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Speaker 1: Physics lets us ask big, fat, juicy questions about the universe.

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Speaker 1: I would claim that these are the biggest, the fattest,

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Speaker 1: the juiciest questions, though chemists and biologists may disagree, of course.

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Speaker 1: But physics lets us discover.

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Speaker 2: New elements of the universe, like dark matter, that tell

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Speaker 2: us our whole picture of what the universe is made

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Speaker 2: of was wrong.

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Speaker 1: It lets us think about the size of the entire

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Speaker 1: universe and whether it's expanding. It gives us the tools

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Speaker 1: that will let us discover the forces that are capable

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Speaker 1: of squeezing and stretching galaxies and clusters and structures beyond

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Speaker 1: even our capacity to hold in our minds. Probably the

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Speaker 1: most powerful and mysterious discovering physics maybe ever is dark energy.

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Speaker 1: The accelerating expansion of the universe has changed our picture

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Speaker 1: of where the energy in the cosmos is, what it does,

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Speaker 1: and how it shapes the present and future of the

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Speaker 1: entire universe. Will things be torn apart, left to huddle

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Speaker 1: together with a few other bits of matter among a

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Speaker 1: vast empty cosmos? Will things rush back together to collapse

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Speaker 1: everything in everyone into incredible density, mimicking the conditions of.

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Speaker 2: The early universe, only dark energy has the sheer scale

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Speaker 2: and scope to determine the faith of the universe, which

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Speaker 2: is why we are all so desperate to understand it.

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Speaker 2: And dark energy is recent, a concept from the last

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Speaker 2: couple of decades, which means we have a lot left

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Speaker 2: to learn and that surprises deliciously await us. Recently, you

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Speaker 2: might have heard that our understanding of dark energy was

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Speaker 2: thrown into new disarray by some recent measurements. What does

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Speaker 2: that mean about dark energy? What does it mean for

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Speaker 2: our understanding of the universe? What does it mean about

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Speaker 2: the future of the universe? Should you still say for

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Speaker 2: retirement or just fly to Vegas tomorrow and blow it

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Speaker 2: all in a weekend of excess and debauchery. Will dig

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Speaker 2: into the history and the latest mystery and let physics

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Speaker 2: do its best to answer these questions. Welcome to Daniel

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Speaker 2: and Kelly's Extraordinary Expanding Universe.

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Speaker 3: Hello.

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Speaker 4: I'm Kelly wider Smith and I study space and parasites

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Speaker 4: and I am so glad we have finally figured out

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Speaker 4: dark energy, Right Daniel, That's what we're talking about today,

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Speaker 4: isn't it?

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Speaker 2: Wow? What a setup? What a setup?

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Speaker 5: Hi?

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Speaker 2: I'm Daniel, I'm a particle physicist, and I wish I

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Speaker 2: was as cool as dark energy sounds.

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Speaker 4: Oh, it does sound pretty cool. You all are really

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Speaker 4: hit and miss in terms of naming stuff, but with

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Speaker 4: dark energy and dark matter, the goth in me really

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Speaker 4: digs it.

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Speaker 2: Yeah. I don't know if they're appropriate in the sense

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Speaker 2: that they describe it well, but they do sound very cool.

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Speaker 2: And you know that's one angle.

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Speaker 4: For sure, you know for sure. So what per scent

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Speaker 4: of the articles that you see online about dark matter

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Speaker 4: and dark energy do you feel are like completely accurate.

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Speaker 2: Completely accurate? Wow, that is a small fraction. Unfortunately, there

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Speaker 2: is so much clickbait nonsense out there, and that really

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Speaker 2: disappoints me because I imagine if I wasn't an expert

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Speaker 2: and I was curious, like lots of our listeners are,

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Speaker 2: who want to understand the universe in good faith, they

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Speaker 2: read these things and they don't know whether it's nonsense

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Speaker 2: or not. So if you're out there and you're reading

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Speaker 2: an article and it tickles your nonsensimeter, feel free to

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Speaker 2: send it to us. I will let you know if

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Speaker 2: you should believe it or not. But unfortunately, on average

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Speaker 2: the answer is no. Because science journalism is hard and

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Speaker 2: getting all the nuances right, is very very hard.

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Speaker 4: Yeah, that's true. But I got to say, you know

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Speaker 4: Ed Young for example, So he's our biology king of

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Speaker 4: science journalism, and he does a really good job of

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Speaker 4: like running stuff by people to check. So, like, you

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Speaker 4: can't possibly know everything as a science journalist if you're

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Speaker 4: covering a broad range of topics. But I do feel

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Speaker 4: like if you run it by experts, like why aren't

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Speaker 4: you getting an email every single day from like people

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Speaker 4: writing about this to be like, hey, can I run

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Speaker 4: it by an expert before I put it online?

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Speaker 2: Mm hmm, Yeah, Well there's a lot to dig into there.

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Speaker 2: I think that a lot of folks don't run things

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Speaker 2: by experts. They read other popular science coverage and get

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Speaker 2: their information from there, because not that many experts are accessible.

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Speaker 2: You know, professors don't usually answer their emails, though some

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Speaker 2: of us do, and they don't respond on time, and

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Speaker 2: you have a deadline, and so instead of talking to

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Speaker 2: somebody who is a professor about dark matter, you read

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Speaker 2: a bunch of other articles about dark matter, especially if

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Speaker 2: you're not a physicist yourself, so you can't read the

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Speaker 2: primary literature and decode those weird scientific squiggles. So yeah,

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Speaker 2: I think a lot of us are inaccessible. But hey,

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Speaker 2: that's what this podcast is about, right, is making all

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Speaker 2: this science accessible without dumbing it down, digging deep into

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Speaker 2: what's actually going on, and giving everybody out there and

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Speaker 2: understanding and an opportunity to ask questions. So, if you're

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Speaker 2: a science journalist and you want to write an article

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Speaker 2: about dark matter and dark energy and you have a

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Speaker 2: question or something you don't think you fully understand, don't

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Speaker 2: write about it. If you don't understand it, ask me

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Speaker 2: and I will explain it to you.

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Speaker 4: There you go. Well, today we are tackling a topic

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Speaker 4: that is really making the rounds that is not quite accurate.

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Speaker 4: Is that safe to say?

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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.

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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?

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Speaker 4: And I'll be honest, I thought the standard model just

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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

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Speaker 4: does the standard model I'm thinking of also encompass dark energy?

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Speaker 2: So the standard model you're probably thinking of is the

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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

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Speaker 2: about gravity. It's just the quantum forces and the particles

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Speaker 2: and that kind of stuff. So that's of particle physics.

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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

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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

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Speaker 2: standard model of cosmology.

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Speaker 4: Okay, that sounds super interesting.

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Speaker 2: Yeah, And this is sort of standard model in a

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Speaker 2: lower case sense. Standard model of particle physics often written

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Speaker 2: with upper case sense and just refers to as the

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Speaker 2: standard model. But you know, you could have a standard

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Speaker 2: model of I don't know, parasite interactions are something I imagine, right,

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Speaker 2: And it's sort of just like the normal usage of the.

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Speaker 4: Words, and for that one it would be capital letters

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Speaker 4: the best standard model or the most interesting standard model.

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Speaker 4: But anyway, moving on, we asked our audience, is the

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Speaker 4: standard model of dark energy in trouble? And here's what

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Speaker 4: they had to say.

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Speaker 5: Yes, because recent research has indicated that dark energy weakens

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Speaker 5: over time and therefore is not constant as astrophysicists first belief.

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Speaker 6: I would say yes, and I wouldn't be surprised about it.

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Speaker 5: So quantum energy that disagrees with the Standard model, So yes.

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Speaker 1: Well, what would you expect if all you do is

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Speaker 1: hide out in shadowy places and make yourself unknown.

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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

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Speaker 7: say it could be in trouble.

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Speaker 2: This can only be a good thing, as we are

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Speaker 2: becoming one step closer to understanding the truth.

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Speaker 5: Given how little we understand today of dark energy, I

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Speaker 5: really hope the latest findings do put the model in trouble,

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Speaker 5: because otherwise, what's it going to do? Run away from

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Speaker 5: us at an accelerating rate.

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Speaker 3: Forever I didn't think the Standard model included dark matter

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Speaker 3: or dark energy. So I'm going to surmise that the

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Speaker 3: Standard model is not in trouble.

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Speaker 6: Judging from the headlines, I would say yes.

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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

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Speaker 2: to appear before Congress.

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Speaker 6: It might well be in trouble. From some of the headlines,

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Speaker 6: you read, but a lot to go further. And so

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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.

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Speaker 2: I seem to remember hearing something about the expansion of

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Speaker 2: space being variable. Is that something to do with it?

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Speaker 2: Wasn't worried that there was a standard model for dark energy,

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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

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Speaker 4: writing in.

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Speaker 2: You two can participate send us your response to the

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Speaker 2: questions of the day. Just write to us to questions

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Speaker 2: at Danielankelly dot org and we will hook you up.

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Speaker 4: What did you think of these responses?

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Speaker 2: I thought there were great, some very insightful, some totally hilarious,

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Speaker 2: some echoing your question about like hold on, if you're

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Speaker 2: talking about the standard model that already doesn't include dark

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Speaker 2: matter and dark energy, So yeah, great stuff.

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Speaker 4: Yeah, I bet there were a bunch of people who

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Speaker 4: are like this is another trick question from Daniel because

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Speaker 4: he loves those.

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Speaker 2: They're not trick questions. It's just that, you know, if

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Speaker 2: I'm asking about something, then we expect it's probably something

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Speaker 2: interesting we learned recently in the news.

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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,

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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,

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Speaker 2: you can avoid a lot of talking past each other

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Speaker 2: if you're clear out what you mean. And so the

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Speaker 2: best way to understand dark energy is to understand that

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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,

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Speaker 2: what we used to think was natural or made sense

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Speaker 2: only like one hundred years ago, before Hubble and Levitt

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Speaker 2: and those folks, we thought the universe was static. We

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Speaker 2: thought it was just a single galaxy, just a bunch

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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.

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Speaker 2: There weren't stars that went on forever. It's just like one,

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Speaker 2: our little blob of stars hanging out in space. And

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Speaker 2: that was people's mental picture of the universe. Your mental picture,

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Speaker 2: probably influenced by wonderful programs like Nova and pictures from

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Speaker 2: James Webb, is of a universe filled with galaxies upon

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Speaker 2: galaxies upon galaxies. It's a very different context, and for me,

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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

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Speaker 2: we think we're living in.

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Speaker 4: I mean, if there were more parasites in space, I'd

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Speaker 4: probably be way more excited. But that is an inspirational

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Speaker 4: thing to think about.

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Speaker 2: The day that James web Space Telescope discovers space parasites,

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Speaker 2: I'm also gonna be excited about parasites.

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Speaker 4: Oh that's what it would dig.

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Speaker 2: At a minimum. All right. So before Hubble, we think

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Speaker 2: there's just one galaxy hanging in space and that's natural,

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Speaker 2: and people imagine, like, oh, it's probably been like that forever,

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Speaker 2: because why wouldn't it be. You know, the idea of

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Speaker 2: an infinite past was sort of fine, not a big deal.

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Speaker 2: But then Hubble and Henriette eleven figured out a way

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Speaker 2: to measure the distance to stuff. This is really important

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Speaker 2: because when you're looking out into space and you're looking

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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

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Speaker 2: of dim or actually kind of dim and like not

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Speaker 2: terribly far away. Cosmologically speaking, you can't tell the difference

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Speaker 2: if you're just looking at the intensity of the star

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Speaker 2: because you don't know how bright it actually is. And

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Speaker 2: if you want to make a three D map of

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Speaker 2: the universe, knowing how far away things are it is crucial, right,

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Speaker 2: because otherwise you're just looking at like the equivalent of

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Speaker 2: a two D screen that surrounds the Earth.

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Speaker 4: And so how do you calibrate so that you can

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Speaker 4: figure that stuff out?

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Speaker 2: Yeah, so we can actually tell how far away stuff

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Speaker 2: is if it's pretty close by using parallax. It's the

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Speaker 2: same principle that you can use to tell whether a

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Speaker 2: baseball is close to you or far away from you.

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Speaker 2: It's the fact that you have two eyes binocular vision,

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Speaker 2: and they give a different view of the same object,

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Speaker 2: and if something is close by, your eyes have a

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Speaker 2: very different perspective on them, and if something is far away,

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Speaker 2: they have basically the same perspective. Like if you hold

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Speaker 2: up your coffee cup in front of your face and

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Speaker 2: you close one eye and open the other one and

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Speaker 2: go back and forth, you can see that the picture

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Speaker 2: looks very different, and your brain uses that information to say, Okay,

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Speaker 2: the coffee cup is close. But if it's farther away

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Speaker 2: and you do the same thing, it's hardly a difference.

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Speaker 2: Your brain does all the math and tells you where

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Speaker 2: the baseball or the coffee cup is, So that's parallax.

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Speaker 2: We can do the same thing in space because the

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Speaker 2: Earth goes around the Sun and so over the year

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Speaker 2: we have different views of the cosmos. So if something

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Speaker 2: is pretty close to us, then it looks pretty different

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Speaker 2: from one side of the Sun and the other side

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Speaker 2: of the Sun, whereas if it's like a gazillion light

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Speaker 2: years away, that hardly matters. Wow, So we can use

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Speaker 2: that to measure the distance to nearby stuff.

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Speaker 4: So you've got to be pretty patient to figure this

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Speaker 4: stuff out then, because it's like six months or something

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Speaker 4: in between data collection moments.

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Speaker 2: Yeah, and this is actually the reason that the Greeks

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Speaker 2: got the solar system wrong. The Greeks knew about this method,

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Speaker 2: and they used this method and they tried to see

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Speaker 2: how far away the stars were, and they couldn't see

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Speaker 2: any wiggles at all. Because the stars are pretty far away,

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Speaker 2: they assumed they were pretty close, and so because they

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Speaker 2: didn't see the stars wiggling, they assumed the Earth doesn't

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Speaker 2: move around the Sun.

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Speaker 4: Oh, that's fascinating, but we have better instruments, so we

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Speaker 4: can calculate that. Is that the difference?

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Speaker 2: Yeah, exactly. It wasn't until like the eighteen hundreds that

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Speaker 2: we could see the stars wiggle because the wiggle is small, right,

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Speaker 2: And so with out those instruments and without the assumption

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Speaker 2: that the stars are close, you can actually tell how

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Speaker 2: much the stars are wiggling, and then you can tell

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Speaker 2: the distance to them. So the Greeks assumed the stars

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Speaker 2: were close and they couldn't see them wiggling, so they

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Speaker 2: assumed the flaw was that the Earth wasn't moving. Of course,

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Speaker 2: the Earth was moving, it's just that the stars were

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Speaker 2: further than they thought. Sort of fascinating history of like

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Speaker 2: what people think is natural.

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Speaker 4: That is a pretty clever way to try to figure

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Speaker 4: out if the Earth is moving or not. Like, good

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Speaker 4: on them, Yeah, exactly.

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Speaker 2: People are always dumping on the Greeks, including me for

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Speaker 2: many years for not doing empirical science. But like this

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Speaker 2: is a good example of coming up with a clever technique,

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Speaker 2: taking some data, using it to draw conclusions. And you know,

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Speaker 2: they got the wrong conclusion because they had one mistake

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Speaker 2: and assumption. But it's pretty solid work. Yeah, anyway, we

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Speaker 2: can do that for nearby stuff. More distant stuff is

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Speaker 2: hard because if it's not wiggling, you can't tell is

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Speaker 2: an a zillion miles away or two zillion or half

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Speaker 2: a zillion. And so what Levitt and Hubble figured out

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Speaker 2: was a way to measure the distant to more distant

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Speaker 2: stars by looking for a petique other kind of star

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Speaker 2: called cephids. Cephids are star that have variable brightness, Like

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Speaker 2: they're not just like the Sun that mostly burns the same.

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Speaker 2: They go brighter and dimmer and brighter and dimmer. And

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Speaker 2: that's because of stuff that's happening on the inside. There's

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Speaker 2: like hot layers that rise to the surface and then collapses,

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Speaker 2: like you know, crazy stellar chemistry going on.

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Speaker 4: There are they made out of different things than our sun.

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Speaker 2: It's definitely connected to what they're made out of it

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Speaker 2: because part of the star is opaque to its own radiation,

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Speaker 2: and so the glow from the inner part of the

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Speaker 2: star then pushes that part of the star out, and

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Speaker 2: so you have to have some sort of opaque layers.

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Speaker 2: And they think this might be involved with helium, but

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Speaker 2: it's not totally understood. There's some similar stuff going on

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Speaker 2: inside our star with layers of opacity and transparency. We

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Speaker 2: can talk about that another time we talk about the

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Speaker 2: solar magnetic field. But the cool thing about these stars

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Speaker 2: is that the variability in their brightness is very closely

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Speaker 2: connected to their actual brightness. So if you, for example,

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Speaker 2: watch one of these and you say, oh, it goes

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Speaker 2: bright and dim in the period of a day or

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Speaker 2: five days or ten days, you can use that to

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Speaker 2: determine how bright it actually is. So you can measure

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Speaker 2: the actual brightness of it just by measuring its variability.

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Speaker 4: Wow, okay, all right, So now we know about variability

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Speaker 4: of brightness and we know how it appears to change

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Speaker 4: as you move locations. And what do those two pieces

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Speaker 4: of information tell us?

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Speaker 2: So they allow us to weave together what we call

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Speaker 2: a distance ladder for nearby stuff we use parallax, and

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Speaker 2: then near the edge of our abilities to do parallax,

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Speaker 2: there are some sephids, some of these variable stars, and

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Speaker 2: we can use parallax to calibrate the cephids, and then

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Speaker 2: we can use sephids to go even further. Because if

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Speaker 2: you know how bright a star is actually it's true brightness,

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Speaker 2: and then you measure its brightness here on Earth, you

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Speaker 2: can tell how far away it is. That was the

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Speaker 2: missing piece, right, we didn't know if this star is

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Speaker 2: bright and far away or dim and close. But now

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Speaker 2: because we know whether it's actually bright or actually dim,

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Speaker 2: we can tell if it's close or far by its

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Speaker 2: apparent brightness here on Earth. And the crucial thing is

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Speaker 2: that these two las matters, the parallax and the cephids overlap,

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Speaker 2: so it's a period where we can use parallax to

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Speaker 2: calibrate the cephids and then extrapolate further for stuff that

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Speaker 2: we couldn't use parallax for. And this gave Hubble this

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Speaker 2: incredible three dview of the universe we didn't have before.

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Speaker 2: He could tell the distance to all kinds of stuff

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Speaker 2: that nobody knew. Hey, is that actually a smudge in

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Speaker 2: the sky but pretty close, or is it something incredible

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Speaker 2: and massive but deeply, deeply distant?

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Speaker 4: And is this how he figured out that the universe

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Speaker 4: was expanding because things changed their location over time.

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Speaker 2: Well, Number one, he discovered that there are other galaxies.

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Speaker 2: We used to see these things in the sky, and

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Speaker 2: we called them nebulae because there were sort of like

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Speaker 2: smudge in our telescopes, and people were like, hmm, maybe

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Speaker 2: they're just big clouds of gas. It turns out no,

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Speaker 2: they're actually entire galaxies that are much bigger in many

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Speaker 2: cases than our galaxy, like Andromeda, so much bigger than

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Speaker 2: our galaxy. He was able to unravel this puzzle because

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Speaker 2: he could measure the distance to them. He found cephids

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Speaker 2: in those nebulae, and he was able to tell, oh

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Speaker 2: my gosh, that thing is so much further away than

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Speaker 2: anything else, any of the other stars. It's its own galaxy.

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Speaker 4: Oh my god.

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Speaker 2: Instantly, this like mental picture of the universe just expands

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Speaker 2: from we have one galaxy with some fuzzy clouds in it,

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Speaker 2: to take all those fuzzy clouds and promote them to

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Speaker 2: their own super distant, incredibly large galaxies, and the universe

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Speaker 2: now filled with galaxies. That's often overlooked in the story

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Speaker 2: about the expanding universe, because what Hubble actually discovered is

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Speaker 2: that the universe is filled with galaxies, not just.

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Speaker 4: Our own and around When was that happening.

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Speaker 2: This is the nineteen twenties, so this is like one

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Speaker 2: hundred years ago. Right, most of humanity had no idea

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Speaker 2: that this was the case, But you're right. The other

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Speaker 2: crucial thing that Hubble discovered is he was able to

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Speaker 2: measure the apparent velocity of these galaxies by looking at

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Speaker 2: the light that came from the galaxies and how it

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Speaker 2: was shifted by velocity. If something is moving away from you,

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Speaker 2: its wavelengths are lengthened, and if it's moving towards you,

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Speaker 2: its wavelength are shrunk. And so if something is red shifted,

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Speaker 2: it means it's moving away from you. And all the

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Speaker 2: galaxies were red shifted, and the ones that were further

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Speaker 2: were red shifted more. And so this is Hubble's discovery

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Speaker 2: that there's a close relationship between the distance to a

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Speaker 2: galaxy and it's apparent velocity. Things that are close by

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Speaker 2: are moving away from us slowly, Things that are further

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Speaker 2: away and moving away from us faster. Things that are

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Speaker 2: very very distant, are moving away from us even faster.

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Speaker 2: So this is Hubble's view of the expanding universe. And

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Speaker 2: this was like second mind blowing revelation. Not only is

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Speaker 2: the universe filled with galaxies, they're all running away from us.

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Speaker 1: Yeah.

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Speaker 4: Right, So if everything is running away from us, does

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Speaker 4: that mean that we're the stinky galaxy or does that

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Speaker 4: mean that we're at the center of everything? Or like,

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Speaker 4: why is everything moving away from us?

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Speaker 2: Mm hmm. Everything is moving away from us, but everything

400
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Speaker 2: is moving away from everything. The whole universe is expanding

401
00:19:47,560 --> 00:19:50,480
Speaker 2: the mental picture in your mind. Actually, velocity is not

402
00:19:50,560 --> 00:19:53,119
Speaker 2: the best way to think about it, because when we

403
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Speaker 2: get to acceleration in a minute, somebody's going to be like,

404
00:19:55,400 --> 00:19:58,640
Speaker 2: hold on, Daniel said, you could measure acceleration. Acceleration is absolute,

405
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Speaker 2: and they're going to be right. The right way to

406
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Speaker 2: think about it is in terms of expansion. Space is growing,

407
00:20:05,040 --> 00:20:08,639
Speaker 2: so everywhere space is just stretching, which is why the

408
00:20:08,720 --> 00:20:11,080
Speaker 2: raisin bread analogy is actually kind of perfect, like all

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Speaker 2: the raisins and the raisin bread are getting further away

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Speaker 2: from all the other raisins. No matter where you look

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Speaker 2: in the universe, everything is moving away from you. It's

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Speaker 2: not because we're in the center. We're not special. There

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Speaker 2: is no center.

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Speaker 1: Everywhere in the universe sees everything moving away from it.

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Speaker 4: Well, I also try to move away from raisins as

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Speaker 4: much as I can. But all right, so where do

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Speaker 4: we go from here?

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Speaker 2: So Hubble measured this relationship between the velocity of distant

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Speaker 2: galaxies and their distance from us. If you plot those

420
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Speaker 2: on a graph, you get a straight line. The slope

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Speaker 2: of that line is the Hubble constant. Is this relationship

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Speaker 2: between them? And this we know now is a number

423
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Speaker 2: that's something like seventy kilometers per second per megaparsek, which

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Speaker 2: essentially is a measurement of the expansion rate of the universe.

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Speaker 2: It's not a velocity, it's a velocity per distance because

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Speaker 2: as distance is grow, the apparent velocity the galaxies are

427
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Speaker 2: moving away from each other with grows also, so you

428
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Speaker 2: can't like compare this to the speed of light has

429
00:21:07,920 --> 00:21:10,760
Speaker 2: the wrong units. But this is the crucial number. It

430
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Speaker 2: tells us how fast is the universe expanding. And it's

431
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Speaker 2: called the Hubble constant, even though it's not a constant.

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Speaker 4: Thanks physics time, I know.

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Speaker 2: But we have now this new view of the universe

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Speaker 2: that everything is expanding, And for decades and decades, that's

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Speaker 2: what people thought was happening. The universe was expanding, And

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Speaker 2: then we're wondering about the future, like, hmm, is it

437
00:21:32,520 --> 00:21:34,800
Speaker 2: going to continue to expand or is gravity going to

438
00:21:34,800 --> 00:21:38,160
Speaker 2: eventually win and pull all these galaxies back together into

439
00:21:38,200 --> 00:21:41,560
Speaker 2: some sort of big crunch. That was the big question

440
00:21:41,680 --> 00:21:44,480
Speaker 2: being asked in like the nineteen nineties when people tried

441
00:21:44,480 --> 00:21:46,399
Speaker 2: to look even further into space.

442
00:21:46,840 --> 00:21:49,639
Speaker 4: That sounds existential. But don't be scared. We're going to

443
00:21:49,640 --> 00:21:51,440
Speaker 4: give you some more information when we get back from

444
00:21:51,440 --> 00:22:12,000
Speaker 4: the break. All right, we're back. Daniel just made us

445
00:22:12,000 --> 00:22:14,240
Speaker 4: all a little bit nervous that the universe might have

446
00:22:14,480 --> 00:22:17,200
Speaker 4: a big crunch at some point where everything sort of

447
00:22:17,240 --> 00:22:21,040
Speaker 4: smooshes back in on itself. So Daniel, help me sleep tonight.

448
00:22:21,080 --> 00:22:22,040
Speaker 4: Give me some more information.

449
00:22:22,680 --> 00:22:24,719
Speaker 2: Well, I can sell you some big crunch insurance if

450
00:22:24,720 --> 00:22:26,879
Speaker 2: you like. It's a really big payout. If the universe

451
00:22:26,920 --> 00:22:30,040
Speaker 2: collapses into a mega black hole, you will get a

452
00:22:30,119 --> 00:22:32,200
Speaker 2: big deposit in your bank account. How about that.

453
00:22:32,320 --> 00:22:35,520
Speaker 4: Doesn't make any sense. I'm not convinced.

454
00:22:36,960 --> 00:22:39,400
Speaker 2: Some people just buy insurance to feel better. Remember those

455
00:22:39,400 --> 00:22:42,080
Speaker 2: folks who were buying like Y two K insurance, Like

456
00:22:42,119 --> 00:22:45,480
Speaker 2: they say, if society collapses, we will helicopter you a

457
00:22:45,520 --> 00:22:48,280
Speaker 2: bunker with weapons and food and whiskey. And I was like,

458
00:22:48,440 --> 00:22:50,760
Speaker 2: they're never getting that delivery como.

459
00:22:51,160 --> 00:22:54,919
Speaker 4: No, I've started researching having pigs, and I've been watching

460
00:22:55,000 --> 00:22:58,360
Speaker 4: videos about pigs. And one of the videos, you know, nonchalantly,

461
00:22:58,400 --> 00:23:00,760
Speaker 4: they said, oh, no, it was geese. It was geese.

462
00:23:00,800 --> 00:23:02,320
Speaker 4: I've been researching a lot of animals lately.

463
00:23:02,359 --> 00:23:06,240
Speaker 2: Anyway, it's not that easy to confuse pigs and geese.

464
00:23:06,280 --> 00:23:07,400
Speaker 4: Well, I want both of them.

465
00:23:08,240 --> 00:23:10,320
Speaker 2: Make sure you click the right button when you order,

466
00:23:10,400 --> 00:23:12,080
Speaker 2: because and I hate to be the one to bring

467
00:23:12,200 --> 00:23:14,680
Speaker 2: up cannibalism. Oh, pigs will eat your children and geese

468
00:23:14,720 --> 00:23:15,000
Speaker 2: will not.

469
00:23:15,400 --> 00:23:17,359
Speaker 4: That's true, and pigs will lead each other, as we

470
00:23:17,440 --> 00:23:19,560
Speaker 4: learned in the Trick and Ella episode. Anyway, one of

471
00:23:19,600 --> 00:23:22,600
Speaker 4: the videos that I was watching in a totally nonchalant

472
00:23:22,680 --> 00:23:25,199
Speaker 4: voice was like, well, and from a prepper perspective, and

473
00:23:25,240 --> 00:23:27,320
Speaker 4: I was like, oh, this is the community that I'm

474
00:23:27,400 --> 00:23:31,560
Speaker 4: associated with. Now my interests aligned with this community, all right. Anyway,

475
00:23:32,000 --> 00:23:33,080
Speaker 4: back to dark energy.

476
00:23:33,440 --> 00:23:35,320
Speaker 2: So in the nineteen nineties, we wanted to look even

477
00:23:35,359 --> 00:23:38,840
Speaker 2: further into space to understand the broader scope of this expansion,

478
00:23:39,240 --> 00:23:41,800
Speaker 2: because the further we look into space, the further back

479
00:23:41,840 --> 00:23:44,879
Speaker 2: we look in time, right, because remember light travel at

480
00:23:44,920 --> 00:23:47,359
Speaker 2: finite speed, and so if something is happening across the

481
00:23:47,440 --> 00:23:50,800
Speaker 2: universe right now, we can't see it for billions of years.

482
00:23:51,200 --> 00:23:53,600
Speaker 2: But when we do look out deep into the universe

483
00:23:53,840 --> 00:23:55,960
Speaker 2: and we see life that has taken billions of years

484
00:23:55,960 --> 00:23:58,119
Speaker 2: to get here, we're seeing things that happen billions of

485
00:23:58,160 --> 00:24:00,679
Speaker 2: years ago. So if you want to tell timeline of

486
00:24:00,720 --> 00:24:03,399
Speaker 2: the expansion of the universe so you can better predict

487
00:24:03,400 --> 00:24:05,920
Speaker 2: the future, for example, like what is the trajectory, it's

488
00:24:06,000 --> 00:24:08,359
Speaker 2: useful to look further into the universe and to know

489
00:24:08,400 --> 00:24:11,119
Speaker 2: how far away is that stuff and how quickly is

490
00:24:11,160 --> 00:24:13,280
Speaker 2: it moving away from us. That gives you like a

491
00:24:13,320 --> 00:24:16,560
Speaker 2: deeper picture and lets you extrapolate to the future. And

492
00:24:16,600 --> 00:24:19,239
Speaker 2: sephids are cool, but only if you can pick them

493
00:24:19,280 --> 00:24:21,840
Speaker 2: out right, Only if you can find an isolated sephid

494
00:24:21,840 --> 00:24:25,080
Speaker 2: in that distant galaxy so you can identify it. That

495
00:24:25,160 --> 00:24:27,800
Speaker 2: works great for stars and for regions of our galaxy,

496
00:24:28,040 --> 00:24:31,800
Speaker 2: and for nearby galaxies it's okay, But thinking about really

497
00:24:31,840 --> 00:24:35,400
Speaker 2: distant galaxies in the early universe. Sephid's basically peter out.

498
00:24:35,640 --> 00:24:38,080
Speaker 2: So we needed a new technique, a new element of

499
00:24:38,119 --> 00:24:40,679
Speaker 2: our distance ladder to look further into the universe and

500
00:24:40,760 --> 00:24:42,639
Speaker 2: into the history of the expansion.

501
00:24:43,080 --> 00:24:46,080
Speaker 4: Okay, and I keep asking tell us about dark energy,

502
00:24:46,080 --> 00:24:47,280
Speaker 4: but we don't really get to it. So it is

503
00:24:47,359 --> 00:24:48,560
Speaker 4: dark energy going to be the answer?

504
00:24:48,600 --> 00:24:48,800
Speaker 8: Now?

505
00:24:50,320 --> 00:24:52,800
Speaker 2: We're just about to get to the dark energy because

506
00:24:53,040 --> 00:24:56,040
Speaker 2: in the nineties people figured out another standard candle. These

507
00:24:56,040 --> 00:24:59,600
Speaker 2: are Type one A supernova, and these are incredible collisions

508
00:24:59,600 --> 00:25:01,840
Speaker 2: when a new on star which failed to go nova

509
00:25:01,920 --> 00:25:04,159
Speaker 2: or failed to become a black hole, gobbles up a

510
00:25:04,200 --> 00:25:06,919
Speaker 2: little extra bit of matter and goes supernova in this

511
00:25:07,080 --> 00:25:10,800
Speaker 2: very precise, very predictable way, the light curve rises and

512
00:25:10,840 --> 00:25:13,159
Speaker 2: then it drops. And it's not that all Type one

513
00:25:13,160 --> 00:25:15,560
Speaker 2: A supernova are the same, but from the shape of

514
00:25:15,560 --> 00:25:18,239
Speaker 2: the light curve you can determine the true brightness, just

515
00:25:18,280 --> 00:25:20,920
Speaker 2: like what the cephids. There's something you can measure without

516
00:25:20,960 --> 00:25:23,760
Speaker 2: knowing the distance that tells you the true brightness, and

517
00:25:23,760 --> 00:25:25,840
Speaker 2: then from the true brightness and the apparent brightness you

518
00:25:25,880 --> 00:25:28,880
Speaker 2: can tell the actual distance. And Type one A supernova

519
00:25:28,960 --> 00:25:31,840
Speaker 2: are perfect for looking deep into the universe because they're

520
00:25:32,040 --> 00:25:36,840
Speaker 2: incredibly mind bogglingly bright, like a Type one A supernova

521
00:25:36,880 --> 00:25:40,200
Speaker 2: can be brighter than its entire galaxy for a moment.

522
00:25:40,400 --> 00:25:40,880
Speaker 4: Oh my god.

523
00:25:41,040 --> 00:25:43,840
Speaker 2: So people realize this and then there's a huge race.

524
00:25:43,880 --> 00:25:45,479
Speaker 2: There was a team in Australia and a team at

525
00:25:45,480 --> 00:25:48,080
Speaker 2: Berkeley that realized if they gathered enough of these Type

526
00:25:48,080 --> 00:25:50,240
Speaker 2: one A supernova and watch them, they can make a

527
00:25:50,280 --> 00:25:52,760
Speaker 2: three D map of the universe that dwarfed Hubbles map

528
00:25:53,119 --> 00:25:55,680
Speaker 2: and when deeper in the history of the universe, which

529
00:25:55,680 --> 00:25:57,800
Speaker 2: would allow us to make a fit and project and

530
00:25:57,800 --> 00:25:59,680
Speaker 2: predict what's going to happen for the future of the

531
00:25:59,720 --> 00:26:02,639
Speaker 2: universe verse. Like, what an exciting moment when you realize

532
00:26:02,840 --> 00:26:05,600
Speaker 2: you have an ability just on this tiny little planet

533
00:26:05,640 --> 00:26:07,879
Speaker 2: in the corner of the universe to understand the fate

534
00:26:07,920 --> 00:26:12,240
Speaker 2: of the entire costmos Like, oh my god, drunk with power, Right.

535
00:26:12,480 --> 00:26:14,880
Speaker 4: Were you at Berkeley at this time? This was before you.

536
00:26:15,240 --> 00:26:17,320
Speaker 2: All this stuff was happening while I was at Berkeley.

537
00:26:17,320 --> 00:26:19,480
Speaker 2: I was not involved in it at all, but yeah,

538
00:26:19,480 --> 00:26:21,439
Speaker 2: I knew it was happening at the time. It was

539
00:26:21,480 --> 00:26:23,920
Speaker 2: really exciting and they were like really racing. Both teams

540
00:26:24,000 --> 00:26:25,560
Speaker 2: knew that, like, okay, we know how to do this,

541
00:26:25,600 --> 00:26:27,560
Speaker 2: and it's going to take a few months. Let's not

542
00:26:27,640 --> 00:26:29,680
Speaker 2: be scooped. Yeah, in the end, it was kind of

543
00:26:29,680 --> 00:26:32,760
Speaker 2: a big tie, which is great. But they discovered something shocking,

544
00:26:33,080 --> 00:26:35,640
Speaker 2: you know. They discovered that the expansion of the universe

545
00:26:35,760 --> 00:26:38,880
Speaker 2: is not slowing down, and it's not just continuing smoothly.

546
00:26:38,960 --> 00:26:43,480
Speaker 2: It's speeding up. Right. That's dark energy. Dark energy is

547
00:26:43,520 --> 00:26:46,879
Speaker 2: the observation that the expansion of the universe is accelerating,

548
00:26:47,280 --> 00:26:50,439
Speaker 2: that year after year, this quantity we call the Hubble

549
00:26:50,560 --> 00:26:53,159
Speaker 2: constant is going to be growing. The expansion of the

550
00:26:53,200 --> 00:26:54,560
Speaker 2: universe is increasing.

551
00:26:54,800 --> 00:26:56,200
Speaker 4: And I remember that you told us in a prior

552
00:26:56,280 --> 00:26:59,280
Speaker 4: episode what is energy or how where does energy come from?

553
00:26:59,760 --> 00:27:02,520
Speaker 4: That as the universe expands, it seems like more dark

554
00:27:02,640 --> 00:27:06,160
Speaker 4: energy is made. Is that right? But I'm still having

555
00:27:06,160 --> 00:27:11,360
Speaker 4: trouble thinking of dark energy as the expansion of the universe.

556
00:27:11,440 --> 00:27:14,120
Speaker 4: Is it like the battery that's fueling the motion outward?

557
00:27:15,680 --> 00:27:16,479
Speaker 4: How do I think of this?

558
00:27:17,000 --> 00:27:19,439
Speaker 2: Yeah, So the phrase dark energy is sometimes used to

559
00:27:19,480 --> 00:27:22,919
Speaker 2: describe this observation. We know the universe is expanding and

560
00:27:22,960 --> 00:27:25,920
Speaker 2: that expansion is accelerating, and then naturally you're like, well,

561
00:27:25,920 --> 00:27:29,359
Speaker 2: what's doing it? What's an explanation, Daniel, what's the theory

562
00:27:29,520 --> 00:27:32,320
Speaker 2: of it? And there are a few possible explanations for

563
00:27:32,400 --> 00:27:35,880
Speaker 2: what could be creating this accelerating expansion, and sometimes they

564
00:27:35,880 --> 00:27:39,280
Speaker 2: are described as dark energy, but really they're all very

565
00:27:39,359 --> 00:27:44,000
Speaker 2: loose placeholders. And the sort of leading candidate until recently

566
00:27:44,920 --> 00:27:48,200
Speaker 2: was what you described, the idea that space might have

567
00:27:48,240 --> 00:27:52,480
Speaker 2: some inherent energy within it, a potential energy, and energy

568
00:27:52,480 --> 00:27:54,720
Speaker 2: in general relativity is complicated. A lot of people think, oh,

569
00:27:54,720 --> 00:27:58,679
Speaker 2: general relativities tells us energy makes curvature, you know, just

570
00:27:58,720 --> 00:28:02,359
Speaker 2: like mass and anything causes things to collapse. But general

571
00:28:02,359 --> 00:28:05,240
Speaker 2: relativity is complicated. We talked about in our Potato episode.

572
00:28:05,320 --> 00:28:07,600
Speaker 2: Different kind of energies contribute differently, and if you have

573
00:28:07,680 --> 00:28:11,720
Speaker 2: potential energy in all the space, it actually creates repulsive gravity,

574
00:28:11,800 --> 00:28:15,520
Speaker 2: pushes things apart, it accelerates the expansion of the universe.

575
00:28:15,840 --> 00:28:18,600
Speaker 2: So on one hand we observe the accelerating expansion of

576
00:28:18,640 --> 00:28:20,960
Speaker 2: the universe. On the other hand, we have a way

577
00:28:21,000 --> 00:28:24,800
Speaker 2: within general relativity to create accelerating expansion of the universe.

578
00:28:24,840 --> 00:28:28,080
Speaker 2: It's a knob there. It's called the cosmological constant. And

579
00:28:28,240 --> 00:28:31,000
Speaker 2: just put this number into the equations and say, if

580
00:28:31,000 --> 00:28:34,520
Speaker 2: space has this energy inherently in it, then that would

581
00:28:34,560 --> 00:28:38,680
Speaker 2: cause the accelerating expansion. Now we haven't observed that energy directly.

582
00:28:38,760 --> 00:28:40,800
Speaker 2: It's not like we found that energy, not like we

583
00:28:41,040 --> 00:28:43,400
Speaker 2: identified where it comes from or what quantum field it

584
00:28:43,440 --> 00:28:46,880
Speaker 2: would be or whatever. It's just like, Okay, this number

585
00:28:47,040 --> 00:28:49,480
Speaker 2: would work if we could figure out if that's what's

586
00:28:49,600 --> 00:28:52,480
Speaker 2: really happening. But that number, as you say, assumes dark

587
00:28:52,560 --> 00:28:55,600
Speaker 2: energy is constant. That you make more space, you get

588
00:28:55,640 --> 00:28:58,960
Speaker 2: more dark energy, and that predicts a very specific way

589
00:28:59,000 --> 00:29:02,080
Speaker 2: in which dark energy grows rows over time because it

590
00:29:02,080 --> 00:29:05,840
Speaker 2: actually starts to take over as the universe expands. Matter

591
00:29:06,080 --> 00:29:08,400
Speaker 2: gets diluted, right, you have the same number of protons

592
00:29:08,440 --> 00:29:12,280
Speaker 2: more space, its density goes down. Radiation gets diluted even

593
00:29:12,360 --> 00:29:15,920
Speaker 2: more because it also gets red shifted, but dark energy doesn't.

594
00:29:16,320 --> 00:29:18,920
Speaker 2: But a cosmological constant dark energy. See just used it

595
00:29:18,960 --> 00:29:23,280
Speaker 2: to describe the explanation, not the observation. It doesn't get diluted.

596
00:29:23,280 --> 00:29:26,520
Speaker 2: It's the universe expands more space. It's a constant in space,

597
00:29:26,600 --> 00:29:30,000
Speaker 2: and so therefore it goes up in its fraction. And

598
00:29:30,120 --> 00:29:32,440
Speaker 2: the naive prediction then of the future is that dark

599
00:29:32,560 --> 00:29:36,040
Speaker 2: energy just is a runaway effect because as the universe expands,

600
00:29:36,120 --> 00:29:38,440
Speaker 2: its density is the same, which means it's overall fraction

601
00:29:38,600 --> 00:29:43,040
Speaker 2: keeps rising. So that's sort of the standard model of cosmology.

602
00:29:43,120 --> 00:29:45,680
Speaker 2: Until very recently people were like, well, look, this works

603
00:29:45,720 --> 00:29:47,680
Speaker 2: pretty well. We have some dark energy, we have some

604
00:29:47,760 --> 00:29:50,480
Speaker 2: dark matter, we have this history of stuff, how matter

605
00:29:50,600 --> 00:29:53,360
Speaker 2: used to dominate, how radiation used to dominate, how as

606
00:29:53,360 --> 00:29:56,960
Speaker 2: the universe expands, those things change, and that described things

607
00:29:56,960 --> 00:29:59,320
Speaker 2: pretty well, and people are like, Okay, let's really nail

608
00:29:59,360 --> 00:30:02,440
Speaker 2: it down. Let's measure things super duper precisely in lots

609
00:30:02,480 --> 00:30:04,560
Speaker 2: of different ways and make sure we always get a

610
00:30:04,600 --> 00:30:07,080
Speaker 2: consistent answer, because if so, that tells us we know

611
00:30:07,120 --> 00:30:09,800
Speaker 2: what we're doing. Over the last few years, though, there's

612
00:30:09,800 --> 00:30:13,840
Speaker 2: been some tension in this concept, this standard model of cosmology,

613
00:30:14,120 --> 00:30:16,040
Speaker 2: and it goes by the name of the Hubble tension,

614
00:30:16,480 --> 00:30:18,920
Speaker 2: and it's old news, but it's important to keep in

615
00:30:18,920 --> 00:30:21,840
Speaker 2: your mind when we talk about the new news and

616
00:30:21,920 --> 00:30:25,600
Speaker 2: dark energy, because the two tell very different stories about

617
00:30:25,600 --> 00:30:28,600
Speaker 2: the future. So the Hubble tension is like a great

618
00:30:28,600 --> 00:30:30,880
Speaker 2: piece of science. You know, anytime you see somebody new

619
00:30:30,880 --> 00:30:33,000
Speaker 2: in the universe, you want to check your assumptions. You

620
00:30:33,000 --> 00:30:36,360
Speaker 2: want to measure three different ways with different assumptions, because

621
00:30:36,360 --> 00:30:38,120
Speaker 2: that could reveal that, oh, actually we don't know what

622
00:30:38,160 --> 00:30:40,800
Speaker 2: we're doing, or no, we really do understand this. Like

623
00:30:41,120 --> 00:30:42,840
Speaker 2: you know, we saw the top cork of the tepatron,

624
00:30:42,880 --> 00:30:45,440
Speaker 2: we measured its properties. Then we measured it in completely

625
00:30:45,480 --> 00:30:47,959
Speaker 2: different collisions and a different collider in a different country,

626
00:30:47,960 --> 00:30:50,440
Speaker 2: with different detectors and different people. We got the same numbers.

627
00:30:50,480 --> 00:30:53,480
Speaker 2: We're like, Okay, probably was there. We got that right.

628
00:30:53,840 --> 00:30:56,680
Speaker 2: If not, we'd be upset, right, or we'd be confused

629
00:30:56,840 --> 00:30:59,240
Speaker 2: and we'd think there's a hint. So they did the

630
00:30:59,280 --> 00:31:02,320
Speaker 2: same thing with measuring the Hubble constant. The measurement I

631
00:31:02,360 --> 00:31:05,640
Speaker 2: told you about is what we call the late universe measurement.

632
00:31:05,880 --> 00:31:09,320
Speaker 2: We're looking at the expansion in recent times. We're using parallax,

633
00:31:09,360 --> 00:31:12,600
Speaker 2: we're using cephids, we're using type one a supernova. That's

634
00:31:12,640 --> 00:31:14,880
Speaker 2: like you know, in the last ten billion years of

635
00:31:14,960 --> 00:31:17,920
Speaker 2: the expansion of the universe, they can't penetrate all the

636
00:31:17,920 --> 00:31:19,760
Speaker 2: way to the very beginning because you need toype on

637
00:31:19,840 --> 00:31:22,640
Speaker 2: a supernova and they do eventually get dim But that's

638
00:31:22,640 --> 00:31:25,360
Speaker 2: what we call the late universe measurement. So you measure that,

639
00:31:25,400 --> 00:31:27,960
Speaker 2: you get one number for the Hubble constant, it's like

640
00:31:28,120 --> 00:31:32,240
Speaker 2: seventy four kilometers per second per mega parsek and a

641
00:31:32,280 --> 00:31:34,440
Speaker 2: lot of careful work has been done there because like,

642
00:31:34,760 --> 00:31:36,840
Speaker 2: what if you don't understand supernova, what are they are

643
00:31:36,840 --> 00:31:39,160
Speaker 2: different kinds of supernova? What if the life is passing

644
00:31:39,160 --> 00:31:42,800
Speaker 2: through different stuff? And there's like entire batteries of people

645
00:31:42,840 --> 00:31:46,120
Speaker 2: whose entire PhD was like thinking about a way maybe

646
00:31:46,160 --> 00:31:49,400
Speaker 2: this went wrong and finding some clever way to check it.

647
00:31:49,400 --> 00:31:51,840
Speaker 2: It's incredible what folks are doing in astrophysics.

648
00:31:52,040 --> 00:31:55,200
Speaker 4: So you had mentioned that the Hubble constant isn't actually constant,

649
00:31:55,200 --> 00:31:57,160
Speaker 4: it's a number that's changing. So that number that you

650
00:31:57,280 --> 00:32:01,400
Speaker 4: gave us, is that a value for March twenty third

651
00:32:01,600 --> 00:32:02,680
Speaker 4: or okay.

652
00:32:02,480 --> 00:32:05,000
Speaker 2: Yeah, it's the recent measurement, right, it's the late time

653
00:32:05,040 --> 00:32:08,240
Speaker 2: expansion number. But you can also measure this in the

654
00:32:08,280 --> 00:32:11,280
Speaker 2: early universe because if we look at the most ancient

655
00:32:11,400 --> 00:32:14,360
Speaker 2: light in the universe, the cosmic microwave background light, so

656
00:32:14,480 --> 00:32:16,480
Speaker 2: light from when the universe was very dense, it was

657
00:32:16,480 --> 00:32:19,560
Speaker 2: a hot plasma and it was glowing and suddenly it

658
00:32:19,640 --> 00:32:23,320
Speaker 2: became transparent. So instead of that light continuously being emitted

659
00:32:23,360 --> 00:32:25,960
Speaker 2: and absorbed, it was just emitted, not absorbed and is

660
00:32:26,000 --> 00:32:28,360
Speaker 2: still around. And if you look at that light, you

661
00:32:28,360 --> 00:32:31,080
Speaker 2: can learn so much about the density of the universe

662
00:32:31,120 --> 00:32:33,040
Speaker 2: and what it was made out of. You can tell

663
00:32:33,040 --> 00:32:35,200
Speaker 2: how much dark matter there was, you can tell the

664
00:32:35,240 --> 00:32:37,680
Speaker 2: expansion rate, you can tell how much matter there was.

665
00:32:37,720 --> 00:32:40,480
Speaker 2: It's really incredibly rich, and we could have a whole

666
00:32:40,480 --> 00:32:43,320
Speaker 2: other episode digging into that science. But essentially what you

667
00:32:43,320 --> 00:32:46,440
Speaker 2: can do is from the wiggles in the cosmic microwave

668
00:32:46,480 --> 00:32:50,400
Speaker 2: background radiation, you can measure the expansion rate of the universe,

669
00:32:50,440 --> 00:32:52,800
Speaker 2: and then you can propagate that forward and say, if

670
00:32:52,800 --> 00:32:55,080
Speaker 2: we measure the number from the early universe, what number

671
00:32:55,160 --> 00:32:57,880
Speaker 2: should we measure today. So now you can compare these

672
00:32:57,920 --> 00:33:01,520
Speaker 2: two numbers apples to apples, and the CNB measurement, what

673
00:33:01,600 --> 00:33:04,800
Speaker 2: we call the early time measurement, propagated forward to compare,

674
00:33:05,040 --> 00:33:07,080
Speaker 2: gives us a different number, gives us a number like

675
00:33:07,160 --> 00:33:10,520
Speaker 2: sixty seven. And when these two numbers came out, people

676
00:33:10,520 --> 00:33:13,080
Speaker 2: were like, hmm, that's weird, but you know, the uncertainties

677
00:33:13,120 --> 00:33:15,920
Speaker 2: were kind of big, like sixty seven isn't that different

678
00:33:15,920 --> 00:33:18,200
Speaker 2: from seventy four if they both have like a plus

679
00:33:18,240 --> 00:33:21,720
Speaker 2: or minus ten on them. But as people spent more

680
00:33:21,720 --> 00:33:25,000
Speaker 2: time and more energy. Whittling down these uncertainties and measuring

681
00:33:25,000 --> 00:33:28,880
Speaker 2: these more precisely. The numbers didn't change, just the uncertainty shrink.

682
00:33:29,200 --> 00:33:31,520
Speaker 2: And now we're like, yeah, these are two different numbers.

683
00:33:32,040 --> 00:33:34,880
Speaker 2: And that's a concern because if it's right, it means

684
00:33:34,920 --> 00:33:38,080
Speaker 2: dark energy can't be constant. It means like, maybe dark

685
00:33:38,200 --> 00:33:41,400
Speaker 2: energy is growing with time, right, dark energy, it was

686
00:33:41,440 --> 00:33:44,840
Speaker 2: weaker and now it's stronger in late times. So this

687
00:33:44,880 --> 00:33:48,040
Speaker 2: is the sort of context for these recent measurements by

688
00:33:48,120 --> 00:33:49,960
Speaker 2: Daisy and dark energy. We're going to talk about in

689
00:33:50,000 --> 00:33:53,160
Speaker 2: a minute. Dark energy, this incredible story of discovering the

690
00:33:53,200 --> 00:33:56,160
Speaker 2: accelerating expansion of the universe, an attempt to describe it

691
00:33:56,280 --> 00:33:59,640
Speaker 2: using a simple model, the cosmological constant, which requires dark

692
00:33:59,720 --> 00:34:03,000
Speaker 2: energy be constant in space and therefore grow in a

693
00:34:03,000 --> 00:34:06,600
Speaker 2: certain way. But then our observation, this hubble tension, that

694
00:34:06,680 --> 00:34:08,879
Speaker 2: it doesn't quite work, that our measurements from the early

695
00:34:08,960 --> 00:34:11,680
Speaker 2: universe and our measurements from the late universe don't jibe

696
00:34:11,760 --> 00:34:14,799
Speaker 2: with the way we think dark energy operated, that maybe

697
00:34:14,800 --> 00:34:17,480
Speaker 2: it wasn't a constant in space, right, Maybe that whole

698
00:34:17,480 --> 00:34:20,200
Speaker 2: assumption was wrong. Maybe it's not a cosmological constant. Maybe

699
00:34:20,239 --> 00:34:22,359
Speaker 2: it's some other weird thing that's sort of similar but

700
00:34:22,400 --> 00:34:24,799
Speaker 2: not quite so that was sort of the context for

701
00:34:24,920 --> 00:34:25,880
Speaker 2: this recent study.

702
00:34:26,320 --> 00:34:29,719
Speaker 4: Okay, so the tension is that seventy four is not

703
00:34:29,840 --> 00:34:30,520
Speaker 4: sixty seven.

704
00:34:30,960 --> 00:34:33,480
Speaker 2: That's right. And remember to explain this tension, you need

705
00:34:33,520 --> 00:34:36,680
Speaker 2: some theory where dark energy is getting stronger recently.

706
00:34:36,920 --> 00:34:38,719
Speaker 4: All right, Well, let's take a break and when we

707
00:34:38,760 --> 00:34:40,759
Speaker 4: come back, we're going to find out what this new

708
00:34:40,800 --> 00:34:43,600
Speaker 4: experiment tells us about this tension. And also, I hope

709
00:34:43,600 --> 00:34:46,600
Speaker 4: one day there'll be a Wiener Smith conflict to match

710
00:34:46,640 --> 00:34:47,440
Speaker 4: the Hubble tension.

711
00:34:51,239 --> 00:35:23,760
Speaker 8: Well, it's good to have goals, and zionis Yeah.

712
00:35:10,520 --> 00:35:12,600
Speaker 4: All right, we're back. So, Daniel, you were telling us

713
00:35:12,640 --> 00:35:16,120
Speaker 4: about the Hubble tension and that labs have been working

714
00:35:16,160 --> 00:35:18,520
Speaker 4: hard to try to figure out what is causing this

715
00:35:18,560 --> 00:35:20,759
Speaker 4: difference between the two different measures for the expansion of

716
00:35:20,800 --> 00:35:23,120
Speaker 4: the universe. What have we learned recently?

717
00:35:23,400 --> 00:35:25,200
Speaker 2: Yeah, so there's been a lot of really interesting stuff

718
00:35:25,200 --> 00:35:28,440
Speaker 2: happening with dark energy, including new theories like I want

719
00:35:28,440 --> 00:35:30,880
Speaker 2: to spend one minute talking about this time scape theory.

720
00:35:30,880 --> 00:35:33,840
Speaker 2: A lot of people heard about huge pr echo chamber

721
00:35:33,880 --> 00:35:37,000
Speaker 2: from this one paper where somebody suggested that wait, maybe

722
00:35:37,000 --> 00:35:40,680
Speaker 2: the universe isn't actually accelerating in its expansion. Maybe we've

723
00:35:40,719 --> 00:35:43,800
Speaker 2: messed it all up. And his theory was that time

724
00:35:43,880 --> 00:35:46,319
Speaker 2: is slowed down near massive objects. We know that to

725
00:35:46,360 --> 00:35:49,279
Speaker 2: be true, so maybe the universe is act lumpier than

726
00:35:49,280 --> 00:35:51,800
Speaker 2: we thought, and they're parts of it that are denser,

727
00:35:51,840 --> 00:35:55,080
Speaker 2: and that's affecting the way we're interpreting this stuff. And

728
00:35:55,160 --> 00:35:57,319
Speaker 2: so this theory went by the very cool name of

729
00:35:57,640 --> 00:36:01,440
Speaker 2: time scape around the internet, and I got a bunch

730
00:36:01,440 --> 00:36:03,160
Speaker 2: of emails and a bunch of listeners heard about it

731
00:36:03,200 --> 00:36:04,600
Speaker 2: and thought, oh my gosh, are we getting rid of

732
00:36:04,640 --> 00:36:07,040
Speaker 2: dark energy? And that would be very cool, and we're

733
00:36:07,080 --> 00:36:09,960
Speaker 2: open to that. But this theory requires the universe to

734
00:36:09,960 --> 00:36:11,960
Speaker 2: be a lot lumpier than we see it to be,

735
00:36:12,520 --> 00:36:14,920
Speaker 2: like it would require a lot more mass in areas

736
00:36:14,960 --> 00:36:18,200
Speaker 2: to create this kind of effect. So the data just

737
00:36:18,280 --> 00:36:21,600
Speaker 2: are not consistent with the timescape theory. Nobody I know

738
00:36:21,680 --> 00:36:24,640
Speaker 2: in cosmology is taking that seriously at all, even though

739
00:36:24,680 --> 00:36:26,839
Speaker 2: we got a lot of press. So there's not often

740
00:36:26,880 --> 00:36:30,160
Speaker 2: a lot of correlation between like how excited the science

741
00:36:30,239 --> 00:36:32,799
Speaker 2: journalism core is about an idea and how excited the

742
00:36:32,840 --> 00:36:36,760
Speaker 2: actual scientists are about an idea. But there is something

743
00:36:36,840 --> 00:36:40,600
Speaker 2: that happened very recently measurements from the Daisy experiment. They

744
00:36:40,680 --> 00:36:43,719
Speaker 2: used a completely different method to measure the expansion of

745
00:36:43,760 --> 00:36:46,560
Speaker 2: the universe, one that fits sort of very nicely between

746
00:36:46,600 --> 00:36:49,840
Speaker 2: the very early universe measurements from the cosmic microwave background

747
00:36:50,160 --> 00:36:52,839
Speaker 2: and sort of later time measurements from the supernova crew.

748
00:36:53,280 --> 00:36:57,440
Speaker 2: They use something called bury on acoustic oscillations where they

749
00:36:57,480 --> 00:37:01,520
Speaker 2: see these rings of matter from USCI in the early universe.

750
00:37:01,760 --> 00:37:04,440
Speaker 4: And by looking at these rings of matter, it sounds

751
00:37:04,480 --> 00:37:06,360
Speaker 4: like you just said that it agreed with both of

752
00:37:06,360 --> 00:37:09,520
Speaker 4: the value. So it agrees with sixty seven and seventy four.

753
00:37:09,920 --> 00:37:12,360
Speaker 2: So this is a new technique, and it's cool that

754
00:37:12,400 --> 00:37:15,200
Speaker 2: it's complementary. By complementary, I just mean like they're using

755
00:37:15,239 --> 00:37:18,280
Speaker 2: another approach. Okay, When I say it fits nicely in between,

756
00:37:18,320 --> 00:37:20,960
Speaker 2: I don't mean that their measurement is in agreement with

757
00:37:21,040 --> 00:37:23,560
Speaker 2: the other folks. I mean that the time period they

758
00:37:23,560 --> 00:37:28,240
Speaker 2: can study is deeper into the past than the supernova folks,

759
00:37:28,640 --> 00:37:30,400
Speaker 2: and not all the way back to the beginning of

760
00:37:30,400 --> 00:37:33,000
Speaker 2: the universe. So in the universe timeline is sort of

761
00:37:33,040 --> 00:37:36,440
Speaker 2: a nice like probe of the sort of middle section. Okay,

762
00:37:36,440 --> 00:37:39,040
Speaker 2: all right, cool, and it's very cool study. What they're

763
00:37:39,080 --> 00:37:43,359
Speaker 2: looking for are these incredible echoes in hot plasma from

764
00:37:43,400 --> 00:37:46,239
Speaker 2: the early universe. And so, you know, you imagine the

765
00:37:46,280 --> 00:37:48,759
Speaker 2: early universe. It's very hot, it's very dense, you got

766
00:37:48,880 --> 00:37:51,759
Speaker 2: like protons, you got electrons, you got photons, you've got

767
00:37:51,840 --> 00:37:55,680
Speaker 2: dark matter in there. It's incredible, and it's mostly radiation dominated,

768
00:37:55,719 --> 00:38:00,320
Speaker 2: like the early universe, mostly photons, like a billion photons

769
00:38:00,400 --> 00:38:03,560
Speaker 2: for every electron. It's hard to wrap your mind around

770
00:38:03,560 --> 00:38:07,000
Speaker 2: because we're definitely not photon dominated now. And that's because

771
00:38:07,000 --> 00:38:10,040
Speaker 2: the very early universe made matter and antimatter, which then

772
00:38:10,080 --> 00:38:14,880
Speaker 2: mostly annihilated into photons. So that's why it's bathed in photons. Anyway,

773
00:38:14,920 --> 00:38:18,719
Speaker 2: these photons flying around, and they're pushing on the electrons

774
00:38:18,719 --> 00:38:21,399
Speaker 2: and on the protons, right, because that's what photons do.

775
00:38:21,760 --> 00:38:25,600
Speaker 2: They interact with charge particles. And so this plasma made

776
00:38:25,600 --> 00:38:28,560
Speaker 2: of protons and electrons is opaque to the photons. It's

777
00:38:28,600 --> 00:38:31,040
Speaker 2: pushing on them, just like the light inside the variable

778
00:38:31,080 --> 00:38:35,640
Speaker 2: stars creates this outward pressure, creates this density waves, right.

779
00:38:36,040 --> 00:38:38,120
Speaker 2: But dark matter, on the other hand, is pulling the

780
00:38:38,160 --> 00:38:41,120
Speaker 2: stuff in because of gravity. Dark matter ignores all this

781
00:38:41,200 --> 00:38:43,719
Speaker 2: pressure photons fly right through it. So you have these

782
00:38:43,719 --> 00:38:46,600
Speaker 2: two different effects, the photons pushing out and the dark

783
00:38:46,640 --> 00:38:49,400
Speaker 2: matter pulling in, and you get these density ripples.

784
00:38:49,760 --> 00:38:52,480
Speaker 4: So we know that dark matter does act on electrons

785
00:38:52,480 --> 00:38:53,880
Speaker 4: and protons, Is that what you were saying?

786
00:38:54,000 --> 00:38:56,640
Speaker 2: It acts on electrons and protons only through its gravity.

787
00:38:56,719 --> 00:38:58,440
Speaker 2: But there's a lot of it in the early universe,

788
00:38:58,480 --> 00:39:00,640
Speaker 2: and it's very dense, so this does have an effect.

789
00:39:01,239 --> 00:39:03,520
Speaker 2: And so these density ripples are moving through the early

790
00:39:03,600 --> 00:39:06,879
Speaker 2: universe at a really incredible rate. You know, the speed

791
00:39:06,960 --> 00:39:10,600
Speaker 2: of sound depends on the density of something. So for example,

792
00:39:10,680 --> 00:39:13,520
Speaker 2: speed of sound through air is pretty high, but it's

793
00:39:13,560 --> 00:39:15,640
Speaker 2: tiny compared to the speed of light. But the speed

794
00:39:15,719 --> 00:39:18,520
Speaker 2: of sound through water or through the Earth is faster, right,

795
00:39:18,560 --> 00:39:21,160
Speaker 2: the speed of sound through steel. That's why you could

796
00:39:21,160 --> 00:39:24,200
Speaker 2: like feel a herd of buffalo coming through the ground

797
00:39:24,239 --> 00:39:26,640
Speaker 2: before you heard them salivating over crushing you.

798
00:39:26,680 --> 00:39:31,399
Speaker 4: For example, they're herbivores, I think, Daniel, they would still

799
00:39:31,400 --> 00:39:32,640
Speaker 4: crush you. Ye, that's true.

800
00:39:32,680 --> 00:39:35,319
Speaker 2: Anyway, in the early universe, it's so dense that the

801
00:39:35,320 --> 00:39:39,120
Speaker 2: speed of sound is about half of the speed of light. Wow,

802
00:39:39,239 --> 00:39:43,480
Speaker 2: incredible density. So these pressure waves are shooting out at

803
00:39:43,520 --> 00:39:45,880
Speaker 2: half the speed of light. But then at some moment

804
00:39:45,920 --> 00:39:49,360
Speaker 2: the universe is expanding and it's cooling, and so protons

805
00:39:49,360 --> 00:39:52,920
Speaker 2: and electrons come together to make neutral hydrogen. Right, And

806
00:39:53,000 --> 00:39:56,200
Speaker 2: now they are transparent to those photons, so photons are

807
00:39:56,200 --> 00:39:59,040
Speaker 2: flying through them instead of pushing on them. And that's

808
00:39:59,080 --> 00:40:01,400
Speaker 2: a little bit of quantumic right there, you know, because

809
00:40:01,640 --> 00:40:04,359
Speaker 2: a free electron one that's just flying around, it's not

810
00:40:04,400 --> 00:40:07,640
Speaker 2: a hydrogen atom. Same with the free proton, can absorb

811
00:40:07,680 --> 00:40:10,680
Speaker 2: a photon of any energy. It's just like, no big deal.

812
00:40:11,080 --> 00:40:12,960
Speaker 2: It's only when you can find them you get the

813
00:40:13,160 --> 00:40:16,279
Speaker 2: energy levels. This quantization of the energy levels that the

814
00:40:16,280 --> 00:40:18,759
Speaker 2: electrons become so picky and say I'm only going to

815
00:40:18,800 --> 00:40:21,840
Speaker 2: absorb a photon of this energy or of that energy.

816
00:40:22,080 --> 00:40:25,319
Speaker 2: Paush electrons, I know, they become all snobby in their

817
00:40:25,320 --> 00:40:29,400
Speaker 2: fancy houses. And now the universe is transparent, so the

818
00:40:29,400 --> 00:40:32,520
Speaker 2: pressure stops. So you get these rings that were created

819
00:40:32,560 --> 00:40:34,799
Speaker 2: and then at some moment they get like frozen in

820
00:40:35,120 --> 00:40:38,279
Speaker 2: because they can no longer change. It's no more outward pressure. Right,

821
00:40:38,640 --> 00:40:41,000
Speaker 2: So you get these high density regions in the universe.

822
00:40:41,040 --> 00:40:43,440
Speaker 2: You might think, why do I care about early universe

823
00:40:43,520 --> 00:40:47,040
Speaker 2: high density regions? Well, dense regions in the early universe

824
00:40:47,280 --> 00:40:50,239
Speaker 2: lead to structure in the later universe, Like, why do

825
00:40:50,320 --> 00:40:52,880
Speaker 2: we have a galaxy here and not over there, because

826
00:40:52,920 --> 00:40:55,520
Speaker 2: fourteen billion years ago there was a little bit higher

827
00:40:55,520 --> 00:40:58,480
Speaker 2: density of stuff and then gravity took over and gathered

828
00:40:58,480 --> 00:41:00,720
Speaker 2: that together into a big blobb of star that became

829
00:41:00,800 --> 00:41:04,120
Speaker 2: a galaxy. So what they do in this experiment is

830
00:41:04,160 --> 00:41:06,520
Speaker 2: they don't look at the early universe plasma. They look

831
00:41:06,560 --> 00:41:09,480
Speaker 2: at the distribution of galaxies in the universe. They just

832
00:41:09,480 --> 00:41:11,920
Speaker 2: like make a huge map of galaxies and they look

833
00:41:12,000 --> 00:41:16,040
Speaker 2: for rings and they find these bubbles, these same literal bubbles.

834
00:41:16,040 --> 00:41:19,200
Speaker 2: You can see them in the universe. It's incredible, I know.

835
00:41:19,800 --> 00:41:22,040
Speaker 1: So you have this like foam of galaxies where the

836
00:41:22,080 --> 00:41:25,080
Speaker 1: galaxies are mostly on the edges, and then you also

837
00:41:25,160 --> 00:41:27,520
Speaker 1: have galaxies in the middle, but there's a higher density

838
00:41:27,800 --> 00:41:29,160
Speaker 1: along these bubbles.

839
00:41:29,239 --> 00:41:32,840
Speaker 2: So incredible, so much cleverness here to see this early

840
00:41:32,960 --> 00:41:36,120
Speaker 2: history of the universe. So around twenty years ago we

841
00:41:36,239 --> 00:41:38,799
Speaker 2: saw these first evidence that we can actually see the

842
00:41:38,800 --> 00:41:43,000
Speaker 2: baryon acoustic oscillations from the early universe as it transforms

843
00:41:43,320 --> 00:41:46,640
Speaker 2: into the structure of the universe today. And the recent

844
00:41:46,680 --> 00:41:50,160
Speaker 2: measurement by Daisy is like a super big camera that

845
00:41:50,239 --> 00:41:54,040
Speaker 2: looked at more galaxies than anybody ever had measured them,

846
00:41:54,080 --> 00:41:56,760
Speaker 2: deep into time, deep into the history of the universe,

847
00:41:56,800 --> 00:41:59,320
Speaker 2: all the way back to like three hundred million years.

848
00:41:59,880 --> 00:42:02,000
Speaker 2: You can see this structure early on, you can see

849
00:42:02,000 --> 00:42:04,480
Speaker 2: it later. And because it was sort of a fixed

850
00:42:04,560 --> 00:42:07,240
Speaker 2: yard stick, you can measure the expansion of the universe

851
00:42:07,280 --> 00:42:10,200
Speaker 2: by seeing the size of these bubbles over time. It's

852
00:42:10,200 --> 00:42:13,839
Speaker 2: sort of like, you know, a standard candill Again. So

853
00:42:13,880 --> 00:42:17,080
Speaker 2: they recently came out with the results, and this fills

854
00:42:17,080 --> 00:42:19,280
Speaker 2: in the gap. Right we saw the early universe measurement,

855
00:42:19,320 --> 00:42:21,200
Speaker 2: we saw the pretty late universe measurement. This is sort

856
00:42:21,200 --> 00:42:24,239
Speaker 2: of like the middle aged universe measurement. People wondering like,

857
00:42:24,280 --> 00:42:26,400
Speaker 2: what's it going to say, and it's consistent with the

858
00:42:26,440 --> 00:42:29,200
Speaker 2: dark energy density that's like constant in space, or what's

859
00:42:29,239 --> 00:42:32,920
Speaker 2: the behavior of it? And so the results very confusing.

860
00:42:33,280 --> 00:42:35,280
Speaker 4: Oh no, I thought you're gonna give me a clear answer,

861
00:42:35,360 --> 00:42:36,040
Speaker 4: Danyel Oh no.

862
00:42:36,200 --> 00:42:40,800
Speaker 2: Unfortunately, or excitingly, it's in chaos. So they see something

863
00:42:40,800 --> 00:42:43,800
Speaker 2: that doesn't look like dark energy is constant in space.

864
00:42:44,360 --> 00:42:46,520
Speaker 2: The expansion of the universe that they measure is not

865
00:42:46,680 --> 00:42:50,520
Speaker 2: consistent with a dark energy that just has constant density,

866
00:42:50,560 --> 00:42:52,640
Speaker 2: and it therefore grows at a certain rate as the

867
00:42:52,760 --> 00:42:55,840
Speaker 2: universe is expanding. And you might think, Okay, that's cool.

868
00:42:56,080 --> 00:42:58,759
Speaker 2: The hubble tension already told us that, right, Yes, but

869
00:42:58,760 --> 00:43:01,560
Speaker 2: the hubble tension told it was different from constant in

870
00:43:01,640 --> 00:43:05,640
Speaker 2: a different way. The two are inconsistent. This new measurement

871
00:43:05,680 --> 00:43:09,040
Speaker 2: from the very on acoustic oscillations is inconsistent with constant

872
00:43:09,120 --> 00:43:14,480
Speaker 2: dark energy and inconsistent with the hubble tension explanation. Yeah,

873
00:43:14,560 --> 00:43:19,000
Speaker 2: so this sees dark energy as weakening. According to Daisy,

874
00:43:19,280 --> 00:43:22,520
Speaker 2: dark energy is getting weaker over time. The hubble tension

875
00:43:22,600 --> 00:43:24,960
Speaker 2: needs something that's getting stronger at the end of the

876
00:43:25,000 --> 00:43:27,240
Speaker 2: late universe. I mean, there are other ways to explain

877
00:43:27,280 --> 00:43:30,080
Speaker 2: it as well, But it's not like, oh, this nicely

878
00:43:30,120 --> 00:43:32,880
Speaker 2: clicks together with this other story we already were getting

879
00:43:32,960 --> 00:43:35,600
Speaker 2: hints of from these other experiments. So I talked to

880
00:43:35,600 --> 00:43:38,480
Speaker 2: a cosmologist in my department here, keV Abazanjin, and he

881
00:43:38,560 --> 00:43:43,560
Speaker 2: calls this chaos cosmology because something basic is wrong, you know.

882
00:43:44,080 --> 00:43:46,280
Speaker 2: And that's fine. It's early days. We've only been studying

883
00:43:46,360 --> 00:43:48,520
Speaker 2: dark energy for a couple of decades, right, so like,

884
00:43:48,800 --> 00:43:51,640
Speaker 2: of course we're still learning really basic things about how

885
00:43:51,640 --> 00:43:54,520
Speaker 2: it works. And what we've done is apply a very

886
00:43:54,520 --> 00:43:57,920
Speaker 2: simple model, take the cosmological constant, use it to describe

887
00:43:57,960 --> 00:44:00,480
Speaker 2: dark energy. See if that works. Amazing. It kind of

888
00:44:00,480 --> 00:44:02,680
Speaker 2: worked for twenty years until we made more and more

889
00:44:02,719 --> 00:44:06,120
Speaker 2: precise measurements. Now we're saying that doesn't really work, and

890
00:44:06,239 --> 00:44:09,080
Speaker 2: we don't have a better framework right now. We don't

891
00:44:09,080 --> 00:44:12,359
Speaker 2: have an explanation that can explain these recent results from

892
00:44:12,400 --> 00:44:16,240
Speaker 2: Daisy the barrier on acoustic ostellations and the Hubble tension

893
00:44:16,320 --> 00:44:18,640
Speaker 2: that we've been puzzling over for the last ten years

894
00:44:18,760 --> 00:44:21,520
Speaker 2: or so. So there's a lot of exciting discoveries to

895
00:44:21,560 --> 00:44:21,879
Speaker 2: be made.

896
00:44:22,120 --> 00:44:26,560
Speaker 4: Does this mean that the universe is not necessarily expanding anymore,

897
00:44:26,680 --> 00:44:31,480
Speaker 4: or just that our understanding of the mechanism is not good.

898
00:44:31,880 --> 00:44:35,319
Speaker 2: The universe is definitely expanding, we don't really know if

899
00:44:35,320 --> 00:44:38,520
Speaker 2: it's accelerating at the same level as we thought it was,

900
00:44:39,760 --> 00:44:43,200
Speaker 2: and we don't know how that acceleration is changing. Right,

901
00:44:43,239 --> 00:44:45,800
Speaker 2: So there's sort of like another derivative there, the jerk

902
00:44:45,960 --> 00:44:49,040
Speaker 2: of the universe, if you will, and that says a

903
00:44:49,080 --> 00:44:52,560
Speaker 2: lot of important stuff about the future. Right. The previous view,

904
00:44:52,640 --> 00:44:55,840
Speaker 2: the simple view, the cosmological constant, that dark energy was

905
00:44:55,880 --> 00:44:58,960
Speaker 2: constant in space and therefore increasing as a fraction of

906
00:44:59,000 --> 00:45:02,000
Speaker 2: the universe over time. That painted a picture of a

907
00:45:02,080 --> 00:45:05,359
Speaker 2: universe torn apart by dark energy, because as things get

908
00:45:05,400 --> 00:45:08,279
Speaker 2: further apart and dark energy takes over, then they just

909
00:45:08,360 --> 00:45:11,160
Speaker 2: move apart faster and faster and faster and faster, And

910
00:45:11,320 --> 00:45:13,600
Speaker 2: the future of that universe is a bunch of galaxies

911
00:45:13,600 --> 00:45:17,040
Speaker 2: that collapse into black holes that are just like, incredibly

912
00:45:17,120 --> 00:45:19,839
Speaker 2: far away from all the other black holes. That would

913
00:45:19,840 --> 00:45:22,520
Speaker 2: be the future of the universe if the cosmological constant

914
00:45:23,160 --> 00:45:27,440
Speaker 2: was the thing causing the accelerating expansion. But if Daisy

915
00:45:27,520 --> 00:45:29,719
Speaker 2: is right and dark energy is somehow weakening, then that

916
00:45:29,840 --> 00:45:34,239
Speaker 2: acceleration is not necessarily going to keep ramping up, and

917
00:45:34,600 --> 00:45:36,640
Speaker 2: it could be that it slows down, and it could

918
00:45:36,640 --> 00:45:39,759
Speaker 2: even turn around. We could be heading for a time

919
00:45:39,800 --> 00:45:43,359
Speaker 2: when you wish you had purchased Daniel's extra premium dark

920
00:45:43,400 --> 00:45:48,680
Speaker 2: Crunch insurance policy. You con man, this whole episode is

921
00:45:48,719 --> 00:45:51,600
Speaker 2: just a grift for me to sell my insurance. Look,

922
00:45:51,680 --> 00:45:53,920
Speaker 2: I promise you, Kelly, if the universe collapses into a

923
00:45:53,920 --> 00:45:56,880
Speaker 2: black hole, I will be there with a cabin and

924
00:45:57,040 --> 00:45:59,960
Speaker 2: goats and whiskey and whatever you need to survive the.

925
00:46:00,239 --> 00:46:01,760
Speaker 4: Times and pigs and geeks.

926
00:46:01,800 --> 00:46:04,880
Speaker 2: Exactly. We'll put that on your policy, no extra charge.

927
00:46:04,960 --> 00:46:11,520
Speaker 4: Oh thanks, Daniel, Think I love a good deal. A

928
00:46:11,560 --> 00:46:14,279
Speaker 4: lot of information came at me today, So forgive me

929
00:46:14,280 --> 00:46:15,759
Speaker 4: if I'm totally giving this wrong. But I thought the

930
00:46:15,800 --> 00:46:20,319
Speaker 4: explanation for why the galaxy has rings depended on our

931
00:46:20,440 --> 00:46:25,120
Speaker 4: understanding of dark energy, dark matter, dark matter. Ah, I'm

932
00:46:25,160 --> 00:46:26,600
Speaker 4: always mixing those two up.

933
00:46:26,880 --> 00:46:29,560
Speaker 2: Dark matter is providing a gravity to pull it back

934
00:46:29,960 --> 00:46:32,200
Speaker 2: and to make these things oscillates exactly. That's why it's

935
00:46:32,239 --> 00:46:35,759
Speaker 2: called baryon acoustic oscillation. And then it's frozen in time

936
00:46:35,960 --> 00:46:39,319
Speaker 2: one certain moment in those oscillations because the photons can

937
00:46:39,320 --> 00:46:42,520
Speaker 2: no longer push on that stuff because it becomes neutral. Yeah,

938
00:46:42,880 --> 00:46:45,279
Speaker 2: dark matter, dark energy, I know it's also dark. It's

939
00:46:45,320 --> 00:46:46,520
Speaker 2: a dark universe out there.

940
00:46:46,680 --> 00:46:49,359
Speaker 4: Yep, yep. Okay, So now what do we do. We've

941
00:46:49,400 --> 00:46:51,319
Speaker 4: got this third way of measuring it and we're even

942
00:46:51,360 --> 00:46:53,439
Speaker 4: more confused. Do we just look for a fourth way

943
00:46:53,440 --> 00:46:53,920
Speaker 4: to measure it?

944
00:46:55,600 --> 00:46:57,480
Speaker 2: Yes, and of course we're going to work on that,

945
00:46:58,000 --> 00:47:00,640
Speaker 2: But also we have some theoretical work to do. We

946
00:47:00,719 --> 00:47:03,680
Speaker 2: need to understand how you could describe what we see

947
00:47:03,719 --> 00:47:06,600
Speaker 2: in a way that's consistent and makes sense across these

948
00:47:06,640 --> 00:47:09,440
Speaker 2: different experiments. That's why it's so important to do these

949
00:47:09,440 --> 00:47:12,000
Speaker 2: measurements in so many different ways, because we need to

950
00:47:12,040 --> 00:47:14,200
Speaker 2: unravel like, well, what assumption are we making in this

951
00:47:14,239 --> 00:47:16,959
Speaker 2: one the same way like the Greeks made the wrong

952
00:47:17,040 --> 00:47:19,439
Speaker 2: conclusion about the Solar system because they had one wrong

953
00:47:19,480 --> 00:47:22,320
Speaker 2: assumption that the stars were pretty close. Maybe there's a

954
00:47:22,360 --> 00:47:26,160
Speaker 2: basic assumption about the universe we're all making that's leading

955
00:47:26,239 --> 00:47:29,160
Speaker 2: us to miss the obvious explanation for what's going on here,

956
00:47:29,200 --> 00:47:31,839
Speaker 2: and podcast in five thousand years can be like, ha

957
00:47:31,880 --> 00:47:34,680
Speaker 2: ha ha, they didn't realize. I don't know what it is,

958
00:47:35,360 --> 00:47:37,560
Speaker 2: but it makes it so obvious why they were seeing

959
00:47:37,600 --> 00:47:38,240
Speaker 2: what they saw.

960
00:47:38,480 --> 00:47:40,520
Speaker 4: Well, I hope we figure out immortality so that you

961
00:47:40,600 --> 00:47:42,719
Speaker 4: and I could be having that discussion. We'll look back

962
00:47:42,760 --> 00:47:44,880
Speaker 4: and be like, oh, we were so silly when we

963
00:47:44,880 --> 00:47:45,359
Speaker 4: were young.

964
00:47:47,800 --> 00:47:50,800
Speaker 2: Life insurance policy is basically like immortality insurance.

965
00:47:50,920 --> 00:47:51,239
Speaker 1: M h.

966
00:47:51,719 --> 00:47:54,279
Speaker 2: Anyway, I'm not selling any insurance. I'm just hoping that

967
00:47:54,280 --> 00:47:57,200
Speaker 2: everybody out there enjoys the mysteries of the universe. We

968
00:47:57,320 --> 00:48:00,560
Speaker 2: live in a very turbulent time when we don't understand universe,

969
00:48:00,760 --> 00:48:03,759
Speaker 2: and we're constantly getting these updates that remind us that

970
00:48:03,760 --> 00:48:08,000
Speaker 2: they're huge discoveries to be made. So aspiring young cosmologists

971
00:48:08,040 --> 00:48:10,319
Speaker 2: out there don't worry. There are lots of things for

972
00:48:10,400 --> 00:48:11,319
Speaker 2: you to figure out.

973
00:48:18,680 --> 00:48:22,520
Speaker 4: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We

974
00:48:22,560 --> 00:48:24,960
Speaker 4: would love to hear from you, We really would.

975
00:48:25,120 --> 00:48:27,880
Speaker 2: We want to know what questions you have about this

976
00:48:28,080 --> 00:48:29,760
Speaker 2: Extraordinary Universe.

977
00:48:29,880 --> 00:48:32,840
Speaker 4: We want to know your thoughts on recent shows, suggestions

978
00:48:32,840 --> 00:48:35,839
Speaker 4: for future shows. If you contact us, we will get

979
00:48:35,880 --> 00:48:36,279
Speaker 4: back to you.

980
00:48:36,520 --> 00:48:40,000
Speaker 2: We really mean it. We answer every message. Email us

981
00:48:40,040 --> 00:48:43,200
Speaker 2: at Questions at Danielankelly.

982
00:48:42,320 --> 00:48:44,360
Speaker 4: Dot org, or you can find us on social media.

983
00:48:44,480 --> 00:48:48,279
Speaker 4: We have accounts on x, Instagram, Blue Sky and on

984
00:48:48,360 --> 00:48:50,319
Speaker 4: all of those platforms. You can find us at D

985
00:48:50,760 --> 00:48:51,279
Speaker 4: and K.

986
00:48:51,840 --> 00:48:53,920
Speaker 2: Universe will be shy right to us