Listener Questions Volume #1

Daniel and Kelly answer questons about dark energy, slime molds and Hawking radiation! 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?

  This is an iHeart Podcast. Guaranteed Human.

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• 1:11Daniel Whiteson?

  Every discovery, every moment of insight, every aha or eureka, where the ideas click together in someone's mind to reveal a deep truth about the universe, all of those begin the same way, with a question. In fact, all of science starts with questions. The reason we know things about clouds and beetles and black holes is because someone out there had a question that kept them up at night, so they were willing to stay up late looking at the stars or counting beetles until they figured it out. Science is just people asking questions they couldn't let go. But it's not just professional scientists who ask questions and move us forward, it's everyone. It's you.

• 1:51Daniel Whiteson?

  And we think your questions also deserve answers, or at least replies that make sense and help you grapple with what we do and don't know about the topic. So if you have a question about science or whatever, please write to us to [email protected]. We'd love to hear from you. And sometimes we'll answer those questions right here on the pod. And so on today's episode, we're going to be answering questions submitted by listeners. And more than that, and I'll admit to being a little bit nervous about this part, we're going to go back to those listeners with our answers and follow up to see if our explanations scratched their itch or not. Today, Daniel and Kelly are getting graded by the listeners. So today

• 2:35Daniel Whiteson?

  on Daniel and Kelly's Extraordinary Universe, we'll be answering questions from listeners, volume one.

• 2:55Kelly Weinersmith?

  Hello, I'm Kelly Wiener Smith, and I am so excited that we're having our first listener questions episode today.

• 3:02Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist, and I love answering questions from the internet about physics, about philosophy, even about dating.

• 3:11Kelly Weinersmith?

  Really? You've answered questions on the show about dating?

• 3:15Daniel Whiteson?

  People send me all sorts of questions. You know, they send me their treatise on the nature of the universe. They send me questions about career advice, how to get into physics. And yes, sometimes people ask me questions about their dating life. And hey, I don't claim any particular expertise there, but I'll share my thoughts.

• 3:32Kelly Weinersmith?

  Sure. Yeah, no, I'll share my thoughts on anything. Well, so I was actually going to ask you, what is the weirdest or most surprising, like no negative connotation needed, but weirdest or most surprising question you've ever been asked, related to your career as a physicist?

• 3:47Daniel Whiteson?

  Oh, wow, that is such a good question. Now, mentally cycling through the thousands of questions I've gotten over the years, I think one of the most challenging questions to answer are ones about people's personal experiences. People writing sometimes about like their UFO experiences or their paranormal experiences, and they want my physics knowledge and like what else could have explained it. And that's a delicate line to walk because you don't want to suggest that what they experienced is not what they think they experienced, but you also want to help them disentangle it and think about what Else might have explained it. That's maybe like the most oddball and challenging kind of question to answer. I also sometimes get really touching stories like a woman who

• 4:29Daniel Whiteson?

  went through her father's old belongings. He was, of course, a retired engineer and she found in there a treatise on the nature of the universe. And she sent it to me and she's like, look, I don't know if this is anything, but if it is something, I feel terrible not sharing it with the world. Can you tell me if this is worthwhile or not?

• 4:46Kelly Weinersmith?

  Oh, that's so cute.

• 4:48Daniel Whiteson?

  I know.

• 4:49Kelly Weinersmith?

  Was it worthwhile or was it fun to read, but maybe not earth changing?

• 4:54Daniel Whiteson?

  There was nothing really earth shattering in there, but I think she was happy to know that at least somebody had looked at it.

• 4:59Kelly Weinersmith?

  Well, it's so cool that you were able to provide that.

• 5:01Daniel Whiteson?

  And how about you? Do you get weird questions from the internet about parasites? People send you pictures of bits of their body and be like, Kelly, what is this? Do I need to go to the ER?

• 5:09Kelly Weinersmith?

  I do get photos of feces from time to time. And it's worth noting that I cannot identify parasitic infections from a picture of a bowel movement. They're microscopic and I can't. Also, I'm not a medical professional.

• 5:21Daniel Whiteson?

  So everybody out there who was about to email Kelly a picture of their poop, not worth your time.

• 5:26Kelly Weinersmith?

  Please don't. I think the hardest question for me to answer, though, was I was doing an interview for our book Soonish, and I think the person doing the interview hadn't really read the book. And so his question was, so tell me about the robots.

• 5:42Kelly Weinersmith?

  And there was like a different robot in every single chapter. And so I didn't have any idea what he was talking about. This is when I learned the trick that when you do an interview, if someone asks you a question that you don't really know what they're trying to get at, you just decide what is the most interesting thing I feel like talking about right now. And so I just picked like my favorite robot and went off on that tangent. It was a learning experience.

• 6:06Daniel Whiteson?

  Sounds like you're ready to run for higher office now. I'm gonna dodge your question and talk about the thing I want to talk about instead.

• 6:13Kelly Weinersmith?

  I don't think I'd make a good politician.

• 6:15Daniel Whiteson?

  All right. Well, you know, I would vote for you to represent Virginia, but not California. I don't think you can really appreciate everything that California has to offer.

• 6:23Kelly Weinersmith?

  I lived in California for a while. Is it that you don't like Virginia? And that's why you would vote for me for Virginia? You want to harm Virginia in some way?

• 6:30Daniel Whiteson?

  No, no, no, Virginia's for lovers. It's fantastic. I just don't feel like you appreciate California. I mean, you did leave, right? And so clearly you don't understand that it's objectively the best place in the world to live.

• 6:40Kelly Weinersmith?

  You know, I have not regretted leaving. Sorry to say. So I guess you're right. I shouldn't be representing California and maybe I'm going to regret that a decade from now when I run for governor of California after I've moved back. But for now, I think we're just going to go with no politics for Kelly.

• 6:55Daniel Whiteson?

  That sounds good because I'm going to have to hold off on endorsing you until I hear you change your opinion on California. All right. But let's not talk about Kelly's future plans to take over the world slash solar system slash universe. Let's get to questions from listeners because today on Daniel and Kelly's extraordinary universe, we are answering questions from you. We think your questions are important. We want you to understand the universe. We want you to get that satisfying moment where everything clicks in your mind. And so we encourage you to write to us with your questions to questions at daniel and kelly.org. We will write back to you. You'll hear what we do and don't know about whatever it is you're interested in.

• 7:34Kelly Weinersmith?

  We can't wait to hear from you.

• 7:36Daniel Whiteson?

  Our first question today is from a really fun guy named Barima who lives in Germany. He has a question about gravity. Here is Barima's question.

• 7:46Speaker 04

  Hello, my name is Barima, living in Germany from England. I'm a big fan of the podcast and I love what you guys are about. So gravity becomes so strong that it tears spacetime. And I was thinking dark energy basically does the same, but in reverse because it's expanding the universe. Both of these phenomena bend or expand the fabric of spacetime. So my question is, could dark energy be anti-gravity? Thank you for your time, and I hope you guys have a great day.

• 8:14Kelly Weinersmith?

  Thank you so much for the question, Barima. Well, you know, Daniel, that sounds like a question for you.

• 8:20Daniel Whiteson?

  Gravity, spacetime, and dark energy. Ooh, this is my jam for sure.

• 8:25Kelly Weinersmith?

  We've recently recorded episodes on what is time and what is space, which might provide some important context. But how do we answer this question more directly?

• 8:34Daniel Whiteson?

  This is a great question because it gives us an opportunity to connect a lot of ideas you hear a lot about. Spacetime as a fabric, black holes having extreme gravity, dark energy pulling space apart. How does it all work? How do you think about that altogether? My interpretation of Barima's question is that he's thinking about black holes, and he's heard that black holes tear spacetime. So he's thinking about that as like pulling space itself apart. And he's also heard that the universe is expanding in an accelerating way, which feels like it's ripping space apart. And so he's wondering, like, are those the same thing? Or are they the opposite? Because black holes attract and dark energy is pulling space apart. How does it all work? And is dark energy actually the opposite form of gravity?

• 9:19Daniel Whiteson?

  So we're going to give Barima a way to think about dark energy in terms of gravity and general relativity, and link all these ideas together. But we should probably start with black holes and spacetime and think about what it means to tear spacetime apart.

• 9:33Kelly Weinersmith?

  And does this have anything to do? We had a conversation about a map and how you can like make the cities closer or farther apart. Is that the right way to start thinking about this problem? Or now that we're talking about black holes, we're in a totally different universe?

• 9:45Daniel Whiteson?

  No, that's exactly the right way to start thinking about this. Let's get a mental picture of what space is or spacetime is and what it means to tear spacetime, or what happens when gravity gets really, really strong. So let's start with a model of space. What is space? Space, we don't know what it is fundamentally, but we know that we can measure the distance between two points. You have like a ruler. You can measure how many ticks are between two points. And you can do that between LA and Virginia, or you can do that. Between Canada and Mexico, or between Seattle and Miami, or whatever. You can measure distances between points. So we know that we can measure these distances. We don't understand what is the underlying fabric and what is it doing? And how does it work? But we can measure these distances.

• 10:26Daniel Whiteson?

  And we notice if you put a mass in space, like a star or a planet or whatever, those distances get kind of wonky, like things get closer together, things get further apart. This is what we mean when we say space is curved. It's not like it's curving in some external dimension with the whole crazy rubber sheet analogy. It just means that it's changing the intrinsic distances between stuff. The curvature of space is not external in some other dimension. It's internal, it's intrinsic. It's just a relative change of distances. And so when we say space is curved, we just mean you're tweaking all of those distances.

• 11:01Kelly Weinersmith?

  I think if I were listening to the podcast, this is where I would pause it and just stare at the wall for five minutes and be like, how do I make sense of this? It's all kind of complicated, but yeah, I'm following.

• 11:11Daniel Whiteson?

  Yeah, and you called up this mental picture of a map. So imagine you had a map of the United States and you laid it flat on a table and you measure the distances between these cities. Those distances have to follow some rules because the map is flat. If you measure all those distances, like from LA to Seattle and Seattle to New York and New York to Miami and Miami back to LA, that's a kind of a square, right? You measure all those distances and those distances have to follow some rules because the map is flat on the table. Like from those distances, I can tell you how far it is from LA to New York. It's constrained by those other measurements. But what if I told you, I'm just going to go in and make LA and New York closer together? I'm just squeezing them together. Well, then the map can no longer be flat because I have to like bunch up

• 11:55Daniel Whiteson?

  the material between LA and New York. And that's what curving space does. It changes the relative distances between these points. So they no longer add up in the same way they would if they were on flat space. That's what curved space is, just changes those relative distances. And the crazy thing is that you can do that. You can develop a model of space that incorporates all these weird changes of distances. And that's what we call curved space.

• 12:20Kelly Weinersmith?

  All right, so it's never tearing. There's never a spot where it like breaks and then there's nothing in between. It just kind of gets like curvy like a roller coaster at some point.

• 12:29Daniel Whiteson?

  Exactly. You can't really tear spacetime. That's like a dramatic visual people use, but it's not a helpful way to think about it. And remember, we don't know what space is. We have this beautiful mathematical description from Einstein that lets us think about this concept of curvature in terms of these changing relative distances, but that's just our model. It's useful for describing space, doesn't always tell us what space actually is. But it does predict crazy stuff, like if you have a huge amount of mass, the curvature gets really, really strong and you get things like black holes, places where space is so curved that light can no longer escape. Because not only does it change the relative distances, it changes like the directions. And inside a black hole, space is now one directional.

• 13:11Daniel Whiteson?

  Every direction inside a black hole is just towards the center. It's not that light can't escape because the force of gravity is so strong, it's because every direction is towards the center now. There are no other directions inside a black hole. So a black hole is so massive, it like rearranges the relationships between points in space.

• 13:30Kelly Weinersmith?

  Okay, so the order of the direction there is that the black hole starts pulling on space. It's not that like space gets bent for some other reason and that causes a black hole?

• 13:38Daniel Whiteson?

  Yeah, that's right. The presence of mass causes the bending of space and that's where the black hole is. Yeah, exactly. So that's the way to think about like gravity and black holes and bending of spacetime. But Barima is asking us to connect that to the expansion of the universe and how the universe we've noticed in the last 20 years or so is not just getting bigger, it's getting bigger faster and faster as time goes on. And this is the mystery we call dark energy, because we don't understand the source of that expansion or why it's accelerating.

• 14:10Kelly Weinersmith?

  Okay, so we know that it's accelerating and we're using dark energy as the explanation? And is that the extent of what we know about dark energy? Is that it is the magical way that this all works out?

• 14:20Daniel Whiteson?

  Essentially, dark energy is shorthand for saying, we see the universe is accelerating its expansion, we don't understand why. Please, somebody figure it out. And we don't have a working explanation. We have sort of like a sketch on the back of a napkin idea that might work out, but currently the calculations are not connecting and they're off by like 10 with 100 zeros. But the sketch of the explanation actually comes from general relativity. General relativity, of course, is Einstein's generalization of Newton's gravity. Newton says masses attract each other because there's a force. Einstein says, no, actually, it's more complicated spacetime curves and it gives mostly the same behavior. But there's a little bit more to Einstein's general relativity than just mass bends spacetime.

• 15:05Daniel Whiteson?

  Einstein's relativity also lets other things happen. So for example, Einstein says, yes, if you have mass in spacetime, then space curves and things get closer together. But also, if you fill the universe with potential energy, not mass energy, but some weird kind of potential energy, then it causes the opposite effect. It causes things to move apart. It's like a negative pressure. This is the fascinating thing is that Newton's gravity is just attractive. You can only pull stuff together. Einstein's gravity is a generalization of that and allows in some weird situations for things to get pushed apart by general relativity.

• 15:41Kelly Weinersmith?

  Okay, so we've got gravity and dark energy. Gravity pulls in, dark energy pushes out. How do we determine who wins where?

• 15:48Daniel Whiteson?

  Yes. All right, great question. But first, I want to be technical about what we mean by gravity, because when some people hear gravity, they think the pulling together part. Other people hear gravity, they think general relativity, which can include dark energy. So in some sense, gravity could be the attractive part and the dark energy part. Or some people could just think about gravity as the attractive part. So let's just call gravity the attractive part. And when we're talking about the whole shebang, we'll call it that general relativity. So you're asking about like, when is the attractive part of gravity, things tugging on each other when? And when does dark energy, the universe pulling itself apart, when? And that depends on distance. So the attractive part, the parts like Newton, that gets strong when things are closer together. Like the closer

• 16:32Daniel Whiteson?

  you are to a star, the more its gravity is going to pull on you. The more spacetime is bent in a way that's going to move you closer. And as you get further away, that fades. So like, we don't feel much gravity from Jupiter because it's kind of far away. We don't feel much gravity from other stars because they're even further away, et cetera, et cetera. So gravity gets weaker with distance. Dark energy has the opposite relationship. Dark energy is like, every chunk of space is getting bigger. So if you just have one little chunk of space, it's getting bigger by a tiny amount. But if you have lots of chunks of space, huge distances, then that adds up. And so over big distances, dark energy becomes very, very powerful. So like, between our galaxy

• 17:13Daniel Whiteson?

  and other galaxies, there's a lot of space. If all that space is expanding by a little bit, all those little bits add up to a huge expansion. So dark energy gets more powerful at greater distances. So for example, between our cluster of galaxies and the neighboring cluster of galaxies, dark energy is winning. There's not enough gravity to hold those together, and they're getting pulled apart by dark energy. All that space is expanding faster than gravity can hold stuff together. But in our solar system, though there is dark energy here and is expanding the space between our planet and the sun, gravity is more powerful because it's a fairly small distance. So gravity wins. So shorter distances,

• 17:53Daniel Whiteson?

  like smaller than a galactic supercluster, gravity wins. Big distances, bigger than a galactic supercluster, dark energy wins.

• 18:02Kelly Weinersmith?

  Okay, so that makes sense to me. And so you said that dark energy is a form of kinetic energy.

• 18:10Daniel Whiteson?

  Potential energy, actually.

• 18:11Kelly Weinersmith?

  Wow, they're the same thing.

• 18:12Daniel Whiteson?

  They're so 100% not the same thing.

• 18:15Kelly Weinersmith?

  Okay, it's a form of potential energy. And so, does that make dark energy like, negative potential energy? Are gravity and dark energy just opposites of one another?

• 18:27Daniel Whiteson?

  Yeah, great question. So number one, we don't know where the potential energy comes from. That's the big mystery. Like, to have enough potential energy to explain the accelerating expansion we see, you'd need a lot more energy than we can account for. If you add up all the potential energy we know about in the universe, from the Higgs field and all the other fields and all that stuff, you get a number. That number we calculate doesn't match the acceleration. Accelerating expansion we see in the universe, and it's not even close. The two numbers are off by 10 to the 120. So general relativity has a mechanism to create this negative pressure, requires positive potential energy. We can't explain the source of that potential energy. We don't know. So that's the remaining mystery. Like, there is no potential energy we know about that is capable

• 19:12Daniel Whiteson?

  of doing this, which might mean there's some other field out there we don't understand. But it requires positive potential energy to create this negative pressure, this pulling things apart. So to bring this sort of back to Barima's question, he's asking like, could dark energy be anti-gravity? And the answer is kind of yes. Like, dark energy is a component of general relativity that allows for pulling things apart, sort of opposite to the attractive part of gravity. So if you consider gravity to just be the attractive part of general relativity, then yeah, dark energy is sort of the opposite of that. It's still a component of general relativity, but it has the opposite effect that creates negative pressure.

• 19:51Kelly Weinersmith?

  Okay. Well, thank you for that great question, Barima.

• 19:54Daniel Whiteson?

  And so now I'm curious whether we answered Barima's question, whether we scratched his itch, or whether we totally misunderstood, or whether we just confused him further with our crazy description of LA and Miami. So I reached out to Barima and I sent him our conversation to hear what he had to say. Here's Barima's reaction. Okay, thank you very much, Barima, for joining us here on the podcast and for sending in such a wonderful and fun question. So tell me, what did you think of our answer? Did we answer your question? Did we create more questions in your mind? I'm dying to hear your thoughts.

• 20:27Speaker 04

  Yeah, so thank you for answering the question. It's great to be here. I think you guys pretty much answered the question bang on. It did blow my mind, if I'm being 100% honest, because at first I was like, okay, where is this going? And then at the end, sort of just landed it very nicely. It did raise another question that I have. You mentioned the dark energy sort of being caused by potential energy. And my sort of follow-up question was... Does that have anything to do with the zero-point energy?

• 20:59Daniel Whiteson?

  Yeah, so the two things are definitely connected. Zero-point energy is a description of basically the minimum energy that a quantum field can have. You know, quantum fields are like oscillating in space. They're zigging and zagging, they're whizzing back and forth. There's energy there of their motion, the changing of their values. That's kinetic energy. And they can also have potential energy if they're in some weird configuration. Zero-point energy just says that the total energy, the combination of kinetic and potential and any other kind of energy can never go to zero because quantum fields can never be totally flat. Like a classical field, an electrical field can be just zero. You can have like no electric field because you have no electric charges. It can be totally zero. But if it's a quantum field, it's always buzzing and frothing a tiny little bit. There's a minimum energy there.

• 21:44Daniel Whiteson?

  But the potential energy we think is causing dark energy comes from a field we don't know. We don't know what field is out there doing it. There's only one field we know about that has a lot of potential energy. That's the Higgs field. We know that it fills space with this weird potential energy that gives all particles mass. But when we sit down and try to calculate, is the potential energy from the Higgs field enough to explain dark energy and acceleration? We find that it's not. Like, they're different by 10 with 100 zeros. So, yeah, we're not even close to understanding the source of dark energy. Yeah, we're not even close to being close.

• 22:21Speaker 04

  Yeah, okay. Yeah, well, thank you. Yeah.

• 22:24Daniel Whiteson?

  Yeah, well, thanks very much for sending in your question and for doing this follow-up. Lots of fun to chat with you.

• 22:29Speaker 04

  Yeah, thank you very much. It's been a pleasure and I learned something.

• 22:34Daniel Whiteson?

  And that's our entire goal. All right. Thanks, everyone. And if you have a question about the nature of the universe, or if you'd heard something you haven't quite understood, please send it to us. We'd love to answer your question.

• 22:45Kelly Weinersmith?

  All right. Well, that was our first question. Now we're going to move on to a question in Kelly's wheelhouse, which we'll get to after the break.

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• 25:47Kelly Weinersmith?

  All right, we're back from the break and we're going to tackle our first biology-oriented listener question. So Charlie Davidson had this question for us.

• 25:57Speaker 06

  Hi, Daniel and Kelly. I've got a question for your new podcast about slime mold computation. How is it possible for a bunch of single-celled organisms to perform programmable computational tasks for people? It just seems wild to me, so I'd love to hear more about it and find out how on earth that works. Thanks very much. Bye-bye.

• 26:19Kelly Weinersmith?

  Oh, man, Charlie. In my family, we call this the $10,000 question because that's how much money we lost thinking about this problem. So here is the story. All right, so slime molds are single-celled organisms that are thought to be really great at solving mazes. This has become like a fact that's entered the, you know, general consciousness. You say something about slime molds and they'll be like, oh, they're really great at solving mazes. And they've become famous for like solving straight-up mazes. They've also become famous for being able to recreate transportation systems. So if you put a bunch of different cities on a map and you put a piece of oat on the different cities, the slime mold will start growing on that oat.

• 27:04Kelly Weinersmith?

  I believe it's actually eating the bacteria and the fungus on that oat. And then it will spread out and it will find the other oats. And if it's working the way we want it to work, it will then contract and only have the shortest paths between those things. And so perhaps you've seen videos that like where the slime molds have created this map that is almost exactly the same as like the map of the transportation system matches up almost perfectly with what the slime mold did. It's really impressive.

• 27:32Daniel Whiteson?

  This is really appealing. I understand why people are into this because this suggests like there's another way to do calculations or this is like a biological computer or maybe even some like awareness, right? I feel like we're so hungry to discover we're not alone in the universe that we're looking for like aliens here on earth, even in slime molds.

• 27:49Kelly Weinersmith?

  Yeah, well, I mean, if slime molds can be that smart, what else have we missed? Right? That's incredible. And did you see the dark matter example?

• 27:56Daniel Whiteson?

  Mm hmm. I did. Yeah, they used slime molds to understand the filaments of dark matter between galaxies, which was pretty cool.

• 28:04Kelly Weinersmith?

  I think that they used a computational model based on the behavior of slime molds.

• 28:09Daniel Whiteson?

  Yeah.

• 28:09Kelly Weinersmith?

  Since it's like a 3D thing, so it'd be a little bit harder to do.

• 28:11Daniel Whiteson?

  No, I don't think they had like cosmic slime molds between actual galaxies. That would be awesome. Wow.

• 28:16Kelly Weinersmith?

  That would be maybe scary, but interesting. So my husband and I got really excited about these slime molds. We're like, you know, this seems like such an easy thing that you should be able to recreate at home. And so many science experiments are, you know, that we remembered that we did at school when we were kids, we're like, not super exciting. They didn't necessarily stay with you. So we got really excited about making slime mold mazes that you could sell pretty cheaply to classrooms so that they could recreate these experiments.

• 28:45Daniel Whiteson?

  I'm getting an ironic foreshadowing vibe here that you're setting us up for a big disappointment. Is this going to be another Kelly throws cold water on things?

• 28:52Kelly Weinersmith?

  I mean, that's what I do, right? How else could this have gone?

• 28:55Daniel Whiteson?

  You gotta lean into your skills, Kelly.

• 28:57Kelly Weinersmith?

  You know, yeah, I didn't think this was going to be my niche, but it is. So here we go.

• 29:01Daniel Whiteson?

  All right.

• 29:02Kelly Weinersmith?

  So Zach was excited about this first. I was busy with something else at the time. So we were living in Alabama and he was like in our humid garage, trying to use Legos to build mazes. And then he was pouring agar in there and agar is this thing that like when it's hot, it's sort of like viscous. And fluidy, but when it cools, it cools to like kind of smooshy surface that something can grow on. So he was trying to like make mazes in our garage out of this stuff. And then he went to Carolina Biological website. And he bought slime mold specifically, he bought Fisarum Polycephalus, which is the main like yellow species that people usually see when they're thinking of these mazes.

• 29:37Daniel Whiteson?

  But tell us briefly, what is a slime mold exactly? Is it a mold? Is it slime? Is it totally badly named?

• 29:43Kelly Weinersmith?

  It's not really a slime. It's not really a mold. It's its own thing. It has a complicated life cycle. But when it's at the part of its life cycle where it is solving these mazes, it's a single cell with a bunch of nuclei in it. Which is kind of amazing. I think we should actually have a whole episode on why organisms would ever have multiple nuclei in the same cell. Like what problems does that solve? Cause my brain like more than one nucleus. That just doesn't make sense. So he was trying to do it. That wasn't working. And so then we moved to Virginia and he was like, okay, you know what? I'm going to like outsource to experts. So he hired an engineer and he was like, all right, engineer, I want you to make me a really nice maze because the auger kept like seeping through my Legos. It just wasn't working the way I wanted it to.

• 30:27Kelly Weinersmith?

  Make me a really nice maze with a really nice cover. And the engineer is like, okay, great. I'll do that. Uh, but it's going to cost $10,000 to make an injection molded maze. And Zach was like, oh, that's a little steep, but I really think kids would enjoy this and we're gonna do it. And so he pays and he does it. Yeah, I know. And so, uh, he ran it by me and I was like, I don't know that that's a great decision, but okay, let's try it.

• 30:51Daniel Whiteson?

  This is what happens when you have one family with two nuclei, right? You have different nuclei, making different decisions like, you know, this slime mold is spending 10K over here and that nuclei is objecting to it. You know, it's like a model of a family.

• 31:02Kelly Weinersmith?

  That's totally true. I should have known this problem was coming. So he gets this maze and you know, we'd had a lot of conversations about like, oh, it's so funny that Carolina Biological sells slime mold, but they don't sell these mazes. I wonder why they don't sell these mazes. And so we get the mazes and then Zach's like, okay, so now I'm taking this project to the biologist. So I got a bunch of auger. I got a bunch of slime molds. I'm like using my sterile technique and I'm trying to run these mazes and it's my job to write the protocol and the directions. So the classrooms can do this. And so I start doing it and it's not working. The slime pewter. Is not solving the maze the way it's supposed to.

• 31:38Daniel Whiteson?

  So what is it supposed to do exactly? Like you put it in the beginning and you put an O at the end and it's supposed to find the shortest path through the maze?

• 31:45Kelly Weinersmith?

  Exactly.

• 31:45Daniel Whiteson?

  And how could it possibly do that? Like it's supposed to explore every direction and then eventually figure out which of the paths is found is the shortest and then slowly coalesce onto that? Is that the best case scenario?

• 31:57Kelly Weinersmith?

  So that's what we thought was supposed to be happening. And so I contacted an expert who works in this field and I was like, it's not working for me. Why is it not working for me?

• 32:06Daniel Whiteson?

  Meaning what were you seeing? Like it just didn't find the end or found the wrong path? Or you just didn't go anywhere or?

• 32:11Kelly Weinersmith?

  It was not finding the shortest path.

• 32:13Daniel Whiteson?

  I see.

• 32:13Kelly Weinersmith?

  Something like 20 to 30% of the time, it would end up at the right path, which was essentially like random chance. And I contacted a person who was doing even simpler experiments in their class, but it was like a Petri dish and then an oat in the middle as a starting point and an oat on one side. And so it should have been very simple to just like it expands and then it was supposed to just sort of contract to just be the short, straight line distance. And they were like, oh yeah, that experiment never worked. But apparently it always, well, maybe your students are doing something wrong. So I reached out to this expert and he's like, well, first of all, the way that it solves it is it's following a chemical trail. And so the chemical trail needs to be incredibly easy to detect.

• 32:56Kelly Weinersmith?

  So instead of oatmeal, you could try something that's like creates more chemicals and makes a more clear path. And I was like, well, that's not how I had been taught that this works. And I was like, okay, well, what percent of the time, if I'm doing it right, should I expect it to solve the maze? Cause like, I'm thinking the answer should be close to 100% based on what people are saying on Twitter.

• 33:17Daniel Whiteson?

  Always a reliable resource. Twitter is basically one big documentary, right? You can rely on it.

• 33:21Kelly Weinersmith?

  Yeah, right. We spent 10K based on Twitter advice. It was a great choice.

• 33:24Daniel Whiteson?

  I cite Twitter in my science papers all the time.

• 33:27Kelly Weinersmith?

  Ah, wow.

• 33:29Daniel Whiteson?

  No, I don't, of course.

• 33:30Kelly Weinersmith?

  It's a good thing you've got tenure.

• 33:33Daniel Whiteson?

  Anyway, so you're told that these things don't actually solve the problem. They just follow a trail, which is very different from like considering all the past and figuring out which is shortest and then coalescing on that one. That's like they just walked through to the solution.

• 33:45Kelly Weinersmith?

  Sometimes I'll smell a hot dog and I'll just walk towards the source of the hot dog and it's like, not that different. That's not impressive that I can do that.

• 33:52Daniel Whiteson?

  Can you actually resist hot dogs? Like if you walk past a hot dog?

• 33:58Daniel Whiteson?

  Everybody knows you're kryptonite now. Wow, just like.

• 34:01Kelly Weinersmith?

  I actually can. I worked at the zoo once and we switched from all beef hot dogs to all meat hot dogs.

• 34:07Daniel Whiteson?

  Ooh.

• 34:07Kelly Weinersmith?

  And wondering what that downgrade meant, uh, put me off hot dogs because I started thinking about it too hard. Uh, but anyway, let's not dwell on hot dogs. So I asked, okay, if I find the perfect, very smelly thing that the slime mold can like queue in on, that's gonna work better than my oats, what percent of the time should I expect this to work? And they said 30 or 40%.

• 34:29Daniel Whiteson?

  That's not great.

• 34:30Kelly Weinersmith?

  No, and that's when I realized, I went back through all the papers and I was like, oh my gosh, it says for the slime molds that solved the maze, but they don't include the number of times the maze wasn't solved. And so I think a lot of times what's happening is like these scenarios are set up and the one time out of 100 that the slime mold gets it close, they're like, whoa, that's incredible. And that's what makes the news. And maybe I'm missing something, but it seems to me that like maybe under absolutely perfect conditions, when you replicate things a bunch of times, slime molds come up with the right answer. But as far as I can tell, mostly they're following a chemical gradient, probably chemical gradients aren't that strong in nature, like as strong as you're able to make it in these enclosed mazes.

• 35:12Kelly Weinersmith?

  So I am personally not super impressed with slime mold computational abilities. And maybe that's just me being bitter that we weren't able to make these kits to give to classrooms and we like tanked all this time and money on the project. But that is my take on slime mold computational ability.

• 35:29Daniel Whiteson?

  It sounds to me like somebody's got a room full of monkeys and one of them typed up Shakespeare and they're like, look, monkeys can type Shakespeare. Let's make a meme about it. I mean, is it better than that? Is it actually a little bit better than random or is it completely exaggerated?

• 35:41Kelly Weinersmith?

  I think it is probably. A little better than random. Some of the problems that they're being asked to solve are really complicated. But I do think it's mostly following a chemical gradient, which is less interesting than doing computations about the shortest way to get to a thing or whatever. But I just feel like the whole answer has been kind of oversold. And if somebody thinks that I'm wrong and I have missed something, I would love to hear that because actually we just found out that we have to make a decision about whether or not we're going to throw out that injection mold thing.

• 36:08Daniel Whiteson?

  You still have it?

• 36:09Kelly Weinersmith?

  It's in a warehouse somewhere and they're like, you can either pay $200 to get rid of it or we can ship it to you on a pallet. And I'm like, on a pallet? Where am I going to keep this thing? Let us know if you know the answer, but like slime molds are still awesome. Those paths that they're creating, that is a single cell with multiple nuclei. There's also slime molds called dog vomit slime mold, which you often find in your mulch on moist, warm summer days. And it does kind of look like dog vomit and it's one of my favorite, Phyllocephalosceptica. And so slime molds are fascinating and we had them miscategorized for a while. We kind of couldn't figure out what they were. But I'm not totally convinced that they are amazing problem solvers. Sorry.

• 36:53Daniel Whiteson?

  And are they always single cells? I mean, we're talking about an extended thing, right? It's like this single cell can be like a meter across. That kind of blows my mind.

• 37:01Kelly Weinersmith?

  They have different stages in their life cycle. I think at other stages, they might not be single celled. Not an expert on these, but at the stage that everybody is seeing for the maze solving stage, they are a single cell with a bunch of nuclei.

• 37:17Daniel Whiteson?

  And are there other examples of things out there in nature that can do something similar and that are also oversold? Or is there anything out there that actually can solve this kind of problem in an impressive way? Or is biology all just a dank meme?

• 37:32Kelly Weinersmith?

  I'm reaching real far back here. I watched this really interesting lecture from a woman who studied crows. So this isn't like maze solving, but they're super clever. Like if there was another crow in the room, they would bury their treat. And then when the crow turned around, they would take the treat out and they'd bury it somewhere else. So they knew like that bird was watching me and I want to trick it and that's not watching now. So now it's time for me to move where I hid my cash.

• 37:57Daniel Whiteson?

  Clever.

• 37:57Kelly Weinersmith?

  There are very smart organisms. I think this is just an exciting thing that escaped that has maybe since been oversold.

• 38:05Daniel Whiteson?

  It sounds like the puzzle you really solved was why Carolina Biological doesn't carry maces in their catalog.

• 38:12Kelly Weinersmith?

  Exactly. That is the puzzle we solved. And so now we need to find out, does Charlie Davidson like answers that are kind of a bummer? And did I mistakenly assume that he wanted to talk about slime molds, but he had another single-celled organism in mind? Let's hear from Charlie and find out.

• 38:31Speaker 06

  Thank you for answering the question, guys. That's exactly what I wanted to have answered. The computational abilities of slime molds are no longer impressive to me either. But never mind, can't win them all. I was hoping it would be something far more amazing. But it's the way it is, I guess. Thank you so much, though. I do believe we have dog vomit slime mold in the UK. We call it witches brew. If it's the same thing, not sure which name I prefer, but either way, it goes. Thanks very much. Look forward to future podcasts. Bye.

• 39:02Daniel Whiteson?

  All right, enough about single cell organisms, hot dogs and slime molds. When we come back, we're going to tackle another question about space and time and black holes.

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• 42:05Daniel Whiteson?

  All right, we're back and we are answering questions from the audience, questions from people like you. If there's something about the universe that's never clicked in your mind, or if you've heard us talk about something that didn't quite make sense to you, please write to us. We want to follow up. We want those ideas to connect in your head so that you feel like you understand as well. We will answer any questions you send to us, to [email protected], even dating questions, though we don't claim any expertise.

• 42:33Kelly Weinersmith?

  Oh, I'm an expert. I did a lot of dating, but I don't know if anyone wants my advice.

• 42:39Daniel Whiteson?

  Well, if they know, Zach, then they can evaluate whether they think that went well for you or not.

• 42:44Kelly Weinersmith?

  Yeah, it's up in the air.

• 42:47Daniel Whiteson?

  TBD. All right. In the meantime, here's a question we got from Derek in New Hampshire, who's thinking about black holes and Hawking radiation. I was wondering, can a black hole be so massive that not even Hawking's radiation

• 43:03Kelly Weinersmith?

  can escape from its gravitational pull? Look forward to hearing your answer. Thanks. All right. So this is a great question. We did a little bit of an intro into black holes as part of the very first question. Maybe the right place to start is what is Hawking radiation?

• 43:19Daniel Whiteson?

  Yeah, great. So Derek's basically asking about the glow that we think black holes might make. We talked in the earlier question about what black holes are. They're regions of spacetime that are so bent, so deformed, that space is now only pointing inwards. So you shine a flashlight inside a black hole, it's only going to go towards the center. There's no path out from behind the event horizon. And that's a description of a black hole that comes from general relativity. It's Einstein's theory that says space gets bent, and the space tells matter how to move and all this kind of stuff. But we know that general relativity can't be the final story of the universe, because it's not compatible with the other story we have about the universe, which is quantum mechanics. And in particular,

• 44:02Daniel Whiteson?

  Einstein's theory of black holes predicts that they're totally black, that if you look at a black hole, there's no glow, it's not emitting anything, no light comes off of the black hole. But if you do try to account a little bit for quantum mechanical effects, and this is what Hawking did, it predicts something different. It predicts that black holes are not actually totally black, that they glow very faintly with this radiation he called, of course, Hawking radiation.

• 44:28Kelly Weinersmith?

  He named it after himself? Isn't someone supposed to do that for you?

• 44:32Daniel Whiteson?

  He actually worked it out with a student of his. But yeah, it's called Hawking radiation, and not Hawking-Bekenstein radiation.

• 44:38Kelly Weinersmith?

  The next wasp I discover is going to be Wiener Smith's wasp.

• 44:42Daniel Whiteson?

  Do it, of course.

• 44:45Daniel Whiteson?

  And this is really a very impressive bit of physics. It's like an end run around a bigger problem. The biggest problem in modern physics right now is like, how do we reconcile quantum mechanics, which tells us that like, stuff doesn't have a specific location. It can be here or it can be there. And general relativity, which tells us like, space gets bent based on where stuff is. And general relativity can't handle if stuff doesn't have a specific location. Like if the particles may be here and maybe there, is space maybe bent here and maybe bent there, or partially bent here, or partially bent there? Nobody knows how to bring these two things together, which is what you have to do if you want a theory of general relativity that's consistent with quantum mechanics. Nobody knows how to do that. Big question. Lots of Nobel prizes waiting.

• 45:29Daniel Whiteson?

  But what Hawking did was like an end run around that. He's like, can't figure out the big problem, but maybe I can sort of chip away at it a little bit. So he found a little trick that let him think about what happened to quantum fields near an event horizon. And his trick let him make this prediction that black holes should glow a little bit.

• 45:47Kelly Weinersmith?

  Can you remind me what an event horizon is?

• 45:49Daniel Whiteson?

  Right, thank you. An event horizon is what we think of as like the edge of the black hole. Inside the event horizon, everything is trapped forever. Outside the event horizon, you're still free. So you can approach a black hole, be near the event horizon, and then escape and go back to your planet and live a happy life. If you cross the event horizon, you're in the black hole forever. I think there's also a lot of confusion out there about Hawking radiation and what it means and how to think about it. Because I've said that we don't understand how particles are affected by really strong gravity. And the typical story you hear is that Hawking radiation comes from particles being created near the event horizon, like particle antiparticle pairs popping out of the vacuum, and one falls into the event horizon and the other doesn't.

• 46:34Daniel Whiteson?

  And so to do that calculation, it feels like you'd need to understand how gravity works for particles. Well, the thing is, that's not how Hawking radiation works. That's the like, well-worn, pop-si cartoon version of it, but it doesn't actually make any sense. I mean, virtual particles can't be treated like real particles. They're not real particles. You shouldn't. Think of the vacuum as like filled with actual particles that can fall into black holes. And we don't know how to do those calculations for gravity of particles. Instead, what Hawking did was take a very different approach. He just said, what happens to quantum fields if there's a discontinuity in space? If there's an event horizon? How do I solve the mathematics of a quantum field near an event horizon?

• 47:18Daniel Whiteson?

  And what he found was the only way to make the math work for a quantum field near an event horizon was to have an outgoing wave of radiation. And that's what he interpreted as Hawking radiation. He doesn't have a microscopic particle picture of Hawking radiation. What's happening to individual particles? We don't know how to do that. But we do know that quantum mechanics says if there's an event horizon in space, then your quantum fields have to radiate. And the really cool thing about this is that you don't need a complete solution to quantum gravity to attack it in this way. This is really Hawking's brilliance of finding a sort of an end run around having to have the whole picture and still getting this one result from this mathematical trick. And there's another beautiful angle to this to make it a little bit more satisfying.

• 48:03Daniel Whiteson?

  Even though you can't think about the individual particles and how they're affected by gravity, you can think about Hawking radiation like thermodynamically. The way Hawking thought about it and his student Beckenstein was that black holes eat information. Black holes eat entropy, right? All the disorder in the universe, if it falls into a black hole, is it decreasing? Is it violating the second law of thermodynamics? They showed that on one hand, you can think about it mathematically. Quantum fields radiating energy near an event horizon. But you could also think about it thermodynamically, meaning that black holes, if they have information, if they have entropy, they should have temperature. And if they have temperature, then they glow like everything else in the universe that has temperature. I glow, you glow, the sun glows.

• 48:47Daniel Whiteson?

  Things glow based on their temperatures. Hotter things glow with higher frequency. Colder things glow with lower frequency, more infrared. Hot things glow in like the X-ray in the ultraviolet. So it turns out you can model black holes as if they are black body radiators. Things that glow just based on their temperature. Of course, they're extraordinarily cold, tiny, tiny temperatures. And the weird thing is that as a black hole gets bigger, it gets more massive. It actually gets colder and it glows more dimly. So smaller black holes glow more brightly and evaporate more quickly. And larger black holes glow more dimly because they're colder. So that's another fun way that you can think about Hawking radiation.

• 49:30Daniel Whiteson?

  That helps you sort of get a mental picture of it.

• 49:33Kelly Weinersmith?

  Okay, and then one more follow up question. So when we've talked in the past, we've said that quantum mechanics and general relativity, they don't make the same predictions, but usually that doesn't matter because any question that you have usually just requires you to think in one of those terms.

• 49:50Daniel Whiteson?

  That's right.

• 49:50Kelly Weinersmith?

  Why with black holes is it important to understand both of them?

• 49:54Daniel Whiteson?

  Yeah, great question. Usually you can ignore general relativity when you're doing quantum mechanics because particles have almost no mass and so they hardly bend space. Their gravity is basically irrelevant. Usually you could ignore quantum mechanics when you're doing general relativity because you're dealing with big masses like planets. And for planets, the quantum mechanical effects all average out to zero. So usually you could ignore one or the other. When you're dealing with black holes, you're dealing with very short distances or very, very strong gravity. So now you want to know the answer to like, what happens to a particle near the edge of an event horizon? You have like very, very strong gravity, enough to pull on a particle. And you want to know like, what's going to happen to my electron? Is it going to go this way or is it going to go that way? Or if it splits into two other particles, what happens to it?

• 50:38Daniel Whiteson?

  Now you want to answer questions about the gravity of particles. You need to be able to include the effects of gravity and to be able to describe that particle as a quantum mechanical object. So you need both. Usually you don't care about the gravity on individual electron. But if you want to understand things like Hawking radiation, what happens to a particle near the event horizon, you need the answers to those.

• 50:57Kelly Weinersmith?

  Okay, so let's suggest black holes. If we could understand them, that might be the way that we merge our understanding of those two things.

• 51:04Daniel Whiteson?

  Oh, absolutely. If we could see inside an event horizon, we would know the answer to how to unify quantum mechanics and gravity because we would see, is there a singularity like general relativity predicts? Quantum mechanics says it's impossible? Or is there something else weird and fuzzy? But of course, we can't. So we know the answer is there, but it's frustratingly hiding behind the veil of the black hole. But Derek's question was basically, could you make a black hole so massive that even its Hawking radiation can't escape? Right? So here you have a black hole and it's emitting radiation. Could it suck it back in? Could the Hawking radiation get trapped by the black hole? The answer is, we don't really know, because what you're asking requires us to be able to think about the gravity on particles near a black hole. And we just don't know how to do that, right?

• 51:50Daniel Whiteson?

  Because we don't know how to think about gravity for things where we don't have a way to describe their location, exactly where they are through space and time. General relativity is basically a classical theory. It assumes that everything has a location and a momentum, and that can be well defined, and you can do those calculations. So short answer is, Derek, we don't know. The best answer, though, is probably not. Hawking's calculations suggest that black holes glow outside of the event horizon. Basically, what he did in his calculation is figure out what happens to a quantum field near an event horizon. And his solution suggests there has to be outgoing radiation. And that radiation is past the event horizon. So even if the gravity is very, very strong, it's past the event horizon, which means technically, it can still escape. That's the definition of the event horizon.

• 52:35Daniel Whiteson?

  So if it couldn't escape, it would be within the event horizon. But Hawking radiation is always emitted past the event horizon. So probably, it's free.

• 52:43Kelly Weinersmith?

  All right, so Derek, we want to know if that explanation was satisfying. So we've reached out to Derek, and here's what he said. You did an excellent job at answering the question as best as you could. I often want to have a big fear of missing out, and I can only hope that technology will allow us to have the answers for these types of questions. Thank you. Okay, so that's it for today. Thank you so much to Barima and Charlie and Derek for sending in their questions. We hope to get more questions. Actually, we already have a stack ready for listener questions number two. So if you send your questions, be patient. We are going to get to all of them, and we really appreciate your questions. Can't wait to hear from you. Send us emails at [email protected].

• 53:30Daniel Whiteson?

  Because it's not just our curiosity that drives science forward, it's yours. It's the reason we're doing it. It's collective curiosity of humanity is why we have science. So thanks, everyone, for pushing knowledge forward.

• 53:49Kelly Weinersmith?

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

• 53:54Daniel Whiteson?

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

• 54:00Kelly Weinersmith?

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

• 54:07Daniel Whiteson?

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

• 54:13Kelly 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.

• 54:22Daniel Whiteson?

  Don't be shy, write to us.

• 54:28Daniel Whiteson?

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  Hello? Hey, it's me, your wallet. Oh, hey. I was just wondering if we could maybe take it easy this week? Absolutely. Really? Yep. I'm shopping at Food Lion. Wait, you mean low prices? And MVP savings. Oh, you do care. Obviously. Okay, I feel better. Good. Now, let's go get some snacks.

• 56:48Speaker 06

  At Food Lion, low prices and MVP savings make it easier to shop for what you need without spending more than you have to. When your wallet needs a little TLC, head to your local Food Lion or shop at foodlion.com. Hey, it's Covino and Rich Davis from Covino and Rich. Buy smart, drive for less, and trade for more. That's Toyota affordability. And it starts with a great deal on an off-road Ready Tacoma or half-ton Tundra, two of Toyota's most capable and longest-lasting trucks. Combining power for work, tech for adventures, and style in between. Built on reputation for quality and reliability, Toyota trucks are known for holding their value, which can mean big savings when it's time for your next Toyota. So get a great deal today and great value tomorrow.

• 57:33Speaker 06

  Shop toyota.com for more. Toyota, let's go places. This is an iHeart Podcast. Guaranteed human.