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Speaker 1: Hey, hoory, how tall are you these days?

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Speaker 2: What do you mean these days?

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Speaker 1: Well, I don't know. It's been a while since I've

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Speaker 1: seen you in person and measured you up. Maybe you've

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Speaker 1: had that popular leg lengthening surgery.

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Speaker 2: Well I haven't, And even if I did see you,

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Speaker 2: how do you know you've been enshrin? Also because it's

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Speaker 2: all relative, But no, I seriously haven't measured my height

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Speaker 2: in like years.

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Speaker 1: Well, it might be that you're headed in the other direction.

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Speaker 1: People tend to shrink as they get older, so maybe

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Speaker 1: your greatest heights are behind you.

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Speaker 2: It could be are you saying I peaked already?

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Speaker 1: It's all downhills from here or down joorge?

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Speaker 2: Well I heard that your tallest in the morning, so

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Speaker 2: you know that's why I try to sleep all day.

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Speaker 1: Is that still true if you don't get out of

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Speaker 1: bed until the afternoon?

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Speaker 2: Yeah, just a tall tale. Hi am Hohem a cartoonist

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Speaker 2: and the creator of PhD comics.

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Speaker 1: I'm Daniel. I'm a particle of physicist and a professor

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Speaker 1: UC Irvine, and I'm very happy to be half an

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Speaker 1: inch taller than my older brother.

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Speaker 2: But how happy is your older brother?

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Speaker 1: Less happy? But who cares?

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Speaker 2: What about your younger brother.

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Speaker 1: He's at half an inch taller than me. Oh boy, yeah,

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Speaker 1: I remember when we were kids and we realized that

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Speaker 1: my older brother might not always be the taller brother.

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Speaker 1: He had a moment of terror.

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Speaker 2: Yeah, yeah, that's tough. I am taller than my older

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Speaker 2: brother as well.

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Speaker 1: And so now you get to look down on him.

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Speaker 2: Nice to look up.

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Speaker 1: To him only figuratively, though.

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Speaker 2: But I I just did it from a higher panthage point.

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Speaker 2: But anyways, welcome to our podcast Daniel and Jorge Explain

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Speaker 2: the Universe, a production of iHeartRadio.

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Speaker 1: In which we try to climb the heights of understanding

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Speaker 1: in the universe. We look at this great cosmic mystery

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Speaker 1: as a journey to some kind of understanding. We want

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Speaker 1: to slowly make our way up the path towards understanding

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Speaker 1: the universe a little bit better, wondering if there is

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Speaker 1: some sort of final illumination at the top, or if

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Speaker 1: this mountain even has a top.

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Speaker 2: It's right, We stand tall and try to take a

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Speaker 2: view of the universe from this little vantage point we

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Speaker 2: have in our little planet floating around in space, wondering

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Speaker 2: how big is this giant universe that we live.

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Speaker 1: In, and what's it doing? After all, the more we

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Speaker 1: look out in the universe, the more we are surprised

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Speaker 1: by what's going on, not just in our cosmic neighborhood,

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Speaker 1: but in the farthest reaches, the deepest parts of space

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Speaker 1: that we are just barely able to see. Every time

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Speaker 1: scientists look out with some new kind of technological marvel,

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Speaker 1: they come back with news that shocks us about what's

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Speaker 1: going on out there in the furthest reaches of space.

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Speaker 1: It seems like the universe is destined to.

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Speaker 2: Keep the Yeah, it is a very surprising universe, still

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Speaker 2: full of giant mysteries. There seems to be a lot

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Speaker 2: that we don't know about the universe at a very

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Speaker 2: basic level still, you know, just basic facts about the

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Speaker 2: universe we still don't know.

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Speaker 1: Yeah, on one hand, we feel fairly accomplished because of

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Speaker 1: our incredible technology and everything we have learned and all

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Speaker 1: of the science that we have mastered. On the other hand,

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Speaker 1: there are still very basic things about the universe that

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Speaker 1: we don't know. How big is it, where did it

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Speaker 1: come from? What's it doing right now? What is its

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Speaker 1: future hold? It feels like scientists or even children in

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Speaker 1: a few hundred years will look back in this time

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Speaker 1: and think, boy, those folks really didn't know what was

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Speaker 1: going on.

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Speaker 2: Yeah, Like we don't know basic things like how tall

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Speaker 2: is the universe, you know, and like how tall is

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Speaker 2: it in comparison to its brother or sister?

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Speaker 1: Is there another universe and the multiverse that our universe

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Speaker 1: has like a sibling rivalry with I'm bigger than you are?

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Speaker 2: Maybe yeah, But then the question would be is our

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Speaker 2: universe the older sibling or the younger sibling? Is it

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Speaker 2: trying to get attention on? Is it the mediator sibling?

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Speaker 1: And if you're a universe, where do you go for therapy? Anyway?

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Speaker 2: Boy, it'd be interesting to be like a universe psychologist.

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Speaker 1: There would be big problems to solve, for sure. But

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Speaker 1: I think that every universe should be judged on its

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Speaker 1: own merits and not relative to some other kind of

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Speaker 1: universe out there that could be bigger or smaller, or

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Speaker 1: faster or taller or able to get higher scores on

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Speaker 1: math tests.

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Speaker 2: Yeah, I'm sure our universes are grand Universe's favorite.

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Speaker 1: I like to think we're all the favorite in some way.

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Speaker 2: Yeah, although it's always good to have a favorite uncle

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Speaker 2: or aunt. Maybe there's like a cool universe out there.

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Speaker 2: That's our uncle or aunt.

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Speaker 1: Oh, I know, like a universe that doesn't care so

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Speaker 1: much about the rules, maybe like flaunts causality, doesn't care

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Speaker 1: about locality. It's just like the Rebel universe.

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Speaker 2: Yeah, it just showers you with gifts and stuff, takes

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Speaker 2: you out for ice cream.

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Speaker 1: Well, we are still trying to figure out which universe

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Speaker 1: we are in. We don't really know what the rules

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Speaker 1: of the universe are. All we can do is turn

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Speaker 1: our heads skywards and gather the information that it sends us.

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Speaker 1: By looking at photons and other particles that arrive on Earth,

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Speaker 1: we do get little bits of information, little clues that

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Speaker 1: tell us what's happening out there in the universe, and

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Speaker 1: they tell a really fascinating story, but one that we

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Speaker 1: are still unraveling.

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Speaker 2: Yeah, it is a pretty amazing universe full of interesting

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Speaker 2: stuff out there, like antimatter. Do you think our favorite

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Speaker 2: universes are anti matter universe?

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Speaker 1: I think that's definitely like our other twin universe that's

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Speaker 1: our rival.

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Speaker 2: But as you said, it is a giant universe and

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Speaker 2: it seems to be getting bigger, right, that's the idea.

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Speaker 2: It's a huge universe and not only is our view

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Speaker 2: of it expanding every day, but the universe itself space

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Speaker 2: itself seems to be getting bigger and bigger.

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Speaker 1: Yeah, we are about six billion years into a growth

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Speaker 1: spurt where we have been getting bigger and bigger, faster

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Speaker 1: and faster, and unlike your children, it doesn't seem like

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Speaker 1: that has an end. Scientists suspect that this might go

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Speaker 1: on forever until the universe is almost unfathomably large. If

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Speaker 1: it isn't already infinite.

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Speaker 2: Well, I guess that's the big question. Is how fast

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Speaker 2: is it growing? And does it seem like it is

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Speaker 2: going to keep growing forever exactly?

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Speaker 1: That is the question. And we look out into space,

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Speaker 1: which allows us to look further and further back in time.

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Speaker 1: It's sort of like looking at the marks you make

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Speaker 1: on that door jam as your kids grow up. You

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Speaker 1: can see not just how tall they were, but how

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Speaker 1: fast they grew based on the spaces between the marks.

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Speaker 1: We do the same thing by looking out into the

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Speaker 1: universe and seeing how big it is now and how

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Speaker 1: fast it was expanding in the past, and trying to

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Speaker 1: tell the whole story of the universe's expansion and extrapolate

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Speaker 1: that into the murky future.

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Speaker 2: So today on the podcast, we'll be asking the question

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Speaker 2: what's the best way to measure the expansion of the universe.

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Speaker 1: Definitely some kind of cosmic door jam, Oh.

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Speaker 2: My gosh, that would be a gigantic door. Where does

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Speaker 2: that door lead to? And how big does your pencil

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Speaker 2: need to be in order to make those marks exactly?

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Speaker 2: And is that doorjay part of the universe or part

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Speaker 2: of some metaverse or multiverse or multi metaverse. Well, it's

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Speaker 2: a door, I guess it's a doorway or doorway's part

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Speaker 2: of things.

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Speaker 1: I suppose if it's just sort of a dotted line,

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Speaker 1: But if you're going to make a mark on it,

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Speaker 1: it's got to have something in it that can hold

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Speaker 1: that information. So I guess then it would still be

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Speaker 1: part of the universe. So yeah, it's a tricky problem.

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Speaker 1: How do you use the universe to measure the universe?

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Speaker 2: That is a pretty tricky question because I guess if

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Speaker 2: you think about it, we're just floating on this tiny

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Speaker 2: rock called Earth in a little corner of a galaxy,

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Speaker 2: which is in a corner of some giant supercluster of galaxies,

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Speaker 2: And like, how can we possibly even think that we

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Speaker 2: can measure the size of the universe from this little

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Speaker 2: vantage point.

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Speaker 1: It is kind of incredible and almost fantastical what we

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Speaker 1: can do. And astronomers are really clever. As I was

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Speaker 1: prepping for today's episode, I was reading some recent papers

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Speaker 1: about really amazing ideas astronomers have for how to measure

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Speaker 1: how far away things are. And boy, those are some

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Speaker 1: clever folks. It's almost like they are magicians.

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Speaker 2: Yeah, because you know, I guess we're usedeing our everyday

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Speaker 2: lives of measuring things directly. You know, like if I

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Speaker 2: want to measure how tall my kid is, you just

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Speaker 2: you know, line them up against the wall and make

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Speaker 2: a mark and then use a ruler. Or if you

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Speaker 2: want to measure how far away another town is, you

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Speaker 2: kind of have to just drive there and see how

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Speaker 2: long it takes you, right.

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Speaker 1: Mm hmm. Even when we measure the distance to the Moon,

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Speaker 1: we do it by bouncing a laser off of a

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Speaker 1: mirror that astronauts left on the Moon and measure the

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Speaker 1: round trip time. So even that is kind of direct.

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Speaker 2: Yeah, And although we also had to go to the

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Speaker 2: mood to put that mirror there, right.

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Speaker 1: Yeah, too, exactly, It's sort of like we went to

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Speaker 1: the Moon and unfurled a huge measuring tape on the way.

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Speaker 1: It's just that measuring tape is made of laser beams.

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Speaker 2: Ooh nice. But with the universe that's kind of harder, right,

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Speaker 2: I mean, you can kind of have to go to

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Speaker 2: the other side of the universe and then put a

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Speaker 2: mirror there or at the end of a measuring tape

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Speaker 2: in order to directly measure how big the universe is.

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Speaker 1: Yeah, we'd love to be able to do that, but

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Speaker 1: without such a cosmic measuring tape. Astronomers and cosmologists, and

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Speaker 1: I guess cosmetologists have figured out ways to measure the

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Speaker 1: expansion of the universe over time.

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Speaker 2: Did you just say cosmetologists? Did you loop them in

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Speaker 2: in the same sentence as a cosmologist.

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Speaker 1: I did because I was watching this hilarious video clip

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Speaker 1: this morning of news coverage of the James web Space telescope,

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Speaker 1: where they said that it was a very powerful tool

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Speaker 1: that helped cosmetologists understand the universe. And I've been chuckling

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Speaker 1: about that all morning.

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Speaker 2: Oh my goodness, does it like the news anchor said that.

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Speaker 1: Yes, exactly. Cosmetologists and astrologists all over the world are

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Speaker 1: excited about the James web Space telescope.

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Speaker 2: Well, that could be true. I guess you never know.

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Speaker 2: I'm sure there are many cosmetologists listeners listening to us

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Speaker 2: right now who are fans of the universe and excited

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Speaker 2: about the James Webb tel.

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Speaker 1: Yeah, and they're very interested in the makeup of the

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Speaker 1: universe haha, nice and foundational questions in science.

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Speaker 2: Yeah, they're ready for us to lay on some bass

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Speaker 2: and blush at the amazing mysteries of the universe. But anyways,

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Speaker 2: as usually, we were wondering how many people out there

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Speaker 2: had thought about this question, and we're curious about what

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Speaker 2: is the best way to measure the expansion of the universe.

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Speaker 1: So thanks very much to those of you who answer

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Speaker 1: these questions for this fun segment of our podcast. If

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Speaker 1: you'd like to hear your voice, please don't be shy.

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Speaker 1: Write to me two questions at Danielandjorge dot com.

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Speaker 2: So think about it for a second. What do you

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Speaker 2: think is the best way to measure the expansion of

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Speaker 2: the universe. Here's what people had to say.

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Speaker 3: What we do is we analyze the red shift of

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Speaker 3: a particularly distinct galaxy and we compare it from the

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Speaker 3: previous data. The difference is how we calculate the rate

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Speaker 3: of expansion.

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Speaker 4: It's gotta be something I do with redshift. I see

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Speaker 4: how much something really far away, maybe the farthest thing

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Speaker 4: away we know is redshift, and then check it again

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Speaker 4: in a couple of months, see how far it's gone.

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Speaker 4: You know, carry the ones.

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Speaker 2: I guess you could build a universe's longest measuring tape. Oh,

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Speaker 2: maybe let's pose us. I don't know.

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Speaker 5: As far as I know, the best way to measure

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Speaker 5: the expansion rate of the universe is using a red shift.

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Speaker 1: You know, you look at the.

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Speaker 5: Red shift of galaxies very far away and compare them

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Speaker 5: to the red shift of galaxies that are closer, and

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Speaker 5: it can probably give you the right that way.

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Speaker 2: All right, A lot of people think maybe using some

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Speaker 2: kind of light and red shift of the light seems

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Speaker 2: to be the best way.

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Speaker 1: Mm hmmm. Well, of course there was the cosmic measuring

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Speaker 1: tape answer, and definitely the right approach in the sense that,

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Speaker 1: like what is the best way? We didn't ask what's

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Speaker 1: the best possible way? So in terms of like the

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Speaker 1: most impossible ideas, cosmic measuring tape is definitely the best way.

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Speaker 2: Hmmm. I wonder if that's even possible. Like hmm, Like,

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Speaker 2: is there enough material in the universe to make a

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Speaker 2: universe long measuring tape?

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Speaker 1: You wouldn't even have to make a universe long. Even

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Speaker 1: if we could just measure the distance to other galaxies,

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Speaker 1: that would be very helpful. But you know, galaxies are

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Speaker 1: millions of light years away, sometimes billions, and so that

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Speaker 1: would be a pretty incredible construction job. By the time

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Speaker 1: you finished it, the galaxies would have already moved.

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Speaker 2: Well, I think I know what you're saying. You're saying

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Speaker 2: that maybe to measure the expansion of the universe, we

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Speaker 2: don't actually need to measure the size of the universe.

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Speaker 1: Oh, that's right. The size and the expansion are different.

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Speaker 1: The universe could be infinite when it started, in infinite

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Speaker 1: now and could still be expanding because the expansion is

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Speaker 1: an intrinsic thing. It's a relative thing. Measures the growing

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Speaker 1: distances between things in the universe. And many of the

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Speaker 1: listeners commented about redshift, which is important to all understanding

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Speaker 1: the relative velocity of things, but we also need to

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Speaker 1: know their distances. That's going to turn out to be

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Speaker 1: the bigger challenge. Mm.

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Speaker 2: But it's weird that you don't need to know the

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Speaker 2: size of the universe to know how fast it is expanding, Like,

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Speaker 2: don't you need to know how big it is before

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Speaker 2: you can tell how big it's getting.

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Speaker 1: Well, what we're interested in is sort of the relative expansion.

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Speaker 1: Like if you're inside a blob of raisin bread, you

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Speaker 1: can use the raisins to measure how fast the raisin

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Speaker 1: bread is expanding, even if you don't know if there's

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Speaker 1: a crust to it and if you're near that crust

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Speaker 1: or if the raisin bread goes on forever. Right, you

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Speaker 1: can just measure the sort of local expansion and then

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Speaker 1: speculate that the expansion might be the same everywhere else.

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Speaker 2: Well, that's kind of what I mean, Like, how do

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Speaker 2: you know that your universe is not just expanding around you,

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Speaker 2: but maybe it's shrinking everywhere else, in which case the

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Speaker 2: universe itself as a whole is not expanding.

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Speaker 1: Yeah, you're absolutely right, we don't. All we can do

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Speaker 1: is measure the expansion in the part of the universe

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Speaker 1: that we can see, and then we can wonder what's

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Speaker 1: going on in the parts of the universe that we

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Speaker 1: can't see. It would be really weird if our part

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Speaker 1: of the universe was expanding, and the rest of it

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Speaker 1: was like contracting or doing something else weird and frothing.

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Speaker 1: But that's actually one of the ideas people have to

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Speaker 1: explain the strange results we get when we do try

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Speaker 1: to measure the expansion of the universe.

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Speaker 2: All right, well, let's dig into it, Daniel. What exactly

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Speaker 2: do you mean then, by the expansion of the universe.

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Speaker 1: This is a bit of a counterintuitive idea because people

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Speaker 1: think about the expansion usually relative to something else, Like

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Speaker 1: if you were making raisin bread in your oven, you

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Speaker 1: might measure the expansion relative to some ruler or your

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Speaker 1: oven and hope that, for example, the raisin bread still

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Speaker 1: fits in your oven and you didn't make too big

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Speaker 1: a loaf. In our case, though, because we're inside the universe,

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Speaker 1: there is no outside the universe. There is no ruler

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Speaker 1: outside of it that's not also affected by the universe.

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Speaker 1: All we can do is measure the relative expansion of

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Speaker 1: the universe, meaning how far apart are things. So if

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Speaker 1: we're here and there's another galaxy a million light years away,

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Speaker 1: or we're interested in, is how far apart is that

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Speaker 1: galaxy in a year, or in ten years, or in

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Speaker 1: a thousand.

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Speaker 2: Years, and This is a little bit different from any

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Speaker 2: sort of relative velocity our galaxy might have to a

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Speaker 2: different galaxy, Like our galaxy could be moving away from

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Speaker 2: or closer to the Andromeda galaxy. But that doesn't mean

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Speaker 2: that the universe is getting smaller. It just means that

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Speaker 2: we're both in out of this universe, and we both

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Speaker 2: happen to be moving towards each other exactly.

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Speaker 1: We're talking about an expansion of space itself.

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Speaker 2: I think you're talking about, like, what is the average

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Speaker 2: rate at which everything is moving closer or farther away

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Speaker 2: from us? Because you know, we're all sort of moving

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Speaker 2: inside of this universe, but on average, if things are

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Speaker 2: getting further apart, that kind of means that the universe

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Speaker 2: is expanding, right.

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Speaker 1: Yeah, And there's sort of two ways to think about it.

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Speaker 1: One is to think about space between us and other

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Speaker 1: galaxies expanding, like that the universe is creating more space

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Speaker 1: between us and other galaxies, and it's happening faster and

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Speaker 1: faster every year, So this expansion is accelerating. The weird

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Speaker 1: thing is that in those galaxies you don't feel that acceleration.

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Speaker 1: It's not like there's this force that's pushing on those

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Speaker 1: galaxies and accelerating them away from us. If you had

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Speaker 1: like an accelerometer in that galaxy, you wouldn't measure any acceleration.

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Speaker 1: And yet you see the velocities between these galaxies increasing

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Speaker 1: every year, So like the distances are increasing and the

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Speaker 1: velocities are increasing, but we don't measure any acceleration because

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Speaker 1: space itself is expanding. It's not like there's some explosion

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Speaker 1: that's pushing us further and further apart, faster and faster

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Speaker 1: every year.

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Speaker 2: But I guess that made me think about, like how

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Speaker 2: do you tell the difference, Like how do you know

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Speaker 2: if space is expanding between the two of you or

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Speaker 2: if you're just moving further and further away from you,

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Speaker 2: faster and faster. Maybe they're repulsed by us and they're

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Speaker 2: trying to get away from us, and they're like, it's

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Speaker 2: not you, it's just the space between us. We're just

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Speaker 2: growing apart.

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Speaker 1: You can think about it in two different ways. One

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Speaker 1: way is to think about space expanding between the different

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Speaker 1: galaxies and say like we have a little frame here

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Speaker 1: and within our galaxy everything makes sense, and they have

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Speaker 1: a little reference frame there and in their galaxy everything

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Speaker 1: makes sense, and between it. Space is expanding, And there's

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Speaker 1: another way to think about it, which is to put

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Speaker 1: the whole universe in a single reference frame and say, look,

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Speaker 1: I'm just going to measure the distance to stuff, and

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Speaker 1: I'm going to measure the distance to stuff later, and

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Speaker 1: I'm going to compare them, and I'm going to call

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Speaker 1: that velocity. And if you do that, you get weird results,

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Speaker 1: like things that are super duper far away seem to

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Speaker 1: be moving away from us faster than the speed of light.

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Speaker 1: And that second view of like thinking about everything in

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Speaker 1: terms of our frame doesn't really work because you can't

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Speaker 1: extend our frame to the entire universe because between us

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Speaker 1: and them, space is doing weird things. It's expanding, which

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Speaker 1: is why you get strange results like things seem to

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Speaker 1: be moving away from you faster than the speed of

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Speaker 1: light if you try to extend our frame all the

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Speaker 1: way to the end of the universe. So there are

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Speaker 1: two ways to think about it, and in some sense

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Speaker 1: they're equivalent. But cosmologists and cosmetologists prefer to think about

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Speaker 1: space expanding because then you get to have like a

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Speaker 1: nice little frame at each galaxy and think about it

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Speaker 1: expanding between frames.

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Speaker 2: What about astrologists, no comment, or comecologists.

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Speaker 1: No comment. But I didn't really answer your other question,

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Speaker 1: which is how can you tell the difference, And you

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Speaker 1: can tell the difference in terms of acceleration, Like acceleration

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Speaker 1: is something you can measure locally, you know, like if

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Speaker 1: you have a box or the ball inside of it,

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Speaker 1: it'll tell you whether you're accelerating because the ball will

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Speaker 1: get like pushed to one side. Like if you're in

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Speaker 1: a spaceship and you have a box or the ball

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Speaker 1: inside of it and the spaceship accelerates right, the ball

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Speaker 1: will roll to one side of the box, and if

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Speaker 1: the spaceship breaks, the ball will roll to the other

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Speaker 1: side of the box. So you can measure your own acceleration.

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Speaker 1: And if you're in that distant galaxy and you have

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Speaker 1: that accelerometer, you won't measure any acceleration, and yet your

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Speaker 1: velocity relative to other galaxies is increasing, So that tells

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Speaker 1: you that it really is the expansion of space itself

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Speaker 1: and not some like force that's pushing these things apart

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Speaker 1: and accelerating them.

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Speaker 2: But would you know, how do you know that that

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Speaker 2: other galaxy is not being accelerated? Like what if everything

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Speaker 2: in our in our local galaxy is being accelerated at

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Speaker 2: the same time.

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Speaker 1: Well, you're right, we haven't measured accelerometers in distant galaxies.

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Speaker 1: We do have accelerometers here, and we can tell that

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Speaker 1: there's no like Grand force pushing us all in some direction.

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Speaker 1: There's no overall acceleration of the Milky Way. And so

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Speaker 1: either we're very very unusual as a galaxy, we're the

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Speaker 1: only one not being accelerated and we're like at the center,

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Speaker 1: or none of those galaxies are being accelerated, and so

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Speaker 1: in general we prefer not to assume that we're at

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Speaker 1: the center of the universe. You can make the same

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Speaker 1: argument for the expansion, right. We look out in every

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Speaker 1: direction and we see things moving away from us. So

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Speaker 1: either we happen to be at the center of all

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Speaker 1: the expansion of the universe and everything is moving away

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Speaker 1: from where we are, or everything is expanding from every

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Speaker 1: point simultaneously, which we think is a simpler explanation and

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Speaker 1: less suspicious because it doesn't put us at the center

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Speaker 1: of the universe.

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Speaker 2: Right right, I guess you don't want to believe that

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Speaker 2: we are that repulsive that the whole universe is just

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Speaker 2: trying to get away from us mean, we need a

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Speaker 2: better cosmetologism.

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Speaker 1: And so we prefer to think about it in terms

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Speaker 1: of space expanding between us and other galaxies, because that's

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Speaker 1: also something that we can measure. We can look at

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Speaker 1: the space between us and other galaxies and we can

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Speaker 1: measure their velocities right now. We can look further and

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Speaker 1: further back in time, and we can see how that

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Speaker 1: velocity changes with time.

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Speaker 2: But it seems like it's all kind of based on

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Speaker 2: the idea or the discover that things are moving away

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Speaker 2: from us faster and faster in time, like things are

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Speaker 2: it seemed to be accelerating away from us, And then

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Speaker 2: you're saying that because there's an acceleration there, we have

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Speaker 2: to assume that space.

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Speaker 1: Is expanding mm hmm exactly.

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Speaker 2: But what if we had non measured an acceleration, could

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Speaker 2: we tell the difference? Like, what if the space was

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Speaker 2: happened to be expanding at a constant rate or a

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Speaker 2: rate that makes the velocity seem constant, would we then

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Speaker 2: know if things were moving away from us or if

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Speaker 2: space was expanding.

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Speaker 1: If there was no acceleration, no dark energy, then essentially

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Speaker 1: everything would be in one big inertial frame. And those

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Speaker 1: two pictures would be equivalent, but because there is acceleration,

442
00:20:37,800 --> 00:20:41,160
Speaker 1: you can't put everything into one big inertial frame, so

443
00:20:41,200 --> 00:20:43,960
Speaker 1: they really would be equivalent pictures if there was no acceleration.

444
00:20:44,040 --> 00:20:47,399
Speaker 1: The acceleration is what means those things really are in

445
00:20:47,440 --> 00:20:48,840
Speaker 1: their own separate frames.

446
00:20:49,160 --> 00:20:51,800
Speaker 2: All right, Well, thank you dark energy, I guess for

447
00:20:51,880 --> 00:20:54,480
Speaker 2: giving us a cluid that space itself is expanding. Otherwise

448
00:20:54,520 --> 00:20:57,240
Speaker 2: we would not know at all that it could expand.

449
00:20:56,880 --> 00:20:59,320
Speaker 1: Maybe yeah, Otherwise there'd be lots of different ways to

450
00:20:59,320 --> 00:21:01,479
Speaker 1: think about it. And you know, we would love to

451
00:21:01,600 --> 00:21:04,639
Speaker 1: measure the expansion in the universe by like trotting out

452
00:21:04,640 --> 00:21:07,200
Speaker 1: a ruler to other galaxies and measuring it and then

453
00:21:07,440 --> 00:21:11,000
Speaker 1: waiting a thousand years and measuring it again. But number one,

454
00:21:11,040 --> 00:21:13,600
Speaker 1: you could never really build that ruler. You'd have to

455
00:21:13,640 --> 00:21:16,760
Speaker 1: like stop the expansion of space as you stretch out

456
00:21:16,800 --> 00:21:19,680
Speaker 1: the ruler, which is like not practical, And of course

457
00:21:19,680 --> 00:21:21,560
Speaker 1: you don't want to wait a thousand years for measurement

458
00:21:21,640 --> 00:21:25,639
Speaker 1: number two. So that sort of measurement of the expansion

459
00:21:25,680 --> 00:21:28,280
Speaker 1: of space and its acceleration is not like a real

460
00:21:28,359 --> 00:21:30,760
Speaker 1: measurement that you could make. It's not something you could

461
00:21:30,800 --> 00:21:33,200
Speaker 1: actually measure, whereas thinking about it from the other point

462
00:21:33,200 --> 00:21:35,760
Speaker 1: of view, and just thinking about how distant galaxies are

463
00:21:35,800 --> 00:21:38,080
Speaker 1: moving away from us and measuring their velocity, and then

464
00:21:38,080 --> 00:21:40,399
Speaker 1: looking further and further back in time, the way you

465
00:21:40,520 --> 00:21:43,640
Speaker 1: like look down the door jam to see how far

466
00:21:43,680 --> 00:21:46,520
Speaker 1: away things were further back in time is the best

467
00:21:46,560 --> 00:21:49,160
Speaker 1: way to measure the expansion history of the universe.

468
00:21:49,560 --> 00:21:52,720
Speaker 2: Hmmm interesting. All right, Well, let's get into how you

469
00:21:52,800 --> 00:21:55,000
Speaker 2: actually make that measurement, how we can confirm that the

470
00:21:55,119 --> 00:21:57,960
Speaker 2: universe is expanding, and what does that mean for the

471
00:21:58,000 --> 00:22:01,399
Speaker 2: future of our cosmos. First, let's take a quick break.

472
00:22:13,920 --> 00:22:16,560
Speaker 2: All right, we're talking about the expansion of the universe

473
00:22:16,640 --> 00:22:19,480
Speaker 2: and how we would measure that. You can't just kind

474
00:22:19,480 --> 00:22:21,639
Speaker 2: of like loop a belt around it. We're a measuring

475
00:22:21,680 --> 00:22:23,919
Speaker 2: tape around it and see how much it's lately.

476
00:22:24,160 --> 00:22:26,920
Speaker 1: If you have the funding for that giant measuring tape,

477
00:22:26,920 --> 00:22:29,440
Speaker 1: I suggest we spend it on other science projects.

478
00:22:30,160 --> 00:22:33,200
Speaker 2: I guess what's tricky is that, like there's no edge

479
00:22:33,240 --> 00:22:36,080
Speaker 2: to the universe, even from our advantage point or any

480
00:22:36,160 --> 00:22:37,880
Speaker 2: vantage points, So you can't just kind of like look

481
00:22:37,880 --> 00:22:40,479
Speaker 2: out in one direction and look at the other direction

482
00:22:40,600 --> 00:22:44,080
Speaker 2: and see how far apart the edges of the universe

483
00:22:44,119 --> 00:22:45,880
Speaker 2: are right, we have to kind of go by what's

484
00:22:45,880 --> 00:22:46,920
Speaker 2: inside of the universe.

485
00:22:47,080 --> 00:22:48,879
Speaker 1: Exactly what we have to do since there isn't like

486
00:22:48,920 --> 00:22:50,919
Speaker 1: a ruler laid out for us, is we have to

487
00:22:51,000 --> 00:22:53,480
Speaker 1: find rulers. We have to like find things in the

488
00:22:53,560 --> 00:22:55,880
Speaker 1: universe where we think we know how big they were

489
00:22:56,000 --> 00:22:58,280
Speaker 1: a long time ago and see how big they are now.

490
00:22:58,880 --> 00:23:00,920
Speaker 1: Or we have to do things where we figure out

491
00:23:00,920 --> 00:23:03,439
Speaker 1: how far away things are and how fast they're moving,

492
00:23:03,800 --> 00:23:06,760
Speaker 1: which lets us sort of make a picture backwards in

493
00:23:06,840 --> 00:23:09,560
Speaker 1: time of how fast things have been moving away from

494
00:23:09,680 --> 00:23:13,239
Speaker 1: us as time spools back to the very beginning. And

495
00:23:13,280 --> 00:23:16,040
Speaker 1: so those are the basic ideas is to try to

496
00:23:16,119 --> 00:23:19,280
Speaker 1: put down some measuring points where we can look back

497
00:23:19,320 --> 00:23:21,040
Speaker 1: in time and see how things have changed.

498
00:23:21,200 --> 00:23:22,600
Speaker 2: But I think the main point you were trying to

499
00:23:22,600 --> 00:23:24,959
Speaker 2: make before is that it doesn't make sense to measure

500
00:23:25,440 --> 00:23:28,520
Speaker 2: like distances or how those distances are changing between us

501
00:23:28,560 --> 00:23:30,760
Speaker 2: and other galaxies. It makes more sentis to look at

502
00:23:30,760 --> 00:23:34,680
Speaker 2: their velocititers right, because space itself it's expanding. So if

503
00:23:34,680 --> 00:23:37,200
Speaker 2: you sort of try to measure the space between us,

504
00:23:37,200 --> 00:23:39,919
Speaker 2: you're going to run into trouble because that space is changing.

505
00:23:40,040 --> 00:23:42,320
Speaker 1: That space is changing but we do want to know

506
00:23:42,400 --> 00:23:44,480
Speaker 1: the distances to things, and that actually turns out to

507
00:23:44,480 --> 00:23:46,720
Speaker 1: be the crucial thing we're trying to measure, because the

508
00:23:46,760 --> 00:23:50,240
Speaker 1: distance also tells us the time. Right, things that are

509
00:23:50,240 --> 00:23:52,760
Speaker 1: really far away, we're getting information from them from a

510
00:23:52,760 --> 00:23:55,439
Speaker 1: long time ago. A galaxy that sent us light a

511
00:23:55,480 --> 00:23:57,959
Speaker 1: billion years ago and that is just now arriving on

512
00:23:58,040 --> 00:24:01,360
Speaker 1: Earth is telling us about it's a lifevelocity a billion

513
00:24:01,440 --> 00:24:04,000
Speaker 1: years ago. And we're curious about how that velocity varies

514
00:24:04,040 --> 00:24:06,520
Speaker 1: with distance now in the universe, and also how that

515
00:24:06,600 --> 00:24:09,639
Speaker 1: velocity varies with distance as we go backwards in time

516
00:24:09,680 --> 00:24:13,399
Speaker 1: in the universe, Like are the expansion velocities changing? Are

517
00:24:13,440 --> 00:24:15,920
Speaker 1: they getting faster? Are they getting slower? These are the

518
00:24:16,000 --> 00:24:18,000
Speaker 1: kind of measurements we want to make, and so knowing

519
00:24:18,040 --> 00:24:21,119
Speaker 1: that distance is crucial also to understanding the time and

520
00:24:21,280 --> 00:24:24,280
Speaker 1: history when that measurement left that object.

521
00:24:24,359 --> 00:24:26,720
Speaker 2: All right, well, let's dig into it, Daniel. What are

522
00:24:26,720 --> 00:24:28,680
Speaker 2: some of the ways that we can measure the expansion

523
00:24:28,720 --> 00:24:29,280
Speaker 2: of the universe.

524
00:24:29,320 --> 00:24:30,960
Speaker 1: In the end, we want to look out of the universe,

525
00:24:31,080 --> 00:24:34,240
Speaker 1: find a bunch of objects and know their relative velocity

526
00:24:34,600 --> 00:24:37,679
Speaker 1: and their distance. Right, we know their relative velocity, we

527
00:24:37,720 --> 00:24:39,720
Speaker 1: can tell how fast they're moving away from us. That's

528
00:24:39,760 --> 00:24:42,280
Speaker 1: just what the velocity is. And if we know their distance,

529
00:24:42,320 --> 00:24:44,919
Speaker 1: we can tell when that light left them, so we

530
00:24:44,960 --> 00:24:47,240
Speaker 1: can put it in the right spot in history. And

531
00:24:47,320 --> 00:24:49,199
Speaker 1: so those are two things we want to know when

532
00:24:49,240 --> 00:24:51,280
Speaker 1: to look at the sky, point to the galaxy and

533
00:24:51,320 --> 00:24:53,960
Speaker 1: say how far away is that and how fast is

534
00:24:54,000 --> 00:24:56,480
Speaker 1: it moving away from us? Turns out one of those

535
00:24:56,520 --> 00:24:58,600
Speaker 1: things is pretty easy and the other one is very

536
00:24:58,720 --> 00:25:03,520
Speaker 1: very hard. So measuring the velocity is pretty easy because

537
00:25:03,560 --> 00:25:06,880
Speaker 1: galaxies shine at us, and that light we look at

538
00:25:06,960 --> 00:25:09,800
Speaker 1: has a certain spectrum, meaning the colors of that light

539
00:25:09,840 --> 00:25:12,200
Speaker 1: are things we understand. It's like a lot of green

540
00:25:12,280 --> 00:25:15,000
Speaker 1: light or less blue light or more red light. If

541
00:25:15,040 --> 00:25:18,200
Speaker 1: you plot like the intensity of different colors, you get

542
00:25:18,240 --> 00:25:20,720
Speaker 1: like a certain wiggle. We call that the spectrum. But

543
00:25:20,800 --> 00:25:24,199
Speaker 1: that spectrum is shifted based on the velocity. So if

544
00:25:24,200 --> 00:25:26,879
Speaker 1: the galaxy is moving away from us really fast, then

545
00:25:26,920 --> 00:25:29,119
Speaker 1: the wavelength of the light that comes towards us is

546
00:25:29,200 --> 00:25:33,800
Speaker 1: stretched out, it's shifted towards longer wavelength, it's red shifted.

547
00:25:33,920 --> 00:25:35,680
Speaker 1: And because we have a pretty good idea what the

548
00:25:35,720 --> 00:25:38,320
Speaker 1: spectrum looked like when it left the galaxy, because it

549
00:25:38,400 --> 00:25:41,320
Speaker 1: just comes from like basic physics of atomic emission spectru

550
00:25:41,480 --> 00:25:43,920
Speaker 1: we can tell how much it's been shifted, So the

551
00:25:44,000 --> 00:25:47,200
Speaker 1: velocities are pretty easy to measure just using red shifts.

552
00:25:47,400 --> 00:25:51,080
Speaker 2: Because I guess you're assuming that all the lighte from

553
00:25:51,119 --> 00:25:54,400
Speaker 2: every galaxy should basically look sort of the same when

554
00:25:54,440 --> 00:25:57,240
Speaker 2: it leaves the galaxy, right, Like, you're assuming that other

555
00:25:57,280 --> 00:25:59,320
Speaker 2: galaxies are made of the same kinds of stars that

556
00:25:59,400 --> 00:26:02,120
Speaker 2: we are, with the same materials, And so when light

557
00:26:02,680 --> 00:26:05,920
Speaker 2: in general leaves a galaxy, basically all galaxies look the same,

558
00:26:06,000 --> 00:26:06,879
Speaker 2: is what you're saying.

559
00:26:06,720 --> 00:26:09,760
Speaker 1: Almost like, not exactly that all galaxies look the same,

560
00:26:09,760 --> 00:26:11,800
Speaker 1: but that all galaxies are made of the same kinds

561
00:26:11,840 --> 00:26:14,679
Speaker 1: of stuff, and we know how that stuff shines. We

562
00:26:14,760 --> 00:26:17,159
Speaker 1: know how hydrogen shines, and we think it shines the

563
00:26:17,160 --> 00:26:20,679
Speaker 1: same way in Andromeda as it does in other galaxies,

564
00:26:20,920 --> 00:26:24,520
Speaker 1: And we know how oxygen shines, and nitrogen and carbon shines.

565
00:26:24,560 --> 00:26:27,359
Speaker 1: Different galaxies have different mixtures of those kinds of things,

566
00:26:27,440 --> 00:26:29,159
Speaker 1: but they all shine the same way. So when you

567
00:26:29,200 --> 00:26:31,359
Speaker 1: look at the spectrum of a galaxy, you can measure

568
00:26:31,760 --> 00:26:34,280
Speaker 1: what's in that galaxy. Oh look there's water there. Oh

569
00:26:34,320 --> 00:26:37,000
Speaker 1: look there's nitrogen there. And because each of these things

570
00:26:37,040 --> 00:26:39,280
Speaker 1: shines differently. You can break it apart and say, oh, look,

571
00:26:39,280 --> 00:26:41,000
Speaker 1: that galaxy is a lot of water. This one has

572
00:26:41,040 --> 00:26:43,200
Speaker 1: a lot of nitrogen, and you can tell how much

573
00:26:43,240 --> 00:26:46,399
Speaker 1: they're shifted. So there's an incredible amount of information just

574
00:26:46,640 --> 00:26:49,879
Speaker 1: in the spectrum of light from these galaxies. You can

575
00:26:49,920 --> 00:26:52,080
Speaker 1: tell the components they're made out of and how much

576
00:26:52,119 --> 00:26:53,040
Speaker 1: they're all shifted.

577
00:26:53,280 --> 00:26:56,719
Speaker 2: I think technically, like oxygen doesn't glow, does it, It

578
00:26:56,800 --> 00:26:57,400
Speaker 2: blocks light.

579
00:26:57,720 --> 00:26:59,560
Speaker 1: So there's a couple of nuances there. Some of these

580
00:26:59,560 --> 00:27:02,720
Speaker 1: things low and some of these things absorb light. In

581
00:27:02,760 --> 00:27:06,080
Speaker 1: both cases, there are characteristic lines to it. If it's glowing,

582
00:27:06,160 --> 00:27:09,240
Speaker 1: it's giving off light at a certain frequency. If it's

583
00:27:09,280 --> 00:27:13,040
Speaker 1: absorbing light, then it's subtracting that frequency from the spectrum.

584
00:27:13,320 --> 00:27:15,440
Speaker 1: So you're looking for like dips in the spectrum and

585
00:27:15,600 --> 00:27:19,119
Speaker 1: also peaks in the spectrum. All those things astronomers can

586
00:27:19,200 --> 00:27:22,639
Speaker 1: use to figure out what's in that galaxy, And based

587
00:27:22,680 --> 00:27:24,679
Speaker 1: on the location of those lines, you can tell how

588
00:27:24,760 --> 00:27:27,480
Speaker 1: much they're shifted because of the velocity of the galaxy.

589
00:27:27,640 --> 00:27:30,080
Speaker 1: So yeah, there's emission and absorption going on.

590
00:27:30,359 --> 00:27:33,160
Speaker 2: So we get these wiggles of the light from other galaxies,

591
00:27:33,359 --> 00:27:36,840
Speaker 2: and it has like certain markers stories. I think that's

592
00:27:36,840 --> 00:27:38,880
Speaker 2: what you're saying. Like, if you get a wiggle from

593
00:27:38,880 --> 00:27:41,240
Speaker 2: a galaxy, there's a certain like a little spike or

594
00:27:41,280 --> 00:27:44,240
Speaker 2: a little dip or oxygen usually is, for example, and

595
00:27:44,280 --> 00:27:46,920
Speaker 2: you can tell if that's in the same spot as

596
00:27:47,000 --> 00:27:50,520
Speaker 2: the oxygen wiggle from our galaxy, then it's like not

597
00:27:50,640 --> 00:27:53,160
Speaker 2: moving relative to us at all. But if it is shifted,

598
00:27:53,200 --> 00:27:56,000
Speaker 2: then it's moving at a certain velocity away or towards us.

599
00:27:55,920 --> 00:27:58,159
Speaker 1: Right exactly, the more light you can gather from that

600
00:27:58,200 --> 00:28:01,080
Speaker 1: galaxy and the broader the spectrum, like a better handle.

601
00:28:01,320 --> 00:28:04,280
Speaker 1: You see more examples of this. This is why, for example,

602
00:28:04,480 --> 00:28:07,520
Speaker 1: recent images from the James Web Space Telescope of very

603
00:28:07,600 --> 00:28:10,880
Speaker 1: very distant galaxies have a lot of uncertainty in their

604
00:28:11,000 --> 00:28:13,480
Speaker 1: recession velocity because they haven't measured a whole lot of

605
00:28:13,560 --> 00:28:15,960
Speaker 1: light yet, and they don't have a very long curve.

606
00:28:16,000 --> 00:28:18,080
Speaker 1: They only have seen a part of the spectrum. If

607
00:28:18,119 --> 00:28:19,639
Speaker 1: they point hubble at it and they get like a

608
00:28:19,680 --> 00:28:22,520
Speaker 1: longer spectrum and more light, they'll get a better measurement

609
00:28:22,600 --> 00:28:23,879
Speaker 1: of that recession velocity.

610
00:28:24,080 --> 00:28:24,240
Speaker 4: Right.

611
00:28:24,280 --> 00:28:27,040
Speaker 2: And so this method tells you the relative velocity of

612
00:28:27,080 --> 00:28:29,879
Speaker 2: those stars and those galaxies, but that doesn't tell you

613
00:28:30,040 --> 00:28:31,879
Speaker 2: like where it is or how far away it is

614
00:28:31,920 --> 00:28:34,320
Speaker 2: from you. Right, Like, if I measure something with a

615
00:28:34,359 --> 00:28:36,960
Speaker 2: certain redshift that's piving away from me, that could be

616
00:28:37,040 --> 00:28:38,720
Speaker 2: like right next door to us, or it could be

617
00:28:38,800 --> 00:28:41,040
Speaker 2: a bazillion light years away, right exactly.

618
00:28:41,040 --> 00:28:45,360
Speaker 1: And we're interested in this relationship between distance and velocity

619
00:28:45,640 --> 00:28:48,480
Speaker 1: and how that relationship is changing over time. So we

620
00:28:48,600 --> 00:28:51,400
Speaker 1: really need to know the distance to these objects. And

621
00:28:51,440 --> 00:28:54,440
Speaker 1: that's hard because in general, if you don't know how

622
00:28:54,480 --> 00:28:58,040
Speaker 1: bright something actually is, you can't tell the difference between

623
00:28:58,040 --> 00:29:01,000
Speaker 1: it being like kind of dim and close by or

624
00:29:01,040 --> 00:29:03,880
Speaker 1: really really far away and super dup or bright. Those

625
00:29:03,880 --> 00:29:06,160
Speaker 1: two things look the same if you don't know how

626
00:29:06,200 --> 00:29:09,479
Speaker 1: bright it is originally, like what the true brightness is

627
00:29:09,960 --> 00:29:13,480
Speaker 1: of these objects, And so measuring the distances is much

628
00:29:13,520 --> 00:29:15,440
Speaker 1: more challenging, and that's what people have been doing a

629
00:29:15,440 --> 00:29:17,800
Speaker 1: lot of creative work, coming up with really clever.

630
00:29:17,680 --> 00:29:20,080
Speaker 2: Techniques, right because like if you just get a photon

631
00:29:20,160 --> 00:29:22,600
Speaker 2: from a distant galaxy, like you don't know where that

632
00:29:22,600 --> 00:29:26,800
Speaker 2: photon has been basically, right, that photon could have come

633
00:29:26,840 --> 00:29:30,160
Speaker 2: from a star really really really far away or close by,

634
00:29:30,480 --> 00:29:33,080
Speaker 2: Like the intensity of the time doesn't tell you much, right,

635
00:29:33,120 --> 00:29:35,200
Speaker 2: It could be from a dim star that's close by

636
00:29:35,360 --> 00:29:38,400
Speaker 2: or a super bright star that's really far away. Like

637
00:29:38,480 --> 00:29:39,960
Speaker 2: you wouldn't know just from the photon.

638
00:29:40,120 --> 00:29:43,400
Speaker 1: Yeah, well, intensity is the key. An intensity of light

639
00:29:43,720 --> 00:29:45,400
Speaker 1: comes from the number of photons.

640
00:29:45,480 --> 00:29:45,560
Speaker 3: Right.

641
00:29:45,600 --> 00:29:48,120
Speaker 1: A single photon isn't intense or non intense. It just

642
00:29:48,280 --> 00:29:51,440
Speaker 1: is a photon. It's really about a blob of photons,

643
00:29:51,480 --> 00:29:54,440
Speaker 1: a bunch of photons. You got ten photons from this star.

644
00:29:55,080 --> 00:29:57,360
Speaker 1: Is that because it's pretty close by and it's sent

645
00:29:57,360 --> 00:29:59,680
Speaker 1: one hundred and you got ten of them? Or is

646
00:29:59,720 --> 00:30:01,920
Speaker 1: it beca because it's super far away and it made

647
00:30:01,920 --> 00:30:04,040
Speaker 1: a zillion of them and you only got ten of them.

648
00:30:04,120 --> 00:30:07,280
Speaker 1: You can't tell how many went other directions. How diluted

649
00:30:07,680 --> 00:30:10,280
Speaker 1: is this packet of photons? As you get further and

650
00:30:10,320 --> 00:30:12,640
Speaker 1: further away from a star, you get a smaller and

651
00:30:12,680 --> 00:30:16,440
Speaker 1: smaller fraction of its number of photon outputs. The intensity

652
00:30:16,480 --> 00:30:19,160
Speaker 1: of your viewing dims as you get further away. So

653
00:30:19,200 --> 00:30:21,640
Speaker 1: that's the whole ambiguity. You can't tell if you're nearby

654
00:30:21,800 --> 00:30:25,000
Speaker 1: to something pretty dim or really far from something really bright.

655
00:30:25,120 --> 00:30:26,680
Speaker 2: All right, Well, what are some of the ways that

656
00:30:26,720 --> 00:30:29,480
Speaker 2: we can use to measure distance? Out there in a

657
00:30:29,520 --> 00:30:30,240
Speaker 2: big old space.

658
00:30:30,320 --> 00:30:32,960
Speaker 1: The classic way is a distance ladder. We use a

659
00:30:33,000 --> 00:30:35,640
Speaker 1: bunch of different methods to try to like extrapolate from

660
00:30:35,680 --> 00:30:39,120
Speaker 1: here to other galaxies. For very very close by stuff,

661
00:30:39,160 --> 00:30:42,479
Speaker 1: we can actually measure pretty directly how far away it

662
00:30:42,560 --> 00:30:45,480
Speaker 1: is just by seeing how it wiggles in the sky

663
00:30:45,840 --> 00:30:48,440
Speaker 1: as the Earth goes around the Sun, Because as the

664
00:30:48,480 --> 00:30:50,240
Speaker 1: Earth goes around the Sun, we get sort of like

665
00:30:50,280 --> 00:30:53,560
Speaker 1: a different view of a star. If it's pretty close by,

666
00:30:53,800 --> 00:30:55,600
Speaker 1: then we'll sort of see a different side of it.

667
00:30:55,600 --> 00:30:57,800
Speaker 1: It looks like it's in a different part of our sky.

668
00:30:58,280 --> 00:31:01,240
Speaker 1: If it's really really far away, then it won't change,

669
00:31:01,640 --> 00:31:03,760
Speaker 1: just the same way that you can measure the distance

670
00:31:03,920 --> 00:31:06,720
Speaker 1: like a basketball somebody has thrown you, because your two

671
00:31:06,760 --> 00:31:10,280
Speaker 1: eyeballs get different views of it. They see like different

672
00:31:10,280 --> 00:31:12,640
Speaker 1: parts of it, and your brain automatically reconstructs that and

673
00:31:12,680 --> 00:31:15,240
Speaker 1: tells you, oh, that basketball is really far away, or

674
00:31:15,280 --> 00:31:18,720
Speaker 1: the basketball is pretty close by. Or if you hold

675
00:31:18,800 --> 00:31:20,880
Speaker 1: up your finger and look at it with one eye

676
00:31:20,920 --> 00:31:23,440
Speaker 1: and then the other eye, you see that it changes,

677
00:31:23,840 --> 00:31:26,560
Speaker 1: and that change is greater as the finger gets closer

678
00:31:26,600 --> 00:31:29,120
Speaker 1: to your face, and the change is smaller as the

679
00:31:29,120 --> 00:31:31,880
Speaker 1: finger gets further from your face. So that's called parallax.

680
00:31:32,320 --> 00:31:34,600
Speaker 1: We can do that for pretty nearby objects.

681
00:31:34,760 --> 00:31:37,480
Speaker 2: It's also called triangulation in a way, right, because you're

682
00:31:37,520 --> 00:31:40,400
Speaker 2: making a triangle between, for example, and the basketball. You're

683
00:31:40,400 --> 00:31:43,080
Speaker 2: making a triangle between your left eye, your right eye

684
00:31:43,080 --> 00:31:46,440
Speaker 2: and the basketball. And because you form a triangle there

685
00:31:46,440 --> 00:31:48,480
Speaker 2: and you can measure those angles, you can tell how

686
00:31:48,520 --> 00:31:51,400
Speaker 2: far away the basketball is. You can sort of do

687
00:31:51,480 --> 00:31:53,760
Speaker 2: that with like the Earth and one side of the

688
00:31:53,760 --> 00:31:56,040
Speaker 2: Solar system, and the Earth and the other side of

689
00:31:56,040 --> 00:31:58,680
Speaker 2: the Solar system. You kind of form two points of

690
00:31:58,720 --> 00:32:01,600
Speaker 2: a triangle. And then depending on where the star looks

691
00:32:01,640 --> 00:32:04,040
Speaker 2: like it is, you can make the triangle and measure

692
00:32:04,160 --> 00:32:05,440
Speaker 2: its distance exactly.

693
00:32:05,520 --> 00:32:07,600
Speaker 1: And if the star is super duper far away, you

694
00:32:07,640 --> 00:32:10,240
Speaker 1: won't notice any difference, but if the star is pretty

695
00:32:10,240 --> 00:32:12,120
Speaker 1: close by, it has a pretty big effect. This is

696
00:32:12,120 --> 00:32:15,000
Speaker 1: actually a really fun story about how the Greeks got

697
00:32:15,040 --> 00:32:17,520
Speaker 1: it wrong. You know, the Greeks saw that the Earth

698
00:32:17,640 --> 00:32:19,560
Speaker 1: was at the center of the Solar system because they

699
00:32:19,600 --> 00:32:22,240
Speaker 1: figured if the Earth was moving around the Sun, they

700
00:32:22,280 --> 00:32:25,520
Speaker 1: would see this parallax effect. Like there were masters of geometry,

701
00:32:25,680 --> 00:32:28,600
Speaker 1: triangles were not going to escape them. And they figured, look,

702
00:32:28,640 --> 00:32:29,800
Speaker 1: we look up in the night sky, and we don't

703
00:32:29,840 --> 00:32:32,520
Speaker 1: see any stars wiggling. Therefore the Earth is not moving.

704
00:32:32,680 --> 00:32:34,440
Speaker 1: And their mistake was that they thought the stars were

705
00:32:34,480 --> 00:32:36,720
Speaker 1: all pretty close by, so they figured they should all

706
00:32:36,760 --> 00:32:39,000
Speaker 1: be wiggling if we're moving. They didn't realize the stars

707
00:32:39,000 --> 00:32:42,360
Speaker 1: are much much further away than they actually were. And

708
00:32:42,360 --> 00:32:44,840
Speaker 1: that's the thing about parallax. It only works for pretty

709
00:32:44,840 --> 00:32:48,080
Speaker 1: close by stars. Even still, the wiggle is pretty subtle.

710
00:32:48,200 --> 00:32:50,440
Speaker 1: We didn't detect it until like the nineteenth century.

711
00:32:50,640 --> 00:32:53,520
Speaker 2: Yeah, it's also trigger because what if there's a giant

712
00:32:53,560 --> 00:32:56,720
Speaker 2: three D glasses out there space, Then you get fooled

713
00:32:56,760 --> 00:33:00,520
Speaker 2: into thinking at a certain distance always concern.

714
00:33:00,680 --> 00:33:02,600
Speaker 1: So that's the sort of like most direct way we

715
00:33:02,600 --> 00:33:05,239
Speaker 1: can measure the distance to pretty nearby stuff. And then

716
00:33:05,240 --> 00:33:08,120
Speaker 1: about one hundred years ago, Henrietta Levitt figured out a

717
00:33:08,120 --> 00:33:11,080
Speaker 1: way to measure the distances to other kinds of things.

718
00:33:11,280 --> 00:33:14,520
Speaker 1: That there's special kind of stars called cephids. Cephids are

719
00:33:14,600 --> 00:33:18,920
Speaker 1: stars that do something really cool. They vary in their brightness,

720
00:33:18,960 --> 00:33:21,480
Speaker 1: like they get brighter and dimmer, brighter and.

721
00:33:21,400 --> 00:33:24,040
Speaker 2: Dimmer because of something that's going on in the stars right,

722
00:33:24,080 --> 00:33:26,920
Speaker 2: Like there's some process that seems to happen not just

723
00:33:26,960 --> 00:33:29,400
Speaker 2: in one star, but in a certain kind of star.

724
00:33:29,640 --> 00:33:32,840
Speaker 1: Exactly. It has to do with the internal like dynamics

725
00:33:32,880 --> 00:33:36,160
Speaker 1: of the star. They get opaque and then they absorb

726
00:33:36,240 --> 00:33:38,480
Speaker 1: their own radiation which puffs them out and they get

727
00:33:38,520 --> 00:33:40,760
Speaker 1: dim and then they collapse and they get brighter again,

728
00:33:40,880 --> 00:33:43,840
Speaker 1: and then they absorb that radiation. So there's this cycle

729
00:33:43,880 --> 00:33:46,520
Speaker 1: that goes on. And the really interesting thing is that

730
00:33:46,560 --> 00:33:49,960
Speaker 1: there's a close connection between how long that cycle takes

731
00:33:50,000 --> 00:33:52,440
Speaker 1: to happen between like the bright and the dim moments,

732
00:33:52,680 --> 00:33:55,320
Speaker 1: and how bright it is at its origin. So if

733
00:33:55,320 --> 00:33:57,479
Speaker 1: you measure the period, if you measure how long it

734
00:33:57,520 --> 00:34:00,640
Speaker 1: is between like peaks of brightness, then you know how

735
00:34:00,680 --> 00:34:04,480
Speaker 1: bright it actually is, which means you can tell how

736
00:34:04,560 --> 00:34:06,720
Speaker 1: far away it is because you measure how bright we

737
00:34:06,800 --> 00:34:08,759
Speaker 1: see it, and you know how bright it is if

738
00:34:08,800 --> 00:34:11,400
Speaker 1: you were really close by, and you can extrapolate.

739
00:34:11,560 --> 00:34:13,879
Speaker 2: But I guess we had to know how far away

740
00:34:13,920 --> 00:34:17,520
Speaker 2: they were before to make that connection right exactly.

741
00:34:17,560 --> 00:34:20,320
Speaker 1: So to calibrate this, to make sure this really works,

742
00:34:20,680 --> 00:34:24,920
Speaker 1: you need some sephids whose distance you can measure using parallax.

743
00:34:25,440 --> 00:34:27,880
Speaker 1: So there's a few stars where it overlaps. There are a

744
00:34:27,880 --> 00:34:30,040
Speaker 1: few sephids that are close enough where we can measure

745
00:34:30,040 --> 00:34:33,160
Speaker 1: their distance using parallax, and we can measure their distance

746
00:34:33,280 --> 00:34:36,280
Speaker 1: using their period, and we see that the two things agree.

747
00:34:36,520 --> 00:34:38,440
Speaker 1: So that's why it's called the distance ladder because we

748
00:34:38,480 --> 00:34:40,680
Speaker 1: have like a little bit of overlap. And then we

749
00:34:40,760 --> 00:34:44,120
Speaker 1: assume the sephids and like other galaxies, operate the same way,

750
00:34:44,280 --> 00:34:46,359
Speaker 1: and that way we can measure the distance to other

751
00:34:46,440 --> 00:34:48,400
Speaker 1: galaxies where parallax doesn't work.

752
00:34:49,040 --> 00:34:51,040
Speaker 2: So it's thanks to these sephods that we have a

753
00:34:51,080 --> 00:34:53,920
Speaker 2: better view of how far things are, right, because it

754
00:34:54,080 --> 00:34:56,520
Speaker 2: just so happens that because of the mechanics as the star,

755
00:34:56,800 --> 00:34:59,400
Speaker 2: those two things are related the period of their blinking

756
00:34:59,560 --> 00:35:01,920
Speaker 2: and kind of like their size or how bright they

757
00:35:02,000 --> 00:35:03,200
Speaker 2: are exactly.

758
00:35:03,360 --> 00:35:05,839
Speaker 1: But you know, it's a big extrapolation, right. We are

759
00:35:05,840 --> 00:35:08,160
Speaker 1: talking about like things we measure in our galaxy and

760
00:35:08,280 --> 00:35:11,279
Speaker 1: we're extrapolating to distant galaxies and we're assuming that we

761
00:35:11,360 --> 00:35:14,280
Speaker 1: understand how this works. But we're relying on those stars

762
00:35:14,560 --> 00:35:16,640
Speaker 1: where we can check it, those sephids where we can

763
00:35:16,719 --> 00:35:19,120
Speaker 1: have parallax measurements, and there's not a lot of them.

764
00:35:19,400 --> 00:35:23,120
Speaker 1: There's like ten or twelve, right, So this whole distance

765
00:35:23,200 --> 00:35:26,560
Speaker 1: ladder is calibrated on like a handful of stars in

766
00:35:26,600 --> 00:35:27,920
Speaker 1: the overlap region, and we.

767
00:35:27,920 --> 00:35:31,040
Speaker 2: Have pretty good measurements of that parallax where we're confident

768
00:35:31,040 --> 00:35:32,600
Speaker 2: we know where they are. But I guess maybe you're

769
00:35:32,640 --> 00:35:36,520
Speaker 2: not confident that ten sephids really represents all sephords in

770
00:35:36,520 --> 00:35:37,080
Speaker 2: the universe.

771
00:35:37,280 --> 00:35:40,040
Speaker 1: Yeah, there's a lot of uncertainties there, like the uncertainties

772
00:35:40,040 --> 00:35:43,560
Speaker 1: on the parallax for those sephids, and are those typical

773
00:35:43,960 --> 00:35:46,040
Speaker 1: and is there some uncertainty due to like how much

774
00:35:46,080 --> 00:35:48,840
Speaker 1: metallicity there are in these sephids. There's a lot of

775
00:35:48,840 --> 00:35:51,000
Speaker 1: work going on to try to like nail that down

776
00:35:51,040 --> 00:35:53,760
Speaker 1: more precisely. And then there's another step in the distance

777
00:35:53,800 --> 00:35:57,080
Speaker 1: ladder because cephids are great and they're in distant galaxies,

778
00:35:57,120 --> 00:35:59,319
Speaker 1: but they're not that bright, so for like really far

779
00:35:59,400 --> 00:36:02,400
Speaker 1: away galaxy you can't see them. And then about twenty

780
00:36:02,480 --> 00:36:05,560
Speaker 1: years ago people found another element to add to the

781
00:36:05,560 --> 00:36:09,279
Speaker 1: distance ladder, which were type one, a supernova sort of

782
00:36:09,320 --> 00:36:12,759
Speaker 1: like cephe's. You can tell how bright they are in reality,

783
00:36:12,800 --> 00:36:15,120
Speaker 1: like if you were close by by looking at how

784
00:36:15,200 --> 00:36:18,560
Speaker 1: their brightness fades. So these are stars that are very

785
00:36:18,680 --> 00:36:21,040
Speaker 1: very bright because it's a supernova it's like as bright

786
00:36:21,040 --> 00:36:24,480
Speaker 1: as the galaxy that contains it, very very briefly, and

787
00:36:24,480 --> 00:36:26,879
Speaker 1: then it fades away, and by looking at the rate

788
00:36:26,920 --> 00:36:29,600
Speaker 1: of which it declines, you can calculate how bright it

789
00:36:29,680 --> 00:36:30,520
Speaker 1: is in reality.

790
00:36:31,360 --> 00:36:33,200
Speaker 2: I guess you're assuming that you know the laws of

791
00:36:33,239 --> 00:36:35,919
Speaker 2: physics are the same here as they are in other

792
00:36:36,000 --> 00:36:38,480
Speaker 2: parts of the universe and other galaxies, and so you're

793
00:36:38,480 --> 00:36:40,880
Speaker 2: saying that when a star goes super nova with this

794
00:36:41,000 --> 00:36:44,759
Speaker 2: type one A, it usually happens the same way, and

795
00:36:44,880 --> 00:36:47,000
Speaker 2: it happens in a way that tells you like, oh,

796
00:36:47,000 --> 00:36:50,200
Speaker 2: if it's decaying, if it's the brightness of that flashes

797
00:36:50,760 --> 00:36:53,640
Speaker 2: slower or faster, it tells you like how explosive that

798
00:36:53,719 --> 00:36:54,520
Speaker 2: supernova was.

799
00:36:54,800 --> 00:36:57,399
Speaker 1: Exactly All these techniques have the same basic strategy, which

800
00:36:57,480 --> 00:37:01,640
Speaker 1: is find some other way to predict how bright it

801
00:37:01,719 --> 00:37:04,320
Speaker 1: is at the source, assuming that the physics is happening

802
00:37:04,400 --> 00:37:07,080
Speaker 1: the same way there and here, And if you can

803
00:37:07,120 --> 00:37:09,200
Speaker 1: do that, you can predict how bright it actually is,

804
00:37:09,239 --> 00:37:11,000
Speaker 1: and you can compare it to how bright you see

805
00:37:11,000 --> 00:37:13,319
Speaker 1: it to be, then you can tell how far away

806
00:37:13,320 --> 00:37:15,359
Speaker 1: it is. And people knew this for a long time.

807
00:37:15,360 --> 00:37:18,000
Speaker 1: People understood type one A supernova might be a good

808
00:37:18,000 --> 00:37:21,120
Speaker 1: technique for this, but again we didn't have enough overlap.

809
00:37:21,200 --> 00:37:23,680
Speaker 1: It wasn't until Hubble launched and we got a bunch

810
00:37:23,680 --> 00:37:26,640
Speaker 1: of like far away sephids that we could calibrate these

811
00:37:26,680 --> 00:37:29,279
Speaker 1: Type one A supernova. So now we have again just

812
00:37:29,320 --> 00:37:32,760
Speaker 1: a handful of galaxies that have both sephids and Type

813
00:37:32,760 --> 00:37:35,600
Speaker 1: one A supernova in them where we can cross calibrate

814
00:37:35,640 --> 00:37:38,120
Speaker 1: and add like another plank to our distance ladder.

815
00:37:38,640 --> 00:37:40,279
Speaker 2: I feel like it's not so much a ladder that

816
00:37:40,360 --> 00:37:44,279
Speaker 2: you're building, but like it's a stack of stools, you

817
00:37:44,280 --> 00:37:46,240
Speaker 2: know what I mean. Like you start with a short

818
00:37:46,560 --> 00:37:50,640
Speaker 2: stool or stepping stool, and then you're not attaching another step.

819
00:37:50,760 --> 00:37:53,640
Speaker 2: It's like you're just putting another stepping stool on top

820
00:37:53,640 --> 00:37:56,239
Speaker 2: of your first stepping stool, and the whole thing is

821
00:37:56,320 --> 00:37:56,880
Speaker 2: kind of shaky.

822
00:37:57,000 --> 00:37:59,680
Speaker 1: The whole thing is pretty shaky, yeah, exactly. And this

823
00:38:00,040 --> 00:38:02,759
Speaker 1: lot of uncertainty and how these things overlap, because there's

824
00:38:02,800 --> 00:38:05,000
Speaker 1: not a lot of data where we have things on

825
00:38:05,080 --> 00:38:09,000
Speaker 1: both kinds of stools, right, And another big uncertainty is dust,

826
00:38:09,680 --> 00:38:11,839
Speaker 1: Like there are other ways things can get dim. It's

827
00:38:11,920 --> 00:38:14,640
Speaker 1: not just being far away. There's a big dust cloud

828
00:38:14,680 --> 00:38:17,880
Speaker 1: between us and one of these galaxies that'll make it

829
00:38:17,920 --> 00:38:21,040
Speaker 1: look dimmer, which would make it look further away. So

830
00:38:21,120 --> 00:38:23,920
Speaker 1: unless you know exactly where dust is in the universe,

831
00:38:23,920 --> 00:38:25,719
Speaker 1: that really complicates these measurements.

832
00:38:25,960 --> 00:38:28,759
Speaker 2: M interesting. All right, Well, let's get into other ways

833
00:38:28,760 --> 00:38:31,160
Speaker 2: that we can measure distances out there, and let's see

834
00:38:31,239 --> 00:38:34,640
Speaker 2: how shaky this ladder of stepping stools can get and

835
00:38:34,640 --> 00:38:37,320
Speaker 2: what that tells us about the expansion of the universe.

836
00:38:37,760 --> 00:38:52,680
Speaker 2: But first, let's take another quick work. All right, we're

837
00:38:52,719 --> 00:38:55,040
Speaker 2: talking about the expansion of the universe and how you

838
00:38:55,040 --> 00:38:59,160
Speaker 2: would actually measure how fast the universe is expanding, Because

839
00:38:59,280 --> 00:39:02,560
Speaker 2: I guess we're people, Daniel, we want to know if

840
00:39:02,560 --> 00:39:06,160
Speaker 2: the universe is getting bigger or smaller.

841
00:39:06,280 --> 00:39:09,080
Speaker 1: We definitely want to understand because it affects the fate

842
00:39:09,120 --> 00:39:11,480
Speaker 1: of everything. You know, is the universe going to collapse

843
00:39:11,520 --> 00:39:13,560
Speaker 1: into a big crunch and squish us all? Is it

844
00:39:13,600 --> 00:39:15,279
Speaker 1: going to tear us all apart? Is it going to

845
00:39:15,560 --> 00:39:18,480
Speaker 1: leave us as isolated islands to collapse into our own

846
00:39:18,480 --> 00:39:20,719
Speaker 1: individual black holes? Like it matters?

847
00:39:20,920 --> 00:39:23,399
Speaker 2: Plus we're curious, Well, it doesn't matter to us because

848
00:39:23,400 --> 00:39:25,799
Speaker 2: you're talking about things that would happen billions of years

849
00:39:25,800 --> 00:39:27,719
Speaker 2: from now. But you know, our great great great great

850
00:39:27,760 --> 00:39:31,400
Speaker 2: great great great great grandkids might need to think about

851
00:39:31,440 --> 00:39:34,000
Speaker 2: their retirement plans.

852
00:39:34,880 --> 00:39:37,719
Speaker 1: And I care about my super super great grandkids. You know,

853
00:39:37,760 --> 00:39:39,880
Speaker 1: in fact, there's almost certainly going to be some kid

854
00:39:40,080 --> 00:39:41,799
Speaker 1: deep in the future who's going to have both me

855
00:39:42,040 --> 00:39:43,520
Speaker 1: and you as an ancestor.

856
00:39:43,760 --> 00:39:47,920
Speaker 2: Oh boy, hopefully I'll be the its favorite ancestors, or

857
00:39:47,920 --> 00:39:48,960
Speaker 2: at least a taller one.

858
00:39:49,560 --> 00:39:51,360
Speaker 1: Well, if it listens to the podcast to learn that

859
00:39:51,400 --> 00:39:53,640
Speaker 1: you don't really care about their future, but I do.

860
00:39:53,880 --> 00:39:57,160
Speaker 2: I didn't say that, I say it wasn't my problem,

861
00:39:57,200 --> 00:40:00,799
Speaker 2: but that I mean I don't care about their problem.

862
00:40:01,280 --> 00:40:04,440
Speaker 1: Well, great great great grandkid, your problems are my problems,

863
00:40:04,520 --> 00:40:04,799
Speaker 1: all right.

864
00:40:04,840 --> 00:40:07,520
Speaker 2: Well, we're talking about different ways to measure distances out

865
00:40:07,560 --> 00:40:10,440
Speaker 2: there in a big space, with all this uncertainty and

866
00:40:10,520 --> 00:40:15,160
Speaker 2: all this dust in the universe and these unfathomable distances.

867
00:40:15,320 --> 00:40:20,000
Speaker 2: So far, we've been using three D glasses, certain kinds

868
00:40:20,000 --> 00:40:23,399
Speaker 2: of stars called sephids, and type A supernova's. How else

869
00:40:23,400 --> 00:40:24,960
Speaker 2: can we measure distances in space?

870
00:40:25,280 --> 00:40:27,799
Speaker 1: So this is a big cottage industry recently, so people

871
00:40:27,840 --> 00:40:30,200
Speaker 1: have been figuring out lots of different ways to measure it,

872
00:40:30,320 --> 00:40:33,840
Speaker 1: to try to understand whether these measurements are correct or

873
00:40:33,880 --> 00:40:36,200
Speaker 1: not because it tells a different story. So another way

874
00:40:36,200 --> 00:40:38,680
Speaker 1: people have been measuring distances it is not looking at

875
00:40:38,719 --> 00:40:43,000
Speaker 1: supernova but looking at moments when red giant stars get

876
00:40:43,040 --> 00:40:46,000
Speaker 1: really really bright. Red giants are stars near the end

877
00:40:46,000 --> 00:40:48,319
Speaker 1: of their life when they have been burning hydrogen for

878
00:40:48,360 --> 00:40:52,000
Speaker 1: a long time and collecting helium ash at their core,

879
00:40:52,320 --> 00:40:55,040
Speaker 1: but they aren't hot enough to burn that helium yet.

880
00:40:55,239 --> 00:40:57,799
Speaker 1: Then near the end of their life, suddenly they get

881
00:40:57,880 --> 00:41:00,000
Speaker 1: hot and dense enough to burn that helium and all

882
00:41:00,120 --> 00:41:03,239
Speaker 1: happens very very quickly. It's a huge flash of light

883
00:41:03,480 --> 00:41:07,239
Speaker 1: from this helium burning. So these are peaking red giants,

884
00:41:07,760 --> 00:41:09,920
Speaker 1: and when they do that, they're almost always the same

885
00:41:10,040 --> 00:41:13,080
Speaker 1: similar news type one a supernova or similar to sepids.

886
00:41:13,080 --> 00:41:16,120
Speaker 1: You can tell basically how bright they are from other

887
00:41:16,239 --> 00:41:19,239
Speaker 1: characteristics you measure about them, like their spectrum. So these

888
00:41:19,280 --> 00:41:21,960
Speaker 1: are called tip of the red giant branch because astronomers

889
00:41:21,960 --> 00:41:24,120
Speaker 1: think about all these stars on like a big branch

890
00:41:24,160 --> 00:41:28,960
Speaker 1: of luminosity versus size, and so they use these stars

891
00:41:29,000 --> 00:41:32,319
Speaker 1: to measure the distance to those galaxies that contain them.

892
00:41:32,480 --> 00:41:35,520
Speaker 2: Because I guess all red giant stars are basically the same,

893
00:41:35,600 --> 00:41:37,560
Speaker 2: like if you have a red giant, it means you

894
00:41:37,640 --> 00:41:40,520
Speaker 2: they're a certain size, Like there aren't an infinite number

895
00:41:40,520 --> 00:41:42,520
Speaker 2: of kinds of red giants, right.

896
00:41:42,480 --> 00:41:44,360
Speaker 1: Yeah, exactly. They tend to do it in basically the

897
00:41:44,440 --> 00:41:47,080
Speaker 1: same way. These things are a little harder to find,

898
00:41:47,120 --> 00:41:50,719
Speaker 1: so there aren't as many examples, but recently been working

899
00:41:50,760 --> 00:41:53,400
Speaker 1: really hard on this, using it to measure independently the

900
00:41:53,440 --> 00:41:57,280
Speaker 1: expansion rate of the universe. It's also sensitive to dust,

901
00:41:57,640 --> 00:42:00,440
Speaker 1: like the first measurement we talked about, but it's differently

902
00:42:00,480 --> 00:42:04,560
Speaker 1: sensitive to dust because the best red giant candidates are

903
00:42:04,680 --> 00:42:07,799
Speaker 1: old stars that are on like the outskirts of galaxies,

904
00:42:07,840 --> 00:42:10,719
Speaker 1: which tend to be less dusty, and so it's like

905
00:42:10,880 --> 00:42:14,320
Speaker 1: less sensitive to dust. People think in that distant galaxy.

906
00:42:14,440 --> 00:42:17,080
Speaker 2: And you can actually see these in distant galaxies because

907
00:42:17,120 --> 00:42:18,760
Speaker 2: you know, usually when you look at a distant galaxy

908
00:42:18,800 --> 00:42:20,920
Speaker 2: it just looks like a fuzz. You can actually make

909
00:42:20,920 --> 00:42:22,040
Speaker 2: out little pinpoints in them.

910
00:42:22,160 --> 00:42:24,759
Speaker 1: Yeah, you can actually make out these pinpoints because they're

911
00:42:24,800 --> 00:42:27,080
Speaker 1: very bright when it happens, and it's sudden, doesn't last

912
00:42:27,080 --> 00:42:29,759
Speaker 1: for very long. So if you're watching that galaxy, you

913
00:42:29,800 --> 00:42:33,200
Speaker 1: can see a change in the galaxy that sudden peak

914
00:42:33,280 --> 00:42:35,000
Speaker 1: of brightness the same way you can see a type

915
00:42:35,000 --> 00:42:37,680
Speaker 1: one a supernova in that galaxy, or you can see

916
00:42:37,719 --> 00:42:41,280
Speaker 1: cephids in distant galaxies because they have a period.

917
00:42:41,760 --> 00:42:44,439
Speaker 2: I see, but you're still looking at the overall light

918
00:42:44,520 --> 00:42:46,759
Speaker 2: from the galaxy. You're not looking at like, oh, that

919
00:42:46,960 --> 00:42:49,400
Speaker 2: little corner of this galaxy flashed up, that must be

920
00:42:49,440 --> 00:42:51,520
Speaker 2: a red giant. You're looking at the whole thing, right

921
00:42:51,640 --> 00:42:51,880
Speaker 2: or not.

922
00:42:51,960 --> 00:42:53,720
Speaker 1: You're looking at the whole thing. But you can resolve

923
00:42:53,719 --> 00:42:57,359
Speaker 1: these individual red giants. Yeah, not all galaxies are so

924
00:42:57,600 --> 00:43:00,040
Speaker 1: far away that you can't resolve them.

925
00:43:00,000 --> 00:43:01,600
Speaker 2: All right, Well, are some other ways that we can

926
00:43:01,640 --> 00:43:02,320
Speaker 2: measure distance.

927
00:43:02,640 --> 00:43:05,600
Speaker 1: So people are trying to develop waves that are independent

928
00:43:05,640 --> 00:43:08,040
Speaker 1: of this, that are like less sensitive to dust. For example.

929
00:43:08,239 --> 00:43:12,280
Speaker 1: One really cool way is to use gravitational waves. Because

930
00:43:12,280 --> 00:43:15,120
Speaker 1: this doesn't use light at all, right, it just uses

931
00:43:15,160 --> 00:43:19,600
Speaker 1: gravitational waves. And if you watch two neutron stars, for example,

932
00:43:19,680 --> 00:43:22,319
Speaker 1: and you see them spiraling in towards each other so

933
00:43:22,360 --> 00:43:26,200
Speaker 1: that they're going to collide, you get a gravitational wave signature. Remember,

934
00:43:26,200 --> 00:43:29,480
Speaker 1: everything in the universe that accelerates makes waves in its

935
00:43:29,480 --> 00:43:32,680
Speaker 1: gravitational field, and we can measure those on Earth with

936
00:43:32,920 --> 00:43:36,239
Speaker 1: very powerful interferometers and as they spiral in, they go

937
00:43:36,320 --> 00:43:39,040
Speaker 1: faster and faster and faster, so the gravitational wave gets

938
00:43:39,040 --> 00:43:42,759
Speaker 1: faster and faster, and by watching that frequency change, you

939
00:43:42,800 --> 00:43:46,839
Speaker 1: can calculate the mass of those objects. You can tell like, oh,

940
00:43:46,880 --> 00:43:48,680
Speaker 1: this is a neutron star of that mass, or that

941
00:43:48,719 --> 00:43:51,239
Speaker 1: was a black hole of the other mass, And from

942
00:43:51,280 --> 00:43:53,640
Speaker 1: knowing the mass of those things, you can tell how

943
00:43:53,719 --> 00:43:56,640
Speaker 1: big the waves should be. So you watch sort of

944
00:43:56,640 --> 00:43:58,680
Speaker 1: the speed of the wiggles, which tells you how big

945
00:43:58,719 --> 00:44:02,080
Speaker 1: the objects are, which tells you how high the wave

946
00:44:02,120 --> 00:44:04,719
Speaker 1: should go. And then you measure how high the wave

947
00:44:04,800 --> 00:44:07,319
Speaker 1: is that you got, and that tells you how far

948
00:44:07,360 --> 00:44:09,440
Speaker 1: away it is, because, just like with light, as the

949
00:44:09,440 --> 00:44:12,240
Speaker 1: wave gets further and further away, it gets dimmer and dimmer.

950
00:44:12,320 --> 00:44:14,920
Speaker 1: So by measuring the gravitational wave frequency, you can sort

951
00:44:14,960 --> 00:44:17,719
Speaker 1: of predict the intensity of the gravitational wave as it

952
00:44:17,760 --> 00:44:20,560
Speaker 1: was emitted and compared to the intensity you measure here

953
00:44:20,640 --> 00:44:21,080
Speaker 1: on Earth.

954
00:44:21,280 --> 00:44:24,759
Speaker 2: So if we get a gravitational wiggle wave from two

955
00:44:24,880 --> 00:44:27,719
Speaker 2: neutron stars crashing, you're saying that we can tell how

956
00:44:27,800 --> 00:44:30,880
Speaker 2: far away it is because they all always happen kind

957
00:44:30,920 --> 00:44:32,640
Speaker 2: of the same way. But then how do you know

958
00:44:32,719 --> 00:44:35,480
Speaker 2: where it happen, right, because we're just listening to these

959
00:44:35,480 --> 00:44:38,200
Speaker 2: gravitational waves. How do you know where in the universe

960
00:44:38,280 --> 00:44:39,160
Speaker 2: that crash happens.

961
00:44:39,239 --> 00:44:41,320
Speaker 1: We can tell the direction these things come from because

962
00:44:41,320 --> 00:44:44,520
Speaker 1: we have multiple ears. Essentially, we have one in Louisiana,

963
00:44:44,600 --> 00:44:46,920
Speaker 1: one in Washington, and one in Italy. And as the

964
00:44:46,960 --> 00:44:49,440
Speaker 1: wave passes over the Earth, it doesn't arrive at all

965
00:44:49,480 --> 00:44:51,440
Speaker 1: these things at the same moment. So you can use

966
00:44:51,480 --> 00:44:55,200
Speaker 1: that to tell the directionality. But the distance measurement is different.

967
00:44:55,200 --> 00:44:57,600
Speaker 1: The distance measurement comes from the intensity of it, like

968
00:44:57,640 --> 00:45:00,040
Speaker 1: how loud was it? By looking at the free you

969
00:45:00,040 --> 00:45:01,920
Speaker 1: can see the wiggles. You can tell how loud it

970
00:45:02,040 --> 00:45:04,000
Speaker 1: was when it was created, and we can measure the

971
00:45:04,040 --> 00:45:06,200
Speaker 1: loudness as it arrived on Earth, and so we can

972
00:45:06,239 --> 00:45:10,000
Speaker 1: tell how much it's been quieted by its flight through

973
00:45:10,040 --> 00:45:12,160
Speaker 1: the universe. And that tells us the distance.

974
00:45:12,520 --> 00:45:14,920
Speaker 2: It tells us the distance between us and where those

975
00:45:14,960 --> 00:45:17,239
Speaker 2: two neutrons stars crashed. But what does that tell us

976
00:45:17,239 --> 00:45:20,080
Speaker 2: about if anything else. It just tells us that the

977
00:45:20,160 --> 00:45:22,440
Speaker 2: two neutrons stars crashed at a certain distance from us

978
00:45:22,719 --> 00:45:25,520
Speaker 2: in a certain direction. But does that tell you, like

979
00:45:25,880 --> 00:45:29,360
Speaker 2: the velocity or how galaxies around her are moving.

980
00:45:29,719 --> 00:45:31,400
Speaker 1: Well, if you know where it was in space, you

981
00:45:31,440 --> 00:45:34,239
Speaker 1: know which galaxy those neutron stars were in, So you

982
00:45:34,280 --> 00:45:36,320
Speaker 1: can point to that galaxy and say, oh, it was

983
00:45:36,360 --> 00:45:39,240
Speaker 1: in this galaxy, and now we know how far away

984
00:45:39,280 --> 00:45:41,360
Speaker 1: that galaxy is. In the same way that if you

985
00:45:41,360 --> 00:45:43,560
Speaker 1: spot a galaxy and you see a supernova blow up

986
00:45:43,600 --> 00:45:47,680
Speaker 1: in that galaxy, you know how far away that galaxy is. Now,

987
00:45:47,719 --> 00:45:49,720
Speaker 1: if you spot a galaxy and you see two neutron

988
00:45:49,800 --> 00:45:52,520
Speaker 1: stars collide inside that galaxy, you can use that to

989
00:45:52,560 --> 00:45:54,480
Speaker 1: measure the distance to that galaxy.

990
00:45:54,680 --> 00:45:57,719
Speaker 2: Do we know the directionality that with that much accuracy?

991
00:45:57,800 --> 00:46:00,920
Speaker 2: Like is our stereo or hearing of rotational waves that

992
00:46:01,080 --> 00:46:04,000
Speaker 2: accurate to tell like, oh, that wiggle came from that galaxy?

993
00:46:04,040 --> 00:46:06,000
Speaker 2: Because there are so many there's billions of galaxies out

994
00:46:06,040 --> 00:46:06,799
Speaker 2: there in space.

995
00:46:06,640 --> 00:46:08,880
Speaker 1: Right, there are lots of galaxies out there in space,

996
00:46:08,960 --> 00:46:11,960
Speaker 1: and the directionality of this is not great. You're right,

997
00:46:12,080 --> 00:46:14,960
Speaker 1: because we only have three ears and sometimes they're consistent

998
00:46:14,960 --> 00:46:17,520
Speaker 1: with like a few different directions, so there's a lot

999
00:46:17,520 --> 00:46:20,360
Speaker 1: of uncertainty in this measurement. It's one people are excited

1000
00:46:20,360 --> 00:46:23,160
Speaker 1: about because it's very independent from the other measurements, like

1001
00:46:23,320 --> 00:46:26,040
Speaker 1: not affected by dust at all, but it's not one

1002
00:46:26,040 --> 00:46:29,359
Speaker 1: that yet provides a measurement that's competitive at all. It's

1003
00:46:29,400 --> 00:46:31,400
Speaker 1: like has big error bars for all the reasons you

1004
00:46:31,480 --> 00:46:33,719
Speaker 1: lay it out, and also because we just don't hear

1005
00:46:33,800 --> 00:46:37,440
Speaker 1: many gravitational waves compared to other things. So it's something

1006
00:46:37,480 --> 00:46:39,319
Speaker 1: that we think in the future is going to help.

1007
00:46:39,360 --> 00:46:41,680
Speaker 1: It's a cool new technique, but it hasn't yet provided

1008
00:46:41,680 --> 00:46:44,880
Speaker 1: a measurement that compares with the uncertainty of the other measurements.

1009
00:46:45,239 --> 00:46:47,240
Speaker 2: Right, where are some other ways that we can measure distance.

1010
00:46:47,360 --> 00:46:49,799
Speaker 1: One of the ways that's most amazing and impressive is

1011
00:46:49,880 --> 00:46:52,920
Speaker 1: using something called a mazer. So a mazer is like

1012
00:46:52,920 --> 00:46:55,880
Speaker 1: a laser, but it emits in the microwaves. So what

1013
00:46:55,920 --> 00:46:58,840
Speaker 1: they do is they see these blobs of water orbiting

1014
00:46:58,840 --> 00:47:01,680
Speaker 1: a black hole in a distant galaxy, and so for

1015
00:47:01,800 --> 00:47:04,040
Speaker 1: these blobs of water, what they can do is they

1016
00:47:04,040 --> 00:47:06,640
Speaker 1: can measure the distance between the blob of water and

1017
00:47:06,680 --> 00:47:08,640
Speaker 1: the central black hole. And they do it in two

1018
00:47:08,640 --> 00:47:10,959
Speaker 1: different ways, and one is that they look at how

1019
00:47:11,000 --> 00:47:14,520
Speaker 1: these microwave light from this water blog changes as it

1020
00:47:14,560 --> 00:47:17,040
Speaker 1: goes around the black hole, Like as it's going around

1021
00:47:17,080 --> 00:47:19,440
Speaker 1: the backside of the black hole, it's accelerating away from you.

1022
00:47:19,480 --> 00:47:21,319
Speaker 1: As it's coming around the other side of the black hole,

1023
00:47:21,320 --> 00:47:24,280
Speaker 1: it's accelerating towards you, so it's either like red shifted

1024
00:47:24,360 --> 00:47:27,160
Speaker 1: or blue shifted as it goes around this black hole.

1025
00:47:27,239 --> 00:47:29,799
Speaker 1: So by measuring that acceleration and doing like a little

1026
00:47:29,800 --> 00:47:32,440
Speaker 1: bit of like Kepler's laws, you can figure out what

1027
00:47:32,600 --> 00:47:35,360
Speaker 1: is the radius of its orbit around this black hole.

1028
00:47:35,920 --> 00:47:38,440
Speaker 1: And then they actually point telescopes at these things and

1029
00:47:38,600 --> 00:47:42,280
Speaker 1: measure the radius. They can like see these spots orbiting

1030
00:47:42,360 --> 00:47:45,160
Speaker 1: black holes in distant galaxies, so they know the true

1031
00:47:45,280 --> 00:47:48,200
Speaker 1: radius from like the wiggles, and then they can actually

1032
00:47:48,440 --> 00:47:51,240
Speaker 1: measure the radius in a telescope, and they can compare

1033
00:47:51,280 --> 00:47:54,200
Speaker 1: those two things and tell how far away that galaxy

1034
00:47:54,280 --> 00:47:54,960
Speaker 1: actually is.

1035
00:47:55,440 --> 00:47:59,160
Speaker 2: WHOA wait, how do you measure the radius of something

1036
00:47:59,239 --> 00:48:01,080
Speaker 2: orbiting a black hole in another galaxy?

1037
00:48:01,360 --> 00:48:04,880
Speaker 1: It's hard. They have these very long baseline interferometers that

1038
00:48:04,960 --> 00:48:07,360
Speaker 1: can actually resolve these things. They can like measure the

1039
00:48:07,440 --> 00:48:10,600
Speaker 1: locations of these water blobs. When I was first reading

1040
00:48:10,600 --> 00:48:12,000
Speaker 1: about this, I didn't believe it. I had to go

1041
00:48:12,080 --> 00:48:14,360
Speaker 1: back to the papers and see. But in those papers

1042
00:48:14,400 --> 00:48:16,880
Speaker 1: you can see they actually do measure like the distance

1043
00:48:17,239 --> 00:48:20,640
Speaker 1: of each water blob from the black hole itself. It's

1044
00:48:20,680 --> 00:48:25,320
Speaker 1: incredible what we can do with very long baseline interferometers MM.

1045
00:48:25,719 --> 00:48:27,760
Speaker 2: And by water blob, you don't mean like an actual

1046
00:48:27,880 --> 00:48:30,600
Speaker 2: like blob of water. Probably you mean like a cloud

1047
00:48:30,640 --> 00:48:32,320
Speaker 2: of H two O molecules, right.

1048
00:48:32,280 --> 00:48:34,799
Speaker 1: Yeah, exactly. You have some big cloud that's hot and

1049
00:48:34,800 --> 00:48:36,520
Speaker 1: it has a lot of water in it, and so

1050
00:48:36,560 --> 00:48:39,680
Speaker 1: it's emitting light at a characteristic frequency more like a

1051
00:48:39,680 --> 00:48:43,480
Speaker 1: cloud maybe, yeah, like a cloud of water, like water vapor.

1052
00:48:43,680 --> 00:48:46,520
Speaker 1: And by seeing how that frequency is shifted, we can

1053
00:48:46,560 --> 00:48:49,200
Speaker 1: tell whether it's like going around the backside or accelerating

1054
00:48:49,239 --> 00:48:53,680
Speaker 1: towards us or on the front side. So these megamsers

1055
00:48:53,719 --> 00:48:56,520
Speaker 1: they're called, are a totally separate way to measure the

1056
00:48:56,520 --> 00:48:57,840
Speaker 1: distance to these galaxies.

1057
00:48:57,960 --> 00:48:59,880
Speaker 2: Cool, but how many of these can we see or

1058
00:49:00,080 --> 00:49:03,360
Speaker 2: have we seen enough of them to like calibrate this method.

1059
00:49:03,440 --> 00:49:05,400
Speaker 1: There are enough of them to calibrate these methods, but

1060
00:49:05,480 --> 00:49:08,080
Speaker 1: it's not as accurate yet as the other one because

1061
00:49:08,080 --> 00:49:10,719
Speaker 1: we haven't seen that many. In order for this to work,

1062
00:49:10,719 --> 00:49:13,319
Speaker 1: the masers can't be that far away or you just

1063
00:49:13,400 --> 00:49:16,480
Speaker 1: can't see these water blobs going around the black holes.

1064
00:49:16,560 --> 00:49:19,400
Speaker 1: But it's useful because it's a very independent measurement. And

1065
00:49:19,440 --> 00:49:21,120
Speaker 1: the problem is we have lots of different ways to

1066
00:49:21,120 --> 00:49:23,200
Speaker 1: measure the expansion of the universe, but some of them

1067
00:49:23,239 --> 00:49:25,920
Speaker 1: don't agree. A whole other way to measure the expansion

1068
00:49:25,960 --> 00:49:28,680
Speaker 1: of the universe is to look for evidence very early

1069
00:49:28,760 --> 00:49:32,040
Speaker 1: on in the universe from like the cosmic microwave background radiation,

1070
00:49:32,760 --> 00:49:35,200
Speaker 1: and compare that to what we measure from these kind

1071
00:49:35,239 --> 00:49:37,960
Speaker 1: of measurements like in the universe today. We make those

1072
00:49:37,960 --> 00:49:40,560
Speaker 1: measurements and they don't agree, and we don't understand the difference.

1073
00:49:40,840 --> 00:49:44,960
Speaker 1: So having as many independent measurements as possible is really important.

1074
00:49:45,200 --> 00:49:47,160
Speaker 2: Right, you want to stack as many stepping stools on

1075
00:49:47,160 --> 00:49:52,759
Speaker 2: top of your stepping stools as you can. Right, the

1076
00:49:52,840 --> 00:49:55,400
Speaker 2: more stepping stools, the bigger the structure of stepping stools

1077
00:49:55,440 --> 00:49:56,080
Speaker 2: you can convert.

1078
00:49:56,520 --> 00:49:58,680
Speaker 1: Well, if it is one universe, then it all makes

1079
00:49:58,719 --> 00:50:00,880
Speaker 1: sense to us. Then it should be telling us one story.

1080
00:50:00,920 --> 00:50:04,000
Speaker 1: But right now it's telling us several stories. Like measurements

1081
00:50:04,040 --> 00:50:07,080
Speaker 1: from the cosmic microwave background radiation say the universe is

1082
00:50:07,120 --> 00:50:10,960
Speaker 1: expanding at one rate, and measurements from quoisars and cephids

1083
00:50:11,000 --> 00:50:13,520
Speaker 1: and type on a supernova and masers and all these

1084
00:50:13,560 --> 00:50:16,919
Speaker 1: other things tell us a different story, and the tip

1085
00:50:16,960 --> 00:50:19,600
Speaker 1: of the red giant branch that tells us a story

1086
00:50:19,600 --> 00:50:21,799
Speaker 1: that's right in between them. So we have like three

1087
00:50:21,840 --> 00:50:24,960
Speaker 1: different groups of measurements that kind of overlap but kind

1088
00:50:24,960 --> 00:50:27,440
Speaker 1: of disagree with each other. It's a big problem right

1089
00:50:27,440 --> 00:50:30,960
Speaker 1: now in cosmology. People don't really understand what story this

1090
00:50:31,120 --> 00:50:34,040
Speaker 1: is telling us. Are we measuring these things incorrectly or

1091
00:50:34,120 --> 00:50:36,440
Speaker 1: is the story more complicated than we imagined?

1092
00:50:36,880 --> 00:50:39,759
Speaker 2: Right, But the except the cosmetologies are all unified and

1093
00:50:39,800 --> 00:50:42,080
Speaker 2: they're telling us the same story, so they don't have

1094
00:50:42,120 --> 00:50:42,520
Speaker 2: a problem.

1095
00:50:42,600 --> 00:50:44,960
Speaker 1: They just want to cover up these blemishes with more makeup.

1096
00:50:45,000 --> 00:50:48,520
Speaker 2: That's all that's right, just said lay on that foundation. Well,

1097
00:50:48,560 --> 00:50:51,480
Speaker 2: you just kind of confused me because it seems like

1098
00:50:51,560 --> 00:50:55,000
Speaker 2: there's different things giving us different stories. So you're saying

1099
00:50:55,040 --> 00:50:57,839
Speaker 2: that one story is being told by this idea of

1100
00:50:57,880 --> 00:51:01,000
Speaker 2: measuring objects out there how far they are, and then

1101
00:51:01,040 --> 00:51:04,120
Speaker 2: measuring their velocity using the red shifting of their light.

1102
00:51:04,640 --> 00:51:06,279
Speaker 2: It's one way, but you're saying there's sort of a

1103
00:51:06,480 --> 00:51:09,520
Speaker 2: second general class of methods to measure the expansion of

1104
00:51:09,520 --> 00:51:12,440
Speaker 2: the universe that uses the cosmic microwave background.

1105
00:51:12,760 --> 00:51:16,040
Speaker 1: Yeah, the cosmic microwave background is light left over from

1106
00:51:16,120 --> 00:51:19,080
Speaker 1: very early on in the universe, right when the universe

1107
00:51:19,120 --> 00:51:21,680
Speaker 1: cooled down, so that photons that had been emitted by

1108
00:51:21,719 --> 00:51:24,280
Speaker 1: the hot plasma all of a sudden saw the universe

1109
00:51:24,280 --> 00:51:27,840
Speaker 1: as transparent. So that light is still flying around today

1110
00:51:28,000 --> 00:51:30,080
Speaker 1: and we can measure it, and it tells us something

1111
00:51:30,120 --> 00:51:32,480
Speaker 1: about what was going on early on in the universe,

1112
00:51:32,520 --> 00:51:35,360
Speaker 1: including the expansion. It has encluded in the wiggles of

1113
00:51:35,360 --> 00:51:38,320
Speaker 1: those photons in the hot spots and in the cold spots,

1114
00:51:38,520 --> 00:51:41,680
Speaker 1: how the universe was expanding back then. It's very useful

1115
00:51:41,680 --> 00:51:45,120
Speaker 1: because it captures like a really wide swath of the universe,

1116
00:51:45,360 --> 00:51:48,440
Speaker 1: which since then has expanded very broadly. So it sort

1117
00:51:48,440 --> 00:51:50,400
Speaker 1: of like looking at a baby picture of the universe,

1118
00:51:50,600 --> 00:51:52,759
Speaker 1: and we can measure from the wrinkles on it how

1119
00:51:52,800 --> 00:51:54,799
Speaker 1: much it was expanding back then, and we get a

1120
00:51:54,800 --> 00:51:58,160
Speaker 1: different number, and so we don't understand why the early

1121
00:51:58,280 --> 00:52:01,720
Speaker 1: universe measurements like the cosmic mic or background radiation tells

1122
00:52:01,760 --> 00:52:05,200
Speaker 1: a different story about the expansion than the late measurements

1123
00:52:05,440 --> 00:52:06,960
Speaker 1: like the ones we've been talking about with all these

1124
00:52:07,000 --> 00:52:08,120
Speaker 1: different distance ladders.

1125
00:52:08,320 --> 00:52:11,359
Speaker 2: Wait, the cosmic microwave background radiation tell us is how

1126
00:52:11,400 --> 00:52:13,640
Speaker 2: the universe is expanding when it was little, when it

1127
00:52:13,680 --> 00:52:15,640
Speaker 2: was a baby, not how it's expanding today.

1128
00:52:15,800 --> 00:52:18,239
Speaker 1: That's right exactly. But we can extrapolate and we say,

1129
00:52:18,600 --> 00:52:21,200
Speaker 1: if it was expanding at that rate back then, what

1130
00:52:21,280 --> 00:52:24,880
Speaker 1: should we be measuring today with tapewone supernova and cephids

1131
00:52:24,920 --> 00:52:27,399
Speaker 1: and red giants and all that stuff. And those two

1132
00:52:27,480 --> 00:52:28,360
Speaker 1: things don't agree.

1133
00:52:28,480 --> 00:52:29,799
Speaker 2: Well, how do you extravolate?

1134
00:52:29,960 --> 00:52:33,320
Speaker 1: Yeah, you extrapolate using your model of how the universe expands.

1135
00:52:33,640 --> 00:52:36,319
Speaker 1: And maybe that model is wrong. That's what I mean

1136
00:52:36,320 --> 00:52:38,400
Speaker 1: by we need to tell a different story. We have

1137
00:52:38,440 --> 00:52:41,440
Speaker 1: a model for how the universe should expand using various

1138
00:52:41,440 --> 00:52:45,760
Speaker 1: components matter, radiation, dark matter, dark energy, et cetera.

1139
00:52:46,040 --> 00:52:47,040
Speaker 2: You mean they're just guessing.

1140
00:52:48,760 --> 00:52:50,920
Speaker 1: Well, it's a pretty simple model, but it's been working

1141
00:52:50,960 --> 00:52:53,120
Speaker 1: really really well so far, and this is the first

1142
00:52:53,160 --> 00:52:56,080
Speaker 1: sign of strains. It's really been showing. So maybe that

1143
00:52:56,160 --> 00:52:58,799
Speaker 1: model that compares what happened early on and what we

1144
00:52:58,800 --> 00:53:01,279
Speaker 1: should see today is wrong, or maybe one of these

1145
00:53:01,280 --> 00:53:03,080
Speaker 1: measurements is wrong. We're just not sure.

1146
00:53:03,200 --> 00:53:05,040
Speaker 2: All right, Well, so then what are the two stories

1147
00:53:05,040 --> 00:53:07,840
Speaker 2: that we're getting. You're saying that there are conflicting stories

1148
00:53:07,880 --> 00:53:09,040
Speaker 2: between all these measurements.

1149
00:53:09,160 --> 00:53:11,480
Speaker 1: Yes, so the late measurements the ones from type one

1150
00:53:11,520 --> 00:53:14,440
Speaker 1: A supernova. They measure a hubble constant of like seventy

1151
00:53:14,480 --> 00:53:18,719
Speaker 1: three kilometers per megaparsek per second, whereas the early measurements

1152
00:53:18,719 --> 00:53:21,880
Speaker 1: from like the cosmic microwave background radiation and other measurements

1153
00:53:21,920 --> 00:53:25,240
Speaker 1: from the early universe that agree measure like sixty seven

1154
00:53:25,640 --> 00:53:27,759
Speaker 1: kilometers per second per megaparsek.

1155
00:53:27,880 --> 00:53:29,920
Speaker 2: What are these numbers and units mean? That means that

1156
00:53:29,960 --> 00:53:35,360
Speaker 2: for every megaparsec, that's like a measurement of the size

1157
00:53:35,360 --> 00:53:39,800
Speaker 2: of space, the universe is expanding seventy three kilometers each second.

1158
00:53:39,960 --> 00:53:42,680
Speaker 2: Is that? What that means? That's velocity. That's not acceleration,

1159
00:53:42,840 --> 00:53:43,160
Speaker 2: is it.

1160
00:53:43,160 --> 00:53:46,160
Speaker 1: It's not exactly a velocity. It's velocity per size. Right,

1161
00:53:46,280 --> 00:53:49,680
Speaker 1: kilometers per second is velocity. This is kilometers per second

1162
00:53:49,800 --> 00:53:54,080
Speaker 1: per megaparsec. And so it's a measurement of the expansion

1163
00:53:54,200 --> 00:53:58,440
Speaker 1: rate of the universe every second, every megaparsec grows by

1164
00:53:58,480 --> 00:54:01,879
Speaker 1: seventy kilometers. But a megaparsec is really really long.

1165
00:54:02,120 --> 00:54:05,440
Speaker 2: Oh, I see. You're assuming that locally space is expanding

1166
00:54:05,480 --> 00:54:08,920
Speaker 2: at a constant rate like seventy three kilometers per second

1167
00:54:09,400 --> 00:54:13,880
Speaker 2: for megaparsek. But overall, because the whole universe does happening everywhere.

1168
00:54:13,920 --> 00:54:17,000
Speaker 2: Are you saying that this expansion is accelerating because you're

1169
00:54:17,080 --> 00:54:20,120
Speaker 2: kind of like aggregating all of these local measurements, but

1170
00:54:20,200 --> 00:54:22,520
Speaker 2: locally it's a constant, or you think it's a constant.

1171
00:54:22,640 --> 00:54:25,080
Speaker 1: We think it's a constant in space. We think everywhere

1172
00:54:25,080 --> 00:54:27,839
Speaker 1: in the universe has the same expansion rate. We don't

1173
00:54:27,840 --> 00:54:30,520
Speaker 1: think it's a constant in time. We think it varies

1174
00:54:30,560 --> 00:54:33,760
Speaker 1: in time because it depends on the density of stuff

1175
00:54:33,800 --> 00:54:36,080
Speaker 1: in the universe, Like how much stuff is in the

1176
00:54:36,160 --> 00:54:39,719
Speaker 1: universe affects how the universe is expanding, So as the

1177
00:54:39,800 --> 00:54:43,719
Speaker 1: universe gets less dense, this number decreases, but it is

1178
00:54:43,760 --> 00:54:46,279
Speaker 1: a number that we can measure, And seventy kilometers per

1179
00:54:46,320 --> 00:54:50,080
Speaker 1: second sounds a lot, but a megaparsek is three million

1180
00:54:50,200 --> 00:54:53,600
Speaker 1: light years. So every second, a chunk of space that's

1181
00:54:53,640 --> 00:54:57,799
Speaker 1: three million light years long gets bigger by seventy kilometers,

1182
00:54:58,040 --> 00:55:02,080
Speaker 1: which is like a tiny, tiny, tiny fraction of a megaparsec.

1183
00:55:02,600 --> 00:55:05,879
Speaker 1: But over very very long distances, it does add up.

1184
00:55:05,960 --> 00:55:08,120
Speaker 2: Because there are a lot of megaparsecs in the universe.

1185
00:55:08,320 --> 00:55:10,680
Speaker 1: Oh yeah, we got lots of megaparsecs.

1186
00:55:11,000 --> 00:55:13,319
Speaker 2: Okay, So what does that tell us that all these

1187
00:55:13,320 --> 00:55:17,120
Speaker 2: measurements are disagreeing. Does it mean that things have been

1188
00:55:17,200 --> 00:55:19,480
Speaker 2: changing with time or it just means that there's too

1189
00:55:19,560 --> 00:55:21,160
Speaker 2: much uncertainty in our measurements.

1190
00:55:21,280 --> 00:55:24,040
Speaker 1: It means that maybe our measurements are wrong. But people

1191
00:55:24,040 --> 00:55:26,440
Speaker 1: have been refining these measurements over time and they've been

1192
00:55:26,480 --> 00:55:28,760
Speaker 1: getting better and better. And now we have like alternate

1193
00:55:28,800 --> 00:55:31,279
Speaker 1: ways to make some of these measurements which agree with

1194
00:55:31,360 --> 00:55:34,640
Speaker 1: each other. And so the story's getting more and more precise,

1195
00:55:34,760 --> 00:55:37,839
Speaker 1: but the disagreement is not going away. Sometimes you get

1196
00:55:37,840 --> 00:55:39,760
Speaker 1: a bunch of measurements and they're all kind of sloppy

1197
00:55:39,760 --> 00:55:41,400
Speaker 1: and they don't really agree with each other, and then

1198
00:55:41,400 --> 00:55:43,560
Speaker 1: people make the measurements more precise and they sort of

1199
00:55:43,680 --> 00:55:46,359
Speaker 1: like come into line. That's not what's happening here. As

1200
00:55:46,400 --> 00:55:49,680
Speaker 1: we resolve these things more finely, the disagreement seems to

1201
00:55:49,680 --> 00:55:54,920
Speaker 1: be growing, which means something basically we've misunderstood, Like maybe

1202
00:55:54,920 --> 00:55:57,640
Speaker 1: there's some reason we're making a mistake in these measurements.

1203
00:55:57,880 --> 00:56:00,799
Speaker 1: That seems unlikely as we get more more like very

1204
00:56:00,840 --> 00:56:04,439
Speaker 1: different ways to make the measurements, or there's something wrong

1205
00:56:04,440 --> 00:56:07,200
Speaker 1: about this story about the universe expanding, and maybe it

1206
00:56:07,239 --> 00:56:10,400
Speaker 1: expanded faster early on than it is now because something

1207
00:56:10,400 --> 00:56:13,280
Speaker 1: else happened. We had an episode about early dark energy,

1208
00:56:13,400 --> 00:56:15,600
Speaker 1: which might explain it. Or as you said very early

1209
00:56:15,640 --> 00:56:19,040
Speaker 1: on in the podcast, maybe we're extrapolating from our bubble.

1210
00:56:19,239 --> 00:56:21,760
Speaker 1: Maybe our part of the universe is expanding more slowly

1211
00:56:21,800 --> 00:56:24,239
Speaker 1: than everything else because it's less dense than the rest

1212
00:56:24,280 --> 00:56:26,560
Speaker 1: of the universe. So something has to change in our

1213
00:56:26,600 --> 00:56:28,840
Speaker 1: story of the universe to make sense of these measurements.

1214
00:56:29,760 --> 00:56:32,480
Speaker 2: Interesting, Well, I guess the answer then is it kind

1215
00:56:32,520 --> 00:56:35,759
Speaker 2: of stay tuned right. We're we're fining our measurements of

1216
00:56:35,800 --> 00:56:38,440
Speaker 2: the universe, and with that we are getting a better

1217
00:56:38,719 --> 00:56:41,640
Speaker 2: picture of how the universe is expanding, which might tell

1218
00:56:41,719 --> 00:56:44,720
Speaker 2: us how the universe might end eventually exactly.

1219
00:56:44,800 --> 00:56:47,040
Speaker 1: As we keep building better and better facilities, we develop

1220
00:56:47,120 --> 00:56:50,200
Speaker 1: more techniques for measuring this expansion. We come up with

1221
00:56:50,239 --> 00:56:52,920
Speaker 1: clever ways to see things happening in other galaxies that

1222
00:56:52,960 --> 00:56:55,480
Speaker 1: we can calibrate and so we can measure the distance

1223
00:56:55,520 --> 00:56:57,759
Speaker 1: to them, and so our picture of what's happening out

1224
00:56:57,760 --> 00:57:01,040
Speaker 1: there in the universe gets more precise. As things get clear,

1225
00:57:01,239 --> 00:57:03,080
Speaker 1: more mysteries always emerge.

1226
00:57:03,360 --> 00:57:05,680
Speaker 2: Yeah, because it's very important. We really want to know,

1227
00:57:05,920 --> 00:57:10,080
Speaker 2: is our universe growing faster or slower than our brother

1228
00:57:10,280 --> 00:57:13,040
Speaker 2: or sister universe. The sibling race is on.

1229
00:57:13,360 --> 00:57:15,799
Speaker 1: That's right. We want our common great great great great

1230
00:57:15,840 --> 00:57:18,520
Speaker 1: great great great grandkids to have a leg up over

1231
00:57:18,560 --> 00:57:20,080
Speaker 1: the ones in our sibling universe.

1232
00:57:20,240 --> 00:57:22,360
Speaker 2: All right, well, we hope you enjoyed that. Thanks for

1233
00:57:22,440 --> 00:57:24,480
Speaker 2: joining us, See you next time.

1234
00:57:32,320 --> 00:57:35,120
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

1235
00:57:35,200 --> 00:57:39,200
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1236
00:57:39,200 --> 00:57:43,840
Speaker 1: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1237
00:57:43,920 --> 00:57:45,640
Speaker 1: you listen to your favorite shows.