Speaker 1: Hey, Daniel, what's the most distant object you've ever seen?
Speaker 2: You know, the Andromeda galaxy is pretty far away. It's
Speaker 2: like millions of light years. How about you, what's the
Speaker 2: most distant thing you've ever seen?
Speaker 1: When I am sleepy, it is my couch.
Speaker 2: Your couch is far away.
Speaker 1: Yeah, it's so fun.
Speaker 3: W want mom.
Speaker 4: Hi.
Speaker 2: I'm Daniel. I'm a particle physicist and a professor at
Speaker 2: UC Irvine, and I like to couch all my puns.
Speaker 1: Hi. I am Katie Golden. I a podcast on animals,
Speaker 1: and I am cushion for a never mind. I I
Speaker 1: thought if I just said cushion that a pun would
Speaker 1: come to me, and it didn't. It just made me
Speaker 1: want to take a nap.
Speaker 2: You were pushing for a pun, Cushion.
Speaker 1: I thought I was going to be bruising for a
Speaker 1: cruise in, but I was cushion for a pushing. I
Speaker 1: guess a defenestration.
Speaker 2: Sounds like you're set up for some punishment anyway. Welcome
Speaker 2: to the podcast. Daniel and Jorge explain the universe in
Speaker 2: which we try not to punish you. We try to
Speaker 2: enrapture you. We try to share with you the joy
Speaker 2: of understanding the nature of the universe, or when we
Speaker 2: are mystified by the puzzles, the curiosity, the open questions
Speaker 2: about the nature of this cosmos we find ourselves in,
Speaker 2: we seek to understand it, we seek to explain all
Speaker 2: of it to you.
Speaker 3: On the podcast, Daniel.
Speaker 1: Is this the one coming out on the summer solstice?
Speaker 1: Just the quickest side before we get into our listener question.
Speaker 1: I just visited in near Dublin, Bruno Boyne, these funeral mounds,
Speaker 1: and it was so interesting because these very very ancient
Speaker 1: people created these funeral mounds which had an internal structure
Speaker 1: that they're large mounds like you could actually you can
Speaker 1: go inside it. They can do ceremonies inside, and they
Speaker 1: constructed it such that like during the solstice, the summer solstice,
Speaker 1: on the longest day of the year, it illuminates this
Speaker 1: entire inner chamber. And I just love that. So long
Speaker 1: ago we were already thinking about physics, figuring out the universe,
Speaker 1: and like trying to think about how light works and
Speaker 1: use it for our interesting little Richard.
Speaker 2: Yeah, exactly. I don't think that's a digression at all.
Speaker 2: That's exactly what we're talking about today. People have been
Speaker 2: asking questions about how the universe works, trying to make
Speaker 2: connections with the cosmos. For as long as people have
Speaker 2: been asking questions, all you have to do is look
Speaker 2: up at the night sky and wonder, how does that
Speaker 2: all work? Why does it seem so regular? Why are
Speaker 2: their patterns? And then patterns within those patterns, what do
Speaker 2: they reveal about the nature of the universe. Because one
Speaker 2: of my favorite things about the universe is that it
Speaker 2: does seem to follow laws, and we can figure those
Speaker 2: laws out if we pay attention to those patterns and
Speaker 2: try to draw dotted lines between them. And as you say,
Speaker 2: people have been doing that for a long long time.
Speaker 2: We sometimes dismiss our ancient history as like prescience and
Speaker 2: only take things seriously if it's been figured out in
Speaker 2: the last few hundred years. But you know, the development
Speaker 2: of science is much more gradual than is often described
Speaker 2: in history textbooks. People a long long time ago. We're
Speaker 2: thinking methodically and trying to understand the universe, and that's
Speaker 2: what people are still doing. And one of my favorite
Speaker 2: things is trying to think deeply about the nature of
Speaker 2: time and the universe. How far back in space can
Speaker 2: we see, what do we see, and what do we
Speaker 2: learn about how big and how strange the universe is
Speaker 2: as we look into space. And so on today's episode,
Speaker 2: we're going to be doing exactly that. We're going to
Speaker 2: be answering a question a listener asked us about the
Speaker 2: nature of deep time. So today on the podcast, we'll
Speaker 2: be answering listener questions. Summer Solstice Edition. We're so happy
Speaker 2: to be back and be back in your ear with
Speaker 2: this special episode to celebrate the summer Solstice. Happy Solstice, everybody.
Speaker 1: Happy Solstice. Enjoy your roasted pine combs and your chicken
Speaker 1: feather damp and you're huge bonfires.
Speaker 2: I hope you stay up late in the night, stare
Speaker 2: at the stars, wonder about the nature of the universe,
Speaker 2: and then write to me with your questions about it
Speaker 2: questions at Danielanjorge dot com. Don't be shy, send me
Speaker 2: your questions. You will get an answer. And on today's show,
Speaker 2: we're answering a question from Nick in Florida, who's wondering
Speaker 2: about the very oldest things we see in the sky.
Speaker 2: Here is Nick's question.
Speaker 4: Hey Daniel, this is Nick from Jacksonville, Florida. I came
Speaker 4: across an article this morning that taught me something new
Speaker 4: and amazing about the universe. Apparently, beyond the distance of
Speaker 4: approximately fifteen billion light years, objects we see with telescopes
Speaker 4: start becoming larger again instead of smaller. My question is
Speaker 4: how close are we to being able to see this
Speaker 4: far and what will be the implications for cosmology once
Speaker 4: we get there? Thanks and love the show.
Speaker 1: So this is really interesting. I have never actually heard this,
Speaker 1: that objects that you see beyond a certain distance start
Speaker 1: to appear larger, and I also don't understand how we
Speaker 1: can see this far in the first place.
Speaker 2: Yeah, it's really fascinating. It's one of my favorite facts
Speaker 2: about the universe. It really shows us that the universe
Speaker 2: is expanding and that we have a pretty good grasp
Speaker 2: on how that works, or at least what's been happening,
Speaker 2: which is already kind of astounding. The fact that wall
Speaker 2: we've been trapped on this tiny little rock in one
Speaker 2: corner of the universe, we can measure things that tell
Speaker 2: us about the universe on the grandest scale. You know,
Speaker 2: what's happening over billions and billions of light years, and
Speaker 2: what's been going on over the last few billion years.
Speaker 2: It's really incredible what we are able to piece together
Speaker 2: from just the few photons that happen to land on
Speaker 2: our rock.
Speaker 1: That is wild. I mean, it's also just kind of
Speaker 1: weird that in a way we can time travel, but
Speaker 1: just with our eyes and some fancy shaped glass.
Speaker 2: Yeah, it is really amazing. So there's a few different
Speaker 2: things going on here that all come together to make
Speaker 2: this really weird effect that if you can get them
Speaker 2: all working together in your mind, show you how beautiful
Speaker 2: our explanation is. So let's take them one at a time.
Speaker 2: One concept is the one you just measured that looking
Speaker 2: up into the sky is basically time travel, and that's
Speaker 2: because the speed of light is not instantaneous. You know,
Speaker 2: something happens in Andromeda, you don't see it right away.
Speaker 2: It takes time for light to go from Andromeda to
Speaker 2: our eyeballs. And so when we look up at the
Speaker 2: night sky and we see Andromeda, we're not seeing what's
Speaker 2: happening in Andromeda right now. We're seeing what's happening in
Speaker 2: Andromeda when that light left Andromeda. And because Andromeda is
Speaker 2: several million light years away, it means we're seeing photons
Speaker 2: that left Andromeda several million years ago. Andromeda is not
Speaker 2: even in the same place it was when emitted that light,
Speaker 2: and so what we're seeing really is ancient history. And
Speaker 2: the further we look out into the universe, the deeper
Speaker 2: back in time. We are seeing like things are happening
Speaker 2: out there in the deep universe right now, but we
Speaker 2: won't see them for millions or billions of years, depending
Speaker 2: on how far away they are. So as we look
Speaker 2: out into the universe, we are really seeing further and
Speaker 2: back in time just because of this simple basic physics
Speaker 2: fact that light takes time to get to us.
Speaker 1: So you're saying that if Andromeda has a newspaper that
Speaker 1: is really huge that we can see with a telescope,
Speaker 1: by the time that light reaches us, we're looking at
Speaker 1: a pretty old headline. It is out of date.
Speaker 2: Yeah, exactly. And conversely, it means that if Andromeda has
Speaker 2: aliens that point their telescope at us, they're seeing millions
Speaker 2: of years ago. They would see the Earth as it
Speaker 2: was millions of years ago. They wouldn't even know that
Speaker 2: there was an intelligent technological civilization on our planet for
Speaker 2: millions of years, because that's only the very briefest part
Speaker 2: of our history. And so somewhere out there are photons
Speaker 2: from like when the Earth had dinosaurs on it, or
Speaker 2: even further away, there are photons from the Earth when
Speaker 2: it was like just a ball of magma. All those
Speaker 2: photons are still out there in the universe. Somebody could
Speaker 2: be picking them up where they're alien eyeballs and seeing
Speaker 2: the ancient history of our planet.
Speaker 1: I like to imagine that the reason aliens don't contact
Speaker 1: us is they caught us when we had the weird
Speaker 1: Anomalocaris that came marine explosion, giant disgusting shrimp looking thing,
Speaker 1: and they're like, no, thank you, I'm not gonna get
Speaker 1: in touch with that planet.
Speaker 2: It's too icky.
Speaker 3: Nah.
Speaker 1: Yes, don't like shellfish seafood.
Speaker 2: So that's one concept, right, Things in the sky are
Speaker 2: old news. Right, We're not seeing the universe as it
Speaker 2: is now. We're seeing the universe as it was. And
Speaker 2: on one hand, that's frustrating because it means like we're
Speaker 2: missing out on the latest, greatest news. On the other hand,
Speaker 2: it's a huge gift. It means we can see back
Speaker 2: in time and like on Earth, you want to know
Speaker 2: what happened during the Roman Era or what happened a
Speaker 2: million years ago, you got to look for clues that
Speaker 2: happened to be here and be left over. Most of
Speaker 2: that stuff is destroyed or buried, but in the history
Speaker 2: of the universe, you just look into the sky. It's
Speaker 2: all still there. It's just arriving right now, fresh as
Speaker 2: the day was emitted. So you want to know what
Speaker 2: happened in the universe a million years ago, or a
Speaker 2: billion years ago or ten billion years ago, you just
Speaker 2: build bigger telescopes to capture more distant, fainter photons, and
Speaker 2: you can see it. It's all still they're in the sky.
Speaker 1: So the further back in time we want to go
Speaker 1: in understanding our universe, the further way look exactly.
Speaker 2: So you have to imagine these shells, like in a
Speaker 2: shell that's very close to the Earth, we're seeing the
Speaker 2: more recent past. We can't see the distant past in
Speaker 2: a close by shell, but we can't see the ancient
Speaker 2: past in a more distant shell. So we can't just
Speaker 2: like dial the knob and say I want to see
Speaker 2: what happened over here at that time. We can only
Speaker 2: see a certain time for every certain location because photons
Speaker 2: are just now arriving from that location based on how
Speaker 2: far away they are, all right, So that's one concept.
Speaker 2: The other concept is how big things look in the sky.
Speaker 2: And so to understand this first, let's just imagine the
Speaker 2: universe is not expanding. Imagine that you have galaxies and
Speaker 2: they're just hanging in space and nothing is moving. Everything
Speaker 2: is just hanging there. There's no relative velocity. Then you
Speaker 2: would expect things that are further away look smaller, right, because,
Speaker 2: for example, if you have some galaxy and it's right
Speaker 2: up in your eyeball, then photons from one side of
Speaker 2: the galaxy and photons from the other side of the
Speaker 2: galaxy are gonna come from very very different angles. Now
Speaker 2: you move that galaxy further away in the sky, photons
Speaker 2: from two different edges of the galaxy are now getting
Speaker 2: closer and closer together, so they just seem smaller in
Speaker 2: the sky. This is no magic. It's just like you
Speaker 2: hold your finger close to your eyeball, looks big. You
Speaker 2: push it further away, it looks smaller.
Speaker 1: Right, It's just perspective, I see, Yes, So I have
Speaker 1: been told that people from far away are not tiny people.
Speaker 1: They are just far away. So all right, that makes
Speaker 1: perfect sense.
Speaker 2: Yeah, exactly, And we have an intuition for this exactly
Speaker 2: the way you describe you don't think that people who
Speaker 2: are standing next to you are giants and people who
Speaker 2: are far away are midgets. You know this, and you
Speaker 2: invert it in your mind. When you see people, you
Speaker 2: can tell how far away they are, and so you
Speaker 2: estimate their actual size because you've taken that into account. Right,
Speaker 2: You have this intuition for things looking small far away
Speaker 2: and things looking big close up, and you'll count for
Speaker 2: this naturally. So if the universe was like that and
Speaker 2: nothing was moving, then it would just look like that.
Speaker 2: Things that are further away would look smaller. But there's
Speaker 2: one more effect you have to throw into the mix,
Speaker 2: and that's the expansion of the universe. Things are not
Speaker 2: just hanging in space. There's a relative velocity there. Space
Speaker 2: is expanding between galaxies, or another way to think about
Speaker 2: that is galaxies are running away from us and from
Speaker 2: each other, so everything is getting further and further away.
Speaker 2: And what that means is that the light we're seeing
Speaker 2: from those galaxies is not from where they are now,
Speaker 2: it's from where they were when they emitted that light.
Speaker 2: Oo okay, right, So, for example, imagine something on the
Speaker 2: very distant edge of the universe. We talk about how
Speaker 2: something could be forty five billion light years away, the
Speaker 2: furthest things in our observable universe, all right, But when
Speaker 2: we talk about that, we mean that's how far away
Speaker 2: it is now, not how far away it was when
Speaker 2: it admitted the light that's now coming to us, that's
Speaker 2: now arriving on Earth. It was much much closer when
Speaker 2: it emitted that light. What's happened in the intervening period
Speaker 2: as that photon has flown through space towards us is
Speaker 2: the universe has expanded and it's gotten further and further away.
Speaker 1: Okay, So if I try to think about this on
Speaker 1: human scale, you have various people standing out in a field,
Speaker 1: and it's a very big field. So I need a
Speaker 1: telescope for me to see people, and it's a telescope
Speaker 1: with a slight delay, or a camera, let's say a camera.
Speaker 1: It's got a delay in it, so I will only
Speaker 1: see them after a while. So like, I could be
Speaker 1: looking at these people who are further away, but then
Speaker 1: the people who are closer to me, let's say they
Speaker 1: are running away from me at a faster rate, so
Speaker 1: they might with my delayed camera, look further away by
Speaker 1: the time I get my snapshot than the ones who
Speaker 1: were actually further away from me, but they look bigger
Speaker 1: because they were not running away from me as fast
Speaker 1: as the other.
Speaker 2: Yeah, exactly, you have old information, and so you're taking
Speaker 2: these snapshots and you're seeing people where they were when
Speaker 2: the picture was taken. But if the picture takes a
Speaker 2: while to get to you, by the time it does,
Speaker 2: they could be much further away, right. And that's important
Speaker 2: to think about because that affects how big they look
Speaker 2: in the sky because when we talk about things that
Speaker 2: are really really far away, we're seeing them remember as
Speaker 2: they were when they emitted those photons, and if they
Speaker 2: were much closer when they emitted those photons, they took
Speaker 2: up more space in the sky because they were closer.
Speaker 2: So those photons have been flying towards us those millions
Speaker 2: or billions of years, but they started pretty close by, right,
Speaker 2: So they started further apart because the thing was closer
Speaker 2: to us. So there are two effects happening here. One
Speaker 2: is things that are further away look smaller, right, But
Speaker 2: the other effect is this expansion effect that some of
Speaker 2: those things that are now really really far away were
Speaker 2: closer when they emitted the photons. So these two competing
Speaker 2: effects there. And so what that means is that if
Speaker 2: we look at nearby stuff, mostly the first effect dominates
Speaker 2: that things that are further away look smaller. So as
Speaker 2: you look out into the night sky, stuff that's further
Speaker 2: away looks smaller and smaller and smaller. But then there's
Speaker 2: a point from about ten billion years ago when the
Speaker 2: other effects starts to dominate. When we're seeing stuff that
Speaker 2: was much closer when it admitted that light. Stuff looks
Speaker 2: smaller and smaller and smaller as it gets further away
Speaker 2: until about ten billion years into the past, and then
Speaker 2: stuff starts to look bigger and bigger. So the oldest
Speaker 2: stuff actually looks bigger in the night sky than some
Speaker 2: of the closer stuff, some of the more recent stuff,
Speaker 2: because you have these two effects that are competing with
Speaker 2: each other.
Speaker 1: Because we're basically seeing like an after image of something
Speaker 1: that was going Yeah, it's actually not further from us.
Speaker 1: I mean that the actual star is that was there,
Speaker 1: but those photons that after image are finally hitting us,
Speaker 1: representing where in the sky.
Speaker 2: When we talk about the universe, we talk about where
Speaker 2: things are now, that's where we put them in our
Speaker 2: mental maps, but we don't think about where they were
Speaker 2: when they emitted that light. And so if you just
Speaker 2: line things up based on where they were when they
Speaker 2: emitted that light, then yes, closer things would look bigger,
Speaker 2: and further things would look more distant. But because the
Speaker 2: expansion of the universe, not all the photons that are
Speaker 2: arriving here are perfectly lined up with where things are now,
Speaker 2: So things that are more distant now can actually look
Speaker 2: closer than things that actually are closer still, so there's
Speaker 2: this amazing effect in cosmology. And so Nick is asking
Speaker 2: about this effect, and he's wondering, can we see this yet?
Speaker 2: Can we see far enough out into the universe to
Speaker 2: see this turnover where the really distant stuff starts to
Speaker 2: get larger and larger again, and what does that mean
Speaker 2: for cosmology? And the answer Nick is that yes, we
Speaker 2: already can see that. We can see much further than
Speaker 2: ten billion years into our history. We can see all
Speaker 2: the way back to almost fourteen billion in years. So
Speaker 2: we have observed this. This is not like a theoretical
Speaker 2: concept that people are wondering about and going ooh, maybe
Speaker 2: in the future sometime. This is something we see. We've
Speaker 2: measured this, and this really nicely confirms our whole model
Speaker 2: for how the universe is expanding and how that expansion
Speaker 2: is accelerating. It's all encoded in the distances and the
Speaker 2: intensity of stuff in the sky.
Speaker 1: Did anyone come up with a theory that this might
Speaker 1: be the case before we actually observed it, or did
Speaker 1: we observe it and then come up with the theory
Speaker 1: behind it.
Speaker 2: Oh, yeah, great question. It al sort came together at
Speaker 2: the same moment when we realized that the universe's expansion
Speaker 2: was accelerating. We didn't even know that until we had
Speaker 2: a solid way for measuring how far away things were
Speaker 2: when they are really distant. We only figured that out
Speaker 2: when we were able to calibrate type one A supernova
Speaker 2: around the turn of the century, like twenty five years ago,
Speaker 2: and that's what told us that the expansion of the
Speaker 2: universe was different from what we expected. It's actually accelerating,
Speaker 2: and that changed the whole picture. At the same time,
Speaker 2: gave us a way to measure the distances to these
Speaker 2: big things and showed us that distant objects are actually
Speaker 2: larger than some nearer objects in our sky. And so
Speaker 2: it all sort of came together about the same time
Speaker 2: when we had this revolution in our understanding about the
Speaker 2: expansion history of the universe. It's really nice confirmation of
Speaker 2: that idea.
Speaker 1: That's incredible. I mean, that must be so special as
Speaker 1: a scientist to actually see these things that fit into
Speaker 1: all of this theory and all all of these things
Speaker 1: that you're discovering of like, oh yeah, there is visual
Speaker 1: confirmation of this stuff at ward.
Speaker 2: It's amazing that we can look up the night sky
Speaker 2: and we can piece the story together from again, just
Speaker 2: these photons and the patterns within them. And for thousands
Speaker 2: of years, our ancestors desperately wanted to do that. They
Speaker 2: looked up at the stars and wondered what they meant,
Speaker 2: and found patterns, but never really had an understanding anywhere
Speaker 2: close to what we have until very very recently. So
Speaker 2: many people lived in such deep ignorance. Unfortunately, real blessed
Speaker 2: to live in an era when we know anything about
Speaker 2: the universe. But you know, I wonder about the deep
Speaker 2: future when people will know so much more about how
Speaker 2: the universe works, and wonder what it was like to
Speaker 2: be as ignorant as we are today.
Speaker 1: Uh, blissful is what I would say.
Speaker 2: All right, If you're listening to this podcast in the
Speaker 2: year three thousand know that we were dumb, but we
Speaker 2: were happy.
Speaker 1: We were dumb and happy. Take that future us all right.
Speaker 2: Thanks very much to Nick for your question, and thanks
Speaker 2: to everybody who wonders about how the universe works and
Speaker 2: wants to figure it out. Please don't be shy to
Speaker 2: write to me to questions at Danielandhorgheay dot com. You'll
Speaker 2: always hear back. Happy Summer solsis everybody, and you'll hear
Speaker 2: from us again soon. For more science and curiosity, come
Speaker 2: find us on social media, where we answer questions and
Speaker 2: post videos. We're on Twitter, This org, Instant, and now TikTok.
Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain
Speaker 2: the Universe is a production of Iheartwriting. For more podcasts
Speaker 2: from my Heart Radio, visit the iHeartRadio app, Apple Podcasts,
Speaker 2: or wherever you listen to your favorite shows.