Listener Questions #5

Daniel and Kelly answer questions about chain reactions in space, the chemistry of life, and how a theory is accepted. 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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• 1:05Speaker 04

  Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything. Because every musician remembers the moment where it all began. Experience Before the Moment, a Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 1:43Kelly Weinersmith?

  Are black holes actually black? Is life always built on a carbon stack?

• 1:48Daniel Whiteson?

  Can one star make another explode? What happens if you lick an electrode?

• 1:53Kelly Weinersmith?

  Would biology beat physics in a fair fight? Why is dark chocolate better than white?

• 1:58Daniel Whiteson?

  Hawking predicted that black holes glow. What makes a supernova blow?

• 2:03Kelly Weinersmith?

  Biology, physics, archaeology, forestry, really anything other than chemistry.

• 2:08Daniel Whiteson?

  What diseases do you get from your cat? Well, we'll find the answers to all that.

• 2:13Kelly Weinersmith?

  Whatever questions keep you up at night.

• 2:16Daniel Whiteson?

  Daniel and Kelly's answer will make it right.

• 2:18Kelly Weinersmith?

  Welcome to another Listener Questions episode on Daniel and Kelly's extraordinary universe.

• 2:36Kelly Weinersmith?

  Hello, I'm Kelly Wiener-Smith. I'm a parasitologist and today we're talking about chemistry.

• 2:43Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist because I don't like chemistry. So what am I even doing here today?

• 2:49Kelly Weinersmith?

  Well, so Daniel, my question for you today is why is chemistry the worst science?

• 2:54Daniel Whiteson?

  How much time do you have, Kelly?

• 2:57Kelly Weinersmith?

  I mean, we've got an hour.

• 2:59Daniel Whiteson?

  No, chemistry is amazing because it's the closest thing we have to explaining magic, like the things that you can see happen with your own eyes, you know? Seeing a solid turn into a liquid, turn into a gas is kind of incredible. And the fact that we can take that apart and understand it microscopically is amazing. And it's so much more concrete than particle physics or even astrophysics sometimes. So I have a lot of respect for the relevance of chemistry. But I really struggle with the complexity of it. Like, there's so many different rules to apply in different situations. And we have to remember all the exceptions and this electron and that electron. And it doesn't have the simplicity that I like in particle physics. But, you know, hey, that's purely a subjective preference, right?

• 3:44Daniel Whiteson?

  And I'm really glad that there's different kinds of science for different kinds of folks. So we get all the fun, different kinds of sciences happening here on our planet.

• 3:51Kelly Weinersmith?

  Yeah, no, I agree. And I'm joking. My senior honors research project was in organic chemistry. I minored in chemistry. But man, it was hard taking Ochem over the summer because I'm not good at visualizing things in 3D and seeing those reactions happen in my head is really hard. But I got lucky. So I took it over the summer and it was like four hours of lecture and then two hours of lab. Like every day of the week, it was intense. I had a group of friends. I was one of six. And we called ourselves the benzene ring because there's six carbons in a benzene ring.

• 4:22Daniel Whiteson?

  I got a chemistry joke. Look at that.

• 4:24Kelly Weinersmith?

  And we would pull all-nighters on Thursday nights to study for the Friday exams. And I will always think fondly of those people who got me through like the hardest summer of my life. But anyway, I like it. I just find it way harder than just about anything else I have to think of. But, you know. You know, I take a lot of medications that I'm sure would not be around but for the miracle of chemistry.

• 4:46Daniel Whiteson?

  Exactly. I'm ever so grateful for chemistry. And though I take every opportunity to make fun of chemistry, I also want to make sure people out there understand that I have a lot of respect for it, of course, as a science. And I will say that there are a few listeners who are chemistry professors who write in and say, don't worry, keep joking about chemistry. It makes me laugh. So.

• 5:05Kelly Weinersmith?

  Good. Yes. I joke about it the same way I joke about a sibling where it's like you love them, you're picking fun at them. If somebody else does it, you get a little defensive. But yes, no, I love chemistry. It's just, man, my brain was not made for chemistry, but I'm so glad other people's brains are.

• 5:19Daniel Whiteson?

  And chemistry, like all kinds of science, inspire people to ask questions, to wonder, like, how does this work? How does this fit together? What are the rules for this? And if you have questions about physics, or biology, or even chemistry, please write to us and ask your questions. We would love to dig into it, to understand the benzene rings and everything else about the universe.

• 5:41Kelly Weinersmith?

  And we'll bring another expert on to explain them.

• 5:44Daniel Whiteson?

  And today on the podcast, we'll be doing just that, answering questions from listeners. We have a lot of fun questions, including questions about chain reactions in space, which is sort of like super space chemistry, a question about the chemistry of life, and a question about what it all means, and how we know when to accept a scientific theory.

• 6:03Kelly Weinersmith?

  An amazing set of questions. Let's get started by hearing what Tim wanted to know about.

• 6:09Speaker 06

  I was just listening to your podcast about the brightest thing ever seen in the universe. And it got me thinking, is there such a thing as an event where maybe a chain reaction explosion in space? Maybe it's a binary system supernova? Would the other stargovia as well? Or instead of maybe just disintegrating planets, is it possible for like, the core of a planet to heat up so that it explodes? Just piqued my curiosity and thought I'd ask the question. Thanks.

• 6:43Kelly Weinersmith?

  Whoa. All right. So I can imagine, like, looking out at the stars at night and seeing, like, things starting to explode. And a chain reaction and being like, I should have put my kids to bed before this happened. So they couldn't see it.

• 6:56Daniel Whiteson?

  Yeah, I was wondering what inspired this question. Maybe Tim was worried that like, if something goes wrong in one star and ends cataclysmically, if you could set off a chain reaction that like destroys the whole universe or something, or if we're safe because every star is so far from the other stars that their fates are all independent.

• 7:13Kelly Weinersmith?

  Sounds like Tim and I would have a good time catastrophizing together on a Friday night.

• 7:17Daniel Whiteson?

  But it's a great question because it makes us think about the relationship between one star and another, and also what it takes to like, send a star to explode or to disintegrate a planet. It is a fun question. It sort of thinks about the whole universe as if they were elements of a chemical reaction, right?

• 7:33Kelly Weinersmith?

  That's true. But let's start with what's happening inside of one star and then we'll scale up to multiple stars. You do have chain reactions happening in each star, right?

• 7:42Daniel Whiteson?

  That's right. Yeah. And a chain reaction essentially is a reaction which sets the stage for itself, you know, which makes it more likely for it to happen. And so like a fire is a chain reaction because the combustion produces heat and that heat triggers more combustion. And so there's a loop there, right? Or a chain where one link leads to the next link. And as you say, inside a star is a sort of a chain reaction because we have fusion happening inside a star. You have gravity squeezing this hot ball of hydrogen and maybe a little bit of helium together. And it creates the conditions necessary for fusion, heat and density. And then fusion itself produces more heat and that increases the chances of fusion. The odds of getting fusion grow very steeply with temperature.

• 8:27Daniel Whiteson?

  So the hotter it is, meaning the faster those particles are whizzing around, the more likely you are to have fusion. So heat makes fusion more possible.

• 8:35Kelly Weinersmith?

  Now we have to get to the really exciting part, which is the explosions. Are explosions the result of all of the fusion getting out of control? No. When do we get the explosions?

• 8:45Daniel Whiteson?

  Yeah, essentially. You can think of a star during its normal lifetime, during the millions or billions of years that it's burning stably before it explodes, as in something of a balance, right? You have gravity squeezing in, right? Making things hot and dense. And what It would like to do, if it wasn't constrained, is turn that into a black hole, right? Gravity is always just pushing and pushing and pushing. And if there was nothing else but gravity, everything would collapse into a black hole. But in the star, you have lots of forces resisting gravity. And when the star is burning, the primary force at the frontier resisting gravity is fusion itself, which is pushing out with radiation, right? It produces all this heat, this energy, it's pushing the star out.

• 9:26Daniel Whiteson?

  So fusion is pushing the star out, gravity is pushing the star back in, and there's a balance there. And if you upset that balance, then yes, the star can go kaboom. And there's basically two ways for the star to go supernova. There's the core collapse supernova, and then there's the special fancy type 1A supernova. And the core collapse is the one that we mostly think about. This is like the sort of vanilla supernova. What happens is the fusion is doing its job, it's turning hydrogen into helium, and then if it's hot enough, it's turning helium into carbon. And if it's hot enough, it's turning that carbon into neon and oxygen and all sorts of heavier stuff, all the way up to iron. But fusing those heavier elements requires more temperature. So a star might not be hot enough to fuse a certain element.

• 10:11Daniel Whiteson?

  For example, right now, our star can fuse hydrogen, but it can't fuse helium. So what happens to the helium at the core of our star? It just sits there and kind of gets in the way. It's like ash, it's like the product of a fire. And if you have too much of that, without climbing over that temperature threshold where you can burn it also, it starts to put the fire out. So smaller stars reach their hottest temperature and can't burn something. So for example, our star can't burn helium. If the star was larger, it would get hotter at its core, and it would burn a heavier element, or a heavier element, or an even heavier element, all the way up to iron. When you get up to iron, no star can burn iron and produce energy. Because when you fuse iron together, it actually costs energy, it cools the star.

• 10:55Daniel Whiteson?

  So the short version of the story is at some point you've done so much fusion and you've made something that you can no longer burn that's interfering with your fusion. And so fusion is failing and gravity starts to win and the star starts to collapse because remember the reason it wasn't collapsing was fusion pushing out against gravity. And now you've knocked out those supports, gravity wins, the star implodes. And that implosion then triggers a moment when the star is hot enough to do stuff like burn iron and make super heavy elements. And that triggers the explosion, which is the supernova. So the core collapse supernova comes when the core is not hot enough to burn the ash that's left over, which then triggers the collapse and then an explosion.

• 11:40Kelly Weinersmith?

  That was a great explanation. Okay, so you said our sun is not hot enough to make iron, so we've got a bunch of helium. Does it matter what form the ash takes? They all explode no matter what kind of ash is made? Or do you get a different result if the ash is helium versus if the ash gets to the iron phase?

• 11:57Daniel Whiteson?

  Yeah, so not every star is going to go supernova. Like, for example, our star is not going to go supernova. It's not big enough. It's going to accumulate a lot of helium at its core and then near the very end, it's going to have a brief moment, like maybe minutes in the billions year long life cycle of the star where it can burn that helium in a helium flash and make a little bit of heavier stuff, but it doesn't have enough gravity to actually collapse. Fusion is going to happen in the outer layers because the core is going to be cold helium. And then you're going to have this helium flash and it's going to blow off those outer layers and you're going to be left with a white dwarf, which is just a hot blob of stuff. It's not fusing anymore. It's just like a big rock sitting there in space glowing, just a white dwarf.

• 12:40Daniel Whiteson?

  If it were bigger, then it would have enough gravity to actually collapse and cause a supernova. So our star is not going to become a supernova unless, right, there is a route for white dwarves to become supernovas. White dwarves are just hot stuff sitting there in space, not fusing. Gravity's trying to squeeze them, but it's resisting because of the chemical strength of the stuff, the same reason why like the earth doesn't collapse into a black hole. It's got chemical. ...strength supporting it. But if something comes along and pours extra material onto the white dwarf, then it can increase its gravity and gravity can overcome that strength and cause it to collapse and make a special type 1A supernova. This happens if you have a white dwarf that has like a sister star nearby

• 13:23Daniel Whiteson?

  and it eats some of that sister star and then it gets triggered into a supernova. So that's the second kind of supernova. So our star could eventually have a type 1A supernova, but it's not going to have a core collapse supernova.

• 13:36Kelly Weinersmith?

  So have we already gotten to part of the answer then for why you don't get chain reactions? Because some of the stars in between can't explode. They're just not the right kind. They're little, they don't have sisters, they can eat. Why do we always get to cannibalism? I don't know, we do. And so you can't get the chain reaction because there's a lot of stars, you know, in the line that are just not capable of exploding.

• 13:59Daniel Whiteson?

  Yeah, you need the right kind of star. And so the answer to this question is that it's very unlikely to have lots of chain reactions, but it could be possible if you set up the conditions just perfectly. And I'm a big science fiction reader. And so when I got this question from Tim, I was reminded of this snippet from a Larry Niven novel, Ring World. And there's a scene where they talk about how in the center of the galaxy, the stars are all packed together really, really close. One star goes nova. It releases a lot of heat and gamma rays, and that heats up the neighboring star, which then blow, and it sets off a chain reaction. So it's a super cool idea that you could like have this like set of fireworks going off in the galaxy. But in order to make this work, you really need exactly the right conditions. And what he describes in Ring World

• 14:42Daniel Whiteson?

  probably wouldn't happen the way he described it because adding heat to a star doesn't actually cause it to explode. Remember, we talked about core collapse supernova. The reason they collapse is because they're not hot enough. They can no longer do fusion to burn the ash that's at their core. So adding heat to a star actually supports it, actually makes it more likely to live longer. It prevents its collapse. It doesn't trigger its collapse. Right? These stars explode because they no longer have fusion happening at their core.

• 15:13Kelly Weinersmith?

  Is that true even if the ash is iron? Like, the end of the process, even adding more heat won't help?

• 15:19Daniel Whiteson?

  Yeah, exactly, because the process of fusing iron saps heat from the core. So you have a bunch of iron there, and the star is trying to fuse it. But that fusion process is gobbling the energy instead of creating energy. It's like the opposite of a chain reaction. And if you have an external source of heat that's fueling that, that's providing that energy, then you can sustain the star longer. So a core collapse supernova isn't triggered by external heat, like radiation from another star. But the other kind of supernova, the type 1A supernova, is triggered externally, right? You have a white dwarf, which otherwise wasn't going to go supernova. And you get a deposition of new material from some neighboring star that does trigger it to go over this threshold and then go supernova.

• 16:02Daniel Whiteson?

  And so I asked a friend of mine, David Vartanian. He's a scientist who studies supernovas. He's a Hubble Einstein Fellow at the Carnegie Observatories. And he said, quote, "This may be possible for thermonuclear supernova, which requires some version of runaway nuclear chain reactions on the stellar surface. It's possible to chain this if situations are just right." So the idea is that you have like a series of these white dwarfs, and you add material to one of them, it goes supernova, and then deposits material on the next nearby white dwarf, which causes that to go supernova, dot, dot, dot. You have a chain reaction.

• 16:37Kelly Weinersmith?

  So do my kids have anything to worry about?

• 16:39Daniel Whiteson?

  No, your kids do not have anything to worry about. But if you are designing a universe and you want to see this happen, you might be able to arrange it. So if your kids grow up to be god or masters of their own domain, they could set up a supernova chain reaction if they so desire.

• 16:55Kelly Weinersmith?

  Malevolent gods, not the nice ones. Also, Vartanian, super cool last name, like the polar opposite of Wiener Smith. I guess maybe it reminds me of D'Artagnan, like the Three Musketeers. Okay, on that note, let's get back in touch with Tim and see if he feels like his question was answered.

• 17:12Daniel Whiteson?

  Thanks for the awesome question, Tim. Hope you like the answer.

• 17:15Speaker 06

  Oh, thanks for answering my question, Daniel and Kelly. Yeah, you, you answered it. I'm pretty excited to know that, under the right circumstances, it can happen, so that it's possible. But it doesn't sound like we're going to have a spectacular fireworks show of exploding stars in our night sky anytime soon. So glad your kids are safe, and thanks for answering my question.

• 17:46Speaker 01

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• 18:17Speaker 04

  Hey, it's Niall Rogers, host of Before the Moment, a Lincoln original series. I'm driving across the country, meeting some of today's most fascinating artists. We're exploring the stories before the moment that changed everything. This week, I'm joined by my friend, John Legend. How does music actually enter your mind?

• 18:39Speaker 07

  I'm not sure why or how the music comes to me, but I think people who love music and write music, our brains are just filled with music. Like, we have listened to so much music. We've been a part of so much music. I think of the story that I want to tell, the mood that I want to create with the music, start playing chords, see where they lead me.

• 19:00Speaker 04

  Sometimes I'm just not even thinking about music, right? And I hear this little thing and I go, oh, that could be this.

• 19:11Speaker 07

  You know, you just have to be ready for when the inspiration hits.

• 19:14Speaker 04

  And it comes.

• 19:14Speaker 07

  Yeah.

• 19:15Speaker 04

  Experience Before the Moment, a Lincoln original series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

• 19:32Kelly Weinersmith?

  All right, so next we have a question from Julian from our Discord. Daniel, if somebody wants to play with us on Discord, where do they find the link to our Discord?

• 19:42Daniel Whiteson?

  Go to our website, www.danielandkelly.org, and you'll see an invitation there to the Discord, or you can come and talk and ask questions and make silly jokes.

• 19:52Kelly Weinersmith?

  And be our friends. All right, so let's listen to a question from a New Zealander.

• 19:58Speaker 02

  Hi Dan, you and Kelly. I'm Julian from New Zealand, a long time fan of the pod. What I'm interested in hearing is your opinion on the possibility of non-carbon based life. Given the practically infinite size of the universe, it seems to me that we should consider other life chemistries as probable rather than possible. But I'm interested to hear your thoughts on this and whether there would be any practical way for us to search for biomarkers from other life forms. Thanks and keep up the great work. Bye.

• 20:27Daniel Whiteson?

  I love this kind of question because it takes us like out of the mindset that life on earth is the only way life can be. So I'm dying to hear your thoughts about this, Kelly.

• 20:35Kelly Weinersmith?

  Yeah, well, so I was really excited when I got this question because it had the word life in it. And then as I dug a little farther in, I realized this was a chemistry question. And I remain excited, but here we go. Let's do this. All right. So there's about 94 naturally occurring elements on the periodic table, but the scaffold for life seems to be made of carbon in every case that we've ever looked at. So why carbon and why not something else?

• 21:02Daniel Whiteson?

  So there's 94 naturally occurring elements. So you're talking about basically the building blocks of life out there in the universe. But if we're starting on a rocky planet, I guess we're assuming that there's like a good chunk of silica and carbon and this kind of stuff because that's what you need to make a rocky planet, right?

• 21:18Kelly Weinersmith?

  Yep.

• 21:19Daniel Whiteson?

  All right, cool.

• 21:20Kelly Weinersmith?

  You said that the sun makes everything up to iron. Is that right?

• 21:23Daniel Whiteson?

  Yeah, that's right.

• 21:24Kelly Weinersmith?

  So we would expect everything up to iron to be fairly plentiful in the universe. Is that fair to say?

• 21:29Daniel Whiteson?

  Yeah, although there's a fascinating distribution of which elements are more common and which ones are less common, which involves a lot of chemistry. We'll dig into it one day.

• 21:39Kelly Weinersmith?

  So the three criteria to sort of like enter us in here is one, abundance. So you wouldn't expect nobelium to be the backbone for life because there's not a lot of it out there. But the more common things, you know, they'd be easier for organic organisms to find and incorporate into their bodies. And so what are some of these common atoms?

• 21:57Daniel Whiteson?

  So the universe is mostly hydrogen, you know, because we started with hydrogen and stars have been making heavier stuff for a while, but we're pretty early on in the history of the universe. So mostly hydrogen, like. Seventy four percent of the universe by mass fraction is hydrogen. And then a big chunk of it is helium, so like twenty four percent, which is already like most of the universe. You got seventy four percent plus twenty four percent leaves only two percent of the universe is left. But the next one is kind of a surprise. It's oxygen, right? Oxygen is much more common than anything else. That's not hydrogen or helium. And then you got carbon and neon and then iron. So those are the most common building blocks in the universe.

• 22:38Kelly Weinersmith?

  Okay, all right. So let's go from there. So all right. So abundance is criteria one.

• 22:42Daniel Whiteson?

  Yeah.

• 22:42Kelly Weinersmith?

  So you need stuff that's abundant. So we're not surprised to find out that it's carbon. Although carbon, as you noted, is not as abundant as things like hydrogen, but there's still plenty of it on Earth, for example. And then the next criteria is that it needs to be versatile and able to make a lot of complex molecules. So the proteins that we have, these are very complex. They fold up in different ways. They're made up of lots of different kinds of elements. And the signaling molecules that bacteria make, like every biological organism has lots and lots of super complex molecules that it uses to carry out all of its various functions. So it's thought that ideally you would end up with atoms that are able to bind with the most stuff. And as we move our way across the periodic table, moving across the columns,

• 23:27Kelly Weinersmith?

  when you get to the column that carbon is at the top of, the stuff in that column are able to bond with four other things. And the reason for that is that they've got, now we're getting into electron shells. And I totally went down a like mental rabbit hole being like, oh, but electrons, they're not really like particles. Does it make sense to think of them this way in shells anymore? Because maybe their entire functions and let's not go down that rabbit hole for today. Or maybe we should.

• 23:54Daniel Whiteson?

  No, in terms of bonds, I think it's totally reasonable to count the number of electrons. Because even if electrons are waves or particles or something else alien, they follow the rules of quantum mechanics, which dictate how many you can have in each energy level. And that's what determines the whole structure of the periodic table, right? The reason we put carbon and silicon and germanium and tin and lead in the same column is that they All need four electrons to complete a shell. And if all of the electrons are filled in the shell, then the atom doesn't like to interact very much. It's very happy. And so carbon and silicon both need four electrons to complete their shell. And so I think you're saying that's why they like to interact with four things.

• 24:33Kelly Weinersmith?

  So they can interact with as many as four things, or they can interact with fewer and have like double bonds with one of those things, for example. But their ability to interact with the maximum number of things that you can get interactions with on the periodic table allows them to form these super complicated molecules that are necessary for complex life.

• 24:54Daniel Whiteson?

  So can I ask you a naive chemistry question? Like, I don't understand why carbon is in this situation where it can make the most bonds. Like, I get that it has four valence electrons out of the octet, and so it needs four more. But then you got nitrogen, it's got five, why can't it use its five electrons? Or you got boron, it's only got three, it could take five more electrons. Why can nothing make five bonds?

• 25:17Kelly Weinersmith?

  Well, good start. Okay, nitrogen tends to bond with three other things to fill its eight to get to eight. Whereas boron tends to donate its three to other things as opposed to bonding with five things.

• 25:31Daniel Whiteson?

  I see. So carbon sits right there in the sweet spot out of the octet. It's got four, so it can make four bonds. That's pretty cool.

• 25:38Kelly Weinersmith?

  Yes, and so it's in the position to be the backbone for the most complicated kinds of molecules that you can make.

• 25:44Daniel Whiteson?

  I have another basic question, which is like, why do we call life carbon based? Like, I get carbon is useful, but like, why can't we just have a big mix of different kinds of chemistries? Why does carbon have to be in everything, in every part of life?

• 25:57Kelly Weinersmith?

  So I think part of why we end up with a lot of carbon as the backbone to a lot of this stuff is because carbon not only can bind with a lot of things, but it also forms really strong bonds. So it's stable, the kind of molecules that it makes are stable. So for example, if you moved down the column that has carbon to other things that are also able to bond for things. Silicon can also bond four things, but that bonding is happening in an even farther out shell. And because it's farther away from the nucleus, the bond That it forms are less strong.

• 26:29Daniel Whiteson?

  You're saying that silicon is like carbon in the outermost electron orbitals, but it's a more complex, heavier nucleus. So it's got more electrons. So this outermost electron orbitals are further from the core and they're not as tightly bound. And so things are a little more loosey goosey.

• 26:45Kelly Weinersmith?

  Yeah. So carbon has two shells, an inner shell with two electrons and then this outer shell with four, and then the ability to bond to four other things. And then silicon has three shells. And so it's got, you know, two in the center, eight, the one out from that. And then it's got four in the outer one and the ability to bind with four other things. But because that shell where the binding is happening is farther away from the nucleus, the bonds that it produces are weaker. And so the thought is that when chemical reactions happen, a lot of times what's happening is that one of the things that bonds to, for example, like a carbon backbone, you know, gets sort of like pulled off when a reaction happens. And when something gets pulled off, carbon is strong enough that the backbone stays together and that molecule stays complete.

• 27:29Kelly Weinersmith?

  But when you've got silicone as the backbone, when something breaks off as part of reaction, that process of breaking off could also break the backbone of the silicon. And so the idea is that carbon is not only something that allows you to make super complex molecules, but it's also strong enough to allow reactions to happen. I think if you had anything else that was like creating the backbone for these complicated molecules, the thought is they wouldn't be complex enough or they wouldn't be strong enough to survive reactions.

• 28:00Daniel Whiteson?

  So you need some sort of backbone to hold things together while you have this sort of interaction, this chemistry of life happening.

• 28:07Kelly Weinersmith?

  Yes, yes. And so through this conversation, we've hit on the three criteria. The abundance, versatility and complexity, which is those bonding sites. And then the stability when reactions are happening. So those are the three things that we think are most important. We've talked about why silicon is thought to maybe not be ideal for these reactions. So you'll often hear discussions about like, well, could life be silicon based? And one reason we think that's unlikely is because you might get a lot more breakdown of chemical structures when reactions happen. But another thought, water is really important for a lot of biological processes. In fact, when we look to see where we think life is in the universe, one of the criteria we use is whether or not there's water there.

• 28:48Kelly Weinersmith?

  Water is a helpful solvent, which means it helps move around like nutrients and molecules and stuff like that. But when carbon binds with water, you make carbon dioxide, which is like a gas that like we can breathe out. But when silicon binds with water, you make silicon dioxide, which is sand. And so it's thought that sand is probably not something that's like conducive to the creation of life. And so that is another proposed reason why we don't see silicon based life forms. Although some labs have managed to do like directed evolution studies to get more silicon into molecules. But I feel like that's very different than a molecule as part of a living being that has no carbon at all.

• 29:33Daniel Whiteson?

  So that all does make sense to me as an explanation for like, why the kind of life that we have needs carbon? And why having even silicon wouldn't make the kind of life we have possible. But it doesn't convince me that a totally different kind of life wouldn't be possible. I mean, if we sat here before there was any life and we were just like looking at atoms and speculating like, hey, what could be complicated enough to have weird things like life arise? I don't know that we would have been able to predict like carbon is useful. There's a lot of complexity in the universe that we fail to predict. So isn't it possible that silicon is complex enough to do something else? Which could be the basis of life, even if it's like very different and maybe even pretty sandy?

• 30:16Kelly Weinersmith?

  Yeah, I think maybe, and also, you know, if you move over to nitrogen, where you've got three binding sites instead of four, it's not immediately obvious to me that you couldn't have simple life with a little bit less complexity and that you need four and nitrogen wouldn't be enough. And so I did find myself, while I was reading through these explanations, wondering if we are to some extent a little bit too constrained in our thinking, based on the life that we observe here. But you know, on the other hand, you know, maybe you would have expected to have seen a couple of examples of like nitrogenous life on this planet.

• 30:49Daniel Whiteson?

  Here on earth, you mean, yeah.

• 30:51Kelly Weinersmith?

  Yeah, here on earth, but we don't see that. Yeah, so I don't know, but different temperature or pressure conditions might make nitrogen or silicon based life a little bit more likely to exist. But this is their current, I think, best understanding of why. Why it's carbon based, based on our N of one of life forms that happen to have carbon backbones.

• 31:09Daniel Whiteson?

  Well, why do you think it is that we have one kind of life here on Earth? Like all life shares the same basic biochemistry and we think there's probably a single common ancestor. Why don't we live on a planet where life arose independently multiple times and coexists? Is it for the same reason that we have like one species of humans because we kill all the other ones? We can't tolerate it or do you think it just arose once?

• 31:33Kelly Weinersmith?

  I really don't know.

• 31:34Daniel Whiteson?

  I need answers, Kelly. I need answers.

• 31:37Kelly Weinersmith?

  I don't think anyone knows. Calm down, Daniel. You know that on this podcast, we usually don't have the answers.

• 31:42Daniel Whiteson?

  I know, but it's so frustrating.

• 31:44Kelly Weinersmith?

  It is surprising to me that like in one ocean, we didn't end up with, you know, in one puddle, life arose and then in another puddle on the other side of the planet, life arose. And we still see signs of both of those. I don't know. I don't know. I'd love to know the answer, but I don't.

• 32:01Daniel Whiteson?

  It's so frustrating to only have this one example and to not know how to generalize and what's typical and what's weird. So it'd be fun to find even just one more example of life somewhere else. And maybe on that planet, there's several different kinds of life and several different kinds of chemistries of that life would be amazing.

• 32:19Kelly Weinersmith?

  That would be absolutely amazing and it would blow my mind if we found like, for example, bacteria in the lava tubes or underground on Mars. And if it ended up that that was like an independent evolution of life, I feel like that would be the coolest discovery of my lifetime for sure.

• 32:33Daniel Whiteson?

  Yeah. And I think this is a really healthy way to think like, let's look at the example we have and let's wonder which of these things might be different. It's a good way to like, try to think outside the box, even though it's really hard for us to imagine what else could be out there. And I'm sure that we're failing to describe the complexity of non-Earth life, but at least we're making the effort, right? We're like trying to understand what could be outside the box of our thinking. You mentioned briefly how water is super important for life on Earth. But then I think you said something about how it's maybe not necessary, how you could have life without water. What could replace water?

• 33:08Kelly Weinersmith?

  So there's lakes of liquid ethane and methane on Titan, which is a moon of Saturn and it's. Possible that these could be used as solvents to sort of move stuff around a living organism instead of water if you don't have water present. And maybe this could create different kinds of life forms or create the sort of conditions necessary for something else to become the backbone of life instead of carbon. But I think we're a little bit far away from sending probes out there to deliver samples back, but fun NASA.

• 33:39Daniel Whiteson?

  That's right. We're doing as much as we can to try to think our way outside the box. But really, what we got to do is actually climb outside the box, go to these crazy places in our own backyard where there could be other examples of life right there waiting for us to discover them. And the crazy thing is that all it does is cost money, right? And we spend like more money on an aircraft carrier than it would cost to discover life on Titan. So let's go do it, people. Let's go buy some knowledge.

• 34:06Kelly Weinersmith?

  Sounds like a good investment to me.

• 34:08Daniel Whiteson?

  Cha-ching.

• 34:09Kelly Weinersmith?

  Cha-ching. All right, Julian, I did my best with the chemistry question.

• 34:15Kelly Weinersmith?

  But if you don't feel like you got a sufficient answer, let us know. And maybe we'll have to pull in a chemist to help us answer this question. But I'm looking forward to hearing what you had to say.

• 34:25Speaker 02

  Hi, Daniel and Kelly. First off, I was a little bit worried that I might get kicked off the Discord channel for asking such a chemistry heavy question. But it was really inspiring to hear you guys working at it and tackling a subject where you're not necessarily the most comfortable. And so thanks very much. And that does definitely answer my question. Thanks again. Cheers. Bye.

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• 36:39Kelly Weinersmith?

  All right, now for something a little more philosophical.

• 36:42Speaker 02

  I was listening to your episode about thinking like a physicist. It got me thinking about different theories that have been proposed over the last few decades, which led me to Hawking radiation. There isn't any observational or experimental data confirm Hawking radiation, yet the physics community seems to have accepted it. My question is, why do some theories get accepted and others don't? Please help me figure out where my thought process might be wrong. Thank you for all you do.

• 37:06Daniel Whiteson?

  All right, great question, Eric. I love this because it dives into the process of science itself. Not as much the science questions we're asking, but how as a community we like decide that something is part of the canon or something is not. It's a great question.

• 37:23Kelly Weinersmith?

  It's a great question. Let's start though with what is Hawking radiation? So we can then, you know, compare other theories to it.

• 37:30Daniel Whiteson?

  Hawking radiation is an amazing little bit of science. We talked in the podcast a lot about the biggest question in modern physics is how to reconcile gravity with quantum mechanics. Nobody knows how to do it. This program of quantum gravity, we talked about string theory, we've talked about post quantum gravity, this loop quantum gravity, all sorts of efforts, nobody knows how to do it. Nobody's had any success except Stephen Hawking figured out like one little corner of it. He'd used a really clever mathematical trick to understand what happens to quantum fields when they're near a black hole. So he doesn't have like the big answer to how to unify these things, or what is the gravity of particles, or to do all the calculations.

• 38:15Daniel Whiteson?

  He just was able to figure out what happens to quantum fields when they're near a black hole, using a really clever little mathematical trick.

• 38:23Kelly Weinersmith?

  And how did he do that?

• 38:25Daniel Whiteson?

  It's totally worth digging into it for a minute because the story of Hawking radiation, as it's often told in popular science accounts, is pretty much totally wrong and doesn't describe what was actually done and what Hawking actually figured out. The popular story is a story of what happens to particles. You have fields near an event horizon, and they fluctuate and create like a particle antiparticle pair. One particle falls into the black hole and the other one doesn't, and so escapes, and that's your Hawking radiation. And the problem with that account is that that's not at all what we think happens. We don't know how to describe that. That would require understanding like how gravity affects particles and, you know, are those particles real anyway? Really what Hawking did was he thought about the

• 39:08Daniel Whiteson?

  mathematical solutions to the quantum wave equations. Like quantum fields have waves in them. Those waves are particles or other kinds of ripples, and they slosh around and they follow rules. Those are wave equations, just like the mathematics that describes waves in the ocean, or waves in traffic. Waves are everywhere. And the equations that describe quantum fields are also wave equations. And when you solve wave equations, you have to make sure that they lie Line up on top of each other and they match what you see at boundaries and stuff like this. This is how we figure out like reflection and refraction of light, all sorts of wave equation stuff. And he figured out what happens to those waves if you have a weird barrier, an event horizon.

• 39:48Daniel Whiteson?

  You add that to your quantum fields and he showed that what happens is you have to have a wave coming out of that event horizon. So the short version is that the mathematics of quantum fields require some outgoing radiation from an event horizon. If the quantum fields are ever going to work, so you don't have to know what the gravity is for particles or what's happening inside that event horizon. Or even why you have an event horizon. But very generally, anytime there's an event horizon near a quantum field, there's going to be outgoing radiation. So that's really what Hawking radiation is. That's the prediction. And again, we don't have a complete description of quantum gravity or understand how gravity affects little particles.

• 40:28Daniel Whiteson?

  But he predicts that there's this radiation that comes out of event horizons, just to make the wave equation work for quantum fields.

• 40:35Kelly Weinersmith?

  Okay, so this is a prediction, but it hasn't been tested. So for something that you can't test, you can still feel pretty good about it if it predicts a lot of other things. So like, how good in general is the evidence, even if we can't directly test it?

• 40:48Daniel Whiteson?

  There's absolutely no evidence for Hawking radiation.

• 40:50Kelly Weinersmith?

  Okay.

• 40:51Daniel Whiteson?

  But it's very cool because it connects to other kinds of physics. It also lets you think about black holes thermodynamically. It lets you think about black holes as things that have temperature. In our universe, everything that's made out of some kind of matter has a temperature and glows. Like the sun obviously glows, it's really hot, but the earth also glows. It just glows in a wavelength of light that we can't see, glows in the infrared. And you glow, which is why like if somebody puts on night vision goggles, they can see you because they're seeing you in the infrared, the light that you glow in. And your temperature determines what you glow in. So as you get hotter, you glow in higher frequency light. Which is why, for example, metal, when you heat it up, gets red hot and then white hot, for example.

• 41:35Daniel Whiteson?

  That's all just black body radiation. Everything that has a temperature glows. So now if black holes glow, you can Describe them as having a temperature, which is pretty cool. Ha ha, thermodynamics joke. And it lets you use a whole other branch of mathematics and physics that we've developed for hundreds of years and apply it to black holes and think about their entropy and stuff like this. So people have been having a lot of fun using black holes as a concept and playing around with the mathematics of it. There's absolutely no evidence for Hawking radiation, because if Hawking radiation does exist in the universe, black holes are too far away and Hawking radiation is too dim for us to see it. So it's possible that black holes are all out there emitting this Hawking radiation,

• 42:20Daniel Whiteson?

  but we've never seen it and it's very hard to imagine how we could in the near future, unless we made artificial black holes here on Earth to study their radiation.

• 42:30Kelly Weinersmith?

  All right, so Stephen Hawking is like the rock star of physics, a rock star. Y'all have like three. And so to what extent do you think this theory has been like quote unquote accepted? Because he's a rock star.

• 42:44Daniel Whiteson?

  Well, I think this theory helped make him a rock star, right? So there's some cause and effect there. But Eric's question is a good one, like, why do people pick up on this theory and run with it and build on top of it and other stuff is sort of dismissed? You know, we have like Stephen Wolfram, the kind of theory of everything that not very many people are working on, hasn't become accepted. Lots of fringe theories out there that nobody's taking up. You know, you have to remember that like, science is not some official institution where things like get graded and accepted or rejected. It's just a bunch of people and people work on the things they're excited about. And the reason Hawking radiation has become kind of mainstream is that because it opened

• 43:25Daniel Whiteson?

  the door to working on other things, thinking about black holes as thermodynamic objects and calculating their temperature and thinking about information. It's sort of left things for people to do and to work on and to build on top of them. But you know, that's just personal judgment. People decided, hey, this is fun and interesting. I'm going to go work on this. And so people just sort of vote with their feet. Whereas other ideas that might be more valid or better descriptions of nature are not getting as much attention. Because maybe there's not an obvious problem to work on, or there's nothing to do there, or it just doesn't seem as fun. People have a sort of a simplistic view of how science works and what is science, and think that like, science has to be experimentally proven before it's accepted.

• 44:09Daniel Whiteson?

  But there's no official stamp of accepted science. It's just, what are people doing? What are people working on? What are people thinking about? And so it's possible that we could discover that Hawking was totally wrong. Or it could be that Hawking's ideas lead us to understand quantum gravity in some way. Or it could be that it's a dead end, that he was able to figure this one thing out, but it doesn't give us an opportunity to discover anything else.

• 44:31Kelly Weinersmith?

  Yeah, so ruminating a little bit more on the human side of science. I imagine that when you pick a theory that you want to spend your career on, you probably want to pick a theory that you think is one of the ones that has the highest chance of being right. I know that people are okay with working on theories and finding out that they're wrong, because that is an answer, and answers are important. But I think that probably you pick the ones you want to be correct. But I wonder if when you're picking these ideas, how much does it also have to do with what is testable and what's not? Like, even if you think an idea is correct, but you can't really test it directly, and maybe that makes it hard to like, get grants to fund your lab or something like, how do you think these various human factors sort of all add up?

• 45:12Daniel Whiteson?

  Yeah, I think in theoretical physics, whether it's immediately testable is not always one of the top considerations. I think one of the top considerations is, can I make progress in a reasonable amount of time? Like, personally, as a scientist, when I choose projects, I could choose to work on really big questions like, hey, what came before the Big Bang? But I have no way to make progress on that in a reasonable amount of time. And as a scientist, I have to produce science regularly. So I have to choose projects where I can make some progress. And I think this is a really important thing for young scientists to learn, is to spot opportunities. Like, hey, here's something where if we spend a couple of years on this, we could actually learn something, given the resources and the skills that we have.

• 45:56Daniel Whiteson?

  Right? So it's sort of like spotting a business opportunity. Oh, there's a market for this, and we know how to do it, so. Let's jump on that. And so in my research, for example, you know, we use machine learning. We're always like looking for ways machine learning can solve problems that weren't solved before. But again, in a reasonable amount of time. So on the theoretical physics side, people are looking for problems where they can make some progress, where there's an opening, but they're not always concerned about like, is this immediately going to be testable? Because science isn't just about experiments. You know, science is a big, complex dance that eventually leads to answers. We hear a lot of criticism of string theory, for example, saying, oh, it's not science because you can't test it. But you know, it's a precursor to testing. Sometimes it takes something 50 years,

• 46:40Daniel Whiteson?

  100 years before it bubbles up and produces something that you can test. Doesn't mean that it wasn't science until then, that you retroactively go back and say, okay, now we can test it. So the last 100 years count as science. Whereas if it never leads to something you can test, you say it never was science. I think that's a little bit overly simplistic.

• 46:57Kelly Weinersmith?

  All right. Well, so continuing to think out loud here. So you said that you don't work on questions related to the big bang because you can't produce science regularly by doing that. So how do we get questions to these really important problems that take a long time? Is our system just not set up to answer those questions? Or is it something, so you know, for example, Darwin, he came up with the idea of natural selection, but it was like an idea that was the accumulated result of observations that happened over like maybe decades. But he was publishing a lot of like mollusk papers along the way, or like, you know, observations on other things. So are people working on the really big questions, but just sort of slowly in the background while producing something to keep their jobs? Or like, is it harder and harder to get answers to those big questions that take a

• 47:42Kelly Weinersmith?

  long time today because of the way our funding system is set up?

• 47:44Daniel Whiteson?

  Yeah, there are people working on big questions. A great example are things we call quantum foundations, like which of the quantum mechanical interpretations of reality are real? The Copenhagen interpretation, the many worlds interpretation? How do we grapple with all that? Everybody thinks that's a big problem. A lot of people have no idea how to make progress on it. And so it's sort of a bit of a dangerous thing to dig into for like a young scientist because you could jump into it, work for a couple of years, make no progress. And then what do you have to show for yourself? So it's the kind of thing that people who are well established with like tenured positions, i.e. like Sean Carroll, can dig into and try to make some progress on. And everybody understands it's really important. But yeah, it's hard to know if you're going to make any progress. And so a lot of people don't work on that. There

• 48:28Daniel Whiteson?

  are also some places that specifically fund this kind of work because they realize, hey, it's really important for people to be thinking about these big questions, or we're never going to make any progress on them. And so there are some places that specifically write grants just to support that kind of research. But they're pretty few and far in between. The bigger picture tendency in science, I think, is towards short term promises. A lot of grants that you write require you to know what you're going to learn in advance and to have a lot of preliminary data, because this is arms race in science. You know, this lab has already set up to do that. That lab has already set up to do that. And so a lot of science is more about this sort of short term results, which I think is a shame because

• 49:10Daniel Whiteson?

  we should be doing science as exploratory research. Say, hey, let's see what happens if we give a bunch of smart people money and time and see what they figure out.

• 49:19Kelly Weinersmith?

  Agreed. That's a big complaint of mine for the system. All right. Well, have we said everything that we want to say about Eric's question?

• 49:28Daniel Whiteson?

  I think so. If I had to sum it up, I would say to Eric that there is no such thing as accepted science or not accepted science. There's just the kind of things people are working on right now that people are excited about. And it's a personal decision, not some like institutional label we put on ideas.

• 49:44Kelly Weinersmith?

  And let's see what Eric has to say about that answer.

• 49:47Speaker 06

  Hi, Danielle Kelly. This does help me understand better how science works. I tend to make the mistake of thinking science is monolithic with nothing but cold hard facts. And I forget that behind the science are human beings. My idea of the scientific method comes from high school, which took a more simplistic approach. I think it is more accurate to say science is more the art of human curiosity than than just cold hard facts. It is after all, human beings and all their complexities that ultimately strive to unravel the mysteries of the universe through a blend of creativity and skepticism. And ultimately, if it is a good idea that can stand scrutiny, it will become accepted. Hocking radiation is a prime example of this.

• 50:34Kelly Weinersmith?

  Thank you, Daniel and Kelly, for taking the time to help me understand the process of science a bit more, and I certainly appreciate everything you do. Take care.

• 50:50Kelly Weinersmith?

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

• 50:55Daniel Whiteson?

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

• 51:01Kelly Weinersmith?

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

• 51:08Daniel Whiteson?

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

• 51:14Kelly 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.

• 51:24Daniel Whiteson?

  Don't be shy. Write to us.

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