that I can still give a satisfactory answer, having not read Aristotle's opinion on this. But, you know, I will, I'll note that having things like two eyes and two lungs, but only one heart and one brain is a sort of ancient state. You know, pretty much all land vertebrates have this and land vertebrates have been around for over 300 million years. When you go into like, you know, the water, you find cephalopods that have three hearts. So it is possible to have three hearts. It doesn't have to be the case that you only have one heart. And on land, there are worms that have multiple heart-like things. But we only have one heart.

• 20:40Kelly Weinersmith?

  It does kind of start as like two hearts and it sort of fuses together into one heart that's like symmetrical with, you know, two sets of chambers on each side. So one answer is that it's ancient. This has been around for a long time, so maybe this is the best solution. And that's why we've had it for 300 million years. Or maybe we're just kind of locked in at this point. And the fact that we've had it for 300 million years just shows that this arrangement of things is sort of hard to get out of.

• 21:08Daniel Whiteson?

  Well, what do you mean by 300 million years? What happened 300 million years ago? Was that the Cambrian explosion?

• 21:14Kelly Weinersmith?

  Well, this is when we started to get land vertebrates. So it's when like vertebrates started coming up out of the water and sort of walking around on land and breathing air as opposed to using gills to extract oxygen from the water.

• 21:25Daniel Whiteson?

  Okay, because fish, for example, have two eyes and two ears and one mouth. And there's a lot of similarities there, right? So it must go back even further.

• 21:32Kelly Weinersmith?

  There are a lot of similarities. I mean, they Don't have like two lungs, for example, but they do have, you know, like two gills. But yeah, so there, there are a lot of things that are similar, but I was trying to look for, I had lungs on the brain when I was starting this. And so I was looking for things with two lungs. So I mean, symmetry, if you just want to ask about symmetry, symmetry goes back even farther. Like, there's a lot of organisms that weren't necessarily symmetrical the way we are. So if you were to draw a line, you know, straight through our head that goes down like through our butts, and you fold us over, we're symmetrical that way. I think that's called bilateral symmetry. But there are other organisms that are radially symmetrical. I think that's what it's called. I didn't necessarily plan on going this far back, so I'm pulling this out of my.

• 22:15Daniel Whiteson?

  Aristotelian hole.

• 22:16Kelly Weinersmith?

  Aristotelian hole. So, so being symmetrical is a thing that has been around for a long time. And there's a couple of different hypotheses for why symmetry is good. Couple hypotheses I came across were that like, you know, one, in our very ancient history, when we were like tubes that were symmetrical, the idea was that it was easier for us to like, pull food through our tube and like extract resources from it when we were roughly symmetrical. And then when we became bilaterally symmetrical, so like imagine you have flippers, it's easier to move in a controlled manner when you're symmetrical on both sides. So it was for like locomotory purposes. Does that make sense?

• 22:53Daniel Whiteson?

  Yeah, some things I can totally understand why two makes sense and one doesn't. You know, like two eyes, one on each side of your head to see in both directions or to get binocular vision. Same thing for ears, same thing for flippers, same thing for legs, right? Two legs definitely seem to work better than one leg. But I guess I wonder why then you don't have two of everything, right? Like, isn't it always better to have two? Is there a sort of cost benefit analysis going on here? Where having two things means more to maintain, more to go wrong?

• 23:24Kelly Weinersmith?

  Yeah, so I started thinking about it on like an organ by organ basis. And so you're right, it does feel like from a survival standpoint, having a backup of the organs might be helpful. So for example, if one of your kidneys goes, it would be helpful to have another kidney, although that other kidney has to work really hard if there's just one left. And there's some evidence to suggest that that other kidney is gonna fall apart faster if it's doing essentially twice the work.

• 23:50Daniel Whiteson?

  Yeah, obviously, having a second kidney working as backup for both isn't perfect, but it does extend your life if one kidney fails, right?

• 23:57Kelly Weinersmith?

  Oh, yeah, absolutely, absolutely. But sometimes having two organs isn't just a redundancy thing. So you mentioned that eyes, having two of them, gives you depth perception.

• 24:06Daniel Whiteson?

  Yeah.

• 24:07Kelly Weinersmith?

  Ears, having two of them allows you to do a better job of localizing where sounds are coming from. Nostrils, actually, having two of them is helpful. Your nostrils actually switch off. There's this thing called nasal dominance, where one nostril is the one that is doing the bulk of the breathing. While the other one is like moving air a little bit more slowly. And it looks like there's a couple of different functions here. One of them is a little bit more important for smelling, like the air is moving more slowly over that nostril. And it seems like there's some scents that are better understood when part of it passes over our scent receptors quickly and some part of it passes over our scent receptors slowly.

• 24:52Daniel Whiteson?

  Wow.

• 24:52Kelly Weinersmith?

  And so each of our nostrils are not doing the exact same thing. Our nostrils are alternating. And sometimes when you have a cold, I don't know if you can tell, like, you'll be like, oh, I can breathe out of one of my nose, but not the other. And it's because your nasal passages take turns, with one of them being a little bit more swelled up to like make that be the nostril that passes air a little bit more slowly. And you can really tell that that's the case when you have a cold and you're congested.

• 25:16Daniel Whiteson?

  Wait, so they switch? I thought you were gonna say like one is dominant for a lifetime, like you're a lefty or a righty nose.

• 25:22Kelly Weinersmith?

  No, no, over the course of the day, it switches.

• 25:24Daniel Whiteson?

  The course of the day?

• 25:26Kelly Weinersmith?

  Yes.

• 25:26Daniel Whiteson?

  What?

• 25:27Kelly Weinersmith?

  Yes.

• 25:27Daniel Whiteson?

  I had no idea.

• 25:28Kelly Weinersmith?

  I know, I know. There's like so much you don't even know about your own body, it's crazy.

• 25:33Daniel Whiteson?

  Wow. Are amazing.

• 25:35Kelly Weinersmith?

  Right. Yes. Okay. So your nostrils aren't just redundant. They're actually like, you know, tag teaming each other. Maybe that they're still redundant, but like they're working together to accomplish a goal. And having two of them is helpful. But, okay, so say you wanted to have two mouths and two digestive tracts and a and I to complete the loop. One of the reasons we have such long stretches of digestive tract is that you have the all of this surface area and across that surface area. Nutrients and stuff are being absorbed out of your digestive tract and into the rest of your body. So the more surface area you have, the better job your body can do of like processing the food that you eat. So if you were to have two separate digestive tracts, like maybe in the middle of each one

• 26:19Kelly Weinersmith?

  of your cheeks, you had a mouth.

• 26:21Daniel Whiteson?

  Yeah.

• 26:21Kelly Weinersmith?

  And that sounds pretty freaky now and you had, you know, two butts or something. Each one of those tracks would probably have to have less surface area in order for you to have enough space to fit everything in there. And so that's probably not a more efficient system. And so I don't think it would necessarily be a better system to have two sets of digestive tracts. If you had two hearts and they were connected to the same circulatory system, you'd have to be very careful about coordinating because if you weren't coordinating, you could end up having very high blood pressure or you could end up having, you know, problems with blood like pooling in some areas, depending on how the hearts are pumping together. And so even though it'd be super cool to be kind of like Doctor Who,

• 27:05Kelly Weinersmith?

  you would have to worry about if your hearts are coordinating well enough. And so in order for that to work, you'd have to have completely separate vasculature. And that might get complicated. And if one heart fails, maybe you're still in as much trouble because now everything's not getting enough blood. It's getting half as much blood as it needed. So it's not necessarily clear that having two of those organs would be beneficial. When I think through it, but what do you think?

• 27:28Daniel Whiteson?

  Well, the thing I think about is lungs. I feel like we're so susceptible to choking on something.

• 27:34Kelly Weinersmith?

  Yeah.

• 27:35Daniel Whiteson?

  If you had like two different breathing tubes, then it'd be like, no big deal. If you had a chunk of steak stuck in one, right? It wouldn't be like, you're going to die within minutes. It seems like it would relieve a lot of the emergency status of breeding.

• 27:48Kelly Weinersmith?

  I don't have a good answer for that. That is a good point. That does seem, that's a choke point.

• 27:52Daniel Whiteson?

  Yeah, there you go.

• 27:56Kelly Weinersmith?

  Oh, I'm done.

• 27:57Daniel Whiteson?

  But maybe it's complicated and expensive, and maybe it's not enough of a benefit to make it worth it.

• 28:02Kelly Weinersmith?

  Yeah, yeah, I don't know. I mean, some of this stuff also might just be constraints, like, you know, there's not enough space, or it would be difficult from an evolutionary perspective to get two of them in there. I didn't come up with like a super satisfactory answer for why, I mean, like, you know, so many of us at this point die from like heart issues when we get old.

• 28:20Daniel Whiteson?

  Yeah.

• 28:21Kelly Weinersmith?

  Maybe it would be great if we had a backup or like one we didn't use until we turned 60 and then that one kicked in or something.

• 28:26Daniel Whiteson?

  Well, we do have like a whole second set of teeth that come in after, you know, 15 years or so, which is like super weird if you think about it. It'd be amazing if we had like a backup heart that came in when you were 50.

• 28:37Kelly Weinersmith?

  Yeah.

• 28:37Daniel Whiteson?

  And it was like, all right, let's toss out the old one and, you know, get an upgrade. That would be amazing. Let's do that.

• 28:43Kelly Weinersmith?

  Yeah, let's, let's talk to evolution about that. But, but no, I guess the problem is that by the time most of us are 60 and our hearts are starting to go, we are probably post reproduction, you know, post reproductive age. And I guess evolutionary pressure is probably not selecting for us to have new hearts at that point. But anyway, I didn't really find a super satisfactory answer, to be honest. But hopefully there's been some interesting information here. And I can't find another good connection to butts to end with here. I am so sorry.

• 29:15Daniel Whiteson?

  Well, I think the challenge here with biology is that we can never really know because it's sort of asking a meta question. You know, it's asking like, hey, if you ran the earth as an experiment a million times, how often would you end up with this configuration? Is the result of like some random cosmic ray which ended us down this path, which is unusual? Or is this like really the only efficient way to do it? And you're going to end up with this in most of those earth simulations. And that's definitely a question we can't answer until, you know, we slip into the black hole, come out the white hole on the other end and meet some aliens and discover, oh, look, they do have 17. Butts. And it turns out that we are weird being in the like uni anus part of the universe.

• 30:00Kelly Weinersmith?

  You did such a nice job wrapping that up and I'm going to go ahead and mess it up by continuing this conversation a little bit longer. And so, you know, I feel like in so many depictions of aliens, they're kind of like octopuses, which made me wonder, you know, octopuses have three hearts. Maybe we would have three hearts if it was like the octopus lineage that had moved on to land.

• 30:19Daniel Whiteson?

  Right.

• 30:20Kelly Weinersmith?

  And what would that be like? I don't know. And, and so anyway, now that I've gotten us off track after Daniel's beautiful segue, let's go ahead and find out if we answered the question.

• 30:31Speaker 06

  Thanks for the answer, Daniel and Kelly. Appreciate it. Makes sense. Body symmetry, efficiency of organs. And I guess with two eyes, two ears, you know, back in the plains of Africa, where we came from, keeping away from predators and finding prey, the stereo location certainly helped. I will now run and check and see which one of my nostrils is most dominant. Love the show. Thanks.

• 31:06Speaker 07

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• 31:35Daniel Whiteson?

  Hey, I'm Niall Rogers, producer, songwriter, guitarist, and co-founder of the group Sheik. A great song has a way of defining a moment, a moment of joy, heartbreak, or anything in between.

• 31:52Daniel Whiteson?

  This fall, I'll be driving across the country, dropping in on some of the coolest, most fascinating artists working today. We'll go deep into their lives and careers and hear what it was like before the moment that made them. From hitmakers like Miguel...

• 32:09Speaker 06

  That last year, finishing that record was the hardest experience of my life, regardless of how everyone else buys into this. I believe in this and I'm gonna push.

• 32:21Daniel Whiteson?

  To rising stars like Alex Warren.

• 32:24Speaker 03

  You know, a song is a story and the verse is setting the scene. And for me at least, it's allowing me to be personal and vulnerable with the audience, whether it's about my wife and I'm being vulnerable about her, or it's about, you know, my parents and I'm being vulnerable to them. And it's almost like a cinematic piece in a way where each song tells that beautiful story.

• 32:42Daniel Whiteson?

  It's gonna be one hell of a trip. Experience Before the Moment, a Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 33:05Kelly Weinersmith?

  All right. I always personally love it when we get questions either directly from kids or from kids through their parents. And so today we have a question from Andy and Joss, so let's go ahead and hear it. Hi there, Daniel and Kelly. My son woke up the other morning and he had a new theory about how the universe might end. His theory is that there are many different bubble universes and they're all moving around inside one big greater universe. He drew a lovely diagram showing all the bubble universes with a little plus and minus next to it to demonstrate we don't know how many there are. The theory goes that

• 33:47Kelly Weinersmith?

  the bubble universes are drawn together by gravity and pushed apart by dark...

• 33:54Speaker 03

  Energy till they all perhaps come together at the edge of the greater universe and then burst the greater universes edge and destroy the whole multiverse. Our questions are like this, could this be the nature of our universe? Could science ever know if this was the nature of our universe? Could gravity interact with other universes outside our small bubble universes? Perhaps while traveling through extra dimensions. Thanks very much for any time you can spend on this question on your podcast. Look forward to hearing any thoughts you have.

• 34:33Daniel Whiteson?

  It is wonderful to know that kids are out there thinking about how the universe works and how it might work. And crazy ideas about explaining it and understanding it. I love that these kinds of topics tickle children. And to me, that's why this science is so exciting. It's because it connects with things we've always wanted to know. Basic questions we've been asking about the universe since we were kids and since humans were humans.

• 34:58Kelly Weinersmith?

  Can I tell you a quick story?

• 34:59Daniel Whiteson?

  Yeah.

• 35:00Kelly Weinersmith?

  Yep, my daughter the other day was like, hey, mom, can animals communicate with each other? Like, we can't communicate to dogs, but can, you know, like one bird communicate to another bird? And I was like, I don't know. And then I was listening to this book and they were explaining that actually birds and squirrels and a couple other different kinds of species have calls that they can recognize, like across these species boundaries that tell each other, hey, there's an aerial predator or there's a predatory snake on the ground. And so they can like actually convey pretty complicated information about not only there is a risk, but what kind of risk it is from like, you know, birds to mammals. And the answer was yes. And I think we only figured this out, you know, like not yesterday, but like not that recently,

• 35:44Kelly Weinersmith?

  which makes me feel like, I don't know, maybe we should bring kids into like ecology departments and be like, just like think thoughts at us and we'll go check some of it out. You know, they should do the same thing to physics departments and see what we find out.

• 35:55Daniel Whiteson?

  They definitely should. And that's exciting to think that like squirrels and birds and dogs are talking to each other. But it's also a bit of a bummer. I mean, basically, there's like an earth animal group chat and we are not included.

• 36:07Kelly Weinersmith?

  Okay, but one, we're starting to decipher it. So we know what they're talking about. And two, like, some of it is eavesdropping. Like, I don't necessarily know that the birds want the squirrels to know. And so that makes it a little bit less exciting. And the messages are pretty straightforward. It's not like-

• 36:23Daniel Whiteson?

  Did you see what Kelly was wearing yesterday? Ha, ha, ha.

• 36:26Kelly Weinersmith?

  What a dweeb.

• 36:28Daniel Whiteson?

  You don't think they're roasting us on the group chat?

• 36:30Kelly Weinersmith?

  I mean, they might be. Or like, oh, the acorn cap on your head. It's really cute. You look really nice in that hat. Like, I don't think it's, you know, it's like survival things. It's not too subtle, probably. But still, it's awesome that, like, they are sort of paying attention to each other and communicating in that way.

• 36:47Daniel Whiteson?

  All right. Well, you know what, Kelly? There was no contest already, but I think you just cinched yourself for the award for 2025, getting us the most off-track podcast award.

• 36:57Kelly Weinersmith?

  Yeah. Well, you know what, Daniel? We are, we are, we have one question left and we're only 34 minutes in. So I thought we could take a bit of a detour.

• 37:09Daniel Whiteson?

  So let's veer back from what dogs and squirrels are saying about us and think about Joss's question about bubble universes that could be moving around and drawn together by gravity and pushed apart and what's going on there. So these are fascinating ideas, Joss, and they connect with the real ideas in cosmology. I mean, the concept of a bubble universe is something we have in real physics cosmology. It's a sort of proto idea that's not been proven, but is taken pretty seriously. And the idea is to try to explain where the Big Bang came from. You know, the Big Bang says, we had a hot, dense state about 13.8 billion years ago, which expanded and cooled. It wasn't a dot of matter exploding into

• 37:53Daniel Whiteson?

  empty space. But the Big Bang doesn't tell us where that hot, dense matter came from. It doesn't explain it at all. And there's lots of different theories. And one of them is that that matter came from some earlier kind of stuff, something we call inflationary matter. So imagine now a universe filled with some weird inflationary matter. And this stuff expands super duper rapidly. You know, like my factors of 10 to the 30 every 10 to the minus 20 seconds. Crazy expansion, but occasionally some of it decays. The way like some particles can turn into other particles. This inflationary matter turned into normal matter and created like a little bubble of hot dense stuff.

• 38:36Daniel Whiteson?

  Now, this doesn't really answer the question of where did that hot dense matter come from? It just sort of kicks it down the road and says, maybe it came from some weird inflationary matter. Where did that come from? We don't know. But in this picture, you have like a universe filled with this inflationary matter. And then these little bubbles of normal matter, these little pockets. So our universe could be like one little bubble among this vast landscape of bubbles.

• 39:01Kelly Weinersmith?

  Okay, so you've got these ever growing bubbles that are giant. And then you've got some bubbles that get big and then they stop getting big, but they get really hot. And so then wouldn't they eventually get like swallowed up by the other bubbles?

• 39:11Daniel Whiteson?

  No, the bubbles are our universe. So you have like a landscape that's just filled with this inflationary matter that's expanding. It's not bubbles, just like the whole universe is expanding and filled with this stuff. And then some pockets of it turn into normal matter. So instead of having a universe just filled with inflationary matter, you have these little pockets of normal matter. But between them is still inflationary matter, expanding super duper rapidly. So like we are in one of those little bubbles and there's another one over there. But between us and that other universe is more of this inflationary matter that's expanding like crazy. And so that other bubble gets further and further away from us every nanosecond.

• 39:49Kelly Weinersmith?

  Okay, so the bubbles are filled with little things inside of them.

• 39:55Daniel Whiteson?

  Yeah, our universe is one of those bubbles.

• 39:58Kelly Weinersmith?

  Okay, got it.

• 39:58Daniel Whiteson?

  So this is an attempt to explain some things about the early universe. We don't understand, there's a whole theory about this inflation. But it creates this idea of bubble universes. And it's true that the bubble universes might be pulled together by gravity. Like we have stuff, the other bubble universe has stuff. But it's going to be totally overwhelmed, totally dominated by the inflation between them. Like the inflation is so quick, it's hard to even really wrap your mind around the scale here. Like blowing up by a factor of 10 to the 30 means like taking a grain of sand and turning it into a star and doing that every 10 to the minus 20 seconds.

• 40:40Daniel Whiteson?

  It's just, the numbers are incredible. And so gravity is going to be definitely overwhelmed by that. So you do have these bubbles, but they're just getting further and further apart from each other because of this incredible intense, constant inflation.

• 40:53Kelly Weinersmith?

  Okay, so we know that the universe is expanding and that would be, would that be consistent with what is happening with the bubbles?

• 41:00Daniel Whiteson?

  Yeah, so there's lots of different kinds of expansion going on here, which is a little hard to keep track of. There's the expansion we call the Big Bang, where you have a hot, dense state, and then the universe got bigger and colder and more dilute. And that's something we know and very well established, and we've measured, and we've seen, and we've studied. And of course, there's still questions about it. And that's one kind of expansion. And that's even accelerating because of dark energy. So that's our bubble getting bigger and more dilute. Then there's the inflationary expansion, which is happening between the bubbles, which is much more dramatic and much more powerful.

• 41:32Kelly Weinersmith?

  Okay.

• 41:33Daniel Whiteson?

  And so Josh was asking about whether these bubble universes could be drawn together by gravity and pushed apart by dark energy until they come to the edge of a greater universe and destroy the whole multiverse. Love the dramatic ending to Josh's story. So we don't know if there is an edge to the greater universe. It could be that this landscape filled with inflationary matter then dotted with these bubble universes. It could be that that goes on forever, that it's infinite, right? That there is no edge to it at all. We don't know. Another possibility is that it's finite, that it's like wraps around on itself the way like the surface of a sphere does if the universe was two dimensions. But of course, our universe is more than two dimensions. So you have to imagine like

• 42:15Daniel Whiteson?

  the 3D surface of a four dimensional sphere being closed on itself. So we don't know if that larger space is finite or infinite. And it's possible that we might never know because it's so big and it's so rapidly accelerating and expanding that information Just leaves our cosmic horizon. You know, the way that even inside our universe, the expansion is happening so fast that there are parts of it we will never see because the expansion between us and those parts of the universe is happening so fast that light from that part of the universe will never reach us. Like a photon shot out by some of the most distant galaxies will never get

• 42:55Daniel Whiteson?

  here because space between us and it is expanding so fast. And so in the same way, if there is an edge to the inflationary eternal universe, we might not ever know because it's sort of beyond our ability to probe. The speed of light really limits what fraction of the universe we can ever study. So we don't know if there's an edge to this larger universe, and we don't know if we could ever know. What we can do is look to see if these bubbles ever collide. Like, we think in principle they shouldn't because the material between them is expanding so fast, but you could occasionally, if there are lots of these things, get them bumping into each other sort of by chance. And people have looked for this. If that happened, you would

• 43:39Daniel Whiteson?

  expect to see like an imprint in the sky and the pattern of stars. It wouldn't look quite as random and smoothed out as it does. You would see like basically a big dent somewhere. And we've looked for that and we haven't seen it. So there's no evidence that our bubble universe has collided with any other bubble universes so far.

• 43:57Kelly Weinersmith?

  So if you had to like, put a probability on your thoughts that the bubble universe theory is a valid theory, a valid explanation, what, how likely do you think the bubble universe thing is, is a good explanation?

• 44:11Daniel Whiteson?

  I mean, it's a good working hypothesis. It's like an exploration of what might be going on out there. We can't really evaluate it without having any data, you know, because there could always just be a better idea somebody had. This is the problem with thinking about things that you can't check in the universe. And I don't mean to say that it's not scientific. I'm not a big fan of like drawing arbitrary dotted lines and saying this is science, that's not science. Lots of things that you can't immediately test are still science because they eventually Actually contribute to our understanding of the universe somehow, like all of mathematics. For example, you know, Euclid developed his geometry and that was crucial to understanding a lot of the universe.

• 44:55Daniel Whiteson?

  And other folks developed non-Euclidean geometry, not because they cared about the universe. They were just nerds thinking about stuff. And that turned out to also be crucial. So I think all of it is scientific, but I don't think we can assign numbers to like the probability that we're in a bubble universe. Because there's like a zillion other ideas out there and we don't know how to weigh them against each other without being able to take some measurements. The universe, nature is the ultimate arbiter of these theories, right? Your theory can be beautiful, it can be elegant, it can be amazing, it can also just be wrong. And so we need to sort of consult with nature and we don't have a method to do that because we can't see outside our universe. So it might be that somebody in the future comes up with a really clever way to test these ideas.

• 45:40Daniel Whiteson?

  Never rule out future smart people like the young Joss, but it might be that we never know and that's sort of frustrating.

• 45:47Kelly Weinersmith?

  Well, maybe it's comforting because it means we're unlikely to be destroyed by these bubble universes. But I guess just because we can't measure it doesn't mean it's not going to result in our impending doom. But.

• 45:58Daniel Whiteson?

  There are ways that bubbles could destroy our universe, not from other bubbles interacting with it or bouncing in it, but from our universe changing state. You know, the state of our universe where we have all of these fields and some of them, like the Higgs field have energy stuck in them. We don't know how stable that is. And it's possible that like some errant particle physicist doing an experiment sort of pushes the universe out of its unstable state and collapses the Higgs field down to lower energy, which would change like the masses of all the particles and chemistry would be totally different and life as we know it would be impossible and all atoms would fly apart because electrons would lose their mass. And if this happened, it would happen at one location and then in a bubble moving

• 46:43Daniel Whiteson?

  outwards at the speed of light. And so that eventually would take over the whole universe and convert everything into this sort of new kind of physics. This is the Higgs field collapse. So that's the opposite of bubbles like bumping into each other and destroying the universe. But it's a bubble from within our universe, which wouldn't destroy it, but it would change life fundamentally.

• 47:05Kelly Weinersmith?

  You are such a ray of sunshine.

• 47:08Kelly Weinersmith?

  Do you think physicists is the field that would be like most likely to accidentally destroy humanity?

• 47:13Daniel Whiteson?

  Wow. I think physicists are probably most likely to destroy the planet, but I think destroy humanity, you got viruses and you got pollution and you got all sorts of stuff. So I think chemists and biologists are in the running for, you know, killing off humanity.

• 47:30Kelly Weinersmith?

  Yay.

• 47:31Daniel Whiteson?

  All right. Well, I hope that Joss is out there thinking about ways to save humanity from the ravages of physics and biology and chemistry, and that everything we've taught him contributes to the positive harmonious future of humanity. Thanks for the question, Andy and Joss, and let us know if we answered it. Follow up questions always welcome. Thank you for taking the time to answer our questions. It was exciting to hear you talking about my ideas on the podcast. Soon the Higgs series will get dispersed. I'm sending in any things as I think of them. Thank you, Daniel and Kelly. All right. Thank you, everybody who writes to us with your questions or comments or feedback or cat pictures. Loved all the cat pictures we got last week. Thank you very much. We love hearing from you.

• 48:15Daniel Whiteson?

  We love knowing that you're out there and we hope that we contribute positively to your day.

• 48:19Kelly Weinersmith?

  Yes, thank you so much for writing. It means so much to us.

• 48:28Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 48:34Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 48:40Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 48:46Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 48:53Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 49:02Daniel Whiteson?

  Don't be shy. Write to us.

• 49:06Speaker 03

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• 51:15Speaker 03

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