Listener Questions #28

00:00:07
Speaker 1: How can massless photons add to a black hole's might? Can you really make a singularity out of light?

00:00:15
Speaker 2: Organs that come in twos include the long hand, kidney, foot, and eye? But why do I only have one of some things? And what's the plural of venus?

00:00:26
Speaker 1: Ain't I could drifting bubble universes collide to end our cosmic show my gravity in other dimensions?

00:00:34
Speaker 3: Ever?

00:00:34
Speaker 2: Let us know whatever questions keep you up at night. Daniel and Kelly's answers will make it right.

00:00:41
Speaker 1: Welcome to Daniel and Kelly's Extraordinary Universe.

00:00:44
Speaker 4: We've done twenty eight of these. Hello, Kelly, we or Smith.

00:01:01
Speaker 2: I study parasites and space and whatever it is that y'all ask me when you send us emails.

00:01:07
Speaker 3: Hi, I'm Daniel.

00:01:08
Speaker 1: I'm a particle physicist, and I've answered a lot of questions from listeners, but never any about ANI.

00:01:14
Speaker 2: Oh no, that's Daniel. You'd be taking my questions. I am the ANI experts in this group. Thank you very much. You stick to the black holes and I stick to the biology black holes.

00:01:25
Speaker 1: Isn't there an obvious connection exactly? Aren't black holes a sort of physics anus?

00:01:30
Speaker 4: Yeah?

00:01:31
Speaker 3: Yes, yes, And I of the universe.

00:01:34
Speaker 2: All right, you stick to the ani of the cosmos. I stick to the ani of the Earth.

00:01:39
Speaker 1: But wait now I'm realizing it. We have it all wrong, don't we. Black holes are more like mouths, and white holes would be more like anus'es. Why because things don't come out of black holes?

00:01:48
Speaker 4: Oh, they go in and things go out of white holes.

00:01:51
Speaker 2: Well, you know yet another instance where the physicists did a poor job of naming things.

00:01:56
Speaker 4: Yes, there you go again.

00:01:57
Speaker 1: It is hard to keep the inns in the out streets and time.

00:02:00
Speaker 2: 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 danieland Kelly dot org.

00:02:18
Speaker 1: 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 warrantful questions from listeners. People who are curious about the universe, people who've 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 satisfactory explained, please don't be shy. Write to us questions at danieland Kelly dot org. We really do right back to everybody.

00:02:54
Speaker 2: Daniel worries back to everybody within a day. I am not quite as punk 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.

00:03:08
Speaker 1: I promise you that email address is not a black hole. It's more like a white hole because answers come out of it.

00:03:13
Speaker 2: 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.

00:03:26
Speaker 5: Hi, Daniel and Kelly, it's Stephen from BC 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?

00:03:56
Speaker 3: How can a.

00:03:56
Speaker 5: Photon become a singularity inside a tiny black hole? I look forward to your answers.

00:04:02
Speaker 1: 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?

00:04:23
Speaker 3: I heard?

00:04:24
Speaker 1: So stevens out there doing physics in his mind. Congrats Steven, and I'm very excited to answer this question for you.

00:04:31
Speaker 2: 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 remind us what is gravity?

00:04:50
Speaker 1: Yes, so Newton told us that gravity was a force between masses, but then Einstein revealed that it's actually the curvature of space time. That what we think think of its gravity is actually a pseudo force because we can't see the curvature of space time 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 round 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, it seems like something accelerates it towards the Earth. Really the apple is just following the curvature of space time, and you're the one accelerating against space time. So general relativity reformulates gravity as the curvature of space time that affects the motion of objects in a way that makes us think there's a force we would call gravity.

00:05:55
Speaker 4: Feels like that doesn't make any sense.

00:05:57
Speaker 2: But if Newton got it wrong, I don't feel so bad about getting it wrong too.

00:06:03
Speaker 1: And the crucial thing to understand in the context of this question is that the curvature of space time comes from energy density. We often think about it as mass tells space time 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 contribute to the energy density, and it can make it easier to have a black hole because photons have energy.

00:06:31
Speaker 2: Of course, okay, photons have energy. That is not a controversial statement, right.

00:06:38
Speaker 1: 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 where 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 space time enough to give you a black hole.

00:07:23
Speaker 2: Ooh, all right, So isn't there that 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.

00:07:32
Speaker 4: Are they going to kill us all with a black hole?

00:07:36
Speaker 1: 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 one hundred and ninety six 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 ten to the thirty five jewels in a region like ten to the negative fifteen meters across. You need like more energy than is put out by the Sun every second concentrated into a tiny little 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.

00:08:34
Speaker 3: Men made lasers.

00:08:35
Speaker 4: That's comforting.

00:08:39
Speaker 1: And so Steven'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, it's total charge, and it's spin. No original 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.

00:09:36
Speaker 2: So what happened to the electrons? Did they just get like smoohed into something unrecognizable?

00:09:40
Speaker 1: We don't know, right, Like general relativity tells us that they form a singularity, but that ignores 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 smush them together that tightly, they break open and form some sort of plast of their intermediate states.

00:10:01
Speaker 4: Who knows, Right, we might finally know.

00:10:04
Speaker 1: 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.

00:10:37
Speaker 3: Rats or whatever.

00:10:38
Speaker 4: Oh great, would you pick lab rats? I feel like blue whales.

00:10:41
Speaker 2: Like there's if you're gonna make a black hole out of something, you gotta go go big or go home.

00:10:46
Speaker 1: 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?

00:10:52
Speaker 6: Oh?

00:10:52
Speaker 4: Probably rats?

00:10:53
Speaker 2: Yeah, But what do you think the greatest anus biomass on the planet is.

00:10:58
Speaker 4: I bet it's could be humans, might be humans.

00:11:02
Speaker 1: I can't believe you're a biologist and you don't know the answer to this question off the top of your head.

00:11:06
Speaker 4: I'm a little embarrassed. I'm a little embarrassed.

00:11:10
Speaker 1: 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 dice in 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 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 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 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 pocketive 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.

00:13:05
Speaker 2: No, you're looking at me because it's my turn to say something. But I am still trying to figure out the anus thing.

00:13:11
Speaker 4: I'm so sorry. I mostly was listening, but I can't.

00:13:16
Speaker 1: Oh boy, 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.

00:13:31
Speaker 3: I don't know if that made any sense.

00:13:32
Speaker 4: I don't think so.

00:13:34
Speaker 5: Hi, Daniel and Kelly, it's Stephen from British Columbia. Again, thanks again for answering my question about what is going on inside tiny black holes. That explanation was super helpful.

00:14:06
Speaker 1: 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 in the universe deserves to be understood. Up next, we have an amazing question about the human body, and it's symmetry and asymmetry from Jerry.

00:14:28
Speaker 7: Hey, Daniel and Kelly love the show.

00:14:30
Speaker 8: 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.

00:15:04
Speaker 4: Thanks, Well, I gotta be honest with you.

00:15:07
Speaker 2: I have had this question sitting on my stack for a few months because I just kind of wasn't really sure how how to answer this one, Like what is the answer why sometimes a human body just is the way it is? And uh and so all right, So here's what I came up with, because it is a great a good question. It's a great question.

00:15:27
Speaker 1: Well, let's start with the meta answer, like is there always an answer? What kind of answer do you think Jerry's 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.

00:15:52
Speaker 2: Yes, 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.

00:16:03
Speaker 1: You didn't go for an Aristotilian answer. It isn't the way of humanity, to have one mouth.

00:16:08
Speaker 4: To have one butt, one butt but with two cheeks.

00:16:12
Speaker 1: What was Aristotle's theory of the anis? Was he the first one to think about the anis?

00:16:16
Speaker 4: You know, I didn't get as far back as Aristotle.

00:16:19
Speaker 3: Actually, you always got to go back to Aristotle, Kelly.

00:16:22
Speaker 1: He's like the original, you know, paper out of the Soviet Union that you didn't read and that came out in the nineteen seventies that totally scoops your thesis.

00:16:29
Speaker 3: He was the original dude to do that.

00:16:31
Speaker 2: Well, yes, yes, well I'm really I hope that I can still give a satisfactory answer having not read Aristotle's.

00:16:38
Speaker 4: Opinion on this, but you know, I will.

00:16:42
Speaker 2: 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 a three hundred 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. 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 three hundred million years, or maybe we're just kind of locked in at this point, and the fact that we've had it for three hundred million years just shows that this arrangement of things is sort of hard to get out of.

00:17:44
Speaker 1: Well, what do you mean by three hundred million years? What happened three hundred million years ago? Was that the Cambrian explosion.

00:17:50
Speaker 2: 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.

00:18:01
Speaker 1: Okay, because fish, for example, I 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.

00:18:08
Speaker 2: 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 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 farging, 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 more symmetrical that way. I think that's called bilateral symmetry. But there are other organisms that are radially symmetrical.

00:18:45
Speaker 4: I think that's what it's called.

00:18:46
Speaker 2: I didn't necessarily plan on going this far back, so I'm pulling this out of my uh Aristatilian hole Aristotelian hole. 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 tree is good. A 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.

00:19:26
Speaker 4: So it was for like locomotory purposes. Does that make sense?

00:19:29
Speaker 1: Yeah, some things that 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 to Is there a sort of cost benefit analysis going on here where having two things means more to maintain.

00:19:59
Speaker 3: More to go?

00:20:00
Speaker 2: 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's going to fall apart faster if it's doing essentially twice the work.

00:20:26
Speaker 1: Yeah, obviously having a second kidney working as backup for both isn't perfect, but it does extend your life if one kidney fails.

00:20:33
Speaker 2: Right, 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 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 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 sense 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.

00:21:28
Speaker 3: Wow.

00:21:28
Speaker 2: 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, ah, I can breathe on 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.

00:21:52
Speaker 3: Wait, so they switch.

00:21:53
Speaker 1: I thought you were going to say, like one is dominant for a lifetime, like you're a lefty or a righty.

00:21:57
Speaker 3: News.

00:21:58
Speaker 4: No, No, over the course of the day.

00:22:00
Speaker 1: Switches the course of the day.

00:22:02
Speaker 3: Yes, what Yeah, I had no idea.

00:22:04
Speaker 4: I know, I know, there's like yes, so much you don't even know about your own body. It's crazy.

00:22:09
Speaker 3: Wow, noses are amazing.

00:22:11
Speaker 2: 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 ani to complete the loop. One of the reasons we have such long stretches of digestive tract is that you have 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 of your cheeks you had a mouth 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. 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 tracks. If you add 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 would be super cool to be kind of like doctor who, 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.

00:24:04
Speaker 1: But what do you think, Well, the thing I think about is lungs. I feel like we're so susceptible to choking on something. If you had like two different breeding tubes, then it'd be like, no big deal if you had a chunk of steaks stuck in one all 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.

00:24:24
Speaker 2: I don't have a good answer for that. That is a good point. That does seem that's a choke point.

00:24:28
Speaker 3: Yeah, there you go.

00:24:32
Speaker 4: I'm done.

00:24:33
Speaker 1: But maybe it's complicated and expensive and maybe it's not enough of a benefit to make it worth it.

00:24:38
Speaker 4: Yeah, yeah, I don't know.

00:24:39
Speaker 2: 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. Yeah, maybe it would be great if we had a backup or like one we didn't use until we turn sixty and then that one kicked in or something.

00:25:02
Speaker 1: And well we do have like a whole second set of teeth that come in after you know, fifteen 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 fifty. Yeah, and it was like, all right, let's toss out the old one and you know, get an upgrade.

00:25:17
Speaker 3: That would be amazing. Let's do that now.

00:25:19
Speaker 4: Yeah, let's let's talk to evolution about that.

00:25:21
Speaker 2: But you know, I guess the problem is that by the time most of us are sixty and our hearts are starting to go, we are probably post reproduction or 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.

00:25:51
Speaker 1: 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 seventeen butts, and it turns out that we are weird being in the like unious part.

00:26:35
Speaker 3: Of the universe.

00:26:37
Speaker 2: 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.

00:26:49
Speaker 4: You know, octopuses have three hearts.

00:26:51
Speaker 2: Maybe we would have three hearts if it was like the octopus lineage that had moved on to land.

00:26:56
Speaker 4: And what would that be like? I don't know.

00:26:58
Speaker 2: 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.

00:27:07
Speaker 7: 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 planes of Africa and where we came from, keeping away from predators and finding prey. The stereolocation certainly held. I will now run and check and see which one of my nostrils is most dominant. Love the show, Thanks.

00:27:52
Speaker 4: All right.

00:27:53
Speaker 2: 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 jos So let's go ahead and hear it.

00:28:06
Speaker 6: 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. They 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 the bubble universes are drawn together by gravity and pushed apart by dark energy, so 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 by 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.

00:29:21
Speaker 1: 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 tackle 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.

00:29:45
Speaker 2: Can I tell you a quick story, Yeah, yep. My daughter the other day was like, hey, mom, can.

00:29:51
Speaker 4: Animals communicate with each other?

00:29:52
Speaker 2: Like we can't communicate to dogs, but can you know, like one bird communicate to another bird?

00:29:57
Speaker 4: And I was like, I don't know.

00:29:58
Speaker 2: 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.

00:30:24
Speaker 4: Know, birds to mammals.

00:30:26
Speaker 2: And the answer was yes, And I think we only figured this out, you know, like not yesterday, but like not that recently, 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.

00:30:43
Speaker 1: 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.

00:30:54
Speaker 2: 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.

00:31:07
Speaker 4: And the messages are pretty straightforward. It's not like.

00:31:11
Speaker 1: Did you see what Kelly was wearing yesterday?

00:31:12
Speaker 4: Ha ha?

00:31:13
Speaker 3: What ad we You don't think they're roasting us on the group chat?

00:31:17
Speaker 2: I mean they might be or like, oh the acorn cap on your head.

00:31:21
Speaker 4: Listen, it's really cute. You look really nice in that head Like. I don't think it's you know, it's like survival things.

00:31:27
Speaker 2: 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.

00:31:35
Speaker 1: All right, well, you know what, Kelly, there was no contest already, but I think you just cinched yourself for the award for twenty twenty five, getting us the most Off Track Podcast award.

00:31:45
Speaker 4: Yeah, well you know what, Daniel, we are.

00:31:49
Speaker 2: We have one question left and we're only thirty four minutes in, so I thought we could take a bit of ad tour.

00:31:57
Speaker 1: So let's veer back from what Dogs and Square 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, Jos, and they connect with 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 improven 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 thirteen point eight billion years ago which expanded and cooled. It wasn't a dot of matter exploding into empty space. But the Big Bang doesn't tell us where that hot dance 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 ten to the thirty every ten to the minus twenty 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. 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.

00:33:48
Speaker 2: Okay, so you've got these ever growing bubbles that are giant, and then you've got some bubbles. They 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.

00:33:58
Speaker 3: No, the bubbles are our universe.

00:34:00
Speaker 1: So you have like a landscape that's just filled with this inflationary matter that's expanding. Its 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 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.

00:34:36
Speaker 4: Okay, so the bubbles are filled with little things inside of them.

00:34:43
Speaker 3: Yeah, our universe is one of those bubbles.

00:34:45
Speaker 4: Oka, Yeah, got it.

00:34:46
Speaker 1: So this is an attempt to explain some things about the early universe we don't understand, and there's a whole theory about this inflation. But it creates the 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 ten to the thirty means like taking a grain of sand and turning it into a star and doing that every ten to the minus twenty seconds. 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.

00:35:40
Speaker 2: Okay, so we know that the universe is expanding, and that would be would that be consistent with what is happening with the bubbles.

00:35:47
Speaker 1: 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 it's something we know and very well established and we've measured and we've seen and we've studied. 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, 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 Jos'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.

00:36:48
Speaker 3: Edge to it at all. We don't know.

00:36:50
Speaker 1: 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 has two dimensions, but universe has more than two dimensions, you have to imagine like the three D 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 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 expect to see like an imprint in the sky and the pattern of stars, it wouldn't look quite as random and smooth 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.

00:38:45
Speaker 2: So if you had to like put a probability on your thoughts that the bubble universe theory is a valid theory, a valid explanation, how likely do you think the bubble universe thing is is a good explanation.

00:38:58
Speaker 1: I mean, it's a good word 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.

00:39:24
Speaker 3: That's not science.

00:39:26
Speaker 1: Lots of things that you can't immediately test are still science because they eventually contribute to our understanding of the universe somehow, like all of mathematics. For example, you know euclid developed his geometry and that it was crucial to understanding a lot of the universe, 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 a gazillion 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. Never rule out future smart people like the young Joss, But it might be that we never know, and that's sort of frustrating.

00:40:34
Speaker 2: 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 dual.

00:40:44
Speaker 1: But 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.

00:41:02
Speaker 3: We don't know how stable.

00:41:03
Speaker 1: That is, and it's possible that like some arrant particle physicists 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 in 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 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 is a bubble from within our universe, which wouldn't destroy it, but it would change life fundamentally.

00:41:52
Speaker 2: You are such a ray of sunshine. Do you think physicists is the field that would be like most likely to accidentally just story humanity?

00:42:02
Speaker 3: Wow?

00:42:05
Speaker 1: I think physicists are probably most likely to destroy the planet, But I think destroy humanity. You got viruses, and you've 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. Yea, 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 to the question, Andy and Joss, and let us know if we answered it. Follow up questions always welcome.

00:42:40
Speaker 9: Thank you for taking the science and twerk questions. I was exciting to hear you talking about my ideas on the pollodcast. Assuming the Higgs serials get us first, I've said, did any things as I think of them?

00:42:51
Speaker 3: Thank you Daniel and Kelly all right?

00:42:53
Speaker 1: Thank you everybody who writes to us with your questions or comments or feedback or cat pictures. Loved all the cat pictures we got week.

00:43:00
Speaker 3: Thank you very much.

00:43:01
Speaker 1: We love hearing from you, We love knowing that you're out there, and we hope that we contribute positively to your day.

00:43:06
Speaker 4: Yes, thank you so much for writing. It means so much to us.

00:43:16
Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio.

00:43:19
Speaker 4: We would love to hear from you.

00:43:21
Speaker 3: We really would.

00:43:22
Speaker 1: We want to know what questions you have about this Extraordinary Universe.

00:43:27
Speaker 2: We want to know your thoughts on recent shows, suggestions for future shows.

00:43:31
Speaker 4: If you contact us, we will get back to you.

00:43:33
Speaker 3: We really mean it.

00:43:35
Speaker 1: We answer every message. Email us at Questions at Danielankelly.

00:43:39
Speaker 2: Dot org, or you can find us on social media. We have accounts on x, Instagram, Blue Sky and on all of those platforms.

00:43:46
Speaker 4: You can find us at D and K Universe.

00:43:49
Speaker 3: Don't be shy write to us