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