Daniel and Jorge Explain the UniverseDaniel and Katie answer a question about why distant objects can look surprisingly large in the sky
Hey, Daniel, what's the most distant object you've ever seen?
You know, the Andromeda galaxy is pretty far away. It's like millions of light years. How about you, what's the most distant thing you've ever seen?
When I am sleepy, it is my couch.
Your couch is far away.
Yeah, it's so fun.
W want mom.
Hi.
I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I like to couch all my puns.
Hi. I am Katie Golden. I a podcast on animals, and I am cushion for a never mind. I I thought if I just said cushion that a pun would come to me, and it didn't. It just made me want to take a nap.
You were pushing for a pun, Cushion.
I thought I was going to be bruising for a cruise in, but I was cushion for a pushing. I guess a defenestration.
Sounds like you're set up for some punishment anyway. Welcome to the podcast. Daniel and Jorge explain the universe in which we try not to punish you. We try to enrapture you. We try to share with you the joy of understanding the nature of the universe, or when we are mystified by the puzzles, the curiosity, the open questions about the nature of this cosmos we find ourselves in, we seek to understand it, we seek to explain all of it to you.
On the podcast, Daniel.
Is this the one coming out on the summer solstice? Just the quickest side before we get into our listener question. I just visited in near Dublin, Bruno Boyne, these funeral mounds, and it was so interesting because these very very ancient people created these funeral mounds which had an internal structure that they're large mounds like you could actually you can go inside it. They can do ceremonies inside, and they constructed it such that like during the solstice, the summer solstice, on the longest day of the year, it illuminates this entire inner chamber. And I just love that. So long ago we were already thinking about physics, figuring out the universe, and like trying to think about how light works and use it for our interesting little Richard.
Yeah, exactly. I don't think that's a digression at all. That's exactly what we're talking about today. People have been asking questions about how the universe works, trying to make connections with the cosmos. For as long as people have been asking questions, all you have to do is look up at the night sky and wonder, how does that all work? Why does it seem so regular? Why are their patterns? And then patterns within those patterns, what do they reveal about the nature of the universe. Because one of my favorite things about the universe is that it does seem to follow laws, and we can figure those laws out if we pay attention to those patterns and try to draw dotted lines between them. And as you say, people have been doing that for a long long time. We sometimes dismiss our ancient history as like prescience and only take things seriously if it's been figured out in the last few hundred years. But you know, the development of science is much more gradual than is often described in history textbooks. People a long long time ago. We're thinking methodically and trying to understand the universe, and that's what people are still doing. And one of my favorite things is trying to think deeply about the nature of time and the universe. How far back in space can we see, what do we see, and what do we learn about how big and how strange the universe is as we look into space. And so on today's episode, we're going to be doing exactly that. We're going to be answering a question a listener asked us about the nature of deep time. So today on the podcast, we'll be answering listener questions. Summer Solstice Edition. We're so happy to be back and be back in your ear with this special episode to celebrate the summer Solstice. Happy Solstice, everybody.
Happy Solstice. Enjoy your roasted pine combs and your chicken feather damp and you're huge bonfires.
I hope you stay up late in the night, stare at the stars, wonder about the nature of the universe, and then write to me with your questions about it questions at Danielanjorge dot com. Don't be shy, send me your questions. You will get an answer. And on today's show, we're answering a question from Nick in Florida, who's wondering about the very oldest things we see in the sky. Here is Nick's question.
Hey Daniel, this is Nick from Jacksonville, Florida. I came across an article this morning that taught me something new and amazing about the universe. Apparently, beyond the distance of approximately fifteen billion light years, objects we see with telescopes start becoming larger again instead of smaller. My question is how close are we to being able to see this far and what will be the implications for cosmology once we get there? Thanks and love the show.
So this is really interesting. I have never actually heard this, that objects that you see beyond a certain distance start to appear larger, and I also don't understand how we can see this far in the first place.
Yeah, it's really fascinating. It's one of my favorite facts about the universe. It really shows us that the universe is expanding and that we have a pretty good grasp on how that works, or at least what's been happening, which is already kind of astounding. The fact that wall we've been trapped on this tiny little rock in one corner of the universe, we can measure things that tell us about the universe on the grandest scale. You know, what's happening over billions and billions of light years, and what's been going on over the last few billion years. It's really incredible what we are able to piece together from just the few photons that happen to land on our rock.
That is wild. I mean, it's also just kind of weird that in a way we can time travel, but just with our eyes and some fancy shaped glass.
Yeah, it is really amazing. So there's a few different things going on here that all come together to make this really weird effect that if you can get them all working together in your mind, show you how beautiful our explanation is. So let's take them one at a time. One concept is the one you just measured that looking up into the sky is basically time travel, and that's because the speed of light is not instantaneous. You know, something happens in Andromeda, you don't see it right away. It takes time for light to go from Andromeda to our eyeballs. And so when we look up at the night sky and we see Andromeda, we're not seeing what's happening in Andromeda right now. We're seeing what's happening in Andromeda when that light left Andromeda. And because Andromeda is several million light years away, it means we're seeing photons that left Andromeda several million years ago. Andromeda is not even in the same place it was when emitted that light, and so what we're seeing really is ancient history. And the further we look out into the universe, the deeper back in time. We are seeing like things are happening out there in the deep universe right now, but we won't see them for millions or billions of years, depending on how far away they are. So as we look out into the universe, we are really seeing further and back in time just because of this simple basic physics fact that light takes time to get to us.
So you're saying that if Andromeda has a newspaper that is really huge that we can see with a telescope, by the time that light reaches us, we're looking at a pretty old headline. It is out of date.
Yeah, exactly. And conversely, it means that if Andromeda has aliens that point their telescope at us, they're seeing millions of years ago. They would see the Earth as it was millions of years ago. They wouldn't even know that there was an intelligent technological civilization on our planet for millions of years, because that's only the very briefest part of our history. And so somewhere out there are photons from like when the Earth had dinosaurs on it, or even further away, there are photons from the Earth when it was like just a ball of magma. All those photons are still out there in the universe. Somebody could be picking them up where they're alien eyeballs and seeing the ancient history of our planet.
I like to imagine that the reason aliens don't contact us is they caught us when we had the weird Anomalocaris that came marine explosion, giant disgusting shrimp looking thing, and they're like, no, thank you, I'm not gonna get in touch with that planet.
It's too icky.
Nah.
Yes, don't like shellfish seafood.
So that's one concept, right, Things in the sky are old news. Right, We're not seeing the universe as it is now. We're seeing the universe as it was. And on one hand, that's frustrating because it means like we're missing out on the latest, greatest news. On the other hand, it's a huge gift. It means we can see back in time and like on Earth, you want to know what happened during the Roman Era or what happened a million years ago, you got to look for clues that happened to be here and be left over. Most of that stuff is destroyed or buried, but in the history of the universe, you just look into the sky. It's all still there. It's just arriving right now, fresh as the day was emitted. So you want to know what happened in the universe a million years ago, or a billion years ago or ten billion years ago, you just build bigger telescopes to capture more distant, fainter photons, and you can see it. It's all still they're in the sky.
So the further back in time we want to go in understanding our universe, the further way look exactly.
So you have to imagine these shells, like in a shell that's very close to the Earth, we're seeing the more recent past. We can't see the distant past in a close by shell, but we can't see the ancient past in a more distant shell. So we can't just like dial the knob and say I want to see what happened over here at that time. We can only see a certain time for every certain location because photons are just now arriving from that location based on how far away they are, all right, So that's one concept. The other concept is how big things look in the sky. And so to understand this first, let's just imagine the universe is not expanding. Imagine that you have galaxies and they're just hanging in space and nothing is moving. Everything is just hanging there. There's no relative velocity. Then you would expect things that are further away look smaller, right, because, for example, if you have some galaxy and it's right up in your eyeball, then photons from one side of the galaxy and photons from the other side of the galaxy are gonna come from very very different angles. Now you move that galaxy further away in the sky, photons from two different edges of the galaxy are now getting closer and closer together, so they just seem smaller in the sky. This is no magic. It's just like you hold your finger close to your eyeball, looks big. You push it further away, it looks smaller.
Right, It's just perspective, I see, Yes, So I have been told that people from far away are not tiny people. They are just far away. So all right, that makes perfect sense.
Yeah, exactly, And we have an intuition for this exactly the way you describe you don't think that people who are standing next to you are giants and people who are far away are midgets. You know this, and you invert it in your mind. When you see people, you can tell how far away they are, and so you estimate their actual size because you've taken that into account. Right, You have this intuition for things looking small far away and things looking big close up, and you'll count for this naturally. So if the universe was like that and nothing was moving, then it would just look like that. Things that are further away would look smaller. But there's one more effect you have to throw into the mix, and that's the expansion of the universe. Things are not just hanging in space. There's a relative velocity there. Space is expanding between galaxies, or another way to think about that is galaxies are running away from us and from each other, so everything is getting further and further away. And what that means is that the light we're seeing from those galaxies is not from where they are now, it's from where they were when they emitted that light. Oo okay, right, So, for example, imagine something on the very distant edge of the universe. We talk about how something could be forty five billion light years away, the furthest things in our observable universe, all right, But when we talk about that, we mean that's how far away it is now, not how far away it was when it admitted the light that's now coming to us, that's now arriving on Earth. It was much much closer when it emitted that light. What's happened in the intervening period as that photon has flown through space towards us is the universe has expanded and it's gotten further and further away.
Okay, So if I try to think about this on human scale, you have various people standing out in a field, and it's a very big field. So I need a telescope for me to see people, and it's a telescope with a slight delay, or a camera, let's say a camera. It's got a delay in it, so I will only see them after a while. So like, I could be looking at these people who are further away, but then the people who are closer to me, let's say they are running away from me at a faster rate, so they might with my delayed camera, look further away by the time I get my snapshot than the ones who were actually further away from me, but they look bigger because they were not running away from me as fast as the other.
Yeah, exactly, you have old information, and so you're taking these snapshots and you're seeing people where they were when the picture was taken. But if the picture takes a while to get to you, by the time it does, they could be much further away, right. And that's important to think about because that affects how big they look in the sky because when we talk about things that are really really far away, we're seeing them remember as they were when they emitted those photons, and if they were much closer when they emitted those photons, they took up more space in the sky because they were closer. So those photons have been flying towards us those millions or billions of years, but they started pretty close by, right, So they started further apart because the thing was closer to us. So there are two effects happening here. One is things that are further away look smaller, right, But the other effect is this expansion effect that some of those things that are now really really far away were closer when they emitted the photons. So these two competing effects there. And so what that means is that if we look at nearby stuff, mostly the first effect dominates that things that are further away look smaller. So as you look out into the night sky, stuff that's further away looks smaller and smaller and smaller. But then there's a point from about ten billion years ago when the other effects starts to dominate. When we're seeing stuff that was much closer when it admitted that light. Stuff looks smaller and smaller and smaller as it gets further away until about ten billion years into the past, and then stuff starts to look bigger and bigger. So the oldest stuff actually looks bigger in the night sky than some of the closer stuff, some of the more recent stuff, because you have these two effects that are competing with each other.
Because we're basically seeing like an after image of something that was going Yeah, it's actually not further from us. I mean that the actual star is that was there, but those photons that after image are finally hitting us, representing where in the sky.
When we talk about the universe, we talk about where things are now, that's where we put them in our mental maps, but we don't think about where they were when they emitted that light. And so if you just line things up based on where they were when they emitted that light, then yes, closer things would look bigger, and further things would look more distant. But because the expansion of the universe, not all the photons that are arriving here are perfectly lined up with where things are now, So things that are more distant now can actually look closer than things that actually are closer still, so there's this amazing effect in cosmology. And so Nick is asking about this effect, and he's wondering, can we see this yet? Can we see far enough out into the universe to see this turnover where the really distant stuff starts to get larger and larger again, and what does that mean for cosmology? And the answer Nick is that yes, we already can see that. We can see much further than ten billion years into our history. We can see all the way back to almost fourteen billion in years. So we have observed this. This is not like a theoretical concept that people are wondering about and going ooh, maybe in the future sometime. This is something we see. We've measured this, and this really nicely confirms our whole model for how the universe is expanding and how that expansion is accelerating. It's all encoded in the distances and the intensity of stuff in the sky.
Did anyone come up with a theory that this might be the case before we actually observed it, or did we observe it and then come up with the theory behind it.
Oh, yeah, great question. It al sort came together at the same moment when we realized that the universe's expansion was accelerating. We didn't even know that until we had a solid way for measuring how far away things were when they are really distant. We only figured that out when we were able to calibrate type one A supernova around the turn of the century, like twenty five years ago, and that's what told us that the expansion of the universe was different from what we expected. It's actually accelerating, and that changed the whole picture. At the same time, gave us a way to measure the distances to these big things and showed us that distant objects are actually larger than some nearer objects in our sky. And so it all sort of came together about the same time when we had this revolution in our understanding about the expansion history of the universe. It's really nice confirmation of that idea.
That's incredible. I mean, that must be so special as a scientist to actually see these things that fit into all of this theory and all all of these things that you're discovering of like, oh yeah, there is visual confirmation of this stuff at ward.
It's amazing that we can look up the night sky and we can piece the story together from again, just these photons and the patterns within them. And for thousands of years, our ancestors desperately wanted to do that. They looked up at the stars and wondered what they meant, and found patterns, but never really had an understanding anywhere close to what we have until very very recently. So many people lived in such deep ignorance. Unfortunately, real blessed to live in an era when we know anything about the universe. But you know, I wonder about the deep future when people will know so much more about how the universe works, and wonder what it was like to be as ignorant as we are today.
Uh, blissful is what I would say.
All right, If you're listening to this podcast in the year three thousand know that we were dumb, but we were happy.
We were dumb and happy. Take that future us all right.
Thanks very much to Nick for your question, and thanks to everybody who wonders about how the universe works and wants to figure it out. Please don't be shy to write to me to questions at Danielandhorgheay dot com. You'll always hear back. Happy Summer solsis everybody, and you'll hear from us again soon. For more science and curiosity, come find us on social media, where we answer questions and post videos. We're on Twitter, This org, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of Iheartwriting. For more podcasts from my Heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
