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Speaker 1: Hey, Daniel, what's the most distant object you've ever seen?

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Speaker 2: You know, the Andromeda galaxy is pretty far away. It's

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Speaker 2: like millions of light years. How about you, what's the

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Speaker 2: most distant thing you've ever seen?

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Speaker 1: When I am sleepy, it is my couch.

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Speaker 2: Your couch is far away.

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Speaker 1: Yeah, it's so fun.

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Speaker 3: W want mom.

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Speaker 4: Hi.

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Speaker 2: I'm Daniel. I'm a particle physicist and a professor at

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Speaker 2: UC Irvine, and I like to couch all my puns.

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Speaker 1: Hi. I am Katie Golden. I a podcast on animals,

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Speaker 1: and I am cushion for a never mind. I I

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Speaker 1: thought if I just said cushion that a pun would

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Speaker 1: come to me, and it didn't. It just made me

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Speaker 1: want to take a nap.

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Speaker 2: You were pushing for a pun, Cushion.

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Speaker 1: I thought I was going to be bruising for a

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Speaker 1: cruise in, but I was cushion for a pushing. I

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Speaker 1: guess a defenestration.

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Speaker 2: Sounds like you're set up for some punishment anyway. Welcome

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Speaker 2: to the podcast. Daniel and Jorge explain the universe in

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Speaker 2: which we try not to punish you. We try to

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Speaker 2: enrapture you. We try to share with you the joy

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Speaker 2: of understanding the nature of the universe, or when we

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Speaker 2: are mystified by the puzzles, the curiosity, the open questions

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Speaker 2: about the nature of this cosmos we find ourselves in,

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Speaker 2: we seek to understand it, we seek to explain all

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Speaker 2: of it to you.

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Speaker 3: On the podcast, Daniel.

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Speaker 1: Is this the one coming out on the summer solstice?

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Speaker 1: Just the quickest side before we get into our listener question.

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Speaker 1: I just visited in near Dublin, Bruno Boyne, these funeral mounds,

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Speaker 1: and it was so interesting because these very very ancient

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Speaker 1: people created these funeral mounds which had an internal structure

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Speaker 1: that they're large mounds like you could actually you can

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Speaker 1: go inside it. They can do ceremonies inside, and they

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Speaker 1: constructed it such that like during the solstice, the summer solstice,

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Speaker 1: on the longest day of the year, it illuminates this

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Speaker 1: entire inner chamber. And I just love that. So long

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Speaker 1: ago we were already thinking about physics, figuring out the universe,

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Speaker 1: and like trying to think about how light works and

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Speaker 1: use it for our interesting little Richard.

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Speaker 2: Yeah, exactly. I don't think that's a digression at all.

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Speaker 2: That's exactly what we're talking about today. People have been

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Speaker 2: asking questions about how the universe works, trying to make

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Speaker 2: connections with the cosmos. For as long as people have

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Speaker 2: been asking questions, all you have to do is look

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Speaker 2: up at the night sky and wonder, how does that

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Speaker 2: all work? Why does it seem so regular? Why are

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Speaker 2: their patterns? And then patterns within those patterns, what do

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Speaker 2: they reveal about the nature of the universe. Because one

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Speaker 2: of my favorite things about the universe is that it

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Speaker 2: does seem to follow laws, and we can figure those

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Speaker 2: laws out if we pay attention to those patterns and

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Speaker 2: try to draw dotted lines between them. And as you say,

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Speaker 2: people have been doing that for a long long time.

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Speaker 2: We sometimes dismiss our ancient history as like prescience and

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Speaker 2: only take things seriously if it's been figured out in

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Speaker 2: the last few hundred years. But you know, the development

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Speaker 2: of science is much more gradual than is often described

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Speaker 2: in history textbooks. People a long long time ago. We're

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Speaker 2: thinking methodically and trying to understand the universe, and that's

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Speaker 2: what people are still doing. And one of my favorite

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Speaker 2: things is trying to think deeply about the nature of

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Speaker 2: time and the universe. How far back in space can

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Speaker 2: we see, what do we see, and what do we

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Speaker 2: learn about how big and how strange the universe is

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Speaker 2: as we look into space. And so on today's episode,

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Speaker 2: we're going to be doing exactly that. We're going to

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Speaker 2: be answering a question a listener asked us about the

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Speaker 2: nature of deep time. So today on the podcast, we'll

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Speaker 2: be answering listener questions. Summer Solstice Edition. We're so happy

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Speaker 2: to be back and be back in your ear with

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Speaker 2: this special episode to celebrate the summer Solstice. Happy Solstice, everybody.

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Speaker 1: Happy Solstice. Enjoy your roasted pine combs and your chicken

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Speaker 1: feather damp and you're huge bonfires.

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Speaker 2: I hope you stay up late in the night, stare

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Speaker 2: at the stars, wonder about the nature of the universe,

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Speaker 2: and then write to me with your questions about it

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Speaker 2: questions at Danielanjorge dot com. Don't be shy, send me

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Speaker 2: your questions. You will get an answer. And on today's show,

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Speaker 2: we're answering a question from Nick in Florida, who's wondering

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Speaker 2: about the very oldest things we see in the sky.

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Speaker 2: Here is Nick's question.

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Speaker 4: Hey Daniel, this is Nick from Jacksonville, Florida. I came

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Speaker 4: across an article this morning that taught me something new

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Speaker 4: and amazing about the universe. Apparently, beyond the distance of

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Speaker 4: approximately fifteen billion light years, objects we see with telescopes

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Speaker 4: start becoming larger again instead of smaller. My question is

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Speaker 4: how close are we to being able to see this

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Speaker 4: far and what will be the implications for cosmology once

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Speaker 4: we get there? Thanks and love the show.

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Speaker 1: So this is really interesting. I have never actually heard this,

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Speaker 1: that objects that you see beyond a certain distance start

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Speaker 1: to appear larger, and I also don't understand how we

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Speaker 1: can see this far in the first place.

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Speaker 2: Yeah, it's really fascinating. It's one of my favorite facts

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Speaker 2: about the universe. It really shows us that the universe

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Speaker 2: is expanding and that we have a pretty good grasp

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Speaker 2: on how that works, or at least what's been happening,

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Speaker 2: which is already kind of astounding. The fact that wall

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Speaker 2: we've been trapped on this tiny little rock in one

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Speaker 2: corner of the universe, we can measure things that tell

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Speaker 2: us about the universe on the grandest scale. You know,

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Speaker 2: what's happening over billions and billions of light years, and

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Speaker 2: what's been going on over the last few billion years.

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Speaker 2: It's really incredible what we are able to piece together

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Speaker 2: from just the few photons that happen to land on

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Speaker 2: our rock.

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Speaker 1: That is wild. I mean, it's also just kind of

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Speaker 1: weird that in a way we can time travel, but

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Speaker 1: just with our eyes and some fancy shaped glass.

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Speaker 2: Yeah, it is really amazing. So there's a few different

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Speaker 2: things going on here that all come together to make

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Speaker 2: this really weird effect that if you can get them

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Speaker 2: all working together in your mind, show you how beautiful

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Speaker 2: our explanation is. So let's take them one at a time.

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Speaker 2: One concept is the one you just measured that looking

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Speaker 2: up into the sky is basically time travel, and that's

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Speaker 2: because the speed of light is not instantaneous. You know,

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Speaker 2: something happens in Andromeda, you don't see it right away.

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Speaker 2: It takes time for light to go from Andromeda to

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Speaker 2: our eyeballs. And so when we look up at the

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Speaker 2: night sky and we see Andromeda, we're not seeing what's

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Speaker 2: happening in Andromeda right now. We're seeing what's happening in

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Speaker 2: Andromeda when that light left Andromeda. And because Andromeda is

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Speaker 2: several million light years away, it means we're seeing photons

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Speaker 2: that left Andromeda several million years ago. Andromeda is not

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Speaker 2: even in the same place it was when emitted that light,

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Speaker 2: and so what we're seeing really is ancient history. And

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Speaker 2: the further we look out into the universe, the deeper

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Speaker 2: back in time. We are seeing like things are happening

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Speaker 2: out there in the deep universe right now, but we

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Speaker 2: won't see them for millions or billions of years, depending

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Speaker 2: on how far away they are. So as we look

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Speaker 2: out into the universe, we are really seeing further and

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Speaker 2: back in time just because of this simple basic physics

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Speaker 2: fact that light takes time to get to us.

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Speaker 1: So you're saying that if Andromeda has a newspaper that

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Speaker 1: is really huge that we can see with a telescope,

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Speaker 1: by the time that light reaches us, we're looking at

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Speaker 1: a pretty old headline. It is out of date.

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Speaker 2: Yeah, exactly. And conversely, it means that if Andromeda has

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Speaker 2: aliens that point their telescope at us, they're seeing millions

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Speaker 2: of years ago. They would see the Earth as it

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Speaker 2: was millions of years ago. They wouldn't even know that

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Speaker 2: there was an intelligent technological civilization on our planet for

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Speaker 2: millions of years, because that's only the very briefest part

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Speaker 2: of our history. And so somewhere out there are photons

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Speaker 2: from like when the Earth had dinosaurs on it, or

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Speaker 2: even further away, there are photons from the Earth when

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Speaker 2: it was like just a ball of magma. All those

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Speaker 2: photons are still out there in the universe. Somebody could

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Speaker 2: be picking them up where they're alien eyeballs and seeing

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Speaker 2: the ancient history of our planet.

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Speaker 1: I like to imagine that the reason aliens don't contact

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Speaker 1: us is they caught us when we had the weird

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Speaker 1: Anomalocaris that came marine explosion, giant disgusting shrimp looking thing,

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Speaker 1: and they're like, no, thank you, I'm not gonna get

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Speaker 1: in touch with that planet.

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Speaker 2: It's too icky.

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Speaker 3: Nah.

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Speaker 1: Yes, don't like shellfish seafood.

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Speaker 2: So that's one concept, right, Things in the sky are

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Speaker 2: old news. Right, We're not seeing the universe as it

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Speaker 2: is now. We're seeing the universe as it was. And

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Speaker 2: on one hand, that's frustrating because it means like we're

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Speaker 2: missing out on the latest, greatest news. On the other hand,

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Speaker 2: it's a huge gift. It means we can see back

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Speaker 2: in time and like on Earth, you want to know

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Speaker 2: what happened during the Roman Era or what happened a

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Speaker 2: million years ago, you got to look for clues that

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Speaker 2: happened to be here and be left over. Most of

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Speaker 2: that stuff is destroyed or buried, but in the history

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Speaker 2: of the universe, you just look into the sky. It's

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Speaker 2: all still there. It's just arriving right now, fresh as

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Speaker 2: the day was emitted. So you want to know what

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Speaker 2: happened in the universe a million years ago, or a

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Speaker 2: billion years ago or ten billion years ago, you just

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Speaker 2: build bigger telescopes to capture more distant, fainter photons, and

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Speaker 2: you can see it. It's all still they're in the sky.

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Speaker 1: So the further back in time we want to go

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Speaker 1: in understanding our universe, the further way look exactly.

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Speaker 2: So you have to imagine these shells, like in a

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Speaker 2: shell that's very close to the Earth, we're seeing the

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Speaker 2: more recent past. We can't see the distant past in

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Speaker 2: a close by shell, but we can't see the ancient

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Speaker 2: past in a more distant shell. So we can't just

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Speaker 2: like dial the knob and say I want to see

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Speaker 2: what happened over here at that time. We can only

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Speaker 2: see a certain time for every certain location because photons

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Speaker 2: are just now arriving from that location based on how

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Speaker 2: far away they are, all right, So that's one concept.

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Speaker 2: The other concept is how big things look in the sky.

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Speaker 2: And so to understand this first, let's just imagine the

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Speaker 2: universe is not expanding. Imagine that you have galaxies and

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Speaker 2: they're just hanging in space and nothing is moving. Everything

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Speaker 2: is just hanging there. There's no relative velocity. Then you

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Speaker 2: would expect things that are further away look smaller, right, because,

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Speaker 2: for example, if you have some galaxy and it's right

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Speaker 2: up in your eyeball, then photons from one side of

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Speaker 2: the galaxy and photons from the other side of the

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Speaker 2: galaxy are gonna come from very very different angles. Now

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Speaker 2: you move that galaxy further away in the sky, photons

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Speaker 2: from two different edges of the galaxy are now getting

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Speaker 2: closer and closer together, so they just seem smaller in

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Speaker 2: the sky. This is no magic. It's just like you

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Speaker 2: hold your finger close to your eyeball, looks big. You

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Speaker 2: push it further away, it looks smaller.

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Speaker 1: Right, It's just perspective, I see, Yes, So I have

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Speaker 1: been told that people from far away are not tiny people.

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Speaker 1: They are just far away. So all right, that makes

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Speaker 1: perfect sense.

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Speaker 2: Yeah, exactly, And we have an intuition for this exactly

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Speaker 2: the way you describe you don't think that people who

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Speaker 2: are standing next to you are giants and people who

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Speaker 2: are far away are midgets. You know this, and you

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Speaker 2: invert it in your mind. When you see people, you

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Speaker 2: can tell how far away they are, and so you

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Speaker 2: estimate their actual size because you've taken that into account. Right,

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Speaker 2: You have this intuition for things looking small far away

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Speaker 2: and things looking big close up, and you'll count for

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Speaker 2: this naturally. So if the universe was like that and

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Speaker 2: nothing was moving, then it would just look like that.

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Speaker 2: Things that are further away would look smaller. But there's

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Speaker 2: one more effect you have to throw into the mix,

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Speaker 2: and that's the expansion of the universe. Things are not

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Speaker 2: just hanging in space. There's a relative velocity there. Space

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Speaker 2: is expanding between galaxies, or another way to think about

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Speaker 2: that is galaxies are running away from us and from

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Speaker 2: each other, so everything is getting further and further away.

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Speaker 2: And what that means is that the light we're seeing

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Speaker 2: from those galaxies is not from where they are now,

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Speaker 2: it's from where they were when they emitted that light.

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Speaker 2: Oo okay, right, So, for example, imagine something on the

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Speaker 2: very distant edge of the universe. We talk about how

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Speaker 2: something could be forty five billion light years away, the

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Speaker 2: furthest things in our observable universe, all right, But when

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Speaker 2: we talk about that, we mean that's how far away

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Speaker 2: it is now, not how far away it was when

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Speaker 2: it admitted the light that's now coming to us, that's

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Speaker 2: now arriving on Earth. It was much much closer when

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Speaker 2: it emitted that light. What's happened in the intervening period

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Speaker 2: as that photon has flown through space towards us is

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Speaker 2: the universe has expanded and it's gotten further and further away.

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Speaker 1: Okay, So if I try to think about this on

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Speaker 1: human scale, you have various people standing out in a field,

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Speaker 1: and it's a very big field. So I need a

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Speaker 1: telescope for me to see people, and it's a telescope

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Speaker 1: with a slight delay, or a camera, let's say a camera.

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Speaker 1: It's got a delay in it, so I will only

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Speaker 1: see them after a while. So like, I could be

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Speaker 1: looking at these people who are further away, but then

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Speaker 1: the people who are closer to me, let's say they

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Speaker 1: are running away from me at a faster rate, so

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Speaker 1: they might with my delayed camera, look further away by

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Speaker 1: the time I get my snapshot than the ones who

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Speaker 1: were actually further away from me, but they look bigger

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Speaker 1: because they were not running away from me as fast

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Speaker 1: as the other.

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Speaker 2: Yeah, exactly, you have old information, and so you're taking

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Speaker 2: these snapshots and you're seeing people where they were when

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Speaker 2: the picture was taken. But if the picture takes a

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Speaker 2: while to get to you, by the time it does,

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Speaker 2: they could be much further away, right. And that's important

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Speaker 2: to think about because that affects how big they look

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Speaker 2: in the sky because when we talk about things that

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Speaker 2: are really really far away, we're seeing them remember as

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Speaker 2: they were when they emitted those photons, and if they

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Speaker 2: were much closer when they emitted those photons, they took

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Speaker 2: up more space in the sky because they were closer.

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Speaker 2: So those photons have been flying towards us those millions

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Speaker 2: or billions of years, but they started pretty close by, right,

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Speaker 2: So they started further apart because the thing was closer

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Speaker 2: to us. So there are two effects happening here. One

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Speaker 2: is things that are further away look smaller, right, But

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Speaker 2: the other effect is this expansion effect that some of

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Speaker 2: those things that are now really really far away were

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Speaker 2: closer when they emitted the photons. So these two competing

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Speaker 2: effects there. And so what that means is that if

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Speaker 2: we look at nearby stuff, mostly the first effect dominates

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Speaker 2: that things that are further away look smaller. So as

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Speaker 2: you look out into the night sky, stuff that's further

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Speaker 2: away looks smaller and smaller and smaller. But then there's

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Speaker 2: a point from about ten billion years ago when the

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Speaker 2: other effects starts to dominate. When we're seeing stuff that

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Speaker 2: was much closer when it admitted that light. Stuff looks

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Speaker 2: smaller and smaller and smaller as it gets further away

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Speaker 2: until about ten billion years into the past, and then

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Speaker 2: stuff starts to look bigger and bigger. So the oldest

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Speaker 2: stuff actually looks bigger in the night sky than some

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Speaker 2: of the closer stuff, some of the more recent stuff,

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Speaker 2: because you have these two effects that are competing with

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Speaker 2: each other.

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Speaker 1: Because we're basically seeing like an after image of something

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Speaker 1: that was going Yeah, it's actually not further from us.

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Speaker 1: I mean that the actual star is that was there,

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Speaker 1: but those photons that after image are finally hitting us,

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Speaker 1: representing where in the sky.

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Speaker 2: When we talk about the universe, we talk about where

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Speaker 2: things are now, that's where we put them in our

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Speaker 2: mental maps, but we don't think about where they were

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Speaker 2: when they emitted that light. And so if you just

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Speaker 2: line things up based on where they were when they

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Speaker 2: emitted that light, then yes, closer things would look bigger,

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Speaker 2: and further things would look more distant. But because the

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Speaker 2: expansion of the universe, not all the photons that are

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Speaker 2: arriving here are perfectly lined up with where things are now,

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Speaker 2: So things that are more distant now can actually look

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Speaker 2: closer than things that actually are closer still, so there's

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Speaker 2: this amazing effect in cosmology. And so Nick is asking

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Speaker 2: about this effect, and he's wondering, can we see this yet?

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Speaker 2: Can we see far enough out into the universe to

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Speaker 2: see this turnover where the really distant stuff starts to

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Speaker 2: get larger and larger again, and what does that mean

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Speaker 2: for cosmology? And the answer Nick is that yes, we

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Speaker 2: already can see that. We can see much further than

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Speaker 2: ten billion years into our history. We can see all

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Speaker 2: the way back to almost fourteen billion in years. So

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Speaker 2: we have observed this. This is not like a theoretical

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Speaker 2: concept that people are wondering about and going ooh, maybe

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Speaker 2: in the future sometime. This is something we see. We've

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Speaker 2: measured this, and this really nicely confirms our whole model

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Speaker 2: for how the universe is expanding and how that expansion

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Speaker 2: is accelerating. It's all encoded in the distances and the

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Speaker 2: intensity of stuff in the sky.

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Speaker 1: Did anyone come up with a theory that this might

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Speaker 1: be the case before we actually observed it, or did

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Speaker 1: we observe it and then come up with the theory

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Speaker 1: behind it.

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Speaker 2: Oh, yeah, great question. It al sort came together at

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Speaker 2: the same moment when we realized that the universe's expansion

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Speaker 2: was accelerating. We didn't even know that until we had

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Speaker 2: a solid way for measuring how far away things were

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Speaker 2: when they are really distant. We only figured that out

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Speaker 2: when we were able to calibrate type one A supernova

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Speaker 2: around the turn of the century, like twenty five years ago,

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Speaker 2: and that's what told us that the expansion of the

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Speaker 2: universe was different from what we expected. It's actually accelerating,

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Speaker 2: and that changed the whole picture. At the same time,

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Speaker 2: gave us a way to measure the distances to these

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Speaker 2: big things and showed us that distant objects are actually

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Speaker 2: larger than some nearer objects in our sky. And so

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Speaker 2: it all sort of came together about the same time

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Speaker 2: when we had this revolution in our understanding about the

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Speaker 2: expansion history of the universe. It's really nice confirmation of

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Speaker 2: that idea.

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Speaker 1: That's incredible. I mean, that must be so special as

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Speaker 1: a scientist to actually see these things that fit into

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Speaker 1: all of this theory and all all of these things

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Speaker 1: that you're discovering of like, oh yeah, there is visual

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Speaker 1: confirmation of this stuff at ward.

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Speaker 2: It's amazing that we can look up the night sky

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Speaker 2: and we can piece the story together from again, just

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Speaker 2: these photons and the patterns within them. And for thousands

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Speaker 2: of years, our ancestors desperately wanted to do that. They

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Speaker 2: looked up at the stars and wondered what they meant,

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Speaker 2: and found patterns, but never really had an understanding anywhere

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Speaker 2: close to what we have until very very recently. So

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Speaker 2: many people lived in such deep ignorance. Unfortunately, real blessed

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Speaker 2: to live in an era when we know anything about

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Speaker 2: the universe. But you know, I wonder about the deep

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Speaker 2: future when people will know so much more about how

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Speaker 2: the universe works, and wonder what it was like to

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Speaker 2: be as ignorant as we are today.

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Speaker 1: Uh, blissful is what I would say.

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Speaker 2: All right, If you're listening to this podcast in the

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Speaker 2: year three thousand know that we were dumb, but we

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Speaker 2: were happy.

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Speaker 1: We were dumb and happy. Take that future us all right.

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Speaker 2: Thanks very much to Nick for your question, and thanks

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Speaker 2: to everybody who wonders about how the universe works and

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Speaker 2: wants to figure it out. Please don't be shy to

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Speaker 2: write to me to questions at Danielandhorgheay dot com. You'll

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Speaker 2: always hear back. Happy Summer solsis everybody, and you'll hear

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Speaker 2: from us again soon. For more science and curiosity, come

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Speaker 2: find us on social media, where we answer questions and

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Speaker 2: post videos. We're on Twitter, This org, Instant, and now TikTok.

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Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain

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Speaker 2: the Universe is a production of Iheartwriting. For more podcasts

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Speaker 2: from my Heart Radio, visit the iHeartRadio app, Apple Podcasts,

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Speaker 2: or wherever you listen to your favorite shows.