Henrietta Leavitt and the end of the universe

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Speaker 11 Do do do do do do holding a bicroph.

Speaker 12 Oh, a bicrophone.

Speaker 13 Someone should make a bicrophone.

Speaker 13 Bird,

Speaker 14 hello.

Speaker 15 I'm coming from the lake. I see you down on the lake.
Oh, wait.

Speaker 13 Hey, look to your left.

Speaker 15 I see you.

Speaker 15 All right.

Speaker 15 I'm going to turn on my recorder. Give me a second.

Speaker 15 Okay.

Speaker 15 So

Speaker 15 Noam, here we are. Prospect Park.

Speaker 11 New York City, clear Tuesday night.

Speaker 15 And I brought you here because I want you to try a little thought experiment with me. Okay.
So with the approximately four stars, five stars. Oh, that's a plane.
The approximately four stars.

Speaker 15 We can see the sky. It's a plane.

Speaker 15 I would like you

Speaker 15 to imagine that you are going to make a map of the cosmos. Okay.
So that star there, the one that looks really bright, that star next to it, that star over there.

Speaker 15 How would you figure out how far away from the Earth or how close to the Earth those stars are?

Speaker 13 I'm sure I'm going to get this wrong, but I assume

Speaker 13 something

Speaker 14 about like how big it is, how bright it is.

Speaker 15 Wrong answer.

Speaker 15 Okay.

Speaker 15 So imagine the stars are actually light bulbs.

Speaker 15 Maybe that star, the like bright one right there between the trees, maybe it's it's a hundred watt light bulb, right? And it's it's super bright. Or maybe it's you know a 30 watt light bulb.

Speaker 15 It's actually quite dim, but it's just it's just really close.

Speaker 13 Right. Or like the like one of the dim stars over there could actually be super, super bright, like 100 watts, but just really far.

Speaker 15 Exactly.

Speaker 12 Yeah. Yeah, that's conundrum.
Right.

Speaker 15 So this is the exact problem that astronomers were facing at the end of the 1800s, right? They were looking at these stars in the sky.

Speaker 15 All they had was the brightness to go on, and they had no way of figuring out what is the map of the cosmos.

Speaker 13 And I assume they eventually figured it out.

Speaker 12 Yeah.

Speaker 15 So this episode is going to be not just how they figured it out. Astronomers did develop a yardstick.
to measure the distance to the stars, but also what happened once they did. Because

Speaker 15 the idea of mapping the cosmos turned into kind of reinventing our entire understanding of the cosmos.

Speaker 15 Do you feel set up?

Speaker 13 I mean, I feel I'm intrigued.

Speaker 15 I want to hear the rest.

Speaker 17 Okay.

Speaker 13 That's it. That's it for the intro.

Speaker 15 No, you want more intro?

Speaker 13 All right. I'm Noah Masenfeld.

Speaker 15 I'm Bird Pinkerton.

Speaker 13 And this week on Unexplainable, the yardstick that reinvented the universe.

Speaker 15 The yardstick for measuring the universe came out of a really basic project.

Speaker 15 In the 1890s, Harvard University was trying to build a comprehensive database of the southern sky.

Speaker 15 everything they knew about every star.

Speaker 12 Down at an observatory in Peru, they were doing a survey trying to photograph all different parts of the nighttime sky in the southern hemisphere.

Speaker 15 George Johnson wrote a book about this project.

Speaker 12 And they would do this, you know, several months apart so they could see how stars changed over time.

Speaker 15 They'd collect all these photographs and then they'd bring them home.

Speaker 12 They would pack up these glass photographic plates and then take them down on muleback down the mountain to the harbor and then ship these things by boat to Boston or they would unload them and bring them into Harvard Observatory and put them on a little dumb waiter kind of elevator and bring them up to the level with the computers.

Speaker 15 Back in the 1890s, computers meant people, usually women who were doing the hard work and the number crunching that male scientists didn't necessarily want to do.

Speaker 15 In this case, they were collecting data about stars.

Speaker 12 And they all have these light tables and they would be scrutinizing these glass photographic plates lit from behind and just this meticulous observation.

Speaker 15 A lot of the plates were negatives.

Speaker 12 White sky with little black dots.

Speaker 15 And these computers took measurements of each dot, they compared them to other dots, and then they wrote up these thousands and thousands of dots in neat letters.

Speaker 12 You know, day after day for all of these stars.

Speaker 15 Including some particularly tricky stars.

Speaker 12 One thing that astronomers had noticed is, you know, they look up at the sky and they notice that some of these things aren't always the same brightness. They go brighter, dimmer, brighter, dimmer.

Speaker 12 They pulsate, you know, like beacons.

Speaker 15 Astronomers call these stars Cepheid variables because they were variable, they changed. And the first one was seen in the Cepheus constellation.

Speaker 15 These Harvard scientists, they didn't know why the Cepheid variable stars were pulsing, but they knew that they were finding them all over the night sky.

Speaker 15 So they figured, why not kind of have some projects to track them specifically?

Speaker 12 They just said, here are some plates that have just come up from Peru, and we'd like to know what the rhythm was by which they go from bright to dim to bright to dim.

Speaker 12 So you can imagine how tedious this would be, like lugging around these heavy glass plates and trying not to break them and

Speaker 12 putting them on these viewing frames and measuring these things, jotting them down with ink and a notebook and trying to figure out what the rhythm was of these variable stars.

Speaker 15 Back then, being a computer paid better than working in the cotton mill, for example, and it was actually a pretty good job if you were a woman who was interested in science.

Speaker 15 But the women who were making these calculations were definitely not expected to have insights about the stars that they were cataloging.

Speaker 15 Like, you don't expect your mechanical calculator to suddenly look up and say that it's noticed a pattern in the math that it's doing.

Speaker 15 But these computers were human beings, so that's exactly what happened with one woman in particular.

Speaker 12 Henrietta Levitt.

Speaker 15 Henrietta Levitt.

Speaker 12 Looking very Victorian, you know, with this high collar and her hair up in a bun.

Speaker 15 She spent years tracking and measuring Cepheid variable stars. And then in 1908, she pulled together all her measurements into a paper for Harvard Observatory's publication.

Speaker 12 21 pages, 15 pages of tables. So again, you just imagine all of the work that this took.

Speaker 15 Henrietta had focused on one cluster of stars that were all together in the sky, kind of like a bunch of cosmic grapes.

Speaker 15 And this paper was a detailed list of 1,777 of the Cepheid variable stars in that cluster.

Speaker 12 And almost as an asterthought, it says, it is worthy of notice that the brighter variables have the longer periods.

Speaker 15 It is worthy of notice that the brighter variables have the longer periods.

Speaker 15 This was Henrietta's big insight, and it was the first step to solving the problem that I mentioned at the beginning of the episode, the one that astronomers were grappling with as they stared at the night sky.

Speaker 15 Because remember, they were looking at the stars and they were wondering, is that really a dim star? Is that a 30-watt light bulb?

Speaker 13 Or is it just far away?

Speaker 15 Like, how do we tell?

Speaker 15 But because Henrietta looked at Cepheid variable stars in a single star cluster, she could kind of compare them against each other.

Speaker 15 So she was writing down, all right, this Cepheid variable star overall, on average, it's brighter than nearby stars, and it's pulsing slowly.

Speaker 12 Bright to dim, bright to dim.

Speaker 15 This one over here, it's dimmer overall, and it's pulsing very fast.

Speaker 12 Bright, dim, bright, dim, bright to dim.

Speaker 15 This bright one

Speaker 15 is going very slow.

Speaker 12 Bright to dim.

Speaker 15 And eventually, Henrietta saw a pattern.

Speaker 12 She noticed that there was a relationship between how fast the star pulsed from bright to dim and what its brightness was.

Speaker 15 The slower a Cepheid variable star pulsed, the brighter it was.

Speaker 17 This was a huge realization.

Speaker 15 This was the first time that anyone could tell whether a particular star was actually bright or just looked bright because it was close to us.

Speaker 15 And conveniently, you can find Cepheid variable stars all over the observable universe. So astronomers could use them to tell how far away from Earth lots of star clusters are.

Speaker 15 They could look at any given Cepheid variable and say, okay, this star might look dim to me, but because it's pulsing really slowly, it must actually be bright but far away.

Speaker 15 So everything in that star cluster must also be far away.

Speaker 15 Henrietta's one kind of tossed off sentence gave astronomers a way to say, this star is closer to us than that one, but it's further away than that one over there.

Speaker 12 And that's really still the basis of the whole cosmological yardstick, as they sometimes call it, that we use today, or these measurements that Henrietta Levitt made.

Speaker 15 This one idea from Henrietta's paper, it eventually cracked astronomy wide open.

Speaker 15 Henrietta herself got sick and had to leave Harvard for a long stretch, but her male boss wound up publishing sort of a follow-up paper using her work.

Speaker 15 And after that, other scientists, like Edwin Hubble, for example, took her scale and they gave it concrete numbers. So you could put a firm distance on the stars.

Speaker 12 But really, it's her discovery that sits at the basis of all of the distance scales we use to reach further and further out into the universe.

Speaker 15 And this ability to measure the universe completely transformed how we understood it. We didn't just learn how big it was, but also that it was growing and changing.

Speaker 15 So this yardstick, it helped rewrite textbooks. And as early as the 1920s, a mathematician tried to nominate Henrietta for the Nobel Prize for her contributions.

Speaker 15 At that point, she'd already died of cancer, so she didn't get that recognition then.

Speaker 15 But even now, she's kind of a footnote. For other influential scientists, we have papers and journals and their diaries.

Speaker 12 Very, very little of that existed for Henrietta Leavitt.

Speaker 12 I did find this one letter where she refers to embarking on a ship from

Speaker 12 America to Europe. And,

Speaker 12 you know, and I remember reading that and thinking, God, I wonder if she was with someone. You know, I hope so.
But,

Speaker 12 you know, we just don't know.

Speaker 15 We do know some small details. So we know that Henrietta went deaf at one point.
And we know that she got really sick several times in her life.

Speaker 15 We also know from her ledger books that she had very neat handwriting.

Speaker 15 But unfortunately, we don't really know all that much more than that. Henrietta discovered a way for astronomers to unlock countless mysteries of the universe.

Speaker 15 But at the end of the day, she herself remains kind of a mystery.

Speaker 13 After the break, we're going to get into all the cosmic mysteries that Henrietta's yardstick helped unlock.

Speaker 13 Because ultimately, she didn't just give astronomers a tool to measure the distance to to stars. She helped scientists completely rethink the universe.

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Speaker 19 You are about to take a journey out of this world into the world of the future. Forget the world around you.
Forget the people around you.

Speaker 19 You are entering Unexplainable. Alone with your own thoughts.

Speaker 13 Unexplainable, we're back here with senior reporter Brian Resnick.

Speaker 11 Hey.

Speaker 13 So Bird was talking about Henrietta Levitt and how she kind of came up with this yardstick to measure the universe. And Brian, you were actually working on this story with Bird from the start.

Speaker 13 Where did this yardstick end up taking science? Like,

Speaker 13 I mean, basically,

Speaker 13 what happened next?

Speaker 11 Yeah, like a lot happened next.

Speaker 12 Okay.

Speaker 11 Scientists kept improving on this yardstick. And, you know, once you have a yardstick, you use it to measure stuff.

Speaker 11 So every time scientists took measurements with this yardstick, it was like the whole universe fundamentally changed.

Speaker 17 It was not until we started to be able to measure distances in the cosmos that we knew that other galaxies existed.

Speaker 11 I talked to Katie Mack about all this. She's an astrophysicist.
She's written a great book that gets into a lot of this, like the power of measuring things in space.

Speaker 13 And she's saying basically that before all of this, before this kind of massive measurement, scientists didn't know there were other galaxies.

Speaker 17 Yeah, so there were

Speaker 17 these observations of what were called spiral nebulae or island universes, these little smudges in the sky.

Speaker 17 And those were for a long time thought to be perhaps clusters of stars within our own galaxy or nebulae or some kind of object nearby.

Speaker 11 Do you know Edwin Hubble?

Speaker 13 Sure do.

Speaker 14 Hubble Telescope.

Speaker 11 In the 1920s, he was an astronomer at the Mount Wilson Observatory in California and he was looking at this smudgy area of the sky called Andromeda and Hubble is studying it and he's looking out for one of these pulsating stars, one of the Cepheids.

Speaker 11 And because of Henrietta, he knows if he sees a Cepheid, he can see how far away Andromeda is. And he sees a Cepheid.
He sees one of these variable stars.

Speaker 21 Puts in the calculations and X-Tree, X-Tree, read all about it.

Speaker 11 Realizes Andromeda is so far away, it just must be another galaxy.

Speaker 21 Another universe seen by astronomer.

Speaker 11 This was big, like front-page headline-grabbing news.

Speaker 21 Dr. Hubble describes massive celestial bodies 700,000 light years away.

Speaker 17 So the idea that we can use these variable stars to measure distances to nearby galaxies like the Andromeda galaxy, that lets you know that

Speaker 17 these galaxies are actually outside of our own, that they're actually far away.

Speaker 11 This was astounding.

Speaker 13 Yeah, that old-timey newsboy was saying that this was like seeing another universe.

Speaker 12 Right.

Speaker 11 That newsboy and the New York Times headline he was was reading, it wasn't right. Okay.

Speaker 11 It was just another galaxy, but that just gives you a sense of just how much bigger this whole discovery made the cosmos feel.

Speaker 13 Okay, so the first big thing that Henrietta's yardstick did was it allowed scientists to make the known universe way bigger. What's the next thing?

Speaker 11 So Hubble, once he starts, you know, he has this one measurement of this galaxy, he doesn't stop. He measures more galaxies.

Speaker 11 And then he realizes something even more astounding.

Speaker 17 What Hubble discovered by looking at a lot of distant galaxies is that other galaxies are moving away from us.

Speaker 11 This was actually really huge. Up until this point, a lot of scientists had this pretty clear consensus about the universe.

Speaker 17 There was the idea that the cosmos is static, that it's an eternal, unchanging thing.

Speaker 11 But these new measurements, they showed something completely different.

Speaker 17 The universe is expanding. There's just more space all the time.

Speaker 14 There's more space all the time?

Speaker 11 Yeah, this is just wild. Imagine you have an unfilled balloon out in front of you, and you draw dots along the surface of it.

Speaker 11 When you blow the balloon up, you would see that the number of dots remain the same, but the space between them keeps expanding.

Speaker 11 So, like, the galaxies aren't growing, but the space between them is growing all the time.

Speaker 17 That was a big deal to find out that the universe changes, that it's not just stuck there and everything's in its proper place forever.

Speaker 13 So

Speaker 13 just by measuring the universe, we realized that we totally misunderstood everything about it.

Speaker 12 Yeah.

Speaker 11 And then when you see that the universe is in motion, that just creates so many other questions. So if it's expanding now, does that mean the universe used to be different in the past?

Speaker 11 And particularly when we start rewinding this picture, this brings us to thinking about, wait, how did the universe begin?

Speaker 13 So is this how scientists got the idea for the Big Bang?

Speaker 11 I think the very simplified story about the science of how we got to the Big Bang is like, if we see the universe is expanding,

Speaker 11 we just imagine it going in reverse.

Speaker 13 Okay, so let me just make sure I have this straight.

Speaker 13 We had Henrietta Levitt, who, just by being part of this large catalog project of the brightness of stars, she sort of invented this yardstick to measure the universe.

Speaker 13 Then Hubble ended up using that yardstick to figure out that our galaxy, the Milky Way, is not the entire universe, that there are other galaxies out there.

Speaker 13 And then Hubble again figured out that the universe was actually expanding, which showed us that the universe wasn't static, that it actually had a beginning.

Speaker 12 Yes.

Speaker 11 And, you know, if there's a beginning,

Speaker 11 there might also be an end.

Speaker 14 Okay.

Speaker 11 So this also comes from the yardstick measurements. And it brings us to really the biggest mystery in all the universe.

Speaker 11 So we get here in the 1990s.

Speaker 22 Today's issue of the journal Science reports new information about the evolution of the universe. So

Speaker 17 what these groups were doing is they were looking at the rate of expansion of the universe in order to find out how quickly the expansion is slowing down.

Speaker 20 Our expectation was that the universe would continue to slow down after expanding.

Speaker 17 The reason they thought it was slowing down is because

Speaker 17 there's all this stuff in the universe.

Speaker 20 You see there's gravity in the universe. Everything is pulling on everything else, all the stuff in there, the planets, the stars, and the galaxies.

Speaker 17 And the gravity should be kind of trying to pull things back together and sort of putting on the brakes.

Speaker 20 What we've actually found is a very strange result.

Speaker 17 What they found was that the expansion was not slowing down.

Speaker 11 It was speeding up.

Speaker 17 That's about as weird as if you take a ball and throw it up into the air and it slows down for a little while and then just shoots off into space. You know, like there's,

Speaker 17 you really don't expect that. And these scientists really did not expect to see the expansion of the universe speeding up.

Speaker 13 Yeah, so why is this happening? How could the universe be expanding faster, especially especially when we'd expect gravity to be slowing it down?

Speaker 11 We don't know.

Speaker 17 Properly, whatever's causing the expansion, we call it dark energy.

Speaker 17 We don't know what dark energy is.

Speaker 13 And this is separate from dark matter?

Speaker 11 Yeah, dark is kind of physicists talk for mysterious or, you know, we don't know. So dark matter.
Scientists are pretty sure it's matter. Dark energy is even more of a blank space.

Speaker 11 Scientists have no idea what it is.

Speaker 17 I mean, we have ideas.

Speaker 17 We have lots of ideas. We don't know if any of them are right.

Speaker 11 But what we do know is that dark energy is kind of bad news.

Speaker 17 If something unexpected and unknown does not get us first, dark energy is what will end the universe.

Speaker 9 So, okay, hold on.

Speaker 13 You're saying that we don't know anything about this thing.

Speaker 14 Yeah.

Speaker 13 And it seems like the only thing we know about it is that it's going to end everything.

Speaker 11 Pretty much. You got it.

Speaker 11 Okay.

Speaker 11 But the better question here is, how?

Speaker 11 How will it end everything? And that leads us to some really fun speculation. Oh, fun.
Katie says there are two main possibilities.

Speaker 14 Okay.

Speaker 11 Option one for the end of time is the heat death of the universe.

Speaker 17 The universe will continue expanding. The expansion will continue accelerating.
and the universe will get emptier and emptier and colder and darker and more diffuse.

Speaker 17 And so you get to a point where only in about 100 billion years or so, distant galaxies are invisible.

Speaker 17 They're so far away, they're moving so quickly that light can't catch up and we cannot see them.

Speaker 17 And so if you had the Hubble Space Telescope in 100 billion years looking out at the night sky, you would not see those beautiful spiral galaxies.

Speaker 13 This is basically saying that the universe is just getting bigger and bigger. Why does that mean the universe would end?

Speaker 11 Because when things get so far away from each other, they can't interact with each other anymore.

Speaker 11 And everything on its own, every individual object in the universe, every galaxy, everything falls in part in time.

Speaker 11 This is a key idea in physics and in our understanding of everything. It's entropy.
It's

Speaker 11 the progression from order to disorder.

Speaker 17 You know, you have these nice structures, stars and galaxies and planets, and those are going to decay and more of that energy is going to be radiated out as this kind of waste heat as things are falling apart.

Speaker 17 And eventually, you get to a point where everything's basically done.

Speaker 11 Everything is so far apart that there's no, like,

Speaker 11 nothing can jump-start anything, nothing's interacting, all that's left is this just waste heat.

Speaker 17 We call that the heat death, the ultimate heat death of the universe. It's a state where the universe has a tiny amount of radiation in it that is the waste heat of everything, and

Speaker 17 that's it.

Speaker 13 Not great?

Speaker 11 Yeah.

Speaker 17 Well, it could be worse.

Speaker 13 How could it be worse than nothing happening forever?

Speaker 11 This is where we get to the second scenario,

Speaker 11 the big rip.

Speaker 13 The big rip?

Speaker 11 This is like what Hollywood would choose. Okay.

Speaker 11 So in the previous scenario with heat death, galaxies and planet and things that are like that they're held together fine with gravity, they stay together. But in this scenario,

Speaker 11 everything starts to rip apart.

Speaker 17 So it would first start to pull apart clusters of galaxies. So galaxies that are orbiting each other in a clump, they would start to wander away from each other.

Speaker 17 And then it would start to pull apart galaxies. So the stars at the edge of the Milky Way would start to kind of wander off.
and then

Speaker 17 the planets would start to wander off of our solar system,

Speaker 17 and then it accelerates from there.

Speaker 17 So, then you start to get to a point where there's dark energy inside the Earth that's kind of pulling the Earth apart and it explodes the planet, and then it gets down to molecules, and atoms, and nuclei, and eventually just tears apart space itself.

Speaker 14 Okay,

Speaker 13 so we got two scenarios. I mean, mean, they're equally terrible.

Speaker 13 Which one is more likely to happen? Like, how do we know if we're going to get this increasing isolation or everything will be ripped apart?

Speaker 12 We don't know.

Speaker 15 Okay. Great.

Speaker 11 Katie told me there's probably a little bit more consensus around the heat death scenario. That might be a little bit more likely, but really...
This all depends on what dark energy actually is.

Speaker 11 And right now, dark energy is just such a mystery. We could just be fundamentally wrong about so much here.

Speaker 11 But the real way to get closer to an answer is just to keep measuring.

Speaker 17 If we really understand the expansion rate of the universe, if we understand the expansion history of the universe very, very well, which is based partly on all these measurements of the distance and so on, then we should be able to compare different ideas about dark energy and say which ones are more likely.

Speaker 13 What this all drives home for me is just the power of measurement. I mean, just by measuring a thing, you see this thing in a new light.

Speaker 13 You even end up changing the actual thing, like changing how you understand the thing.

Speaker 13 Like even the tiniest calculations, Henrietta sitting in a room measuring the brightness of stars, those calculations, they gave us the cosmic yardstick.

Speaker 13 And then that yardstick showed us just how how big and weird and constantly surprising the universe is. Like this all comes back to measurement.

Speaker 12 Yeah.

Speaker 11 All this, this incredible story of scientific progress, it just starts with the simplest question.

Speaker 11 How far away is that? How bright is it?

Speaker 11 I love how simple questions can lead you sometimes to extraordinary places. It could lead you to the beginning of the universe and it can even lead you to the end of time.

Speaker 15 This episode was reported and produced by Brian Resnick and by me, Bird Pinkerton. We had edits from Meredith Hodnott and Noam Hasenfeld, who also wrote the lovely, lovely music you heard.

Speaker 15 Mixing and sound design by by the inimitable Christian Ayala, and fact-checking by the wonderful, the thorough Mandine Wen.

Speaker 15 Lauren Katz heads up our newsletter. Thank you, Lauren, and Liz Kelly Nelson is the VP of Vox Audio.

Speaker 15 If you want to read more about The End of Everything, you are in luck because Katie Mack has an excellent book called The End of Everything. astrophysically speaking.

Speaker 15 And if you want to read more about Henrietta Levitt, I cannot recommend enough George Johnson's book, Miss Levitt Stars.

Speaker 15 You can sign up for our newsletter at vox.com/slash unexplainable, and please feel free to send any thoughts to unexplainable at vox.com.

Speaker 15 Unexplainable is part of the Vox Media Podcast Network, and we're taking next week off to work on future stories.

Speaker 15 So get excited about those stories, and we'll be back in your feed on Wednesday, July 14th.

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