Latest / Daniel and Kelly’s Extraordinary Universe / How fast is the universe blowing up?

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How fast is the universe blowing up? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Danny, does the universe just blow your mind? Oh?
0:11
Speaker 1: My god. Constantly I feel like I can't crame enough
0:14
Speaker 1: universe into my brain. Is just excluding what's the most
0:17
Speaker 1: mind blowing thing about the universe in your opinion? I
0:20
Speaker 1: think the thing that drives me the craziest is that
0:22
Speaker 1: the universe itself seems to be blowing up. The universe
0:26
Speaker 1: is blowing up. You mean like it's going viral on
0:29
Speaker 1: social media? Probably hashtag universe, hashtag everything in the universe
0:34
Speaker 1: Twitter account is lit. No, I mean that it's getting bigger,
0:38
Speaker 1: and the speed at which the universe is getting bigger
0:41
Speaker 1: is also getting bigger. Hi am pre hammack Tunis and
1:00
Speaker 1: the creator of PhD Comics. Hi, I'm Daniel Whitson. I'm
1:04
Speaker 1: a particle physicist, but my brain is filled with crazy
1:07
Speaker 1: ideas about space, time and particles. So welcome to our
1:11
Speaker 1: podcast Daniel and Jorge explain The Exploding Universe, a production
1:16
Speaker 1: of My Heart Radio, in which we try to take
1:19
Speaker 1: the entire universe, everything in it, and squeeze it down
1:23
Speaker 1: into this audio connection to you, downloading it into your
1:27
Speaker 1: brain so that it blows up your gray matter. And
1:29
Speaker 1: so are we here to try to blow your mind
1:32
Speaker 1: a little bit of physics at a time, you know,
1:35
Speaker 1: just a little bit of physics each week, twice a week,
1:37
Speaker 1: and hopefully your mind is getting maybe bigger, may be
1:40
Speaker 1: more connected to this giant universe we have out there.
1:44
Speaker 1: That's right, The universe is out there, and we think
1:46
Speaker 1: it's for everybody understanding. This incredible place we live in
1:49
Speaker 1: shouldn't just be the province of cutting edge scientists. It
1:52
Speaker 1: belongs to everybody, and that wonderment, that amazement should be
1:55
Speaker 1: accessible to everybody out there. And so our goal is
1:59
Speaker 1: to make sure that you actually understand the way the
2:01
Speaker 1: universe works and what science does and does not know.
2:05
Speaker 1: Is the universe for everybody? Daniel, I don't know about that.
2:07
Speaker 1: I mean, all solar systems matter, man, All solar systems
2:13
Speaker 1: are made of matter. Yeah, that matter matters, no, But
2:15
Speaker 1: I think that the universe is for everybody. You know,
2:17
Speaker 1: you don't have to be a scientist to look up
2:19
Speaker 1: at the stars and wonder how does this whole crazy
2:22
Speaker 1: universe work? Or to look down at your feet and
2:24
Speaker 1: wonder about the particles that you're made out of. And
2:27
Speaker 1: everybody deserves an explanation. And you know, science is mostly
2:30
Speaker 1: something that's publicly funded, it's put on by governments, it's
2:33
Speaker 1: of the people, by the people, and for the people.
2:35
Speaker 1: And so this is the for the people part where
2:38
Speaker 1: we try to disseminate what science has learned to everybody
2:40
Speaker 1: out there. Yeah, for sure, I think definitely the universe
2:43
Speaker 1: itself is definitely of people and with people in it,
2:47
Speaker 1: and for the people. Yeah, there's a lot of prepositions
2:50
Speaker 1: you can go for there. I just hope it's not
2:52
Speaker 1: through people. You know, we don't don't want to go
2:54
Speaker 1: around people are over people, what do you mean? I
2:57
Speaker 1: think the universe is all those things, the universe going
3:00
Speaker 1: through me right now. Well, the goal of this podcast
3:03
Speaker 1: is to get the universe into people. Well, we're trying
3:05
Speaker 1: to um talk about the universe and just kind of
3:07
Speaker 1: help everyone wrapped their heads around this incredible and complex
3:12
Speaker 1: and really big universe, right and possibly getting bigger. Yeah,
3:16
Speaker 1: And this whole idea of the size of the universe
3:19
Speaker 1: is something which is very very modern and people have
3:21
Speaker 1: been looking at the stars for a long time. People
3:23
Speaker 1: have known about other planets, people had the idea that
3:26
Speaker 1: there are other stars out there, But it's only been
3:28
Speaker 1: a hundred years that we've known that there are other galaxies,
3:31
Speaker 1: and that those galaxies are moving away from us, and
3:33
Speaker 1: that the size of the universe itself might be expanding.
3:37
Speaker 1: So it's very recent in human history that we really
3:39
Speaker 1: have any understanding at all of the entire context of
3:42
Speaker 1: our lives. Yeah, that's wild, Like a hundred only a
3:45
Speaker 1: hundred years ago, we thought it was just us right,
3:49
Speaker 1: like us and the stars around us, and maybe that's it. Yeah,
3:52
Speaker 1: hundred years ago, people thought it was a bunch of
3:53
Speaker 1: stars hanging in space, and it's just sort of been
3:55
Speaker 1: like that forever. So most humans who ever lived had
3:59
Speaker 1: the raw long understanding of the entire universe. Only the
4:03
Speaker 1: people who were awake, alive and listening to this podcast
4:06
Speaker 1: have any sense for the actual context of their lives. Yeah,
4:09
Speaker 1: it's just a small error, you know, just a few
4:12
Speaker 1: Brazilian whatever. And the thing I love about that is
4:16
Speaker 1: it suggests that there might be other enormous contextual errors
4:20
Speaker 1: that we're making, you know, basic assumptions we have about
4:23
Speaker 1: the way the universe works that are just wrong. That
4:26
Speaker 1: in a hundred years some future podcast will be smirking
4:28
Speaker 1: at and twortling at our ignorance, being sarcastic about while
4:32
Speaker 1: eating bananas precisely. Do you think people back then a
4:36
Speaker 1: hundred years ago I thought the universe was a finite size,
4:39
Speaker 1: or did they think it was infinite, or did they
4:41
Speaker 1: think it had a size but just not as big
4:43
Speaker 1: as we know to be right now. I think about
4:45
Speaker 1: a hundred years ago, before Hubble, for example, people thought
4:48
Speaker 1: it was just a bunch of stars and it was finite,
4:51
Speaker 1: and it just sort of a bunch of stars hanging
4:52
Speaker 1: in space. You know, imagine like a single galaxy, whether
4:56
Speaker 1: or not space itself went on beyond the edge of
4:58
Speaker 1: that galaxy. I think there was a lot of debate there,
5:00
Speaker 1: but I don't think people ever imagine that there could
5:02
Speaker 1: be like an infinite number of stars. Well, and so
5:05
Speaker 1: that's the topic for today's podcast is it's about the
5:08
Speaker 1: size of the universe and more specifically, how that size
5:11
Speaker 1: is changing, because the size of the universe is changing, right,
5:16
Speaker 1: that's right, And this is something that Hubble himself began.
5:18
Speaker 1: Hubble is famous not because of the Hubble space telescope,
5:21
Speaker 1: which was named after him, but because he's the guy
5:24
Speaker 1: who discovered that the universe is expanding. The things that
5:27
Speaker 1: are far away from us are moving away from us.
5:29
Speaker 1: Really quickly, where like one raise in an expanding loof
5:33
Speaker 1: of raisin bread. And the thing that's amazing is that
5:36
Speaker 1: we're still learning about that. We're still learning about how
5:39
Speaker 1: fast the universe is expanding, and we're still not sure
5:42
Speaker 1: of it. We still don't really know the answer. Really.
5:45
Speaker 1: We think it's expanding faster and faster, but we are
5:48
Speaker 1: not quite sure how fast it's it's it's growing, or
5:52
Speaker 1: kind of what's causing it. Right, that's exactly right. And
5:55
Speaker 1: people measure this stuff and there's lots of different ways
5:57
Speaker 1: to do it, and those measurements they make don't quite agree.
6:00
Speaker 1: And so that's what we're gonna be talking about in
6:02
Speaker 1: today's podcast. Yeah, So today on the podcast, we'll be
6:05
Speaker 1: tackling the question how fast is the universe blowing up? Yeah?
6:16
Speaker 1: And this is a really fun question and what I've
6:18
Speaker 1: been tracking for a while because different teams of scientists
6:20
Speaker 1: are trying to measure this expansion of the universe in
6:23
Speaker 1: totally different ways, and for a while they sort of
6:25
Speaker 1: agreed until recently their measurements be getting more and more precise,
6:29
Speaker 1: and now they're not agreeing that well, And then I
6:32
Speaker 1: got a question from a listener somebody who wrote in
6:34
Speaker 1: to ask about it, and I thought, all right, it's
6:36
Speaker 1: time to do a podcast on it. So here's a
6:39
Speaker 1: question from Mike and Madison who wanted to know. Hi,
6:42
Speaker 1: Daniel and Jorge. My name is Mike. I'm an engineer
6:44
Speaker 1: from Madison, Wisconsin. Could you guys please explain what we're
6:48
Speaker 1: doing to try and solve the unmatching hubble constant mystery? Also,
6:52
Speaker 1: why does it have to be a single constant? Couldn't
6:54
Speaker 1: the universe be expanding asymmetrically or at changing or different
6:58
Speaker 1: rates depending on where you are in the universe. Also,
7:01
Speaker 1: I'd like to give a shout out to my uncle
7:03
Speaker 1: Jim McClain for introducing me to this amazing podcast. All right,
7:07
Speaker 1: thank you Mike and Madison in medisine. I like how
7:09
Speaker 1: it's alliterative. Yeah, and in a moment we will dig
7:14
Speaker 1: into what the hubble constant is and how it's connected
7:16
Speaker 1: to the expansion the universe and is it a constant
7:19
Speaker 1: after all and all that kind of stuff. Yeah, because
7:22
Speaker 1: it's kind of a very technical question. Like at first
7:24
Speaker 1: I heard this question, but I didn't really even know
7:27
Speaker 1: what he was asking about. Yeah, And the best way
7:29
Speaker 1: to think about it is that the Hubble constant is
7:31
Speaker 1: just one way to understand how fast the universe is accelerating.
7:35
Speaker 1: It sort of helps determine it. But of course it's
7:37
Speaker 1: confusing because it turns out the Hubble constant not actually
7:40
Speaker 1: a constant, so it's an un constant constant. We are
7:46
Speaker 1: constantly messing up the names of things in physics. We
7:49
Speaker 1: are constantly throwing out the dictionary, it seems. You know,
7:54
Speaker 1: if we just redefine the meaning of the word constant,
7:56
Speaker 1: then it's a constant, right, and then we'll redefine the
7:58
Speaker 1: meaning of the word redefine, in which case we'll be
8:02
Speaker 1: do this all the time in physics right where we
8:05
Speaker 1: have particles that spin but it's not really spin, you know,
8:08
Speaker 1: we have particles with flavor, but they don't really taste
8:10
Speaker 1: like anything. And now we have constants that are not
8:13
Speaker 1: really constant. It's like a whole new language. It's like,
8:16
Speaker 1: I feel like you're doing on a purpose, Daniel, just
8:18
Speaker 1: to confuse us, and um makes us, UM makes us
8:24
Speaker 1: wonder about this crazy No, no no, no, we I'm going
8:27
Speaker 1: to use the Donald Trump defense. It's out of pure incompetence.
8:30
Speaker 1: We're not trying to confuse anybody. We're just not capable
8:32
Speaker 1: of doing any better. I see that's a defense name
8:34
Speaker 1: after him, but not necessarily something he does. That's right,
8:39
Speaker 1: But I was wondering are people paying attention to this?
8:41
Speaker 1: Does everybody know what the Hubble constant? Is? Are they
8:44
Speaker 1: aware this tempest and a teapot about how fast the
8:46
Speaker 1: universe is expanding? Or is that something just scientists are
8:50
Speaker 1: thinking about? Yeah, how many people out there even know
8:53
Speaker 1: what the Hubble constant is? So, as usual, Daniel went
8:56
Speaker 1: out there into the streets and as random strangers if
9:00
Speaker 1: they knew what the Hubble constant is, think about it
9:02
Speaker 1: for a second. Do you know what the Hubble constant is?
9:05
Speaker 1: And if somebody asked you on the street to define it,
9:08
Speaker 1: would you be able to give an answer? Here's what
9:09
Speaker 1: people had to say. Something to do with the way
9:13
Speaker 1: things around its space. I guess I don't know. Something
9:15
Speaker 1: do the Hubble telescope? I don't know. It's the only
9:18
Speaker 1: thing that I know that is Hubble esque, like a
9:21
Speaker 1: mathematical equation or something. I feel like, something about how
9:25
Speaker 1: the stretching of the universe that's do with gravity or something.
9:30
Speaker 1: I mean, does it have to do with that one
9:31
Speaker 1: Hubble and like a red blue shift or anything or not.
9:36
Speaker 1: That's that w the extent that I would know, no idea.
9:40
Speaker 1: Have you heard of Hubble? No? I guess it has
9:42
Speaker 1: something to do with lights and the stars and space.
9:48
Speaker 1: The scale you're getting there. Yeah, it's a scale constant
9:53
Speaker 1: of lights through three dimensional space, and it's like a
9:59
Speaker 1: cost bar jegal constant um. Doesn't have to do with
10:02
Speaker 1: the size of the universe. I think that's all I
10:06
Speaker 1: can get from my memory right now. I've heard of Hubble.
10:10
Speaker 1: It's like the telescope, right, And I'm not sure what
10:13
Speaker 1: the Hubble constant is, all right. I feel like some
10:17
Speaker 1: people knew a lot about it, but a lot of
10:19
Speaker 1: people didn't know anything about it or had heard of it. Yeah,
10:22
Speaker 1: and some people were totally wrong. But I love these answers.
10:25
Speaker 1: You know, some people think it has to do with
10:27
Speaker 1: the Hubble space Telescope, which I guess indirectly it does,
10:30
Speaker 1: because you know, the space telescope was named for Hubble,
10:33
Speaker 1: who discovered this thing and and quantified. They've done a
10:38
Speaker 1: lot of really good branding on the Hubble telescope, you know,
10:40
Speaker 1: like it's a thing. People know what it is, and
10:43
Speaker 1: because when most people associated with the name Hubble. Yeah,
10:46
Speaker 1: the Hubble pr team has done a good job. Hey,
10:48
Speaker 1: you know they produced these Instagram ready images all the time.
10:52
Speaker 1: They're beautiful. You know, you just google Hubble and you've
10:54
Speaker 1: got a lot of really gorgeous stuff to look at.
10:56
Speaker 1: Let a Hubble bubble up. Yeah, you know, particle physics
10:59
Speaker 1: service Umble doesn't produce as much like pretty pictures that
11:02
Speaker 1: you can look at and say, oh wow, look at
11:05
Speaker 1: that amazing thing out there in the universe, because it's
11:07
Speaker 1: harder to visualize tiny particles. So from that point of view,
11:10
Speaker 1: astronomy definitely has the lead over particle physics. Well, I
11:13
Speaker 1: I am definitely in league with all of these people
11:17
Speaker 1: on the street. I don't really know or have a
11:19
Speaker 1: good idea of what the Hubble constant. Maybe. Up until
11:22
Speaker 1: a few years ago, I never even heard it. I
11:24
Speaker 1: mean I heard of the Hubble telescope, not the Hubble constant. Really,
11:28
Speaker 1: do you remember the moment you learned about the Hubble constant,
11:31
Speaker 1: probably like five minutes after meeting you. Then I do
11:35
Speaker 1: bring it up pretty quickly in conversation. Hi, how's it going,
11:39
Speaker 1: how's the weather. Let's talk about the Hubble constant. So
11:43
Speaker 1: it's it's not related to the telescope. This telescope was
11:47
Speaker 1: named after Edwin Hubble Um. But Hubble in his time
11:51
Speaker 1: did a lot of amazing discoveries, and one of them
11:55
Speaker 1: was this idea of a constant in the universe. Yeah, precisely.
11:58
Speaker 1: The Hubble constant is related to the Hubble telescope, and
12:00
Speaker 1: we actually do use the Hubble telescope now to help
12:03
Speaker 1: nail down the Hubble constant, which is sort of a
12:05
Speaker 1: fun little loop there. Yeah. Of course Hubble died well
12:08
Speaker 1: before the space telescope launched, But you're right, he was
12:10
Speaker 1: the one who figured out that the universe is expanding. Right.
12:13
Speaker 1: Do you think he named the constant after himself or
12:16
Speaker 1: was it named for him? Oh that's a great question. Um,
12:19
Speaker 1: I have to go back and look at the paper.
12:21
Speaker 1: Now we refer to it as H zero, you know,
12:24
Speaker 1: H for Hubble and zero for constant. But I don't
12:27
Speaker 1: know how the Santa Claus constant is. What if you
12:31
Speaker 1: should have called it? Um No, But I don't know
12:36
Speaker 1: if he called it H in his paper or if
12:38
Speaker 1: he just observed this. The breakthrough the heat provided is
12:41
Speaker 1: that he figured out a way to measure the distance
12:43
Speaker 1: to really far away objects. You remember, we had a
12:46
Speaker 1: whole podcast about how we measured the distance to stars.
12:50
Speaker 1: It's tricky because you don't know when you look at
12:52
Speaker 1: a star if it's really bright and far away or
12:55
Speaker 1: really close and kind of dim. So you have to
12:58
Speaker 1: know the distance um in other way. And he was
13:01
Speaker 1: the first one to figure out a way to measure
13:02
Speaker 1: the distance to far away stars because, as we talked
13:06
Speaker 1: about in that podcast, it's really hard to tell that distance.
13:08
Speaker 1: I mean from here from Earth, things just look like
13:11
Speaker 1: little pinpoints of light and they can be really far,
13:15
Speaker 1: they can be really closed. You don't really know, right,
13:17
Speaker 1: So Hobbi used these really cool stars called Cepid's now
13:21
Speaker 1: another astronomer. Hen we had a Levitt had earlier discovered
13:25
Speaker 1: that there's a way to relate how fast these stars
13:28
Speaker 1: pulsate to how bright they are. And we want to
13:31
Speaker 1: say thank you very much to Marcus Pustle for raising
13:34
Speaker 1: this issue and reminding us of Henrietta Levitt's work. Apologies
13:38
Speaker 1: that we neglected to mention her contributions in an earlier version.
13:42
Speaker 1: So if you know how bright these stars are supposed
13:45
Speaker 1: to be because you can tell how fast they're pulsating,
13:48
Speaker 1: then you know how far away they actually are by
13:51
Speaker 1: measuring their brightness here on Earth. So building on Levitt's discovery,
13:56
Speaker 1: this gave Hubble a way to estimate the distance to
13:59
Speaker 1: those ours. And then that's a moment he made an
14:02
Speaker 1: incredible discovery that some of these things were super duper
14:05
Speaker 1: far away. He's like, Okay, now I have a way
14:08
Speaker 1: to measure the distance to these stars. What are the numbers?
14:11
Speaker 1: The calculation? That's what it sounded like. And they had
14:15
Speaker 1: calculators back there were mechanically and it's probably turned cranker.
14:19
Speaker 1: Maybe somebody was shoveling coal in the side of his calculator.
14:22
Speaker 1: Um no, I guess I probably had a room full
14:24
Speaker 1: of people doing math paper. Here's the sound of it.
14:30
Speaker 1: There's my dramatic recreation of his calculation. But he had
14:33
Speaker 1: this moment of discovery, developed this new tool, a way
14:36
Speaker 1: to understand how far away things are. And the numbers
14:38
Speaker 1: he got were crazy, Like the numbers he got were
14:41
Speaker 1: like these can't even meet inside the galaxy. And that's
14:44
Speaker 1: what made him realize that some of the little dust
14:47
Speaker 1: he was seeing the guy weren't in our galaxy. There
14:49
Speaker 1: were other galaxies far away. So he gave us this
14:52
Speaker 1: ability to understand how far away things were and gave
14:55
Speaker 1: us the first view outside of our galaxy into deep
14:58
Speaker 1: deep space. That's the first he did, was he expanded
15:02
Speaker 1: our idea of how big the universe was and how
15:05
Speaker 1: far away things were. But at that time, I think
15:09
Speaker 1: a lot of people, most people thought that the universe
15:11
Speaker 1: was kind of fixed, right, like it wasn't. Maybe he
15:14
Speaker 1: figured out how big it was, but at the time,
15:16
Speaker 1: most people, I think thought the universe wasn't changing, like
15:19
Speaker 1: it was fixed. Yeah, precisely. Once he was able to
15:22
Speaker 1: know how far away stuff was, he could also measure
15:25
Speaker 1: how fast it was moving away from us, and then
15:27
Speaker 1: he made this plot. He's like, only maybe just plot
15:29
Speaker 1: everything in terms of how far away it is versus
15:32
Speaker 1: how fast it's moving away from us, And it just
15:34
Speaker 1: sort of fell in a line. So the farther away
15:37
Speaker 1: something is the faster it's moving away from us, and
15:40
Speaker 1: that the slope of that line is the hubble constants
15:43
Speaker 1: the ratio between how far something is from us and
15:46
Speaker 1: how fast it's moving away from us. Because that's a
15:49
Speaker 1: weird concept. I think. I think that can you imagine
15:52
Speaker 1: a universe getting bigger? It's kind of not intuitive to
15:57
Speaker 1: think that how fast things are moving and way from
16:00
Speaker 1: us would change. Right, Like if you think of when
16:03
Speaker 1: a grenade explodes out in space, you know, all the
16:06
Speaker 1: bits are moving away from each other, but they're sort
16:08
Speaker 1: of moving at the same rate. They're not moving faster
16:11
Speaker 1: and faster the further out you go in the explosion,
16:14
Speaker 1: right precisely. And the reason you shouldn't think of the
16:16
Speaker 1: universe as a grenade is because of grenade, the explosion
16:20
Speaker 1: comes just from the center. Is that one explosion, and
16:22
Speaker 1: then everything is just getting pushed from there. But the
16:24
Speaker 1: universe's expansion is totally different. It's much more like raisin
16:28
Speaker 1: bread than like a grenade. When you cook a loaf
16:31
Speaker 1: of raisin bread, it doesn't just expand from the center.
16:33
Speaker 1: Every part of the bread is expanding, So all the
16:35
Speaker 1: raisins are moving away from each other. Everything is stretching
16:39
Speaker 1: at the same time. Even the stuff that's way out
16:41
Speaker 1: there is also stretching. Yeah, if you wanted to mix
16:44
Speaker 1: the metaphors, you'd have to, like have a grenade bread
16:47
Speaker 1: loaf of bread that's grenades, you know, that's expanding all
16:49
Speaker 1: the time, A bunch of tiny little grenades. I guess
16:52
Speaker 1: in the end bread is expanding because of all the east.
16:54
Speaker 1: You can think of the east is like microbial grenades.
16:56
Speaker 1: It's like it's always exploding everywhere, and oh, the stuff
17:01
Speaker 1: that's really far away has a lot of yeast between
17:05
Speaker 1: here and there. And so it's the stretching and the
17:08
Speaker 1: expanding compounds, you know, like it's it's getting bigger and
17:11
Speaker 1: bigger and bigger, bigger and bigger and faster and faster.
17:14
Speaker 1: The further away from you you go, precisely between us
17:17
Speaker 1: and things that are far away, there's more space, and
17:19
Speaker 1: so there's more space to be expanding, and so the
17:22
Speaker 1: velocities are larger. And then you're saying that the Hubble constant,
17:25
Speaker 1: it's is what tells us just how fast that's happening, Like,
17:30
Speaker 1: is the raising bread crazy with it's some kind of
17:33
Speaker 1: crazy yeast or was this some kind of you know, dull, old,
17:37
Speaker 1: kind of mild, timid east which is expanding our raising
17:40
Speaker 1: universe a little bit slower. Yeah, And so the Hubble
17:43
Speaker 1: constant is expressed in terms of velocity per distance. For
17:47
Speaker 1: every light year you go, how much faster are things
17:50
Speaker 1: accelerating away from us? All right, let's get into the
17:53
Speaker 1: details of this constant, and let's get into um these
17:56
Speaker 1: apparent controversy about what that constant actually is and how
18:02
Speaker 1: it's changing and why it's changing. But first let's take
18:05
Speaker 1: a quick break, al right, Daniel. So the universe is
18:20
Speaker 1: getting bigger, and the rate at which it is getting
18:24
Speaker 1: bigger is getting bigger itself. And so this idea of
18:27
Speaker 1: the Hubble constant, it's something that tells us how fast
18:30
Speaker 1: it's happening. And the thing that would have blown Hubble's
18:32
Speaker 1: mind is that this expansion is not constant. You know, Hubble, imagine, oh,
18:37
Speaker 1: things are moving away from us at a certain rate,
18:38
Speaker 1: and if you want more expansion, you just need a
18:41
Speaker 1: larger space. And that's cool. But it's only twenty years
18:44
Speaker 1: ago we realized that something else was happening as well,
18:48
Speaker 1: that this expansion wasn't just continuing, but it was actually accelerating.
18:51
Speaker 1: So the Hubble constant is not constant. In time. As
18:55
Speaker 1: the universe is getting older and older, this expansion is
18:57
Speaker 1: sort of picking up speed. Yeah, It's like Yeese is
19:00
Speaker 1: going into overdrive. Yeah. And so that's why the Hubble
19:03
Speaker 1: constant turns out to not be a constant. He thought
19:05
Speaker 1: of a constant. He was just measuring it in one snapshot,
19:08
Speaker 1: but it turns out that it's actually changing. Do you
19:11
Speaker 1: think at some point maybe you'll consider changing the name
19:14
Speaker 1: of it so that you don't have to caveat it
19:18
Speaker 1: is the constant that's not a constant. There's a movement
19:20
Speaker 1: now to call it the Hubble parameter, and I think
19:22
Speaker 1: in most of general relativity they call it the Hubble parameter.
19:26
Speaker 1: But there's also this, there's a Hubble constant which has
19:28
Speaker 1: historical value to it. And so it's going to take
19:31
Speaker 1: a while. You know, we're a hundred years in. Give
19:33
Speaker 1: us another hundred years. Maybe you'll find the right name
19:35
Speaker 1: for you. But it's maybe it's it's more like the
19:39
Speaker 1: Hubble rate. Maybe would that be a better name, like
19:41
Speaker 1: the Hubble rate of expansion of the universe. Yeah. Well,
19:44
Speaker 1: in the end, really I think it's best to connect
19:46
Speaker 1: it to the dark energy fraction of the universe because
19:50
Speaker 1: the thing that's causing the expansion is this thing that's
19:54
Speaker 1: dark energy. Right, it's only twenty years ago we discovered
19:57
Speaker 1: that the universe is not expanding constantly. It's a spending
20:00
Speaker 1: at an accelerating rate, which means that every year it's
20:02
Speaker 1: getting bigger. Faster and faster. And we did this by
20:05
Speaker 1: making another breakthrough by looking even further into the past
20:09
Speaker 1: and into the far universe, by finding these supernove but
20:11
Speaker 1: that we could use sort of in the same way
20:13
Speaker 1: that Hubbo use those sthords to extend our distance ladder
20:16
Speaker 1: even farther. And that told us that this acceleration of
20:20
Speaker 1: the universe started about five billion years ago. And that's
20:23
Speaker 1: what we call dark energy. We say dark energy is
20:25
Speaker 1: some weird, mysterious thing which started dominating about five million
20:29
Speaker 1: years ago, and it's causing the universe's expansion to accelerate.
20:32
Speaker 1: You're saying that, um, the Hubble constant is not a
20:35
Speaker 1: good name for it, and so the solution is not
20:38
Speaker 1: to change the name, but to call it something else mysterious. Well,
20:41
Speaker 1: I think it's to dig into the source of it
20:43
Speaker 1: to understand why is the universe expanding? And I see,
20:48
Speaker 1: let's not worry about the name. Let's focus on what's
20:51
Speaker 1: making the universe get bigger and substance over style, right,
20:55
Speaker 1: that's my motto, because I certainly don't have much style,
20:58
Speaker 1: so I gotta go over a substance. There's I think
21:00
Speaker 1: there's a physics style like it's a thing, isn't it.
21:05
Speaker 1: You're either digging for compliments or you're baiting me into
21:07
Speaker 1: a trap here. I can't tell which one maybe, But
21:13
Speaker 1: the hubble constant, I think it's it's interesting to dig
21:16
Speaker 1: into the units it has, because you were saying earlier
21:19
Speaker 1: the hubble constant, which is not a constant, but I
21:23
Speaker 1: guess that's it has a value right now, which is,
21:26
Speaker 1: you know, kind of around seventy kilometers per second per
21:31
Speaker 1: million light years, seventy kilometers per second per mega parsek
21:36
Speaker 1: mega parsic, which is sort of like a distance, right, Yeah,
21:40
Speaker 1: parsek is a distance, even though in Star Wars they
21:42
Speaker 1: use it as a time like didn't Han Solo do
21:45
Speaker 1: the kettle run in eleven parsecs or something, which makes
21:47
Speaker 1: absolutely no sense. He ran tens and ten or something
21:51
Speaker 1: like that. UM, and those units are sort of hard
21:54
Speaker 1: to understand, so I transformed it to another set of
21:56
Speaker 1: units that makes more sense to me. It's forty six
21:59
Speaker 1: thou thousand miles per hour for every million light years,
22:04
Speaker 1: so stuff around us is moving away from us at
22:07
Speaker 1: forty six thousand miles per hour. For example, UM, if
22:10
Speaker 1: you move a million light years away, things are moving
22:13
Speaker 1: away from us another forty six thousand miles per hour.
22:16
Speaker 1: Things around this are moving away from us at forty
22:18
Speaker 1: six thousand miles per hour, but things a million light
22:21
Speaker 1: years from here are moving at what is it, ninety
22:24
Speaker 1: two thousand miles per hour, And if you go another
22:27
Speaker 1: million years further out, you add another forty six thousand
22:31
Speaker 1: miles per hour that it's moving away from us exactly.
22:34
Speaker 1: And this is changing because as the universe expands, matter
22:38
Speaker 1: and radiation and all that stuff gets diluted, right, it
22:40
Speaker 1: gets thinned out. It's like fewer stars per cubic light year.
22:44
Speaker 1: But dark energy, dark energy does and dark energy is
22:47
Speaker 1: like a property of space. Every new chunk of space
22:50
Speaker 1: that's made has its own dark energy. So dark energy,
22:53
Speaker 1: we think, is probably constant in time while everything else
22:57
Speaker 1: is getting diluted. And that's why the universe started excel
23:00
Speaker 1: rating about five billion years ago, because it's about five
23:02
Speaker 1: billion years ago that dark energy became the dominant thing.
23:05
Speaker 1: It became of the energy density of any chunk of space.
23:09
Speaker 1: The emptier space is, the I guess, the easier it
23:13
Speaker 1: is for dark energy to expand. It is that kind
23:16
Speaker 1: of what you're saying, that like, as it gets emptier
23:18
Speaker 1: and emptier, it's easier for its expand and so it
23:20
Speaker 1: expands fast. Precisely, there's some complicated general relativity there. The
23:23
Speaker 1: expansion of the universe is controlled by how much matter
23:26
Speaker 1: there is and how much radiation there is, which tends
23:28
Speaker 1: to pull it together, and then also how much dark
23:30
Speaker 1: energy there is, which tends to push it apart. And
23:33
Speaker 1: so as matter and radiation get diluted away, dark energy
23:36
Speaker 1: takes over. And and that's assuming that dark energy is constant.
23:40
Speaker 1: That when you create new space, you get more dark energy,
23:43
Speaker 1: and so that's what's causing this acceleration. There's less gravity,
23:47
Speaker 1: I guess right, precisely. And so really what we're doing,
23:51
Speaker 1: we're measuring the Hubble constants. We're trying to get a
23:53
Speaker 1: handle on the dark energy. Like what fraction in the
23:56
Speaker 1: universe is dark energy? We'd like to know about that now.
23:59
Speaker 1: We'd also like you know about that in the future,
24:01
Speaker 1: like is dark energy going to tear our universe apart?
24:04
Speaker 1: And we're curious about it in the past, like the
24:06
Speaker 1: very early universe, what fraction of the universe was dark energy?
24:09
Speaker 1: How do these things all work? Because we just don't
24:12
Speaker 1: understand dark energy like at all and so we know
24:14
Speaker 1: that the Hubble constant or this kind of proportion of
24:18
Speaker 1: dark energy is getting bigger, which means the universe is
24:22
Speaker 1: getting bigger at a faster rate every second right now,
24:26
Speaker 1: which is a little alarming. But I think what you
24:29
Speaker 1: were you were saying is that there's some kind of
24:31
Speaker 1: controversy about just how much dark energy there is because
24:34
Speaker 1: we measure different ways, but they don't come out the
24:38
Speaker 1: same number. That's kind of what Mike was asking about, right.
24:41
Speaker 1: These two physical quantities, the amount of dark energy and
24:44
Speaker 1: the Hubble parameter, they're connected, and so we measure them
24:47
Speaker 1: together and lost to different ways. And when we do that,
24:50
Speaker 1: we measure these using different techniques, we get different answers
24:54
Speaker 1: for the Hubble constant. So that's what he calls the
24:57
Speaker 1: unmatching Hubble constant mystery, precisely precisely, And we do this
25:01
Speaker 1: a lot in science. We say, here's something we think
25:03
Speaker 1: we understand. Let's measure it three different ways and see
25:06
Speaker 1: if it agrees. If it doesn't agree, then that we
25:09
Speaker 1: have to go back and question one of our assumptions.
25:11
Speaker 1: It's like a clue that's something new is going on.
25:14
Speaker 1: So it's a really valuable way to do things to
25:16
Speaker 1: measure something in independent ways and look for a mistake,
25:19
Speaker 1: because one of those ways could be like flawed, right,
25:23
Speaker 1: And so you want to make sure that if you
25:25
Speaker 1: look at it from different angles, it all looks the same. Yeah,
25:27
Speaker 1: one of the techniques could have a problem with it, right,
25:29
Speaker 1: and you don't want that bias to change the way
25:31
Speaker 1: you look at the universe. But also your assumptions that
25:34
Speaker 1: you make when you say, like, these two different techniques
25:37
Speaker 1: should give the same answer, maybe one of those assumptions
25:39
Speaker 1: is wrong. If you're watching a thunderstorm and you say, hey, well,
25:43
Speaker 1: you know how far away was that flash? I'm going
25:45
Speaker 1: to make an assumption about how far away it is
25:47
Speaker 1: based on how long the difference between when the light
25:50
Speaker 1: comes here and the sound comes here. You know, and
25:53
Speaker 1: somebody else makes the same measurement somewhere else, do they
25:56
Speaker 1: get the same answer? If not, that, you know, there's
25:58
Speaker 1: something wrong with your base assumptions. And so you want
26:01
Speaker 1: to make multiple measurements and that helps you check those
26:04
Speaker 1: basic assumptions. You kind of want to double check if
26:07
Speaker 1: you're going to make claims about the universe and the
26:10
Speaker 1: future and how big it is. Yeah, I mean these
26:12
Speaker 1: are grandios results. Yeah, absolutely, you definitely want to get
26:16
Speaker 1: this stuff right. Okay, So there's two ways to measure
26:18
Speaker 1: the Hubble constant or I guess the amount of dark
26:22
Speaker 1: energy in the universe, and they don't agree. So so
26:25
Speaker 1: what are these two ways? Well, the first one is
26:28
Speaker 1: just looking at the distance sladders, like how far away
26:30
Speaker 1: is stuff and what is its velocity? And we can
26:33
Speaker 1: measure the velocity by looking at how much the light
26:36
Speaker 1: from it is red shifted, meaning that if something is
26:39
Speaker 1: moving away from you at a certain speed, it changes
26:42
Speaker 1: the frequency of the light, like stretches the wavelength. And
26:46
Speaker 1: so we can tell how fast something is moving away
26:48
Speaker 1: from us by measuring its velocity directly, and we know
26:51
Speaker 1: how far stuff away is. So this is a natural
26:54
Speaker 1: extension of what Hubble did, and so we can use
26:56
Speaker 1: that basically just to measure directly how fast is stuff
26:59
Speaker 1: moving away from us? And that's I guess this is
27:01
Speaker 1: the most straightforward. I mean, I know it's not simple,
27:04
Speaker 1: but it's it's kind of the most direct way to
27:06
Speaker 1: measure the expansion of the universe. Is you just look
27:08
Speaker 1: at something really far away and you see how fast
27:11
Speaker 1: it's moving, and you look at something really close by
27:13
Speaker 1: and you measure how fast that move that's moving, and
27:16
Speaker 1: so that gives you the whole picture of how the
27:18
Speaker 1: the raising bread is expanded precisely. And the wrinkle there.
27:21
Speaker 1: The thing that makes it not trivial is that the
27:23
Speaker 1: stuff that's far away, we don't see what it's doing
27:26
Speaker 1: right now. We see what it was doing a billion
27:29
Speaker 1: years ago, for example, So we have to do some
27:31
Speaker 1: back calculation to account for the fact that some of
27:33
Speaker 1: the information we're getting is old. On the other hand,
27:36
Speaker 1: that's also a cool clue because it tells you how
27:39
Speaker 1: the expansion is changing over time. That's how we discovered
27:42
Speaker 1: that it was accelerating. We saw stuff really far away
27:46
Speaker 1: moving at a different speed than we expected. But isn't
27:48
Speaker 1: it easy to confuse the two, Like, if something far
27:50
Speaker 1: away is moving really fast, how do you know that
27:54
Speaker 1: it's a factor of the time that's passed in between
27:57
Speaker 1: or the factor of the distance it's from you. Well,
28:00
Speaker 1: we measure those two things separately, right, We measured the
28:03
Speaker 1: distance and the velocity totally separately. And once you know
28:06
Speaker 1: the distance, then you can calculate how long the information
28:08
Speaker 1: took to get here, and so we can sort of
28:10
Speaker 1: triangulate all that stuff. I mean, the best thing would
28:13
Speaker 1: be if we could get a complete snapshot of the
28:15
Speaker 1: universe at every time, then we could get all this
28:18
Speaker 1: crazy information and really triangulates stuff. You don't just get
28:21
Speaker 1: to wish for the data you want, You work with
28:22
Speaker 1: the data you have. I think the real triumph hear
28:25
Speaker 1: of physics here is is the acronym for this project.
28:29
Speaker 1: That's like such a great acronym. Yeah, this is called
28:31
Speaker 1: the Shoes Experiment Supernova each zero for equations of state.
28:38
Speaker 1: And I wish I'd been in that meeting where they
28:39
Speaker 1: were like coming up with acronyms of the white board
28:42
Speaker 1: to to explain this thing. I always wonder about that.
28:46
Speaker 1: They're like did It's like do they try really hard?
28:51
Speaker 1: Do they? You know what sacrifices must you make the
28:53
Speaker 1: science to get the perfect acronym? I don't know what
28:57
Speaker 1: kind of grammatical sacrifices must you mean? That's not even
29:01
Speaker 1: the best slash worst acronym we're gonna talk about today.
29:03
Speaker 1: Hang on for later on we'll be talking about all right.
29:07
Speaker 1: So that's one way to measure the universe. It's just
29:09
Speaker 1: measure things and how fast they're moving and how far
29:12
Speaker 1: our way they are but we can also um do
29:15
Speaker 1: something more interesting, right, Yeah, we can look back at
29:18
Speaker 1: the very early universe. And we've talked about this on
29:21
Speaker 1: the podcast about the surface of last scattering, the moment
29:25
Speaker 1: that the universe went from a hot, opaque plasma and
29:28
Speaker 1: cooled down and ionized and formed atoms that light could
29:31
Speaker 1: fly through, and the light from that plasma, it's called
29:34
Speaker 1: the cosmic microwave background, still flying around through the universe
29:38
Speaker 1: because after that moment, the universe became transparent. And so
29:41
Speaker 1: we get this light from the cosmic microwave background, and
29:44
Speaker 1: we look at it and we look at all the
29:45
Speaker 1: wiggles in it, and we can extract an incredible amount
29:48
Speaker 1: of information from these wiggles, and the most important thing
29:52
Speaker 1: that we pull out of that is we get the
29:54
Speaker 1: fraction of the universe that is matter and the fraction
29:56
Speaker 1: of that universe that was dark energy. But that's really
29:59
Speaker 1: far back in time, at the time of the Big
30:01
Speaker 1: Bank basically, right, Yeah, relatively speaking, it's three hundred thousand
30:05
Speaker 1: years after the Big Bang, and we're getting a sense
30:08
Speaker 1: for what was going on back then. And if you
30:11
Speaker 1: look at it online, look for the cosmic microwave background,
30:14
Speaker 1: it looks just like a massive it looks like a
30:16
Speaker 1: giant soup, and and so and so. But you're saying,
30:20
Speaker 1: you guys, have you know, special formulas that really look
30:24
Speaker 1: into the what the soup looks like. And you can
30:28
Speaker 1: firm that you can tell a lot of things like
30:30
Speaker 1: how much dark energy that there was at the big
30:33
Speaker 1: after the Big band, But how do you how did
30:35
Speaker 1: you extrapolate that to now? Because didn't you tell me
30:38
Speaker 1: that it's changing. Yeah, so we look at this bubbling
30:40
Speaker 1: soup and precisely the arrangement of bubbles and the size
30:43
Speaker 1: of the bubbles tells you a lot about the competing
30:46
Speaker 1: forces on the soup. And some of those forces aren't matter.
30:48
Speaker 1: They're pulling it together, and some of its dark energy
30:51
Speaker 1: that's pushing it apart. And the important thing to understand
30:53
Speaker 1: is we're not measuring the hubble constant itself back then
30:56
Speaker 1: there weren't even stars back then. Or measuring is how
30:59
Speaker 1: much dark energy there was. And you're right, we measured
31:01
Speaker 1: dark energy how much there was back then. And then
31:04
Speaker 1: what we do is we just assume that dark energy
31:06
Speaker 1: hasn't changed. The dark energy is constant, that that every
31:10
Speaker 1: unit of space has the same amount of dark energy
31:12
Speaker 1: now as it did back then. Wasn't there less space
31:14
Speaker 1: back there? So that means there's more dark energy now,
31:18
Speaker 1: there's more dark energy now. Um, it's a bigger fraction
31:21
Speaker 1: in the universe. Right now dark energy dominates the universe.
31:23
Speaker 1: But in the early days it was a tiny irrelevant
31:25
Speaker 1: bit player because most of the energy density was in
31:28
Speaker 1: the form of matter and radiation. But then as the
31:31
Speaker 1: universe expands, that dilutes and now matters like really spread thin.
31:35
Speaker 1: Oh wait, you're saying that, like a cube of like
31:38
Speaker 1: a cubic meter of space always has the same amount
31:41
Speaker 1: of dark energy, no matter if it was now or
31:46
Speaker 1: before when the universe was smaller. That is the key assumption.
31:49
Speaker 1: We are assuming that we think that might be the case.
31:51
Speaker 1: That's sort of the simplest idea. And what we're doing
31:54
Speaker 1: by measuring the Hubble constant or the expansion of the
31:56
Speaker 1: universe at different times, is trying to probe whether that
31:59
Speaker 1: idea is wrecked. And so, assuming that dark energy is constant,
32:03
Speaker 1: you measure what it was back in the time of
32:05
Speaker 1: the Big Bang, you propagate that forward. You can get
32:08
Speaker 1: a number for the Hubble constant, assuming of course, that
32:12
Speaker 1: dark energy is constant and that radiation and matter have
32:15
Speaker 1: just diluted. We don't know that dark energy is constant.
32:17
Speaker 1: We're assuming that. And if you assume that, then you
32:20
Speaker 1: get a number. And this number is different than the
32:23
Speaker 1: number you get when you measure the velocity of the stars. Yeah,
32:27
Speaker 1: if you look at the velocity of stars, you get
32:28
Speaker 1: a number like seventy four with an uncertainty like one
32:31
Speaker 1: and a half units of kilometers per second per megaparsic.
32:35
Speaker 1: But if you look at the early universe, you get
32:38
Speaker 1: a number like sixty seven point three with a smaller
32:41
Speaker 1: uncertainty like half. And so those two numbers, you know,
32:44
Speaker 1: they're different by you know, seven, and the uncertainty item
32:47
Speaker 1: is pretty small. And both of those teams have been
32:50
Speaker 1: working really hard to make their measurements more and more precise.
32:53
Speaker 1: And as the measurements get more and more precise, the
32:55
Speaker 1: numbers have not been getting close together. The errors have
32:58
Speaker 1: been getting smaller, but the numbers have not been changing
33:00
Speaker 1: because you know, as a as someone who's not a physicist,
33:03
Speaker 1: I would look at these numbers and think, oh, that's
33:05
Speaker 1: pretty good. Seventy four sixty seven, what's ten percent different?
33:09
Speaker 1: Government work, you're not good enough to make for engineering.
33:14
Speaker 1: But the key thing here is understanding your uncertainties, like
33:17
Speaker 1: how well do you know these things? And people spend
33:19
Speaker 1: a lot of time, like many many peach DTCs, understanding
33:22
Speaker 1: what are the uncertainties on our distance measurements to supernova
33:26
Speaker 1: or coming up with other ways to make these distance
33:29
Speaker 1: measurements to cross check, or understanding the uncertainties in the
33:32
Speaker 1: cosmic microwave background. And you've got to know those uncertainties
33:35
Speaker 1: so you know how well do I know this thing?
33:37
Speaker 1: Because if you don't know how well you know it,
33:38
Speaker 1: you can't answer the question are these two numbers in
33:41
Speaker 1: agreement or not? So a lot of the work goes
33:44
Speaker 1: into nailing down the size of these uncertainties to knowing
33:47
Speaker 1: how well you know something. So that's the mystery, then,
33:50
Speaker 1: is that we're trying to measure how much dark energy
33:52
Speaker 1: there is in the universe, which is making it grow bigger.
33:56
Speaker 1: And if we measure look at it one way, it's
33:58
Speaker 1: it says there should be seventy four of this dark energy.
34:01
Speaker 1: If you look at it another way, it says it
34:02
Speaker 1: should be sixty seven. And that's that bothers a lot.
34:06
Speaker 1: It bothers them because it seems really unlikely to be
34:10
Speaker 1: an accident. Like, if there really is one Hubble constant
34:13
Speaker 1: and both of these things are measuring the same number,
34:15
Speaker 1: then what are the chances of getting two numbers that
34:18
Speaker 1: are this far apart. It's like we've done into calculation,
34:21
Speaker 1: we do the statistics, and it's like one in ten thousand.
34:24
Speaker 1: So it seems really unlikely. A much more likely explanation
34:27
Speaker 1: is that there's something wrong, either something wrong with our
34:30
Speaker 1: assumptions or something wrong with one of these measurements. All right, well,
34:33
Speaker 1: let's dig into what could explain this mystery and what
34:37
Speaker 1: it means for the future of the universe and for
34:40
Speaker 1: you and for me, and but and for the people
34:44
Speaker 1: for whom the universe is for, but not the people
34:46
Speaker 1: for for whom the universe is not for. But first,
34:51
Speaker 1: let's take a quick break. All right, we have a
35:06
Speaker 1: disagreement in physics in the measurement of how much dark
35:09
Speaker 1: energy there is in the universe. And so how do
35:12
Speaker 1: you guys decide? Do you just fight it out? Do
35:14
Speaker 1: you get into a boxing ring or cage or something
35:18
Speaker 1: and you throw a couple of pencils in and see
35:20
Speaker 1: what happens? Are Yeah, it's too physicist grappling with whiteboard
35:24
Speaker 1: markers and calling each other's faces and stuff. Um, well,
35:28
Speaker 1: maybe one side as a chalk on the other side
35:30
Speaker 1: as a marker. Now, it's all actually very friendly, incongenial,
35:35
Speaker 1: and everybody wants to understand it, and it's sort of
35:38
Speaker 1: a good situation. You know, when you make one of
35:40
Speaker 1: these discoveries that two measurements you make of the same
35:43
Speaker 1: thing don't agree, it's a clue, it's a sign. And
35:46
Speaker 1: that's what we're looking for. We are trying to understand
35:49
Speaker 1: the universe, not just confirm what we thought. And so
35:52
Speaker 1: when the universe tells you that you're understanding is wrong,
35:55
Speaker 1: that's it's the first clue to getting new understanding. And
35:59
Speaker 1: so they're getting room and they try to think, like, well,
36:01
Speaker 1: what could explain this? Is one of us doing it
36:03
Speaker 1: wrong or is one of our assumptions wrong, And that's
36:07
Speaker 1: I think is the most exciting explanation. Right. Well, I
36:09
Speaker 1: have a favorite, Daniel, I don't know if you have
36:12
Speaker 1: a favorite. I like seventy four more than I like.
36:19
Speaker 1: I mean, like one of one of these measurements seems
36:21
Speaker 1: more direct to me, Like if you're measuring the speed
36:25
Speaker 1: of the stars directly through my telescopes. That seems a
36:28
Speaker 1: lot more direct than like looking at a picture of
36:30
Speaker 1: the universe fourteen billion years ago, and then it's replating it. Like,
36:35
Speaker 1: do you guys have a favorite? Do you think one
36:37
Speaker 1: of them in particular is probably wrong? Or what's the
36:41
Speaker 1: general feeling? Well, I like the one from the early
36:44
Speaker 1: universe because it's just so clean and precise, Like you
36:47
Speaker 1: don't need to know how far away anything is, or
36:50
Speaker 1: make some extrapolation from this kind of star and the
36:52
Speaker 1: other kind of star and sort of walk up the ladder.
36:54
Speaker 1: There's a lot of assumptions involved in those distance measurements.
36:57
Speaker 1: Whereas the cosmic microwave background so pure and clean and
37:02
Speaker 1: so much about it works. It's predicted and been confirmed
37:05
Speaker 1: in so many other ways that we have this model
37:08
Speaker 1: of the universe that just really holds together. It's hard
37:10
Speaker 1: to imagine how that is wrong. And so I like
37:13
Speaker 1: that measurement. I'm not sure why. It's maybe just an
37:16
Speaker 1: aesthetic thing. You do have a favorite. I do have
37:18
Speaker 1: a favor. I've just admitted on areas well. So there's
37:24
Speaker 1: some possible explanations that for what could be wrong, right,
37:28
Speaker 1: that's because something must be wrong if these measurements are
37:30
Speaker 1: not matching up. So what's what's a possible explanation. I
37:34
Speaker 1: think one of the favorite explanations of cosmologists is this
37:37
Speaker 1: thing called dynamical dark energy, the idea that dark energy
37:41
Speaker 1: isn't maybe just like a property of space and constant
37:44
Speaker 1: that for every cubic meter is basically the same dark energy,
37:47
Speaker 1: but maybe it's changing in time as the age of
37:50
Speaker 1: the universe. I have to say, holy cow, that's amazing,
37:53
Speaker 1: and that would help resolve because remember, we have this
37:56
Speaker 1: measurement from the early universe that's measuring one dark energy
37:59
Speaker 1: for action that gives you a Hubble constant, and these
38:02
Speaker 1: more recent measurements from nearby stars and supernovas that give
38:06
Speaker 1: you a more recent measurement. So one way to make
38:08
Speaker 1: those two things agrees to say you're not actually measuring
38:11
Speaker 1: the same thing. The thing you're measuring, it's is itself changing.
38:14
Speaker 1: So you're saying, um, one possible explanation is that the
38:18
Speaker 1: Hubble constant, which is not a constant, is actually measuring
38:21
Speaker 1: something that is not a constant. You constantly amaze with
38:25
Speaker 1: your understanding. That's kind of what you say. I feel
38:29
Speaker 1: like that's kind of what you're saying it's not only
38:31
Speaker 1: not a constant, but what you're it's measuring is not
38:33
Speaker 1: a constant. That's right. And to shroud our previous mistakes,
38:36
Speaker 1: we slap a cool label on it and call it dynamical, right, yeah,
38:40
Speaker 1: d D. And then, of course, you know another thing
38:42
Speaker 1: we do is to try to like get an unbiased
38:45
Speaker 1: third estimate, Like, let's come up with a third way
38:47
Speaker 1: to measure this and see if it agrees with one
38:50
Speaker 1: or the other two. Let's do this democratically, let's take
38:53
Speaker 1: a vote. You're saying, there's a third way now to
38:56
Speaker 1: measure this dark energy in the universe, and I think
38:59
Speaker 1: it deserves a Nobel prize right away, just in its
39:04
Speaker 1: awesome acronym. Well, it's an acronym that contains acronyms. So
39:08
Speaker 1: they call it the Holy Cow experiment, uh aged zero
39:13
Speaker 1: lenses in Cosmo Girl well spring, right, and so Cosmo
39:18
Speaker 1: Girl is the name of another experiment that stands for
39:21
Speaker 1: something else. And so these guys have used data from
39:24
Speaker 1: the Cosmo Girl experiment to try to measure the expansion
39:28
Speaker 1: rid of the universe totally independently. Wow, I mean that's
39:32
Speaker 1: just genius in acronym. It's like not only are you
39:36
Speaker 1: betting an acronym in an acronym, that you're betting a
39:39
Speaker 1: whole different project in this project acronym. And then if
39:43
Speaker 1: they discover something awesome, they get to shout, holy cow,
39:45
Speaker 1: we discovered it, Holy cow, holy cow did it. And
39:51
Speaker 1: this is another way essentially to measure how far things
39:54
Speaker 1: are away, and it uses gravitational lenses and says, let's
39:58
Speaker 1: say you have a really bright source of light, like
40:00
Speaker 1: a quasar, and then between you and that source of
40:03
Speaker 1: light is a is a big lens, like a big galaxy.
40:05
Speaker 1: Because remember, galaxies have a lot of gravity, and gravity
40:08
Speaker 1: bend space, so it can act like a lens. And
40:11
Speaker 1: what happens is then that quasar gets distorted and you
40:14
Speaker 1: get multiple versions of it arriving here at Earth because
40:17
Speaker 1: the galaxy between you and the quasar has lensed it.
40:20
Speaker 1: You know, sometimes you get like weird and duplication effects
40:23
Speaker 1: and a lens and so somehow that tells you something
40:26
Speaker 1: about how it's expanding. The university expanding, Yeah, because the
40:29
Speaker 1: different images take different amounts of time to get here,
40:32
Speaker 1: and these quasars flicker as you can watch these different
40:36
Speaker 1: images flicker, and by how much time there is between
40:39
Speaker 1: the flickering in one image and the other image, you
40:42
Speaker 1: can tell essentially how much space it's gone through. And
40:45
Speaker 1: so the delay between the two different images gives you
40:48
Speaker 1: a sense for how far away the original quasar was.
40:51
Speaker 1: Is it kind of like lightning and thunder like precisely
40:55
Speaker 1: you see it and you hear it, and you use
40:56
Speaker 1: those two things to figure out how far away the
40:59
Speaker 1: lightning was and how bright it was. Precisely, that's exactly
41:02
Speaker 1: the way we do it. And so this is a
41:03
Speaker 1: totally different way because it doesn't rely on supernova, doesn't
41:06
Speaker 1: rely on sephids or the other stuff. It's another way
41:08
Speaker 1: to make the distance measurement. And their measurement agrees with
41:12
Speaker 1: the supernova measurement, really with my favorite measurement, not you.
41:17
Speaker 1: I should have said it agrees with you. That was
41:19
Speaker 1: their announcement. Actually, holy cow agrees with cartoon. Holy Cow
41:26
Speaker 1: cartoon is nailed it. The only person surprised was the cartoonist.
41:34
Speaker 1: So so it's agreeing with one of the measurements, which
41:37
Speaker 1: is measuring measuring the stars themselves. And so then, um,
41:41
Speaker 1: doesn't that close the argument doesn't that you know, and
41:44
Speaker 1: the mystery it doesn't because remember they're measuring things at
41:46
Speaker 1: different times in the universe, and so this would have
41:49
Speaker 1: been problematic for the supernova measurement if it had disagreed,
41:52
Speaker 1: because they're measuring the same thing and sort of the
41:54
Speaker 1: same epic of the universe, and they really should This
41:57
Speaker 1: is like confirmation of the supernova measument. And but the
42:01
Speaker 1: early universe one from the cosmic microwave background is measuring
42:04
Speaker 1: something older, and so it could still be that they're
42:07
Speaker 1: both right. And the explanation is that dark energy is changing. Oh,
42:11
Speaker 1: I see, it's it's like there you could say that
42:13
Speaker 1: it's not wrong. It's just that a change between when
42:16
Speaker 1: I measured it and now. Yeah, it's like I didn't
42:19
Speaker 1: get the answer wrong on the test. I was just
42:20
Speaker 1: answering a different question. Maybe this tells us that this
42:24
Speaker 1: dark energy constant is changing or has changed since the
42:27
Speaker 1: beginning of time. Yeah, it could be. Um, there's a
42:30
Speaker 1: lot of things we can do to check the cosmic
42:31
Speaker 1: microwave background radiation measurement, and they've done all those checks
42:34
Speaker 1: and it all works out and it really seems very convincing.
42:37
Speaker 1: It's hard to imagine how they would get that number wrong.
42:40
Speaker 1: On the other hand, the supernova measurement now has independent
42:43
Speaker 1: verification from a completely different way to measure these distances.
42:47
Speaker 1: So it's hard to understand how that one could be wrong.
42:49
Speaker 1: So I think we're going to have to rethink our
42:52
Speaker 1: fundamental understanding of what's going on with dark energy. Right,
42:56
Speaker 1: Maybe dark energy not a constant after all. Maybe it's cool.
43:00
Speaker 1: Maybe we should never be assuming things are constant. You know,
43:02
Speaker 1: that's just sort of like the physics things like, don't
43:06
Speaker 1: call constants constance. We're constantly making that mistake. Well, um,
43:11
Speaker 1: it sounds then, though, that this mystery is getting resolved
43:15
Speaker 1: as we speak right now, So Mike and Madison stay tuned.
43:19
Speaker 1: It sounds like, as we speak, we're resolving this mystery. Yeah,
43:23
Speaker 1: and other stuff is gonna come online to sort of
43:25
Speaker 1: give us more pictures of this. We can use things
43:28
Speaker 1: like gravitational waves from neutron stars collisions to try to
43:32
Speaker 1: measure the distance to things. So that's gonna give us
43:34
Speaker 1: another measurement and hopefully that can peer further back in
43:37
Speaker 1: time than the quasars are. The supernova so we really
43:41
Speaker 1: need to do is get another measurement of dark energy
43:43
Speaker 1: in the very early universe. And so people have ideas
43:46
Speaker 1: for how we might do that, and gravitational waves might help,
43:49
Speaker 1: and so stay tuned. This cosmic mystery might eventually get resolved,
43:53
Speaker 1: and it might get resolved in a way that totally
43:55
Speaker 1: up ends our understanding of the entire universe. But I
43:58
Speaker 1: think one thing is here, which is the mind blowing part,
44:01
Speaker 1: which is that it's pretty clear. And now I guess
44:04
Speaker 1: three measurements that the universe is expanding, and it's expanding
44:08
Speaker 1: faster and faster, like this is not a theory anymore. No,
44:11
Speaker 1: that's for sure. Nobody, no reasonable scientists disagrees with that.
44:15
Speaker 1: It's even more well understood than climate change. Of scientists,
44:20
Speaker 1: that's right. All the scientists except the ones that go
44:22
Speaker 1: on Fox News, believe the universe is expanding and that
44:25
Speaker 1: expansion is accelerating. So I guess, yeah, the next time
44:28
Speaker 1: you can go out there and look at the night sky,
44:30
Speaker 1: just think about maybe the future. You know, in the future,
44:34
Speaker 1: things are going to be even bigger. The future is big.
44:37
Speaker 1: It's looking big, and it's also uncertain because if dark
44:40
Speaker 1: energy is changing, we don't know what's changing it, why
44:43
Speaker 1: it's changing, and how it's planning to change in the future.
44:47
Speaker 1: Is dark energy gonna get stronger and stronger. Is it
44:49
Speaker 1: gonna stop dissipate? Turn around, go the other direction. We
44:52
Speaker 1: really just can't predict the future because we have no
44:55
Speaker 1: understanding of this dominant source of energy in the universe. Alright,
44:59
Speaker 1: so stay two and thank you Mike for sending us
45:02
Speaker 1: this question. If you have a question about the universe
45:06
Speaker 1: or about something that you've always wondered about or read about,
45:11
Speaker 1: send it to us and we will try to answer it.
45:13
Speaker 1: Thanks to everybody who sends in their questions. Remember questions
45:16
Speaker 1: at Daniel and Jorge dot com is your fastest route
45:19
Speaker 1: to an answer about the universe. I hope you enjoyed that.
45:22
Speaker 1: Thanks for joining us. See you next time. Before you
45:32
Speaker 1: still have a question after listening to all these explanations,
45:35
Speaker 1: please drop us a line. We'd love to hear from you.
45:38
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45:41
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45:44
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45:48
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45:51
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