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How do we know what elements the Universe is made of? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: Trapped on this little rock. We are desperate to extend
• 0:09
  Speaker 1: our understanding beyond our cosmic jail cell without visiting any
• 0:14
  Speaker 1: other planets or stars. We want to use our ingenuity
• 0:17
  Speaker 1: to figure out how things work in the rest of
• 0:19
  Speaker 1: the Solar System, in the heart of the Sun, or
• 0:22
  Speaker 1: in distant stars. Until recently, we didn't know the answers
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  Speaker 1: to basic questions about the rest of the universe, questions
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  Speaker 1: like what elements is it made out of? Is the
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  Speaker 1: Sun made out of the same mixture of atoms as
• 0:35
  Speaker 1: the Earth? What about the rest of the universe. Today
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  Speaker 1: we'll tell you the story of how we figured this
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  Speaker 1: all out. It features naked Greeks running down the street,
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  Speaker 1: Scottish people climbing mountains, and a clever young woman pushing
• 0:46
  Speaker 1: back against the established but mistaken orthodoxy and not getting
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  Speaker 1: credit for it until recently. So we're going to do
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  Speaker 1: our bit to set the record straight and to show
• 0:55
  Speaker 1: you how clever little apes can actually learn about the
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  Speaker 1: recipe for making a universe stuck in the confines of
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  Speaker 1: our little planet. Welcome to Daniel and Kelly's Extraordinary Elemental Universe.
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  Speaker 2: Hello, I'm Kelly water Smith. I study parasites and space,
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  Speaker 2: and I'm super excited to learn about another woman that
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  Speaker 2: we haven't heard anywhere near enough about today.
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  Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I study
• 1:32
  Speaker 1: what the universe is made out of. But I'm also
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  Speaker 1: curious what I'm made out of.
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  Speaker 2: Oh, you know, biologists have been working on that for
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  Speaker 2: a while. What is your question in particular?
• 1:43
  Speaker 1: Well, you know, people tell me that I am what
• 1:45
  Speaker 1: I eat, which means I'm mostly dinner.
• 1:47
  Speaker 2: I guess, Oh that's right, because you only eat dinner. Yeah, exactly,
• 1:51
  Speaker 2: what did you have for dinner last night? What are you?
• 1:55
  Speaker 2: What should I expect?
• 1:57
  Speaker 1: Last night? We had a dinner party, actually, so we
• 1:59
  Speaker 1: went a little fancy. We made miso honey chicken. We
• 2:03
  Speaker 1: made asparagus and scallions with barrata. We made a very
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  Speaker 1: fancy salad. I made a lemon butter almond tart.
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  Speaker 2: Wow.
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  Speaker 1: Yeah it was good.
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  Speaker 2: That's amazing. Okay, But so the main part of the
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  Speaker 2: dish was chicken. So I'm gonna expect you to squawk
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  Speaker 2: about physics today.
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  Speaker 1: Oh and a couple of loaves of sour dough bread.
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  Speaker 2: Of course, Oh fantastic.
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  Speaker 1: You gotta have your carb. So yes, I'm chicken and
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  Speaker 1: bread today. I guess, all.
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  Speaker 2: Right, well, don't be sour about the information that we're
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  Speaker 2: going to be sharing. So my question for you today.
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  Speaker 2: So there was this recent result that maybe there's indirect
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  Speaker 2: evidence of life in the Solar System, and I was
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  Speaker 2: just wondering if you had to put a bet on it,
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  Speaker 2: let's say one hundred bucks, and you were betting, yes,
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  Speaker 2: there are microbes somewhere in our solar system, or no.
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  Speaker 1: In our solar system or in our galaxy.
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  Speaker 2: In our solar system, in our solar system, you know,
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  Speaker 2: in lava tubes on Mars, in the oceans of Enceladus.
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  Speaker 2: What do you think? What would you put the odds
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  Speaker 2: on for or whether or not there are microbes in
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  Speaker 2: our universe?
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  Speaker 1: Oh wow, put a number on something we can't possibly
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  Speaker 1: know and then risk money on it.
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  Speaker 2: It's not a ton of money, but no.
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  Speaker 1: I like that. I like framing these as gambling questions
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  Speaker 1: because it really makes you decide on like how much
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  Speaker 1: money you'd be willing to lose. I think I put
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  Speaker 1: the odds of there being alien microbes that is not
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  Speaker 1: derived from Earth and like you know, somehow kicked off
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  Speaker 1: via an asteroid somewhere in our solar system independently evolved
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  Speaker 1: unique apiogenesis somewhere, like, you know, one in a million. Maybe.
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  Speaker 1: I think it's probably pretty unlikely somewhere in the galaxy, though,
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  Speaker 1: I put it like ninety eight percent.
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  Speaker 2: Whoa, yeah, well, how many solar systems are in our galaxy.
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  Speaker 1: There's hundreds of billions of stars in the galaxy and
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  Speaker 1: so many planets around the stars, So I just feel
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  Speaker 1: like that number is so big.
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  Speaker 2: Yeah, those odds sound pretty good.
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  Speaker 1: Yeah, are you gonna take my bet?
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  Speaker 3: Ah?
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  Speaker 1: Ooh, the rubber hits the road people.
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  Speaker 2: That's right, that's right. Can you tell I came up
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  Speaker 2: with this question right before I hit record. I don't know,
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  Speaker 2: you know, it wouldn't absolutely shock me if they found
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  Speaker 2: microbes on Mars, given its wet past, or like evidence
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  Speaker 2: of past microbes or something, and so I, uh, yeah,
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  Speaker 2: I'll take your bet. I'll take the opposite.
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  Speaker 1: I wouldn't wait, does that mean I owe you one
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  Speaker 1: hundred million dollars if you find microbes on Mars?
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  Speaker 4: Oh?
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  Speaker 2: Oh uh no, let's just do let's forget odds. Let's
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  Speaker 2: just do one hundred bucks if you're right, one hundred
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  Speaker 2: bucks if I'm right.
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  Speaker 1: Oh, but then I'm betting against aliens. I don't want
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  Speaker 1: to ever bet against aliens. I'm rooting for aliens. I
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  Speaker 1: don't want to have a conflict of interest where I
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  Speaker 1: hope there aren't aliens. So then I get a hundred
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  Speaker 1: bucks from Kelly.
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  Speaker 2: I know this is difficult for you, but but we're
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  Speaker 2: just talking about microbes.
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  Speaker 1: Yeah, that's true.
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  Speaker 2: So the microbes that will teach you physics, you're not
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  Speaker 2: or sorry, the alien that will teach you physics, you're
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  Speaker 2: not betting against them.
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  Speaker 1: Okay, so all.
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  Speaker 2: Right, don't get sour on me here, Daniel. We're moving on. Okay.
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  Speaker 1: Today we're not talking about what's alive on Mars or
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  Speaker 1: in the oceans of Europa, or what Daniel aid for dinner.
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  Speaker 1: We're talking about what the whole universe is made out of,
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  Speaker 1: what building blocks, what elemental lego bricks are used to
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  Speaker 1: put our cosmos together.
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  Speaker 2: And how the heck did we figure that out, especially
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  Speaker 2: when the stuff is not on Earth?
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  Speaker 1: Yeah, exactly, and we've never left Earth asterisk. We really
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  Speaker 1: did go to the Moon, but kind of counts as
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  Speaker 1: part of Earth.
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  Speaker 2: Okay, but that definitely wasn't fake in it just to
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  Speaker 2: be clear, just to be c I did talk to
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  Speaker 2: a friend the other day who was like, and I
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  Speaker 2: know the moon landing wasn't real, and I was like,
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  Speaker 2: oh that was. Every once in a while you have
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  Speaker 2: one of those moments where you're like, that's I did.
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  Speaker 2: I didn't expect that. What do I say now?
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  Speaker 4: All right?
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  Speaker 2: Anyway, so let's talk to our audience, who almost certainly
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  Speaker 2: believes that we actually landed on the moon, and ask
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  Speaker 2: them how do we know what the universe is made of?
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  Speaker 1: If you would like to contribute your voice for future
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  Speaker 1: segments on the podcast, please don't be shy right to
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  Speaker 1: us to questions at Danielankelly dot org. We really really
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  Speaker 1: love hearing from you. I think we know what the
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  Speaker 1: universe is mde of? Do you just spectroscopy?
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  Speaker 4: I don't think we definitively know what it's made of,
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  Speaker 4: but we probably speculated.
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  Speaker 2: I think scientists can extrapolate from what's in the earth.
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  Speaker 1: Lensing likes spectrums and extrapolation from what's immediately around us.
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  Speaker 1: I don't think we do.
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  Speaker 3: We may live in a simulation, or that we may
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  Speaker 3: actually exist in a two dimensional universe projected onto a
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  Speaker 3: three D hologram. So when you get right down to it.
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  Speaker 3: The truth is nobody probably knows.
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  Speaker 4: Right different observational scientific techniques to try and understand the
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  Speaker 4: different components of it to the best we are able
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  Speaker 4: and make everything else up from there spectroscopy.
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  Speaker 1: Wait, do we know.
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  Speaker 2: That we are the universe?
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  Speaker 5: Yes, the universe is our way and out there. But
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  Speaker 5: if we can know the molecules that make up you
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  Speaker 5: and me and apples and mountains and porcupines and all
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  Speaker 5: the things we know of you're on Earth, that tells
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  Speaker 5: us what the universe is made of.
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  Speaker 1: To spectrocity and gravity.
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  Speaker 2: We know by spectroscopy, a lot of guessing followed by
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  Speaker 2: a lot of testing.
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  Speaker 1: The spectral analysis. We're not sure what dark matter is,
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  Speaker 1: and I seem to remember something about quantum foam, so
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  Speaker 1: maybe we don't really know.
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  Speaker 5: Data collective from ground and space based telescopes.
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  Speaker 3: I guess the bits that aren't dark matter either in
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  Speaker 3: midlight so we can look at the spectrum, or they
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  Speaker 3: have enough gravity to bend light.
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  Speaker 1: Easy.
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  Speaker 2: We take one piece of the universe, smash it into
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  Speaker 2: another piece of the universe and see what comes up.
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  Speaker 1: With a lot.
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  Speaker 2: I love the person who said do we know, because actually,
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  Speaker 2: if it's an episode you and I are doing. There's
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  Speaker 2: a pretty good chance the answer is we don't know,
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  Speaker 2: So throwing it back at us is a pretty good guess.
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  Speaker 1: Yeah, that is a great answer. I also like the
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  Speaker 1: answers that frame the question much more broadly. When I
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  Speaker 1: wrote this, I was thinking about what elements the universe
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  Speaker 1: is made out of, like the atomic matter that you
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  Speaker 1: know makes up the sun and the stars, and the
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  Speaker 1: gas and the dust and the wolverines and the ferrets
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  Speaker 1: and all that kind of stuff. I wasn't yes, exactly,
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  Speaker 1: I wasn't thinking more broadly, like dark matter, dark energy. So, yeah,
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  Speaker 1: these are good answers.
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  Speaker 2: Your question was underspecified.
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  Speaker 1: It was yes, I should have said, how do we
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  Speaker 1: know what elements the universe is made out of?
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  Speaker 2: That's right, We still got some fantastic answers. So what
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  Speaker 2: let's start with how we figured out what elements the
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  Speaker 2: Earth is made out of? What tools do we use
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  Speaker 2: for that here?
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  Speaker 1: Yeah, the story of figuring out what the universe is
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  Speaker 1: made out of goes like, first, let's figure out what
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  Speaker 1: the stuff under our feet and what we are made
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  Speaker 1: out of, and then let's think about whether we can
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  Speaker 1: extrapolate that to the rest of the universe because unfortunately
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  Speaker 1: we still can't go visit most of the universe. So
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  Speaker 1: in terms of like lab science and like getting our
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  Speaker 1: fingers literally dirty, the Earth is the only place we
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  Speaker 1: have to explore. And it's really cool story how we
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  Speaker 1: figured out what the Earth is made out of it
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  Speaker 1: because even though it's under our feet, we can't go
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  Speaker 1: like explore very deep. We haven't drilled very far into
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  Speaker 1: the earth, so a lot of it is still indirect
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  Speaker 1: evidence that we put together by clever humans figuring out
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  Speaker 1: ways to basically see what's inaccessible.
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  Speaker 2: Well not only getting to the center of the Earth,
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  Speaker 2: but just being able to like pick up a handful
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  Speaker 2: of dirt and being like, what kind of elements are
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  Speaker 2: in this handful of dirt. That's amazing to.
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  Speaker 1: Me as well exactly, and this requires a lot of
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  Speaker 1: you know, chemistry, understanding what elements were there and their
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  Speaker 1: properties and their mixture, and so early on in the
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  Speaker 1: last few hundred years, when people are trying to figure out, like, hey,
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  Speaker 1: what is the Earth made out of they're basically three
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  Speaker 1: big questions that were asking. One is like, what is
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  Speaker 1: the density of the earth? Can we figure that out?
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  Speaker 1: Because if we know the density of the Earth. We
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  Speaker 1: know a lot about what it could be made out
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  Speaker 1: of and what it couldn't. Like if you measure the
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  Speaker 1: density of the earth and you discover, oh, it has
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  Speaker 1: the density of whipped then you know it's not mostly ironed, right,
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  Speaker 1: Whereas if you measure the density the earth and it's
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  Speaker 1: like bang on nickel, then you're like, wow, it's probably
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  Speaker 1: most any nickel. Right. And so measuring the density of
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  Speaker 1: the earth is an important question. But this isn't easy, right, Like,
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  Speaker 1: how do you measure the density of something? Well, here
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  Speaker 1: on Earth, You like put it in water and see
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  Speaker 1: if it floats, or you measure its mass and you
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  Speaker 1: measure its volume, right, the famous Eureka moment of figuring
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  Speaker 1: out whether the crown is made of gold by measuring
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  Speaker 1: its volume by dipping it in water, et cetera, et cetera.
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  Speaker 2: This is apparently not a particularly famous Eureka moment because
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  Speaker 2: I've never heard that story.
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  Speaker 1: Oh this is a really fun Mas story. Archimedes was
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  Speaker 1: asked to determine whether the king's crown was made of
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  Speaker 1: pure gold or not, so he said, well, I'll measure
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  Speaker 1: its density, because if it's density lines up with gold,
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  Speaker 1: then we know it's gold, and if it's got something
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  Speaker 1: else in it, it'll come out a different number. Measure
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  Speaker 1: the density requires them in the mass and the volume.
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  Speaker 1: Mass not so hard, Volume not so hard. If you
• 10:55
  Speaker 1: have a simple object like a sphere or a cube,
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  Speaker 1: how do you measure very precisely the volume of a
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  Speaker 1: really complex shape like a crown turns out to be
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  Speaker 1: really challenging. So Archimedies is puzzling over this as he's
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  Speaker 1: slipping into the bath at the end of his day.
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  Speaker 1: And as he gets into the bath, he sees the
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  Speaker 1: water level rise, and he's like, oh, now, I understand
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  Speaker 1: how to measure the volume. You just dip it in
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  Speaker 1: water and you measure how much it rises. And the
• 11:17
  Speaker 1: story goes, probably apocryphally, that he left out of the
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  Speaker 1: baths and naked down the streets of Siracuse or Syracuse,
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  Speaker 1: shouting eureka, eureka. And anyway, that's your famous ancient Greek
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  Speaker 1: nude story for the day.
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  Speaker 2: Amazing. We should have more of those, But okay, I
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  Speaker 2: hadn't heard that story. Thanks for sharing.
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  Speaker 1: But in the case of the earth, you can't just
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  Speaker 1: dip the earth in water, right, you know, we don't
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  Speaker 1: have like a bath of water that we could dip
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  Speaker 1: it in. So what we need to do is measure
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  Speaker 1: the gravitational pull of the Earth. Right, if you knew
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  Speaker 1: the total mass and the volume, then you would have
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  Speaker 1: the density and the volume is pretty straightforward because the
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  Speaker 1: Earth is a spear. So if you could figure out
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  Speaker 1: the mass, then you'd know the answer. But figuring out
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  Speaker 1: the mass is a little bit complicated because to do
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  Speaker 1: that you have to measure the pull of gravity, and
• 11:59
  Speaker 1: to do that you have to know so the constant
• 12:01
  Speaker 1: in the gravitational formula Newton's gravitational formula says that the
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  Speaker 1: pole of gravity depends on two masses and on this
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  Speaker 1: number in between them. And for a long time we
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  Speaker 1: didn't know very precisely that number. And so to get
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  Speaker 1: that number you need like two large known masses that
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  Speaker 1: you can measure their gravitational pole between them, so you
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  Speaker 1: can get that number, and then you can measure gravity
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  Speaker 1: in the Earth and finally figure out what is the
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  Speaker 1: mass of the Earth.
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  Speaker 2: That sounds complicated, and so how did they find two
• 12:33
  Speaker 2: massive objects to do this with?
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  Speaker 1: Yeah, they have to be massive objects because gravity is
• 12:37
  Speaker 1: super duper weak. Right, you can't measure the gravitational pole
• 12:40
  Speaker 1: between like two pennies in your hand. There is a
• 12:42
  Speaker 1: gravitational pole there, but it's unmeasurable, especially like one hundred
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  Speaker 1: two hundred years ago. So what they did is they
• 12:49
  Speaker 1: found a mountain. There's this mountain in Scotland called she Holand,
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  Speaker 1: and in the seventeen seventies that decided this was a
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  Speaker 1: good candidate for measuring the gravitational constant because it's isolated
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  Speaker 1: from lots of other stuff. So it's like a single
• 13:03
  Speaker 1: mountain on a plane, far away from other stuff, and
• 13:06
  Speaker 1: it's kind of symmetrical. It's like not hard to measure
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  Speaker 1: its volume pretty accurately. It's not like the crown of
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  Speaker 1: the King of Syracuse, right, it's like kind of a
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  Speaker 1: simple shape.
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  Speaker 2: Okay, so there's one massive object.
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  Speaker 1: Yeah. So then they took a pendulum and they held
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  Speaker 1: it near the mountain and they measured weather deviated from
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  Speaker 1: straight down, and the deviation of the pendulum from straight
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  Speaker 1: down as you get closer and further from the mountain
• 13:30
  Speaker 1: is a measure of the gravitational pull of the mountain
• 13:33
  Speaker 1: on the pendulum. Right. So here you're like actually measuring
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  Speaker 1: gravity between two things, neither of which are the Earth
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  Speaker 1: that works, actually does work. This was the first measurement
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  Speaker 1: of the gravitational constant, and it required actually a lot
• 13:46
  Speaker 1: of work by surveyors, like converting the shape of the
• 13:49
  Speaker 1: mountain into prisms so they could calculate the volume very accurately.
• 13:52
  Speaker 1: It was a huge project, and that allowed them to
• 13:54
  Speaker 1: measure the gravitational constant and then calculate the density of
• 13:58
  Speaker 1: the Earth. And they discovered that the day to the
• 14:00
  Speaker 1: Earth is like almost twice the density of that mountain.
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  Speaker 2: So this technique sounds incredibly complicated. How close did they
• 14:09
  Speaker 2: get to the value that we believe it is today?
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  Speaker 1: They're within twenty percent.
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  Speaker 2: Nice.
• 14:13
  Speaker 1: Yeah, and that's pretty good, you know for dudes in
• 14:16
  Speaker 1: silly hats with pendulums, you know, walking around mountains like
• 14:20
  Speaker 1: these clever apes are figuring stuff out.
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  Speaker 2: Yeah, no, that's amazing.
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  Speaker 3: You know.
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  Speaker 2: I feel like if you took five biologists in our
• 14:26
  Speaker 2: field clothes or whatever and you were like figure out
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  Speaker 2: the density of the Earth, I'd feel pretty good if
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  Speaker 2: we got within twenty percent. That's pretty solid.
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  Speaker 1: And that is really revealing at the time, because people
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  Speaker 1: had no idea what was inside the earth? Is it
• 14:37
  Speaker 1: like a hall of core? The way like King Kong
• 14:40
  Speaker 1: and Godzilla are fighting down there? Is it mostly made
• 14:42
  Speaker 1: of water? People really just didn't know. And this in
• 14:44
  Speaker 1: a single measurement tells you a lot about what the
• 14:47
  Speaker 1: Earth could and couldn't be made out of. And then
• 14:50
  Speaker 1: there's a really amazing history of the measurements of the
• 14:52
  Speaker 1: gravitational constant, which got more and more precise. Eventually people
• 14:56
  Speaker 1: used torsion experiments like balls hanging on strings that are
• 15:00
  Speaker 1: very sensitive and measured their deflection as it got closer
• 15:03
  Speaker 1: together Cavendish et cetera. There's a whole fun history there.
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  Speaker 1: People made these measurements very precisely to within less than
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  Speaker 1: one percent. So now we have a very accurate estimate
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  Speaker 1: of the Earth's density.
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  Speaker 2: That is incredible. Okay, so we have an estimate of
• 15:16
  Speaker 2: the density, what did it lead us to believe? That
• 15:19
  Speaker 2: most of the Earth is made of yees?
• 15:20
  Speaker 1: So the density of the Earth is more dense than
• 15:23
  Speaker 1: the mountain, which is a hint that there's like heavy
• 15:26
  Speaker 1: stuff in there. Right, it can't just be rock. It's
• 15:28
  Speaker 1: not water, right. Water is much less dense than the Earth,
• 15:32
  Speaker 1: and so that suggests that there's a dense core, that
• 15:34
  Speaker 1: there's something heavy in there. And we now know, of course,
• 15:37
  Speaker 1: there's a lot of nickel and iron in the core
• 15:39
  Speaker 1: of the Earth. And this was our first hint about
• 15:42
  Speaker 1: what was down there.
• 15:43
  Speaker 2: Not a giant open sphere with like dinosaurs hiding in it,
• 15:46
  Speaker 2: because that would have been cooler, Not.
• 15:47
  Speaker 1: A vast chasm filled with swarming parasites, for example. For
• 15:52
  Speaker 1: most people, that's a nightmare. For you, that's heaven.
• 15:55
  Speaker 2: Now, I'm so bummed out to know that this is
• 15:57
  Speaker 2: the Earth I exist on, but it could have been
• 15:59
  Speaker 2: so much better.
• 16:02
  Speaker 1: And people attack this question of what is the Earth
• 16:04
  Speaker 1: made at of? From other angles. We have density, but
• 16:06
  Speaker 1: the next angle was age. People were trying to estimate,
• 16:09
  Speaker 1: like how old is the Earth, because understanding how old
• 16:12
  Speaker 1: the Earth is gives you clues about how it's formed
• 16:15
  Speaker 1: and therefore what it's made out of. And we already
• 16:18
  Speaker 1: knew at this point a couple hundred years ago that
• 16:19
  Speaker 1: the Earth was probably pretty old. And the biggest clue
• 16:23
  Speaker 1: there was like Darwin, Darwin should us that life took
• 16:26
  Speaker 1: a while to come together, you know, this process of
• 16:29
  Speaker 1: evolution was slow, so we had a sense that the
• 16:31
  Speaker 1: Earth was like cosmically old, not thousands of years, but
• 16:35
  Speaker 1: people didn't really know is that like millions, hundreds of millions, billions,
• 16:39
  Speaker 1: even it was still an open question a couple hundred
• 16:41
  Speaker 1: years ago.
• 16:42
  Speaker 2: Now, I love when Darwin gets credit for stuff, but
• 16:46
  Speaker 2: I don't actually know that he should get credit for
• 16:48
  Speaker 2: showing us that life was ancient. I mean he was.
• 16:50
  Speaker 2: He came up with the theory of natural selection to
• 16:52
  Speaker 2: explain how like one form sort of morphs into another.
• 16:55
  Speaker 2: But I think there were geologists already working on this
• 16:57
  Speaker 2: question and finding fossils and postulating Earth has been around
• 17:01
  Speaker 2: for a long time and stuff has been gone. But anyway,
• 17:03
  Speaker 2: Darwin awesome. Maybe he just got some credit for something
• 17:06
  Speaker 2: he didn't deserve, but biologist getting credit for stuff is
• 17:09
  Speaker 2: always awesome, So let's move on.
• 17:11
  Speaker 1: Yeah, that's fair, And I'm about to give some credit
• 17:12
  Speaker 1: to some chemists to hold onto your hats.
• 17:14
  Speaker 2: Oh oh boy, I'm gonna get sour.
• 17:18
  Speaker 1: People were wondering, like, how long would it take the
• 17:20
  Speaker 1: Earth to cool if you have a like a ball
• 17:22
  Speaker 1: of molten stuff sitting in space, how quickly does it
• 17:26
  Speaker 1: form a crust that you can like walk around on.
• 17:29
  Speaker 1: And Lord Kelvin of you know, Kelvin temperature trying to
• 17:32
  Speaker 1: use this to calculate an approximate age for the Earth.
• 17:36
  Speaker 1: He was thinking, like, you have a big ball of
• 17:38
  Speaker 1: lava basically or magma in space, how quickly can you
• 17:41
  Speaker 1: form a crust? And he ignored a bunch of stuff
• 17:44
  Speaker 1: like he didn't understand that there was convection inside the
• 17:47
  Speaker 1: Earth that hot stuff rises, and so you keep getting
• 17:50
  Speaker 1: this like refresher of hot stuff from the core up
• 17:52
  Speaker 1: to the surface. He also didn't know about radioactive decay,
• 17:56
  Speaker 1: which helps heat the Earth, because he didn't know about
• 17:58
  Speaker 1: radiation and quantum mechanics and all that stuff. Nobody had
• 18:01
  Speaker 1: discovered that yet. So in Kelvin's calculation, he missed a
• 18:05
  Speaker 1: lot of the pieces there, and he came up with
• 18:07
  Speaker 1: a range of like twenty to four hundred million years,
• 18:11
  Speaker 1: which is like low by more than a factor of
• 18:13
  Speaker 1: ten because of these pieces he missed. But you know,
• 18:15
  Speaker 1: he's sort of getting up there into the right ballpark.
• 18:18
  Speaker 2: Yeah. And so at the time was the predominant view,
• 18:21
  Speaker 2: the Christian view, that the Earth was like what two
• 18:23
  Speaker 2: or five thousand years old or something. I think postulating
• 18:26
  Speaker 2: millions of years could have really like put you in
• 18:29
  Speaker 2: the crosshairs. But how common was the idea that it
• 18:31
  Speaker 2: was just a couple thousand years old at that point.
• 18:34
  Speaker 1: I think that most educated and scientific people didn't accept
• 18:37
  Speaker 1: the young Earth hypothesis. Even back then, there was a sense,
• 18:40
  Speaker 1: as you said, from geology that things were taking a
• 18:43
  Speaker 1: long time. But then people were trying to make a
• 18:45
  Speaker 1: specific They're like, can we get an actual number? And
• 18:48
  Speaker 1: so I love when people in history are like, well,
• 18:49
  Speaker 1: let's try to sit down and get a calculation of this,
• 18:51
  Speaker 1: and you know they're wildly off, but getting that first
• 18:54
  Speaker 1: estimate is a big step forward, and then you can
• 18:56
  Speaker 1: refine it and think about what you're missing, And like,
• 18:58
  Speaker 1: this is the process of science, right, First do the
• 19:01
  Speaker 1: dumbest thing and then improve it. It's innerative, right.
• 19:04
  Speaker 2: I feel like that's kind of where we are with
• 19:05
  Speaker 2: the Drake equation, Like we're starting to hone in on
• 19:08
  Speaker 2: the things that matter, and exercises like this help you
• 19:11
  Speaker 2: think through stuff.
• 19:11
  Speaker 1: Yeah, exactly. And now, of course we know a lot
• 19:14
  Speaker 1: more precisely how old the Earth.
• 19:16
  Speaker 2: Is, and when we get back from the break, we're
• 19:17
  Speaker 2: going to hear all about that, all right. So Dan
• 19:41
  Speaker 2: was just telling us that Kelvin was thinking about how
• 19:44
  Speaker 2: long it would take a molten earth to cool to
• 19:46
  Speaker 2: get our initial estimates for the age of the Earth,
• 19:48
  Speaker 2: and we ended up with somewhere between twenty and four
• 19:50
  Speaker 2: hundred million years. What was the next step that we
• 19:53
  Speaker 2: took to get more accurate.
• 19:55
  Speaker 1: More accurate understanding the age of the Earth, which again
• 19:58
  Speaker 1: helps you understand what it's made out of. It came
• 20:00
  Speaker 1: in this century when we understood that rocks have little
• 20:03
  Speaker 1: clocks in them, and you can use that to figure
• 20:06
  Speaker 1: out when the rock cooled, so you can figure out
• 20:09
  Speaker 1: like when something was formed, and these clocks actually depend
• 20:13
  Speaker 1: on quantum mechanics. There are these little crystals called zircon
• 20:16
  Speaker 1: crystals that help you understand how old a.
• 20:19
  Speaker 2: Rock is, and what is it about the zircon crystals
• 20:22
  Speaker 2: and why isn't there a watch company called Zircon.
• 20:26
  Speaker 1: Zircon are really weird little crystals that hate lead, like
• 20:29
  Speaker 1: they will not allow lead to form within the crystal,
• 20:32
  Speaker 1: but they will take uranium. So when you get a
• 20:35
  Speaker 1: zircon crystal freshly formed, it has no lead in it,
• 20:38
  Speaker 1: but it does have uranium in it, and then uranium
• 20:41
  Speaker 1: while it's inside the crystal decays naturally into lead at
• 20:45
  Speaker 1: a rate we know. So if you pick up a
• 20:47
  Speaker 1: random zircon crystal and it has no lead in it.
• 20:50
  Speaker 1: You know, this thing is zero years old. It's a
• 20:52
  Speaker 1: baby crystal. If you pick up a zircon crystal and
• 20:55
  Speaker 1: it's got no uranium and it's pure lead, you're like, wow,
• 20:58
  Speaker 1: this thing is old because uranium is slow at decaying.
• 21:02
  Speaker 1: So every zircon crystal is like a little clock that
• 21:05
  Speaker 1: tells you how long it's been since it's formed.
• 21:08
  Speaker 2: That's amazing.
• 21:09
  Speaker 1: And there's a whole incredible story about a Chemisty Patterson,
• 21:12
  Speaker 1: who figured this out and then started measuring the lead
• 21:14
  Speaker 1: and stuff. And he's actually the guy who discovered, oh
• 21:17
  Speaker 1: my gosh, this lead everywhere in our environment because of
• 21:19
  Speaker 1: lead in gasoline, and he led the crusade to get
• 21:22
  Speaker 1: lead out of gasoline because he was realizing, wow, we
• 21:25
  Speaker 1: have poisoned our environment. He was trying to make a
• 21:28
  Speaker 1: clean room to measure these things really precisely, and he
• 21:30
  Speaker 1: just could not get a lead free environment. Wow. And
• 21:33
  Speaker 1: so anyway, another chemist who saved us all.
• 21:36
  Speaker 2: When it's so hard to know, like what study you're
• 21:38
  Speaker 2: doing is going to be the thing that gives you
• 21:40
  Speaker 2: important information for humans, like what sort of off ramps
• 21:43
  Speaker 2: you're going to end up on?
• 21:44
  Speaker 1: And so another argument for funding basic science people. But
• 21:48
  Speaker 1: you never know what you're going to discuss important and
• 21:51
  Speaker 1: so because of his work, we discovered that the Earth
• 21:54
  Speaker 1: is like four and a half billion years old, meaning
• 21:57
  Speaker 1: that the oldest rocks we have cooled around four and
• 21:59
  Speaker 1: a half billion years ago.
• 22:01
  Speaker 2: Oh my gosh. And that's pretty close to our current estimate,
• 22:04
  Speaker 2: isn't it.
• 22:05
  Speaker 1: Yeah, yeah, exactly.
• 22:06
  Speaker 2: That's amazing.
• 22:06
  Speaker 1: And so now understanding that the Earth is really old
• 22:09
  Speaker 1: gives you more information to figure out the puzzle of like, well,
• 22:11
  Speaker 1: what's it made out of? Because you want to understand
• 22:14
  Speaker 1: like how old is the Earth, how quickly did it cool? Well,
• 22:17
  Speaker 1: to know that you have to know like where's the
• 22:18
  Speaker 1: heat coming from? Where are the layers inside the earth?
• 22:21
  Speaker 1: You need a complete model for where stuff is within
• 22:24
  Speaker 1: the earth, and that's why you need this last piece.
• 22:26
  Speaker 1: So we have the age, we have the density. Next
• 22:28
  Speaker 1: thing we need is the structure of the earth to
• 22:31
  Speaker 1: know like how a stuff organized within the earth. And
• 22:34
  Speaker 1: that's where seismology comes in to give us that last piece.
• 22:37
  Speaker 2: Oh so we're getting away from chemistry, whew. Back to
• 22:41
  Speaker 2: the rock people.
• 22:43
  Speaker 1: Of seismology, of course, it's a study of earthquakes and
• 22:46
  Speaker 1: earthquakes are cool. I mean, they're devastating and tragic, but
• 22:49
  Speaker 1: they also do something really useful, which is that they
• 22:52
  Speaker 1: ring the Earth like a bell. And so when there's
• 22:55
  Speaker 1: an earthquake, these seismic waves pass through the Earth and
• 22:59
  Speaker 1: they give you a glimp as to what's going on
• 23:01
  Speaker 1: inside the Earth because these waves bounce off of like interfaces.
• 23:06
  Speaker 1: If the whole Earth was just like one solid rock,
• 23:09
  Speaker 1: then the waves would travel smoothly through it. But if
• 23:11
  Speaker 1: there's an interface where you go from like one kind
• 23:13
  Speaker 1: of rock to another, or you go from like nickel
• 23:15
  Speaker 1: to iron, or liquid to not liquid, then the waves
• 23:18
  Speaker 1: bounce back at that surface and you create complicated patterns.
• 23:22
  Speaker 1: And so by reading the waves that reflect on the surface,
• 23:24
  Speaker 1: you can reconstruct what was going on inside the Earth.
• 23:27
  Speaker 1: It's sort of like a sonogram, right, or an ultrasound.
• 23:30
  Speaker 2: That that is absolutely amazing. And just like parents like
• 23:34
  Speaker 2: to brag about their kids, I like to brag about
• 23:37
  Speaker 2: the human species sometimes, and just note that we've measured
• 23:41
  Speaker 2: Mars quakes and it is just amazing to me that
• 23:44
  Speaker 2: we've been able to like get equipment there that could
• 23:46
  Speaker 2: then measure this happening on another planet in our solar system.
• 23:50
  Speaker 2: So anyway, okay, amazing, all right, so now you can
• 23:53
  Speaker 2: you can do this. And so did we know at
• 23:55
  Speaker 2: the time enough to figure out so like you know,
• 23:57
  Speaker 2: if you hit water and you had been going through nickel,
• 23:59
  Speaker 2: you're like, oh, some thing is different. How much work
• 24:02
  Speaker 2: did we have to do to understand what we were seeing?
• 24:05
  Speaker 2: Like it seems like there's a big difference between saying
• 24:07
  Speaker 2: something changed or something changed and I understand what that means.
• 24:12
  Speaker 1: Yeah, the crucial thing there is having enough instrumented points,
• 24:15
  Speaker 1: like you need to reconstruct these waves all across the Earth,
• 24:18
  Speaker 1: because like a wave from an earthquake in California will
• 24:20
  Speaker 1: propagate down into the Earth and reflect back, but doesn't
• 24:23
  Speaker 1: come straight back to California and like goes to Japan
• 24:26
  Speaker 1: or Hawaii or somewhere else, and it also continues through
• 24:29
  Speaker 1: the Earth, and the different parts of the wave is
• 24:31
  Speaker 1: like s waves and pea waves, and different frequencies reflect
• 24:34
  Speaker 1: at different rates. And so what you really need to
• 24:36
  Speaker 1: do is measure all the different frequencies as many places
• 24:39
  Speaker 1: as you can around the Earth to get this complete picture.
• 24:42
  Speaker 1: So that's what's crucial is having this like global network
• 24:45
  Speaker 1: of seismic grass and yeah, on Mars they have a
• 24:48
  Speaker 1: few of these, but wow, if they had more, they
• 24:50
  Speaker 1: could really get pictures of these marsquakes and understand what's
• 24:53
  Speaker 1: going on inside the Martian core, which is a whole
• 24:56
  Speaker 1: other fascinating question about like whether there is still motion
• 24:59
  Speaker 1: inside the core or whether it's totally frozen. And of
• 25:02
  Speaker 1: course that tells us a lot about like the history
• 25:04
  Speaker 1: of Mars and maybe did it have a magnetic field
• 25:07
  Speaker 1: and could it protect life from cosmic radiation? But anyway,
• 25:11
  Speaker 1: that's off track. Coming back to Earth. We now have
• 25:14
  Speaker 1: an idea of what the structure of the Earth is,
• 25:16
  Speaker 1: where the density of the Earth is, and how long
• 25:19
  Speaker 1: it's been cooling, and altogether that gives us a model
• 25:22
  Speaker 1: for what's going on inside the Earth without drilling down
• 25:25
  Speaker 1: and going to visit. This is enough information to constrain
• 25:28
  Speaker 1: our model and tell us what it has to be
• 25:29
  Speaker 1: made out of, each of the layers and their composition.
• 25:32
  Speaker 2: And so this is how we figured out that the
• 25:33
  Speaker 2: core is mostly nickel and lead, not lead iron.
• 25:37
  Speaker 1: Nickel and iron and iron got it. And so it
• 25:39
  Speaker 1: turns out that the Earth is like thirty two percent
• 25:42
  Speaker 1: iron thirty percent oxygen, which blows my mind. Most of
• 25:45
  Speaker 1: it's like absorbed into rock. Fifteen percent silicon, fourteen percent magnesium,
• 25:51
  Speaker 1: three percent sulfur, two percent nickel, and the rest of
• 25:54
  Speaker 1: a lot of exciting trace elements. But that's the majority
• 25:57
  Speaker 1: of what the Earth is made out of.
• 25:59
  Speaker 2: Well, okay, so that's not a lot of nickel, So
• 26:01
  Speaker 2: with mostly iron and oxygen.
• 26:04
  Speaker 1: Mostly iron and oxygen, huh, yeah, exactly. There's a lot
• 26:07
  Speaker 1: of oxygen in the Earth because rocks gobble up oxygen.
• 26:12
  Speaker 1: Like in the early days of the Earth, when you
• 26:14
  Speaker 1: be produced oxygen in the atmosphere, most of it was
• 26:16
  Speaker 1: just absorbed by rocks. You have to like satisfy all
• 26:19
  Speaker 1: the rocks before you could leave oxygen in the atmosphere
• 26:22
  Speaker 1: for life.
• 26:23
  Speaker 2: I'm glad there was some leftover for us.
• 26:25
  Speaker 1: Yeah, because oxygen is so reactive. So that gives us
• 26:28
  Speaker 1: a sense for what our scoop of the universe is
• 26:30
  Speaker 1: made out of, right, iron, oxygen, silicon, magnesium. But then
• 26:34
  Speaker 1: of course we're wondering, like what's the rest of the
• 26:36
  Speaker 1: universe made out of? Is it the same? Is it different?
• 26:38
  Speaker 1: What's the Sun made out of? And this is a
• 26:41
  Speaker 1: question people had for a long time, like what is
• 26:43
  Speaker 1: the Sun made out of how does it work, what's
• 26:45
  Speaker 1: going on inside of it, and what fuels it?
• 26:47
  Speaker 2: Yeah, because I think all of the techniques that we've
• 26:49
  Speaker 2: talked about require you to be on the surface of
• 26:52
  Speaker 2: that planet to collect the data, so you probably need
• 26:55
  Speaker 2: a whole different set of tools to figure out what's
• 26:57
  Speaker 2: happening on the Sun.
• 26:58
  Speaker 1: Right, Yeah, exactly, And of course we can't go visit
• 27:01
  Speaker 1: the Sun. We had the Parker Solar Probe, which came
• 27:04
  Speaker 1: close to the Sun, but of course didn't go into
• 27:06
  Speaker 1: the Sun. And for a long time we were trying
• 27:08
  Speaker 1: to figure this out, of course, just from Earth and
• 27:10
  Speaker 1: trying to understand what it could be made out of.
• 27:12
  Speaker 1: And we can know some things without going to visit
• 27:14
  Speaker 1: the Sun. Right. We can get a sense of the
• 27:16
  Speaker 1: mass of the Sun if we know the gravitational constant
• 27:19
  Speaker 1: and we know Earth's mass, and then we can calculate
• 27:21
  Speaker 1: from the Earth's orbit how strong the Sun's gravity has
• 27:25
  Speaker 1: to be to keep us in orbit. So already we
• 27:27
  Speaker 1: know the Sun's mass, right, which gives us a lot
• 27:29
  Speaker 1: of clues, but we don't know much about the density
• 27:32
  Speaker 1: and what's going on inside there.
• 27:34
  Speaker 2: Or the age. Right. We decided we needed to know
• 27:36
  Speaker 2: age too, Yeah.
• 27:37
  Speaker 1: And another crucial hint is while the Sun is very bright,
• 27:40
  Speaker 1: so something going on inside the Sun producing that energy,
• 27:43
  Speaker 1: and it's like an incredible amount of energy. I don't
• 27:46
  Speaker 1: think people really appreciate how much energy is being put
• 27:49
  Speaker 1: out by the Sun, Like we capture the tiniest, tiniest
• 27:52
  Speaker 1: little fraction of it. But the Sun's total power outage
• 27:56
  Speaker 1: is four times ten to the twenty six watts. Wow,
• 27:59
  Speaker 1: which is like ten quadrillion times the amount of power
• 28:03
  Speaker 1: released by the most energetic power plants ever constructed on Earth. Wow,
• 28:07
  Speaker 1: it's just we are sipping from an ocean of energy here.
• 28:11
  Speaker 1: That's just like being blasted out into space.
• 28:14
  Speaker 2: And it powers our whole planet.
• 28:15
  Speaker 1: It really does. And people wondered for a long time
• 28:19
  Speaker 1: like what's producing all that energy? How long has the
• 28:22
  Speaker 1: Sun been burning? They're wondering like is there something up
• 28:25
  Speaker 1: there that's on fire? And that of course is a
• 28:28
  Speaker 1: clue to what the Sun might be made out of.
• 28:29
  Speaker 1: People were wondering like is it made at the same
• 28:31
  Speaker 1: stuff as the Earth somehow? Is it made out of
• 28:34
  Speaker 1: something different? So re enter Lord Kelvin, King of approximate
• 28:38
  Speaker 1: initial terrible estimates of what the universe is.
• 28:41
  Speaker 2: Made out of would I. I guess I'd be happy
• 28:44
  Speaker 2: if I was known for anything, but I do feel
• 28:46
  Speaker 2: like I wouldn't really want to be known for that
• 28:48
  Speaker 2: in particular.
• 28:49
  Speaker 1: No, I love that situation, like getting the first bited
• 28:51
  Speaker 1: some apples, some fascinating question nobody's tackled. Those are the
• 28:54
  Speaker 1: funnest ones I'm jealous of, Like the Greeks and the
• 28:57
  Speaker 1: Sumerians and the ancient Chinese and the Mayans who got
• 28:59
  Speaker 1: to think about these questions that nobody had worked on before, right,
• 29:03
  Speaker 1: like the answer could have been anything anyway. I think
• 29:06
  Speaker 1: that's super exciting.
• 29:07
  Speaker 2: One of my favorite stories along this line is there
• 29:11
  Speaker 2: was a guy who studied vaccines. His name was Sir
• 29:13
  Speaker 2: Wright w R I g h T. And he every
• 29:16
  Speaker 2: time got something important incorrect, and he ended up becoming
• 29:21
  Speaker 2: known as Sir not quite right and all right anyway,
• 29:26
  Speaker 2: tangent complete. Where were we?
• 29:29
  Speaker 1: So? Lord Kelvin is trying to understand what's the sun
• 29:31
  Speaker 1: man out of And first he thought, well, what if
• 29:33
  Speaker 1: it's just like fuel. You know, we have fire here
• 29:36
  Speaker 1: on Earth. If the Sun is a huge ball of
• 29:38
  Speaker 1: fuel that's chemically burning, could that explain what we're seeing,
• 29:42
  Speaker 1: you know? And that would tell you like, oh, maybe
• 29:44
  Speaker 1: the Sun is a huge ball of gasoline basically or
• 29:47
  Speaker 1: a curacy no runout. So if you do the calculation,
• 29:50
  Speaker 1: giving your knowledge the mass of the sun, chemical burning
• 29:53
  Speaker 1: can only produce that much power for like tens of
• 29:55
  Speaker 1: thousands of years, not for billions of years. Why because
• 29:59
  Speaker 1: chemical burning is very inefficient, like most of the energy
• 30:03
  Speaker 1: in mass is not released when you just like change
• 30:06
  Speaker 1: the chemical state from one to another. Whereas you know,
• 30:09
  Speaker 1: fusion is what's happening inside the Sun, and that's much
• 30:11
  Speaker 1: more efficient, much more effective release of energy. You get
• 30:14
  Speaker 1: a lot more energy out. And so if you want
• 30:16
  Speaker 1: to produce all the energy that the Sun is producing
• 30:19
  Speaker 1: and do it for billions of years, you can't rely
• 30:21
  Speaker 1: on like burning kerosene or some similar chemical process because
• 30:25
  Speaker 1: there just isn't enough mass in the Sun to keep
• 30:28
  Speaker 1: that going for billions of years.
• 30:29
  Speaker 2: All right, It's not logs on a fire. So how
• 30:32
  Speaker 2: do they figure out what it was?
• 30:34
  Speaker 1: Well, people went down other rabbit holes also, which is
• 30:36
  Speaker 1: really fun. They were thinking, maybe the Sun isn't limited
• 30:38
  Speaker 1: to its current mass. Maybe this is some source of mass?
• 30:41
  Speaker 1: Is it like gobbling up stuff from the Solar system?
• 30:44
  Speaker 1: I mean early days you can think of all sorts
• 30:46
  Speaker 1: of crazy ideas, right, Yeah, but that was ruled out
• 30:49
  Speaker 1: pretty quickly because it would require an enormous amount of mass,
• 30:52
  Speaker 1: Like you'd need a sun to refuel the Sun every
• 30:55
  Speaker 1: ten thousand years, so it's like the Sun is not
• 30:57
  Speaker 1: eating other stars every day. That would leave a huge
• 31:01
  Speaker 1: imprint on the orbits of planets and stuff like that,
• 31:03
  Speaker 1: so that was ruled out. Another thought people had is
• 31:06
  Speaker 1: maybe the Sun is like contracting gravitationally and converting that
• 31:11
  Speaker 1: gravitational potential energy somehow into heat. And this is sort
• 31:15
  Speaker 1: of on the right track, but if you don't understand fusion,
• 31:17
  Speaker 1: you don't have the final piece there. And this would
• 31:19
  Speaker 1: only few the star for like tens of millions of years.
• 31:22
  Speaker 1: And this is actually what's happening to neutron stars and
• 31:25
  Speaker 1: white dwarves that are not undergoing fusion. They're just like
• 31:28
  Speaker 1: being compressed and kept hot by gravity.
• 31:31
  Speaker 2: Was this Kelvin's idea? All these because it matches up
• 31:33
  Speaker 2: with his other All of these were Kelvins.
• 31:35
  Speaker 1: These are Calvin's ideas. Yeah, this is Kelvin, like, you know,
• 31:38
  Speaker 1: smoking whatever he was smoking and thinking about the universe
• 31:41
  Speaker 1: and coming up with dumbers Okay, I love it. I'm
• 31:43
  Speaker 1: a fan of Kelvin.
• 31:43
  Speaker 2: Yeah, he sounds like a fun guy, and I think
• 31:45
  Speaker 2: it would have been fun to read your theories about
• 31:48
  Speaker 2: this kind of stuff. And then I could have called
• 31:50
  Speaker 2: you not quite rights.
• 31:52
  Speaker 1: In, Oh nice, Daniel wrongs and Daniel first a terrible approximation.
• 32:00
  Speaker 2: Of the answer that doesn't roll off the tone quite
• 32:02
  Speaker 2: as nicely. But okay, what else did Calvin think?
• 32:05
  Speaker 1: So that's where the mystery stood until around the early
• 32:08
  Speaker 1: nineteen hundreds, And at that point people sort of naturally
• 32:11
  Speaker 1: assumed that the Sun must be made of the same
• 32:14
  Speaker 1: stuff as the Earth. They were like, hey, the solar
• 32:16
  Speaker 1: system comes together, stuff is formed. Why wouldn't the Sun
• 32:20
  Speaker 1: be made of the same stuff as the Earth? And
• 32:23
  Speaker 1: you know, I think this goes a long way to
• 32:24
  Speaker 1: pointing out how often we accept ideas in science because
• 32:28
  Speaker 1: they make sense to us without really interrogating them. You know,
• 32:32
  Speaker 1: what seems natural doesn't always get as many questions as
• 32:35
  Speaker 1: what seems weird, And so later on, one hundred years later,
• 32:39
  Speaker 1: when something else seems natural, we might wonder like, huh,
• 32:41
  Speaker 1: how could they accept that? But at the time it
• 32:44
  Speaker 1: was the most natural explanation, And now is the time
• 32:47
  Speaker 1: to enter the major villain of this story, Henry Russell.
• 32:51
  Speaker 1: In nineteen fourteen, he wrote, if the Earth's crust should
• 32:55
  Speaker 1: be raised to the temperature of the Sun's atmosphere, it
• 32:57
  Speaker 1: would give a very similar absorption spectrum. The spectrum of
• 33:01
  Speaker 1: the Sun and other stars are similar, so it appears
• 33:03
  Speaker 1: that the relative abundance of elements in the universe was
• 33:06
  Speaker 1: like that in the Earth's crust. So he's saying the
• 33:09
  Speaker 1: Sun is made out of the same stuff as the Earth,
• 33:12
  Speaker 1: and if you heat it up the Earth it would
• 33:13
  Speaker 1: glow just like the Sun.
• 33:15
  Speaker 2: So that sounds wrong, but not villainous. What are we
• 33:19
  Speaker 2: going to get to more? Or do you just really
• 33:20
  Speaker 2: thought this idea was dumb.
• 33:22
  Speaker 1: That's not his villainy, that was just foreshadowing.
• 33:24
  Speaker 2: Oh okay, let's take a break and when we come back,
• 33:27
  Speaker 2: we'll find out what made Russell villainous. All right, Daniel,
• 33:51
  Speaker 2: I'm on pins and needles. Let's get to the story
• 33:53
  Speaker 2: of why Russell was such a villain.
• 33:56
  Speaker 1: So Russell was on the right track and trying to
• 33:58
  Speaker 1: understand what the Sun is made out of, and many
• 34:00
  Speaker 1: of our listeners gave this answer. The answer is spectroscopy,
• 34:04
  Speaker 1: Like if you can't go there. What can you do
• 34:06
  Speaker 1: to understand what something is made out of? And it's
• 34:08
  Speaker 1: similar to what you might do on Earth as you mentioned,
• 34:10
  Speaker 1: like if you needed to know what is a scoop
• 34:13
  Speaker 1: of dirt made out of, you might try to separate
• 34:15
  Speaker 1: into components and then you might heat them up and
• 34:17
  Speaker 1: look at the light that they emit. Because different atoms
• 34:20
  Speaker 1: emit at different wavelengths. Right, every atom has different energy levels.
• 34:24
  Speaker 1: The electrons can be on those energy levels, but not
• 34:26
  Speaker 1: between them. If you heat it up, the electrons go
• 34:29
  Speaker 1: up energy levels. If you let it cool down, the
• 34:31
  Speaker 1: electrons go down energy levels and emit photons. The energy
• 34:35
  Speaker 1: of those photons matches the energy difference between those energy
• 34:39
  Speaker 1: levels and tells you what is the difference between those
• 34:42
  Speaker 1: energy levels. And every atom has a different set of energies,
• 34:45
  Speaker 1: so every atom has a different spectrum. So you take
• 34:48
  Speaker 1: a gas of random stuff, you don't know what it is,
• 34:50
  Speaker 1: you heat it up, you look at the energy levels.
• 34:52
  Speaker 1: You can figure out what it's made out of and
• 34:54
  Speaker 1: what the relative contributions are. You're like, oh, there's a
• 34:57
  Speaker 1: little I see hydrogen in here, I see helium here,
• 35:00
  Speaker 1: I see lithium or magnesium right, it's an amazing way
• 35:03
  Speaker 1: to tell what Earth is made out of. So, in
• 35:05
  Speaker 1: terms of the general approach to the listeners and the
• 35:07
  Speaker 1: villain of today's episode, Henry Russell, are on the right track.
• 35:11
  Speaker 1: The spectroscopy is the way to go.
• 35:13
  Speaker 2: He didn't develop spectroscopy, right, he just applied it incorrectly.
• 35:17
  Speaker 1: That's right. He didn't develop spectroscopy. And you notice in
• 35:20
  Speaker 1: his quote he says if the Earth's crust should be raised,
• 35:23
  Speaker 1: it would give a very similar absorption spectrum. And so
• 35:26
  Speaker 1: he's sort of speculating here, right, And the problem is
• 35:29
  Speaker 1: that this wasn't as easy as we describe it. There
• 35:31
  Speaker 1: was an important complexifying factor here, which is ionization. And
• 35:36
  Speaker 1: so for example, you might think, well, why don't they
• 35:38
  Speaker 1: just look at the light from the Sun and you
• 35:40
  Speaker 1: use that to figure out what the Sun is made of?
• 35:41
  Speaker 1: Boom boom boom. Done right. Well, the problem is the
• 35:44
  Speaker 1: atmosphere of the Sun is complicated, and there's one more
• 35:46
  Speaker 1: factor we didn't describe, which is that the atmosphere is ionized.
• 35:50
  Speaker 1: Like sometimes these gases in the Sun's atmosphere gets so
• 35:53
  Speaker 1: much energy they lose electrons. It's not just like, oh,
• 35:56
  Speaker 1: you've got oxygen and has all of its electrons and
• 35:58
  Speaker 1: they're going up and down and emitting photons can tell
• 36:00
  Speaker 1: it's oxygen. Sometimes those electrons are lost, right, and when
• 36:04
  Speaker 1: an atom gets ionized, its energy levels shift a little bit.
• 36:07
  Speaker 1: Because it's a big complicated thing, and so the spectrum
• 36:11
  Speaker 1: you expect from a star depends on how many electrons
• 36:14
  Speaker 1: are around those nuclei, which depends a little bit on
• 36:18
  Speaker 1: the temperature of the gas. So it turns out to
• 36:20
  Speaker 1: be kind of a complex problem.
• 36:22
  Speaker 2: So does that mean that the spectroscopy results from the
• 36:25
  Speaker 2: sun were wrong? And he didn't realize that, and that
• 36:28
  Speaker 2: was the main problem.
• 36:29
  Speaker 1: The spectroscopy results from the Sun. Nobody could understand yet.
• 36:32
  Speaker 1: They were like, hmm, this is weird. We don't understand
• 36:35
  Speaker 1: these lines. They look different from what we expect. But
• 36:37
  Speaker 1: Russell was convinced anyway that it was made of the
• 36:40
  Speaker 1: same stuff of the Earth. He believed that it was natural.
• 36:42
  Speaker 1: To him. He was like, I'm sure this is just
• 36:44
  Speaker 1: some detail. We'll figure this out. And so now enter
• 36:48
  Speaker 1: the heroine of this episode. Yes, Cecilia Pain. Cecilia Pain
• 36:52
  Speaker 1: is the one who solved this problem. She read a
• 36:55
  Speaker 1: paper by a brilliant guy named Megnad Saha, who understood
• 36:59
  Speaker 1: all the these ionization effects. He like calculated exactly what you
• 37:02
  Speaker 1: should expect for various ionizations at various temperatures of all
• 37:05
  Speaker 1: of the elements. He was just like, he wasn't thinking
• 37:08
  Speaker 1: about the Sun. He was just like, Hey, chemistry is cool,
• 37:10
  Speaker 1: and I want to understand energy levels and let's dig
• 37:12
  Speaker 1: deep into this. And he totally nerded out about this.
• 37:15
  Speaker 1: And Cecily Pain is like, oh, this is a solution
• 37:18
  Speaker 1: to this huge problem that we have over in astrophysics
• 37:20
  Speaker 1: of understanding what we should expect from the sun. So
• 37:23
  Speaker 1: she put these two things together and she was able
• 37:26
  Speaker 1: to interpret correctly the spectrum of light we're getting from
• 37:29
  Speaker 1: the Sun and understand why it looked a little shifted
• 37:32
  Speaker 1: and a little weird from what folks like Henry Russell expected.
• 37:35
  Speaker 2: Amazing, and like note students, the importance of reading widely.
• 37:40
  Speaker 2: I think there are so many connections that you make
• 37:42
  Speaker 2: that you might not be expecting.
• 37:44
  Speaker 1: Yeah, exactly, And so this is a huge breakthrough and like,
• 37:47
  Speaker 1: finally we could understand what the sun is made out of.
• 37:50
  Speaker 1: And the result was a huge surprise, especially to folks
• 37:53
  Speaker 1: like Pain. Number one, the sun is made out of
• 37:56
  Speaker 1: the same stuff as the Earth, Like there's hydrogen in this, helium,
• 37:59
  Speaker 1: this oxygen, iron, this nickel, this all the same stuff,
• 38:01
  Speaker 1: but it comes in very different numbers. Like the relative
• 38:05
  Speaker 1: abundances are very very different in the Sun. Basically the
• 38:08
  Speaker 1: Sun is mostly hydrogen and helium and everything else is there,
• 38:13
  Speaker 1: but it's tiny, Like it's seventy four percent hydrogen, twenty
• 38:17
  Speaker 1: five percent helium, and everything else is one percent.
• 38:21
  Speaker 2: Wow. Yeah, all right, And so I'm just gonna guess,
• 38:24
  Speaker 2: based on some other conversations we've had about women in science,
• 38:27
  Speaker 2: that Russell isn't just the villain because he was wrong,
• 38:31
  Speaker 2: but he probably did something to turf Pain's results. Am
• 38:34
  Speaker 2: I right?
• 38:35
  Speaker 1: Oh? Absolutely?
• 38:36
  Speaker 2: Okay.
• 38:36
  Speaker 1: So she was at Harvard and the director of the
• 38:39
  Speaker 1: observatory was Russell, and Russell had the power at the
• 38:42
  Speaker 1: time to veto any publication he wanted for whatever reason,
• 38:47
  Speaker 1: including her thesis. Aw So he blocked her getting her
• 38:51
  Speaker 1: PhD thesis unless she added the following caveat to her
• 38:54
  Speaker 1: thesis quote. The outstanding discrepancy between the astrophysical and to
• 39:00
  Speaker 1: rrestrial abundances are displayed for hydrogen and helium. The enormous
• 39:04
  Speaker 1: abundance derived for these elements in the atmosphere is almost
• 39:07
  Speaker 1: certainly not real.
• 39:09
  Speaker 2: What he had her at a caveat that was like,
• 39:11
  Speaker 2: but also, probably I'm wrong.
• 39:13
  Speaker 1: Is all this amazing science is huge breakthrough and then
• 39:16
  Speaker 1: he's like, I disagree with it, so probably this is BS.
• 39:19
  Speaker 1: Don't believe these numbers.
• 39:20
  Speaker 2: By the way, Oh my gosh. And what a coward
• 39:23
  Speaker 2: that he did. Sounds like he didn't point out exactly
• 39:26
  Speaker 2: where she had an error right, like because.
• 39:30
  Speaker 1: He just couldn't accept it. He was like, no, the
• 39:32
  Speaker 1: science says, so I don't see a mistake, but no,
• 39:35
  Speaker 1: this flies in the face of what I believe, and
• 39:37
  Speaker 1: so I'm gonna insist that you add this caveat to
• 39:41
  Speaker 1: her thesis. Her advisor was a guy named Harlow Shapley
• 39:44
  Speaker 1: and shapely ordered six hundred copies of her thesis and
• 39:47
  Speaker 1: sent it to all the important astronomers in the world.
• 39:49
  Speaker 2: Oh wow, okay, so he believed in her.
• 39:51
  Speaker 1: He believed in her. Yet did he go through exactly.
• 39:54
  Speaker 2: All six hundred copies and like cross out that line
• 39:56
  Speaker 2: that she had to add.
• 39:59
  Speaker 1: I don't know, but he knew this guy because Russell
• 40:00
  Speaker 1: was also his PhD advisor. So I think they had
• 40:03
  Speaker 1: a common experience there. But it gets even worse because
• 40:06
  Speaker 1: even though Russell said no, this isn't true, this can't
• 40:10
  Speaker 1: be true, a few years later, when the scientific tides
• 40:13
  Speaker 1: turned and everybody accepted this, he took credit for this discovery. No, yes, exactly,
• 40:19
  Speaker 1: And so in most historical records until recently, people gave
• 40:23
  Speaker 1: Henry Russell credit for a discovery of what the sun
• 40:26
  Speaker 1: is made out of, which is like such a tragedy.
• 40:29
  Speaker 2: No it is, I agree, it's exactly.
• 40:32
  Speaker 1: He's a total villain. So only four years after calling
• 40:35
  Speaker 1: it impossible, you find him in the literature taking credit
• 40:38
  Speaker 1: for this discovery. So it's a real shame.
• 40:41
  Speaker 2: It isn't real. Okay, So then how did we rediscover
• 40:43
  Speaker 2: Cecilia Paine?
• 40:44
  Speaker 3: Then?
• 40:44
  Speaker 1: Yeah, that's an important point. Cecia Paine ended up getting
• 40:47
  Speaker 1: her PhD in astronomy, only the second PhD in astronomy
• 40:50
  Speaker 1: ever by a woman at Harvard WOW. And initially she
• 40:53
  Speaker 1: was barred from becoming a professor at Harvard because she
• 40:55
  Speaker 1: was a woman, so she did a lot of less prestigious,
• 40:58
  Speaker 1: lower paid research job, but she ended up becoming the
• 41:01
  Speaker 1: first female tenured professor at Harvard WOW, and the first
• 41:04
  Speaker 1: female chair of a department at Harvard.
• 41:07
  Speaker 4: Wow.
• 41:07
  Speaker 1: So you know, things changed and she ended up having
• 41:10
  Speaker 1: a good career in astrophysics. And then later people digging
• 41:14
  Speaker 1: into the record corrected it, and so, for example, there
• 41:17
  Speaker 1: is an essay by Otto Struve who called it quote
• 41:20
  Speaker 1: undoubtedly the most brilliant Pahd thesis ever written in astronomy.
• 41:24
  Speaker 2: Wow.
• 41:25
  Speaker 1: Wow, that's forty years later. She went forty years before
• 41:31
  Speaker 1: really getting the recognition.
• 41:32
  Speaker 2: Was she still alive, Yeah, she was.
• 41:34
  Speaker 1: She died in seventy nine.
• 41:36
  Speaker 2: I'm glad she got to see her work vindicated in
• 41:38
  Speaker 2: her lifetime. That's amazing.
• 41:40
  Speaker 1: Yeah. She ended up winning some prizes and was elected
• 41:42
  Speaker 1: to the Royal Astronomical Society. The arc of justice is long,
• 41:46
  Speaker 1: but it does point in the right direction, even into astronomy.
• 41:48
  Speaker 2: I mean often, but not.
• 41:50
  Speaker 1: Always eventually, I hope, yes. But to see it, pain
• 41:54
  Speaker 1: taught us a lot about the nature of the universe, right.
• 41:56
  Speaker 1: People thought for a long time that everything in the
• 42:00
  Speaker 1: verse must be made out of the same stuff as
• 42:01
  Speaker 1: the Earth, like that was a natural assumption to them.
• 42:04
  Speaker 1: And now we know, of course that the Sun is
• 42:06
  Speaker 1: mostly hydrogen and helium, and from our models of the
• 42:09
  Speaker 1: formation of the solar system. It makes sense, right, Like
• 42:12
  Speaker 1: the Sun is the center of gravity and most stuff
• 42:15
  Speaker 1: flocks there and it pulls in all the gases in
• 42:17
  Speaker 1: the inner Solar System, and the Earth did have more
• 42:20
  Speaker 1: hydrogen helium early on, but because these are such light elements,
• 42:23
  Speaker 1: they were blasted away by the Sun's radiation in the
• 42:26
  Speaker 1: early part of the formation of the Solar System. So
• 42:29
  Speaker 1: now we have a full and complex and nuanced understanding
• 42:32
  Speaker 1: of the formation of the Solar System and the planets,
• 42:34
  Speaker 1: and we can apply this knowledge to understanding other stars,
• 42:37
  Speaker 1: like our star isn't the only star in the universe,
• 42:40
  Speaker 1: and every star has its own unique pattern. We talked
• 42:43
  Speaker 1: recently about why stars are different colors because they are
• 42:45
  Speaker 1: made of different stuff, and their atmospheres has different stuff
• 42:48
  Speaker 1: and they're different temperatures. And now with this model, with
• 42:51
  Speaker 1: to see a pain's understanding, we can use this to
• 42:54
  Speaker 1: understand what the rest of the universe is made out of.
• 42:57
  Speaker 2: Wow, Okay, And so with these corrections we can now
• 42:59
  Speaker 2: look at out into the universe and without even visiting it,
• 43:02
  Speaker 2: we can know what different celestial bodies are made out of.
• 43:05
  Speaker 1: Yeah, exactly. Thanks to Secila opinion and to Megna Saha,
• 43:09
  Speaker 1: he is an Indian astrophysicist who figured out the ionization equations.
• 43:13
  Speaker 1: His Saha ionization equation is super important for us to
• 43:16
  Speaker 1: figure out the nature of the universe. And it's incredible
• 43:19
  Speaker 1: that we can figure this out. I mean, think about
• 43:21
  Speaker 1: all the little puzzles that people had to solve all
• 43:24
  Speaker 1: the way down to like figuring out how massive the
• 43:26
  Speaker 1: Earth is by measuring a mountain in Scotland. Like, all
• 43:30
  Speaker 1: of these pieces were necessary and they all came together.
• 43:33
  Speaker 1: And when you're solving a puzzle, often there's like a
• 43:35
  Speaker 1: huge unanswered question that you don't even know how to begin.
• 43:38
  Speaker 1: And if you're lucky, people have been working on that
• 43:41
  Speaker 1: question for other reasons for one hundreds of years, making progress,
• 43:44
  Speaker 1: hiking around mountains trying to figure it out, or just
• 43:47
  Speaker 1: nerding out about the chemistry. But sometimes you're not so lucky.
• 43:50
  Speaker 1: And that's why it's so important that we push in
• 43:52
  Speaker 1: so many directions simultaneously, even though we don't know yet
• 43:55
  Speaker 1: how they're going to be useful or what mysteries they
• 43:58
  Speaker 1: might unlock. We need all of these tools so that
• 44:01
  Speaker 1: in the future, clever people can come up with answers
• 44:03
  Speaker 1: to huge questions like what is the universe?
• 44:06
  Speaker 2: Made out of amen. By geeking out and by geeking
• 44:09
  Speaker 2: out together, we can change the world.
• 44:13
  Speaker 1: All right. Thanks very much for coming on this tour
• 44:15
  Speaker 1: of how we figured out what elements of the universe
• 44:18
  Speaker 1: is made out of diving deep into the earth and
• 44:20
  Speaker 1: casting our minds all the way across the universe.
• 44:30
  Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
• 44:33
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• 44:35
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• 44:38
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