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Speaker 3: When you pop a piece of cheese into your mouth,

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Speaker 3: you're probably not thinking about the environmental impact. But the

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Speaker 3: US dairy Tackling greenhouse gases, Many farms use anaerobic digestors

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Speaker 3: last sustainability to learn more.

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Speaker 2: Hey Daniel, Most of the stuff in the universe is

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Speaker 2: dark matter, isn't that right?

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Speaker 3: Yeah, it's about eighty percent of the matter in the universe.

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Speaker 2: And it's all around us, like right here with us

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Speaker 2: immersed in dark matter.

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Speaker 3: Yeah, we are swimming in it.

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Speaker 2: And it's also inside of us, is it?

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Speaker 3: Yeah, it passes through us, it doesn't bounce off your skin.

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Speaker 2: Does that mean that we're partly made out of dark matter?

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Speaker 3: Oh? I guess. So that's kind of dark to think about.

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Speaker 2: So if I discover myself, I'm discovering dark matter.

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Speaker 3: Know thyself. Win a Nobel Prize.

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Speaker 2: Or at least a dark Nobel Prize. Technically all Nobel

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Speaker 2: prizes have dark matter inside of them too.

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Speaker 3: Maybe they'll give you the cash in dark money.

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Speaker 2: Ooh, that got dark quick. Hi. I'm jeham and cartoonist

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Speaker 2: and the author of Oliver's Great Big Universe.

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Speaker 3: Hi. I'm Daniel. I'm a particle physicist at CERN and

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Speaker 3: a professor at UC Irvine. And I'll take your money

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Speaker 3: dark or light.

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Speaker 2: Really you'll take dark money. Isn't that dangerous for a

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Speaker 2: tenured professor?

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Speaker 3: No, that's what ten years for man. I can take

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Speaker 3: money from Dunias Visuals.

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Speaker 2: I guess technically the university takes the money and you

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Speaker 2: get a cut of it.

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Speaker 3: I never really had to worry about that. Like, nobody

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Speaker 3: who got wealthy with dubious techniques ever offered me a

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Speaker 3: slush fund, So I've never had to really grapple with that. Question.

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Speaker 2: Wait, how do you know? I mean, you've taken money.

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Speaker 2: Have you done your due diligence? How deep did you go?

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Speaker 3: You know? Almost all my research money comes from the government,

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Speaker 3: and we all know the various crimes that the government

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Speaker 3: has committed.

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Speaker 2: Exactly all government money is dark money.

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Speaker 3: M do you believe taxes are theft? Is that where

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Speaker 3: this is going?

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Speaker 2: Well, technically funding comes from taxpayers and there must be

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Speaker 2: some sketchy taxpayers out there, so your work is tainted.

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Speaker 3: So you're saying drug dealers who are paying taxes and

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Speaker 3: indirectly funding my research have made me complicit in their crimes.

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Speaker 2: That's right. Yes, assuming drug dealers pay taxes, which I

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Speaker 2: guess they do if they're laundering money, I don't know.

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Speaker 2: I feel like we need a whole podcast episode just

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Speaker 2: to cover dark money.

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Speaker 3: Yeah, and then I suppose everybody's guilty.

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Speaker 2: That's right, We're all guilty of paying taxes, I guess.

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

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Speaker 2: the Universe, a production of iHeartRadio.

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Speaker 3: In which we try not to overtax your brain while

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Speaker 3: explaining all of the mysteries of the universe. We want

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Speaker 3: to reveal the light universe and the dark universe, the

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Speaker 3: visible and the invisible. We want to show you how

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Speaker 3: the universe is not just what you see around you

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Speaker 3: and experience day to day, but so much more, so

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Speaker 3: much deeper, so many more mysteries waiting to be solved.

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Speaker 2: That's why we explore the universe, the dark corner it,

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Speaker 2: the light corners, and the sketchy corners of it, because

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Speaker 2: our understanding of the universe is still a little bit sketchy.

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Speaker 3: Like the Mafia corners of the universe.

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Speaker 2: No, like, not clearly drawn.

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Speaker 3: Oh I see, I thought we're gonna be talking about

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Speaker 3: like the physics of New Jersey or something.

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Speaker 2: Yeah, there's the only some dark matters going on out there.

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Speaker 3: How do you eat all those rich cookies and not

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Speaker 3: gain weight? Really, it's amazing.

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Speaker 2: Yeah, well, I think the secret is dark chocolate. It's

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Speaker 2: lower and fat, isn't it? Is it?

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Speaker 3: Really?

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Speaker 2: I don't know, You're like, what, what?

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Speaker 3: What?

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Speaker 2: Why aren't I eating more dark chocolate.

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Speaker 3: I'm not really stopping myself from eating dark chocolate. But

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Speaker 3: that wasn't the reason. I don't see dark chocolate is

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Speaker 3: like diet chocolate.

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Speaker 2: It's chocolate light. Oh no, wait, it's chocolate dark.

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Speaker 3: It's dark chocolate exactly. But there are lots of fun

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Speaker 3: questions out there in the universe, not just about how

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Speaker 3: waste management organizations in New Jersey are getting their money

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Speaker 3: and the calories that Dangel's eating. We're wondering about the

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Speaker 3: biggest questions in the universe, like where is all the stuff?

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Speaker 3: What is most of the universe made out of? But

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Speaker 3: how has it shaped the night sky that we see

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Speaker 3: today in the galaxy that we live in.

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Speaker 2: That's right, because what the universe is made out of

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Speaker 2: is maybe one of the biggest questions we can ask

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Speaker 2: about the universe. What is this whole place made out of?

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Speaker 2: What are we made out of? Are we made out of?

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Speaker 2: Dark matter? Can we exist without dark matter?

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Speaker 3: And we talk on this podcast a lot about dark matter.

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Speaker 3: We have lots of episodes about what it is and

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Speaker 3: where it is and how it works. And one thing

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Speaker 3: we often stress is that dark matter is part of

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Speaker 3: our galaxy, that most of our galaxy is actually dark

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Speaker 3: matter that has played a big role in the formation

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Speaker 3: of our galaxy. We wouldn't be here without it.

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Speaker 2: Yeah, we do talk a lot about dark matter. Daniel,

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Speaker 2: what percentage of our episodes would you say we talk

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Speaker 2: about dark matter, is the representative of the amount of

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Speaker 2: dark matter in the universe? Are we ignoring dark matter

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Speaker 2: in a way?

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Speaker 3: Is dark matter underrepresented matter on podcasts? That's a good question.

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Speaker 2: Yeah, well, especially our podcast, if we're trying to explain

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Speaker 2: the universe and the universe is twenty seven percent dark matter.

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Speaker 3: You know, we might reach twenty seven percent of our

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Speaker 3: podcast being about dark matter. It's been a lot of them,

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Speaker 3: and I'm pretty sure we don't have two thirds of

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Speaker 3: them about dark energy. Maybe we should.

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Speaker 2: Yeah, yeah, that's what everyone is asking for more dark

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Speaker 2: energy episodes. But it is a pretty important part of

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Speaker 2: the universe. It's a pretty important part of our existence

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Speaker 2: because without dark matter, maybe galaxies would not have formed

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Speaker 2: the same way that they formed. The Milky Way might

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Speaker 2: not be the same way it is now.

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Speaker 3: But we're always tempted to over general life, to say

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Speaker 3: that the way we live in our certain situation over

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Speaker 3: here is the way the whole universe works. It's important

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Speaker 3: to take a step back and to ask whether our

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Speaker 3: way of life and our way of galaxying is the

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Speaker 3: only way that it can be.

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Speaker 2: And so today, own the podcast, we'll be asking the

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Speaker 2: question are there galaxies without dark matter? Would you call

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Speaker 2: these light galaxies then, or galaxies light diet galaxies?

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Speaker 3: I call them tragic galaxies because they're probably galaxy where

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Speaker 3: everybody only eats white chocolate or.

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Speaker 2: Milk chocolate some chocolate snobs. I also call that a.

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Speaker 3: Tragedy, also known as crimes against chocolate.

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Speaker 2: Are you saying Hershey's is dark money as well?

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Speaker 3: Her She's his garbage? Man?

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Speaker 2: Oh my gosh. And there goes our sponsorship deal with Hershe's.

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Speaker 2: We were so close to funding this thing for the

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Speaker 2: next twenty years, and you had to go and insult them.

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Speaker 3: Maybe you could hear my hesitation there. I'm being torn

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Speaker 3: between being honest and truthful on a hard science podcast

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Speaker 3: and pandering to our sponsors, and I just had to

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Speaker 3: be honest about it. I passed on hershe'es. I'd rather

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Speaker 3: have no chocolate than Hershe's.

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Speaker 2: That was pretty harsh to garbage. Oh my gosh. Well,

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Speaker 2: here here's the thing. Like when you eat it. Let's

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Speaker 2: say you eat like a chocolate cake at a restaurant,

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Speaker 2: how do you know they didn't use Hershey's chocolate.

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Speaker 3: You can taste it, man, that's sour affront to chocolate.

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Speaker 3: It's turned so many people off of chocolate when chocolate

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Speaker 3: is this wonderful, amazing thing. Even milk chocolate can be

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Speaker 3: high quality, can be amazing. What they make in Pennsylvania. O, man,

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Speaker 3: it's a crime.

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Speaker 2: Now you're insulting the whole state of Pennsylvania.

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Speaker 3: Let's keep going. See how many people I can offend.

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Speaker 2: Yeah, yes, let's move. Let's insult the whole universe. Why

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Speaker 2: don't you.

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Speaker 3: Fortunately, most of the universe is dark matter and therefore

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Speaker 3: appreciates dark chocolate, and so we're good. We have the

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Speaker 3: majority firmly on our side.

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Speaker 2: But doesn't Hershey's own some fancy brands like Scharfenberger or

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Speaker 2: something like that.

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Speaker 3: I don't know, I hope not.

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Speaker 2: Well, maybe you've been eating Hershey's chocolates all this time.

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Speaker 2: A plot twist. Anyways, we're talking about dark matter and

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Speaker 2: galaxies and could there exist galaxies without dark matter? These

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Speaker 2: would be like galaxies that don't have any dark matter

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Speaker 2: in them or around them.

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Speaker 3: Yeah, exactly, just stars and gas and dust and black holes.

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Speaker 2: No dark matter. All right, Well, whether they are tragic

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Speaker 2: or not. We were wondering how many people out there

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Speaker 2: had wondered about this question. And if they have any

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Speaker 2: ideas about the answer.

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Speaker 3: Thanks very much to everybody out there who answers these questions,

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Speaker 3: whether or not they are supporters of Hershey's crimes against Chocolate.

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Speaker 3: We really appreciate everything you do. If you would like

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Speaker 3: to join this group, just write to me two questions

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Speaker 3: at Danielandjorge dot com.

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Speaker 2: I feel like maybe there's a Hurshi's employee out there

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Speaker 2: who listens to our podcast and it is now very,

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Speaker 2: very sad.

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Speaker 3: There's an easy fix for that, find a new job

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Speaker 3: or a new podcast. No, you got to go to

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Speaker 3: the root of the problem.

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Speaker 2: That's right anyway. So think about it for a second.

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Speaker 2: Do you think there can be galaxies without dark matter?

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

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Speaker 5: I feel like there probably aren't, only because I know

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Speaker 5: that dark matter, as far as I know, is distributed

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Speaker 5: pretty much evenly throughout the universe. I think it tends

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Speaker 5: to be clustered in galaxies, but I think it tends

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Speaker 5: to be pretty uniform, So I would be surprised if

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Speaker 5: there were galaxies without dark matter.

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Speaker 6: I'm going to say why not, because, like going back

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Speaker 6: to an episode about uranium on uranus, there could be

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Speaker 6: a tiny bit here and there in a galaxy. So

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Speaker 6: I'm going to say I don't know why there wouldn't

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Speaker 6: be dark matter in a galaxy. I'm also going to

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Speaker 6: say I don't know why there would.

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Speaker 7: I don't believe there are galaxies without dark matter because

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Speaker 7: dark matter is, in my understanding, a general term for

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Speaker 7: unknown matter, which is this and makes up the overwhelming

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Speaker 7: majority of the universe. Therefore, I think it is not

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Speaker 7: possible for galaxies not to have at least some dark

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Speaker 7: matter in them.

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Speaker 8: I'm not sure that we've observed any galaxies without dark matter,

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Speaker 8: but I suppose anything could be possible in this crazy universe.

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Speaker 8: It's also possible that all galaxies are without dark matter

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Speaker 8: and we just don't understand gravity all right.

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Speaker 2: Most people are skeptical about this question.

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Speaker 3: Yeah, people have the idea that dark matter is everywhere.

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Speaker 3: It's inescapable.

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Speaker 2: You can't get away from it, it seems in our question,

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Speaker 2: although one person has kind of said why not. That's

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Speaker 2: a good attitude to have.

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Speaker 3: Yeah, that's the whole attitude about physics, like, well, maybe

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Speaker 3: everything is different from what we'veoughter. Maybe there's something really

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Speaker 3: weird out there that could teach us something new about

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Speaker 3: the universe.

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Speaker 2: I do feel like that is a guiding question in

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Speaker 2: theoretical physics at least. Why not yes? Why not?

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Speaker 3: Sure? Maybe everything is just tiny cats at the quantum scale.

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Speaker 2: That's orry. Maybe everything's just made out of Hersy's charkga.

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Speaker 3: No no, I got to hop somewhere else in the multiverse.

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Speaker 2: If that's the case, all right, well let's get going

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Speaker 2: before this podcast gets too dark. Daniel, give us the basics.

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Speaker 2: What is dark matter? For those of us who haven't

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Speaker 2: listened to the twenty seven percent of our podcast.

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Speaker 3: Episodes, dark matter is fascinating because we simultaneously know a

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Speaker 3: lot about it and very little, Like we know that

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Speaker 3: there's a lot of dark matter in the universe, and

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Speaker 3: we know that it's matter. We know there's something out

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Speaker 3: there that's creating gravity or curvature of space time, but

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Speaker 3: that it's invisible. It doesn't glow, it doesn't give off light,

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Speaker 3: it doesn't reflect light. We sense it only because we

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Speaker 3: see its gravitational effects on stuff. It's curving space, which

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Speaker 3: changes how things are moving through that space. We see

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Speaker 3: galaxies rotating much faster than their gravity would be able

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Speaker 3: to hold together if there wasn't also dark matter in them,

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Speaker 3: holding them together. On the other hand, we don't know

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Speaker 3: what stuff it is. We know that it has gravity,

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Speaker 3: so it's matter, but we don't know it's some weird

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Speaker 3: new kind of neutrino or a totally different kind of

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Speaker 3: particle we've never seen before, or a thousand new kinds

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Speaker 3: of particles, or something that's not even a particle. So

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Speaker 3: we know a lot about it on the sort of

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Speaker 3: cosmological scale, but very very little or almost nothing about

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Speaker 3: it at the particle level. Right.

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Speaker 2: Dark matter is this kind of mysterious stuff in the

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Speaker 2: universe that we kind of feel its presence. We can

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Speaker 2: see its presence through gravity, but as you said, you

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Speaker 2: can't see it because it doesn't interact with elechormagnetic light

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Speaker 2: or maybe any of the other forces in the universe,

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Speaker 2: and so you can't see it. And that's why you

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Speaker 2: call it dark exactly.

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Speaker 3: And a bunch of listeners write in with the idea

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Speaker 3: that maybe dark matter is matter in another universe that's

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Speaker 3: somehow leaking in to hours. Remember that dark matter is

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Speaker 3: creating gravity in our universe or changing the curvature of

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Speaker 3: space in our universe, which means that it's in that space, right,

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Speaker 3: it shares that space with us, which kind of means

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Speaker 3: that it's in our universe, And so we really do

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Speaker 3: know that dark matter is something in our universe that's

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Speaker 3: changing the shape of space. We can only see sort

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Speaker 3: of indirectly through gravity, which is really frustrating because gravity

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Speaker 3: is the worst way to see things. It's so weak

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Speaker 3: that it makes it very, very difficult the way.

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Speaker 2: Couldn't it bend our space and not be part of

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Speaker 2: our space?

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Speaker 3: That's possible if you overthrow general relativity in our entire

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Speaker 3: understanding of space time. General relativity says that matter tells

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Speaker 3: space how to bend, and space tells matter how to move,

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Speaker 3: and that means matter in our space. Like in general relativity,

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Speaker 3: the curvature or space comes from the energy density in

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Speaker 3: that space. So if you have some like parallel space

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Speaker 3: overlaid on top of it, which can also bend that space,

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Speaker 3: then it seems to me like it'd be part of

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Speaker 3: our space, you know, sort of like the by definition.

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Speaker 3: But yet you could augment or throw out general relativity

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Speaker 3: replace it with something totally different. But the simpler idea

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Speaker 3: is that it's just some kind of mass we can't see.

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Speaker 3: That explains almost everything we see out there in the universe,

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Speaker 3: So it's sort of the best going explanation. You can

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Speaker 3: always make more baroque complicated explanations if you.

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Speaker 2: Like, Well, it kind of might as well be in

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Speaker 2: another universe, right, because if it doesn't feel a lot

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Speaker 2: of the same force as we don't, it's just kind

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Speaker 2: of like ghostly matter that's kind of living on top

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Speaker 2: of us. There might be beings made out of dark matter, right.

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Speaker 3: This is call the different sectors of the universe. If

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Speaker 3: you have like two different sets of particles that don't

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Speaker 3: interact at all except for through gravity, then we call

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Speaker 3: those like the lights of the visible sector and the

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Speaker 3: dark sector of the universe. And that's totally possible that

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Speaker 3: you could have a whole complicated physics happening in the

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Speaker 3: dark sector that we can't see now. Mostly we know

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Speaker 3: that dark matter can't interact with itself. If it did

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Speaker 3: interact with itself, it would form all sorts of complicated

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Speaker 3: structure and do all sorts of interesting things. We think

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Speaker 3: that dark matter is pretty spread out. However, there could

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Speaker 3: be a little component dark dark matter. Dark matter may

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Speaker 3: be lots of different kinds of things, and one little

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Speaker 3: component of it might be more complicated and do complicated

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Speaker 3: things like form life or ice cream, cones or cats

335
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Speaker 3: or good chocolate, without violating what we've seen dark matter do,

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Speaker 3: which is mostly spread out smoothly.

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Speaker 2: All right, Well, the question here today is can there

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Speaker 2: be galaxies without dark better? Why is this even a question? Like,

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Speaker 2: are most of the galaxies that we see out there?

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Speaker 2: Do they all have dark matter?

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Speaker 3: Yeah? The galaxies that you see out there in the

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Speaker 3: sky are like tracers. They're basically telling you where the

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Speaker 3: dark matter is in the universe. Remember that dark matter

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Speaker 3: is not something we can see, but it also dominates

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Speaker 3: the universe. Our estimates are that four fifths of the

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Speaker 3: matter in the universe is dark matter. So if you

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Speaker 3: like spin the wheel and pick our random object in

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Speaker 3: the universe, most likely you're going to get dark matter.

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Speaker 3: It's like overwhelmingly dark matter. So when the universe is

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Speaker 3: forming its structure and the gravity that determines like where

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Speaker 3: things are going to be, it's mostly the gravity of

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Speaker 3: dark matter that decides where things are going to clump

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Speaker 3: together and where things are not going to clump together. Remember,

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Speaker 3: the very early universe is mostly smooth, with a few

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Speaker 3: little blobs that are denser than others. The gravity of

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Speaker 3: those over dense pieces pull things together to form structure,

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Speaker 3: and that's where you get like galaxies in one part

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Speaker 3: of space and not galaxies in another part of space.

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Speaker 3: Where you have galaxies is where you had more dark

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Speaker 3: matter to pull that stuff together to form those galaxies.

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Speaker 2: Yeah, that's pretty wild to think that something we can't see,

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Speaker 2: that is invisible to us basically kind of dictates the

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Speaker 2: entire structure of the universe, right at least at the

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Speaker 2: galaxy level. Does dark matter also dictate things like superclusters

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Speaker 2: and beyond exactly?

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Speaker 3: And so you can imagine like these invisible wells, like

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Speaker 3: dark matter's curving space, which Shepherd's the other kind of

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Speaker 3: matter together. So every time you look up at the

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Speaker 3: night sky and you see a galaxy, you should imagine

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Speaker 3: there's an invisible blob of dark matter surrounding that galaxy.

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Speaker 3: There's a whole halo that's created the conditions to form

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Speaker 3: that galaxy. We run simulations, for example, of a universe

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Speaker 3: without dark matter, and it doesn't form galaxies after fourteen

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Speaker 3: billion years, so quite literally, we would not be alive

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Speaker 3: without dark matter.

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Speaker 2: And now is the same true for things like superclusters

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Speaker 2: and those giant bubbles of galaxies out there in the universe.

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Speaker 2: Is that dictated by dark matter as well, or is

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Speaker 2: that more of the quantum fluctuations of the universe.

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Speaker 3: Well, both, because there's this cosmic web that tells us

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Speaker 3: where dark matter will be denser and where dark matter

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Speaker 3: will not be dense. These filaments, in some places they

383
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Speaker 3: overlap and you get these wells where things pool together.

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Speaker 3: And so the whole cosmic web is dictated by dark

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Speaker 3: matter and the light matter. The normal matter baryons and

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Speaker 3: quarks and electrons just follows that. And so it's not

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Speaker 3: like a supercluster has a super halo. A supercluster is

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Speaker 3: made of galaxies connected together by these filaments.

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Speaker 2: So it also has filaments of dark matter.

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Speaker 3: Absolutely, Yes, there are filaments of dark matter connecting these

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Speaker 3: halos of around each galaxy.

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Speaker 7: Hmmm.

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Speaker 2: Interesting. All right, Well, let's dig into the question of

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Speaker 2: whether a galaxy can be clean of dark matter, or

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Speaker 2: whether it's kind of a requirement for a galaxy to form.

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Speaker 2: So let's dig into that. But first let's take a

397
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447
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448
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450
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451
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453
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459
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460
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461
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462
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465
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Speaker 2: All right, we're asking the question, can you have a

466
00:22:43,600 --> 00:22:46,760
Speaker 2: galaxy without dark matter? Could you maybe have a scripy

467
00:22:46,760 --> 00:22:48,640
Speaker 2: little galaxy out there that was like, No, I don't

468
00:22:48,640 --> 00:22:51,320
Speaker 2: care about dark matter. I'm just going to gather all

469
00:22:51,359 --> 00:22:54,840
Speaker 2: these all this gas and dust and on my own

470
00:22:54,880 --> 00:22:57,320
Speaker 2: without any help. That's kind of what we're asking.

471
00:22:57,000 --> 00:22:58,880
Speaker 3: Today, right, Yeah, exactly.

472
00:22:59,280 --> 00:23:02,120
Speaker 2: And so you talked about how most of the galaxies

473
00:23:02,640 --> 00:23:05,960
Speaker 2: that we see out there probably have dark matter, right,

474
00:23:06,000 --> 00:23:07,960
Speaker 2: We think they have dark matter, right, because they couldn't

475
00:23:07,960 --> 00:23:09,560
Speaker 2: be holding together without dark matter.

476
00:23:09,640 --> 00:23:12,440
Speaker 3: That's right. And it's even more than just most galaxies

477
00:23:12,480 --> 00:23:15,080
Speaker 3: have dark matter. It turns out galaxies are sort of

478
00:23:15,119 --> 00:23:19,040
Speaker 3: like extra rich in dark matter, Like most galaxies have

479
00:23:19,320 --> 00:23:22,199
Speaker 3: more dark matter than the average dark matter density in

480
00:23:22,240 --> 00:23:22,840
Speaker 3: the universe.

481
00:23:23,200 --> 00:23:25,040
Speaker 2: Wait, what what do you mean? Like, why are some numbers?

482
00:23:25,200 --> 00:23:27,480
Speaker 3: So if you average over the whole universe, like what

483
00:23:27,680 --> 00:23:30,680
Speaker 3: fraction of matter in the universe is dark matter, that's

484
00:23:30,720 --> 00:23:33,520
Speaker 3: eighty four percent. And that's not by counting. We don't

485
00:23:33,560 --> 00:23:36,840
Speaker 3: know how many dark matter particles there are. That's by mass. Like,

486
00:23:36,880 --> 00:23:39,720
Speaker 3: what fraction of the mass of stuff in the universe

487
00:23:39,800 --> 00:23:42,280
Speaker 3: is dark matter? That's about eighty four percent. But when

488
00:23:42,280 --> 00:23:44,920
Speaker 3: you look at galaxies and you ask, like, what fraction

489
00:23:45,000 --> 00:23:47,880
Speaker 3: of the mass in a galaxy is dark matter, that's

490
00:23:47,960 --> 00:23:52,119
Speaker 3: more like ninety one percent. So galaxies have like about

491
00:23:52,160 --> 00:23:55,800
Speaker 3: half as much normal matter as the average normal matter

492
00:23:55,840 --> 00:23:59,240
Speaker 3: density in the universe. Galaxies are like concentrated blobs of

493
00:23:59,320 --> 00:23:59,879
Speaker 3: dark matter.

494
00:24:00,080 --> 00:24:03,600
Speaker 2: And we get these numbers by measuring how fast the

495
00:24:03,600 --> 00:24:06,440
Speaker 2: galaxies are rotating and kind of guessing how much dark

496
00:24:06,480 --> 00:24:08,080
Speaker 2: matter you need to hold it all together.

497
00:24:08,920 --> 00:24:11,400
Speaker 3: Yeah, not so much guessing, measuring, right, But you're right,

498
00:24:11,400 --> 00:24:14,439
Speaker 3: it's looking at how the galaxy rotates. We can measure

499
00:24:14,520 --> 00:24:17,119
Speaker 3: the speed of those stars in the galaxy as they

500
00:24:17,119 --> 00:24:20,119
Speaker 3: whizz around the center by looking at their light and

501
00:24:20,160 --> 00:24:22,720
Speaker 3: seeing how it's red shifted or blue shifted. You're looking

502
00:24:22,720 --> 00:24:24,680
Speaker 3: at a galaxy, some of the stars will be moving

503
00:24:24,720 --> 00:24:27,159
Speaker 3: away from you and some moving towards you, so to

504
00:24:27,280 --> 00:24:30,320
Speaker 3: be red or blue shifted their light from the Doppler shift,

505
00:24:30,359 --> 00:24:32,960
Speaker 3: so you can measure their velocities. So you can look

506
00:24:32,960 --> 00:24:35,639
Speaker 3: at the velocity of stars as they get further and

507
00:24:35,880 --> 00:24:38,080
Speaker 3: further away from the center. And in order to hold

508
00:24:38,119 --> 00:24:40,720
Speaker 3: a star at a certain velocity a certain radius, you

509
00:24:40,840 --> 00:24:43,600
Speaker 3: need a gravitational force there, so you can calculate exactly

510
00:24:43,680 --> 00:24:46,480
Speaker 3: how much gravity is needed to hold a star at

511
00:24:46,520 --> 00:24:48,800
Speaker 3: a certain radius. They have all these stars at different

512
00:24:48,840 --> 00:24:52,480
Speaker 3: distances from the center, telling you exactly how much gravity

513
00:24:52,520 --> 00:24:55,119
Speaker 3: you need to keep those stars going at that speed.

514
00:24:55,640 --> 00:24:58,119
Speaker 3: And then you can add up how much you can see,

515
00:24:58,280 --> 00:25:00,800
Speaker 3: like count all the visible stars and the rest you

516
00:25:00,880 --> 00:25:04,040
Speaker 3: suppose is dark matter. I guess that's what you mean by.

517
00:25:03,960 --> 00:25:05,640
Speaker 2: Guessing, Yeah, inferring guessing.

518
00:25:07,040 --> 00:25:09,560
Speaker 3: There's a whole field of statistical inference that we should

519
00:25:09,600 --> 00:25:10,280
Speaker 3: just call guessing.

520
00:25:10,400 --> 00:25:14,000
Speaker 2: Yeah, Well, I mean you don't actually know how many

521
00:25:14,040 --> 00:25:16,400
Speaker 2: stars there are in that galaxy right so far away

522
00:25:16,440 --> 00:25:19,560
Speaker 2: you can't see the individual stars, so you're also sort

523
00:25:19,560 --> 00:25:22,680
Speaker 2: of inferring how many stars there are there. You're guessing

524
00:25:22,720 --> 00:25:23,600
Speaker 2: a little bit, aren't.

525
00:25:23,359 --> 00:25:26,280
Speaker 3: You there's always uncertainty in these measurements. Absolutely, and you're

526
00:25:26,359 --> 00:25:29,840
Speaker 3: right that we cannot resolve individual stars, especially near the

527
00:25:29,840 --> 00:25:32,440
Speaker 3: center where things get very dense. But we can see

528
00:25:32,480 --> 00:25:34,840
Speaker 3: the streams, right, we can see streams of stars. We

529
00:25:34,880 --> 00:25:37,720
Speaker 3: have models for how these galaxies work. But absolutely there's

530
00:25:37,720 --> 00:25:41,600
Speaker 3: always uncertainty. But the uncertainty in these calculations is tiny

531
00:25:41,800 --> 00:25:44,280
Speaker 3: compared to the size of dark matter. So there's no

532
00:25:44,359 --> 00:25:47,200
Speaker 3: uncertainty that there's a lot of dark matter in these galaxies.

533
00:25:47,560 --> 00:25:50,479
Speaker 3: Because remember the fractions we're talking about here, like ninety percent,

534
00:25:50,840 --> 00:25:53,920
Speaker 3: which means you're looking at a star, you're measuring its velocity.

535
00:25:53,960 --> 00:25:56,760
Speaker 3: You figure out how much gravity is needed hold it

536
00:25:56,800 --> 00:26:00,119
Speaker 3: there so it doesn't fly out into intergalactic space. You

537
00:26:00,119 --> 00:26:01,919
Speaker 3: add up all the stars, you get like ten percent

538
00:26:02,320 --> 00:26:05,520
Speaker 3: of the gravity you need. So there's a huge missing chunk.

539
00:26:06,720 --> 00:26:09,440
Speaker 2: And you're sure it's not just you know a lot

540
00:26:09,440 --> 00:26:11,200
Speaker 2: of asteroids or rocks that don't close.

541
00:26:11,400 --> 00:26:13,679
Speaker 3: Yeah, that's a great question. Could dark matter just be

542
00:26:13,920 --> 00:26:16,640
Speaker 3: normal matter that we're not seeing, right, just like dark

543
00:26:16,720 --> 00:26:19,800
Speaker 3: chunks of matter? So people have looked for that directly.

544
00:26:19,960 --> 00:26:25,120
Speaker 3: Those are called MACHOs massive compact halo objects, and we

545
00:26:25,160 --> 00:26:27,520
Speaker 3: think we would see those occasionally, like they would pass

546
00:26:27,600 --> 00:26:29,560
Speaker 3: in front of stars if there was a lot of them.

547
00:26:29,560 --> 00:26:31,520
Speaker 3: If they were really big, we would have spotted them.

548
00:26:31,520 --> 00:26:33,479
Speaker 3: So people have looked for that kind of stuff and

549
00:26:33,560 --> 00:26:36,280
Speaker 3: not seen it. Plus, we know something about how much

550
00:26:36,359 --> 00:26:39,520
Speaker 3: normal matter there was in the very early universe because

551
00:26:39,560 --> 00:26:42,800
Speaker 3: it dictates the fraction of elements that were produced, like

552
00:26:42,840 --> 00:26:45,879
Speaker 3: the hydrogen and helium and lithium very sensitive to the

553
00:26:45,920 --> 00:26:49,760
Speaker 3: density of quarks and electrons. In the early universe. We

554
00:26:49,880 --> 00:26:52,919
Speaker 3: talked about that once Big Bang nucleosynthesis. So we have

555
00:26:52,960 --> 00:26:55,760
Speaker 3: a pretty good handle on like how much normal matter

556
00:26:55,800 --> 00:26:58,439
Speaker 3: there was around, and we can explain where most of

557
00:26:58,440 --> 00:27:00,240
Speaker 3: that is now and the rest of it's got to

558
00:27:00,280 --> 00:27:00,840
Speaker 3: be dark matter.

559
00:27:01,000 --> 00:27:03,440
Speaker 2: And so basically every galaxy out there that we've seen,

560
00:27:04,560 --> 00:27:07,960
Speaker 2: we see that it's spinning faster than it should, or

561
00:27:08,000 --> 00:27:10,440
Speaker 2: it's holding together more than it should, so we think

562
00:27:10,560 --> 00:27:12,119
Speaker 2: it has dark matter. And now is that true for

563
00:27:12,160 --> 00:27:13,480
Speaker 2: every galaxy we've seen out there?

564
00:27:13,520 --> 00:27:16,000
Speaker 3: It turns out there's a pretty wide variety. Like when

565
00:27:16,040 --> 00:27:18,439
Speaker 3: you look at galaxies out there, some of them have

566
00:27:18,600 --> 00:27:20,680
Speaker 3: a lot of dark matter and some of them have

567
00:27:20,760 --> 00:27:23,679
Speaker 3: a huge amount of dark matter. There is a variety.

568
00:27:23,680 --> 00:27:26,960
Speaker 3: It turns out that smaller galaxies tend to have more

569
00:27:27,080 --> 00:27:30,359
Speaker 3: dark matter than really massive galaxies.

570
00:27:29,960 --> 00:27:32,680
Speaker 2: Not by absolutely amounts, but just relative to how many

571
00:27:32,720 --> 00:27:33,240
Speaker 2: stars they have.

572
00:27:33,440 --> 00:27:36,600
Speaker 3: Yeah, exactly higher dark matter fractions, I should say, And

573
00:27:36,640 --> 00:27:39,920
Speaker 3: that's because galaxies are better at holding onto their dark

574
00:27:39,960 --> 00:27:43,640
Speaker 3: matter than they are their normal matter. Galaxies are crazy places.

575
00:27:43,680 --> 00:27:46,119
Speaker 3: There's winds from all the stars right every star is

576
00:27:46,119 --> 00:27:50,200
Speaker 3: a fusion furnace and pushing out protons and electrons. These

577
00:27:50,359 --> 00:27:54,159
Speaker 3: cellar winds are pushing gas out of the galaxies. Then

578
00:27:54,160 --> 00:27:56,600
Speaker 3: there are supernovas going off all the time, blowing things

579
00:27:56,680 --> 00:28:00,600
Speaker 3: up and pushing things out. There's radiation really intense from

580
00:28:00,640 --> 00:28:03,719
Speaker 3: the center of the galaxy that's pushing gas out. So

581
00:28:03,960 --> 00:28:06,879
Speaker 3: galaxies are basically exploding and they're pushing a lot of

582
00:28:06,920 --> 00:28:09,960
Speaker 3: their matter out. And so the smaller a galaxy is,

583
00:28:10,280 --> 00:28:13,440
Speaker 3: the less it's capable of holding onto its normal matter,

584
00:28:13,720 --> 00:28:16,840
Speaker 3: the less it's capable of resisting these forces that push

585
00:28:17,040 --> 00:28:19,240
Speaker 3: gas out of the galaxies.

586
00:28:18,760 --> 00:28:20,679
Speaker 2: Because the bigger galaxies have more gravity.

587
00:28:20,720 --> 00:28:23,320
Speaker 3: Basically right exactly, the bigger galaxies are still doing this,

588
00:28:23,359 --> 00:28:25,240
Speaker 3: but they have more gravity so they can hold onto

589
00:28:25,240 --> 00:28:28,280
Speaker 3: their normal matter. So smaller galaxies, which have weaker gravity

590
00:28:28,400 --> 00:28:31,000
Speaker 3: lose more of this normal matter. So you look out

591
00:28:31,000 --> 00:28:33,399
Speaker 3: there at dwarf galaxies, the really tiny ones, they can

592
00:28:33,480 --> 00:28:35,640
Speaker 3: be like ninety nine percent dark matter.

593
00:28:35,880 --> 00:28:38,560
Speaker 2: But wouldn't the larger galaxies also be better at holding

594
00:28:38,600 --> 00:28:42,480
Speaker 2: onto their dark matter? Like wouldn't smaller galaxies lose some

595
00:28:42,560 --> 00:28:45,120
Speaker 2: dark matter eventually, like it might evaporate or something.

596
00:28:45,240 --> 00:28:48,000
Speaker 3: Yeah, that depends on what dark matter does. And in

597
00:28:48,040 --> 00:28:51,400
Speaker 3: this theory, dark matter does nothing but gravity, and so

598
00:28:51,440 --> 00:28:53,760
Speaker 3: you can't really lose your dark matter. Like to lose

599
00:28:53,760 --> 00:28:55,720
Speaker 3: your dark matter, you need some force that's pushing out

600
00:28:55,720 --> 00:28:58,240
Speaker 3: on it. But gravity is just attractive. So all these

601
00:28:58,240 --> 00:29:00,800
Speaker 3: forces like the solar winds and the radiation and the

602
00:29:00,800 --> 00:29:03,480
Speaker 3: supernova basically have no impact on the dark matter. Dark

603
00:29:03,480 --> 00:29:06,040
Speaker 3: matter just like brushes it right off, Like supernova could

604
00:29:06,040 --> 00:29:08,200
Speaker 3: happen right next to you, and a dark matter particle

605
00:29:08,240 --> 00:29:09,480
Speaker 3: would be like whatever, dude.

606
00:29:09,640 --> 00:29:12,040
Speaker 2: And so we haven't seen any galaxies without dark matter,

607
00:29:12,120 --> 00:29:14,040
Speaker 2: So then why are we asking the question are there

608
00:29:14,080 --> 00:29:16,760
Speaker 2: galaxies without dark matter? Is it more of like, is

609
00:29:16,760 --> 00:29:19,080
Speaker 2: it possible to have a galaxy without dark matter? Or

610
00:29:19,720 --> 00:29:22,000
Speaker 2: are we asking like could there be galaxies where we

611
00:29:22,080 --> 00:29:23,720
Speaker 2: haven't noticed it doesn't have dark matter.

612
00:29:23,800 --> 00:29:26,400
Speaker 3: Yeah, so great question. We're curious about this for lots

613
00:29:26,400 --> 00:29:29,120
Speaker 3: of reasons. Like number one, we have a theory about

614
00:29:29,160 --> 00:29:31,400
Speaker 3: how the structure of the universe came to be and

615
00:29:31,440 --> 00:29:34,240
Speaker 3: how it made galaxies, and this nice story we told

616
00:29:34,280 --> 00:29:38,400
Speaker 3: you about over densities clumping together to form galaxies, et cetera,

617
00:29:38,440 --> 00:29:40,280
Speaker 3: et cetera. But we'd like to test that. We'd like

618
00:29:40,360 --> 00:29:43,560
Speaker 3: to make sure that's correct. We're often surprised when we

619
00:29:43,600 --> 00:29:46,480
Speaker 3: look out in the universe and see how things actually work,

620
00:29:47,120 --> 00:29:49,000
Speaker 3: and so what we'd like to do is check our

621
00:29:49,000 --> 00:29:52,120
Speaker 3: predictions about like the dark matter of fractions of galaxies

622
00:29:52,160 --> 00:29:55,920
Speaker 3: against reality and see is this really the way things work. Also,

623
00:29:55,960 --> 00:29:58,840
Speaker 3: this really helps us understand what dark matter is, because

624
00:29:58,880 --> 00:30:01,640
Speaker 3: seeing how dark matter very across the universe can tell

625
00:30:01,680 --> 00:30:03,680
Speaker 3: us something about the nature of dark matter and help

626
00:30:03,760 --> 00:30:07,360
Speaker 3: us test various alternative theories about what dark matter might

627
00:30:07,560 --> 00:30:09,600
Speaker 3: or might not be. But it's not exactly true that

628
00:30:09,600 --> 00:30:12,200
Speaker 3: we've never seen a galaxy without dark matter. People are

629
00:30:12,240 --> 00:30:14,520
Speaker 3: out there looking for these and they found some pretty

630
00:30:14,520 --> 00:30:15,280
Speaker 3: weird cases.

631
00:30:16,240 --> 00:30:19,280
Speaker 2: Interesting, all right, what are some of these cases?

632
00:30:19,440 --> 00:30:22,360
Speaker 3: So this galaxy group kind of nearby on cosmic scales,

633
00:30:22,400 --> 00:30:24,640
Speaker 3: that sixty three million light years away. It is called

634
00:30:25,160 --> 00:30:29,080
Speaker 3: n GC one zero five to two, and basically it's

635
00:30:29,080 --> 00:30:32,520
Speaker 3: an elliptical galaxy in Nsitis constellation. We've known about it

636
00:30:32,520 --> 00:30:34,440
Speaker 3: for like two hundred and fifty years or so. But

637
00:30:34,480 --> 00:30:36,680
Speaker 3: there's actually a little group of galaxies. It's like a

638
00:30:36,720 --> 00:30:40,200
Speaker 3: major galaxy with a bunch of little galaxies nearby. They

639
00:30:40,240 --> 00:30:42,720
Speaker 3: call these dwarf galaxies. So it's a whole group, so

640
00:30:42,760 --> 00:30:45,800
Speaker 3: they call the group of galaxies. And these little galaxies

641
00:30:45,840 --> 00:30:49,640
Speaker 3: are actually ultra diffuse galaxies. That means there galaxies that

642
00:30:49,680 --> 00:30:52,440
Speaker 3: are not very bright, they have very few stars in them.

643
00:30:52,560 --> 00:30:56,480
Speaker 3: And these ultra diffuse galaxies near this NNGC group they

644
00:30:56,480 --> 00:30:59,320
Speaker 3: think might have no dark matter in them at all.

645
00:31:00,040 --> 00:31:02,080
Speaker 3: They think that so they look at the rotations of

646
00:31:02,120 --> 00:31:04,960
Speaker 3: these galaxies and they do that calculation and they estimate

647
00:31:05,120 --> 00:31:07,880
Speaker 3: zero dark matter. Like every time you're doing this, you're

648
00:31:07,880 --> 00:31:11,240
Speaker 3: not assuming the dark matter. You're measuring it, and sometimes

649
00:31:11,280 --> 00:31:14,160
Speaker 3: it comes out ninety percent, sometimes eighty four percent, sometimes

650
00:31:14,240 --> 00:31:16,640
Speaker 3: ninety nine percent. In this case, it comes out close

651
00:31:16,680 --> 00:31:19,920
Speaker 3: to zero or consistent with zero. So they think these

652
00:31:20,000 --> 00:31:22,560
Speaker 3: are little galaxies that have no dark matter in them

653
00:31:22,600 --> 00:31:22,960
Speaker 3: at all.

654
00:31:23,040 --> 00:31:24,800
Speaker 2: So that's pretty wild. That means that you can have

655
00:31:24,840 --> 00:31:26,080
Speaker 2: a galaxy without dark matter.

656
00:31:26,280 --> 00:31:29,920
Speaker 3: Yeah, it's fascinating because remember our theory of galaxy formation

657
00:31:30,160 --> 00:31:33,520
Speaker 3: is that basically every big galaxy is a merger of

658
00:31:33,560 --> 00:31:36,520
Speaker 3: a bunch of small galaxies. Big galaxies don't like form

659
00:31:36,560 --> 00:31:38,480
Speaker 3: all at once in a single collapse. You have a

660
00:31:38,520 --> 00:31:41,080
Speaker 3: bunch of baby galaxies then merge to make bigger and

661
00:31:41,080 --> 00:31:44,080
Speaker 3: bigger galaxies, so like a bottoms up approach. And so

662
00:31:44,160 --> 00:31:46,080
Speaker 3: if your big galaxy ends up with a lot of

663
00:31:46,160 --> 00:31:48,600
Speaker 3: dark matter in it, that means that the little galaxies

664
00:31:48,600 --> 00:31:50,520
Speaker 3: that made it should each have their own dark matter.

665
00:31:50,600 --> 00:31:52,440
Speaker 3: And we look at a dwarf galaxies and we mostly

666
00:31:52,480 --> 00:31:54,400
Speaker 3: see them having dark matter. In fact, some of them

667
00:31:54,400 --> 00:31:56,520
Speaker 3: have a lot. So it is really weird to see

668
00:31:56,520 --> 00:31:59,520
Speaker 3: these little galaxies without any dark matter at all. And

669
00:31:59,520 --> 00:32:01,560
Speaker 3: the question it is like, did they form this way

670
00:32:01,720 --> 00:32:05,120
Speaker 3: or did something happen to strip them of their dark matter.

671
00:32:05,160 --> 00:32:07,160
Speaker 2: Or maybe they formed later in the universe.

672
00:32:07,400 --> 00:32:10,520
Speaker 3: Yeah, exactly, And so that's a fascinating question. And so

673
00:32:10,560 --> 00:32:12,280
Speaker 3: there's a group that's done a study of these and

674
00:32:12,280 --> 00:32:14,760
Speaker 3: they have a theory about how these little diffuse galaxies

675
00:32:15,160 --> 00:32:17,000
Speaker 3: ended up without any dark matter in them.

676
00:32:17,160 --> 00:32:17,800
Speaker 2: What's the theory?

677
00:32:17,920 --> 00:32:20,400
Speaker 3: So The theory is basically a mini version of the

678
00:32:20,400 --> 00:32:23,680
Speaker 3: Bullet Cluster. You remember, the Bullet cluster is this famous

679
00:32:23,720 --> 00:32:26,000
Speaker 3: example that really convinced a lot of people that dark

680
00:32:26,000 --> 00:32:28,240
Speaker 3: matter was a real thing. It was a cluster of

681
00:32:28,280 --> 00:32:31,400
Speaker 3: galaxies that collided with another cluster of galaxies, and we

682
00:32:31,480 --> 00:32:33,600
Speaker 3: saw that what happened to the gas and the dust

683
00:32:33,600 --> 00:32:36,520
Speaker 3: and the dark matter was very different. So the gas

684
00:32:36,520 --> 00:32:39,480
Speaker 3: and the dust interacted and created collisions that dark matter

685
00:32:39,560 --> 00:32:42,080
Speaker 3: passed right through because it doesn't interact at that level.

686
00:32:42,200 --> 00:32:46,360
Speaker 3: Gravity's not strong enough, so basically separated the dark matter

687
00:32:46,440 --> 00:32:49,120
Speaker 3: from the normal matter. So the bulletluster, now you have

688
00:32:49,120 --> 00:32:50,920
Speaker 3: a blob in the middle with a bunch of normal

689
00:32:50,960 --> 00:32:52,960
Speaker 3: matter in it, and then you have dark matter on

690
00:32:53,080 --> 00:32:56,000
Speaker 3: both sides, so we can see through gravitational lensing. So

691
00:32:56,040 --> 00:32:58,160
Speaker 3: they think that might be similar to what happened in

692
00:32:58,200 --> 00:33:01,040
Speaker 3: this case, that maybe there was a big color between

693
00:33:01,080 --> 00:33:03,640
Speaker 3: two other objects, and these two things that we're seeing

694
00:33:03,640 --> 00:33:06,360
Speaker 3: now they call them DF two and DF four are

695
00:33:06,400 --> 00:33:09,640
Speaker 3: basically the results of that, like chunks of stars and

696
00:33:09,720 --> 00:33:12,440
Speaker 3: gas and dust that got stripped of their dark matter

697
00:33:12,480 --> 00:33:14,360
Speaker 3: and a collision and then tossed aside.

698
00:33:14,840 --> 00:33:18,200
Speaker 2: Well, why wouldn't some little bit of dark matter go with.

699
00:33:18,120 --> 00:33:19,960
Speaker 3: Them, because the dark matter and the normal man have

700
00:33:20,080 --> 00:33:23,120
Speaker 3: very different experiences in a collision, Like dark matter basically

701
00:33:23,200 --> 00:33:25,720
Speaker 3: passes right through. There's not really a collision when it

702
00:33:25,760 --> 00:33:28,200
Speaker 3: comes to dark matter. It's like two ghosts just phasing

703
00:33:28,240 --> 00:33:31,000
Speaker 3: through each other, whereas two people bumping into a hallway

704
00:33:31,000 --> 00:33:33,680
Speaker 3: are going to change their direction. So imagine you have

705
00:33:33,800 --> 00:33:36,240
Speaker 3: like a ghost inside you and somebody else is a

706
00:33:36,240 --> 00:33:38,840
Speaker 3: ghost inside them, and you have a collision in the hallway.

707
00:33:39,000 --> 00:33:41,480
Speaker 3: The ghosts just keep on going and the living people

708
00:33:41,480 --> 00:33:44,120
Speaker 3: bounce off each other. Now you know you're separated from

709
00:33:44,120 --> 00:33:44,520
Speaker 3: your ghost.

710
00:33:44,680 --> 00:33:46,840
Speaker 2: But there's so many that they discovered. Did they all

711
00:33:46,880 --> 00:33:48,160
Speaker 2: get that way from the collision?

712
00:33:48,240 --> 00:33:50,600
Speaker 3: So they've only found these two, and they have this

713
00:33:50,720 --> 00:33:54,280
Speaker 3: reconstruction of the collision that suggests that these two things

714
00:33:54,280 --> 00:33:58,200
Speaker 3: happen somewhere near NGC and created its collision, and it

715
00:33:58,240 --> 00:34:01,040
Speaker 3: should have also created a bunch of other ultra diiffuse

716
00:34:01,080 --> 00:34:04,240
Speaker 3: galaxies that they should be able to spot that there

717
00:34:04,280 --> 00:34:06,440
Speaker 3: should be like five or six of these that came

718
00:34:06,480 --> 00:34:09,279
Speaker 3: out of the collision that also have no dark matter,

719
00:34:09,520 --> 00:34:10,840
Speaker 3: So they're going to go and look for those.

720
00:34:11,560 --> 00:34:13,719
Speaker 2: So these are you said, these are dwarf galaxies.

721
00:34:14,000 --> 00:34:17,320
Speaker 3: Yeah, they're ultra diffuse galaxies. They're also dwarf galaxies, so

722
00:34:17,360 --> 00:34:19,280
Speaker 3: they're small and they're not very bright.

723
00:34:19,480 --> 00:34:21,320
Speaker 2: So in a way they kind of got made later

724
00:34:21,719 --> 00:34:23,400
Speaker 2: or not. Are they as old as the universe?

725
00:34:23,440 --> 00:34:27,200
Speaker 3: Well, they think this collision happened about eight billion years ago,

726
00:34:27,239 --> 00:34:29,800
Speaker 3: and so how you age these things, I guess depends.

727
00:34:29,840 --> 00:34:33,080
Speaker 3: Like the way they are now started about eight billion

728
00:34:33,120 --> 00:34:35,640
Speaker 3: years ago. Now, of course, have some progenitor or something

729
00:34:35,680 --> 00:34:38,560
Speaker 3: that they came from. Right, there was a larger object

730
00:34:38,640 --> 00:34:41,240
Speaker 3: they were a part of which definitely had dark matter

731
00:34:41,320 --> 00:34:43,520
Speaker 3: in it, and their dark matter is now sprayed in

732
00:34:43,640 --> 00:34:47,040
Speaker 3: some other direction. So they become separated from their dark matter.

733
00:34:47,400 --> 00:34:49,799
Speaker 3: And this must have been a pretty mammoth event. I mean,

734
00:34:49,880 --> 00:34:52,160
Speaker 3: they reconstruct this thing and it's like a collision at

735
00:34:52,200 --> 00:34:56,799
Speaker 3: three hundred kilometers per second of these huge cosmic objects. WHOA.

736
00:34:57,400 --> 00:35:00,719
Speaker 2: So these are galaxies that had dark but then they

737
00:35:00,760 --> 00:35:03,000
Speaker 2: got stripped away of their dark matter, and so that

738
00:35:03,080 --> 00:35:05,919
Speaker 2: shows that, hey, you can have a galaxy without dark matter.

739
00:35:05,960 --> 00:35:08,759
Speaker 2: But I guess maybe the larger question is can you

740
00:35:09,080 --> 00:35:10,760
Speaker 2: form a galaxy without dark matter?

741
00:35:11,000 --> 00:35:13,000
Speaker 3: Right? And so as you say, that's the deep question

742
00:35:13,040 --> 00:35:15,880
Speaker 3: about the nature of the formation of structure in the universe,

743
00:35:16,480 --> 00:35:18,560
Speaker 3: and so far, the answer to that is no, we

744
00:35:18,640 --> 00:35:20,960
Speaker 3: do not think it's possible to form a galaxy without

745
00:35:21,040 --> 00:35:23,120
Speaker 3: dark mattery. We think you need that dark matter around

746
00:35:23,160 --> 00:35:25,560
Speaker 3: to gather enough gas and dust to make stars and

747
00:35:25,680 --> 00:35:29,200
Speaker 3: to make a galaxy that without dark matter, normal matter

748
00:35:29,239 --> 00:35:32,200
Speaker 3: doesn't have enough gravity to have formed galaxies this early

749
00:35:32,239 --> 00:35:34,760
Speaker 3: in the universe. If you had a universe without dark matter,

750
00:35:34,960 --> 00:35:37,160
Speaker 3: or big section of it without dark matter and just

751
00:35:37,239 --> 00:35:40,359
Speaker 3: normal matter, it would form galaxies eventually, but it would

752
00:35:40,400 --> 00:35:41,600
Speaker 3: take a lot longer to do so.

753
00:35:41,840 --> 00:35:44,319
Speaker 2: But you know, as I understand it, during the Big Bang,

754
00:35:44,360 --> 00:35:47,719
Speaker 2: things were really hot and dense, and there were pockets

755
00:35:47,719 --> 00:35:50,600
Speaker 2: of things, and there were quantum fluctuations which maybe created

756
00:35:50,640 --> 00:35:54,400
Speaker 2: pockets of extra densities here and there. Couldn't there have

757
00:35:54,560 --> 00:35:57,600
Speaker 2: been a pocket of extra density of normal stuff but

758
00:35:57,680 --> 00:36:00,680
Speaker 2: not dark matter. That then when the universe blew, it

759
00:36:00,719 --> 00:36:03,920
Speaker 2: became a galaxy without dark matter like during the Big Bang.

760
00:36:04,000 --> 00:36:07,319
Speaker 2: Why does the normal matter have to follow the dark matter?

761
00:36:07,440 --> 00:36:10,680
Speaker 3: I guess it does in general because dark matter dominates

762
00:36:10,680 --> 00:36:12,840
Speaker 3: because there's just so much more of it. So it

763
00:36:12,880 --> 00:36:15,440
Speaker 3: basically like sets the scene for everything. But you're right,

764
00:36:15,440 --> 00:36:18,560
Speaker 3: It is theoretically possible to have a downward fluctuation in

765
00:36:18,600 --> 00:36:21,680
Speaker 3: the dark matter and an upward fluctuation in the normal matter.

766
00:36:22,000 --> 00:36:24,080
Speaker 3: So you get some region of space where you have

767
00:36:24,160 --> 00:36:27,480
Speaker 3: like extra super dense normal matter and almost no dark matter.

768
00:36:27,840 --> 00:36:30,640
Speaker 3: That's possible. Yeah, and so in principle that could happen,

769
00:36:30,640 --> 00:36:33,080
Speaker 3: and if it had enough matter, then it would form

770
00:36:33,120 --> 00:36:36,200
Speaker 3: a galaxy on its own. So in principle that's not impossible.

771
00:36:36,400 --> 00:36:38,440
Speaker 3: But we've never seen that, and I don't know what

772
00:36:38,520 --> 00:36:40,839
Speaker 3: the chances are of that happening theoretically, Like.

773
00:36:40,800 --> 00:36:42,880
Speaker 2: How many galaxies have we've done this calculation to make

774
00:36:42,880 --> 00:36:44,360
Speaker 2: sure that it has dark matter in it.

775
00:36:44,560 --> 00:36:47,759
Speaker 3: Yeah, that's a great question. We've measured the rotation velocity

776
00:36:47,760 --> 00:36:51,160
Speaker 3: of thousands and thousands of galaxies, but that's a tiny

777
00:36:51,200 --> 00:36:53,640
Speaker 3: fraction of the number of galaxies that are out there

778
00:36:53,680 --> 00:36:55,719
Speaker 3: and the number of galaxies we can see. Most of

779
00:36:55,719 --> 00:36:57,880
Speaker 3: the galaxies we can see, we can't measure the rotation

780
00:36:58,000 --> 00:37:01,400
Speaker 3: velocity because you're looking at like one or two pixels.

781
00:37:01,719 --> 00:37:03,279
Speaker 3: You need to be able to sort of resolve the

782
00:37:03,320 --> 00:37:05,759
Speaker 3: whole galaxies so you can see light from one side

783
00:37:05,840 --> 00:37:08,759
Speaker 3: versus light from the other side. So it's tricky, but yeah,

784
00:37:08,760 --> 00:37:11,440
Speaker 3: we haven't looked at that many galaxies as possible. There

785
00:37:11,440 --> 00:37:14,439
Speaker 3: are galaxies out there that did really form without dark matter.

786
00:37:15,000 --> 00:37:16,760
Speaker 2: All right, Well, it seems like we kind of answered

787
00:37:16,760 --> 00:37:19,560
Speaker 2: the question of the episode, which is, can you have

788
00:37:19,600 --> 00:37:22,319
Speaker 2: a galaxy without dark matter? The answer is yes, you

789
00:37:22,320 --> 00:37:25,359
Speaker 2: can have maybe galaxies that had dark matter, but then

790
00:37:25,400 --> 00:37:28,600
Speaker 2: they lose it or they get left behind by the

791
00:37:28,719 --> 00:37:32,320
Speaker 2: dark matter and so they're dark matter less. Or maybe

792
00:37:32,360 --> 00:37:34,280
Speaker 2: they could have formed at the beginning of the universe

793
00:37:34,360 --> 00:37:37,160
Speaker 2: in theory, but we haven't seen one yet. All right, Well,

794
00:37:37,239 --> 00:37:40,360
Speaker 2: let's dig into what this all means about our understanding

795
00:37:40,400 --> 00:37:43,400
Speaker 2: of dark matter and also gravity and whether or not

796
00:37:43,520 --> 00:37:47,080
Speaker 2: it needs to be overhauled. But first, let's take another

797
00:37:47,160 --> 00:37:47,680
Speaker 2: quick break.

798
00:37:51,840 --> 00:37:53,600
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799
00:37:53,719 --> 00:37:56,880
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800
00:37:56,920 --> 00:38:00,960
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801
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802
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803
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804
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815
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Speaker 2: All right, we're asking the question, can there be a

848
00:40:31,360 --> 00:40:36,719
Speaker 2: galaxy with no dark chocolate? And the answer is probably,

849
00:40:36,760 --> 00:40:39,000
Speaker 2: But that's not a universe Daniel wants to live in.

850
00:40:39,480 --> 00:40:42,840
Speaker 3: No, that's right, Transport me somewhere else in the multiverse asap.

851
00:40:43,120 --> 00:40:44,680
Speaker 2: What if you end up in a universe where there's

852
00:40:44,760 --> 00:40:46,240
Speaker 2: only milk or white chocolate?

853
00:40:47,080 --> 00:40:48,959
Speaker 3: Just keep smashing that button until I get.

854
00:40:48,880 --> 00:40:50,919
Speaker 2: Somewhere good And no, no, you only get one trip.

855
00:40:50,960 --> 00:40:51,839
Speaker 2: Would you take the risk?

856
00:40:53,680 --> 00:40:55,319
Speaker 3: I'm pretty happy with our universe, you know.

857
00:40:55,360 --> 00:40:58,520
Speaker 2: It's a pretty good one. We're talking about whether galaxies

858
00:40:58,600 --> 00:41:01,120
Speaker 2: can exist without dark matter, and the answer is yes,

859
00:41:01,520 --> 00:41:03,600
Speaker 2: they can be stripped away of their dark matter, or

860
00:41:03,760 --> 00:41:06,200
Speaker 2: theoretically they could form in the early universe, but we

861
00:41:06,239 --> 00:41:09,400
Speaker 2: haven't seen one yet and so maybe probably not. What

862
00:41:09,440 --> 00:41:11,839
Speaker 2: do you think happened? Why haven't we seen any? If

863
00:41:11,840 --> 00:41:14,200
Speaker 2: they can form without dark matter, why haven't we seen any?

864
00:41:14,360 --> 00:41:16,399
Speaker 3: I think that'd be really unlikely. I mean, the kind

865
00:41:16,400 --> 00:41:19,520
Speaker 3: of fluctuations we're talking about are very very large. In

866
00:41:19,520 --> 00:41:21,920
Speaker 3: the early universe, you had just sort of like energy

867
00:41:22,080 --> 00:41:25,440
Speaker 3: and then it decays into matter. As the universe expands

868
00:41:25,480 --> 00:41:28,040
Speaker 3: in cools, and every kind of matter is sort of

869
00:41:28,080 --> 00:41:30,719
Speaker 3: made uniformly, so you get more dark matter made and

870
00:41:30,800 --> 00:41:33,200
Speaker 3: less normal matter. But in order to have no dark

871
00:41:33,239 --> 00:41:36,320
Speaker 3: matter made, you'd need a really big fluctuation. You expect

872
00:41:36,320 --> 00:41:38,520
Speaker 3: to get like eighty five percent and you get zero.

873
00:41:38,640 --> 00:41:40,520
Speaker 3: It's like flipping a coin one hundred times in a

874
00:41:40,600 --> 00:41:43,279
Speaker 3: row and getting only heads instead of half heads and

875
00:41:43,320 --> 00:41:46,520
Speaker 3: half tails. It's pretty unlikely. Now the universe is really big,

876
00:41:46,560 --> 00:41:48,719
Speaker 3: of course, so that means that eventually it's going to happen,

877
00:41:48,800 --> 00:41:52,440
Speaker 3: especially if the universe is infinite, but it's so unlikely

878
00:41:52,800 --> 00:41:54,200
Speaker 3: that it's not going to be the first kind of

879
00:41:54,200 --> 00:41:56,600
Speaker 3: galaxy we see out there, or even in the first trench.

880
00:41:57,080 --> 00:41:58,520
Speaker 3: Eventually we might spot one.

881
00:41:58,600 --> 00:42:00,360
Speaker 2: Well, as you said, it is possible to have a

882
00:42:00,360 --> 00:42:03,839
Speaker 2: galaxy without dark matter. We've seen it in some ultra

883
00:42:03,880 --> 00:42:07,719
Speaker 2: diffuse galaxies, and they've done the measurement on these galaxies, right,

884
00:42:08,040 --> 00:42:10,440
Speaker 2: They've measured how fast it's spinning, and they're pretty sure

885
00:42:10,440 --> 00:42:11,759
Speaker 2: there's no dark matter in them.

886
00:42:11,840 --> 00:42:14,560
Speaker 3: Yeah, there were a series of papers where people said, oh,

887
00:42:14,640 --> 00:42:16,919
Speaker 3: there's no dark matter, and another group did a different

888
00:42:16,960 --> 00:42:19,319
Speaker 3: measurement said no, there is some dark matter, and then

889
00:42:19,320 --> 00:42:21,920
Speaker 3: there were follow up papers arguing, and now they're pretty

890
00:42:21,960 --> 00:42:24,279
Speaker 3: sure there's no dark matter in these, but there's always

891
00:42:24,320 --> 00:42:26,879
Speaker 3: somebody out there who disagrees. I mean, it's astronomy after all.

892
00:42:26,920 --> 00:42:28,120
Speaker 2: That's right, they're all just guessing.

893
00:42:30,040 --> 00:42:32,800
Speaker 3: They're all just doing their best statistical inference.

894
00:42:34,280 --> 00:42:38,800
Speaker 2: That's right. That's a great word for guessing. I'm just kidding.

895
00:42:39,840 --> 00:42:42,759
Speaker 2: A best guessing. How about that best guessing? Nobody has

896
00:42:42,760 --> 00:42:43,400
Speaker 2: a better guess.

897
00:42:43,480 --> 00:42:45,480
Speaker 3: You know, those whole departments of people who do nothing

898
00:42:45,560 --> 00:42:49,879
Speaker 3: but statistics for a living. I'm trashing Hershey's, but you're

899
00:42:49,920 --> 00:42:51,200
Speaker 3: trashing statistics. Man.

900
00:42:51,880 --> 00:42:54,799
Speaker 2: No, there's nothing wrong with guessing wrong.

901
00:42:56,520 --> 00:42:58,000
Speaker 3: How do you know the universe is the way it is.

902
00:42:58,120 --> 00:42:58,920
Speaker 3: We're just guessing.

903
00:42:59,160 --> 00:43:01,840
Speaker 2: A best guess does mean that you're making things up randomly.

904
00:43:01,960 --> 00:43:04,319
Speaker 2: You're just using the best information you have to make

905
00:43:04,440 --> 00:43:07,240
Speaker 2: a best estimate or inference, right, I suppose.

906
00:43:07,280 --> 00:43:07,360
Speaker 8: So.

907
00:43:07,719 --> 00:43:09,759
Speaker 3: I think if it's very well informed, it's not really

908
00:43:09,840 --> 00:43:10,839
Speaker 3: a guess, you know.

909
00:43:10,920 --> 00:43:13,560
Speaker 2: But if you're one hundred percent sure, it's also not

910
00:43:13,640 --> 00:43:14,080
Speaker 2: a fact.

911
00:43:14,160 --> 00:43:17,000
Speaker 3: Yeah, that's true. That's why we use statistics to describe

912
00:43:17,040 --> 00:43:21,080
Speaker 3: our uncertainties. Anyway, One of the things we are uncertain

913
00:43:21,120 --> 00:43:23,920
Speaker 3: about is the nature of dark matter. Like a lot

914
00:43:23,960 --> 00:43:25,719
Speaker 3: of the stuff we talk about for dark matter is

915
00:43:25,800 --> 00:43:28,719
Speaker 3: kind of unsatisfyingly indirect, and a lot of people out

916
00:43:28,719 --> 00:43:32,040
Speaker 3: there treat dark matter like it's some placeholder, not a

917
00:43:32,080 --> 00:43:36,080
Speaker 3: real theory of the universe because we never see it directly.

918
00:43:36,080 --> 00:43:38,560
Speaker 3: We don't can't really grapple with it and grasp it.

919
00:43:38,560 --> 00:43:40,880
Speaker 2: Directly, right right, Well, I think it's interesting that we

920
00:43:40,960 --> 00:43:45,239
Speaker 2: have or that astronomers have found galaxies without dark matter,

921
00:43:45,280 --> 00:43:47,400
Speaker 2: because it almost gives you kind of like a test

922
00:43:47,480 --> 00:43:50,120
Speaker 2: case to confirm that the other galaxies that we have

923
00:43:50,160 --> 00:43:52,600
Speaker 2: seen with dark matter actually have dark matter and it's

924
00:43:52,640 --> 00:43:56,200
Speaker 2: not just some weird, you know, fluke or mistake in

925
00:43:56,239 --> 00:43:57,560
Speaker 2: our theory of gravity.

926
00:43:57,840 --> 00:44:00,360
Speaker 3: Mm hmm. Yeah, it's a cool test case. It's like

927
00:44:00,400 --> 00:44:03,959
Speaker 3: a control right would you see galaxies without dark matter

928
00:44:04,040 --> 00:44:05,840
Speaker 3: if they were there? So it's nice to have some

929
00:44:05,960 --> 00:44:09,040
Speaker 3: verification that we're seeing that. It's also, as you say,

930
00:44:09,080 --> 00:44:12,760
Speaker 3: a great test bed for comparing various theories of dark matter,

931
00:44:13,040 --> 00:44:15,920
Speaker 3: which make different predictions about what would happen in these scenarios.

932
00:44:16,040 --> 00:44:18,600
Speaker 2: M Yeah, different guesses about dark.

933
00:44:18,440 --> 00:44:22,280
Speaker 3: Matter, different ideas, different theoretical.

934
00:44:23,960 --> 00:44:26,640
Speaker 2: All right, well, how do these galaxies help us decide

935
00:44:26,719 --> 00:44:28,000
Speaker 2: what dark matter is made out of.

936
00:44:28,120 --> 00:44:30,640
Speaker 3: Well, one of the most popular alternatives to dark matter

937
00:44:30,760 --> 00:44:33,200
Speaker 3: as a theory of matter, some kind of stuff in

938
00:44:33,239 --> 00:44:37,000
Speaker 3: the universe is an alternative theory of gravity to say, well,

939
00:44:37,040 --> 00:44:39,320
Speaker 3: there's no other stuff in the universe. We're seeing everything

940
00:44:39,400 --> 00:44:42,680
Speaker 3: there is. It's just that gravity works differently from what

941
00:44:42,680 --> 00:44:45,600
Speaker 3: we expected. Because remember, the argument for dark matter is like,

942
00:44:45,680 --> 00:44:48,279
Speaker 3: we understand gravity, and there's a lot more gravity than

943
00:44:48,280 --> 00:44:50,439
Speaker 3: we can explain with the visible stuff, So there must

944
00:44:50,440 --> 00:44:52,960
Speaker 3: be more stuff, but there must be invisible stuff creating

945
00:44:53,000 --> 00:44:56,400
Speaker 3: that gravity. But what if instead we just don't understand

946
00:44:56,440 --> 00:45:00,239
Speaker 3: how gravity works and it can be explained by all

947
00:45:00,239 --> 00:45:03,200
Speaker 3: the visible stuff if you tweak your theory of gravity.

948
00:45:02,920 --> 00:45:05,920
Speaker 2: Meaning like, what if gravity just gets stronger the bigger

949
00:45:05,920 --> 00:45:09,600
Speaker 2: the distances, that might account for why galaxies are holding

950
00:45:09,600 --> 00:45:13,360
Speaker 2: on together without needing dark matter. That's kind of the idea, right.

951
00:45:13,200 --> 00:45:16,120
Speaker 3: That's kind of the idea. More specifically, there's this theory

952
00:45:16,160 --> 00:45:21,719
Speaker 3: called mond modified Newtonian dynamics that suggests that gravity's mostly

953
00:45:21,840 --> 00:45:24,840
Speaker 3: like Newton described, but there are some tweaks. It depends

954
00:45:24,840 --> 00:45:28,800
Speaker 3: on the acceleration of these objects, and for some accelerations,

955
00:45:28,840 --> 00:45:31,600
Speaker 3: gravity gets stronger or weaker, and you know it's a

956
00:45:31,600 --> 00:45:35,000
Speaker 3: little baroquely like added these terms and these tweaks basically

957
00:45:35,000 --> 00:45:38,240
Speaker 3: to explain these rotation curves, say like, oh, these stars

958
00:45:38,280 --> 00:45:41,040
Speaker 3: are accelerating more than those stars. So if we change

959
00:45:41,080 --> 00:45:44,200
Speaker 3: the way gravity works, can we describe the rotation curves

960
00:45:44,200 --> 00:45:47,640
Speaker 3: that we see. The answer is yes, you can devise

961
00:45:47,840 --> 00:45:51,000
Speaker 3: a theory to describe the rotation curves that explain how

962
00:45:51,040 --> 00:45:54,239
Speaker 3: these galaxies are rotating without needing dark matter. If you

963
00:45:54,320 --> 00:45:57,120
Speaker 3: tweak gravity, right, you have to tweak something, either change

964
00:45:57,120 --> 00:45:58,920
Speaker 3: the amount of matter that's there, or you change the

965
00:45:58,920 --> 00:45:59,759
Speaker 3: way gravity works.

966
00:46:00,000 --> 00:46:02,080
Speaker 2: Well, first of all, you just insulted the whole period

967
00:46:02,120 --> 00:46:03,680
Speaker 2: of human history, the Baroque period.

968
00:46:04,640 --> 00:46:07,920
Speaker 3: I meant that in a positive way, right right.

969
00:46:08,640 --> 00:46:11,280
Speaker 2: The second I know that we've talked about before, how

970
00:46:11,440 --> 00:46:15,160
Speaker 2: you know, maybe Mond modified Newtonian dynamics. It could replace

971
00:46:15,200 --> 00:46:18,520
Speaker 2: dark matter, but we confirm dark matter in other ways.

972
00:46:18,320 --> 00:46:21,000
Speaker 3: Right exactly. So Mon is a success in describing the

973
00:46:21,080 --> 00:46:26,440
Speaker 3: rotations of galaxies by making these beautiful baroque extensions to

974
00:46:26,840 --> 00:46:29,160
Speaker 3: Newton's theory. But there's lots of other ways we've seen

975
00:46:29,280 --> 00:46:32,200
Speaker 3: dark matter, like in the ripples of the cosmic microwave

976
00:46:32,239 --> 00:46:35,040
Speaker 3: background from the very early universe. We can see how

977
00:46:35,040 --> 00:46:38,960
Speaker 3: that early universe plasmo sloshing around, and that depends very

978
00:46:39,000 --> 00:46:42,560
Speaker 3: sensitively on the amount of dark matter, which slashes differently

979
00:46:42,800 --> 00:46:45,800
Speaker 3: in that plasma than normal matter did, and Mond cannot

980
00:46:45,840 --> 00:46:49,040
Speaker 3: explain that. Also, the Bullet cluster shows us that dark

981
00:46:49,080 --> 00:46:52,080
Speaker 3: matter can be separated from normal matter. It's not just

982
00:46:52,480 --> 00:46:55,279
Speaker 3: a different way that gravity works from normal matter. It

983
00:46:55,360 --> 00:46:58,439
Speaker 3: really is something else with its own gravity. So Mond

984
00:46:58,480 --> 00:47:01,520
Speaker 3: really struggles to explain and everything that the theory of

985
00:47:01,560 --> 00:47:04,520
Speaker 3: dark matter can explain, but it's still a popular alternative.

986
00:47:04,560 --> 00:47:06,960
Speaker 3: And this is another way. These dark matter free galaxies

987
00:47:07,040 --> 00:47:10,160
Speaker 3: are another way to draw contrast between what Mond predicts

988
00:47:10,239 --> 00:47:12,520
Speaker 3: and what dark matter predict because according to Mond, there

989
00:47:12,600 --> 00:47:15,000
Speaker 3: is no dark matter and gravity only depends on the

990
00:47:15,080 --> 00:47:17,799
Speaker 3: visible matter, and so these altered diffuse galaxies with no

991
00:47:17,920 --> 00:47:20,080
Speaker 3: dark matter should behave the same way all the other

992
00:47:20,120 --> 00:47:23,120
Speaker 3: galaxies do because there's no dark matter in any of them.

993
00:47:23,200 --> 00:47:25,200
Speaker 3: But we do see a difference. We see that these

994
00:47:25,200 --> 00:47:29,560
Speaker 3: guys are rotating more slowly, right, and so Mond struggles

995
00:47:29,560 --> 00:47:33,279
Speaker 3: to explain how slowly rotating these galaxies are without any

996
00:47:33,400 --> 00:47:36,000
Speaker 3: dark matter, whereas dark matter can explain all of it.

997
00:47:36,000 --> 00:47:37,680
Speaker 3: It's like, well, this has more dark matter, that has

998
00:47:37,760 --> 00:47:40,800
Speaker 3: less dark matter. So because dark matter can be variable

999
00:47:41,080 --> 00:47:43,960
Speaker 3: in the universe, some galaxies have more and some have less,

1000
00:47:44,120 --> 00:47:46,800
Speaker 3: whereas the rules of gravity have to be the same,

1001
00:47:47,080 --> 00:47:50,120
Speaker 3: Mond is sort of hamstrung and can't really explain the

1002
00:47:50,239 --> 00:47:52,440
Speaker 3: variation of all these galaxies.

1003
00:47:52,680 --> 00:47:54,319
Speaker 2: Well, I feel like Mond was already kind of dead

1004
00:47:54,320 --> 00:47:56,840
Speaker 2: in the water for all these other reasons for a while.

1005
00:47:57,040 --> 00:47:59,520
Speaker 2: But it is kind of interesting that seeing a galaxy

1006
00:47:59,560 --> 00:48:02,920
Speaker 2: without dark matter almost kind of helps prove that it exists.

1007
00:48:03,000 --> 00:48:04,799
Speaker 3: Yeah, that is really interesting, and I agree with you

1008
00:48:04,840 --> 00:48:07,360
Speaker 3: that Mond is not a theory we should take terribly seriously.

1009
00:48:07,400 --> 00:48:11,279
Speaker 3: In dark matter is overwhelming the better guess for what's

1010
00:48:11,320 --> 00:48:12,200
Speaker 3: going on in the universe.

1011
00:48:12,280 --> 00:48:14,320
Speaker 2: Yeah, there you go. See I brought you on board.

1012
00:48:16,360 --> 00:48:17,240
Speaker 3: I'm loving that word.

1013
00:48:17,280 --> 00:48:18,799
Speaker 2: Now you're like, I guess, I.

1014
00:48:18,760 --> 00:48:21,239
Speaker 3: Guess so, but you know, full caveats. There are some

1015
00:48:21,320 --> 00:48:23,359
Speaker 3: things that dark matter can't explain. There are a few

1016
00:48:23,400 --> 00:48:25,440
Speaker 3: galaxies out there that don't make any sense that no

1017
00:48:25,600 --> 00:48:28,120
Speaker 3: dark matter can really explain. Some people think that some

1018
00:48:28,280 --> 00:48:30,960
Speaker 3: hybrid like mostly dark matter with a little bit of

1019
00:48:31,040 --> 00:48:33,560
Speaker 3: mind is what we need to explain everything. That's out

1020
00:48:33,560 --> 00:48:35,759
Speaker 3: there in the universe, and so it's best to keep

1021
00:48:35,760 --> 00:48:37,880
Speaker 3: an open mind. It's also always nice to find a

1022
00:48:37,920 --> 00:48:40,440
Speaker 3: new way to test our understanding of dark matter and

1023
00:48:40,520 --> 00:48:43,840
Speaker 3: gravity in general, and so these galaxies without dark matter

1024
00:48:43,920 --> 00:48:45,000
Speaker 3: are a nice test bed for.

1025
00:48:44,960 --> 00:48:50,000
Speaker 2: That interesting you could call the new theory darkmond All right, well,

1026
00:48:50,040 --> 00:48:54,080
Speaker 2: another interesting example of how the universe just always has surprises.

1027
00:48:54,160 --> 00:48:56,880
Speaker 2: Like you think that maybe you need dark matter to

1028
00:48:56,960 --> 00:49:00,440
Speaker 2: have a galaxy, but only one day you find galaxies

1029
00:49:00,440 --> 00:49:02,279
Speaker 2: without dark matter, and it makes you think, and it

1030
00:49:02,320 --> 00:49:05,640
Speaker 2: actually maybe helps you confirm the existence of something as

1031
00:49:05,680 --> 00:49:07,200
Speaker 2: mysterious as dark matter.

1032
00:49:07,360 --> 00:49:09,279
Speaker 3: And it goes to show you that the universe does

1033
00:49:09,360 --> 00:49:12,000
Speaker 3: all these experiments for us. We can just look up

1034
00:49:12,000 --> 00:49:14,799
Speaker 3: in the night sky and find the examples of galaxies

1035
00:49:14,840 --> 00:49:18,479
Speaker 3: smashing into other galaxies or black holes colliding. All these

1036
00:49:18,480 --> 00:49:21,840
Speaker 3: things are wonderful experiments that help reveal the nature of

1037
00:49:21,840 --> 00:49:24,080
Speaker 3: the universe, the rules that it follows, and how it

1038
00:49:24,120 --> 00:49:24,880
Speaker 3: all works.

1039
00:49:25,280 --> 00:49:29,760
Speaker 2: Yeah, I guess, or you guess.

1040
00:49:30,960 --> 00:49:32,720
Speaker 3: In the end, aren't we all just guessing?

1041
00:49:32,760 --> 00:49:32,960
Speaker 12: Man?

1042
00:49:33,520 --> 00:49:36,480
Speaker 2: All right, Well, we hope you enjoyed that. Thanks for

1043
00:49:36,560 --> 00:49:38,720
Speaker 2: joining us. See you next time.

1044
00:49:43,680 --> 00:49:46,560
Speaker 3: For more science and curiosity. Come find us on social

1045
00:49:46,600 --> 00:49:50,160
Speaker 3: media where we answer questions and post video. We're on

1046
00:49:50,200 --> 00:49:53,360
Speaker 3: Twitter at this word instant and now TikTok and remember

1047
00:49:53,400 --> 00:49:56,200
Speaker 3: that Daniel and Jorge explain the Universe is a production

1048
00:49:56,320 --> 00:49:59,799
Speaker 3: of my Heart Radio. For more podcast from my Heart Radio.

1049
00:50:00,080 --> 00:50:03,759
Speaker 3: Is it the iHeartRadio app, Apple Podcasts or wherever you

1050
00:50:03,840 --> 00:50:05,360
Speaker 3: listen to your favorite shows.

1051
00:50:10,840 --> 00:50:13,720
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