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Is the standard model of dark energy in trouble? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: Physics lets us ask big, fat, juicy questions about the universe.
• 0:11
  Speaker 1: I would claim that these are the biggest, the fattest,
• 0:14
  Speaker 1: the juiciest questions, though chemists and biologists may disagree, of course.
• 0:19
  Speaker 1: But physics lets us discover.
• 0:21
  Speaker 2: New elements of the universe, like dark matter, that tell
• 0:24
  Speaker 2: us our whole picture of what the universe is made
• 0:26
  Speaker 2: of was wrong.
• 0:27
  Speaker 1: It lets us think about the size of the entire
• 0:30
  Speaker 1: universe and whether it's expanding. It gives us the tools
• 0:34
  Speaker 1: that will let us discover the forces that are capable
• 0:36
  Speaker 1: of squeezing and stretching galaxies and clusters and structures beyond
• 0:41
  Speaker 1: even our capacity to hold in our minds. Probably the
• 0:45
  Speaker 1: most powerful and mysterious discovering physics maybe ever is dark energy.
• 0:51
  Speaker 1: The accelerating expansion of the universe has changed our picture
• 0:54
  Speaker 1: of where the energy in the cosmos is, what it does,
• 0:57
  Speaker 1: and how it shapes the present and future of the
• 1:00
  Speaker 1: entire universe. Will things be torn apart, left to huddle
• 1:04
  Speaker 1: together with a few other bits of matter among a
• 1:07
  Speaker 1: vast empty cosmos? Will things rush back together to collapse
• 1:11
  Speaker 1: everything in everyone into incredible density, mimicking the conditions of.
• 1:15
  Speaker 2: The early universe, only dark energy has the sheer scale
• 1:19
  Speaker 2: and scope to determine the faith of the universe, which
• 1:23
  Speaker 2: is why we are all so desperate to understand it.
• 1:26
  Speaker 2: And dark energy is recent, a concept from the last
• 1:29
  Speaker 2: couple of decades, which means we have a lot left
• 1:32
  Speaker 2: to learn and that surprises deliciously await us. Recently, you
• 1:36
  Speaker 2: might have heard that our understanding of dark energy was
• 1:39
  Speaker 2: thrown into new disarray by some recent measurements. What does
• 1:42
  Speaker 2: that mean about dark energy? What does it mean for
• 1:45
  Speaker 2: our understanding of the universe? What does it mean about
• 1:47
  Speaker 2: the future of the universe? Should you still say for
• 1:51
  Speaker 2: retirement or just fly to Vegas tomorrow and blow it
• 1:53
  Speaker 2: all in a weekend of excess and debauchery. Will dig
• 1:56
  Speaker 2: into the history and the latest mystery and let physics
• 1:59
  Speaker 2: do its best to answer these questions. Welcome to Daniel
• 2:03
  Speaker 2: and Kelly's Extraordinary Expanding Universe.
• 2:20
  Speaker 3: Hello.
• 2:20
  Speaker 4: I'm Kelly wider Smith and I study space and parasites
• 2:23
  Speaker 4: and I am so glad we have finally figured out
• 2:25
  Speaker 4: dark energy, Right Daniel, That's what we're talking about today,
• 2:30
  Speaker 4: isn't it?
• 2:32
  Speaker 2: Wow? What a setup? What a setup?
• 2:35
  Speaker 5: Hi?
• 2:35
  Speaker 2: I'm Daniel, I'm a particle physicist, and I wish I
• 2:39
  Speaker 2: was as cool as dark energy sounds.
• 2:41
  Speaker 4: Oh, it does sound pretty cool. You all are really
• 2:44
  Speaker 4: hit and miss in terms of naming stuff, but with
• 2:47
  Speaker 4: dark energy and dark matter, the goth in me really
• 2:49
  Speaker 4: digs it.
• 2:50
  Speaker 2: Yeah. I don't know if they're appropriate in the sense
• 2:52
  Speaker 2: that they describe it well, but they do sound very cool.
• 2:56
  Speaker 2: And you know that's one angle.
• 2:57
  Speaker 4: For sure, you know for sure. So what per scent
• 3:00
  Speaker 4: of the articles that you see online about dark matter
• 3:04
  Speaker 4: and dark energy do you feel are like completely accurate.
• 3:09
  Speaker 2: Completely accurate? Wow, that is a small fraction. Unfortunately, there
• 3:13
  Speaker 2: is so much clickbait nonsense out there, and that really
• 3:17
  Speaker 2: disappoints me because I imagine if I wasn't an expert
• 3:20
  Speaker 2: and I was curious, like lots of our listeners are,
• 3:22
  Speaker 2: who want to understand the universe in good faith, they
• 3:25
  Speaker 2: read these things and they don't know whether it's nonsense
• 3:27
  Speaker 2: or not. So if you're out there and you're reading
• 3:30
  Speaker 2: an article and it tickles your nonsensimeter, feel free to
• 3:33
  Speaker 2: send it to us. I will let you know if
• 3:35
  Speaker 2: you should believe it or not. But unfortunately, on average
• 3:38
  Speaker 2: the answer is no. Because science journalism is hard and
• 3:42
  Speaker 2: getting all the nuances right, is very very hard.
• 3:45
  Speaker 4: Yeah, that's true. But I got to say, you know
• 3:47
  Speaker 4: Ed Young for example, So he's our biology king of
• 3:51
  Speaker 4: science journalism, and he does a really good job of
• 3:54
  Speaker 4: like running stuff by people to check. So, like, you
• 3:57
  Speaker 4: can't possibly know everything as a science journalist if you're
• 4:00
  Speaker 4: covering a broad range of topics. But I do feel
• 4:02
  Speaker 4: like if you run it by experts, like why aren't
• 4:04
  Speaker 4: you getting an email every single day from like people
• 4:07
  Speaker 4: writing about this to be like, hey, can I run
• 4:09
  Speaker 4: it by an expert before I put it online?
• 4:11
  Speaker 2: Mm hmm, Yeah, Well there's a lot to dig into there.
• 4:13
  Speaker 2: I think that a lot of folks don't run things
• 4:16
  Speaker 2: by experts. They read other popular science coverage and get
• 4:20
  Speaker 2: their information from there, because not that many experts are accessible.
• 4:24
  Speaker 2: You know, professors don't usually answer their emails, though some
• 4:27
  Speaker 2: of us do, and they don't respond on time, and
• 4:30
  Speaker 2: you have a deadline, and so instead of talking to
• 4:32
  Speaker 2: somebody who is a professor about dark matter, you read
• 4:35
  Speaker 2: a bunch of other articles about dark matter, especially if
• 4:38
  Speaker 2: you're not a physicist yourself, so you can't read the
• 4:40
  Speaker 2: primary literature and decode those weird scientific squiggles. So yeah,
• 4:44
  Speaker 2: I think a lot of us are inaccessible. But hey,
• 4:46
  Speaker 2: that's what this podcast is about, right, is making all
• 4:48
  Speaker 2: this science accessible without dumbing it down, digging deep into
• 4:52
  Speaker 2: what's actually going on, and giving everybody out there and
• 4:55
  Speaker 2: understanding and an opportunity to ask questions. So, if you're
• 4:59
  Speaker 2: a science journalist and you want to write an article
• 5:01
  Speaker 2: about dark matter and dark energy and you have a
• 5:03
  Speaker 2: question or something you don't think you fully understand, don't
• 5:06
  Speaker 2: write about it. If you don't understand it, ask me
• 5:08
  Speaker 2: and I will explain it to you.
• 5:10
  Speaker 4: There you go. Well, today we are tackling a topic
• 5:12
  Speaker 4: that is really making the rounds that is not quite accurate.
• 5:17
  Speaker 4: Is that safe to say?
• 5:18
  Speaker 2: I think there's a lot of coverage of this issue
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  Speaker 2: which misses a lot of the important details.
• 5:23
  Speaker 4: Yeah, okay, all right. So the question we're asking today
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  Speaker 4: is is the standard model of dark energy in trouble?
• 5:31
  Speaker 4: And I'll be honest, I thought the standard model just
• 5:33
  Speaker 4: referred to a thing and I didn't think that it
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  Speaker 4: included dark energy. So are there multiple standard models or
• 5:38
  Speaker 4: does the standard model I'm thinking of also encompass dark energy?
• 5:43
  Speaker 2: So the standard model you're probably thinking of is the
• 5:45
  Speaker 2: standard model of particle physics, and you're right, that does
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  Speaker 2: not encompass dark energy. In fact, it doesn't include anything
• 5:50
  Speaker 2: about gravity. It's just the quantum forces and the particles
• 5:53
  Speaker 2: and that kind of stuff. So that's of particle physics.
• 5:56
  Speaker 2: There's another standard model of cosmology, sometimes called LAMB to CDM,
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  Speaker 2: and that's like our picture of the history of the
• 6:05
  Speaker 2: universe and how it expands and dark matter and dark
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  Speaker 2: energy and all of those things. It's sort of the
• 6:10
  Speaker 2: standard model of cosmology.
• 6:12
  Speaker 4: Okay, that sounds super interesting.
• 6:14
  Speaker 2: Yeah, And this is sort of standard model in a
• 6:16
  Speaker 2: lower case sense. Standard model of particle physics often written
• 6:19
  Speaker 2: with upper case sense and just refers to as the
• 6:21
  Speaker 2: standard model. But you know, you could have a standard
• 6:24
  Speaker 2: model of I don't know, parasite interactions are something I imagine, right,
• 6:28
  Speaker 2: And it's sort of just like the normal usage of the.
• 6:30
  Speaker 4: Words, and for that one it would be capital letters
• 6:34
  Speaker 4: the best standard model or the most interesting standard model.
• 6:38
  Speaker 4: But anyway, moving on, we asked our audience, is the
• 6:42
  Speaker 4: standard model of dark energy in trouble? And here's what
• 6:46
  Speaker 4: they had to say.
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  Speaker 5: Yes, because recent research has indicated that dark energy weakens
• 6:51
  Speaker 5: over time and therefore is not constant as astrophysicists first belief.
• 6:56
  Speaker 6: I would say yes, and I wouldn't be surprised about it.
• 6:59
  Speaker 5: So quantum energy that disagrees with the Standard model, So yes.
• 7:03
  Speaker 1: Well, what would you expect if all you do is
• 7:06
  Speaker 1: hide out in shadowy places and make yourself unknown.
• 7:10
  Speaker 2: Of course you'd get into trouble.
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  Speaker 7: The cosmological constant is not a constant, so yeah, I'd
• 7:16
  Speaker 7: say it could be in trouble.
• 7:17
  Speaker 2: This can only be a good thing, as we are
• 7:19
  Speaker 2: becoming one step closer to understanding the truth.
• 7:22
  Speaker 5: Given how little we understand today of dark energy, I
• 7:25
  Speaker 5: really hope the latest findings do put the model in trouble,
• 7:29
  Speaker 5: because otherwise, what's it going to do? Run away from
• 7:32
  Speaker 5: us at an accelerating rate.
• 7:34
  Speaker 3: Forever I didn't think the Standard model included dark matter
• 7:38
  Speaker 3: or dark energy. So I'm going to surmise that the
• 7:41
  Speaker 3: Standard model is not in trouble.
• 7:44
  Speaker 6: Judging from the headlines, I would say yes.
• 7:48
  Speaker 7: So I'm just curious.
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  Speaker 2: Woul the Standard model of dark energy have to hear
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  Speaker 2: to the principal's office, have to hire a lawyer, have
• 7:55
  Speaker 2: to appear before Congress.
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  Speaker 6: It might well be in trouble. From some of the headlines,
• 8:01
  Speaker 6: you read, but a lot to go further. And so
• 8:08
  Speaker 6: what doctor Dan's got to say.
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  Speaker 7: Dark energy may be changing over time and may not
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  Speaker 7: at all be constant. The standard model of dark energy
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  Speaker 7: is no longer in line with data that's coming in.
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  Speaker 7: So yeah, I think it needs to go to the
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  Speaker 7: principal's office.
• 8:26
  Speaker 2: I seem to remember hearing something about the expansion of
• 8:33
  Speaker 2: space being variable. Is that something to do with it?
• 8:38
  Speaker 2: Wasn't worried that there was a standard model for dark energy,
• 8:40
  Speaker 2: but I suppose the question being asked assumes that it is. Yes.
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  Speaker 4: As always, I love you. All the answers are either
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  Speaker 4: deeply insightful or absolutely hilariou and so thank you for
• 9:01
  Speaker 4: writing in.
• 9:02
  Speaker 2: You two can participate send us your response to the
• 9:06
  Speaker 2: questions of the day. Just write to us to questions
• 9:08
  Speaker 2: at Danielankelly dot org and we will hook you up.
• 9:12
  Speaker 4: What did you think of these responses?
• 9:14
  Speaker 2: I thought there were great, some very insightful, some totally hilarious,
• 9:17
  Speaker 2: some echoing your question about like hold on, if you're
• 9:20
  Speaker 2: talking about the standard model that already doesn't include dark
• 9:22
  Speaker 2: matter and dark energy, So yeah, great stuff.
• 9:26
  Speaker 4: Yeah, I bet there were a bunch of people who
• 9:27
  Speaker 4: are like this is another trick question from Daniel because
• 9:29
  Speaker 4: he loves those.
• 9:31
  Speaker 2: They're not trick questions. It's just that, you know, if
• 9:36
  Speaker 2: I'm asking about something, then we expect it's probably something
• 9:39
  Speaker 2: interesting we learned recently in the news.
• 9:42
  Speaker 4: So yeah, all right, well let's start from the beginning.
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  Speaker 4: What is dark energy? I mean, I know, because it's physics,
• 9:47
  Speaker 4: you're going to be like, oh, we don't know.
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  Speaker 2: It's great to define these terms because, like just in philosophy,
• 9:56
  Speaker 2: you can avoid a lot of talking past each other
• 9:59
  Speaker 2: if you're clear out what you mean. And so the
• 10:02
  Speaker 2: best way to understand dark energy is to understand that
• 10:05
  Speaker 2: it's just our observation of how the universe is expanding
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  Speaker 2: and accelerating. And that's a very recent observation and s important.
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  Speaker 2: I think that put that in historical context. And remember,
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  Speaker 2: like what we used to think was happening to the universe,
• 10:19
  Speaker 2: what we used to think was natural or made sense
• 10:21
  Speaker 2: only like one hundred years ago, before Hubble and Levitt
• 10:25
  Speaker 2: and those folks, we thought the universe was static. We
• 10:28
  Speaker 2: thought it was just a single galaxy, just a bunch
• 10:31
  Speaker 2: of stars hanging out in space, and that was it.
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  Speaker 2: That was the universe, and it wasn't shrinking, it wasn't expanding.
• 10:37
  Speaker 2: There weren't stars that went on forever. It's just like one,
• 10:40
  Speaker 2: our little blob of stars hanging out in space. And
• 10:42
  Speaker 2: that was people's mental picture of the universe. Your mental picture,
• 10:46
  Speaker 2: probably influenced by wonderful programs like Nova and pictures from
• 10:49
  Speaker 2: James Webb, is of a universe filled with galaxies upon
• 10:52
  Speaker 2: galaxies upon galaxies. It's a very different context, and for me,
• 10:56
  Speaker 2: the context of our lives. That's what physics is about, right,
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  Speaker 2: So this like is a complete shit in the universe
• 11:02
  Speaker 2: we think we're living in.
• 11:03
  Speaker 4: I mean, if there were more parasites in space, I'd
• 11:05
  Speaker 4: probably be way more excited. But that is an inspirational
• 11:09
  Speaker 4: thing to think about.
• 11:10
  Speaker 2: The day that James web Space Telescope discovers space parasites,
• 11:13
  Speaker 2: I'm also gonna be excited about parasites.
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  Speaker 4: Oh that's what it would dig.
• 11:19
  Speaker 2: At a minimum. All right. So before Hubble, we think
• 11:22
  Speaker 2: there's just one galaxy hanging in space and that's natural,
• 11:26
  Speaker 2: and people imagine, like, oh, it's probably been like that forever,
• 11:28
  Speaker 2: because why wouldn't it be. You know, the idea of
• 11:31
  Speaker 2: an infinite past was sort of fine, not a big deal.
• 11:35
  Speaker 2: But then Hubble and Henriette eleven figured out a way
• 11:38
  Speaker 2: to measure the distance to stuff. This is really important
• 11:41
  Speaker 2: because when you're looking out into space and you're looking
• 11:43
  Speaker 2: at a star, you can't tell, hey, is that star
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  Speaker 2: incredibly bright but really far away so it looks kind
• 11:49
  Speaker 2: of dim or actually kind of dim and like not
• 11:52
  Speaker 2: terribly far away. Cosmologically speaking, you can't tell the difference
• 11:55
  Speaker 2: if you're just looking at the intensity of the star
• 11:57
  Speaker 2: because you don't know how bright it actually is. And
• 12:00
  Speaker 2: if you want to make a three D map of
• 12:02
  Speaker 2: the universe, knowing how far away things are it is crucial, right,
• 12:05
  Speaker 2: because otherwise you're just looking at like the equivalent of
• 12:08
  Speaker 2: a two D screen that surrounds the Earth.
• 12:10
  Speaker 4: And so how do you calibrate so that you can
• 12:13
  Speaker 4: figure that stuff out?
• 12:14
  Speaker 2: Yeah, so we can actually tell how far away stuff
• 12:17
  Speaker 2: is if it's pretty close by using parallax. It's the
• 12:21
  Speaker 2: same principle that you can use to tell whether a
• 12:23
  Speaker 2: baseball is close to you or far away from you.
• 12:26
  Speaker 2: It's the fact that you have two eyes binocular vision,
• 12:29
  Speaker 2: and they give a different view of the same object,
• 12:32
  Speaker 2: and if something is close by, your eyes have a
• 12:34
  Speaker 2: very different perspective on them, and if something is far away,
• 12:37
  Speaker 2: they have basically the same perspective. Like if you hold
• 12:40
  Speaker 2: up your coffee cup in front of your face and
• 12:41
  Speaker 2: you close one eye and open the other one and
• 12:44
  Speaker 2: go back and forth, you can see that the picture
• 12:46
  Speaker 2: looks very different, and your brain uses that information to say, Okay,
• 12:49
  Speaker 2: the coffee cup is close. But if it's farther away
• 12:51
  Speaker 2: and you do the same thing, it's hardly a difference.
• 12:53
  Speaker 2: Your brain does all the math and tells you where
• 12:56
  Speaker 2: the baseball or the coffee cup is, So that's parallax.
• 12:59
  Speaker 2: We can do the same thing in space because the
• 13:01
  Speaker 2: Earth goes around the Sun and so over the year
• 13:04
  Speaker 2: we have different views of the cosmos. So if something
• 13:07
  Speaker 2: is pretty close to us, then it looks pretty different
• 13:10
  Speaker 2: from one side of the Sun and the other side
• 13:11
  Speaker 2: of the Sun, whereas if it's like a gazillion light
• 13:14
  Speaker 2: years away, that hardly matters. Wow, So we can use
• 13:17
  Speaker 2: that to measure the distance to nearby stuff.
• 13:19
  Speaker 4: So you've got to be pretty patient to figure this
• 13:21
  Speaker 4: stuff out then, because it's like six months or something
• 13:24
  Speaker 4: in between data collection moments.
• 13:26
  Speaker 2: Yeah, and this is actually the reason that the Greeks
• 13:29
  Speaker 2: got the solar system wrong. The Greeks knew about this method,
• 13:32
  Speaker 2: and they used this method and they tried to see
• 13:35
  Speaker 2: how far away the stars were, and they couldn't see
• 13:38
  Speaker 2: any wiggles at all. Because the stars are pretty far away,
• 13:41
  Speaker 2: they assumed they were pretty close, and so because they
• 13:44
  Speaker 2: didn't see the stars wiggling, they assumed the Earth doesn't
• 13:47
  Speaker 2: move around the Sun.
• 13:48
  Speaker 4: Oh, that's fascinating, but we have better instruments, so we
• 13:51
  Speaker 4: can calculate that. Is that the difference?
• 13:54
  Speaker 2: Yeah, exactly. It wasn't until like the eighteen hundreds that
• 13:56
  Speaker 2: we could see the stars wiggle because the wiggle is small, right,
• 13:59
  Speaker 2: And so with out those instruments and without the assumption
• 14:02
  Speaker 2: that the stars are close, you can actually tell how
• 14:05
  Speaker 2: much the stars are wiggling, and then you can tell
• 14:06
  Speaker 2: the distance to them. So the Greeks assumed the stars
• 14:09
  Speaker 2: were close and they couldn't see them wiggling, so they
• 14:10
  Speaker 2: assumed the flaw was that the Earth wasn't moving. Of course,
• 14:13
  Speaker 2: the Earth was moving, it's just that the stars were
• 14:15
  Speaker 2: further than they thought. Sort of fascinating history of like
• 14:19
  Speaker 2: what people think is natural.
• 14:20
  Speaker 4: That is a pretty clever way to try to figure
• 14:22
  Speaker 4: out if the Earth is moving or not. Like, good
• 14:24
  Speaker 4: on them, Yeah, exactly.
• 14:26
  Speaker 2: People are always dumping on the Greeks, including me for
• 14:29
  Speaker 2: many years for not doing empirical science. But like this
• 14:32
  Speaker 2: is a good example of coming up with a clever technique,
• 14:35
  Speaker 2: taking some data, using it to draw conclusions. And you know,
• 14:38
  Speaker 2: they got the wrong conclusion because they had one mistake
• 14:41
  Speaker 2: and assumption. But it's pretty solid work. Yeah, anyway, we
• 14:44
  Speaker 2: can do that for nearby stuff. More distant stuff is
• 14:47
  Speaker 2: hard because if it's not wiggling, you can't tell is
• 14:50
  Speaker 2: an a zillion miles away or two zillion or half
• 14:52
  Speaker 2: a zillion. And so what Levitt and Hubble figured out
• 14:55
  Speaker 2: was a way to measure the distant to more distant
• 14:58
  Speaker 2: stars by looking for a petique other kind of star
• 15:01
  Speaker 2: called cephids. Cephids are star that have variable brightness, Like
• 15:05
  Speaker 2: they're not just like the Sun that mostly burns the same.
• 15:08
  Speaker 2: They go brighter and dimmer and brighter and dimmer. And
• 15:10
  Speaker 2: that's because of stuff that's happening on the inside. There's
• 15:13
  Speaker 2: like hot layers that rise to the surface and then collapses,
• 15:16
  Speaker 2: like you know, crazy stellar chemistry going on.
• 15:19
  Speaker 4: There are they made out of different things than our sun.
• 15:22
  Speaker 2: It's definitely connected to what they're made out of it
• 15:24
  Speaker 2: because part of the star is opaque to its own radiation,
• 15:27
  Speaker 2: and so the glow from the inner part of the
• 15:30
  Speaker 2: star then pushes that part of the star out, and
• 15:33
  Speaker 2: so you have to have some sort of opaque layers.
• 15:35
  Speaker 2: And they think this might be involved with helium, but
• 15:38
  Speaker 2: it's not totally understood. There's some similar stuff going on
• 15:41
  Speaker 2: inside our star with layers of opacity and transparency. We
• 15:46
  Speaker 2: can talk about that another time we talk about the
• 15:48
  Speaker 2: solar magnetic field. But the cool thing about these stars
• 15:52
  Speaker 2: is that the variability in their brightness is very closely
• 15:55
  Speaker 2: connected to their actual brightness. So if you, for example,
• 15:59
  Speaker 2: watch one of these and you say, oh, it goes
• 16:01
  Speaker 2: bright and dim in the period of a day or
• 16:03
  Speaker 2: five days or ten days, you can use that to
• 16:06
  Speaker 2: determine how bright it actually is. So you can measure
• 16:09
  Speaker 2: the actual brightness of it just by measuring its variability.
• 16:13
  Speaker 4: Wow, okay, all right, So now we know about variability
• 16:16
  Speaker 4: of brightness and we know how it appears to change
• 16:19
  Speaker 4: as you move locations. And what do those two pieces
• 16:22
  Speaker 4: of information tell us?
• 16:23
  Speaker 2: So they allow us to weave together what we call
• 16:25
  Speaker 2: a distance ladder for nearby stuff we use parallax, and
• 16:29
  Speaker 2: then near the edge of our abilities to do parallax,
• 16:31
  Speaker 2: there are some sephids, some of these variable stars, and
• 16:33
  Speaker 2: we can use parallax to calibrate the cephids, and then
• 16:36
  Speaker 2: we can use sephids to go even further. Because if
• 16:39
  Speaker 2: you know how bright a star is actually it's true brightness,
• 16:42
  Speaker 2: and then you measure its brightness here on Earth, you
• 16:44
  Speaker 2: can tell how far away it is. That was the
• 16:46
  Speaker 2: missing piece, right, we didn't know if this star is
• 16:48
  Speaker 2: bright and far away or dim and close. But now
• 16:51
  Speaker 2: because we know whether it's actually bright or actually dim,
• 16:54
  Speaker 2: we can tell if it's close or far by its
• 16:56
  Speaker 2: apparent brightness here on Earth. And the crucial thing is
• 16:59
  Speaker 2: that these two las matters, the parallax and the cephids overlap,
• 17:02
  Speaker 2: so it's a period where we can use parallax to
• 17:05
  Speaker 2: calibrate the cephids and then extrapolate further for stuff that
• 17:08
  Speaker 2: we couldn't use parallax for. And this gave Hubble this
• 17:11
  Speaker 2: incredible three dview of the universe we didn't have before.
• 17:15
  Speaker 2: He could tell the distance to all kinds of stuff
• 17:17
  Speaker 2: that nobody knew. Hey, is that actually a smudge in
• 17:20
  Speaker 2: the sky but pretty close, or is it something incredible
• 17:23
  Speaker 2: and massive but deeply, deeply distant?
• 17:26
  Speaker 4: And is this how he figured out that the universe
• 17:28
  Speaker 4: was expanding because things changed their location over time.
• 17:32
  Speaker 2: Well, Number one, he discovered that there are other galaxies.
• 17:35
  Speaker 2: We used to see these things in the sky, and
• 17:37
  Speaker 2: we called them nebulae because there were sort of like
• 17:38
  Speaker 2: smudge in our telescopes, and people were like, hmm, maybe
• 17:41
  Speaker 2: they're just big clouds of gas. It turns out no,
• 17:43
  Speaker 2: they're actually entire galaxies that are much bigger in many
• 17:47
  Speaker 2: cases than our galaxy, like Andromeda, so much bigger than
• 17:50
  Speaker 2: our galaxy. He was able to unravel this puzzle because
• 17:53
  Speaker 2: he could measure the distance to them. He found cephids
• 17:55
  Speaker 2: in those nebulae, and he was able to tell, oh
• 17:57
  Speaker 2: my gosh, that thing is so much further away than
• 18:00
  Speaker 2: anything else, any of the other stars. It's its own galaxy.
• 18:04
  Speaker 4: Oh my god.
• 18:06
  Speaker 2: Instantly, this like mental picture of the universe just expands
• 18:09
  Speaker 2: from we have one galaxy with some fuzzy clouds in it,
• 18:12
  Speaker 2: to take all those fuzzy clouds and promote them to
• 18:14
  Speaker 2: their own super distant, incredibly large galaxies, and the universe
• 18:18
  Speaker 2: now filled with galaxies. That's often overlooked in the story
• 18:22
  Speaker 2: about the expanding universe, because what Hubble actually discovered is
• 18:25
  Speaker 2: that the universe is filled with galaxies, not just.
• 18:29
  Speaker 4: Our own and around When was that happening.
• 18:31
  Speaker 2: This is the nineteen twenties, so this is like one
• 18:33
  Speaker 2: hundred years ago. Right, most of humanity had no idea
• 18:37
  Speaker 2: that this was the case, But you're right. The other
• 18:40
  Speaker 2: crucial thing that Hubble discovered is he was able to
• 18:42
  Speaker 2: measure the apparent velocity of these galaxies by looking at
• 18:46
  Speaker 2: the light that came from the galaxies and how it
• 18:48
  Speaker 2: was shifted by velocity. If something is moving away from you,
• 18:51
  Speaker 2: its wavelengths are lengthened, and if it's moving towards you,
• 18:54
  Speaker 2: its wavelength are shrunk. And so if something is red shifted,
• 18:58
  Speaker 2: it means it's moving away from you. And all the
• 19:00
  Speaker 2: galaxies were red shifted, and the ones that were further
• 19:03
  Speaker 2: were red shifted more. And so this is Hubble's discovery
• 19:06
  Speaker 2: that there's a close relationship between the distance to a
• 19:09
  Speaker 2: galaxy and it's apparent velocity. Things that are close by
• 19:12
  Speaker 2: are moving away from us slowly, Things that are further
• 19:14
  Speaker 2: away and moving away from us faster. Things that are
• 19:17
  Speaker 2: very very distant, are moving away from us even faster.
• 19:21
  Speaker 2: So this is Hubble's view of the expanding universe. And
• 19:23
  Speaker 2: this was like second mind blowing revelation. Not only is
• 19:27
  Speaker 2: the universe filled with galaxies, they're all running away from us.
• 19:30
  Speaker 1: Yeah.
• 19:30
  Speaker 4: Right, So if everything is running away from us, does
• 19:32
  Speaker 4: that mean that we're the stinky galaxy or does that
• 19:35
  Speaker 4: mean that we're at the center of everything? Or like,
• 19:38
  Speaker 4: why is everything moving away from us?
• 19:40
  Speaker 2: Mm hmm. Everything is moving away from us, but everything
• 19:43
  Speaker 2: is moving away from everything. The whole universe is expanding
• 19:47
  Speaker 2: the mental picture in your mind. Actually, velocity is not
• 19:50
  Speaker 2: the best way to think about it, because when we
• 19:53
  Speaker 2: get to acceleration in a minute, somebody's going to be like,
• 19:55
  Speaker 2: hold on, Daniel said, you could measure acceleration. Acceleration is absolute,
• 19:58
  Speaker 2: and they're going to be right. The right way to
• 20:00
  Speaker 2: think about it is in terms of expansion. Space is growing,
• 20:05
  Speaker 2: so everywhere space is just stretching, which is why the
• 20:08
  Speaker 2: raisin bread analogy is actually kind of perfect, like all
• 20:11
  Speaker 2: the raisins and the raisin bread are getting further away
• 20:13
  Speaker 2: from all the other raisins. No matter where you look
• 20:16
  Speaker 2: in the universe, everything is moving away from you. It's
• 20:19
  Speaker 2: not because we're in the center. We're not special. There
• 20:21
  Speaker 2: is no center.
• 20:22
  Speaker 1: Everywhere in the universe sees everything moving away from it.
• 20:26
  Speaker 4: Well, I also try to move away from raisins as
• 20:28
  Speaker 4: much as I can. But all right, so where do
• 20:31
  Speaker 4: we go from here?
• 20:32
  Speaker 2: So Hubble measured this relationship between the velocity of distant
• 20:35
  Speaker 2: galaxies and their distance from us. If you plot those
• 20:38
  Speaker 2: on a graph, you get a straight line. The slope
• 20:40
  Speaker 2: of that line is the Hubble constant. Is this relationship
• 20:43
  Speaker 2: between them? And this we know now is a number
• 20:46
  Speaker 2: that's something like seventy kilometers per second per megaparsek, which
• 20:52
  Speaker 2: essentially is a measurement of the expansion rate of the universe.
• 20:55
  Speaker 2: It's not a velocity, it's a velocity per distance because
• 20:59
  Speaker 2: as distance is grow, the apparent velocity the galaxies are
• 21:02
  Speaker 2: moving away from each other with grows also, so you
• 21:06
  Speaker 2: can't like compare this to the speed of light has
• 21:07
  Speaker 2: the wrong units. But this is the crucial number. It
• 21:10
  Speaker 2: tells us how fast is the universe expanding. And it's
• 21:14
  Speaker 2: called the Hubble constant, even though it's not a constant.
• 21:17
  Speaker 4: Thanks physics time, I know.
• 21:20
  Speaker 2: But we have now this new view of the universe
• 21:23
  Speaker 2: that everything is expanding, And for decades and decades, that's
• 21:27
  Speaker 2: what people thought was happening. The universe was expanding, And
• 21:29
  Speaker 2: then we're wondering about the future, like, hmm, is it
• 21:32
  Speaker 2: going to continue to expand or is gravity going to
• 21:34
  Speaker 2: eventually win and pull all these galaxies back together into
• 21:38
  Speaker 2: some sort of big crunch. That was the big question
• 21:41
  Speaker 2: being asked in like the nineteen nineties when people tried
• 21:44
  Speaker 2: to look even further into space.
• 21:46
  Speaker 4: That sounds existential. But don't be scared. We're going to
• 21:49
  Speaker 4: give you some more information when we get back from
• 21:51
  Speaker 4: the break. All right, we're back. Daniel just made us
• 22:12
  Speaker 4: all a little bit nervous that the universe might have
• 22:14
  Speaker 4: a big crunch at some point where everything sort of
• 22:17
  Speaker 4: smooshes back in on itself. So Daniel, help me sleep tonight.
• 22:21
  Speaker 4: Give me some more information.
• 22:22
  Speaker 2: Well, I can sell you some big crunch insurance if
• 22:24
  Speaker 2: you like. It's a really big payout. If the universe
• 22:26
  Speaker 2: collapses into a mega black hole, you will get a
• 22:30
  Speaker 2: big deposit in your bank account. How about that.
• 22:32
  Speaker 4: Doesn't make any sense. I'm not convinced.
• 22:36
  Speaker 2: Some people just buy insurance to feel better. Remember those
• 22:39
  Speaker 2: folks who were buying like Y two K insurance, Like
• 22:42
  Speaker 2: they say, if society collapses, we will helicopter you a
• 22:45
  Speaker 2: bunker with weapons and food and whiskey. And I was like,
• 22:48
  Speaker 2: they're never getting that delivery como.
• 22:51
  Speaker 4: No, I've started researching having pigs, and I've been watching
• 22:55
  Speaker 4: videos about pigs. And one of the videos, you know, nonchalantly,
• 22:58
  Speaker 4: they said, oh, no, it was geese. It was geese.
• 23:00
  Speaker 4: I've been researching a lot of animals lately.
• 23:02
  Speaker 2: Anyway, it's not that easy to confuse pigs and geese.
• 23:06
  Speaker 4: Well, I want both of them.
• 23:08
  Speaker 2: Make sure you click the right button when you order,
• 23:10
  Speaker 2: because and I hate to be the one to bring
• 23:12
  Speaker 2: up cannibalism. Oh, pigs will eat your children and geese
• 23:14
  Speaker 2: will not.
• 23:15
  Speaker 4: That's true, and pigs will lead each other, as we
• 23:17
  Speaker 4: learned in the Trick and Ella episode. Anyway, one of
• 23:19
  Speaker 4: the videos that I was watching in a totally nonchalant
• 23:22
  Speaker 4: voice was like, well, and from a prepper perspective, and
• 23:25
  Speaker 4: I was like, oh, this is the community that I'm
• 23:27
  Speaker 4: associated with. Now my interests aligned with this community, all right. Anyway,
• 23:32
  Speaker 4: back to dark energy.
• 23:33
  Speaker 2: So in the nineteen nineties, we wanted to look even
• 23:35
  Speaker 2: further into space to understand the broader scope of this expansion,
• 23:39
  Speaker 2: because the further we look into space, the further back
• 23:41
  Speaker 2: we look in time, right, because remember light travel at
• 23:44
  Speaker 2: finite speed, and so if something is happening across the
• 23:47
  Speaker 2: universe right now, we can't see it for billions of years.
• 23:51
  Speaker 2: But when we do look out deep into the universe
• 23:53
  Speaker 2: and we see life that has taken billions of years
• 23:55
  Speaker 2: to get here, we're seeing things that happen billions of
• 23:58
  Speaker 2: years ago. So if you want to tell timeline of
• 24:00
  Speaker 2: the expansion of the universe so you can better predict
• 24:03
  Speaker 2: the future, for example, like what is the trajectory, it's
• 24:06
  Speaker 2: useful to look further into the universe and to know
• 24:08
  Speaker 2: how far away is that stuff and how quickly is
• 24:11
  Speaker 2: it moving away from us. That gives you like a
• 24:13
  Speaker 2: deeper picture and lets you extrapolate to the future. And
• 24:16
  Speaker 2: sephids are cool, but only if you can pick them
• 24:19
  Speaker 2: out right, Only if you can find an isolated sephid
• 24:21
  Speaker 2: in that distant galaxy so you can identify it. That
• 24:25
  Speaker 2: works great for stars and for regions of our galaxy,
• 24:28
  Speaker 2: and for nearby galaxies it's okay, But thinking about really
• 24:31
  Speaker 2: distant galaxies in the early universe. Sephid's basically peter out.
• 24:35
  Speaker 2: So we needed a new technique, a new element of
• 24:38
  Speaker 2: our distance ladder to look further into the universe and
• 24:40
  Speaker 2: into the history of the expansion.
• 24:43
  Speaker 4: Okay, and I keep asking tell us about dark energy,
• 24:46
  Speaker 4: but we don't really get to it. So it is
• 24:47
  Speaker 4: dark energy going to be the answer?
• 24:48
  Speaker 8: Now?
• 24:50
  Speaker 2: We're just about to get to the dark energy because
• 24:53
  Speaker 2: in the nineties people figured out another standard candle. These
• 24:56
  Speaker 2: are Type one A supernova, and these are incredible collisions
• 24:59
  Speaker 2: when a new on star which failed to go nova
• 25:01
  Speaker 2: or failed to become a black hole, gobbles up a
• 25:04
  Speaker 2: little extra bit of matter and goes supernova in this
• 25:07
  Speaker 2: very precise, very predictable way, the light curve rises and
• 25:10
  Speaker 2: then it drops. And it's not that all Type one
• 25:13
  Speaker 2: A supernova are the same, but from the shape of
• 25:15
  Speaker 2: the light curve you can determine the true brightness, just
• 25:18
  Speaker 2: like what the cephids. There's something you can measure without
• 25:20
  Speaker 2: knowing the distance that tells you the true brightness, and
• 25:23
  Speaker 2: then from the true brightness and the apparent brightness you
• 25:25
  Speaker 2: can tell the actual distance. And Type one A supernova
• 25:28
  Speaker 2: are perfect for looking deep into the universe because they're
• 25:32
  Speaker 2: incredibly mind bogglingly bright, like a Type one A supernova
• 25:36
  Speaker 2: can be brighter than its entire galaxy for a moment.
• 25:40
  Speaker 4: Oh my god.
• 25:41
  Speaker 2: So people realize this and then there's a huge race.
• 25:43
  Speaker 2: There was a team in Australia and a team at
• 25:45
  Speaker 2: Berkeley that realized if they gathered enough of these Type
• 25:48
  Speaker 2: one A supernova and watch them, they can make a
• 25:50
  Speaker 2: three D map of the universe that dwarfed Hubbles map
• 25:53
  Speaker 2: and when deeper in the history of the universe, which
• 25:55
  Speaker 2: would allow us to make a fit and project and
• 25:57
  Speaker 2: predict what's going to happen for the future of the
• 25:59
  Speaker 2: universe verse. Like, what an exciting moment when you realize
• 26:02
  Speaker 2: you have an ability just on this tiny little planet
• 26:05
  Speaker 2: in the corner of the universe to understand the fate
• 26:07
  Speaker 2: of the entire costmos Like, oh my god, drunk with power, Right.
• 26:12
  Speaker 4: Were you at Berkeley at this time? This was before you.
• 26:15
  Speaker 2: All this stuff was happening while I was at Berkeley.
• 26:17
  Speaker 2: I was not involved in it at all, but yeah,
• 26:19
  Speaker 2: I knew it was happening at the time. It was
• 26:21
  Speaker 2: really exciting and they were like really racing. Both teams
• 26:24
  Speaker 2: knew that, like, okay, we know how to do this,
• 26:25
  Speaker 2: and it's going to take a few months. Let's not
• 26:27
  Speaker 2: be scooped. Yeah, in the end, it was kind of
• 26:29
  Speaker 2: a big tie, which is great. But they discovered something shocking,
• 26:33
  Speaker 2: you know. They discovered that the expansion of the universe
• 26:35
  Speaker 2: is not slowing down, and it's not just continuing smoothly.
• 26:38
  Speaker 2: It's speeding up. Right. That's dark energy. Dark energy is
• 26:43
  Speaker 2: the observation that the expansion of the universe is accelerating,
• 26:47
  Speaker 2: that year after year, this quantity we call the Hubble
• 26:50
  Speaker 2: constant is going to be growing. The expansion of the
• 26:53
  Speaker 2: universe is increasing.
• 26:54
  Speaker 4: And I remember that you told us in a prior
• 26:56
  Speaker 4: episode what is energy or how where does energy come from?
• 26:59
  Speaker 4: That as the universe expands, it seems like more dark
• 27:02
  Speaker 4: energy is made. Is that right? But I'm still having
• 27:06
  Speaker 4: trouble thinking of dark energy as the expansion of the universe.
• 27:11
  Speaker 4: Is it like the battery that's fueling the motion outward?
• 27:15
  Speaker 4: How do I think of this?
• 27:17
  Speaker 2: Yeah, So the phrase dark energy is sometimes used to
• 27:19
  Speaker 2: describe this observation. We know the universe is expanding and
• 27:22
  Speaker 2: that expansion is accelerating, and then naturally you're like, well,
• 27:25
  Speaker 2: what's doing it? What's an explanation, Daniel, what's the theory
• 27:29
  Speaker 2: of it? And there are a few possible explanations for
• 27:32
  Speaker 2: what could be creating this accelerating expansion, and sometimes they
• 27:35
  Speaker 2: are described as dark energy, but really they're all very
• 27:39
  Speaker 2: loose placeholders. And the sort of leading candidate until recently
• 27:44
  Speaker 2: was what you described, the idea that space might have
• 27:48
  Speaker 2: some inherent energy within it, a potential energy, and energy
• 27:52
  Speaker 2: in general relativity is complicated. A lot of people think, oh,
• 27:54
  Speaker 2: general relativities tells us energy makes curvature, you know, just
• 27:58
  Speaker 2: like mass and anything causes things to collapse. But general
• 28:02
  Speaker 2: relativity is complicated. We talked about in our Potato episode.
• 28:05
  Speaker 2: Different kind of energies contribute differently, and if you have
• 28:07
  Speaker 2: potential energy in all the space, it actually creates repulsive gravity,
• 28:11
  Speaker 2: pushes things apart, it accelerates the expansion of the universe.
• 28:15
  Speaker 2: So on one hand we observe the accelerating expansion of
• 28:18
  Speaker 2: the universe. On the other hand, we have a way
• 28:21
  Speaker 2: within general relativity to create accelerating expansion of the universe.
• 28:24
  Speaker 2: It's a knob there. It's called the cosmological constant. And
• 28:28
  Speaker 2: just put this number into the equations and say, if
• 28:31
  Speaker 2: space has this energy inherently in it, then that would
• 28:34
  Speaker 2: cause the accelerating expansion. Now we haven't observed that energy directly.
• 28:38
  Speaker 2: It's not like we found that energy, not like we
• 28:41
  Speaker 2: identified where it comes from or what quantum field it
• 28:43
  Speaker 2: would be or whatever. It's just like, Okay, this number
• 28:47
  Speaker 2: would work if we could figure out if that's what's
• 28:49
  Speaker 2: really happening. But that number, as you say, assumes dark
• 28:52
  Speaker 2: energy is constant. That you make more space, you get
• 28:55
  Speaker 2: more dark energy, and that predicts a very specific way
• 28:59
  Speaker 2: in which dark energy grows rows over time because it
• 29:02
  Speaker 2: actually starts to take over as the universe expands. Matter
• 29:06
  Speaker 2: gets diluted, right, you have the same number of protons
• 29:08
  Speaker 2: more space, its density goes down. Radiation gets diluted even
• 29:12
  Speaker 2: more because it also gets red shifted, but dark energy doesn't.
• 29:16
  Speaker 2: But a cosmological constant dark energy. See just used it
• 29:18
  Speaker 2: to describe the explanation, not the observation. It doesn't get diluted.
• 29:23
  Speaker 2: It's the universe expands more space. It's a constant in space,
• 29:26
  Speaker 2: and so therefore it goes up in its fraction. And
• 29:30
  Speaker 2: the naive prediction then of the future is that dark
• 29:32
  Speaker 2: energy just is a runaway effect because as the universe expands,
• 29:36
  Speaker 2: its density is the same, which means it's overall fraction
• 29:38
  Speaker 2: keeps rising. So that's sort of the standard model of cosmology.
• 29:43
  Speaker 2: Until very recently people were like, well, look, this works
• 29:45
  Speaker 2: pretty well. We have some dark energy, we have some
• 29:47
  Speaker 2: dark matter, we have this history of stuff, how matter
• 29:50
  Speaker 2: used to dominate, how radiation used to dominate, how as
• 29:53
  Speaker 2: the universe expands, those things change, and that described things
• 29:56
  Speaker 2: pretty well, and people are like, Okay, let's really nail
• 29:59
  Speaker 2: it down. Let's measure things super duper precisely in lots
• 30:02
  Speaker 2: of different ways and make sure we always get a
• 30:04
  Speaker 2: consistent answer, because if so, that tells us we know
• 30:07
  Speaker 2: what we're doing. Over the last few years, though, there's
• 30:09
  Speaker 2: been some tension in this concept, this standard model of cosmology,
• 30:14
  Speaker 2: and it goes by the name of the Hubble tension,
• 30:16
  Speaker 2: and it's old news, but it's important to keep in
• 30:18
  Speaker 2: your mind when we talk about the new news and
• 30:21
  Speaker 2: dark energy, because the two tell very different stories about
• 30:25
  Speaker 2: the future. So the Hubble tension is like a great
• 30:28
  Speaker 2: piece of science. You know, anytime you see somebody new
• 30:30
  Speaker 2: in the universe, you want to check your assumptions. You
• 30:33
  Speaker 2: want to measure three different ways with different assumptions, because
• 30:36
  Speaker 2: that could reveal that, oh, actually we don't know what
• 30:38
  Speaker 2: we're doing, or no, we really do understand this. Like
• 30:41
  Speaker 2: you know, we saw the top cork of the tepatron,
• 30:42
  Speaker 2: we measured its properties. Then we measured it in completely
• 30:45
  Speaker 2: different collisions and a different collider in a different country,
• 30:47
  Speaker 2: with different detectors and different people. We got the same numbers.
• 30:50
  Speaker 2: We're like, Okay, probably was there. We got that right.
• 30:53
  Speaker 2: If not, we'd be upset, right, or we'd be confused
• 30:56
  Speaker 2: and we'd think there's a hint. So they did the
• 30:59
  Speaker 2: same thing with measuring the Hubble constant. The measurement I
• 31:02
  Speaker 2: told you about is what we call the late universe measurement.
• 31:05
  Speaker 2: We're looking at the expansion in recent times. We're using parallax,
• 31:09
  Speaker 2: we're using cephids, we're using type one a supernova. That's
• 31:12
  Speaker 2: like you know, in the last ten billion years of
• 31:14
  Speaker 2: the expansion of the universe, they can't penetrate all the
• 31:17
  Speaker 2: way to the very beginning because you need toype on
• 31:19
  Speaker 2: a supernova and they do eventually get dim But that's
• 31:22
  Speaker 2: what we call the late universe measurement. So you measure that,
• 31:25
  Speaker 2: you get one number for the Hubble constant, it's like
• 31:28
  Speaker 2: seventy four kilometers per second per mega parsek and a
• 31:32
  Speaker 2: lot of careful work has been done there because like,
• 31:34
  Speaker 2: what if you don't understand supernova, what are they are
• 31:36
  Speaker 2: different kinds of supernova? What if the life is passing
• 31:39
  Speaker 2: through different stuff? And there's like entire batteries of people
• 31:42
  Speaker 2: whose entire PhD was like thinking about a way maybe
• 31:46
  Speaker 2: this went wrong and finding some clever way to check it.
• 31:49
  Speaker 2: It's incredible what folks are doing in astrophysics.
• 31:52
  Speaker 4: So you had mentioned that the Hubble constant isn't actually constant,
• 31:55
  Speaker 4: it's a number that's changing. So that number that you
• 31:57
  Speaker 4: gave us, is that a value for March twenty third
• 32:01
  Speaker 4: or okay.
• 32:02
  Speaker 2: Yeah, it's the recent measurement, right, it's the late time
• 32:05
  Speaker 2: expansion number. But you can also measure this in the
• 32:08
  Speaker 2: early universe because if we look at the most ancient
• 32:11
  Speaker 2: light in the universe, the cosmic microwave background light, so
• 32:14
  Speaker 2: light from when the universe was very dense, it was
• 32:16
  Speaker 2: a hot plasma and it was glowing and suddenly it
• 32:19
  Speaker 2: became transparent. So instead of that light continuously being emitted
• 32:23
  Speaker 2: and absorbed, it was just emitted, not absorbed and is
• 32:26
  Speaker 2: still around. And if you look at that light, you
• 32:28
  Speaker 2: can learn so much about the density of the universe
• 32:31
  Speaker 2: and what it was made out of. You can tell
• 32:33
  Speaker 2: how much dark matter there was, you can tell the
• 32:35
  Speaker 2: expansion rate, you can tell how much matter there was.
• 32:37
  Speaker 2: It's really incredibly rich, and we could have a whole
• 32:40
  Speaker 2: other episode digging into that science. But essentially what you
• 32:43
  Speaker 2: can do is from the wiggles in the cosmic microwave
• 32:46
  Speaker 2: background radiation, you can measure the expansion rate of the universe,
• 32:50
  Speaker 2: and then you can propagate that forward and say, if
• 32:52
  Speaker 2: we measure the number from the early universe, what number
• 32:55
  Speaker 2: should we measure today. So now you can compare these
• 32:57
  Speaker 2: two numbers apples to apples, and the CNB measurement, what
• 33:01
  Speaker 2: we call the early time measurement, propagated forward to compare,
• 33:05
  Speaker 2: gives us a different number, gives us a number like
• 33:07
  Speaker 2: sixty seven. And when these two numbers came out, people
• 33:10
  Speaker 2: were like, hmm, that's weird, but you know, the uncertainties
• 33:13
  Speaker 2: were kind of big, like sixty seven isn't that different
• 33:15
  Speaker 2: from seventy four if they both have like a plus
• 33:18
  Speaker 2: or minus ten on them. But as people spent more
• 33:21
  Speaker 2: time and more energy. Whittling down these uncertainties and measuring
• 33:25
  Speaker 2: these more precisely. The numbers didn't change, just the uncertainty shrink.
• 33:29
  Speaker 2: And now we're like, yeah, these are two different numbers.
• 33:32
  Speaker 2: And that's a concern because if it's right, it means
• 33:34
  Speaker 2: dark energy can't be constant. It means like, maybe dark
• 33:38
  Speaker 2: energy is growing with time, right, dark energy, it was
• 33:41
  Speaker 2: weaker and now it's stronger in late times. So this
• 33:44
  Speaker 2: is the sort of context for these recent measurements by
• 33:48
  Speaker 2: Daisy and dark energy. We're going to talk about in
• 33:50
  Speaker 2: a minute. Dark energy, this incredible story of discovering the
• 33:53
  Speaker 2: accelerating expansion of the universe, an attempt to describe it
• 33:56
  Speaker 2: using a simple model, the cosmological constant, which requires dark
• 33:59
  Speaker 2: energy be constant in space and therefore grow in a
• 34:03
  Speaker 2: certain way. But then our observation, this hubble tension, that
• 34:06
  Speaker 2: it doesn't quite work, that our measurements from the early
• 34:08
  Speaker 2: universe and our measurements from the late universe don't jibe
• 34:11
  Speaker 2: with the way we think dark energy operated, that maybe
• 34:14
  Speaker 2: it wasn't a constant in space, right, Maybe that whole
• 34:17
  Speaker 2: assumption was wrong. Maybe it's not a cosmological constant. Maybe
• 34:20
  Speaker 2: it's some other weird thing that's sort of similar but
• 34:22
  Speaker 2: not quite so that was sort of the context for
• 34:24
  Speaker 2: this recent study.
• 34:26
  Speaker 4: Okay, so the tension is that seventy four is not
• 34:29
  Speaker 4: sixty seven.
• 34:30
  Speaker 2: That's right. And remember to explain this tension, you need
• 34:33
  Speaker 2: some theory where dark energy is getting stronger recently.
• 34:36
  Speaker 4: All right, Well, let's take a break and when we
• 34:38
  Speaker 4: come back, we're going to find out what this new
• 34:40
  Speaker 4: experiment tells us about this tension. And also, I hope
• 34:43
  Speaker 4: one day there'll be a Wiener Smith conflict to match
• 34:46
  Speaker 4: the Hubble tension.
• 34:51
  Speaker 8: Well, it's good to have goals, and zionis Yeah.
• 35:10
  Speaker 4: All right, we're back. So, Daniel, you were telling us
• 35:12
  Speaker 4: about the Hubble tension and that labs have been working
• 35:16
  Speaker 4: hard to try to figure out what is causing this
• 35:18
  Speaker 4: difference between the two different measures for the expansion of
• 35:20
  Speaker 4: the universe. What have we learned recently?
• 35:23
  Speaker 2: Yeah, so there's been a lot of really interesting stuff
• 35:25
  Speaker 2: happening with dark energy, including new theories like I want
• 35:28
  Speaker 2: to spend one minute talking about this time scape theory.
• 35:30
  Speaker 2: A lot of people heard about huge pr echo chamber
• 35:33
  Speaker 2: from this one paper where somebody suggested that wait, maybe
• 35:37
  Speaker 2: the universe isn't actually accelerating in its expansion. Maybe we've
• 35:40
  Speaker 2: messed it all up. And his theory was that time
• 35:43
  Speaker 2: is slowed down near massive objects. We know that to
• 35:46
  Speaker 2: be true, so maybe the universe is act lumpier than
• 35:49
  Speaker 2: we thought, and they're parts of it that are denser,
• 35:51
  Speaker 2: and that's affecting the way we're interpreting this stuff. And
• 35:55
  Speaker 2: so this theory went by the very cool name of
• 35:57
  Speaker 2: time scape around the internet, and I got a bunch
• 36:01
  Speaker 2: of emails and a bunch of listeners heard about it
• 36:03
  Speaker 2: and thought, oh my gosh, are we getting rid of
• 36:04
  Speaker 2: dark energy? And that would be very cool, and we're
• 36:07
  Speaker 2: open to that. But this theory requires the universe to
• 36:09
  Speaker 2: be a lot lumpier than we see it to be,
• 36:12
  Speaker 2: like it would require a lot more mass in areas
• 36:14
  Speaker 2: to create this kind of effect. So the data just
• 36:18
  Speaker 2: are not consistent with the timescape theory. Nobody I know
• 36:21
  Speaker 2: in cosmology is taking that seriously at all, even though
• 36:24
  Speaker 2: we got a lot of press. So there's not often
• 36:26
  Speaker 2: a lot of correlation between like how excited the science
• 36:30
  Speaker 2: journalism core is about an idea and how excited the
• 36:32
  Speaker 2: actual scientists are about an idea. But there is something
• 36:36
  Speaker 2: that happened very recently measurements from the Daisy experiment. They
• 36:40
  Speaker 2: used a completely different method to measure the expansion of
• 36:43
  Speaker 2: the universe, one that fits sort of very nicely between
• 36:46
  Speaker 2: the very early universe measurements from the cosmic microwave background
• 36:50
  Speaker 2: and sort of later time measurements from the supernova crew.
• 36:53
  Speaker 2: They use something called bury on acoustic oscillations where they
• 36:57
  Speaker 2: see these rings of matter from USCI in the early universe.
• 37:01
  Speaker 4: And by looking at these rings of matter, it sounds
• 37:04
  Speaker 4: like you just said that it agreed with both of
• 37:06
  Speaker 4: the value. So it agrees with sixty seven and seventy four.
• 37:09
  Speaker 2: So this is a new technique, and it's cool that
• 37:12
  Speaker 2: it's complementary. By complementary, I just mean like they're using
• 37:15
  Speaker 2: another approach. Okay, When I say it fits nicely in between,
• 37:18
  Speaker 2: I don't mean that their measurement is in agreement with
• 37:21
  Speaker 2: the other folks. I mean that the time period they
• 37:23
  Speaker 2: can study is deeper into the past than the supernova folks,
• 37:28
  Speaker 2: and not all the way back to the beginning of
• 37:30
  Speaker 2: the universe. So in the universe timeline is sort of
• 37:33
  Speaker 2: a nice like probe of the sort of middle section. Okay,
• 37:36
  Speaker 2: all right, cool, and it's very cool study. What they're
• 37:39
  Speaker 2: looking for are these incredible echoes in hot plasma from
• 37:43
  Speaker 2: the early universe. And so, you know, you imagine the
• 37:46
  Speaker 2: early universe. It's very hot, it's very dense, you got
• 37:48
  Speaker 2: like protons, you got electrons, you got photons, you've got
• 37:51
  Speaker 2: dark matter in there. It's incredible, and it's mostly radiation dominated,
• 37:55
  Speaker 2: like the early universe, mostly photons, like a billion photons
• 38:00
  Speaker 2: for every electron. It's hard to wrap your mind around
• 38:03
  Speaker 2: because we're definitely not photon dominated now. And that's because
• 38:07
  Speaker 2: the very early universe made matter and antimatter, which then
• 38:10
  Speaker 2: mostly annihilated into photons. So that's why it's bathed in photons. Anyway,
• 38:14
  Speaker 2: these photons flying around, and they're pushing on the electrons
• 38:18
  Speaker 2: and on the protons, right, because that's what photons do.
• 38:21
  Speaker 2: They interact with charge particles. And so this plasma made
• 38:25
  Speaker 2: of protons and electrons is opaque to the photons. It's
• 38:28
  Speaker 2: pushing on them, just like the light inside the variable
• 38:31
  Speaker 2: stars creates this outward pressure, creates this density waves, right.
• 38:36
  Speaker 2: But dark matter, on the other hand, is pulling the
• 38:38
  Speaker 2: stuff in because of gravity. Dark matter ignores all this
• 38:41
  Speaker 2: pressure photons fly right through it. So you have these
• 38:43
  Speaker 2: two different effects, the photons pushing out and the dark
• 38:46
  Speaker 2: matter pulling in, and you get these density ripples.
• 38:49
  Speaker 4: So we know that dark matter does act on electrons
• 38:52
  Speaker 4: and protons, Is that what you were saying?
• 38:54
  Speaker 2: It acts on electrons and protons only through its gravity.
• 38:56
  Speaker 2: But there's a lot of it in the early universe,
• 38:58
  Speaker 2: and it's very dense, so this does have an effect.
• 39:01
  Speaker 2: And so these density ripples are moving through the early
• 39:03
  Speaker 2: universe at a really incredible rate. You know, the speed
• 39:06
  Speaker 2: of sound depends on the density of something. So for example,
• 39:10
  Speaker 2: speed of sound through air is pretty high, but it's
• 39:13
  Speaker 2: tiny compared to the speed of light. But the speed
• 39:15
  Speaker 2: of sound through water or through the Earth is faster, right,
• 39:18
  Speaker 2: the speed of sound through steel. That's why you could
• 39:21
  Speaker 2: like feel a herd of buffalo coming through the ground
• 39:24
  Speaker 2: before you heard them salivating over crushing you.
• 39:26
  Speaker 4: For example, they're herbivores, I think, Daniel, they would still
• 39:31
  Speaker 4: crush you. Ye, that's true.
• 39:32
  Speaker 2: Anyway, in the early universe, it's so dense that the
• 39:35
  Speaker 2: speed of sound is about half of the speed of light. Wow,
• 39:39
  Speaker 2: incredible density. So these pressure waves are shooting out at
• 39:43
  Speaker 2: half the speed of light. But then at some moment
• 39:45
  Speaker 2: the universe is expanding and it's cooling, and so protons
• 39:49
  Speaker 2: and electrons come together to make neutral hydrogen. Right, And
• 39:53
  Speaker 2: now they are transparent to those photons, so photons are
• 39:56
  Speaker 2: flying through them instead of pushing on them. And that's
• 39:59
  Speaker 2: a little bit of quantumic right there, you know, because
• 40:01
  Speaker 2: a free electron one that's just flying around, it's not
• 40:04
  Speaker 2: a hydrogen atom. Same with the free proton, can absorb
• 40:07
  Speaker 2: a photon of any energy. It's just like, no big deal.
• 40:11
  Speaker 2: It's only when you can find them you get the
• 40:13
  Speaker 2: energy levels. This quantization of the energy levels that the
• 40:16
  Speaker 2: electrons become so picky and say I'm only going to
• 40:18
  Speaker 2: absorb a photon of this energy or of that energy.
• 40:22
  Speaker 2: Paush electrons, I know, they become all snobby in their
• 40:25
  Speaker 2: fancy houses. And now the universe is transparent, so the
• 40:29
  Speaker 2: pressure stops. So you get these rings that were created
• 40:32
  Speaker 2: and then at some moment they get like frozen in
• 40:35
  Speaker 2: because they can no longer change. It's no more outward pressure. Right,
• 40:38
  Speaker 2: So you get these high density regions in the universe.
• 40:41
  Speaker 2: You might think, why do I care about early universe
• 40:43
  Speaker 2: high density regions? Well, dense regions in the early universe
• 40:47
  Speaker 2: lead to structure in the later universe, Like, why do
• 40:50
  Speaker 2: we have a galaxy here and not over there, because
• 40:52
  Speaker 2: fourteen billion years ago there was a little bit higher
• 40:55
  Speaker 2: density of stuff and then gravity took over and gathered
• 40:58
  Speaker 2: that together into a big blobb of star that became
• 41:00
  Speaker 2: a galaxy. So what they do in this experiment is
• 41:04
  Speaker 2: they don't look at the early universe plasma. They look
• 41:06
  Speaker 2: at the distribution of galaxies in the universe. They just
• 41:09
  Speaker 2: like make a huge map of galaxies and they look
• 41:12
  Speaker 2: for rings and they find these bubbles, these same literal bubbles.
• 41:16
  Speaker 2: You can see them in the universe. It's incredible, I know.
• 41:19
  Speaker 1: So you have this like foam of galaxies where the
• 41:22
  Speaker 1: galaxies are mostly on the edges, and then you also
• 41:25
  Speaker 1: have galaxies in the middle, but there's a higher density
• 41:27
  Speaker 1: along these bubbles.
• 41:29
  Speaker 2: So incredible, so much cleverness here to see this early
• 41:32
  Speaker 2: history of the universe. So around twenty years ago we
• 41:36
  Speaker 2: saw these first evidence that we can actually see the
• 41:38
  Speaker 2: baryon acoustic oscillations from the early universe as it transforms
• 41:43
  Speaker 2: into the structure of the universe today. And the recent
• 41:46
  Speaker 2: measurement by Daisy is like a super big camera that
• 41:50
  Speaker 2: looked at more galaxies than anybody ever had measured them,
• 41:54
  Speaker 2: deep into time, deep into the history of the universe,
• 41:56
  Speaker 2: all the way back to like three hundred million years.
• 41:59
  Speaker 2: You can see this structure early on, you can see
• 42:02
  Speaker 2: it later. And because it was sort of a fixed
• 42:04
  Speaker 2: yard stick, you can measure the expansion of the universe
• 42:07
  Speaker 2: by seeing the size of these bubbles over time. It's
• 42:10
  Speaker 2: sort of like, you know, a standard candill Again. So
• 42:13
  Speaker 2: they recently came out with the results, and this fills
• 42:17
  Speaker 2: in the gap. Right we saw the early universe measurement,
• 42:19
  Speaker 2: we saw the pretty late universe measurement. This is sort
• 42:21
  Speaker 2: of like the middle aged universe measurement. People wondering like,
• 42:24
  Speaker 2: what's it going to say, and it's consistent with the
• 42:26
  Speaker 2: dark energy density that's like constant in space, or what's
• 42:29
  Speaker 2: the behavior of it? And so the results very confusing.
• 42:33
  Speaker 4: Oh no, I thought you're gonna give me a clear answer,
• 42:35
  Speaker 4: Danyel Oh no.
• 42:36
  Speaker 2: Unfortunately, or excitingly, it's in chaos. So they see something
• 42:40
  Speaker 2: that doesn't look like dark energy is constant in space.
• 42:44
  Speaker 2: The expansion of the universe that they measure is not
• 42:46
  Speaker 2: consistent with a dark energy that just has constant density,
• 42:50
  Speaker 2: and it therefore grows at a certain rate as the
• 42:52
  Speaker 2: universe is expanding. And you might think, Okay, that's cool.
• 42:56
  Speaker 2: The hubble tension already told us that, right, Yes, but
• 42:58
  Speaker 2: the hubble tension told it was different from constant in
• 43:01
  Speaker 2: a different way. The two are inconsistent. This new measurement
• 43:05
  Speaker 2: from the very on acoustic oscillations is inconsistent with constant
• 43:09
  Speaker 2: dark energy and inconsistent with the hubble tension explanation. Yeah,
• 43:14
  Speaker 2: so this sees dark energy as weakening. According to Daisy,
• 43:19
  Speaker 2: dark energy is getting weaker over time. The hubble tension
• 43:22
  Speaker 2: needs something that's getting stronger at the end of the
• 43:25
  Speaker 2: late universe. I mean, there are other ways to explain
• 43:27
  Speaker 2: it as well, But it's not like, oh, this nicely
• 43:30
  Speaker 2: clicks together with this other story we already were getting
• 43:32
  Speaker 2: hints of from these other experiments. So I talked to
• 43:35
  Speaker 2: a cosmologist in my department here, keV Abazanjin, and he
• 43:38
  Speaker 2: calls this chaos cosmology because something basic is wrong, you know.
• 43:44
  Speaker 2: And that's fine. It's early days. We've only been studying
• 43:46
  Speaker 2: dark energy for a couple of decades, right, so like,
• 43:48
  Speaker 2: of course we're still learning really basic things about how
• 43:51
  Speaker 2: it works. And what we've done is apply a very
• 43:54
  Speaker 2: simple model, take the cosmological constant, use it to describe
• 43:57
  Speaker 2: dark energy. See if that works. Amazing. It kind of
• 44:00
  Speaker 2: worked for twenty years until we made more and more
• 44:02
  Speaker 2: precise measurements. Now we're saying that doesn't really work, and
• 44:06
  Speaker 2: we don't have a better framework right now. We don't
• 44:09
  Speaker 2: have an explanation that can explain these recent results from
• 44:12
  Speaker 2: Daisy the barrier on acoustic ostellations and the Hubble tension
• 44:16
  Speaker 2: that we've been puzzling over for the last ten years
• 44:18
  Speaker 2: or so. So there's a lot of exciting discoveries to
• 44:21
  Speaker 2: be made.
• 44:22
  Speaker 4: Does this mean that the universe is not necessarily expanding anymore,
• 44:26
  Speaker 4: or just that our understanding of the mechanism is not good.
• 44:31
  Speaker 2: The universe is definitely expanding, we don't really know if
• 44:35
  Speaker 2: it's accelerating at the same level as we thought it was,
• 44:39
  Speaker 2: and we don't know how that acceleration is changing. Right,
• 44:43
  Speaker 2: So there's sort of like another derivative there, the jerk
• 44:45
  Speaker 2: of the universe, if you will, and that says a
• 44:49
  Speaker 2: lot of important stuff about the future. Right. The previous view,
• 44:52
  Speaker 2: the simple view, the cosmological constant, that dark energy was
• 44:55
  Speaker 2: constant in space and therefore increasing as a fraction of
• 44:59
  Speaker 2: the universe over time. That painted a picture of a
• 45:02
  Speaker 2: universe torn apart by dark energy, because as things get
• 45:05
  Speaker 2: further apart and dark energy takes over, then they just
• 45:08
  Speaker 2: move apart faster and faster and faster and faster, And
• 45:11
  Speaker 2: the future of that universe is a bunch of galaxies
• 45:13
  Speaker 2: that collapse into black holes that are just like, incredibly
• 45:17
  Speaker 2: far away from all the other black holes. That would
• 45:19
  Speaker 2: be the future of the universe if the cosmological constant
• 45:23
  Speaker 2: was the thing causing the accelerating expansion. But if Daisy
• 45:27
  Speaker 2: is right and dark energy is somehow weakening, then that
• 45:29
  Speaker 2: acceleration is not necessarily going to keep ramping up, and
• 45:34
  Speaker 2: it could be that it slows down, and it could
• 45:36
  Speaker 2: even turn around. We could be heading for a time
• 45:39
  Speaker 2: when you wish you had purchased Daniel's extra premium dark
• 45:43
  Speaker 2: Crunch insurance policy. You con man, this whole episode is
• 45:48
  Speaker 2: just a grift for me to sell my insurance. Look,
• 45:51
  Speaker 2: I promise you, Kelly, if the universe collapses into a
• 45:53
  Speaker 2: black hole, I will be there with a cabin and
• 45:57
  Speaker 2: goats and whiskey and whatever you need to survive the.
• 46:00
  Speaker 4: Times and pigs and geeks.
• 46:01
  Speaker 2: Exactly. We'll put that on your policy, no extra charge.
• 46:04
  Speaker 4: Oh thanks, Daniel, Think I love a good deal. A
• 46:11
  Speaker 4: lot of information came at me today, So forgive me
• 46:14
  Speaker 4: if I'm totally giving this wrong. But I thought the
• 46:15
  Speaker 4: explanation for why the galaxy has rings depended on our
• 46:20
  Speaker 4: understanding of dark energy, dark matter, dark matter. Ah, I'm
• 46:25
  Speaker 4: always mixing those two up.
• 46:26
  Speaker 2: Dark matter is providing a gravity to pull it back
• 46:29
  Speaker 2: and to make these things oscillates exactly. That's why it's
• 46:32
  Speaker 2: called baryon acoustic oscillation. And then it's frozen in time
• 46:35
  Speaker 2: one certain moment in those oscillations because the photons can
• 46:39
  Speaker 2: no longer push on that stuff because it becomes neutral. Yeah,
• 46:42
  Speaker 2: dark matter, dark energy, I know it's also dark. It's
• 46:45
  Speaker 2: a dark universe out there.
• 46:46
  Speaker 4: Yep, yep. Okay, So now what do we do. We've
• 46:49
  Speaker 4: got this third way of measuring it and we're even
• 46:51
  Speaker 4: more confused. Do we just look for a fourth way
• 46:53
  Speaker 4: to measure it?
• 46:55
  Speaker 2: Yes, and of course we're going to work on that,
• 46:58
  Speaker 2: But also we have some theoretical work to do. We
• 47:00
  Speaker 2: need to understand how you could describe what we see
• 47:03
  Speaker 2: in a way that's consistent and makes sense across these
• 47:06
  Speaker 2: different experiments. That's why it's so important to do these
• 47:09
  Speaker 2: measurements in so many different ways, because we need to
• 47:12
  Speaker 2: unravel like, well, what assumption are we making in this
• 47:14
  Speaker 2: one the same way like the Greeks made the wrong
• 47:17
  Speaker 2: conclusion about the Solar system because they had one wrong
• 47:19
  Speaker 2: assumption that the stars were pretty close. Maybe there's a
• 47:22
  Speaker 2: basic assumption about the universe we're all making that's leading
• 47:26
  Speaker 2: us to miss the obvious explanation for what's going on here,
• 47:29
  Speaker 2: and podcast in five thousand years can be like, ha
• 47:31
  Speaker 2: ha ha, they didn't realize. I don't know what it is,
• 47:35
  Speaker 2: but it makes it so obvious why they were seeing
• 47:37
  Speaker 2: what they saw.
• 47:38
  Speaker 4: Well, I hope we figure out immortality so that you
• 47:40
  Speaker 4: and I could be having that discussion. We'll look back
• 47:42
  Speaker 4: and be like, oh, we were so silly when we
• 47:44
  Speaker 4: were young.
• 47:47
  Speaker 2: Life insurance policy is basically like immortality insurance.
• 47:50
  Speaker 1: M h.
• 47:51
  Speaker 2: Anyway, I'm not selling any insurance. I'm just hoping that
• 47:54
  Speaker 2: everybody out there enjoys the mysteries of the universe. We
• 47:57
  Speaker 2: live in a very turbulent time when we don't understand universe,
• 48:00
  Speaker 2: and we're constantly getting these updates that remind us that
• 48:03
  Speaker 2: they're huge discoveries to be made. So aspiring young cosmologists
• 48:08
  Speaker 2: out there don't worry. There are lots of things for
• 48:10
  Speaker 2: you to figure out.
• 48:18
  Speaker 4: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
• 48:22
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• 48:25
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• 48:28
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• 48:29
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• 48:35
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• 48:36
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• 48:42
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• 48:51
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