#17: Redshift at the batting cages
TRANSCRIPT
Corinne Caputo
Welcome to Pale Blue Pod, the astronomy podcast for people who are overwhelmed by the universe but want to be its friend.
Moiya McTier
Thats's us. Hello, I'm Dr. Moiya McTier. I'm an astrophysicist a folklorist, and, but to the universe.
Corinne Caputo
Yes you are and I'm Corinne Caputo a writer, comedian although you know, light on the comedian these days.
Moiya McTier
Corinne, you're funny.
Corinne Caputo
Ah thank you. Yeah, sometimes I'm like, can you use that if you've written funny things, but don't perform on the stage anymore?
Moiya McTier
Yeah, absolutely. I think so. So as a science communicator, I've been doing a lot more speaking than writing lately. But there are so many science communicators who are just writers. And you know, I still call myself a writer.
Corinne Caputo
Yeah.
Moiya McTier
I get to pick.
Corinne Caputo
Yeah.
Moiya McTier
It's like a king or queen of Narnia situation. Once you do this, you're always this.
Corinne Caputo
I love that. And that's me then. And I'm also friend to the universe. And you know, just this weekend, somebody said to me that they are afraid of space. And I was like, boy, do I have the podcast for you?
Moiya McTier
Did it feel like a weird self plug? Do you ever feel weird about promoting your own work
Corinne Caputo
so often, all the time, like, I'm always like, proud of the work that I'm doing. I think I'm lucky in that I'm not really doing stuff ever that I don't like, but it's still like it feels kind of braggy. And like, that's not a thing I've ever gotten super comfortable with, like the most challenging part of like, this work to me is playing like the manager or the agent for yourself. So I'm always like, Ah, I kind of have to like, pretend that it's not me for a second and be like, how would I talk about myself as a client?
Moiya McTier
Oh that's smart. That's a smart way to think of it. I just don't I just avoid it.
Corinne Caputo
Yeah.
Moiya McTier
It does. Also, it helps a little bit that my friends in college realized pretty quickly that the surest fire way to embarrass me was to give me compliments and like brag about me, because I hate it. Like it's the one of the only things that will make me blush so they do it.
Corinne Caputo
Yeah, of course.
Moiya McTier
I don't have to.
Corinne Caputo
Well, it's so weird. I hate doing it. But when I took that love language quiz, when everyone was words of affirmation was my love language. It's a good one. I'm a Leo.
Moiya McTier
I'm a touch person.
Corinne Caputo
A lot of people are. So is my husband, Eli. And I'm just like, couldn't be me. We speak different love languages, right?
Moiya McTier
It's so important. Well, that's that on love languages. And our anxiety around self promotion. Today, we're not talking about that. That's not what this episode is about. Surprise, surprise.
Corinne Caputo
But if you want to recommend us to your friends do it.
Moiya McTier
Please do, because you know we're not going to. So today we are recording in some batting cages.
Corinne Caputo
Yeah, we are.
Moiya McTier
I do not like baseball. I am so bad at hitting a ball with a bat. I think that my fine motor skills just aren't that refined.
Corinne Caputo
I totally get it.
Moiya McTier
Give me like a rugby ball or a basketball. I'm good, but I guess I just you need a larger object. I need to work with bigger balls.
Corinne Caputo
I get it. I have never been good at baseball either. I was on a softball team for years in New York.
Moiya McTier
Oh
Corinne Caputo
It was like a recreational softball league. It was a coed league. So you need like a minimum number of women, like they were really specific about COVID rules, because I think what had happened is the past is like, it's just male teams would join, and it would like wouldn't be the vibe they wanted.
Moiya McTier
That makes sense.
Corinne Caputo
So I played was never very good. But I created a system for homeruns, which is if you get to first base, it's a quarter homerun. And if you get to second base, it's a half homerun, you know, and so on. And I think we should use that all the time in baseball, because it makes you feel really good.
Moiya McTier
They call that just a run Corinne.
Corinne Caputo
I know, but if you say it's a half home run, it's like, Oh, my God, you gotta half home run.
Moiya McTier
You're, you're so half impressive. So neither one of us super into baseball. But I thought that for what we're talking about today, it'd be helpful to be around batting cages, because I think that I can use it to help demonstrate a point I'm going to make later.
Corinne Caputo
I love this.
Moiya McTier
So today, we are talking about the amazingly useful phenomenon in science in general and in astronomy, more specifically, of redshift, and its counterpart blueshift.
Corinne Caputo
I feel like I have heard of this, but I don't know if I have I think I'm just confusing it with the matrix.
Moiya McTier
Oh, with the red pill blue pill thing?
Corinne Caputo
Yep. Yep. I mean.
Moiya McTier
I think a lot of people have heard of Redshift and blueshift in the context of the Doppler effect. Yeah. Do you remember hearing about that in like, physics class?
Corinne Caputo
Exactly. I remember that in physics. I had a physics teacher I loved in high school. And that was a fun day.
Moiya McTier
This is different from the person who told you the moon landing was fake, right?
Corinne Caputo
Different! Oh my gosh, that was my middle school teacher. Okay, high school was a lot better. Great.
Moiya McTier
Good. Stepping up in the world. Yeah. So Redshift and blue shift. These are both phenomena that work with any type of wave. A lot of people when they learned about the Doppler effect in physics class in school, it's most likely going to be about sound you know, like the the classic ambulance. Yes, type of thing was that good?
Corinne Caputo
There's an episode of The Big Bang Theory, which is like I maybe I've said this I watched I binge watched the day I failed my driver's license exam because I never watched it again. It was just like, I need something anything. And there's an episode where Sheldon dresses up as the Doppler effect for Halloween.
Moiya McTier
How does he do that? Is it just like red on the top and blue on the board? Front and back? I always
Corinne Caputo
No, he dresses in black. And it's like, I think it's like sound waves like, you know how when we record we see the like bars going?
Moiya McTier
Yeah,
Corinne Caputo
So it's kind of like that, where it's like quiet on the sides and like loud in the middle. Oh, okay. If I remember correctly, this is a long time ago.
Moiya McTier
Well, you know, there's a lot of potential for error propagation here, because you might be remembering it correctly. But they could have just did it wrong. This show, like that show had it's great things about it, but not a lot of quirks isn't all gems.
Corinne Caputo
Yeah.
Moiya McTier
But because a lot of people hear about the Doppler effect for the first time with regards to sound, they don't necessarily realize that it can also be applied to light. And that's true. The Doppler effect works with all I'll say, like redshift, in general. And we're gonna get into the different types of redshift in this episode. Because there are three different types of redshifts that we're going to talk about. But in general, this phenomena works with all types of waves, sound waves, which are pressure waves that travel through a pressurized medium, like our atmosphere, light waves, which we know from the electromagnetic spectrum episode that can just travel through the empty vacuum of space, but also gravity waves, which travel through the fabric of space time in our entire universe. And we talked about that a little bit, I think in the black hole episode. But we are going to start with the most common type of redshift. And that's going to be from this Doppler effect that people have heard of this effect was, I guess, it feels weird to say discovered because I'm sure a lot of people before this dude had heard something with sound moving by them, and they realized that the pitch of the sound changes or the the frequency of the sound waves changes, but he was the first person to put it in a paper that we have. So his name was Christian Andreas Doppler. He's an Austrian mathematician, slash physicist, slash astronomer. He wore many hats. And he was born in the very early 1800s. Over his career, he published more than 50 papers about different things in physics and astronomy. But one of them published in in the original German because he was Austrian was called Über das farbige Licht der Doppelsterne.
I'm just I heard uber
flexing my German pronunciation skills because everything else that I pronounced in the show is so wrong.
Corinne Caputo
I saw it coming up in the outline and I was like, I wonder if she's gonna say this or not? Yes, I am.
Moiya McTier
Again, for the people in the back,Über das farbige Licht der Doppelsterne was a paper by Christian Doppler, published in 1842. And the English translation to that is concerning or on the colored light of double or binary stars. So this dude was looking at binary star systems, these pairs of stars that orbit each other, and he was studying how their color changes as they orbit each other, which they do, because as they orbit each other, each star is going to move like towards us and away from us as they're making the orbit. So, the idea behind this Doppler effect that Christian Doppler proposed in this paper was that if you observe an apparent color change, as the stars move with respect to us, then you can link that to the frequency of the stars and their motion, the velocity of their motion. So because the color that we perceive is a consequence of the frequency or wavelength of light, you know, like 500 nanometers, we're going to see that as green light. Because there's that relationship. A stars change in color is related to its change in light frequency, or the apparent change in light frequency. And binary stars. As they're doing the stance moving towards and away from us, we will see this change in color or frequency. But Doppler was wrong, in some ways, like this effect is fantastic. But he incorrectly assumed that all stars are either white or yellow in color. And we know from this stellar types episode, that that's just not true.
Corinne Caputo
But that is how I drew all my pictures in school, right? Like stars are yellow. That's it.
Moiya McTier
Yeah but you're drawing the sun.
Corinne Caputo
Yeah, exactly.
Moiya McTier
The sun our most famous star, the most famous. So Doppler made that incorrect assumption. So many scientists throughout history have made incorrect assumptions, but they still contributed to our knowledge as a whole. And five years after Doppler published this paper, a French physicist named Hippolyta physico-
Corinne Caputo
Perfect.
Moiya McTier
-probably confirmed the effect. And added that it would be more useful to observe this Doppler effect by studying the stars spectral lines, instead of studying the color because the spectral lines, it's more precise, if you study those, because we have very precise measurements of where these lines these spectral lines should be. And if the star is moving towards or away from us, then those spectral lines also shift.
Corinne Caputo
Okay. And these are not the spectral lines that like, like the colorful spectrum that tells us like, what it's made of Is it?
Moiya McTier
it is that same spectral lines. Yeah. So when you look at that type of spectrum that shows you the absorption and emission features of a star or a galaxy, or whatever you're observing those emission and absorption lines should be at very specific wavelengths. So like, if you have a molecular hydrogen line, for example, an h2 line, that should be at 21 centimeters, we have measured this in labs, we've measured this out in space, we know where that line should be. But if the object that is emitting that molecular hydrogen is moving, if it's coming towards us, if it's blue shifted, or if it's moving away from us, ie red shifted, then those spectral features will also move. And we can measure how much those features have moved from their baseline point. To get a sense of how fast that object is moving.
Corinne Caputo
I think I got it, I think, well, I'm familiar with like the spectrum lines from Space Center days. So it's really helpful to picture that. And I will make a note to share one of those on our Instagram. Yes, please do.
Moiya McTier
So even though Doppler got that a little bit wrong, it still stands that the observed frequency of an object and the actual frequency that it is emitting with and the speed of that object, all of those things are related. So if you know two of them, you can solve for the third, if you know the observed frequency and the actual emitting frequency, you can solve for the velocity. If you know the velocity and the observed frequency, you can solve for the actual emitted frequency. They're all connected like that. And you can just do some fun algebra to rearrange the equation. Now we're getting to the point which where this is why I want to be at the batting cages today for this episode, so red shifting with the Doppler effect means that an object is moving further away from you. Blue shifting means that the object is coming closer, but please remember that this is only an apparent shift in the stars color or frequency or spectrum. The inherent quality of the star is not changing. It's just kind of like an illusion as the star is moving. So this is why how I like to think of it instead of picturing a star giving off photons picture the pitching machine. At the batting cage,
Corinne Caputo
Okay
Moiya McTier
Pitching machines, by the way, invented in California by a man named Lorenzo Ponza. In the 1950s.
Corinne Caputo
Cool sounds Italian.
Moiya McTier
So picture the pitching machine and the machine is pitching out balls at a set rate and it throws one ball every five seconds,
Corinne Caputo
Okay.
Moiya McTier
The pitching machine is always going to throw one ball every five seconds. But if that pitching machine, we're moving towards us-
Corinne Caputo
Yeah,
Moiya McTier
It would seem like the balls are coming to us faster or closer together, because they essentially have to travel less distance to get to us even though the rate of pitching hasn't changed, our rate of receiving the balls has changed. And the opposite is true, too. If the pitching machine is moving away from us, then the balls have to travel further. And instead of getting a ball every five seconds, were then getting a ball like every 10 seconds as the machine moves away.
Corinne Caputo
Okay,
Moiya McTier
so that's Redshift and blueshift. Right there, the stars are always emitting photons at the same rate. But if the star is moving away from us, then we're going to feel like we're getting photons more slowly.
Corinne Caputo
Sure.
Moiya McTier
Yeah. That's the Doppler effect. And we can use it in so many areas of science to learn some really cool shit. So I looked up some examples outside of astronomy. One of them is radar, which is apparently an acronym for RAdio Detection, and ranging, essentially, you have this transmitter that will send out waves, most likely light waves, or, like electromagnetic waves, but sometimes also sound waves, I guess I don't know, I'm not a radar technician. And because the radar machine knows how quickly it is sending out those signals, when the waves hit something and get bounced back, we can determine if that object that it hit was stationary or moving towards or away from us based on the waves that the radar machine receives in return.
Corinne Caputo
Sure, yeah.
Moiya McTier
So that's radar. We can also use the Doppler effect for medical imaging, I saw a paper that talks about how it's used in echocardiogram. So imaging your heart and how healthy your heart is, and how it is pumping blood around your body, because that's what hearts do. And that is the extent of my knowledge on hearts.
Corinne Caputo
I do feel like an expert in like medical knowledge now because I started rewatching some of house and I was like, oh, yeah, I get it
Moiya McTier
I haven't watched house in so long.
Corinne Caputo
No, it was like a high school show for me. But I do hear the house theme song a lot. It's like always at a coffee shop. That house theme song is playing
Moiya McTier
Yeah. Mass Effect, I think
Corinne Caputo
Yes. Yeah.
Moiya McTier
Because it's an actual song. They didn't get it for the show.
Corinne Caputo
No, no
Moiya McTier
be out in the wild. And all of a sudden here that helps. And you're like, Oh, am I about to see some? Some bad prognosis?
Corinne Caputo
Yeah, the next time you hear the house theme song, tweet at pale blue pod and let us know.
Moiya McTier
Please do we want to know the rate.
Corinne Caputo
And imagine the Doppler effect of the house theme song on your closer.
Moiya McTier
Yes, we will do this science but you listeners you have to provide the data.
Hi, it's Moiya here to give a shout out to our incredible patrons, Corrine and I really appreciate your support, because honestly, this show just wouldn't exist without it. So thank you as always to our sunlight stars Sean Llewellyn Finn, Ian Williams and Meghan moon. We love you all so much. Thank you for your support. And you too can support us you can hear your name on this pod and make it to our patrons star chart all by supporting us on Patreon for just about $1 per episode, patrons get access to our research notes for every single episode with extra resources about each week's topic. The first 50 patrons will all be eligible to receive a free signed and personalized copy of my book, The Milky Way and Autobiography of our galaxy and we are so close to 50 so please consider joining our Patreon or sending its link to your friends who just have like too much money and are looking for a podcast to throw their money at. So you can find our star chart and our Patreon info and more at our website pale blue pod.com Or just go right to patreon.com/pale blue pod. We would love you forever. Thank you.
Corinne Caputo
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Moiya McTier
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And, of course, the the use of the Doppler effect that is nearest and dearest to my heart, is that we can use the Doppler shift to study the radial velocities of stars that have planets orbiting around them. radial velocity means how fast are you moving towards or away from us. So it's specifically in that direction, there's a different type of velocity for motion to the left and right and motion up and down.
Corinne Caputo
Oh, okay.
Moiya McTier
So with the radial velocity method, this is like the second most successful method of finding exoplanets out there. And we're gonna do a whole episode about exoplanet detection methods, so I'm not gonna get too into it. But as the planet orbits around the star, it actually tugs on the star a little bit and makes the star wobble or orbit a tiny little bit around the center of mass of the whole system. And as the star is wobbling, it will move towards and away from us. It spectrum that we are studying will shift blue shifting and red shifting. And we can measure how much the spectral features have been shifted to study how fast the star is moving. And that stellar velocity is going to be directly related to the mass of the planet that is tugging the star-
Corinne Caputo
cool,
Moiya McTier
which is how we determine the masses of exoplanets. That's amazing. There are such indirect methods and I love it. That's the Doppler effect read shifting from the Doppler effect. But I said there are three types of redshift. So we still have more to learn. Any thoughts? Or questions on on that bit?
Corinne Caputo
By have one question? And you tell me if this question means I don't understand. When it says closer and further to us? Is it relative to like, where we are on earth or just general to planet earth? Like if I'm in the southern hemisphere? Is there any difference?
Moiya McTier
No, the size of Earth is so much smaller than the distances to these objects that it doesn't really make a difference.
Corinne Caputo
That makes sense.
Moiya McTier
So you do understand it?
Corinne Caputo
I do get it. Yeah.
Moiya McTier
That's so exciting. The next type of redshift that I want to cover is gravitational redshift, which means we're gonna have to go back to Einstein and his theory of general relativity because it just keeps coming up. Which I guess is what happens when one guy discovers how gravity works. And we live in a universe where like, almost everything is about that is about gravity. Yeah. Yeah, we're going back to general relativity. Einstein, in his theory of general relativity, not special relativity, predicted that light, or photons. Remember, light is both a particle and a wave. So photon particles and light waves can be redshifted as they move away from a very massive object. The language that I saw a lot when I was researching this and some language that you might have heard in the past is I As the light is climbing out of a gravity well, it will get redshifted because we often talk about big, strong gravitational fields as wells as pits that things can fall into.
Corinne Caputo
Yes, scary.
Moiya McTier
So we can also think about things climbing out of those pits. If we can think about things falling in.
Corinne Caputo
All I'm picturing right now is the ring is the movie the ring? The well in the ring, but I'm trying to but in that movie is very dark. And in this scenario, we are discussing lights.
Moiya McTier
What is what's the opposite of a ring? Like what's the what would be the opposite of this movie? What would be the light version of the ring?
Corinne Caputo
Monsters Inc? I'm just picturing movies I love that are nice.
Moiya McTier
Yes, well, if if the person from the ring was crawling out of a deep enough gravity well and also happened to be a photon, then she would get redshifted as she climbs out,
Corinne Caputo
that would be amazing for her. Good for her.
Moiya McTier
Getting redshifted actually, I don't know if that's a good thing in the context of like the human experience.
Corinne Caputo
So true. But she's already bad news.
Moiya McTier
Yeah, so like, it can't get much worse, right? We're only only up from there.
Corinne Caputo
I'm going to not like her no matter what. So I don't really care.
Moiya McTier
I have never seen this movie. I don't plan on ever watching this movie. So-
Corinne Caputo
I don't recommend
Moiya McTier
Okay, good to know. Thank you. Thank you, Corinne because I'm a little wuss. The universe does not scare me. But horror movies absolutely do.
Corinne Caputo
Yes. Too Scary,
Moiya McTier
Too scary. Gotta watch with the fingers deployed. And the thing is like when you take your hands and you split your fingers down the middle. So you are still watching. Yeah, Star Trek style. So you're still watching. But you can very quickly close the shutters, you know
Corinne Caputo
exactly.
Moiya McTier
So let's, let's explain this gravitational well thing. It takes a lot of energy to escape a strong gravitational pool, or to climb out of a gravity well, but the thing about photons is that they're always going to travel at the speed of light in a vacuum, like in the vacuum of space, they're going to travel at three times 10 to the eight meters per second, that is their speed. And that doesn't change. But that's like the most effective way to absorb or release energy is to change your velocity. So photons have to do something different in order to maintain the amount of energy in the system, because another rule of physics is that energy cannot be created or destroyed, it has to go somewhere. So when these photons are trying to climb out of a strong gravity, well, the only way that they can save or like trade their energy, instead of going slower, they have to shift their frequency to one with less energy. So a photon that typically would have a wavelength of I'm going to use 500 nanometers, again, a green light photon, if it were escaping a gravity, well, it can't move slower. Instead, it has to go down to a lower frequency, which has a longer wavelength, and it now has a wavelength of like 700 nanometers, which is red. So these photons are essentially getting red shifted.
Corinne Caputo
Got it.
Moiya McTier
We can see this, we've seen this in practice, we've seen this in labs, we have seen this out in space around neutron stars. But neutron stars, even though they are the second densest objects in the universe after black holes, they will only produce the tiniest shifts. One person who did the math that I didn't want to do. The result was that it's less than one part in 30,000. Like that's how minute
Corinne Caputo
That's tiny.
Moiya McTier
these shifts aren't Yes, in my notes, I wrote tiny and I put like 10 eyes. That's how small it is. tiny, but the reverse is also true. So if a photon is falling into a gravity well, and we see this with black holes that are attracting stuff all the time, well, then you're picking up energy from the system, but you can't move faster as a photon. So instead, you have to shift your frequency to one with more energy. So it's kind of like imagine you're bungee jumping, right. And normally, as a human, when you jump you would be you would succumb to the acceleration of gravity, you would fall at a rate of almost 10 meters per second per second, and you would get faster as you get closer to the ground. But if you are bungee jumping as a photon, you're already going as fast as you can go. So you can't speed up you can't increase your velocity, but that kinetic energy has to go somewhere. So it's almost like the photon absorbs the kinetic energy and you can use that through glowing or like screaming or something I don't know. But this is how this is how gravitational redshift Ng and blue shifting both work. We have definitely observed Gravitational Red shifting out in space. Honestly, I didn't look for examples or evidence of gravitational blue shifting because like we know, we know stuff is falling into these black holes like we don't
Corinne Caputo
Yeah. If we listen carefully enough, we'll hear them scream.
Moiya McTier
We'll hear the Yeah, the photos. As they bungee jump into a black hole.
Corinne Caputo
It's a happy yell.
Moiya McTier
Yeah, you're right. You're right. I think I just really want to go bungee jumping soon.
Corinne Caputo
Oh, my gosh, have you ever gone?
Moiya McTier
No, but I am kind of a thrill seeker. Have you? Would you?
Corinne Caputo
I Think I probably would. I don't know. Maybe,
Moiya McTier
Would you go if you were a photon, and you knew you wouldn't go fast? Or at least not faster than you're used to going?
Corinne Caputo
Probably yes, maybe? Well, but in that scenario, it's a black hole.
Moiya McTier
Yeah.
Corinne Caputo
And we did soothe a lot of my fears of them.
Moiya McTier
Good.
Corinne Caputo
But I don't know if I like thrills, I get my thrills from watching the ring. And
Moiya McTier
you and I have such different ways of getting our adrenaline pumping. So we will not be doing a pale blue pod bungee jumping trip is what I'm hearing.
Corinne Caputo
I'll meet you at the bottom for a drink.
Moiya McTier
Okay and then you can watch the ring while I drink that drink and look away.
Corinne Caputo
Exactly, exactly. And that would be a great day,
Moiya McTier
Of course Alright, so that is gravitational redshift. Now we're moving on to cosmic redshift, or like cosmological redshift. It's sometimes called and this is, I think, my favorite redshift. It's not why I saved it for last. I save it for last because it's like redshift on the biggest scales. But I also think that it's really interesting because it teaches us about the expansion of the universe, cool. Edwin Hubble back in 1929, was responsible for finding evidence that the universe was expanding, instead of sitting in this static, non moving state, which is what people like Einstein thought the universe was doing. So like, No, fuck you, Einstein. That's what Edwin Hubble would say. I'm sure
Corinne Caputo
His words not mine. I'm just the messenger.
Moiya McTier
So it's 1929. Edwin Hubble is like kind of fresh out of grad school, he has attended the Great Debate talking about whether or not there are other galaxies in the universe. And now he is studying those other galaxies to see how they are moving. And what he finds is that those galaxies are moving away from us. But there are two important facts here that tell us that this red shift is not the same as the Doppler effect, because like, that's an easy assumption to make, oh, those galaxies, they look red, they're moving away from us, it could very well be the Doppler effect. But no, it's not. And we know that for a couple of reasons. One, the galaxies that are farther away from us are moving away from us more quickly.
Corinne Caputo
Okay.
Moiya McTier
Does that make sense? Yeah. So like a galaxy that is 10, kiloparsecs away from us, is moving faster than a galaxy five kiloparsecs away from us. And you don't have to know what a kiloparsec is. That's just a unit of distance, you know that 10 is bigger than five. So that's fine.
Corinne Caputo
Yes.
Moiya McTier
So if this were due to the Doppler effect, then there wouldn't be that coherent trend, galaxies closer to us could move faster than galaxies more distant. But instead, we see this very strong correlation. It's a line, we fit a line to this, the galaxies that are further away, move faster, which tells us it's probably not the Doppler effect. But there's also something else that tells us that these galaxies, where we see this effect, in all directions, so no matter where we point our telescopes, we see that more distant galaxies are moving away from us at faster speeds. And you could take a very simple read on this situation and say, Oh, well, all the galaxies, they're moving away from us, because we're the central point in some big universal explosion. But really, that's so anthropocentric, like that's the highest level of humans are the center of the universe that you could possibly get to. And it's just not likely, it's much more likely, it makes a lot more sense for the entire universe to be expanding away from itself because we are not special.
Corinne Caputo
Wow
Moiya McTier
We really aren't?
Corinne Caputo
It's true.
Moiya McTier
So a lot of people when they hear about the expansion of the universe, a common balloon analogy comes to mind and I think I've talked about this in previous episodes, but that balloon analogy is fantastic. Only if it's described well.
Corinne Caputo
Okay,
Moiya McTier
So like people will put markings on a balloon and they'll blow it up and people will think that it's the volume of the balloon that we're talking about that It's like the, the space inside the balloon that represents the expanding universe. But that's not true. It is the surface of the balloon that represents the expanding universe. Because it's not that everything in the universe is moving away from stuff. It's that the space itself is stretching.
Corinne Caputo
Ah,
Moiya McTier
so these galaxies that are moving away from us that are redshifted. It's not that those galaxies are moving through the universe. They're like, they're trapped in the soup. And the soup itself is stretching
Corinne Caputo
is ballooning.
Moiya McTier
Exactly. They're just like, they're just sitting there and getting carried away.
Corinne Caputo
That makes sense. That's a good way to think about it. I was telling moiya I went to a child's birthday party this weekend, and I did blow up balloons. So this is good. It's close to home.
Moiya McTier
Yeah. You could have taught them about the universe expanding.
Corinne Caputo
Yeah, I was just trying to get him to not eat it. Because he's one. Next birthday.
Moiya McTier
Next time. Two years old is the right time. Yeah. the expanding universe Exactly. Other things about cosmological redshift. So we can measure this, we can measure how much cosmic redshift galaxy or some other target is experiencing, and then we can work backwards to figure out how far away that object must be. The unit for redshift that we use or like the variable that we use to denote redshift is a Z, a big Z? Confusingly, z is also the variable that we use to denote a star's or a galaxy's metallicity. Do you remember about metallicity? Corinne,
Corinne Caputo
I remember the word and I remember being like, I've never heard that word before.
Moiya McTier
It is the fraction of elements in a star or galaxy that are heavier than helium because astronomers call anything heavier than helium, a metal. And both metallicity and cosmic redshift are denoted with the letter Z because we suck
Corinne Caputo
because they want to make it hard.
Moiya McTier
Exactly. But this z, this redshift is a unitless parameter, meaning it doesn't have units of like, time or length or mass or anything. It is a unitless number that we can use to figure out how far away something is. I just I really like talking about cosmological redshift. Because I've studied what I thought were distant galaxies, I once studied a galaxy that was 250 million light years away from us
Corinne Caputo
woah
Moiya McTier
and that for most people, like that's a distant galaxy, it's well outside of our local group. But in terms of cosmology, for people who study the entire universe that was nearby, and you know, that it's nearby because its redshift number was like, point oh, one or something like point one. we see galaxies that have redshifts of like, 12.
Corinne Caputo
Wow,
Moiya McTier
those galaxies with high redshifts would be billions of light years away. Like when we observe a galaxy with redshift, 12. We're looking at a galaxy as it was less than a billion years after the Big Bang. It's amazing. So I really like redshift.
That's cool.
But I also I love it because astronomers now understand cosmological redshift well enough to use it to determine distances to these most distant objects, these most faraway objects. In fact, cosmic redshift is the final rung on what astronomers call the distance ladder. Have you ever heard the term distance ladder?
Corinne Caputo
No.
Moiya McTier
yeah, why would you?
Corinne Caputo
I like it.
Moiya McTier
I devote almost an entire chapter of my Milky Way book to the distance letter. Because I think it's so valuable to understand astronomy, and we should absolutely do an episode about this in the future. But yeah, the distance ladder itself is a sequence of methods that astronomers use to determine astronomical distances, there are several rungs on this ladder that are each useful for more and more distant objects. So like the first rung on the ladder is something called parallax, which we will get to in that episode on the distance ladder. But that method only works for very nearby objects, objects that are like within, definitely within our local group, most likely within our galaxy. To measure distances to more distant objects. You have to work your way up the distance ladder, and cosmological redshift is used for the most distant objects. It is the final rung on this ladder.
Corinne Caputo
Cool,
Moiya McTier
which I just think is fun, because of that relationship between the distance to an object and the velocity with which it moves away from us.
Corinne Caputo
Yeah.
Moiya McTier
Any questions about cosmological redshift?
Corinne Caputo
So for cosmological redshift is the color and involved as much
Moiya McTier
Yeah, yes. Oh, thank you. That's a really good question. So in the Doppler effect redshift with the Doppler effect, the wavelength of light is not actually changing. It's just that Because the object is moving further away from you, it's taking that light longer to reach you. So, like the wavelength has shifted with cosmological redshift, as the fabric of space time gets stretched, so do the waves of light. Yeah, so do the light waves in the fabric of spacetime. So like these light waves actually are getting shifted towards the red or the, it's just the red there is no cosmological blueshift,
Corinne Caputo
shift cosmological. Sounds cool.
Moiya McTier
I mean, once and we'll also do an episode on this. But one potential scenario for the end of the universe is called the Big Crunch. And in that scenario, the universe expands until whatever is fueling that expansion loses out to gravity because of all of the matter in the universe. And so the expansion stops, and then it rebounds on itself and it comes back together. And I guess in that case, there would be cosmological blue shift, because the universe would be like the fabric of space time would be contracting. And so with the light waves,
Corinne Caputo
would it be when I hear crunching of something very quick, would it be like a quick contraction or in this theory, or would it be like slow?
Moiya McTier
It would be about as slow as the expansion of the Universe has been, it would speed up as stuff got closer together? It's called the Big Crunch. Because at the end, you know how, according to The Big Bang Theory, everything in the universe was once contained in a tiny little primordial atom. We call this scenario the Big Crunch because eventually everything would crunch back into that primordial atom.
Corinne Caputo
Yeah, that makes me hungry.
Moiya McTier
do kind of want to crunch bar now.
Corinne Caputo
I love crunching
Moiya McTier
not to be confused with crunches,
Corinne Caputo
no,
Moiya McTier
but just the opposite of eating a crunch bar,
Corinne Caputo
which I don't like
Moiya McTier
No. Also, they're not that they're not that effective. There are better exercises.
Corinne Caputo
Exactly.
Moiya McTier
Yeah. And they just hurt your back.
Corinne Caputo
Yes. The I they're not comfortable to do. And like standing core work is like more satisfying for me.
Moiya McTier
Yeah.
Corinne Caputo
And I have tight hip flexors. So crunches aren't for me, but a big crunch
Moiya McTier
The Big Crunch is for everyone.
But I would do a big crunch.
Things you never expect to hear on an astronomy podcast. The efficacy of crunches versus other deep core excersises.
Corinne Caputo
Yeah.
Moiya McTier
Do some weighted marches.
Corinne Caputo
Yeah.
Moiya McTier
Yeah, like you got it. Yeah, that's all I have to say on on the three types of redshift. Do you have a favorite type of redshift?
Corinne Caputo
I'm really into this cosmic redshift too.
Moiya McTier
Yeah, that's great.
Corinne Caputo
I really like it. And I think it's just, I mean, I think that's such a fun and mysterious part of the the universe to me is like the expansion and I think I'm always gonna kind of like the stuff that contributes to our knowledge about it.
Moiya McTier
Yeah I agree. Okay. So my friend Sean and I, Sean is a comedian writer, who I am developing a TV show with so like, hopefully that helps, yeah, becomes a thing. But Sean is very funny. And one time I was talking to Sean about my dating life, and the topic of ghosting came up. And he was like, Oh, I've never really ghosted anyone, but I have just, like, slowly petered out my communication with someone so that eventually they got the hint. You know, like, yeah, you start off texting every day. And then it's like, every three days, and then it's once a week. I was like, oh, Sean, you redshifted them?
Corinne Caputo
Yes, that's good. It's good, right? Because you're
Moiya McTier
like, you're just slowly you're essentially weaning someone off of your presence. But it is very similar to a galaxy that's just like moving further away. And it feels like they are communicating with you less and less, it feels like the wavelength is growing. That's really fun. Is there any other definition that you can think of for redshifting any other scenario where that might be useful?
Corinne Caputo
Huh, regifting really makes me think of like, personality change. Oh, and maybe that's too dramatic, but it's cool for red shift or a blue shift personality change? I mean, I'm so in my head about politics right now. So I'm really thinking of like the political spectrum
Moiya McTier
not it I thought you were gonna go like anger versus peace you know, like if someone is in anger management therapy they're being blue shifted.
Corinne Caputo
Exactly. I think of blue maybe that's maybe this is funny about me but I think of blue as a very calm peaceful emotion and read as like a lot of energy and a lot of anger. And I guess the
Moiya McTier
opposite Yeah. Hmm. Well,
Corinne Caputo
I wouldn't be thinking of right now that Pixar movie Inside Out not to just mentioned Pixar so many times.
Moiya McTier
Oh, yeah.
Corinne Caputo
But Blue was the like, sad character and red is like the little angry guy. And I can really You relate to both of them?
Moiya McTier
We all contain each of them within us.
Corinne Caputo
Exactly.
Moiya McTier
All right. Well, I hope that you are not out there getting redshifted in the romantic or platonic setting, but I do believe unfortunately, Corinne, I signed us up for slots in the batting cages just to see how we do and it's almost our time so we should get going. When
Corinne Caputo
What if I'm amazing.
Moiya McTier
I think you will be. I believe it.
Corinne Caputo
I think you're gonna get better by the end of this session.
Moiya McTier
The jury's still out on me, but I'm here to watch you. Once you shine. Like, like a baseball star.
Corinne Caputo
I'm gonna get a half homerun.
Moiya McTier
And no matter how many fractions of a homerun you are hitting tonight, remember, you are space.
Corinne Caputo
Bye.
Moiya McTier
pale blue pod was created by Moiya McTier and Corrine Caputo with help from the multitude productions team. Our theme music is by Evan Johnston and our cover art is by Shea McMullen. Our audio editing is handled by the incomparable Misha Stanton.
Corinne Caputo
Stay in touch with us and the universe by following at pale blue pod on Twitter and Instagram. Or check out our website pale blue pod.com. We're a member of multitude and independent podcast collective and production studio. If you like pale blue pod you will love the other shows that live on our website at multitude dot productions.
Moiya McTier
If you want to support pale blue pod financially, join our community over at patreon.com/pale blue pod for just about $1 per episode, you get a shout out on one of our shows and access to director's commentary for each episode. The very best way though to help pale blue pod grow is to share it with your friends. So send this episode this link to one person who you think will like it and we will appreciate you for forever.
Corinne Caputo
Thanks for listening to pale blue pod. You'll hear us again next week. Bye.