Listener Questions #30

25:01And that's where Descartes was. And it's very hard to go anywhere from there. So you just got to make some assumptions and move forward as best you can, because it's not clear what we know and what we don't know and what knowing even means. All right, so I hope we've confused you enough, Jared. Let us know if that helped you at all. And thank you again for your question. Wow, thank you so much, Daniel and Kelly, for the amazing and detailed answer. You've certainly given us all a lot to think about. We promise our next question won't be as difficult next time. We'll keep it simpler. Certainly next time when we're talking about our cat, Oreo, and we're talking about her learned behavior over time and how she's picked up on certain human words, We'll now have more context to kind of discuss that.

25:45And yeah, we don't have any follow-up questions. Just keep up the great work. We love the podcasts. Thank you, Daniel and Kelly.

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28:42Okay, we're back and we're answering questions from listeners. And today we're tackling deep philosophical questions like, do rocks feel pain? And also ancient questions like, what came first, the chicken or the egg? And this is a question that people, you know, sometimes enjoy having long, deep philosophical questions about. but I love ruining fun and evolution has a clear answer. Oh my gosh. Wow. And so let's hear Noah's question and then I'm going to give you a clear answer. Nice. Hi, Daniel and Kelly. I would love to hear about the evolutionary history of chickens and eggs. Is there an answer to which came first?

29:21You're just going to give a clear answer to make me look bad because of my philosophical ramblings. You should have just said no. You could have saved us all 20 minutes, Daniel. No, that was fun. All right. So great question, Noah. Kelly, tell us, what does science say about the chicken versus egg debate? Well, eggs have been around for a really long time. OK, so like we think of women as having eggs and men as having sperm. And so if you think of it that way, then eggs have been around for, you know, since we've had fish and since we've had amphibians and millions and millions and millions of years.

29:57But I understand that that's not actually what we're talking about. We're talking about, you know, chicken eggs as in like having that hard shell. But let's take a few steps back. OK, so initially we had, you know, fish swimming around in the oceans and we had amphibians and they were laying eggs in water. When you lay eggs in water, you've got this sort of perk that you're in this aquatic environment. So when you lay your eggs, you don't have to worry about them drying out and dying. But is that where eggs begin with amphibians in the water or are there precursors to that? Well, invertebrates like starfish also make eggs.

30:29But if we're talking about vertebrates making eggs, then shark and fish were making eggs before the amphibians were. But so when four limbed vertebrates like reptiles started leaving the ocean to move on land, we started having this problem, which is that, well, now that we're out of the water, our eggs are going to start drying out. And so what do we do? Our eggs needed to become more complicated. And thus arose the amniotes. And that's just kind of a fancy word for saying we ended up getting fancier eggs. And so amniotes includes birds, reptiles and mammals. And so amniotes, these are fancy eggs that have three extra layers.

31:09and what these three extra layers do is they uh first they provide an extra little fluid filled sack and this is like the amnion and essentially encloses the embryo and it's like a protective fluid and so if your egg were to go rolling down a hill which you probably should try to make sure your egg doesn't do but if it does uh it like will protect it against bumps and bruises and uh sort of give it a bit of a cushion and it just sort of suspends the embryo and it's almost like you've brought your aquatic environment with you by putting it in this like sack. It's like we're still stuck on ocean-based life and all of land-based life is like carrying around little bags of ocean.

31:50Yes. Yes. We are carrying our past with us in that sense, which is kind of cool. Which is fascinating because like all of the life that we build, like robots, it's all dry, right? Why don't we build robots that are based on gooey bags? Well, you're the computer scientist. My sense is that when you start adding water to computers, things don't go real well. That's true. All right. So we have the amnion. What are the other extra layers that the amniotes added? All right. So you also have the corion and the alantois. I'm sure that I am mispronouncing those, as everyone has come to expect. And anyway, those two layers are helpful for a gas exchange.

32:29So you still need to be able to get oxygen into the egg to give that oxygen to the embryo inside. And you need to be able to manage waste. And so these two layers essentially allow for gas exchange and they contain the waste that's produced by the embryo inside. Waste-related question. Are the amniotes the first ones to accidentally poo on their eggs or did fish do that also? Oh, let's see. Okay, so that's a really great question, Daniel. How did you not research that? How did I not research that? I have had the experience of mixing gametes from fish, which essentially means you very gently run your fingers along their abdomen to get them to release eggs or sperm.

33:19And they have occasionally released waste as well. What's the verb you use to describe that? Some people call it milking. I wasn't going to go there, but. The way you might like, you know, milk a bull. Mm-hmm. Yep, yep. That way. That way. The glorious labor of science. Yes. So the world of an ecologist. And so anyway, so yeah, so these extra layers made our eggs more complicated and allowed us to come on land. But I think the chicken and the egg question isn't about, you know, this slightly more complicated egg. So, you know, for example, in humans, we essentially brought a lot of this system inside of our bodies.

34:05So we have an amniotic sack. So we've got this fluid filled sack. We put the ocean inside of our bodies and we allowed gas exchange with like our placenta and stuff like that. But birds and reptiles, they made this system where you can essentially have the whole thing outside of the body and you can like lay it in a nest. Seems like a better plan, doesn't it? Yeah. Yeah. I mean, there's some benefits to being able to carry the baby around with you all the time. You always know where it is. That's true. There's some definite benefits, but it is also a bit difficult. I will admit. Okay, but so then the question is, when did like bird eggs, as we come to think of them, come about?

34:47And the answer is that birds evolved during the Jurassic period, which was 150 million years ago. So what we think of as bird eggs arose 150 million years ago. Amniotic eggs in general are 300 million years old, so older than birds. But now the question is, when do we get chickens? All right. Wait. So already eggs came before birds broadly. Yes. Yeah. Eggs. So like reptiles have eggy things. Also, they're a little bit different than what you think of as a chicken egg. But like amniotic eggs, 300 million years old. Birds in general, 150 million years old. But chickens weren't like the first birds.

35:27Chickens come later. And chickens appear to be about 66 million years old. there's a fossil that appears to be the ancestor of chickens and ducks and they have named this fossil wonder chicken no yes no really wonder chicken oh my gosh wonderful name yeah i i wasn't able to find a lot more information uh i mean i suppose it could have been they found it in like germany and it was like wonder chicken or like i don't i don't know the details was it like six feet tall and 800 pounds or something i hope so when it walked the earth shook

36:08here cometh the wonder chicken that's right your dinner this time netflix please call us that's right i'm available to consult I'll write jokes too but not poems don't worry okay so but so so what we really want to know is like all right so we've had chickens in the wild and there are wild chickens uh so for example there are red jungle fowl that you can find in southeast asia like so in china and india and stuff like that and there's green jungle fowl and gray jungle fowl and the red jungle fowl in particular, if you look up pictures of them on like Wikipedia, they look like the kind of chicken you'd find in your backyard.

36:50Actually, kind of surprisingly, they have like the beautiful colors and the, you know, the males look like any rooster that you would expect to see in your backyard. They poo on their eggs. Probably. I mean, humans poo on their babies sometimes too. It's like, it's a messy process, man. And so anyway, all right. So then the question is, when did we start getting domestic chickens. And that is apparently something that scientists fight about a lot. I found a lot of papers where they were like, you know, arguing about methods and this person was mad at that person. And so it does look like domestic chickens came from red jungle fowl.

37:29There may have been some hybridization with some other wild chicken species, but mostly it came from red jungle fowl. somewhere in Asia, maybe 10 ,000 years ago. There's some archaeological evidence, and that archaeological evidence tends to be like they found chicken eggs. And it's not necessarily clear if the chickens were there because of the eggs or because we were eating the chickens or because there were cockfights. And there could have been a lot of different reasons we had chickens around. But you do see things like chickens, like beautiful roosters, on coins in different cultures. And so chickens do look like they were an important part of our cultures for a really long time.

38:11There was one study that estimated that based on like DNA stuff, maybe chickens have been with us for 50 ,000 years. We've been like carrying them around with us. But anyway, definitely we are sure that the ancient Greeks around 600 BC, so something like 2 ,600 years ago, you can see chicken imagery in like the Greek pottery, And so we're sure that we had chickens, at least at that point, maybe even much earlier. Do you think there's any relationship between domesticating chickens and agriculture? And I can understand like domesticating dogs when you're still a hunter-gatherer community. You hunt, you kill, you share with the dogs.

38:50What about chickens? I mean, I always think about feeding chickens grains. But actually, now that I think about it, chickens eat anything, don't they? So you could have chickens eat your kill also. Yeah, so I can see it being much, much easier to have chickens if you're staying in one place, which would be easier if you were in agricultural society. But on the other hand, yeah, I mean, we feed our chickens everything. Including chicken, right? Yeah. Cannibalism for the win. Oh, yes. Pull out your DKU bingo card. All right. Yeah, okay. So the answer is eggs came first, then came chickens. But you can still have fun philosophical debates, just not when Kelly's around.

39:31But I think that's only because you've interpreted the question as what came first, the chicken or any kind of egg. But I think the question is what came first, the chicken or the chicken egg? Oh. But no, because eggs came first. You had to have – The answer's the same. All right. The answer's the same. The red jungle fowl came first. And at some point, there was – anyway, domestication happened and blah, blah, blah. So let's see if Noah has more whimsy in his heart than I do, and maybe he will disagree with my answer. I'm endlessly amazed at how much of the story of many millions of years that humans have accumulated.

40:12Previously, I kind of assumed that this answer would be neither or both, just played out in time. But I agree with Kelly. Eggs seem like the clear winner here. At least there's no shortage of as-yet-unsolved paradoxes to think about. Many thanks to both of you. I love the show.

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43:18All right, we are moving from eggs to gravitational waves. And next up, we have a question from Gerard, which sounds like a really good setup to a new sci-fi book. I've heard that if we could read gravitational waves from the Big Bang, someday we would also be able to see further into the past than with light. My question is, how would we be able to tell which gravity waves originated in that very early time and which formed later? Is there some analog with lights redshifting? I've also heard the same possibility with neutrinos. Again, would there be a way of distinguishing early neutrinos from later?

43:50All right. Thank you very much, Gerard, for this wonderful question. I love digging into the early universe, the cosmic egg, if you will. Oh, you are so good at making connections. I think someone should write a book about aliens that can read gravitational waves. Maybe somebody has. Yes. Ooh, yes. Well, we can read gravitational waves, and we hope by doing so we can learn something about the history of the universe. So far, most of what we've learned about the very, very early universe comes from photons. And this is the light, the cosmic microwave background light, that comes from a moment when the universe was very hot and very dense and went from being opaque, like the center of the sun, to cooling enough that protons captured electrons and became neutral hydrogen, which is transparent, like hydrogen gas.

44:38So photons that were made just before that moment, instead of getting absorbed, flew free through the universe and are still around. Any light made before that time was immediately absorbed, just like light made inside the sun is absorbed. So the earliest we're used to seeing the universe, like concrete data from what happened a long time ago, is 13.8 billion years ago plus 380 ,000 years. That's how long it took for the universe to cool enough to become transparent. And as far as we can imagine, there is no way for light to tell us anything about what happened before that point. That's right, because none of those photons are still around.

45:18If they were, we could see them and we could learn stuff. There were photons made, lots and lots and lots of them, but they're not around anymore. They were gobbled up by the atoms and the electrons. It's like when your great-great-grandparents are gone and they can't tell you their stories anymore. Exactly. But we would like to dig further, right? And before we dig further, just a note on the timeline. We'll define a moment, call it t equals zero, the first moment. We don't mean that that's the first moment of the universe. It's the first moment where our laws of physics apply at all, where we can think about this stuff, where we can hypothesize what might have happened because quantum mechanics and general relativity separate enough that we can just use one of them.

45:58Before that moment, things were so hot and so dense and so nasty, we can't even think about them. We can't do calculations. We don't have a theory to explain it because we don't have quantum gravity. So we don't know what happened before T equals zero. T equals zero and then forwards we can think about theoretically. And the gap there is that we can think from T equals zero to 380 ,000 years afterwards, but we can't see yet before 380 ,000 years. Does that make sense? Yes. and is gravitational waves going to help us get back earlier? Yes, exactly. And so Gerard is asking about how we can see past that boundary, not with light, but with other probes.

46:38And so he talks about two of them, gravitational waves and neutrinos. And the reason you could see earlier with gravitational waves and neutrinos is that the universe was transparent to those earlier and then it was transparent to light. Like many things in the universe are transparent to neutrinos that are not transparent to light. like the Earth. Photons will not fly through the Earth. The Earth is opaque to photons, but it's transparent to neutrinos. Neutrinos will fly right through it. So the fact that the universe was opaque to photons for the first 380 ,000 years doesn't mean it was opaque to neutrinos.

47:12In fact, it was transparent to neutrinos. The same story applies to gravitational waves. Gravitational waves pass through basically everything, and they scatter a little bit or they're affected by matter, but everything but black holes are transparent to gravitational waves. So they're an amazing way to look even earlier than light can show us what happened in the early universe. And Gerard's excellent question is, cool, but aren't there neutrinos and gravitational waves everywhere? How could we tell the difference between a neutrino that came from the very early universe and one that was made eight minutes ago in the sun or gravitational waves that are made from black holes, how do we know the difference between those and gravitational waves from the very early universe?

47:56You check their ID.

48:00That was a joke, but it's actually basically the answer. Great. So let's start with neutrinos because they're a little easier. Neutrinos decoupled from matter, meaning that they stopped really interacting with matter about a second after t equals zero. So neutrinos do interact with matter. If it's very, very dense, then even neutrinos will interact with it. But it only took about a second after that t equals zero moment for the universe to become dilute enough for neutrinos to just fly through and essentially ignore everything. So for the first second, neutrinos were absorbed. But that surface of last scattering, the cosmic neutrino background, comes from one second after t equals zero instead of 380 ,000 years.

48:46which is amazing. And so like, wow, we could see a lot of stuff we hadn't ever seen before. Super fun. Now, the issue is that these neutrinos are very, very low energy. Just like the cosmic microwave background light is very, very red shifted. These neutrinos have been super duper red shifted down to low energies. Like the plasma that made the cosmic microwave background light was really, really hot. And when those photons were made, they were very high energy, very short wavelength, but the universe has expanded since then. And when it expands, it also expands those photons and makes them super duper red, which is why it's often said that the CMB light is like light from a black body at like three degrees Kelvin, because you'd have to be that cold now to emit photons at that wavelength.

49:36And the same thing has happened to neutrinos. Neutrinos from the sun, for example, are like one to 10 million electron volts in energy. Neutrinos from supernova, maybe twice that down to a few MeV. But the neutrinos from the very early universe are very, very, very low energy, which makes them very, very challenging to see. Not impossible, but it means they're not going to interact as much as neutrinos with higher energy. So we have plans to see them and we hope to see them. Current experiments that look for dark matter, for example, are very, very sensitive to things that go bump in the night.

50:11And they very recently become sensitive enough to see like the neutrino background, this neutrino fog that fills the universe, not from the early universe yet, but from like everything else that's emitting neutrinos. And we hope on one day to be sensitive enough to these cosmic neutrino background from the very early universe, but not yet. And we'll know that they're there because we'll see them lower energy than basically anything else makes neutrinos. Am I remembering correctly that you told me it's hard to measure neutrinos, period? Yes, because they hardly interact. You build a big detector and like one in a trillion or one in a quadrillion neutrinos that fly through your detector will interact with it.

50:49Oh, man. Yeah. All right. The lower the energy, the more challenging it is. So yeah, it's hard. It's a good thing there's so much money for science. Now, gravitational waves are also an excellent source of information about the early universe. For the same reason as neutrinos. Neutrinos hardly interact with matter because they only use the weak force, which is very, very weak. Gravitational waves only use gravity, which is even weaker than the weak force. And so they decouple from everything else in the universe almost immediately, right? So using gravitational waves, you can see even further back than one second after T equals zero.

51:26Amazing. Yeah. Yes. But again, they are also affected by redshift. And so these would be very, very low frequency gravitational waves, very long wavelengths. Now, the gravitational waves that we're used to thinking about are the ones from like black holes that collide with each other. And before they do, they orbit each other and emit a huge amount of energy gravitational waves. Those are fairly high frequency. And we can see those with our detectors. And so those detectors like LIGO, they can see gravitational waves with really long wavelengths because they don't make any change on the scale of like the Earth even.

52:00You need like a galaxy-sized detector to see really long wavelength gravitational waves. Amazingly, humans have a galaxy-sized detector for gravitational waves. People have used pulsars, which are extraordinary neutron stars that rotate with extreme regularity. And by variations in their rotations, we can tell whether space between us and the pulsar has been squeezed or stretched. In the last couple of years, we've even seen evidence of very long wavelength gravitational waves using pulsar timing arrays. Really an amazing piece of science. But even those might be too short wavelength to see the early universe gravitational waves because they're going to be extremely low frequency.

52:47The pulsar timing arrays probably are seeing like a general gravitational wave background from all sorts of black holes and acceleration. I mean, everything you do creates gravitational waves. You wave your hand in front of you, you're creating gravitational waves because any kind of acceleration is going to create them. So there's just like a gravitational wave noise through the universe. But the ones from the early universe will be unique because they won't have like any specific source. They won't come from this black hole or from that black hole. They'll just fill the universe sort of the way the cosmic microwave background light will.

53:20and they'll be very broadly spread out across various frequencies. There'll be no big peak, no clear power structure. It'll be a very broad frequency signal. Even that will be very, very hard to see. And so the way people hope to see gravitational waves from the early universe is not actually by seeing the gravitational waves directly, but instead by seeing those gravitational waves affect the cosmic microwave background light. So that light we talked about earlier that was made 380 ,000 years after T equals zero, when it was made, it was affected by these gravitational waves that were already around from the early universe because it gives that light a special twist.

54:02Remember that light is a ripple in the electromagnetic field. And a field is just like numbers in space. And the Higgs field, for example, is just like a number at every location in space. But light is a vector field, which means it's not just one number. it's like three numbers. Or equivalently, you can think about it like a little arrow with a length and a direction at every point in space. And as light moves, those arrows ripple. And it can do more than just move. It can also spin, right? So this is what we call polarization of light. The same way that like if you have a jump rope, you can shake it up and down, or you can shake it sideways, or you can shake it in like a swirly motion.

54:40There's different way for waves to propagate along that string. Same thing for photons. And mathematically, you can decompose them into what are called E-modes that are radial patterns and B-modes that are like twisting, swirling patterns. Gravitational waves are the only way we know to give B-mode polarization to the CMB light. There's something about how those gravitational waves are stretching and squeezing the space while light is being formed that gives it those B-modes. Other gravitational waves like black hole collisions late in the universe cannot give like a broad pattern of B-mode polarization.

55:18So if you look at the cosmic microwave background light and you measure its polarization and you see B-modes, that would be fascinating information about the early universe. And a few years ago, an experiment called BICEP-2 claimed to have discovered it. Huge news rocked the science community until it turned out that they made a mistake in their analysis. And they were relying on data from another experiment to remove the effect of dust, but they didn't actually have that data from that experiment. They took a screenshot of a PowerPoint slide and misinterpreted it and used that as the basis for their analysis.

55:55And they came up with these big claims and had to walk it back. Very embarrassing. Brian King wrote a book about it called Losing the Nobel Prize. It's a fun story. Not for the people involved.

56:10He tells it with a smile on his face, I think. Was Brian Keating involved? Oh, yes. Oh. Deeply. No, he's not embarrassing other people. He's owning up to his own mistakes. Oh, okay. Their own mistakes. Got it. Anyway, we have not yet seen that. So, Gerard, that's how we might differentiate early universe neutrinos from later universe neutrinos. Or we might spot evidence for early universe gravitational waves, either of which could tell us amazing things about what happened in the first few moments after T equals zero. None of which could tell us about what happened before T equals zero. That's a whole other question mark.

56:47Which one do you think is more likely to tell us something first? Oh, wow. Great question. I think we probably will figure out this B-mode polarization of the CMB before we figure out how to see these very low energy neutrinos. But both communities are filled with super smart people working hard and coming up with clever ideas that I could never anticipate. So we'll see. Okay, and we'll see what Gerard thinks about the answer. Gerard listened to our answer and wrote back to me, and he preferred to send a written response. I'll read it for you now. Here's his reply. Quote, I didn't know the gravitational waves would be like photons and be stretched by their long journey through expanding space, lowering their frequency.

57:30The idea of indirectly detecting them by their effect on the CMB photon polarization is ingenious. I wonder how precise the measurements would need to be before scientists could reconstruct any earlier-than-CMB features. Nor did I know that neutrinos would also lose energy through stretching space. I guess I've always thought of them as particles, but we can think of them as waves in a field? I am always fascinated when science builds on an idea by extending it to another domain, as in this example, light waves stretch, so gravity waves should stretch too. A further question evoked by your description of the hot, dense early universe, what kind of structure might it have had?

58:09Would the high energy simply prevent anything from coalescing? I'm sure we will be surprised by something no one has even imagined. Thank you very much for that response, Gerard. Let me answer some of your follow-up questions. Yes, neutrinos also lose energy as they move through space because space is stretching. This is a great example of the non-conservation of energy in an expanding universe. It applies to everything, particles and waves. Particles in the end are really just ripples in quantum fields, and they are affected by the expanding universe. You also ask, what was the structure like in the hot, dense, early universe?

58:47It's a great question, and structure is a tough way to think about it because in the very early universe, you have these quantum fields that are filled with frothing energy. It's not like now when you have isolated energy and you can think about a little ripple in the field as a particle. It's like taking a thousand drops and putting them in a glass. You don't really think about drops anymore. Now you think about other emergent forms of that water, waves and other sorts of things. And so what's going to happen in the very early universe is that those quantum fields will be filled with energy and we'll get all sorts of weird, bizarre effects.

59:25Thank you very much to these listeners for sending in your questions and to everybody out there who drives this podcast forward with your personal curiosity about the universe. Please send us your questions at questions at danielannkelly.org. And if you like the podcast and you think about leaving us a rating, we would really appreciate that. Yes, exactly. Help other people find the podcast so that they can share their questions too. Come for the science, stay for the poo on the eggs. Or whatever gross stuff floats your boat.

1:00:02Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you. We really would. We want to know what questions you have about this extraordinary universe. We want to know your thoughts on recent shows, suggestions for future shows, If you contact us, we will get back to you. We really mean it. We answer every message. Email us at questions at danielandkelly.org. 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 &K Universe. Don't be shy. Write to us. Maintenance fee, overdraft fee, minimum balance fee, maximum balance fee.

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