Trapped on this little rock. We are desperate to extend our understanding beyond our cosmic jail cell without visiting any other planets or stars. We want to use our ingenuity to figure out how things work in the rest of the Solar System, in the heart of the Sun, or in distant stars. Until recently, we didn't know the answers to basic questions about the rest of the universe, questions like what elements is it made out of? Is the Sun made out of the same mixture of atoms as
the Earth? What about the rest of the universe. Today we'll tell you the story of how we figured this all out. It features naked Greeks running down the street, Scottish people climbing mountains, and a clever young woman pushing back against the established but mistaken orthodoxy and not getting
credit for it until recently. So we're going to do our bit to set the record straight and to show you how clever little apes can actually learn about the recipe for making a universe stuck in the confines of our little planet. Welcome to Daniel and Kelly's Extraordinary Elemental Universe.
Hello, I'm Kelly water Smith. I study parasites and space, and I'm super excited to learn about another woman that we haven't heard anywhere near enough about today.
Hi, I'm Daniel. I'm a particle physicist, and I study what the universe is made out of. But I'm also curious what I'm made out of.
Oh, you know, biologists have been working on that for a while. What is your question in particular?
Well, you know, people tell me that I am what I eat, which means I'm mostly dinner.
I guess, Oh that's right, because you only eat dinner. Yeah, exactly, what did you have for dinner last night? What are you? What should I expect?
Last night? We had a dinner party, actually, so we went a little fancy. We made miso honey chicken. We made asparagus and scallions with barrata. We made a very fancy salad. I made a lemon butter almond tart.
Wow.
Yeah it was good.
That's amazing. Okay, But so the main part of the dish was chicken. So I'm gonna expect you to squawk about physics today.
Oh and a couple of loaves of sour dough bread.
Of course, Oh fantastic.
You gotta have your carb. So yes, I'm chicken and bread today. I guess, all.
Right, well, don't be sour about the information that we're going to be sharing. So my question for you today. So there was this recent result that maybe there's indirect evidence of life in the Solar System, and I was just wondering if you had to put a bet on it, let's say one hundred bucks, and you were betting, yes, there are microbes somewhere in our solar system, or no.
In our solar system or in our galaxy.
In our solar system, in our solar system, you know, in lava tubes on Mars, in the oceans of Enceladus. What do you think? What would you put the odds on for or whether or not there are microbes in our universe?
Oh wow, put a number on something we can't possibly know and then risk money on it.
It's not a ton of money, but no.
I like that. I like framing these as gambling questions because it really makes you decide on like how much money you'd be willing to lose. I think I put the odds of there being alien microbes that is not derived from Earth and like you know, somehow kicked off via an asteroid somewhere in our solar system independently evolved unique apiogenesis somewhere, like, you know, one in a million. Maybe.
I think it's probably pretty unlikely somewhere in the galaxy, though, I put it like ninety eight percent.
Whoa, yeah, well, how many solar systems are in our galaxy.
There's hundreds of billions of stars in the galaxy and so many planets around the stars, So I just feel like that number is so big.
Yeah, those odds sound pretty good.
Yeah, are you gonna take my bet?
Ah?
Ooh, the rubber hits the road people.
That's right, that's right. Can you tell I came up with this question right before I hit record. I don't know, you know, it wouldn't absolutely shock me if they found microbes on Mars, given its wet past, or like evidence of past microbes or something, and so I, uh, yeah, I'll take your bet. I'll take the opposite.
I wouldn't wait, does that mean I owe you one hundred million dollars if you find microbes on Mars?
Oh?
Oh uh no, let's just do let's forget odds. Let's just do one hundred bucks if you're right, one hundred bucks if I'm right.
Oh, but then I'm betting against aliens. I don't want to ever bet against aliens. I'm rooting for aliens. I don't want to have a conflict of interest where I hope there aren't aliens. So then I get a hundred bucks from Kelly.
I know this is difficult for you, but but we're just talking about microbes.
Yeah, that's true.
So the microbes that will teach you physics, you're not or sorry, the alien that will teach you physics, you're not betting against them.
Okay, so all.
Right, don't get sour on me here, Daniel. We're moving on. Okay.
Today we're not talking about what's alive on Mars or in the oceans of Europa, or what Daniel aid for dinner. We're talking about what the whole universe is made out of, what building blocks, what elemental lego bricks are used to put our cosmos together.
And how the heck did we figure that out, especially when the stuff is not on Earth?
Yeah, exactly, and we've never left Earth asterisk. We really did go to the Moon, but kind of counts as part of Earth.
Okay, but that definitely wasn't fake in it just to be clear, just to be c I did talk to a friend the other day who was like, and I know the moon landing wasn't real, and I was like, oh that was. Every once in a while you have one of those moments where you're like, that's I did. I didn't expect that. What do I say now?
All right?
Anyway, so let's talk to our audience, who almost certainly believes that we actually landed on the moon, and ask them how do we know what the universe is made of?
If you would like to contribute your voice for future segments on the podcast, please don't be shy right to us to questions at Danielankelly dot org. We really really love hearing from you. I think we know what the universe is mde of? Do you just spectroscopy?
I don't think we definitively know what it's made of, but we probably speculated.
I think scientists can extrapolate from what's in the earth.
Lensing likes spectrums and extrapolation from what's immediately around us. I don't think we do.
We may live in a simulation, or that we may actually exist in a two dimensional universe projected onto a three D hologram. So when you get right down to it. The truth is nobody probably knows.
Right different observational scientific techniques to try and understand the different components of it to the best we are able and make everything else up from there spectroscopy.
Wait, do we know.
That we are the universe?
Yes, the universe is our way and out there. But if we can know the molecules that make up you and me and apples and mountains and porcupines and all the things we know of you're on Earth, that tells us what the universe is made of.
To spectrocity and gravity.
We know by spectroscopy, a lot of guessing followed by a lot of testing.
The spectral analysis. We're not sure what dark matter is, and I seem to remember something about quantum foam, so maybe we don't really know.
Data collective from ground and space based telescopes.
I guess the bits that aren't dark matter either in midlight so we can look at the spectrum, or they have enough gravity to bend light.
Easy.
We take one piece of the universe, smash it into another piece of the universe and see what comes up.
With a lot.
I love the person who said do we know, because actually, if it's an episode you and I are doing. There's a pretty good chance the answer is we don't know, So throwing it back at us is a pretty good guess.
Yeah, that is a great answer. I also like the answers that frame the question much more broadly. When I wrote this, I was thinking about what elements the universe is made out of, like the atomic matter that you know makes up the sun and the stars, and the gas and the dust and the wolverines and the ferrets and all that kind of stuff. I wasn't yes, exactly, I wasn't thinking more broadly, like dark matter, dark energy. So, yeah, these are good answers.
Your question was underspecified.
It was yes, I should have said, how do we know what elements the universe is made out of?
That's right, We still got some fantastic answers. So what let's start with how we figured out what elements the Earth is made out of? What tools do we use for that here?
Yeah, the story of figuring out what the universe is made out of goes like, first, let's figure out what the stuff under our feet and what we are made out of, and then let's think about whether we can extrapolate that to the rest of the universe because unfortunately we still can't go visit most of the universe. So in terms of like lab science and like getting our fingers literally dirty, the Earth is the only place we
have to explore. And it's really cool story how we figured out what the Earth is made out of it because even though it's under our feet, we can't go like explore very deep. We haven't drilled very far into the earth, so a lot of it is still indirect evidence that we put together by clever humans figuring out ways to basically see what's inaccessible.
Well not only getting to the center of the Earth, but just being able to like pick up a handful of dirt and being like, what kind of elements are in this handful of dirt. That's amazing to.
Me as well exactly, and this requires a lot of you know, chemistry, understanding what elements were there and their properties and their mixture, and so early on in the last few hundred years, when people are trying to figure out, like, hey, what is the Earth made out of they're basically three big questions that were asking. One is like, what is the density of the earth? Can we figure that out? Because if we know the density of the Earth. We know a lot about what it could be made out
of and what it couldn't. Like if you measure the density of the earth and you discover, oh, it has the density of whipped then you know it's not mostly ironed, right, Whereas if you measure the density the earth and it's like bang on nickel, then you're like, wow, it's probably most any nickel. Right. And so measuring the density of the earth is an important question. But this isn't easy, right, Like,
how do you measure the density of something? Well, here on Earth, You like put it in water and see if it floats, or you measure its mass and you measure its volume, right, the famous Eureka moment of figuring out whether the crown is made of gold by measuring its volume by dipping it in water, et cetera, et cetera.
This is apparently not a particularly famous Eureka moment because I've never heard that story.
Oh this is a really fun Mas story. Archimedes was asked to determine whether the king's crown was made of pure gold or not, so he said, well, I'll measure its density, because if it's density lines up with gold, then we know it's gold, and if it's got something else in it, it'll come out a different number. Measure the density requires them in the mass and the volume.
Mass not so hard, Volume not so hard. If you have a simple object like a sphere or a cube, how do you measure very precisely the volume of a really complex shape like a crown turns out to be really challenging. So Archimedies is puzzling over this as he's slipping into the bath at the end of his day. And as he gets into the bath, he sees the water level rise, and he's like, oh, now, I understand how to measure the volume. You just dip it in
water and you measure how much it rises. And the story goes, probably apocryphally, that he left out of the baths and naked down the streets of Siracuse or Syracuse, shouting eureka, eureka. And anyway, that's your famous ancient Greek nude story for the day.
Amazing. We should have more of those, But okay, I hadn't heard that story. Thanks for sharing.
But in the case of the earth, you can't just dip the earth in water, right, you know, we don't have like a bath of water that we could dip it in. So what we need to do is measure the gravitational pull of the Earth. Right, if you knew the total mass and the volume, then you would have the density and the volume is pretty straightforward because the Earth is a spear. So if you could figure out
the mass, then you'd know the answer. But figuring out the mass is a little bit complicated because to do that you have to measure the pull of gravity, and to do that you have to know so the constant in the gravitational formula Newton's gravitational formula says that the pole of gravity depends on two masses and on this number in between them. And for a long time we
didn't know very precisely that number. And so to get that number you need like two large known masses that you can measure their gravitational pole between them, so you can get that number, and then you can measure gravity in the Earth and finally figure out what is the mass of the Earth.
That sounds complicated, and so how did they find two massive objects to do this with?
Yeah, they have to be massive objects because gravity is super duper weak. Right, you can't measure the gravitational pole between like two pennies in your hand. There is a gravitational pole there, but it's unmeasurable, especially like one hundred two hundred years ago. So what they did is they
found a mountain. There's this mountain in Scotland called she Holand, and in the seventeen seventies that decided this was a good candidate for measuring the gravitational constant because it's isolated from lots of other stuff. So it's like a single mountain on a plane, far away from other stuff, and it's kind of symmetrical. It's like not hard to measure its volume pretty accurately. It's not like the crown of the King of Syracuse, right, it's like kind of a simple shape.
Okay, so there's one massive object.
Yeah. So then they took a pendulum and they held it near the mountain and they measured weather deviated from straight down, and the deviation of the pendulum from straight down as you get closer and further from the mountain is a measure of the gravitational pull of the mountain on the pendulum. Right. So here you're like actually measuring gravity between two things, neither of which are the Earth
that works, actually does work. This was the first measurement of the gravitational constant, and it required actually a lot of work by surveyors, like converting the shape of the mountain into prisms so they could calculate the volume very accurately. It was a huge project, and that allowed them to measure the gravitational constant and then calculate the density of the Earth. And they discovered that the day to the Earth is like almost twice the density of that mountain.
So this technique sounds incredibly complicated. How close did they get to the value that we believe it is today?
They're within twenty percent.
Nice.
Yeah, and that's pretty good, you know for dudes in silly hats with pendulums, you know, walking around mountains like these clever apes are figuring stuff out.
Yeah, no, that's amazing.
You know.
I feel like if you took five biologists in our field clothes or whatever and you were like figure out the density of the Earth, I'd feel pretty good if we got within twenty percent. That's pretty solid.
And that is really revealing at the time, because people had no idea what was inside the earth? Is it like a hall of core? The way like King Kong and Godzilla are fighting down there? Is it mostly made of water? People really just didn't know. And this in a single measurement tells you a lot about what the Earth could and couldn't be made out of. And then there's a really amazing history of the measurements of the
gravitational constant, which got more and more precise. Eventually people used torsion experiments like balls hanging on strings that are very sensitive and measured their deflection as it got closer together Cavendish et cetera. There's a whole fun history there. People made these measurements very precisely to within less than one percent. So now we have a very accurate estimate of the Earth's density.
That is incredible. Okay, so we have an estimate of the density, what did it lead us to believe? That most of the Earth is made of yees?
So the density of the Earth is more dense than the mountain, which is a hint that there's like heavy stuff in there. Right, it can't just be rock. It's not water, right. Water is much less dense than the Earth, and so that suggests that there's a dense core, that there's something heavy in there. And we now know, of course, there's a lot of nickel and iron in the core of the Earth. And this was our first hint about what was down there.
Not a giant open sphere with like dinosaurs hiding in it, because that would have been cooler, Not.
A vast chasm filled with swarming parasites, for example. For most people, that's a nightmare. For you, that's heaven.
Now, I'm so bummed out to know that this is the Earth I exist on, but it could have been so much better.
And people attack this question of what is the Earth made at of? From other angles. We have density, but the next angle was age. People were trying to estimate, like how old is the Earth, because understanding how old the Earth is gives you clues about how it's formed and therefore what it's made out of. And we already knew at this point a couple hundred years ago that
the Earth was probably pretty old. And the biggest clue there was like Darwin, Darwin should us that life took a while to come together, you know, this process of evolution was slow, so we had a sense that the Earth was like cosmically old, not thousands of years, but people didn't really know is that like millions, hundreds of millions, billions, even it was still an open question a couple hundred years ago.
Now, I love when Darwin gets credit for stuff, but I don't actually know that he should get credit for showing us that life was ancient. I mean he was. He came up with the theory of natural selection to explain how like one form sort of morphs into another. But I think there were geologists already working on this question and finding fossils and postulating Earth has been around for a long time and stuff has been gone. But anyway,
Darwin awesome. Maybe he just got some credit for something he didn't deserve, but biologist getting credit for stuff is always awesome, So let's move on.
Yeah, that's fair, And I'm about to give some credit to some chemists to hold onto your hats.
Oh oh boy, I'm gonna get sour.
People were wondering, like, how long would it take the Earth to cool if you have a like a ball of molten stuff sitting in space, how quickly does it form a crust that you can like walk around on. And Lord Kelvin of you know, Kelvin temperature trying to use this to calculate an approximate age for the Earth. He was thinking, like, you have a big ball of lava basically or magma in space, how quickly can you
form a crust? And he ignored a bunch of stuff like he didn't understand that there was convection inside the Earth that hot stuff rises, and so you keep getting this like refresher of hot stuff from the core up to the surface. He also didn't know about radioactive decay, which helps heat the Earth, because he didn't know about radiation and quantum mechanics and all that stuff. Nobody had
discovered that yet. So in Kelvin's calculation, he missed a lot of the pieces there, and he came up with a range of like twenty to four hundred million years, which is like low by more than a factor of ten because of these pieces he missed. But you know, he's sort of getting up there into the right ballpark.
Yeah. And so at the time was the predominant view, the Christian view, that the Earth was like what two or five thousand years old or something. I think postulating millions of years could have really like put you in the crosshairs. But how common was the idea that it was just a couple thousand years old at that point.
I think that most educated and scientific people didn't accept the young Earth hypothesis. Even back then, there was a sense, as you said, from geology that things were taking a long time. But then people were trying to make a
specific They're like, can we get an actual number? And so I love when people in history are like, well, let's try to sit down and get a calculation of this, and you know they're wildly off, but getting that first estimate is a big step forward, and then you can refine it and think about what you're missing, And like, this is the process of science, right, First do the dumbest thing and then improve it. It's innerative, right.
I feel like that's kind of where we are with the Drake equation, Like we're starting to hone in on the things that matter, and exercises like this help you think through stuff.
Yeah, exactly. And now, of course we know a lot more precisely how old the Earth.
Is, and when we get back from the break, we're going to hear all about that, all right. So Dan was just telling us that Kelvin was thinking about how long it would take a molten earth to cool to get our initial estimates for the age of the Earth, and we ended up with somewhere between twenty and four hundred million years. What was the next step that we took to get more accurate.
More accurate understanding the age of the Earth, which again helps you understand what it's made out of. It came in this century when we understood that rocks have little clocks in them, and you can use that to figure out when the rock cooled, so you can figure out like when something was formed, and these clocks actually depend on quantum mechanics. There are these little crystals called zircon crystals that help you understand how old a.
Rock is, and what is it about the zircon crystals and why isn't there a watch company called Zircon.
Zircon are really weird little crystals that hate lead, like they will not allow lead to form within the crystal, but they will take uranium. So when you get a zircon crystal freshly formed, it has no lead in it, but it does have uranium in it, and then uranium while it's inside the crystal decays naturally into lead at a rate we know. So if you pick up a random zircon crystal and it has no lead in it. You know, this thing is zero years old. It's a
baby crystal. If you pick up a zircon crystal and it's got no uranium and it's pure lead, you're like, wow, this thing is old because uranium is slow at decaying. So every zircon crystal is like a little clock that tells you how long it's been since it's formed.
That's amazing.
And there's a whole incredible story about a Chemisty Patterson, who figured this out and then started measuring the lead and stuff. And he's actually the guy who discovered, oh my gosh, this lead everywhere in our environment because of lead in gasoline, and he led the crusade to get lead out of gasoline because he was realizing, wow, we have poisoned our environment. He was trying to make a clean room to measure these things really precisely, and he
just could not get a lead free environment. Wow. And so anyway, another chemist who saved us all.
When it's so hard to know, like what study you're doing is going to be the thing that gives you important information for humans, like what sort of off ramps you're going to end up on?
And so another argument for funding basic science people. But you never know what you're going to discuss important and so because of his work, we discovered that the Earth is like four and a half billion years old, meaning that the oldest rocks we have cooled around four and a half billion years ago.
Oh my gosh. And that's pretty close to our current estimate, isn't it.
Yeah, yeah, exactly.
That's amazing.
And so now understanding that the Earth is really old gives you more information to figure out the puzzle of like, well, what's it made out of? Because you want to understand like how old is the Earth, how quickly did it cool? Well, to know that you have to know like where's the heat coming from? Where are the layers inside the earth? You need a complete model for where stuff is within the earth, and that's why you need this last piece.
So we have the age, we have the density. Next thing we need is the structure of the earth to know like how a stuff organized within the earth. And that's where seismology comes in to give us that last piece.
Oh so we're getting away from chemistry, whew. Back to the rock people.
Of seismology, of course, it's a study of earthquakes and earthquakes are cool. I mean, they're devastating and tragic, but they also do something really useful, which is that they ring the Earth like a bell. And so when there's an earthquake, these seismic waves pass through the Earth and they give you a glimp as to what's going on inside the Earth because these waves bounce off of like interfaces. If the whole Earth was just like one solid rock,
then the waves would travel smoothly through it. But if there's an interface where you go from like one kind of rock to another, or you go from like nickel to iron, or liquid to not liquid, then the waves bounce back at that surface and you create complicated patterns. And so by reading the waves that reflect on the surface, you can reconstruct what was going on inside the Earth. It's sort of like a sonogram, right, or an ultrasound.
That that is absolutely amazing. And just like parents like to brag about their kids, I like to brag about the human species sometimes, and just note that we've measured Mars quakes and it is just amazing to me that we've been able to like get equipment there that could then measure this happening on another planet in our solar system. So anyway, okay, amazing, all right, so now you can
you can do this. And so did we know at the time enough to figure out so like you know, if you hit water and you had been going through nickel, you're like, oh, some thing is different. How much work did we have to do to understand what we were seeing? Like it seems like there's a big difference between saying something changed or something changed and I understand what that means.
Yeah, the crucial thing there is having enough instrumented points, like you need to reconstruct these waves all across the Earth, because like a wave from an earthquake in California will propagate down into the Earth and reflect back, but doesn't come straight back to California and like goes to Japan or Hawaii or somewhere else, and it also continues through the Earth, and the different parts of the wave is like s waves and pea waves, and different frequencies reflect
at different rates. And so what you really need to do is measure all the different frequencies as many places as you can around the Earth to get this complete picture.
So that's what's crucial is having this like global network of seismic grass and yeah, on Mars they have a few of these, but wow, if they had more, they could really get pictures of these marsquakes and understand what's going on inside the Martian core, which is a whole other fascinating question about like whether there is still motion inside the core or whether it's totally frozen. And of course that tells us a lot about like the history of Mars and maybe did it have a magnetic field
and could it protect life from cosmic radiation? But anyway, that's off track. Coming back to Earth. We now have an idea of what the structure of the Earth is, where the density of the Earth is, and how long it's been cooling, and altogether that gives us a model for what's going on inside the Earth without drilling down and going to visit. This is enough information to constrain our model and tell us what it has to be made out of, each of the layers and their composition.
And so this is how we figured out that the core is mostly nickel and lead, not lead iron.
Nickel and iron and iron got it. And so it turns out that the Earth is like thirty two percent iron thirty percent oxygen, which blows my mind. Most of it's like absorbed into rock. Fifteen percent silicon, fourteen percent magnesium, three percent sulfur, two percent nickel, and the rest of a lot of exciting trace elements. But that's the majority of what the Earth is made out of.
Well, okay, so that's not a lot of nickel, So with mostly iron and oxygen.
Mostly iron and oxygen, huh, yeah, exactly. There's a lot of oxygen in the Earth because rocks gobble up oxygen. Like in the early days of the Earth, when you be produced oxygen in the atmosphere, most of it was just absorbed by rocks. You have to like satisfy all the rocks before you could leave oxygen in the atmosphere for life.
I'm glad there was some leftover for us.
Yeah, because oxygen is so reactive. So that gives us a sense for what our scoop of the universe is made out of, right, iron, oxygen, silicon, magnesium. But then of course we're wondering, like what's the rest of the universe made out of? Is it the same? Is it different? What's the Sun made out of? And this is a question people had for a long time, like what is the Sun made out of how does it work, what's going on inside of it, and what fuels it?
Yeah, because I think all of the techniques that we've talked about require you to be on the surface of that planet to collect the data, so you probably need a whole different set of tools to figure out what's happening on the Sun.
Right, Yeah, exactly, And of course we can't go visit the Sun. We had the Parker Solar Probe, which came close to the Sun, but of course didn't go into the Sun. And for a long time we were trying to figure this out, of course, just from Earth and trying to understand what it could be made out of. And we can know some things without going to visit
the Sun. Right. We can get a sense of the mass of the Sun if we know the gravitational constant and we know Earth's mass, and then we can calculate from the Earth's orbit how strong the Sun's gravity has to be to keep us in orbit. So already we know the Sun's mass, right, which gives us a lot of clues, but we don't know much about the density and what's going on inside there.
Or the age. Right. We decided we needed to know age too, Yeah.
And another crucial hint is while the Sun is very bright, so something going on inside the Sun producing that energy, and it's like an incredible amount of energy. I don't think people really appreciate how much energy is being put out by the Sun, Like we capture the tiniest, tiniest little fraction of it. But the Sun's total power outage is four times ten to the twenty six watts. Wow, which is like ten quadrillion times the amount of power
released by the most energetic power plants ever constructed on Earth. Wow, it's just we are sipping from an ocean of energy here. That's just like being blasted out into space.
And it powers our whole planet.
It really does. And people wondered for a long time like what's producing all that energy? How long has the Sun been burning? They're wondering like is there something up there that's on fire? And that of course is a clue to what the Sun might be made out of. People were wondering like is it made at the same stuff as the Earth somehow? Is it made out of something different? So re enter Lord Kelvin, King of approximate initial terrible estimates of what the universe is.
Made out of would I. I guess I'd be happy if I was known for anything, but I do feel like I wouldn't really want to be known for that in particular.
No, I love that situation, like getting the first bited some apples, some fascinating question nobody's tackled. Those are the funnest ones I'm jealous of, Like the Greeks and the Sumerians and the ancient Chinese and the Mayans who got to think about these questions that nobody had worked on before, right, like the answer could have been anything anyway. I think that's super exciting.
One of my favorite stories along this line is there was a guy who studied vaccines. His name was Sir Wright w R I g h T. And he every time got something important incorrect, and he ended up becoming known as Sir not quite right and all right anyway, tangent complete. Where were we?
So? Lord Kelvin is trying to understand what's the sun man out of And first he thought, well, what if it's just like fuel. You know, we have fire here on Earth. If the Sun is a huge ball of fuel that's chemically burning, could that explain what we're seeing, you know? And that would tell you like, oh, maybe the Sun is a huge ball of gasoline basically or
a curacy no runout. So if you do the calculation, giving your knowledge the mass of the sun, chemical burning can only produce that much power for like tens of thousands of years, not for billions of years. Why because chemical burning is very inefficient, like most of the energy in mass is not released when you just like change the chemical state from one to another. Whereas you know, fusion is what's happening inside the Sun, and that's much
more efficient, much more effective release of energy. You get a lot more energy out. And so if you want to produce all the energy that the Sun is producing and do it for billions of years, you can't rely on like burning kerosene or some similar chemical process because there just isn't enough mass in the Sun to keep that going for billions of years.
All right, It's not logs on a fire. So how do they figure out what it was?
Well, people went down other rabbit holes also, which is really fun. They were thinking, maybe the Sun isn't limited to its current mass. Maybe this is some source of mass? Is it like gobbling up stuff from the Solar system? I mean early days you can think of all sorts of crazy ideas, right, Yeah, but that was ruled out pretty quickly because it would require an enormous amount of mass, Like you'd need a sun to refuel the Sun every ten thousand years, so it's like the Sun is not
eating other stars every day. That would leave a huge imprint on the orbits of planets and stuff like that, so that was ruled out. Another thought people had is maybe the Sun is like contracting gravitationally and converting that gravitational potential energy somehow into heat. And this is sort of on the right track, but if you don't understand fusion, you don't have the final piece there. And this would only few the star for like tens of millions of years.
And this is actually what's happening to neutron stars and white dwarves that are not undergoing fusion. They're just like being compressed and kept hot by gravity.
Was this Kelvin's idea? All these because it matches up with his other All of these were Kelvins.
These are Calvin's ideas. Yeah, this is Kelvin, like, you know, smoking whatever he was smoking and thinking about the universe and coming up with dumbers Okay, I love it. I'm a fan of Kelvin.
Yeah, he sounds like a fun guy, and I think it would have been fun to read your theories about this kind of stuff. And then I could have called you not quite rights.
In, Oh nice, Daniel wrongs and Daniel first a terrible approximation.
Of the answer that doesn't roll off the tone quite as nicely. But okay, what else did Calvin think?
So that's where the mystery stood until around the early nineteen hundreds, And at that point people sort of naturally assumed that the Sun must be made of the same stuff as the Earth. They were like, hey, the solar system comes together, stuff is formed. Why wouldn't the Sun be made of the same stuff as the Earth? And you know, I think this goes a long way to pointing out how often we accept ideas in science because
they make sense to us without really interrogating them. You know, what seems natural doesn't always get as many questions as what seems weird, And so later on, one hundred years later, when something else seems natural, we might wonder like, huh, how could they accept that? But at the time it was the most natural explanation, And now is the time to enter the major villain of this story, Henry Russell.
In nineteen fourteen, he wrote, if the Earth's crust should be raised to the temperature of the Sun's atmosphere, it would give a very similar absorption spectrum. The spectrum of the Sun and other stars are similar, so it appears that the relative abundance of elements in the universe was like that in the Earth's crust. So he's saying the Sun is made out of the same stuff as the Earth, and if you heat it up the Earth it would glow just like the Sun.
So that sounds wrong, but not villainous. What are we going to get to more? Or do you just really thought this idea was dumb.
That's not his villainy, that was just foreshadowing.
Oh okay, let's take a break and when we come back, we'll find out what made Russell villainous. All right, Daniel, I'm on pins and needles. Let's get to the story of why Russell was such a villain.
So Russell was on the right track and trying to understand what the Sun is made out of, and many of our listeners gave this answer. The answer is spectroscopy, Like if you can't go there. What can you do to understand what something is made out of? And it's similar to what you might do on Earth as you mentioned, like if you needed to know what is a scoop of dirt made out of, you might try to separate into components and then you might heat them up and
look at the light that they emit. Because different atoms emit at different wavelengths. Right, every atom has different energy levels. The electrons can be on those energy levels, but not between them. If you heat it up, the electrons go up energy levels. If you let it cool down, the electrons go down energy levels and emit photons. The energy of those photons matches the energy difference between those energy levels and tells you what is the difference between those
energy levels. And every atom has a different set of energies, so every atom has a different spectrum. So you take a gas of random stuff, you don't know what it is, you heat it up, you look at the energy levels. You can figure out what it's made out of and what the relative contributions are. You're like, oh, there's a little I see hydrogen in here, I see helium here, I see lithium or magnesium right, it's an amazing way
to tell what Earth is made out of. So, in terms of the general approach to the listeners and the villain of today's episode, Henry Russell, are on the right track. The spectroscopy is the way to go.
He didn't develop spectroscopy, right, he just applied it incorrectly.
That's right. He didn't develop spectroscopy. And you notice in his quote he says if the Earth's crust should be raised, it would give a very similar absorption spectrum. And so he's sort of speculating here, right, And the problem is that this wasn't as easy as we describe it. There was an important complexifying factor here, which is ionization. And so for example, you might think, well, why don't they just look at the light from the Sun and you use that to figure out what the Sun is made of?
Boom boom boom. Done right. Well, the problem is the atmosphere of the Sun is complicated, and there's one more factor we didn't describe, which is that the atmosphere is ionized. Like sometimes these gases in the Sun's atmosphere gets so much energy they lose electrons. It's not just like, oh, you've got oxygen and has all of its electrons and they're going up and down and emitting photons can tell
it's oxygen. Sometimes those electrons are lost, right, and when an atom gets ionized, its energy levels shift a little bit. Because it's a big complicated thing, and so the spectrum you expect from a star depends on how many electrons are around those nuclei, which depends a little bit on the temperature of the gas. So it turns out to be kind of a complex problem.
So does that mean that the spectroscopy results from the sun were wrong? And he didn't realize that, and that was the main problem.
The spectroscopy results from the Sun. Nobody could understand yet. They were like, hmm, this is weird. We don't understand these lines. They look different from what we expect. But Russell was convinced anyway that it was made of the same stuff of the Earth. He believed that it was natural. To him. He was like, I'm sure this is just some detail. We'll figure this out. And so now enter the heroine of this episode. Yes, Cecilia Pain. Cecilia Pain
is the one who solved this problem. She read a paper by a brilliant guy named Megnad Saha, who understood all the these ionization effects. He like calculated exactly what you should expect for various ionizations at various temperatures of all of the elements. He was just like, he wasn't thinking about the Sun. He was just like, Hey, chemistry is cool, and I want to understand energy levels and let's dig deep into this. And he totally nerded out about this.
And Cecily Pain is like, oh, this is a solution to this huge problem that we have over in astrophysics of understanding what we should expect from the sun. So she put these two things together and she was able to interpret correctly the spectrum of light we're getting from the Sun and understand why it looked a little shifted and a little weird from what folks like Henry Russell expected.
Amazing, and like note students, the importance of reading widely. I think there are so many connections that you make that you might not be expecting.
Yeah, exactly, And so this is a huge breakthrough and like, finally we could understand what the sun is made out of. And the result was a huge surprise, especially to folks like Pain. Number one, the sun is made out of the same stuff as the Earth, Like there's hydrogen in this, helium, this oxygen, iron, this nickel, this all the same stuff,
but it comes in very different numbers. Like the relative abundances are very very different in the Sun. Basically the Sun is mostly hydrogen and helium and everything else is there, but it's tiny, Like it's seventy four percent hydrogen, twenty five percent helium, and everything else is one percent.
Wow. Yeah, all right, And so I'm just gonna guess, based on some other conversations we've had about women in science, that Russell isn't just the villain because he was wrong, but he probably did something to turf Pain's results. Am I right?
Oh? Absolutely?
Okay.
So she was at Harvard and the director of the observatory was Russell, and Russell had the power at the time to veto any publication he wanted for whatever reason, including her thesis. Aw So he blocked her getting her PhD thesis unless she added the following caveat to her thesis quote. The outstanding discrepancy between the astrophysical and to
rrestrial abundances are displayed for hydrogen and helium. The enormous abundance derived for these elements in the atmosphere is almost certainly not real.
What he had her at a caveat that was like, but also, probably I'm wrong.
Is all this amazing science is huge breakthrough and then he's like, I disagree with it, so probably this is BS. Don't believe these numbers.
By the way, Oh my gosh. And what a coward that he did. Sounds like he didn't point out exactly where she had an error right, like because.
He just couldn't accept it. He was like, no, the science says, so I don't see a mistake, but no, this flies in the face of what I believe, and so I'm gonna insist that you add this caveat to her thesis. Her advisor was a guy named Harlow Shapley and shapely ordered six hundred copies of her thesis and sent it to all the important astronomers in the world.
Oh wow, okay, so he believed in her.
He believed in her. Yet did he go through exactly.
All six hundred copies and like cross out that line that she had to add.
I don't know, but he knew this guy because Russell was also his PhD advisor. So I think they had a common experience there. But it gets even worse because even though Russell said no, this isn't true, this can't be true, a few years later, when the scientific tides
turned and everybody accepted this, he took credit for this discovery. No, yes, exactly, And so in most historical records until recently, people gave Henry Russell credit for a discovery of what the sun is made out of, which is like such a tragedy.
No it is, I agree, it's exactly.
He's a total villain. So only four years after calling it impossible, you find him in the literature taking credit for this discovery. So it's a real shame.
It isn't real. Okay, So then how did we rediscover Cecilia Paine?
Then?
Yeah, that's an important point. Cecia Paine ended up getting her PhD in astronomy, only the second PhD in astronomy ever by a woman at Harvard WOW. And initially she was barred from becoming a professor at Harvard because she was a woman, so she did a lot of less prestigious, lower paid research job, but she ended up becoming the first female tenured professor at Harvard WOW, and the first female chair of a department at Harvard.
Wow.
So you know, things changed and she ended up having a good career in astrophysics. And then later people digging into the record corrected it, and so, for example, there is an essay by Otto Struve who called it quote undoubtedly the most brilliant Pahd thesis ever written in astronomy.
Wow.
Wow, that's forty years later. She went forty years before really getting the recognition.
Was she still alive, Yeah, she was.
She died in seventy nine.
I'm glad she got to see her work vindicated in her lifetime. That's amazing.
Yeah. She ended up winning some prizes and was elected to the Royal Astronomical Society. The arc of justice is long, but it does point in the right direction, even into astronomy.
I mean often, but not.
Always eventually, I hope, yes. But to see it, pain taught us a lot about the nature of the universe, right. People thought for a long time that everything in the verse must be made out of the same stuff as the Earth, like that was a natural assumption to them. And now we know, of course that the Sun is mostly hydrogen and helium, and from our models of the
formation of the solar system. It makes sense, right, Like the Sun is the center of gravity and most stuff flocks there and it pulls in all the gases in the inner Solar System, and the Earth did have more hydrogen helium early on, but because these are such light elements, they were blasted away by the Sun's radiation in the
early part of the formation of the Solar System. So now we have a full and complex and nuanced understanding of the formation of the Solar System and the planets, and we can apply this knowledge to understanding other stars, like our star isn't the only star in the universe, and every star has its own unique pattern. We talked recently about why stars are different colors because they are made of different stuff, and their atmospheres has different stuff
and they're different temperatures. And now with this model, with to see a pain's understanding, we can use this to understand what the rest of the universe is made out of.
Wow, Okay, And so with these corrections we can now look at out into the universe and without even visiting it, we can know what different celestial bodies are made out of.
Yeah, exactly. Thanks to Secila opinion and to Megna Saha, he is an Indian astrophysicist who figured out the ionization equations. His Saha ionization equation is super important for us to figure out the nature of the universe. And it's incredible that we can figure this out. I mean, think about all the little puzzles that people had to solve all the way down to like figuring out how massive the
Earth is by measuring a mountain in Scotland. Like, all of these pieces were necessary and they all came together. And when you're solving a puzzle, often there's like a huge unanswered question that you don't even know how to begin. And if you're lucky, people have been working on that question for other reasons for one hundreds of years, making progress, hiking around mountains trying to figure it out, or just nerding out about the chemistry. But sometimes you're not so lucky.
And that's why it's so important that we push in so many directions simultaneously, even though we don't know yet how they're going to be useful or what mysteries they might unlock. We need all of these tools so that in the future, clever people can come up with answers to huge questions like what is the universe?
Made out of amen. By geeking out and by geeking out together, we can change the world.
All right. Thanks very much for coming on this tour of how we figured out what elements of the universe is made out of diving deep into the earth and casting our minds all the way across the universe.
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