Speaker 1: From twitching leaves to thinking minds, Where does I begin?
Speaker 1: Is it wiring roots or loops that inspires thinking?
Speaker 2: Birds have been around for one hundred and fifty million years,
Speaker 2: but chickens less than half of that. So did chickens
Speaker 2: come first? Or was it eggs? Go ahead, have a
Speaker 2: guess it. It was kind of long.
Speaker 1: These rhymes get better every time. To see the early universe,
Speaker 1: we need neutrinos or gravitational ways. But how will we
Speaker 1: know what to look for in all of that particle haze?
Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's
Speaker 2: answers will make it right.
Speaker 1: Welcome to Daniel and Kelly's Extraordinary Universe.
Speaker 2: Listener Questions, Episode thirty.
Speaker 3: Hi.
Speaker 1: I'm Daniel. I'm a particle physicist, and I never get
Speaker 1: tired of hearing questions from listeners.
Speaker 2: Hello. I'm Kelly Leadersmith. I study parasites and space, and
Speaker 2: I also never get tired of your questions. They're always wonderful.
Speaker 2: And Daniel, I have a question for you. Do you
Speaker 2: prefer eggs that have been sitting in the refrigerator or
Speaker 2: eggs that have been sitting on your counter?
Speaker 1: Oh my gosh, I am not prepared to have an
Speaker 1: opinion about that. Oh, why do they taste the same?
Speaker 2: Well, you know, I just kind of they probably taste
Speaker 2: pretty similar. But I've noticed that there are cultural differences.
Speaker 2: I think in Europe you're more likely to get eggs
Speaker 2: that don't need to be refrigerated, and so the differences
Speaker 2: in the United States. I think we've rinse off our eggs,
Speaker 2: and once you've rinsed them off, they need to be refrigerated.
Speaker 2: But if you don't rinse off your eggs, they come
Speaker 2: out of the chicken with a layer called a bloom,
Speaker 2: which protects against bacteria and stuff like that. And so
Speaker 2: you can just leave chickens on your counter for a while.
Speaker 1: You mean eggs on your counter.
Speaker 2: We're chickens. Yeah, I wouldn't recommend it, but yes, eggs.
Speaker 1: Come to Kelly's Deli where chickens roam the counter.
Speaker 2: Yeah, I bet I probably would not get a very
Speaker 2: good health rating if we didn't.
Speaker 1: Then, yeah, well there's something fascinating there that eggs are
Speaker 1: protected from infection. But we usually rinse things because we
Speaker 1: want them clean and uninfected. But here rinsing things makes
Speaker 1: them more vulnerable to infection.
Speaker 2: Yeah, I feel like in America, we want like ultimate
Speaker 2: control over everything, and we just feel like we have
Speaker 2: more control if we've shoved things in the fridge. And also,
Speaker 2: I suppose every once in a while when an egg
Speaker 2: comes out, it gets a little poo on it, and
Speaker 2: so if you can rinse it and then stick it
Speaker 2: in a fridge, you know, maybe you feel better about
Speaker 2: it that way.
Speaker 1: I don't really want any poo on my counter, is
Speaker 1: the truth.
Speaker 2: Yeah, yeah, no, I get that. I get that. That
Speaker 2: is one of the downsides of farm fresh chicken eggs
Speaker 2: is every once in a while you're like, oh, yes,
Speaker 2: biology happened here and there is some.
Speaker 1: Poo and on your counter in your house at home
Speaker 1: on the science farm, are there unwashed chicken eggs and
Speaker 1: occasional pooh?
Speaker 2: There are unwashed chicken eggs? Like, the answer is yes.
Speaker 2: I was gonna try to figure out a nice way
Speaker 2: to say it. You know, we've got like brushes to
Speaker 2: clean them off before you crack them, to make sure
Speaker 2: that none of that pooh ends up. Please come back
Speaker 2: to our house and visit.
Speaker 1: Sure, I will. Well, why don't you rinse them before
Speaker 1: you crack them, because once you rinse them, they're not
Speaker 1: protected but there's then there's just moments before you crack them.
Speaker 2: Oh, we rinse and brush well, I mean, you know,
Speaker 2: when the poo dries, it's harder to get off, and
Speaker 2: so it's nice to have a brush, and so yeah,
Speaker 2: we clean it all off right before we crack it
Speaker 2: to make sure that, like you know, sometimes when I
Speaker 2: crack eggs, I get shell in the bowl and we
Speaker 2: just want to make sure that that's clean, because I'm
Speaker 2: not so good at cracking eggs.
Speaker 1: But you are very good at answering questions from listeners.
Speaker 1: And that's what we're doing today on the podcast. We
Speaker 1: are hearing from all of you everything that makes you
Speaker 1: wonder about the universe, all the extraordinary fascinating mysteries about
Speaker 1: the universe that you want to hear about. And so
Speaker 1: today we are tackling three fascinating topics from biology to physics,
Speaker 1: to the origins of the universe to the origins of
Speaker 1: chickens and eggs.
Speaker 2: Yes we are, so let's jump right in and hear
Speaker 2: our question from Jared.
Speaker 3: Hello. My name is Jared, and I'm a huge fan
Speaker 3: of you both. I absolutely love your show. My three
Speaker 3: children enjoyed the podcast. Also, my two preteen sons and
Speaker 3: Joy Kelly's gross biology explanations, and my six year old
Speaker 3: daughter likes to fall asleep to Daniel's voice during car rides.
Speaker 3: My question today is about how we classify and explain
Speaker 3: the different levels of self awareness in the universe. I've
Speaker 3: been reading about how across the spectrum from reactivity to sapiens,
Speaker 3: living systems exhibit increasingly complex forms of awareness, ranging from
Speaker 3: basic stimulus response to sentience, self awareness, and ultimately sapiens,
Speaker 3: which I now know is different than santhians. I've been
Speaker 3: reading about how concepts like metacognition, reflective consciousness, and theory
Speaker 3: of minds see the mark pivotal transitions along this continuum.
Speaker 3: But the boundaries we've set up to define and described
Speaker 3: as kind of spectrum of awareness are still fuzzy to me,
Speaker 3: and it's led me to having like a ton of
Speaker 3: smaller questions, like what's the difference between plants and machines
Speaker 3: in terms of reactivity? Could mammals have moments of sapience
Speaker 3: or could the boundaries be crossed accidentally temporarily? So I
Speaker 3: was just hoping, with your distinct scientific advantage points that
Speaker 3: you could help explain the fundamental physical or biological thresholds
Speaker 3: that enable these higher levels of awareness to emerge from
Speaker 3: simpler matter in life. And perhaps even let me know
Speaker 3: if there are any overlooked mechanisms or principles perhaps at
Speaker 3: the intersection of physics and biology that would be cool
Speaker 3: that could help explain not only how these layers of
Speaker 3: awareness arise, but also the current limits of our scientific
Speaker 3: understanding of awareness and what might be the next breakthrough
Speaker 3: that could reshape how we define or recognize it in
Speaker 3: the universe. All right, thank you very.
Speaker 1: Much, so thank you Jared number one for sharing the
Speaker 1: podcast with your kids and helping raise the next generation
Speaker 1: of curious people in the universe. Awesome, we love that.
Speaker 1: Thank you so much. And also for asking such a hard,
Speaker 1: such a deep question about the nature of sentience and
Speaker 1: consciousness and whether we can understand how that emerges from
Speaker 1: like core physical activity.
Speaker 2: And I'd also like to note that I am so
Speaker 2: glad that the next generation is still excited about gross stuff.
Speaker 2: So thank you to the preteens for digging the gross biology.
Speaker 2: But anyway, yes, wow, where do we start with this
Speaker 2: difficult question? Daniel?
Speaker 1: Yes, so we got to start by saying we're not
Speaker 1: going to be offering any solid answers because there are none. Right,
Speaker 1: we just do not understand this stuff. There are so
Speaker 1: many issues here, from never being able to probe the
Speaker 1: awareness of another object in the universe, not to mention
Speaker 1: another human being right, first person experience this like subjective
Speaker 1: existence that we have where I feel like I'm in
Speaker 1: my head and I'm feeling my body. That's not something
Speaker 1: I can share with you, not something you can probe
Speaker 1: from the outside, not something you can verify. I don't
Speaker 1: even know, Kelly, if you are any different fundamentally from
Speaker 1: a rock in terms of your inner life.
Speaker 2: Thanks Daniel.
Speaker 1: I mean I think that you are. You seem different,
Speaker 1: but I don't know from a philosophical skeptical point of view,
Speaker 1: and that's fundamentally going to limit us from having any
Speaker 1: solid answers.
Speaker 2: Well, I think the good news is that people don't
Speaker 2: really come to our podcast for solid answers. They come
Speaker 2: to our podcast for the we don't really know version
Speaker 2: of answers and so, and.
Speaker 1: You do that much better than a rock does that.
Speaker 1: By the way, You're much better podcast host than like
Speaker 1: a lump of granite.
Speaker 2: Thanks question Mark.
Speaker 1: But Jared is asking a really interesting question. About like
Speaker 1: the spectrum of reactivity, right, Like, how do we categorize
Speaker 1: these things? How do things get more complicated? Is there
Speaker 1: a way that we can under stand not just reactivity,
Speaker 1: but like sentience and conscious experience by gradually scanning up
Speaker 1: from simple reactivity to the universe all the way up
Speaker 1: to you know, having a first person experience. So let's
Speaker 1: take a walk from the simplest to the more complex.
Speaker 1: We can start with like physical reactivity. Things in the
Speaker 1: universe react to other things, you know, like if you
Speaker 1: have a rock out there in the sun, it will
Speaker 1: absorb photons, it will gain mass, it will change the
Speaker 1: nature of the chemical bonds, it will store that energy.
Speaker 1: So that's you know, direct causal reaction to something outside
Speaker 1: the universe, just like if you press a button on
Speaker 1: your toaster or you write a program for your computer.
Speaker 1: The universe seems to be causal. It seems like you
Speaker 1: can influence the future, and so things that happen in
Speaker 1: the universe affect the future. Right, that's like the most
Speaker 1: basic level at which things in the universe interact.
Speaker 2: Got it, Yes, rocks and Kelly warm up. Let's uh,
Speaker 2: let's move to more comp.
Speaker 1: Before we get to more complex though you can already
Speaker 1: ask does the rock feel anything like the rock is
Speaker 1: sitting in the sun, it's getting warmed up. Does it
Speaker 1: go in its own rocky way? Like, mmm, that feels nice,
Speaker 1: the way like when you have your face in the sun,
Speaker 1: it feels nice. Obviously, what it's like to be a
Speaker 1: rock is not going to be what it's like to
Speaker 1: be Kelly or Daniel or Jared or any of his kids.
Speaker 1: But there might be something it's like to be that rock,
Speaker 1: and we can't say that it isn't. And there are
Speaker 1: even theories out there that everything in the universe is aware,
Speaker 1: it is conscious at some level, so that by the
Speaker 1: time we get to podcast host, we can say that
Speaker 1: that podcast hosts rich inner life, which enjoys poo free eggs,
Speaker 1: for example, comes emerges from the basic elements of consciousness
Speaker 1: that begin with fundamental particles. You know that electrons have
Speaker 1: like a little bit of consciousness and it comes together.
Speaker 1: I'm not ascribing to that theory. I'm just saying there
Speaker 1: are people who already, at this level of interaction with
Speaker 1: the universe put a little dot of awareness and experience.
Speaker 2: Is there an interesting question to be asked here about,
Speaker 2: like if you asked AI, and it gave you an
Speaker 2: answer about its experienced, like because it can answer. Is
Speaker 2: that an interesting answer?
Speaker 1: Well, it's interesting because an AI, unlike a rock, can
Speaker 1: tell you that it has an inner life. Right, if
Speaker 1: you ask Gemini or chat GPT, they can tell you
Speaker 1: that they think that they feel that they have thoughts whatever.
Speaker 1: You can't tell the difference between them having those thoughts
Speaker 1: and claiming those thoughts, or them not having those thoughts
Speaker 1: and yet claiming those thoughts, because you could write a
Speaker 1: program which claims those thoughts and you don't know that
Speaker 1: it actually has them. Right, Claiming them and having them
Speaker 1: are different things. And in philosophy we have this concept
Speaker 1: of a philosophical zombie, and the thought experiment is like, could,
Speaker 1: for example, there be a version of Kelly who claims
Speaker 1: to have a rich inner life and acts unless she
Speaker 1: has a rich inner life, and yet doesn't.
Speaker 2: You did compare me to a rock earlier.
Speaker 1: In a flattering, complimentary west You're better than a rock,
Speaker 1: much much better than thank you. In fact, you rock, Kelly.
Speaker 1: But the point of that thought experiment, the philosophical zombie,
Speaker 1: is to point out that the subjective experience we're talking
Speaker 1: about that inner life is not revealed by your actions.
Speaker 1: That there's nothing on the exterior you can do to
Speaker 1: probe it, so that even somebody who seems to have it,
Speaker 1: even somebody you fall in love with, might not have
Speaker 1: an interior life. And there are examples of people out
Speaker 1: there who like fall in love with ch at GPT
Speaker 1: and have like AI boyfriends and feel real emotions about them,
Speaker 1: and imagine that the AI also feels real emotions in response,
Speaker 1: even if it doesn't. So my point is that already
Speaker 1: at this level, the philosophical questions are complicated.
Speaker 2: M hm, yes, and I am already sort of feeling
Speaker 2: existential dreads. So all right, let's move on to the
Speaker 2: next level.
Speaker 1: All right, So the next level is like biological. We
Speaker 1: have simple plants that can do things like organize their cells.
Speaker 1: They maintain gradients across cell walls. Plants can orient their
Speaker 1: leaves to the sun. This is more than just like
Speaker 1: a rock absorbing a photon. There's like a feedback here,
Speaker 1: there's like memory, you know, there's maybe even goal like behavior.
Speaker 1: The plants move towards the sun, trees grow up, the
Speaker 1: roots go down. There's goal like behavior here, but sort
Speaker 1: of implicit, right, We don't know if the plant is
Speaker 1: like stretching towards the sun and enjoying having its leaves toasted,
Speaker 1: but it's definitely more self organized and reactive to the
Speaker 1: universe than just a rock. And there are some cases
Speaker 1: that some people tout slime molds for example of you
Speaker 1: know what seems like maybe intelligent behavior exploring a maze.
Speaker 1: Though I know, Kelly, that you are not in the
Speaker 1: top ten list of people who are impressed by slime
Speaker 1: mold intelligence.
Speaker 2: Check out one of our earlier Listener Questions episode to
Speaker 2: hear a Kelly throw cold water on slimbles solved mazes.
Speaker 1: And you do that even better than a bucket of
Speaker 1: cold water. I have to.
Speaker 2: Say, thank you, and maybe better than a rock. And
Speaker 2: there's all kinds of inanimate objects that I can outperform.
Speaker 1: All right, So now let's take one more step up
Speaker 1: the perceptual ladder to critters that have like explicit sensory organs,
Speaker 1: you know, even simple things like ants and flies. They
Speaker 1: have eyes, they can experience the world. They have chemical sensors.
Speaker 1: They communicate with each other, They leave trails for each other,
Speaker 1: you know, they make sounds, they leave chemicals. They definitely
Speaker 1: can learn. I have a friend who does experiments on
Speaker 1: fruit flies, and they definitely can learn sounds and songs
Speaker 1: and all sorts of stuff. We don't know what it's
Speaker 1: like to be an ant. There doesn't have to be
Speaker 1: anything it's like to be an ant or fruitfly. You
Speaker 1: could have like a little robot which accomplishes exactly the
Speaker 1: same thing and doesn't have any internal state. But there
Speaker 1: also could be something it's like to be an ant
Speaker 1: or a fruit fly. We just don't know.
Speaker 2: Do you think that there's some chance that we're sort
Speaker 2: of biasing this towards ourselves by saying, like, oh, they
Speaker 2: need to have sense organs, like the kinds of sense
Speaker 2: organs I recognize in myself, you know, because like plants
Speaker 2: are detecting where the sun is so that they can
Speaker 2: turn towards it, so they've got something like sense organs.
Speaker 2: Are we essentially defining oh yeah, things, yeah, to match
Speaker 2: what we do.
Speaker 1: Absolutely and obviously, and I don't know that we could
Speaker 1: do anything else. The only thing we can do is
Speaker 1: ask about similar experience. Is we can try to think
Speaker 1: about what it might be like to be something else,
Speaker 1: But in the end, we're always translating the unfamiliar back
Speaker 1: into the language of the familiar. You know, this is
Speaker 1: like a big theme of my book about alien physics
Speaker 1: is that it's really hard to think outside of your
Speaker 1: own little box. And so it could be that there's
Speaker 1: something it's like to be a rock and a plant
Speaker 1: which is very, very different from what it's like to
Speaker 1: be human, and it's rich and complicated in a way
Speaker 1: we just can't underst stand or even conceive of. Even
Speaker 1: if we could talk to them and they could try
Speaker 1: to explain it to us, we might never really be
Speaker 1: able to crock it because there are some things that
Speaker 1: are just untranslatable.
Speaker 2: Do aliens speak? Physics available through fine bookstores everywhere.
Speaker 1: And also terrible bookstores. Yeah, so we've gone from rocks
Speaker 1: to like plants to now critters with explicit sensory organs.
Speaker 1: You can take them the next step up and say, well,
Speaker 1: what about more intelligent animals, Animals that have a model
Speaker 1: of the world within them. You know that they can
Speaker 1: integrate sensory information over time, They have memory, they can
Speaker 1: be trained, they can make predictions. You know, they don't
Speaker 1: just react to the world and have basic memory. They
Speaker 1: have like a model of themselves in the world. And
Speaker 1: they use that to make predictions. That's clearly a more
Speaker 1: sophisticated way to respond to the world. And in that case,
Speaker 1: it's tempting to say, look, if you have a mind,
Speaker 1: and in that mind you have a model of yourself,
Speaker 1: then clearly referring to yourself. And isn't that a kind
Speaker 1: of experience. It seems very likely. And you know, when
Speaker 1: I interact with my dog, it's very easy for me
Speaker 1: to see parallels in my dog's emotional response to my own,
Speaker 1: Like he likes being scratched, and I can tell that
Speaker 1: he likes it, right, Or if I'm upset with him,
Speaker 1: he knows, and I can tell that he doesn't like
Speaker 1: when I'm upset with him. All these things, And again,
Speaker 1: maybe it's just the slice of humanity that is reflected
Speaker 1: in the dog, but there's definitely some overlap there. Right,
Speaker 1: whatever it's like to be a dog, there are parts
Speaker 1: of it that are similar enough to what it's like
Speaker 1: to be human that we can have that emotional connection, right,
Speaker 1: And so it's very tempting to say, well, clearly my
Speaker 1: dog has an inner life. It is something it's like
Speaker 1: to be Daniel's dog. But again, how do I really
Speaker 1: know if somebody came along and like magically removed that
Speaker 1: experience from my dog but kept all the same behavior. Obviously,
Speaker 1: I couldn't tell by construction. So it's frustratingly opaque.
Speaker 2: Yeah, it does kind of feel like you were a
Speaker 2: little bit more will to entertain the idea that your
Speaker 2: dog has a rich inner life than you were to
Speaker 2: entertain the idea that your co host has a rich
Speaker 2: inner life.
Speaker 1: I'll say, in my defense, I made that argument as
Speaker 1: an example of ridiculous but unrefutable arguments.
Speaker 2: Right, I'm just giving you a hard time.
Speaker 1: Okay, go on, No, but I mean I only have
Speaker 1: a dog in my house. You have a whole spectrum
Speaker 1: of critters. Give us a sordid list from most to
Speaker 1: least likely to have an inner life.
Speaker 2: Chickens, no inner life.
Speaker 1: Chickens are just robots, you're saying.
Speaker 2: Just robots, just robots. And my doggy milo very rich
Speaker 2: inner life. And my goats, you know, I think my
Speaker 2: goats are very frustrated when I don't let them out
Speaker 2: on time or when I come out without animal crackers,
Speaker 2: and they've got a rich inner life.
Speaker 1: And then you know, the next step, of course, is
Speaker 1: full sapience. You know where you can think, you have language,
Speaker 1: you can have abstract concepts, you can think about thinking,
Speaker 1: you can argue about it, arguing to have a rich
Speaker 1: inner life and a model of the world that includes
Speaker 1: yourself and your own model of the world in it.
Speaker 1: And it's recursive all the way down. Where along this
Speaker 1: spectrum does experience emerge, We just don't know, right This
Speaker 1: is what they call the hard problem of consciousness. Even
Speaker 1: if you can understand mechanically how the brain works, signals
Speaker 1: go up the optic nerve dot dot dot, that doesn't
Speaker 1: tell you why there's something it's like to be a person.
Speaker 1: And so you know, there's all these various approaches that
Speaker 1: people take in the philosophical community. We mentioned one of
Speaker 1: them already, pan psychism, where mentality is a fundamental aspect
Speaker 1: of reality, like mass or charge. It's not the idea that,
Speaker 1: like electrons have political opinions, but that there's some sort
Speaker 1: of minimal experiential properties of all matter at the most
Speaker 1: basic level, and that the experience doesn't emerge suddenly but
Speaker 1: gradually from the simple experiences combining into richer experiences of
Speaker 1: complex systems. That's a not of like widely held or
Speaker 1: mainstream view, but it is an opinion I've seen out there.
Speaker 2: I feel like I've sort of lost track of what
Speaker 2: we mean by experience and mentality at this point, So like,
Speaker 2: experience must mean more than like a photon has hit
Speaker 2: me and I have recognized that the photon has hit me,
Speaker 2: and mentality must be Yeah, Like, what do we mean
Speaker 2: now by experience and mentality?
Speaker 1: I mean that there's something it's like to be you. Okay,
Speaker 1: you know that you're having a first person experience, got it?
Speaker 2: Okay?
Speaker 1: And there are people who deny that, right, Folks like
Speaker 1: Daniel Dennett, a school of thought called reductive physicalism, say
Speaker 1: there's no first person experience, that there is no moment
Speaker 1: of Now. What you think you are experiencing right now
Speaker 1: is just your brain analyzing what recently happened, right that
Speaker 1: the moment of the present itself is an illusion, and
Speaker 1: it's constructed by your brain putting together a bunch of
Speaker 1: sensor reinformation telling a story about what just happened. And
Speaker 1: it's so recent. You surf along the edge of it
Speaker 1: and it feels like there's a you, but there isn't really,
Speaker 1: So you weirdly remember being conscious, but never really are.
Speaker 1: It's a fascinating idea.
Speaker 2: Are we in like a simulation or we're just like.
Speaker 1: No, no, we are not in a simulation. We are
Speaker 1: just remembering a present we never experienced. This is a
Speaker 1: fascinating idea and it's hard to wrap your mind around.
Speaker 1: It's in Daniel Denni's book Consciousness Explained, which is like, wow,
Speaker 1: ambitious title. Right, Yeah, it's a really fun book and
Speaker 1: we should dive into it more another time. Another idea
Speaker 1: is called functionalism. It says, look, it's all about information.
Speaker 1: It doesn't matter what matter it is. It's not like
Speaker 1: the sentience is built into the electron and then it
Speaker 1: all comes together. It's about how this stuff is arranged,
Speaker 1: and it's about the model in your head of the universe.
Speaker 1: But there's no real explanation there for like how that emerges,
Speaker 1: Like where along that spectrum we just described it begins
Speaker 1: that there's something that's like to be an ant or
Speaker 1: a bird, just that it comes out of the information.
Speaker 1: And here the implication is that if you build a
Speaker 1: simulation of Kelly, it would have the same experience as Kelly.
Speaker 1: It's nothing about the wet weear or the kellyness of
Speaker 1: your particles. It's just the arrangements of the stuff.
Speaker 2: It's arrangement.
Speaker 1: And then the last sort of broad philosophical approach is
Speaker 1: called strong emergence, and it says, hey, this whole argument
Speaker 1: that things need to bubble up from the littlest bits,
Speaker 1: that somehow the first person experience needs to be emerging
Speaker 1: from the towing and froing of the little particles inside.
Speaker 1: You forget all that, even though it seems to be
Speaker 1: like the foundation of modern science and physics at least,
Speaker 1: and say, look, things emerge because there are just new
Speaker 1: fundamental laws at every level. So it's not like the
Speaker 1: behavior the biggest stuff bubbles up somehow from the behavior
Speaker 1: of the smallest stuff. It's got its own laws, and
Speaker 1: maybe things flow the other way. And like consciousness emergence
Speaker 1: because there's some weird new law of the universe and
Speaker 1: it can control the microscopic instead of the microscopic controlling
Speaker 1: the macroscopic. So you know, the short answer is nobody
Speaker 1: knows the answer, and there's an enormous variety of totally
Speaker 1: contradictory approaches in the philosophical community to this very very
Speaker 1: hard problem.
Speaker 2: I feel like this is the kind of conversation where
Speaker 2: I need to like, hear a sentence and then sit
Speaker 2: for ten or fifteen minutes to be like, what did
Speaker 2: that sentence mean? And then start again.
Speaker 1: Yeah, yeah, yeah, that's philosophy for you, exactly, and you're
Speaker 1: going to go all the way down to like what
Speaker 1: does meaning mean? Anyway?
Speaker 2: That's right? Am I real? Is this is any of
Speaker 2: this real? What is real?
Speaker 1: Yeah? Exactly, And then you'll discover that at the foundations
Speaker 1: of philosophy you know nothing and we know nothing, and
Speaker 1: you know, that's where de Karte was and it's very
Speaker 1: hard to go anywhere from there. So you just got
Speaker 1: to make some assumptions and move forward as best you
Speaker 1: can because it's not clear what we know and what
Speaker 1: we don't know and what knowing even means. All right,
Speaker 1: So I hope we've confused you enough. Jared. Let us
Speaker 1: know if that helped you at all. And thank you
Speaker 1: again for your question.
Speaker 4: Wow.
Speaker 3: Thank you so much, Daniel and Kelly for the amazing
Speaker 3: and detailed answer. You've certainly given us all a lot
Speaker 3: to think about. We promise our next question won't be
Speaker 3: as difficult next time. We'll keep it simpler. Certainly next
Speaker 3: time when we're talking about our cat oreo and we're
Speaker 3: talking about her learned behavior over time and how she's
Speaker 3: picked up on certain human words. We'll now have a
Speaker 3: more context to kind of discuss that. And yeah, we
Speaker 3: don't have any follow up questions. Just keep up the
Speaker 3: great work. We love the podcast.
Speaker 4: Kelly.
Speaker 1: Okay, we're back and we're answering questions from listeners. And
Speaker 1: today we're tackling deep philosophical questions like do rocks feel pain?
Speaker 1: And also ancient questions like what came first? The chicken
Speaker 1: or the egg?
Speaker 2: And this is a question that people, you know, sometimes
Speaker 2: enjoy having long, deep philosophical questions about. But I love
Speaker 2: runing fun and evolution has a clear answer.
Speaker 1: Oh my gosh. Wow.
Speaker 2: And so let's hear Noah's question and then I'm gonna
Speaker 2: give you a clear answer.
Speaker 4: Nice, Hi, Daniel and Kelly. I would love to hear
Speaker 4: about the evolutionary history of chickens and eggs? Is there
Speaker 4: an answer to which came first?
Speaker 1: You're just going to give a clear answer to make
Speaker 1: me look bad because of my philosophical ramblings.
Speaker 2: Yeah, you should have just said no moving. I'm gonna
Speaker 2: saved us all twenty minutes, Daniel, No, that was fun.
Speaker 1: All right, So great question. Noah Kelly, tell us what
Speaker 1: a science say about the chicken versus egg debate.
Speaker 2: Well, eggs have been around for a really long time, Okay, So,
Speaker 2: like we think of women as having eggs and men
Speaker 2: as having sperm, and so if you think of it
Speaker 2: that way, then eggs have been around for you know,
Speaker 2: since we've had fish and since we've had amphibians and
Speaker 2: millions and millions and millions of years. But I understand
Speaker 2: that that's not actually what we're talking about. We're talking
Speaker 2: about you know, chicken eggs as in like having that
Speaker 2: hard shell. But let's take a few steps back. Okay,
Speaker 2: So initially we had you know, fish swimming around in
Speaker 2: the oceans, and we had amphibians and they were laying
Speaker 2: eggs in water. When you lay eggs in water, you've
Speaker 2: got this sort of perk that you're in this aquatic environment,
Speaker 2: so when you lay your eggs, you don't have to
Speaker 2: worry about them drying out and dying.
Speaker 1: But is that where eggs begin with amphibians in the
Speaker 1: water or are their precursors to that.
Speaker 2: Well, invertebrates like starfish also make eggs. But if we're
Speaker 2: talking about vertebrates, making eggs. Then shark and fish were
Speaker 2: making eggs before the amphibians were. But so when four
Speaker 2: limbed verts like reptiles started leaving the ocean to move
Speaker 2: on land, we started having this problem, which is that, well,
Speaker 2: now that we're out of the water, our eggs are
Speaker 2: gonna start drying out, and so what do we do.
Speaker 2: Our eggs needed to become more complicated, and thus arose
Speaker 2: the amniotes, and that's just kind of a fancy word
Speaker 2: for saying we ended up getting fancier eggs, and so
Speaker 2: amniotes includes birds, reptiles, and mammals, and so amniotes these
Speaker 2: are fancy eggs that have three extra layers. And what
Speaker 2: these three extra layers do is they first they provide
Speaker 2: an extra little fluid filled sack and this is like
Speaker 2: the amnion and essentially encloses the embryo and it's like
Speaker 2: a protective fluid. And so if you are egg were
Speaker 2: to go rolling down a hill, which you probably should,
Speaker 2: try to make sure your egg doesn't do. But if
Speaker 2: it does, it like will protect it against bumps and
Speaker 2: bruises and sort of give it a bit of a
Speaker 2: cushion and it just sort of suspends the embryo, and
Speaker 2: it's almost like you've brought your aquatic environment with you
Speaker 2: by putting it in this like sac.
Speaker 1: It's like we're still stuck on ocean based life and
Speaker 1: all of land based life is like carring around little
Speaker 1: bags of ocean.
Speaker 2: Yes, yes, we are carrying our past with us in
Speaker 2: that sense, which is kind of.
Speaker 1: Cool, which is fascinating because like all of the life
Speaker 1: that we build, like robots, it's all dry. Right, why
Speaker 1: don't we build robots that are based on guie bags.
Speaker 2: Well, you're the computer scientist. My sense is that when
Speaker 2: you start adding water to computers, things don't go real well.
Speaker 1: All right, so we have the amnion. What are the
Speaker 1: other extra layers that the amniotes added?
Speaker 2: All right, so you also have the coreon and the alantois.
Speaker 2: I'm sure that I am mispronouncing those as everyone has
Speaker 2: come to expect it. Anyway, those two layers are helpful
Speaker 2: for gas exchange. So you still need to be able
Speaker 2: to get oxygen into the egg to give that oxygen
Speaker 2: to the embryo inside, and you need to be able
Speaker 2: to manage waste. And so these two layers essentially allow
Speaker 2: for gas exchange, and they contain the waste that's produced
Speaker 2: by the embryo inside.
Speaker 1: Waste related question, huh are the amniotes the first ones
Speaker 1: to accidentally pooh on their eggs? Or did fish do that? Also?
Speaker 2: Oh, let's see. Okay, so that's really great question, Daniel.
Speaker 1: How did you not research that?
Speaker 2: Did I not research that? I have had the experience
Speaker 2: of mixing gammeats from fish, which essentially means you very
Speaker 2: gently run your fingers along their abdomen to get them
Speaker 2: to release eggs or sperm, and they have occasionally released
Speaker 2: waste as well.
Speaker 1: What's the furb you used to describe that?
Speaker 2: Some people call it milking. I wasn't gonna go there, but.
Speaker 1: The way you might, like, you know, milk a bowl.
Speaker 2: Yep, yep, that way, that way.
Speaker 1: The glorious labor of science.
Speaker 2: Yes, so the world of an ecologist and so anyway,
Speaker 2: So yeah, so these extra layers made our eggs more
Speaker 2: complicated and allowed us to come on land. But I
Speaker 2: think the chicken in the egg question isn't about you know,
Speaker 2: this slightly more complicated egg. So you know, for example,
Speaker 2: in humans, we essentially brought a lot of this system
Speaker 2: inside of our bodies, so we have an amniotic sack.
Speaker 2: So we've got this fluid filled sack. We put the
Speaker 2: ocean inside of our bodies, and we allowed gas exchange
Speaker 2: with like our placenta and stuff like that. But birds
Speaker 2: and reptiles they made this system where you can essentially
Speaker 2: have the whole thing outside of the body and you
Speaker 2: can like lay it in a nest.
Speaker 1: Seems like a better plan, doesn't it.
Speaker 2: Yeah, yeah, I mean there's there's some benefits to being
Speaker 2: able to carry the baby around with you all the time.
Speaker 2: You always know where it is. There's there's some definite benefits,
Speaker 2: but it is also a bit difficult, I will admit. Okay.
Speaker 2: But so then the question is when did like bird
Speaker 2: eggs as we come to think of them come about.
Speaker 2: And the answer is that birds evolved during the Jurassic period,
Speaker 2: which was one hundred and fifty million years ago, So
Speaker 2: what we think of as bird eggs arose one hundred
Speaker 2: and fifty million years ago. Amniotic eggs in general are
Speaker 2: three hundred million years old, so older than birds. But
Speaker 2: now the question is when do we get chickens?
Speaker 1: All right, wait, so already eggs came before birds broadly.
Speaker 2: Yes, yeah, eggs, so like reptiles have eggy things. Also,
Speaker 2: they're a little bit different than what you think of
Speaker 2: as a chicken egg, but like amniotic eggs three hundred
Speaker 2: million years old. Birds in general one hundred and fifty
Speaker 2: million years old, but chickens weren't like the first birds.
Speaker 2: Chickens come later, and chickens appear to be about sixty
Speaker 2: six million years old. There's a fossil that appears to
Speaker 2: be the ancestor of chickens and ducks. And they have
Speaker 2: named this fossil wonder chicken. No, yes, no, really, wonder chicken.
Speaker 1: Wonderful name.
Speaker 4: Yeah.
Speaker 2: I wasn't able to find a lot more information. I mean,
Speaker 2: I suppose it could have been they found it in
Speaker 2: like Germany and it was like vondo chicken or like
Speaker 2: don't I don't know the details.
Speaker 1: Was it like six feet tall and eight hundred pounds
Speaker 1: or something.
Speaker 2: I hope.
Speaker 1: So when it walked, the earth shook.
Speaker 2: That's right.
Speaker 1: Here come the wonder chicken.
Speaker 2: That's right, Your dinner this time?
Speaker 1: Netflix, please call us.
Speaker 2: That's right. I'm available to consult. I'll write jokes too,
Speaker 2: but not poems. Don't worry, okay, so, but so, so,
Speaker 2: what we really want to know is like, all right,
Speaker 2: so we've had chickens in the wild, and there are
Speaker 2: wild chickens. So, for example, there are a red jungle
Speaker 2: fowl that you can find in Southeast Asia, like so
Speaker 2: in China and India and stuff like that. And there's
Speaker 2: green jungle fowl and gray jungle fowl and the red
Speaker 2: jungle fowl in particular, if you look up pictures of
Speaker 2: them on like Wikipedia, they look like the kind of
Speaker 2: chicken you'd find in your backyard actually kind of surprisingly.
Speaker 2: They have like the beautiful colors and the you know,
Speaker 2: the males look like any rooster that you would expect
Speaker 2: to see in your backyard.
Speaker 1: They poo on their eggs.
Speaker 2: Probably, I mean, yeah, humans pooh on their babies sometimes too.
Speaker 2: It's like it's a it's a messy process, man. And
Speaker 2: so anyway, all right, so then the question is when
Speaker 2: did we start getting domestic chickens? Uh? And that is
Speaker 2: apparently something that scientists fight about a lot. I've got
Speaker 2: a lot of papers where they were, like, you know,
Speaker 2: arguing about methods and this person was mad at that person.
Speaker 2: And it's so it does look like domestic chickens came
Speaker 2: from red jungle fowl. There may have been some hybridization
Speaker 2: with some other wild chicken species, but mostly it came
Speaker 2: from red jungle fowl somewhere in Asia, maybe ten thousand
Speaker 2: years ago. There's some archaeological evidence, and that archaeological evidence
Speaker 2: tends to be like they found chicken eggs, and it's
Speaker 2: not necessarily clear if the chickens were there because of
Speaker 2: the eggs, or because we were eating the chickens, or
Speaker 2: because there were cock fights, and there could have been
Speaker 2: a lot of different reasons we had chickens around. But
Speaker 2: you do see things like chickens, like you know, beautiful
Speaker 2: roosters on coins in different cultures, and so chickens do
Speaker 2: look like they were important part of our cultures for
Speaker 2: a really long time. There was one study that estimated
Speaker 2: that based on like DNA stuff, maybe chickens have been
Speaker 2: with us for fifty thousand years. We've been like carrying
Speaker 2: them around with us. But anyway, definitely, we are sure
Speaker 2: that the ancient Greeks around six hundred BC, so something
Speaker 2: like two thousand, six hundred years ago, you can see
Speaker 2: chicken imagery in like the Greek pottery, and so we're
Speaker 2: sure that we had chickens at least at that point,
Speaker 2: maybe even much earlier.
Speaker 1: Do you think there's any relationship between domesticating chickens and agriculture?
Speaker 1: And I can understand, like domesticating dogs, when you still
Speaker 1: a hunter gatherer community, you can hunt, you kill, you
Speaker 1: share with the dogs. What about chickens. I mean, I
Speaker 1: always think about feeding chickens grains, But actually, now that
Speaker 1: I think about it, chickens eat anything, don't they. So
Speaker 1: you could have chickens eat your kill also.
Speaker 2: Yeah, so I can see it being much much easier
Speaker 2: to have chickens if you're staying in one place, which
Speaker 2: would be easier if you were in agricultural society. But
Speaker 2: on the other hand, yeah, I mean we feed our
Speaker 2: chickens everything.
Speaker 1: Including chicken, right, yeah, cannibalism for the role.
Speaker 2: Yes, pull out your dKu Bingo card, all right, yeah, Okay,
Speaker 2: So the answer is eggs came first, then came chickens.
Speaker 2: But you can still have fun philosophical debates, just not
Speaker 2: when Kelly's around.
Speaker 1: But I think that's only because you've interpreted the question
Speaker 1: as what came first the chicken or any kind of egg.
Speaker 1: But I think the question is what came first the
Speaker 1: chicken or the chicken egg?
Speaker 2: Oh but but no, because eggs came first, you had
Speaker 2: to have.
Speaker 1: Answer the same.
Speaker 2: The red jungle fowl came first, and at some point
Speaker 2: there was anyway domestication happened, and blah blah blah. So
Speaker 2: let's let's see if Noah has more whimsy in his
Speaker 2: heart than I do, and maybe he will disagree with
Speaker 2: my answer.
Speaker 4: I'm endlessly amazed at how much of the story of
Speaker 4: many millions of years that humans have accumulated previously. I
Speaker 4: kind of assumed that this answer would be neither or
Speaker 4: both just played out in time. But I agree with Kelly.
Speaker 4: Eggs seem like the clear winner here. At least there's
Speaker 4: no shortage of as yet unsolved paradoxes to think about
Speaker 4: many things to both of you, I love the show.
Speaker 2: All right, we are moving from eggs to gravitational waves,
Speaker 2: and next up we have a question from Gerard which
Speaker 2: sounds like a really good setup to a new sci
Speaker 2: fi book.
Speaker 5: I've heard that if we could read gravitational waves from
Speaker 5: the Big Thing, someday we would also be able to
Speaker 5: see further into the past than with light. My question is,
Speaker 5: how would we be able to tell which gravity waves
Speaker 5: are visionated in that very early time and which formed later.
Speaker 5: Is there some analog with lights redshifting. I've also heard
Speaker 5: the same possibility with nutrinos again. Would there be a
Speaker 5: wave of distinguishing early in nutrinos from later?
Speaker 1: All right, thank you very much Gerard for this wonderful question.
Speaker 1: I love digging into the early universe, the cosmic egg.
Speaker 1: If you will.
Speaker 2: Oh, you are so good at making connections. I think
Speaker 2: someone should write a book about aliens that can read
Speaker 2: gravitational waves. Maybe somebody has yes.
Speaker 1: Yes, well, we can read gravitational waves, and we hope
Speaker 1: by doing so we can learn something about the history
Speaker 1: of the universe. So far, most of what we've learned
Speaker 1: about the very, very early universe comes from photons, and
Speaker 1: this is the light, the cosmic microwave background light that
Speaker 1: comes from a moment when the universe was very hot
Speaker 1: and very dense and went from being opaque like the
Speaker 1: center of the sun, to cooling enough that protons captured electrons.
Speaker 1: It became neutral hydrogen, which is transparent like hydrogen gas.
Speaker 1: So photons that were made just before that moment, instead
Speaker 1: of getting absorbed, flew free through the universe and are
Speaker 1: still around. Any light made before that time was immediately
Speaker 1: absorbed just like light made inside the sun is absorbed.
Speaker 1: So the earliest we're used to seeing the universe like
Speaker 1: concrete data from what happened a long time ago is
Speaker 1: thirteen point eight billion years ago plus three hundred and
Speaker 1: eighty thousand years. That's how long it took for the
Speaker 1: universe to cool enough to become transparent, and.
Speaker 2: As far as we can imagine, there is no way
Speaker 2: for light to tell us anything about what happened before
Speaker 2: that point.
Speaker 1: That's right, because none of those photons are still around.
Speaker 1: If they were, we could see them and we could
Speaker 1: learn stuff. They were photons made lots and lots of
Speaker 1: lots of them, but they're not around anymore. They were
Speaker 1: gobbled up by the atoms and the electrons.
Speaker 2: Oh, it's like when your great great grandparents are gone
Speaker 2: and they can't tell you their stories anymore exactly.
Speaker 1: But we would like to dig further, right, and before
Speaker 1: we dig further, just a note on the timeline. We'll
Speaker 1: define a moment, call it T equal zero, the first moment.
Speaker 1: We don't mean that that's the first moment of the universe.
Speaker 1: It's the first moment where our laws of physics apply
Speaker 1: at all, where we can think about this stuff where
Speaker 1: we can hypothesize what might have happened, because quantum mechanics
Speaker 1: and general relativity separate enough that we can just use
Speaker 1: one of them. Before that moment, things were so hot
Speaker 1: and so dense and so nasty we can't even think
Speaker 1: about them. We can't do calculations. We don't have a
Speaker 1: theory to explain it because we don't have quantum gravity,
Speaker 1: So we don't know what happened before T equals zero
Speaker 1: T equals zero, and then forwards we can think about theoretically,
Speaker 1: and the gap there is that we can think from
Speaker 1: T equal zero to three hundred and eighty thousand years afterwards,
Speaker 1: but we can't see yet before three hundred and eighty
Speaker 1: thousand years. Does that make sense?
Speaker 2: Yes? And is gravitational waves going to help us get
Speaker 2: back earlier?
Speaker 1: Yes, exactly, And so Gerard is asking about how we
Speaker 1: can see past that boundary, not with light but with
Speaker 1: other probes, and so he talks about two of them,
Speaker 1: gravitational waves and neutrinos. And the reason you could see
Speaker 1: earlier with gravitational waves and neutritos is that the universe
Speaker 1: was transparent to those earlier, and then it was transparent
Speaker 1: to light like many things in the universe are transparent
Speaker 1: to neutrinos that are not transparent to light, like the Earth.
Speaker 1: Photons will not fly through the Earth. The Earth is
Speaker 1: opaque to photons, but it's transparent to neutrinos. Neutrinos will
Speaker 1: fly right through it. So the fact that the universe
Speaker 1: was opaque to photons for the first three hundred eight
Speaker 1: thousand years doesn't mean it was opaque to neutrinos. In fact,
Speaker 1: it was transparent to neutrinos. The same story applies to
Speaker 1: gravitational waves. Gravitational waves pass through basically everything, and they
Speaker 1: scatter a little bit or they're affected by matter, But
Speaker 1: everything but black holes are transparent to gravitational waves. So
Speaker 1: they're an amazing way to look even earlier than light
Speaker 1: can show us what happened in the early universe. And
Speaker 1: Gerard's excellent question is cool, But aren't there neutrinos and
Speaker 1: gravitational waves everywhere? How could we tell the difference between
Speaker 1: a neutrino that came from the very early universe and
Speaker 1: one that was made eight minutes ago in the sun,
Speaker 1: or gravitational waves that are made from black holes? How
Speaker 1: do we know the difference between those and gravitational waves
Speaker 1: from the very early universe.
Speaker 2: You check their ideas.
Speaker 1: That was a joke, but it's actually basically the answer, right,
Speaker 1: So let's start with neutrinos because they're a little easier.
Speaker 1: Neutrinos decoupled from matter, meaning that they stopped really interacting
Speaker 1: with matter about a second after tea equal zero. So
Speaker 1: neutrinos do interact with matter. If it's very very dense,
Speaker 1: then even neutrinos will interact with it. But it only
Speaker 1: took about a second after that te equal zero moment
Speaker 1: for the universe to become dilute enough for neutrinos to
Speaker 1: just fly through and essentially ignore everything. So for the
Speaker 1: first second, neutrinos were absorbed, but that surface of last
Speaker 1: scattering the cosmic neutrino background comes from one second after
Speaker 1: tequal zero instead of three hundred and eighty thousand years,
Speaker 1: which is amazing. Yeah, and so like wow, we could
Speaker 1: see a lot of stuff we hadn't ever seen before.
Speaker 1: Super fun. Now, the issue is that these neutrinos are
Speaker 1: very very low energy, just like the cosmic microwave background
Speaker 1: light is very very red shifted. These neutrinos have been
Speaker 1: super duper red shifted down to low energy. Like the
Speaker 1: plasma that made the cosmic microwave background light was really
Speaker 1: really hot, and when those photons were made, they were
Speaker 1: very high energy, very short wavelength. But the universe has
Speaker 1: expanded since then, and when it expands, it also expands
Speaker 1: those photons and makes them super duper red, which is
Speaker 1: why it's often said that the CMB light is like
Speaker 1: light from a black body at like three degrees kelvin,
Speaker 1: because you'd have to be that cold now to emit
Speaker 1: photons at that wavelength, and the same things happen to neutrinos.
Speaker 1: Neutrinos from the Sun, for example, are like one to
Speaker 1: ten million electron bolts and energy. Neutrinos from supernova maybe
Speaker 1: twice that down to a few MeV. But the neutrinos
Speaker 1: from the very early universe are very very very low energy,
Speaker 1: which makes them very very challenging to see. Not impossible,
Speaker 1: but it means they're not going to interact as much
Speaker 1: as neutrinos with higher energy. So we have plans to
Speaker 1: see them, and we hope to see them. Current experiments
Speaker 1: that look for dark matter, for example, are very very
Speaker 1: sen to things that go bump in the night and
Speaker 1: they very recently become sensitive enough to see like the
Speaker 1: neutrino background, this neutrino fog that fills the universe, not
Speaker 1: from the early universe yet, but from like everything else
Speaker 1: that's emitting neutrinos. And we hope on one day to
Speaker 1: be sensitive enough to these cosmic neutrino background from the
Speaker 1: very early universe, but not yet, and we'll know that
Speaker 1: they're there because we'll see them at lower energy than
Speaker 1: basically anything else makes neutrinos.
Speaker 2: Am I remembering correctly that you told me it's hard
Speaker 2: to measure neutrino's period, Yes.
Speaker 1: Because they hardly interact. You build a big detector, and
Speaker 1: like one in a trillion or one in a quadrillion
Speaker 1: neutrinos that fly through your detector will interact with it.
Speaker 2: Oh man, Yeah, all right.
Speaker 1: The lower the energy, the more challenging it is. So yeah,
Speaker 1: it's hard.
Speaker 2: It's a good thing. There's so much money for science.
Speaker 1: Now. Gravitational waves are also an excellent source of information
Speaker 1: about the early universe, all for the same reason as neutrinos.
Speaker 1: Neutrinos hardly interact with matter because they only use the
Speaker 1: weak force, which is very, very weak gravitational waves only
Speaker 1: use gravity, which is even weaker than the weak force,
Speaker 1: and so they decouple from everything else in the universe
Speaker 1: almost immediately. Right, So using gravitational waves you can see
Speaker 1: even further back than one second after T equals zero.
Speaker 1: Amazing yes, But again they are also affected by redshift,
Speaker 1: and so these would be very very low frequency gravitational waves,
Speaker 1: very long wavelengths. Now, the gravitational waves that we're used
Speaker 1: to thinking about are the ones from like black holes
Speaker 1: that collide with each other, and before they do, they
Speaker 1: orbit each other and emit a huge amount of energy
Speaker 1: gravitational waves. Those are fairly high frequency, and we can
Speaker 1: see those with our detectors. And so those detectors like Lago,
Speaker 1: they can't see gravitational waves with really long wavelengths because
Speaker 1: they don't make any change on the scale of like
Speaker 1: the Earth. Even you need like a galaxy size detector
Speaker 1: to see really long wavelengths gravitational waves. Amazingly, humans have
Speaker 1: a galaxy size detector for gravitational waves. People have used pulsars,
Speaker 1: which are extraordinary neutron stars that rotate with extreme regularity,
Speaker 1: and by variations and their rotations, we can tell whether
Speaker 1: space between us, and the pulsar has been squeezed or stretched.
Speaker 1: In the last couple of years, we've even seen evidence
Speaker 1: of very long wavelength gravitational waves using pulsar timing arrays.
Speaker 1: Really an amazing piece of science. But even those might
Speaker 1: be too short wavelength to see the early universe gravitational
Speaker 1: waves because they're going to be extremely low frequency. The
Speaker 1: pulsar timing arrays probably are seeing like a general gravitational
Speaker 1: wave background from all sorts of black holes and acceleration.
Speaker 1: I mean, everything you do creates gravitational waves. You wave
Speaker 1: your hand in front of you, you're creating gravitational waves
Speaker 1: because any kind of acceleration is going to create them.
Speaker 1: So this is just like a gravitational wave noise through
Speaker 1: the universe. But the ones from the early universe will
Speaker 1: be unique because they won't have any specific source. They
Speaker 1: won't come from this black hole, from that black hole.
Speaker 1: They'll just fill the universe sort of the way the
Speaker 1: cosmic microwave background light will, and they'll be very broadly
Speaker 1: spread out across various frequencies. There'll be no big peak,
Speaker 1: no clear power structure. It'll be a very broad frequency signal.
Speaker 1: Even that will be very very hard to see, and
Speaker 1: so the way people hope to see gravitational waves from
Speaker 1: the early universe is not actually by seeing the gravitational
Speaker 1: waves directly, but instead by seeing those gravitational waves affect
Speaker 1: the cosmic microwave background light. So that light we talked
Speaker 1: about earlier that was made three hundred and eighty thousand
Speaker 1: years after T equals zero. When it was made, it
Speaker 1: was affected by these gravitational waves that were already around
Speaker 1: from the early universe. Because it gives that light a
Speaker 1: special twist. Remember that light is a ripple in the
Speaker 1: electromagnetic field, and the field is just like numbers in
Speaker 1: space and the Higgs fields, for example, it's just like
Speaker 1: a number at every location in space. But light is
Speaker 1: a vector field, which means it's not just one number,
Speaker 1: it's like three numbers. Or equivalently, you can think about
Speaker 1: it like a little arrow with a length and a
Speaker 1: direction and every point in space. And as light moves,
Speaker 1: those arrows ripple, and it can do more than just move,
Speaker 1: it can also spin right. So this is what we
Speaker 1: call polarization of light. The same way that like if
Speaker 1: you have a jump rope, you can shake it up
Speaker 1: and down, or you can shake it sideways, or you
Speaker 1: can shake it in like a swirly motion. This different
Speaker 1: way for waves to propagate along that string. Same thing
Speaker 1: for photons, and mathematically you can decompose them into what
Speaker 1: are called emodes that are radial patterns and B modes
Speaker 1: that are like twisting swirling patterns. Gravitational waves are the
Speaker 1: only way we know to give B mode polarization to
Speaker 1: the CMB light. There's something about how those gravitational waves
Speaker 1: are stretching and squeezing the space while light is being
Speaker 1: formed that gives it those B modes. Other gravitational waves
Speaker 1: like black hole collisions late in the universe cannot give
Speaker 1: like a broad pattern of B mode polarization. So if
Speaker 1: you look at the cosmic microwave background light and you
Speaker 1: measure its polarization and you see B modes, that would
Speaker 1: be fascinating information about the early universe. And a few
Speaker 1: years ago an experiment called BICEP two claimed to have
Speaker 1: discovered it. Huge news rocked the science community until it
Speaker 1: turned out that they made a mistake in their analysis
Speaker 1: and they were relying on data from another experiment to
Speaker 1: remove the effect of dust, but they didn't actually have
Speaker 1: that data from that experiment. They took a screenshot of
Speaker 1: a PowerPoint slide and misinterpreted it and used that as
Speaker 1: the basis for their analysis. And they came up with
Speaker 1: these big claims and had to walk it back. Very embarrassing.
Speaker 1: Brian King wrote a book about it called Losing the
Speaker 1: Nobel Prize. It's a fun.
Speaker 2: Story, not for the people involved.
Speaker 1: He tells it with a smile on his face.
Speaker 2: I think was Brian Keating involved?
Speaker 1: Oh yes, deeply. No, he's not embarrassing other people. He's
Speaker 1: owning up to his own mistakes. Oh okay, their own mistakes. Anyway,
Speaker 1: we have not yet seen that, So Gerard, that's how
Speaker 1: we might differentiate early universe neutrinos from later universe neutrinos.
Speaker 1: Or we might spot evidence for early universe gravitational waves,
Speaker 1: either of which could tell us amazing things about what
Speaker 1: happened in the first few moments after T equal zero,
Speaker 1: none of which could tell us about what happened before
Speaker 1: T equal zero. That's a whole other question.
Speaker 2: Mark, which one do you think is more likely to
Speaker 2: tell us something first?
Speaker 1: Oh? Wow, great question. I think we probably will figure
Speaker 1: out this be mode polarization of the CMB before we
Speaker 1: figure out how to see these very low energy neutrinos.
Speaker 1: But both communities are filled with super smart people working
Speaker 1: hard and coming up with clever ideas that I could
Speaker 1: never anticipate.
Speaker 2: So we'll see, okay, and we'll see what Gerard thinks
Speaker 2: about the answer.
Speaker 1: Gerard listened to our answer and wrote back to me,
Speaker 1: and he preferred to send a written response. I'll read
Speaker 1: it for you now. Here's his reply quote. I didn't
Speaker 1: know the gravitational waves would be like photons and be
Speaker 1: stretched by their long journey through expanding space, lowering their frequency.
Speaker 1: The idea of indirectly detecting them by their effect on
Speaker 1: the CMB photon polarization is ingenious. I wonder how precise
Speaker 1: the measurements would need to be before scientists could reconstruct
Speaker 1: any earlier than CMB features. Nor did I know that
Speaker 1: neutrinos would also lose energy through stretching space. I guess
Speaker 1: I've always thought of them as particles, but we can
Speaker 1: think of them as waves and a field. I am
Speaker 1: always fascinated when science builds on an idea by extending
Speaker 1: it to another domain, as in this example. Light waves stretch,
Speaker 1: so gravity waves should stretch too. A further question evoked
Speaker 1: by your description in the hot dense early universe, what
Speaker 1: kind of structure might it have had. Would high energy
Speaker 1: simply prevent anything from coalescing. I'm sure we will be
Speaker 1: surprised by something no one has even imagined. Thank you
Speaker 1: very much for that response, Giard. Let me answer some
Speaker 1: of your follow up questions. Yes, neutrinos also lose energy
Speaker 1: as they move through space because space is stretching. This
Speaker 1: is a great example of the non conservation of energy
Speaker 1: in an expanding universe. It applies to everything, particles and waves.
Speaker 1: Particles in the end are really just ripples in quantum fields,
Speaker 1: and they are affected by the expanding universe. You also ask,
Speaker 1: what was the structure like in the hot dense early universe.
Speaker 1: It's a great question, and structure is a tough way
Speaker 1: to think about it, because in the very early universe
Speaker 1: you have these quantum fields that are filled with frothing energy.
Speaker 1: It's not like now when you have isolated energy and
Speaker 1: you can think about a little ripple in the field
Speaker 1: as a particle. It's like taking a thousand drops and
Speaker 1: putting them in a glass. You don't really think about
Speaker 1: drops anymore. Now you think about other emerging forms of
Speaker 1: that water waves and other sorts of things. And so
Speaker 1: what's going to happen the very early universe is that
Speaker 1: those quantum fields will be filled with energy and we'll
Speaker 1: get all sorts of weird bizarre effects. Thank you very
Speaker 1: much to these listeners for sending in your questions, and
Speaker 1: to everybody out there who drives this podcast forward with
Speaker 1: your personal curiosity about the universe.
Speaker 2: Please send us your questions at questions at danieland Kelly
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Speaker 1: Come for the science, stay for the pooh on.
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