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Speaker 3: Hey, Daniel, I have a question about dark Matt oh Man,

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Speaker 3: don't we all? I mean, I know that we don't

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Speaker 3: know what it is, right, but what is it like?

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Speaker 3: I mean, is it wushy?

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Speaker 1: We don't know.

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Speaker 3: What does it taste like?

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Speaker 1: Well, you know, our tongues can't taste it, so again

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Speaker 1: we don't really know.

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Speaker 3: How about is it fuzzy maybe we don't know, or scratching?

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Speaker 1: Probably not. But again we just don't know.

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Speaker 3: You know, for such a hot topic, you would think

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Speaker 3: you guys would know more about it.

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Speaker 1: Well, that's one thing we do know, whether dark matter

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Speaker 1: is hot or not.

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Speaker 3: Hi am Horehem, a cartoonist and the creator of PhD comics.

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Speaker 1: Hi I'm Daniel. I'm a particle physicist, and I have

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Speaker 1: no opinion about the attractiveness of dark matter.

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Speaker 3: Well, it's definitely attractive, right, gravitationally speaking, on a cosmological level.

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Speaker 1: That's right. It is the great attractor from that point

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Speaker 1: of view.

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Speaker 3: But welcome to our podcast Daniel and Jorge Explain the Universe,

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Speaker 3: a production of iHeartRadio.

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Speaker 1: In which we talk about all the amazing and crazy

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Speaker 1: things in our universe, the things that scientists have understood,

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Speaker 1: and the things that scientists are now working to understand.

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Speaker 1: We break down all the crazy for you and explain

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Speaker 1: it in a way that hopefully makes you smile.

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Speaker 3: That's right, all the things that are hot in this

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Speaker 3: universe and all the things that are not hot or

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Speaker 3: cold or super cold, because the universe has a broad range, right,

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Speaker 3: things can be hot as a million degrees or as

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Speaker 3: cold as zero degree.

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Speaker 1: That's right. Everything has a temperature, even black holes, we

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Speaker 1: all have a rating. That's right. Most of the universe

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Speaker 1: out there is at a very cold two point seventy

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Speaker 1: three degrees kelvin. But there are a few hot spots

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Speaker 1: a place like Earth where hot little bits of temperature

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Speaker 1: collude to make life an interesting podcast.

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Speaker 3: And so we like to talk about in this podcast

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Speaker 3: about dark matter a lot, and I feel like we

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Speaker 3: talk about it a lot because it's such a huge mystery.

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Speaker 3: I mean, it's twenty seven percent of the universe and

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Speaker 3: we don't know what it's made out of.

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Speaker 1: I think it's one of the biggest open questions in science.

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Speaker 1: You know, the person or the group that figures out,

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Speaker 1: like what is dark matter? Anyway, that will be a

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Speaker 1: historic moment, that will be an understanding and achievement, a

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Speaker 1: breakthrough that will go down in history for sure.

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Speaker 3: Or do you think a Nobel Prize would be enough

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Speaker 3: for that discovery or do you need to like stack

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Speaker 3: him up or something, or maybe make up like a

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Speaker 3: special Nobel Prize.

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Speaker 1: The dark Nobel Prize. You know, they should have already

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Speaker 1: given a Nobel Prize to Vera Ruben for the discovery

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Speaker 1: that dark matter was out there. Even if we don't

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Speaker 1: know what it is, we know it's there, we know

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Speaker 1: it's matter. And Nobel Prize committee overlooked Vera Ruben. Some

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Speaker 1: say because she's a woman.

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Speaker 3: Mmm, that's terrible.

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Speaker 1: That's the dark history of the Nobel Prize.

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Speaker 3: It's the dark history of dark matter. But we know

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Speaker 3: some things a little bit about dark matter, that it's there,

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Speaker 3: and that it's affecting things gravitationally and keeping galaxies together.

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Speaker 3: But the question is how much more do we know

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Speaker 3: about it? What else do we know about this mysterious thing,

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Speaker 3: if it even is a thing.

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Speaker 1: That's right, We would love to know what dark matter

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Speaker 1: is made out of, And particle physicists like me scratch

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Speaker 1: their heads all day wondering what kind of particle is

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Speaker 1: it made out of? Or many particles or is it

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Speaker 1: a particle at all? But along the way, while we're

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Speaker 1: looking for its particle nature, we have other ways to

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Speaker 1: try to get clues as to what might be. By

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Speaker 1: looking at how it moves and how it clumps, and

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Speaker 1: how it squishes and how it buzzes, we can try

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Speaker 1: to get a handle on what it is or isn't.

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Speaker 3: Yeah, and so to the on the program, we'll be

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Speaker 3: asking the question is dark matter hot or not? Well,

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Speaker 3: for those of you who are a little bit older,

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Speaker 3: you might remember a popular website a few decades ago

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Speaker 3: called hot or Not, which was probably inappropriate these days,

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Speaker 3: totally inappropriate exactly, Yeah, rated people based on their hotness.

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Speaker 3: And I'm guessing it was not the temperature.

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Speaker 1: No, it was not the temperature, although maybe we should

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Speaker 1: revive it in a physics version, like is the top

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Speaker 1: quark hot or not? Our nutrino is hot or not?

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Speaker 1: That might be.

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Speaker 3: Interesting or cold maybe based on how much funding you

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Speaker 3: can get for it.

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Speaker 1: That's right. And it's a weird combination of ideas, you know,

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Speaker 1: dark matter, mysterious blobs of stuff out there in the universe,

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Speaker 1: and temperature. But it turns out to be very important

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Speaker 1: and it's one of the most powerful handles we have

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Speaker 1: on the nature of matter and one of the most

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Speaker 1: valuable clues we have that tells us what it is

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Speaker 1: and what it can't be.

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Speaker 3: Yeah, So, as usual, we were wondering how many people

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Speaker 3: out there had thought about this question of whether dark

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Speaker 3: matter is hot or cold? And so as usual Daniel

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Speaker 3: went out there into the wilds of the Internet to

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Speaker 3: ask people this question.

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Speaker 1: That's right. So thank you to everybody who was willing

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Speaker 1: to participate in our random person on the Internet questions.

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Speaker 1: And if you'd like to answer random questions from me

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Speaker 1: in preparation for a future podcast, please write to us

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Speaker 1: to questions at Daniel and Jorge dot com.

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Speaker 3: So think about it for a second. What would you

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Speaker 3: answer if someone asked you is dark matter hot or cold.

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Speaker 3: Here's what people have to say.

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Speaker 4: I guess it seems most natural to me that dark

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Speaker 4: matter would interact with itself, so I guess doing so,

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Speaker 4: it is reasonable to think that it could have a temperature.

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Speaker 4: It's relative to other dark matter, so I guess it

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Speaker 4: would be hot.

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Speaker 5: What I think it's that our parts that of the

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Speaker 5: dark matter that can be hot and parts that are

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Speaker 5: gonna be colder.

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Speaker 4: I think dark matter is cold, or at least cooler

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Speaker 4: than normal matter.

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Speaker 1: On average.

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Speaker 5: The average temperature of the universe is a few coins

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Speaker 5: about zero. And since we have no idea, what is

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Speaker 5: what are the consistent particles of darkness?

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Speaker 1: I think the answer is we have no idea.

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Speaker 6: I don't know a whole lot about dark matter, but

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Speaker 6: I don't usually think of matter having a specific temperature.

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Speaker 3: I'd say we don't know, because we don't even know

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Speaker 3: what it is.

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Speaker 7: I would say that it's probably not hot. Well, hot

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Speaker 7: and cold are relative terms, So if what you mean

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Speaker 7: is does dark matter have a temperature, then I would

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Speaker 7: say probably not, because everything with the temperature gives off

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Speaker 7: infrared radiation.

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Speaker 3: I had to consult my eleven year old who is

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Speaker 3: the cosmologist in our family.

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Speaker 7: So we think that dark matter is cold.

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Speaker 6: The only reason we know it exists is because it

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Speaker 6: reacts gravity, and I don't think it reacts with anything

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Speaker 6: on the electromagnetic spectrum, so it wouldn't be hot or cold.

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Speaker 6: Both knowing scientists, they fan some intrinsic property of dark

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Speaker 6: matter and named it hot and cold, even though it

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Speaker 6: doesn't mean anything like hot or cold.

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Speaker 3: Right. I like how people evaded the question very expertly.

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Speaker 1: You're impressed by that? Are you disappointed?

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Speaker 3: I'm impressed. They're like, oh, they're thinking like physicists avoid

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Speaker 3: answering the question. It's like, what is hot and cold?

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Speaker 3: Let's divert into that discussion.

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Speaker 1: Well, we do this a lot in physics. We apply

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Speaker 1: weird sounding characteristics to things. You know, like we were

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Speaker 1: talking about particles. We're talking about their spin that's not

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Speaker 1: really spin, and we're talking about their mass, but they

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Speaker 1: don't have any stuff to them. And so I understand

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Speaker 1: why people are a little wary of interpreting like the

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Speaker 1: temperature of dark matter, Like what does that actually mean?

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Speaker 1: What are we really talking about?

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Speaker 3: Yeah, like, we don't even know if it's a thing,

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Speaker 3: So how can I have temperature.

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Speaker 1: That's right, it feels like a detail, Like are you

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Speaker 1: worried about what color it is? You don't even know

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Speaker 1: if it exists. Why do you care if it's purple

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Speaker 1: or brown?

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Speaker 3: Right? Yeah? Yeah? What color is dark matter? Than you?

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Speaker 1: It's dark?

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Speaker 3: All right? So let's break it down for folks. First

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Speaker 3: of all, I guess the question is, how can dark

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Speaker 3: matter even have a temperature if we don't know what

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Speaker 3: it is?

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Speaker 1: Right, Well, let's remember what temperature really means for us.

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Speaker 1: Temperature is a macroscopic quantity. Right, you touch something, it

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Speaker 1: feels hot or it feels cold, and that's really actually

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Speaker 1: about the heat difference, Like if something has more energy

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Speaker 1: in it then you do. Then the heat flows from

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Speaker 1: it into your finger, like when you touch a hot burner,

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Speaker 1: and that's what you're feeling. So you don't actually measure

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Speaker 1: temperature with your finger. You measure like a relative heat.

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Speaker 1: But when we think about temperature like microscopically, we try

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Speaker 1: to understand how that experience of feeling things being hot

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Speaker 1: or cold translates to like the motion of the particles

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Speaker 1: inside it, And so most loosely, we think about temperature

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Speaker 1: as relating to how fast those particles inside something are moving.

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Speaker 3: At a gas. If it's a hot gas, then the

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Speaker 3: particles in it are moving really fast.

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Speaker 1: That's right, and that's in fact what's happening. But also

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Speaker 1: for liquids and for solids, and in fact, that's why

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Speaker 1: liquids and solids are more solid than gases, right, because

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Speaker 1: their particles are not moving as much. They're more easily

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Speaker 1: trapped by all the bonds, and solid has various temperatures

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Speaker 1: because the atoms in it can wiggle more or less,

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Speaker 1: they can shake and vibrate in that kind of stuff.

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Speaker 1: So it's all about the energy stored in those parts.

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Speaker 3: Like the motion of the particles inside, like the speed. Almost.

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Speaker 1: Yeah, if you're talking about a gas, then it's mostly

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Speaker 1: about the speed. And I think this is really interesting

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Speaker 1: stuff to take something that's macroscopic and kind of qualitative,

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Speaker 1: you know, this feeling of temperature and try to understand

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Speaker 1: it on the microscopic scale, and it sometimes works, and

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Speaker 1: it doesn't always work. And we had a whole podcast

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Speaker 1: where we talked about like the hottest things in the universe,

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Speaker 1: and some of these things are counterintuitive. Like some of

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Speaker 1: the hottest stuff in the universe is the interstellar plasma,

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Speaker 1: which is like some raisy high temperature like three hundred

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Speaker 1: thousand degrees kelvin. But if we dropped you in it,

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Speaker 1: you would freeze to death immediately, right, And that feels counterintuitive.

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Speaker 3: Because there isn't much of it out there. That's right,

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Speaker 3: of this plasma hot plasma, it's very hot, but it's

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Speaker 3: very dilute, so it doesn't contain a lot of heat,

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Speaker 3: and so you're much denser blob of heat. If we

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Speaker 3: drop you in it, most of your heat would leak out.

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Speaker 3: But the particles of that plasma individually are moving super

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Speaker 3: duper fast, and so you can still call it hot. Right,

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Speaker 3: So it's related to the speed and or the vibration

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Speaker 3: or like the kinetic energy of the molecules and particles

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Speaker 3: in something. But how does that apply to dark matter,

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Speaker 3: because we don't really know if dark matter is made

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Speaker 3: out of particles or not.

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Speaker 1: We don't really know. Well, we know that something is

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Speaker 1: out there creating gravity. We know this a kind of matter,

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Speaker 1: and that's really about it. We know sort of where

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Speaker 1: it is in the universe. But you're right, we don't

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Speaker 1: know that it's a particle. It could turn out to

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Speaker 1: be something else. And you know, all the matter that

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Speaker 1: we've ever seen in the universe so far has been

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Speaker 1: made out of particles, So it seems tempting to say, well,

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Speaker 1: then the dark matter must also be made out of particles.

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Speaker 1: But you know, remember that dark matter is most of

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Speaker 1: the stuff in the universe. We've only seen a little slice.

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Speaker 1: We've seen five percent of the universe, so it's dangerous

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Speaker 1: to extrapolate to like a full twenty five percent and

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Speaker 1: say the rest of it must also be made out

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Speaker 1: of particles. Right, But we don't really have better ideas,

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Speaker 1: and so we typically just assume dark matters made out

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Speaker 1: of particles.

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Speaker 3: So that's kind of like the working hypothesis.

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Speaker 1: Yeah, it's like, let's try this, let's see if it works.

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Speaker 1: If it breaks, then we'll go back and examine all

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Speaker 1: the assumptions we made. But when you're exploring the unknown,

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Speaker 1: you've got to make some assumptions just to like have

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Speaker 1: something to do, because you can't just sit at home

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Speaker 1: and go like, I don't know what dark matter is.

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Speaker 1: You know, it sort of ends there. So we say,

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Speaker 1: maybe dark matter is a particle, and then we can ask,

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Speaker 1: if dark matter is made of particles, are those particles

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Speaker 1: moving fast or are they moving slow?

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Speaker 3: Right, Are they hot or not?

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Speaker 1: Are they hot or not? That's exactly what that really means.

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Speaker 1: It means is dark matter made out of super fast,

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Speaker 1: zippy particles moving realavistic speeds or is it made of

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Speaker 1: like heavier, slower moving particles that just sort of like

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Speaker 1: float around at slower speeds.

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Speaker 3: I guess it's kind of weird to think of something

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Speaker 3: being hot but not being able to touch it, you

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Speaker 3: know what I mean? Like, that's weird, right, I was

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Speaker 3: just thinking, do neutrinos have a temperature? Like in a

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Speaker 3: neutrino who we can't interact with through electromagnetism, can that

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Speaker 3: have a temperature?

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Speaker 1: Yes? Absolutely, neutrinos are very hot, and the reason is

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Speaker 1: that neutrinos have almost no mass, and so they zip

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Speaker 1: through the universe at very very high speeds, and so

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Speaker 1: they contain a lot of energy. You would say they

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Speaker 1: have a high temperature, but you're right that you can't

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Speaker 1: feel them, and the reason is that you have no

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Speaker 1: interaction in common with them, or almost none, because all

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Speaker 1: they feel is the weak force. So they have all

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Speaker 1: this energy, but they have no way to transmit it

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Speaker 1: to you, So it's like you pass right through each other.

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Speaker 1: And so they can have that high temperature, they can

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Speaker 1: have that high energy, but if there's no common interaction,

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Speaker 1: no way to communicate, then there's no way for that

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Speaker 1: energy to flow to you, and so you won't feel

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Speaker 1: them being hot.

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Speaker 3: What about like, what if dark matter is not a particle?

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Speaker 3: Can it still have a temperature and something that's not

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Speaker 3: a particle still be hot?

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Speaker 1: WHOA, you just blew my mind. Could something that's not

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Speaker 1: made of particles have a temperature? We've never seen anything

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Speaker 1: that's not made of particles, so that's quite a reach.

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Speaker 1: But I guess macroscopically you could, like see if it

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Speaker 1: emits light, and everything in the universe that does emit

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Speaker 1: light has a temperature, it's black body radiation. But I

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Speaker 1: don't know. That would be an amazing thing to explore

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Speaker 1: if we discover the dark matter wasn't made of particles,

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Speaker 1: because we do know something about its temperature, which is

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Speaker 1: what we're going to talk about today.

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Speaker 3: Oh, I see, So that it's made out of particles

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Speaker 3: is not just a working hypothesis. It's like your only hypothesis.

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Speaker 1: It's all we got at this point. It's like the

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Speaker 1: one idea we've been using for one hundred years or

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Speaker 1: you know, empty box for crazy new ideas somebody should

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Speaker 1: come up with.

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Speaker 3: Really, like, could be something that's not a particle.

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Speaker 1: It certainly could be. I mean, we have no conc

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Speaker 1: create evidence that it is a particle other than all

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Speaker 1: matter so far discovered is made of particles, right, but

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Speaker 1: it certainly could be. We're open to surprises. I mean,

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Speaker 1: dark matter itself is a surprise. Its existence was a surprise,

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Speaker 1: and there have been some ideas about unparticles matter made

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Speaker 1: out of things that are not quite particles that you know,

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Speaker 1: don't have a definitive size, but it's a bit fuzzy,

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Speaker 1: and nobody's really worked out the math for how it

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Speaker 1: could be dark matter, so they're just sort of like

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Speaker 1: the beginnings of ideas.

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Speaker 3: I guess. I mean, you know, like energy is energy

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Speaker 3: also particle based, because you know, energy can have gravity

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Speaker 3: or exert gravity or effect gravity.

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Speaker 1: Energy density certainly has gravity, and some energy is particle based,

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Speaker 1: like photons, right, Photons are basically just energy. They have

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Speaker 1: no mass to them, and photons contribute to the energy

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Speaker 1: density of the universe, and therefore it's curvature.

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Speaker 3: So certainly, m all right, Well, I guess there's no,

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Speaker 3: maybe room in your equations so far to account for

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Speaker 3: something that's not a particle. Is that kind of what

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Speaker 3: you're saying.

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Speaker 1: That's right, Yeah, but I would love to blow up

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Speaker 1: those equations. I would love if we found something about

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Speaker 1: dark matter that proved that it wasn't the particle, and

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Speaker 1: then we had to go back to the drawing board

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Speaker 1: and think from scratch. That would be a tremendous breakthrough,

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Speaker 1: an intellectual crack in the very foundations of physics, which

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Speaker 1: is the kind of thing we're all hoping will happen,

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Speaker 1: you know, because those are the moments you get, like

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Speaker 1: the real insights, You pull back the curtain and discover

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Speaker 1: something surprising and fascinating about the universe. So, yeah, this

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Speaker 1: is all we got so far, and I would love

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Speaker 1: to see it break into pieces.

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Speaker 3: You'd love to prove that they're not so hot. Yeah,

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Speaker 3: all these theories precisely. All right, Well, let's get into

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Speaker 3: how we could tell whether or not dark matter has

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Speaker 3: a temperature. Besides, like I guess, feeling its forehead, Daniel.

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Speaker 1: That's right. These days we're very sensitive to high temperatures.

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Speaker 3: But let's get into how we could tell and what

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Speaker 3: it tells us about dark matter. But first, let's take

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Speaker 3: All right, Daniel, we're talking about whether dark matter is

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Speaker 3: hot or cold, and so we talked about how we

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Speaker 3: have to kind of assume that it's a particle because

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Speaker 3: that's the only idea that we have. And so if

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Speaker 3: it's a particle, then you can talk about whether those

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Speaker 3: dark matter particles are moving a lot or vibrating a lot,

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Speaker 3: which case wouldn't make them technically hot even though we

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Speaker 3: can't feel it.

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Speaker 1: That's right, And we're really interested in whether dark mapp

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Speaker 1: is fast moving or slow moving because it tells us

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Speaker 1: also whether the particle is heavy, in which case is

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Speaker 1: more likely slow moving and cold or very very low mass,

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Speaker 1: in which case it is probably faster moving and hot.

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Speaker 1: So we're using this as a way to sort of

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Speaker 1: get a clue as to the nature of dark matter itself.

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Speaker 3: But it could dark matter be both like I mean,

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Speaker 3: could it be like regular matter that some of it

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Speaker 3: is hot and some of it is cold?

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Speaker 1: Totally? Absolutely, dark matter could be lots of different particles,

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Speaker 1: some of which are very heavy and some of which

427
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Speaker 1: are very light. But we know that dark matter sticks

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Speaker 1: around for a very very long time. It's like cosmologically stable.

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Speaker 1: It's been here since the beginning. It's affected the structure

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Speaker 1: of the universe. We've seen it put its imprint on

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Speaker 1: the whole history of the universe. And so that suggests

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Speaker 1: that it's probably stable, that it's not changing a lot

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Speaker 1: from one kind of mass to another. But you know,

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Speaker 1: we really just don't know.

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Speaker 3: All right, Well, let's get into now how we could

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Speaker 3: tell whether dark matter has a temperature or not, Like,

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Speaker 3: how would you even measure the temperature of dark matter

438
00:20:56,240 --> 00:20:58,200
Speaker 3: if a particle of dark matter was moving a lot

439
00:20:58,280 --> 00:21:00,760
Speaker 3: or bribraying a lot or not, could we even tell

440
00:21:00,800 --> 00:21:01,200
Speaker 3: the difference?

441
00:21:01,280 --> 00:21:03,480
Speaker 1: We can actually tell the difference and I think this

442
00:21:03,520 --> 00:21:05,840
Speaker 1: is really clever. It's one of the most elegant pieces

443
00:21:05,880 --> 00:21:09,040
Speaker 1: of science that I've seen recently. We can tell whether

444
00:21:09,160 --> 00:21:12,439
Speaker 1: dark matter is moving fast or slow because of the

445
00:21:12,440 --> 00:21:15,440
Speaker 1: way it makes an imprint on the growth of the universe.

446
00:21:15,920 --> 00:21:18,240
Speaker 1: You know, the universe started from like the Big Bang,

447
00:21:18,760 --> 00:21:22,520
Speaker 1: and back then things were hot and dense and mostly uniform,

448
00:21:23,160 --> 00:21:26,600
Speaker 1: and then you got little quantum fluctuations, little pockets of

449
00:21:26,640 --> 00:21:29,600
Speaker 1: density here and less density there, and those pockets are

450
00:21:29,600 --> 00:21:32,960
Speaker 1: critical because that's what seeds the whole structure of the universe.

451
00:21:33,040 --> 00:21:35,159
Speaker 1: Like the reason we have a galaxy here and not

452
00:21:35,240 --> 00:21:38,159
Speaker 1: over there is because some initial fluctuation made things a

453
00:21:38,200 --> 00:21:41,160
Speaker 1: little dense, and then gravity clumped them together and clumped

454
00:21:41,160 --> 00:21:44,680
Speaker 1: them together even further. So you got these little fluctuations

455
00:21:44,720 --> 00:21:48,160
Speaker 1: in the early universe, which see the structure of the universe, right,

456
00:21:48,200 --> 00:21:52,320
Speaker 1: because gravity takes over from these little wrinkles. But dark

457
00:21:52,359 --> 00:21:54,880
Speaker 1: matter plays a really big role in that because dark

458
00:21:54,920 --> 00:21:58,040
Speaker 1: matter basically is gravity, right, It's the biggest source of

459
00:21:58,080 --> 00:22:01,720
Speaker 1: gravity in the universe. And so where dark matter is

460
00:22:02,040 --> 00:22:05,560
Speaker 1: and how it's distributed determines the shape and the structure

461
00:22:05,600 --> 00:22:06,560
Speaker 1: of the whole universe.

462
00:22:06,600 --> 00:22:08,840
Speaker 3: And so we can tell from like pictures of the

463
00:22:09,000 --> 00:22:11,720
Speaker 3: Big Bang until the temperature of dark matter at the

464
00:22:11,760 --> 00:22:13,080
Speaker 3: beginning of time or right now.

465
00:22:13,160 --> 00:22:14,960
Speaker 1: Well, we can tell the temperature of dark matter is

466
00:22:14,960 --> 00:22:17,080
Speaker 1: sort of over the history of the universe. Everything is

467
00:22:17,119 --> 00:22:20,199
Speaker 1: cooling down, but we can tell whether dark matter was

468
00:22:20,320 --> 00:22:23,960
Speaker 1: made hot or made cold. Everything is getting colder over time,

469
00:22:24,280 --> 00:22:26,960
Speaker 1: but we can tell whether dark matter started out hotter

470
00:22:27,160 --> 00:22:30,080
Speaker 1: or colder. And we can do that by seeing whether

471
00:22:30,160 --> 00:22:32,560
Speaker 1: or not it's moved around a lot, whether or not

472
00:22:32,680 --> 00:22:36,000
Speaker 1: it's been wiggling around and that's affecting the structured universe,

473
00:22:36,040 --> 00:22:38,159
Speaker 1: or whether it's been mostly staying in the places it

474
00:22:38,200 --> 00:22:38,560
Speaker 1: was made.

475
00:22:38,560 --> 00:22:40,280
Speaker 3: Oh, I see, because I guess you assume that it's

476
00:22:40,359 --> 00:22:42,919
Speaker 3: kind of like a gas, right, Like you don't assume

477
00:22:42,920 --> 00:22:46,080
Speaker 3: it's a solid. You assume that it's you know, kind

478
00:22:46,080 --> 00:22:49,640
Speaker 3: of moving around freely. It's not tied together to itself

479
00:22:49,720 --> 00:22:50,640
Speaker 3: except with gravity.

480
00:22:50,720 --> 00:22:52,840
Speaker 1: That's right, only held together with gravity, and so we

481
00:22:52,880 --> 00:22:55,520
Speaker 1: think of it like a diffuse gas, like a pressureless

482
00:22:55,560 --> 00:22:58,919
Speaker 1: gas that doesn't even bounce against itself, and so basically

483
00:22:59,000 --> 00:23:01,520
Speaker 1: it just has gravitation effects. And so we can sort

484
00:23:01,520 --> 00:23:04,000
Speaker 1: of walk through the history of the universe with a

485
00:23:04,080 --> 00:23:06,480
Speaker 1: cold version of dark matter a version where dark matter

486
00:23:06,560 --> 00:23:08,760
Speaker 1: is mostly staying where it was, and then we can

487
00:23:08,800 --> 00:23:10,600
Speaker 1: walk through a version of the universe where dark matter

488
00:23:10,640 --> 00:23:13,080
Speaker 1: is hot, where it's zipping around really fast, and we

489
00:23:13,119 --> 00:23:16,080
Speaker 1: see that those two things predict different shapes of the

490
00:23:16,200 --> 00:23:18,960
Speaker 1: universe that we see today and also different histories of

491
00:23:19,000 --> 00:23:21,600
Speaker 1: the universe, and then we can compare those histories to

492
00:23:21,640 --> 00:23:22,760
Speaker 1: what we actually.

493
00:23:22,400 --> 00:23:24,879
Speaker 3: See, because like, if the dark matter at the beginning

494
00:23:24,920 --> 00:23:31,320
Speaker 3: of time was super cold, then I guess it particles

495
00:23:31,359 --> 00:23:34,280
Speaker 3: themselves don't have enough speed to like go off and

496
00:23:34,480 --> 00:23:36,800
Speaker 3: spread out. They would sort of stay clumped together.

497
00:23:37,040 --> 00:23:40,160
Speaker 1: That's exactly right. So if dark matter is very cold,

498
00:23:40,280 --> 00:23:42,880
Speaker 1: then the structure of the universe forms sort of bottom up.

499
00:23:43,119 --> 00:23:45,520
Speaker 1: Everything is where it was and it's not zipping around

500
00:23:45,600 --> 00:23:47,720
Speaker 1: very much, and so you get these little clumps of

501
00:23:47,760 --> 00:23:50,639
Speaker 1: density from those initial wrinkles, and that's what seeds like

502
00:23:50,800 --> 00:23:54,320
Speaker 1: the formation of stars, and then stars get together and

503
00:23:54,359 --> 00:23:58,240
Speaker 1: they form galaxies, and galaxies pull themselves together to form

504
00:23:58,320 --> 00:24:01,320
Speaker 1: galaxy clusters, so you get the structure formation that's sort

505
00:24:01,320 --> 00:24:04,840
Speaker 1: of bottom up. Everything starts clumping where it was and

506
00:24:05,000 --> 00:24:09,639
Speaker 1: then pulls together, so you get, for example, galaxies forming

507
00:24:09,720 --> 00:24:13,880
Speaker 1: before galaxy clusters. You get stars forming, then galaxies, then

508
00:24:13,960 --> 00:24:17,160
Speaker 1: galaxy clusters in that order. And we can look back

509
00:24:17,200 --> 00:24:19,440
Speaker 1: through the history of time because remember as we look

510
00:24:19,480 --> 00:24:22,240
Speaker 1: out through space, we're looking backwards in times, so we

511
00:24:22,240 --> 00:24:25,040
Speaker 1: can see where there galaxies a billion years after the

512
00:24:25,119 --> 00:24:28,880
Speaker 1: universe started, where there's stars, Which order did things get made?

513
00:24:28,920 --> 00:24:31,119
Speaker 1: We can tell by looking deep into the history of

514
00:24:31,119 --> 00:24:33,600
Speaker 1: the universe just by looking far out into space.

515
00:24:33,800 --> 00:24:36,600
Speaker 3: Right, And I guess you're using relative terms right, like

516
00:24:36,720 --> 00:24:39,160
Speaker 3: cold and hot here. You're not thinking about a specific

517
00:24:39,160 --> 00:24:42,720
Speaker 3: temperature because that could maybe also depend on how heavy

518
00:24:42,760 --> 00:24:43,640
Speaker 3: these particles are.

519
00:24:43,960 --> 00:24:47,000
Speaker 1: That's right. We're mostly talking about whether or not they're relativistic,

520
00:24:47,160 --> 00:24:49,359
Speaker 1: like are they moving it close to the speed of

521
00:24:49,440 --> 00:24:52,240
Speaker 1: light or are they not relativistic? You know, they're moving

522
00:24:52,280 --> 00:24:53,400
Speaker 1: a much less than that SA.

523
00:24:53,920 --> 00:24:56,160
Speaker 3: So when you say hot, you mean like super duper

524
00:24:56,200 --> 00:24:58,000
Speaker 3: hot light speed hot.

525
00:24:58,240 --> 00:25:01,600
Speaker 1: Yeah, exactly. And when we think about what hot dark

526
00:25:01,640 --> 00:25:04,280
Speaker 1: matter would look like, well, you have the early universe,

527
00:25:04,600 --> 00:25:07,000
Speaker 1: and you know dark matter is made just with everything else.

528
00:25:07,040 --> 00:25:09,479
Speaker 1: Then you get these initial little clumps of density from

529
00:25:09,560 --> 00:25:12,480
Speaker 1: quantum fluctuations. But if dark matter is most of the

530
00:25:12,560 --> 00:25:15,640
Speaker 1: stuff and it's moving really really fast, then those initial

531
00:25:15,680 --> 00:25:18,680
Speaker 1: little blobs of density don't really matter because dark matter

532
00:25:18,720 --> 00:25:21,359
Speaker 1: sort of washes them all out, like the dark matters

533
00:25:21,400 --> 00:25:24,520
Speaker 1: flying everywhere super duper fast, and so those initial little

534
00:25:24,520 --> 00:25:27,600
Speaker 1: clumps get evened out, they get smoothed out, so you

535
00:25:27,640 --> 00:25:30,600
Speaker 1: don't get stars forming first. Instead you get these like

536
00:25:30,880 --> 00:25:35,680
Speaker 1: these really big super massive blobs of stuff because only

537
00:25:35,720 --> 00:25:39,240
Speaker 1: the really big over densities, only the really big clumps

538
00:25:39,240 --> 00:25:42,000
Speaker 1: from the beginning stick around and survive the dark matter

539
00:25:42,080 --> 00:25:44,400
Speaker 1: spreading everything out to form some structure.

540
00:25:44,440 --> 00:25:46,639
Speaker 3: What do you mean? So if the dark matter is hot,

541
00:25:46,840 --> 00:25:49,640
Speaker 3: it means that the it's particles are moving a lot.

542
00:25:49,960 --> 00:25:52,560
Speaker 3: And so are you saying that dark matter is more

543
00:25:52,640 --> 00:25:55,560
Speaker 3: diffuse or like the blobs are moving around fast.

544
00:25:55,600 --> 00:25:58,320
Speaker 1: Both, they're moving around faster and so they spread out

545
00:25:58,359 --> 00:26:00,880
Speaker 1: and so it gets more even and so it's harder

546
00:26:00,920 --> 00:26:04,120
Speaker 1: for gravity to get a handle and start forming stars,

547
00:26:04,160 --> 00:26:07,480
Speaker 1: for example, because things get smooth. For gravity to form

548
00:26:07,520 --> 00:26:10,280
Speaker 1: a star, you need like a little blob that's denser

549
00:26:10,320 --> 00:26:12,560
Speaker 1: than the stuff around it that it can gather stuff

550
00:26:12,560 --> 00:26:15,639
Speaker 1: together using gravity. But if dark matter, which is most

551
00:26:15,640 --> 00:26:18,880
Speaker 1: of the stuff, is moving fast, then it's spread everything out,

552
00:26:18,880 --> 00:26:21,399
Speaker 1: it's smoothed everything over. There's nothing for gravity to get

553
00:26:21,440 --> 00:26:24,200
Speaker 1: a handle on, except for the really really big stuff

554
00:26:24,240 --> 00:26:27,560
Speaker 1: because that's the stuff that dark matter can't smooth out, right,

555
00:26:27,720 --> 00:26:30,879
Speaker 1: And so instead of getting stars and then galaxies and

556
00:26:30,880 --> 00:26:34,159
Speaker 1: then galaxy clusters and then superclusters, you start out with

557
00:26:34,320 --> 00:26:38,679
Speaker 1: supercluster sized blobs of stuff and then it breaks up

558
00:26:38,680 --> 00:26:42,280
Speaker 1: into galaxy cluster sized blobs of stuff, and those break

559
00:26:42,359 --> 00:26:45,280
Speaker 1: up into galaxy sized blobs of stuff, and then you

560
00:26:45,359 --> 00:26:48,160
Speaker 1: get stars forming. So it's sort of like top down

561
00:26:48,240 --> 00:26:49,440
Speaker 1: instead of bottom up.

562
00:26:49,680 --> 00:26:53,160
Speaker 3: Interesting, just based off of the temperature of dark matter.

563
00:26:53,280 --> 00:26:56,200
Speaker 1: Yeah, so the temperature of dark matter totally determines the

564
00:26:56,359 --> 00:26:59,280
Speaker 1: entire history of the universe. Like the universe would be

565
00:26:59,440 --> 00:27:01,960
Speaker 1: very different if we had no dark matter because it

566
00:27:01,960 --> 00:27:04,760
Speaker 1: wouldn't have been around to clump the normal matter together

567
00:27:04,800 --> 00:27:07,639
Speaker 1: into stars and galaxies. And also the universe would be

568
00:27:07,640 --> 00:27:10,159
Speaker 1: different if we had hot or cold dark matter, just

569
00:27:10,440 --> 00:27:13,200
Speaker 1: it's such a dominant force. It's most of the gravity.

570
00:27:13,600 --> 00:27:15,840
Speaker 1: So it affects how the universe came together.

571
00:27:16,040 --> 00:27:19,680
Speaker 3: Wow, And we can actually tell the history of the

572
00:27:19,760 --> 00:27:22,840
Speaker 3: universe whether things form buttom up or top down.

573
00:27:22,920 --> 00:27:24,760
Speaker 1: Yeah, because we can look back in time and we

574
00:27:24,760 --> 00:27:27,840
Speaker 1: can say, well, were there galaxies in the first billion

575
00:27:27,920 --> 00:27:31,000
Speaker 1: or two years after the Big Bang, or did it

576
00:27:31,040 --> 00:27:33,760
Speaker 1: take a while for galaxies to form? And so we

577
00:27:33,800 --> 00:27:36,879
Speaker 1: can look back in time and we can ask whether

578
00:27:36,920 --> 00:27:39,200
Speaker 1: these things were made, in what order were they made.

579
00:27:39,520 --> 00:27:42,800
Speaker 1: And also it affects the way things look today because

580
00:27:42,840 --> 00:27:45,960
Speaker 1: things would be smoother today if dark matter was hot,

581
00:27:46,000 --> 00:27:48,800
Speaker 1: and things would be sort of clumpier today if dark

582
00:27:48,840 --> 00:27:52,280
Speaker 1: matter was cold, like for example, our galaxy is the

583
00:27:52,280 --> 00:27:55,479
Speaker 1: Milky Way, and if dark matter was cold, then we

584
00:27:55,520 --> 00:27:57,520
Speaker 1: expect that the Milky Way has a bunch of like

585
00:27:57,880 --> 00:28:00,600
Speaker 1: little galaxies orbiting it, like the way the Earth has

586
00:28:00,640 --> 00:28:03,199
Speaker 1: the Moon. We expect that the Milky Way has its

587
00:28:03,240 --> 00:28:07,080
Speaker 1: own little like mini galaxies that orbit our galaxy.

588
00:28:07,119 --> 00:28:10,040
Speaker 9: If dark matter was super cold, if dark matter was cold,

589
00:28:10,280 --> 00:28:12,879
Speaker 9: then there should have been these blobs of stuff formed

590
00:28:12,920 --> 00:28:16,240
Speaker 9: outside of our galaxy, these dwarf galaxies, which would now

591
00:28:16,280 --> 00:28:19,280
Speaker 9: be orbiting the Milky Way, and that we should see

592
00:28:19,320 --> 00:28:21,520
Speaker 9: that today, So that would be a sign that dark

593
00:28:21,560 --> 00:28:23,760
Speaker 9: matter is cold. It affects not just the history of

594
00:28:23,800 --> 00:28:26,080
Speaker 9: the universe, but it also affects the shape of the

595
00:28:26,080 --> 00:28:27,280
Speaker 9: way things look today.

596
00:28:27,840 --> 00:28:30,080
Speaker 3: Yeah, I guess it's I mean, it's such a huge

597
00:28:30,119 --> 00:28:32,760
Speaker 3: part of the universe that you know, whether it's hot

598
00:28:32,840 --> 00:28:35,440
Speaker 3: or not. It should be no surprise that it determines

599
00:28:35,440 --> 00:28:37,320
Speaker 3: the fate of the universe because it's such a huge

600
00:28:37,440 --> 00:28:37,840
Speaker 3: chunk of it.

601
00:28:37,960 --> 00:28:40,240
Speaker 1: Yeah, exactly, it's not a little detail. It's not like

602
00:28:40,440 --> 00:28:43,000
Speaker 1: a tiny bit of salt that you add to your recipe. Right,

603
00:28:43,040 --> 00:28:45,680
Speaker 1: It's most of the stuff in the universe, and so

604
00:28:45,760 --> 00:28:48,640
Speaker 1: of course it's going to have big consequences for how

605
00:28:48,640 --> 00:28:50,360
Speaker 1: the universe looks and how it comes together.

606
00:28:50,760 --> 00:28:54,480
Speaker 3: Mm. All right, it could be hot or cold, and

607
00:28:54,520 --> 00:28:57,440
Speaker 3: we could probably tell by looking at the structure and

608
00:28:57,480 --> 00:28:59,480
Speaker 3: the history. I guess the history is also important of

609
00:28:59,480 --> 00:29:01,440
Speaker 3: the universe. The history kind of tells us a clue

610
00:29:01,440 --> 00:29:02,440
Speaker 3: about whether it's hot or not.

611
00:29:02,520 --> 00:29:05,880
Speaker 1: That's right. Did the structure form top down big stuff

612
00:29:05,920 --> 00:29:08,800
Speaker 1: first and then small stuff or to deform bottom up

613
00:29:08,840 --> 00:29:11,720
Speaker 1: like small stuff first, which then came together to make

614
00:29:11,760 --> 00:29:14,760
Speaker 1: the bigger stuff. And it also affects the way things

615
00:29:14,800 --> 00:29:16,479
Speaker 1: look in our universe today.

616
00:29:16,680 --> 00:29:20,040
Speaker 3: Right, all right, Let's now answer the question whether dark

617
00:29:20,120 --> 00:29:22,719
Speaker 3: matter is hot or not and what that tells us

618
00:29:22,720 --> 00:29:24,920
Speaker 3: about it. The first, let's take another quick break.

619
00:29:29,040 --> 00:29:30,840
Speaker 1: When you pop a piece of cheese into your mouth,

620
00:29:30,960 --> 00:29:34,080
Speaker 1: or enjoy a rich spoonful of Greeky yogurt. You're probably

621
00:29:34,120 --> 00:29:38,160
Speaker 1: not thinking about the environmental impact of each and every bite,

622
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Speaker 1: but the people in the dairy industry are. US Dairy

623
00:29:40,880 --> 00:29:45,160
Speaker 1: has set themselves some ambitious sustainability goals, including being greenhouse

624
00:29:45,200 --> 00:29:47,760
Speaker 1: gas neutral by twenty to fifty. That's why they're working

625
00:29:47,800 --> 00:29:50,160
Speaker 1: hard every day to find new ways to reduce waste,

626
00:29:50,200 --> 00:29:54,440
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627
00:29:54,480 --> 00:29:57,560
Speaker 1: for example, most dairy farms reuse water up to four

628
00:29:57,600 --> 00:30:01,080
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629
00:30:01,120 --> 00:30:03,920
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630
00:30:03,920 --> 00:30:07,680
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631
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632
00:30:11,680 --> 00:30:13,760
Speaker 1: and electric cars. So the next time you grab a

633
00:30:13,760 --> 00:30:15,800
Speaker 1: slice of pizza or lick an ice cream cone, know

634
00:30:15,880 --> 00:30:18,560
Speaker 1: that dairy farmers and processors around the country are using

635
00:30:18,600 --> 00:30:22,080
Speaker 1: the latest practices and innovations to provide the nutrient dense

636
00:30:22,200 --> 00:30:24,920
Speaker 1: dairy products we love with less of an impact. Visit

637
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Speaker 1: us dairy dot com slash sustainability to learn more.

638
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648
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Speaker 10: Hi, I'm David Eagleman from the podcast Inner Cosmos, which

649
00:31:34,160 --> 00:31:37,400
Speaker 10: recently hit the number one science podcast in America. I

650
00:31:37,480 --> 00:31:41,280
Speaker 10: mean neuroscientists at Stanford, and I've spent my career exploring

651
00:31:41,360 --> 00:31:43,480
Speaker 10: the three pound universe in our heads.

652
00:31:43,800 --> 00:31:44,960
Speaker 1: We're looking at a whole new.

653
00:31:44,880 --> 00:31:48,680
Speaker 10: Series of episodes this season to understand why and how

654
00:31:49,160 --> 00:31:51,840
Speaker 10: our lives looked the way they do. Why does your

655
00:31:51,920 --> 00:31:55,600
Speaker 10: memory drift so much? Why is it so hard to

656
00:31:55,680 --> 00:31:59,320
Speaker 10: keep a secret? When should you not trust your intuition,

657
00:32:00,160 --> 00:32:03,120
Speaker 10: Why do brains so easily fall for magic tricks?

658
00:32:03,360 --> 00:32:05,480
Speaker 1: And why do they love conspiracy theories.

659
00:32:06,160 --> 00:32:09,800
Speaker 10: I'm hitting these questions and hundreds more because the more

660
00:32:09,840 --> 00:32:12,880
Speaker 10: we know about what's running under the hood, the better

661
00:32:12,920 --> 00:32:16,800
Speaker 10: we can steer our lives. Join me weekly to explore

662
00:32:16,840 --> 00:32:20,560
Speaker 10: the relationship between your brain and your life by digging

663
00:32:20,600 --> 00:32:25,000
Speaker 10: into unexpected questions. Listen to Inner Cosmos with David Eagleman

664
00:32:25,120 --> 00:32:28,320
Speaker 10: on the iHeartRadio app, Apple Podcasts, or wherever you get

665
00:32:28,320 --> 00:32:36,960
Speaker 10: your podcasts.

666
00:32:39,960 --> 00:32:43,160
Speaker 3: All right, Daniel, is dark matter hot or not? Is

667
00:32:43,160 --> 00:32:45,040
Speaker 3: it a swipe laughter, a swipe right for you?

668
00:32:46,320 --> 00:32:49,360
Speaker 1: Well, I love dark matter. I'm very excited about dark matter.

669
00:32:49,560 --> 00:32:52,600
Speaker 1: I'm very tracted to dark matter. But I have to

670
00:32:52,640 --> 00:32:55,480
Speaker 1: say that the universe tells us that dark matter is

671
00:32:55,600 --> 00:32:56,400
Speaker 1: quite cold.

672
00:32:57,120 --> 00:32:57,960
Speaker 3: It's not hot.

673
00:32:58,160 --> 00:32:59,240
Speaker 1: It's definitely not hot.

674
00:32:59,320 --> 00:33:01,920
Speaker 3: I mean beautiful. It's just you know, a little chili.

675
00:33:02,360 --> 00:33:05,440
Speaker 1: That's right. It's got its own standards of beauty. And

676
00:33:05,600 --> 00:33:08,520
Speaker 1: it's pretty cool, you know, dark matter. And we know

677
00:33:08,640 --> 00:33:10,760
Speaker 1: that because we look at the history of the universe

678
00:33:10,800 --> 00:33:13,880
Speaker 1: and we see that stars formed first, and that then

679
00:33:13,960 --> 00:33:17,880
Speaker 1: galaxies formed, and that then galaxy structure is formed. Because

680
00:33:17,920 --> 00:33:19,760
Speaker 1: we look back in the very early universe, and we

681
00:33:19,800 --> 00:33:23,200
Speaker 1: see galaxies forming before there were clusters, and we see

682
00:33:23,240 --> 00:33:25,240
Speaker 1: stars forming before there was galaxies.

683
00:33:25,360 --> 00:33:27,360
Speaker 3: Can we tell that? Can we? How can we tell?

684
00:33:27,400 --> 00:33:29,960
Speaker 3: I thought like, we can only see really far out

685
00:33:30,080 --> 00:33:33,400
Speaker 3: and till the distance and the age of things by

686
00:33:33,480 --> 00:33:36,760
Speaker 3: looking at like supernova's. So how can we tell how

687
00:33:36,800 --> 00:33:40,280
Speaker 3: things formed if our only way of knowing is through stars?

688
00:33:40,360 --> 00:33:42,840
Speaker 1: That's right? Well, the supernovas tell us sort of like

689
00:33:43,000 --> 00:33:46,680
Speaker 1: the distance ladder, and so we can tell how far

690
00:33:46,720 --> 00:33:50,080
Speaker 1: away something is and therefore when it happened. And you're

691
00:33:50,160 --> 00:33:52,560
Speaker 1: right that we need stars to happen to give us

692
00:33:52,560 --> 00:33:54,880
Speaker 1: that distance ladder. But we can go back and look

693
00:33:54,920 --> 00:33:57,600
Speaker 1: at the early universe, right that tells us like, okay,

694
00:33:57,600 --> 00:34:00,800
Speaker 1: this is really really far away. And for example, you

695
00:34:00,840 --> 00:34:05,160
Speaker 1: would expect that there would be galaxy clusters formed in

696
00:34:05,200 --> 00:34:07,960
Speaker 1: the very early universe if dark matter was hot. And

697
00:34:08,000 --> 00:34:10,919
Speaker 1: so we look out past the most distant supernovas into

698
00:34:10,920 --> 00:34:13,480
Speaker 1: the deep early universe, you know, and we can tell

699
00:34:13,480 --> 00:34:16,439
Speaker 1: that these things happened, you know, thirteen billion years ago,

700
00:34:16,520 --> 00:34:19,759
Speaker 1: for example, and we don't see galaxy clusters forming out

701
00:34:19,840 --> 00:34:21,799
Speaker 1: there in the very edges of the things that we

702
00:34:21,840 --> 00:34:24,480
Speaker 1: can observe that's the very earliest universe. And you're right.

703
00:34:24,520 --> 00:34:28,000
Speaker 1: We can't get as precise an estimate for those distances

704
00:34:28,000 --> 00:34:30,719
Speaker 1: because we don't have the supernovas, but we can extrapolate

705
00:34:30,760 --> 00:34:33,360
Speaker 1: a little bit. And also we know it's super duper old.

706
00:34:33,480 --> 00:34:36,960
Speaker 3: Oh I see, So like the oldest stars that we

707
00:34:37,000 --> 00:34:40,120
Speaker 3: can see tell us that things were not as formed

708
00:34:40,440 --> 00:34:43,480
Speaker 3: as they are closer to us or closer to the present.

709
00:34:43,600 --> 00:34:46,799
Speaker 1: That's right. They tell us that the structure formed bottom up,

710
00:34:46,960 --> 00:34:49,680
Speaker 1: that things came together in small clumps first, and then

711
00:34:49,719 --> 00:34:53,799
Speaker 1: those small clumps organize themselves into bigger stuff. So you

712
00:34:53,880 --> 00:34:57,600
Speaker 1: get stars, and then galaxies, and then galaxy clusters, and

713
00:34:57,640 --> 00:35:01,360
Speaker 1: then super clusters of galaxies, which is the latest structure

714
00:35:01,400 --> 00:35:05,120
Speaker 1: to form, and that's why they're the biggest gravitationally bound

715
00:35:05,120 --> 00:35:08,120
Speaker 1: objects in the universe because they have most recently come together.

716
00:35:08,160 --> 00:35:11,000
Speaker 1: It takes a while for gravity to do this, and

717
00:35:11,080 --> 00:35:14,520
Speaker 1: galaxy superclusters are the last thing to have formed. It's

718
00:35:14,680 --> 00:35:17,320
Speaker 1: although we've had time to form so far in the universe.

719
00:35:17,360 --> 00:35:19,520
Speaker 3: All right, Well, I guess, so then that tells us

720
00:35:19,560 --> 00:35:23,759
Speaker 3: that dark matter is cold, And I guess do we

721
00:35:23,800 --> 00:35:26,120
Speaker 3: have a sense of how cold it is? Like? You know,

722
00:35:26,280 --> 00:35:28,399
Speaker 3: not going at the speed of light. I know that's

723
00:35:28,440 --> 00:35:31,880
Speaker 3: how you define cold. But is it like chili or

724
00:35:31,960 --> 00:35:34,000
Speaker 3: is it like warm? Or is are we talking like

725
00:35:34,040 --> 00:35:36,480
Speaker 3: the temperature of the sun. What are we talking about.

726
00:35:36,560 --> 00:35:38,640
Speaker 1: It's definitely not the temperature of the Sun. I mean,

727
00:35:38,800 --> 00:35:41,200
Speaker 1: if it's out there and it's a particle, it's going

728
00:35:41,239 --> 00:35:43,440
Speaker 1: to be very, very cold. You know, it's going to

729
00:35:43,480 --> 00:35:44,800
Speaker 1: be a few degrees kelvin.

730
00:35:44,920 --> 00:35:48,520
Speaker 3: Really, we think dark matter is only a few degrees kelvin.

731
00:35:48,320 --> 00:35:50,960
Speaker 1: Probably, yeah, And you know, it's not interacting in the

732
00:35:51,000 --> 00:35:53,360
Speaker 1: same way that like hydrogen does in the core of

733
00:35:53,400 --> 00:35:56,080
Speaker 1: the Sun to produce a huge amount of energy. But

734
00:35:56,080 --> 00:35:57,839
Speaker 1: there's still a lot we don't know about dark matter

735
00:35:57,880 --> 00:36:00,520
Speaker 1: that could have self interactions that contain energy that we

736
00:36:00,560 --> 00:36:02,920
Speaker 1: are not aware of. And so everything we say here

737
00:36:02,960 --> 00:36:05,080
Speaker 1: should be taken with a big grain of salt because

738
00:36:05,120 --> 00:36:08,320
Speaker 1: it's all pretty speculative. But you know, also, the cold

739
00:36:08,400 --> 00:36:11,719
Speaker 1: dark matter picture is pretty good. It works pretty well,

740
00:36:11,760 --> 00:36:15,160
Speaker 1: but it's not perfect, Like, it doesn't perfectly explain everything

741
00:36:15,200 --> 00:36:15,759
Speaker 1: that we see.

742
00:36:15,920 --> 00:36:18,200
Speaker 3: Right, Like you were saying, cold dark matter predicts that

743
00:36:18,239 --> 00:36:20,799
Speaker 3: we would have baby galaxies floating around us.

744
00:36:20,920 --> 00:36:22,759
Speaker 1: That's right. We expect to see a bunch of these

745
00:36:22,840 --> 00:36:25,719
Speaker 1: dwarf galaxies orbiting the Milky Way, and we see some,

746
00:36:26,200 --> 00:36:28,800
Speaker 1: but we don't see nearly as many as we expect,

747
00:36:29,120 --> 00:36:31,319
Speaker 1: and we don't know yet. Is that because dark matter

748
00:36:31,360 --> 00:36:33,439
Speaker 1: isn't as cold as we thought, or is it because

749
00:36:33,480 --> 00:36:36,160
Speaker 1: those dwarf galaxies are harder to see than we thought

750
00:36:36,160 --> 00:36:39,319
Speaker 1: they would be. And recently people have developed extra good

751
00:36:39,360 --> 00:36:42,040
Speaker 1: techniques to find dwarf galaxies and they found a few more,

752
00:36:42,080 --> 00:36:44,399
Speaker 1: and that sort of closes the gap a little bit.

753
00:36:44,840 --> 00:36:47,080
Speaker 1: But there's still some tension there. It's still something that

754
00:36:47,120 --> 00:36:50,360
Speaker 1: we don't quite understand. And you know, we like those details.

755
00:36:50,360 --> 00:36:52,880
Speaker 1: We like getting those things right because those are the

756
00:36:52,920 --> 00:36:55,320
Speaker 1: things that tell us that our theory is really working.

757
00:36:55,800 --> 00:36:58,080
Speaker 1: And so there's still some question marks about it. But

758
00:36:58,120 --> 00:37:01,360
Speaker 1: it's definitely not hot. It's some version of cold.

759
00:37:01,880 --> 00:37:05,160
Speaker 3: I guess we can't make any version in our simulations

760
00:37:05,400 --> 00:37:07,520
Speaker 3: work out to be just like the universe we have now,

761
00:37:07,600 --> 00:37:10,440
Speaker 3: Like if you tweak it further, you don't get the

762
00:37:10,520 --> 00:37:13,520
Speaker 3: right proportion of dwarf or baby galaxies.

763
00:37:13,040 --> 00:37:15,600
Speaker 1: Not yet. But you know, these simulations are very very

764
00:37:15,600 --> 00:37:18,719
Speaker 1: hard to do because you're simulating an enormous number of

765
00:37:18,760 --> 00:37:22,000
Speaker 1: particles and when they do these simulations, they usually just

766
00:37:22,120 --> 00:37:24,960
Speaker 1: like leave out all the normal matter because the normal

767
00:37:24,960 --> 00:37:27,719
Speaker 1: matter is a small fraction and it's much harder to

768
00:37:27,800 --> 00:37:31,319
Speaker 1: model because normal matter has complicated interactions, right, you know,

769
00:37:31,440 --> 00:37:34,680
Speaker 1: stars and gas and all that stuff. It has pressure

770
00:37:34,800 --> 00:37:38,400
Speaker 1: and complicated flows because of the electromagnetic interactions and the

771
00:37:38,440 --> 00:37:41,680
Speaker 1: strong interactions and all that stuff. So until recently, these

772
00:37:41,680 --> 00:37:44,960
Speaker 1: simulations have mostly just removed all the baryonic matter. But

773
00:37:45,080 --> 00:37:48,320
Speaker 1: you know, baryons are important. I'm a baryon, You're a baryon.

774
00:37:48,480 --> 00:37:51,440
Speaker 1: Stars are baryons. The whole visible part of the galaxies

775
00:37:51,480 --> 00:37:52,200
Speaker 1: made of baryons.

776
00:37:52,239 --> 00:37:54,719
Speaker 3: So what does it mean, Like, that's the particles that

777
00:37:54,760 --> 00:37:57,480
Speaker 3: we're made out of regular yeah matter, Yeah, like quarks

778
00:37:57,520 --> 00:37:58,440
Speaker 3: and electronics, m.

779
00:37:58,760 --> 00:38:01,680
Speaker 1: And so when they do these to describe the structure

780
00:38:01,680 --> 00:38:04,759
Speaker 1: of the universe, they don't have the computational power to

781
00:38:04,800 --> 00:38:07,440
Speaker 1: describe all the baryons, all the things that make me

782
00:38:07,600 --> 00:38:10,320
Speaker 1: and you, quarks and all that stuff, So they mostly

783
00:38:10,360 --> 00:38:13,719
Speaker 1: just remove it as a simplification because that's the most

784
00:38:13,719 --> 00:38:17,200
Speaker 1: complicated stuff to describe, and so our simulations are really

785
00:38:17,239 --> 00:38:20,239
Speaker 1: approximate right now. So people are working on ways to

786
00:38:20,360 --> 00:38:23,000
Speaker 1: include normal matter in these simulations. And try to get

787
00:38:23,280 --> 00:38:27,000
Speaker 1: more precise estimates, more precise predictions for how many dwarf

788
00:38:27,040 --> 00:38:28,040
Speaker 1: galaxies we should see.

789
00:38:28,120 --> 00:38:31,319
Speaker 3: Yeah, I guess people are complicated. They're hard to predict, for.

790
00:38:31,320 --> 00:38:34,520
Speaker 1: Sure, they are. They are hard to describe.

791
00:38:34,560 --> 00:38:37,279
Speaker 3: So we know we think dark matter is made out

792
00:38:37,280 --> 00:38:39,719
Speaker 3: of particles, and if it is, we think it's cold,

793
00:38:39,960 --> 00:38:42,040
Speaker 3: because that's what the universe is telling is So what

794
00:38:42,080 --> 00:38:44,359
Speaker 3: does that tell us about dark matter? Does it give

795
00:38:44,440 --> 00:38:46,600
Speaker 3: us a clue about what it is or what kind

796
00:38:46,600 --> 00:38:49,759
Speaker 3: of particle it is, or you know, is the fact

797
00:38:49,800 --> 00:38:53,440
Speaker 3: that it's cold. Does that tell you something about how

798
00:38:53,480 --> 00:38:54,800
Speaker 3: it interacts with other forces?

799
00:38:54,880 --> 00:38:56,520
Speaker 1: Yeah, it tells us a lot. And what it can

800
00:38:56,560 --> 00:39:01,040
Speaker 1: do is remove candidate particles from the list, and most specifically,

801
00:39:01,239 --> 00:39:04,880
Speaker 1: it acts as the neutrino as a candidate for dark matter.

802
00:39:05,360 --> 00:39:07,520
Speaker 1: For a long time, people thought, oh, there's a lot

803
00:39:07,560 --> 00:39:10,400
Speaker 1: of invisible matter out there, matter that almost never or

804
00:39:10,480 --> 00:39:14,600
Speaker 1: never interacts with us except for gravitationally, maybe it's just neutrinos.

805
00:39:15,080 --> 00:39:17,600
Speaker 1: And it's a very tempting candidate because we already know

806
00:39:17,640 --> 00:39:21,160
Speaker 1: about neutrinos. We know neutrinos are these wispy particles that

807
00:39:21,200 --> 00:39:23,920
Speaker 1: can pass through a light year of lead without interacting.

808
00:39:24,320 --> 00:39:27,040
Speaker 1: The air around us is filled with neutrinos, but we

809
00:39:27,120 --> 00:39:29,359
Speaker 1: can't feel them or taste them. They have a lot

810
00:39:29,400 --> 00:39:31,759
Speaker 1: of energy, but they don't deposit it on us. And

811
00:39:31,840 --> 00:39:35,839
Speaker 1: so it's tempting to assign these two mysteries together, right,

812
00:39:36,200 --> 00:39:38,960
Speaker 1: the weirdness of neutrinos and the mystery of the missing matter.

813
00:39:39,239 --> 00:39:42,319
Speaker 1: Maybe one plus one just equals too, and so for

814
00:39:42,320 --> 00:39:45,680
Speaker 1: a long time people suspected maybe the missing matter was

815
00:39:45,760 --> 00:39:49,799
Speaker 1: just like a ridiculous number of neutrinos. And remember, neutrinos

816
00:39:49,800 --> 00:39:52,840
Speaker 1: are very very light that have hardly any mass per particle.

817
00:39:52,880 --> 00:39:55,719
Speaker 1: It's not zero, but it's a small number. So if

818
00:39:55,719 --> 00:39:58,480
Speaker 1: you're gonna explain most of the stuff in the universe

819
00:39:58,520 --> 00:40:01,480
Speaker 1: with neutrinos, it would have to be an ungodly number

820
00:40:01,520 --> 00:40:02,480
Speaker 1: of neutrinos.

821
00:40:02,800 --> 00:40:05,120
Speaker 3: Could it be like a heavy neutrino? Like I know,

822
00:40:05,239 --> 00:40:07,240
Speaker 3: neutrinos they can have different masses, right.

823
00:40:07,360 --> 00:40:10,160
Speaker 1: The neutrinos that we're aware of, the three, the electronmew

824
00:40:10,200 --> 00:40:13,000
Speaker 1: and in toown neutrinos all have very very very small masses.

825
00:40:13,440 --> 00:40:14,759
Speaker 1: And so what we can do is we can rule

826
00:40:14,800 --> 00:40:16,319
Speaker 1: out those. We can say it's not one of the

827
00:40:16,320 --> 00:40:17,440
Speaker 1: neutrinos that we know.

828
00:40:17,560 --> 00:40:18,800
Speaker 3: Not one of the neutrino lights.

829
00:40:18,880 --> 00:40:22,120
Speaker 1: Yeah, exactly, because those neutrinos have such small mass that

830
00:40:22,120 --> 00:40:24,960
Speaker 1: they're always moving basically at the speed of light. Are

831
00:40:25,040 --> 00:40:27,480
Speaker 1: very close to the speed of light. For example, when

832
00:40:27,480 --> 00:40:31,280
Speaker 1: neutrinos come from a supernova, they arrive, you know, very

833
00:40:31,280 --> 00:40:33,919
Speaker 1: close to the same time as the photons arrive because

834
00:40:33,960 --> 00:40:36,680
Speaker 1: they're traveling basically at the speed of light. Actually, the

835
00:40:36,680 --> 00:40:40,160
Speaker 1: neutrinos get here first because the photons get slowed down

836
00:40:40,200 --> 00:40:43,480
Speaker 1: by interacting with the star. But it's basically a race.

837
00:40:43,480 --> 00:40:45,520
Speaker 1: The neutrinos fly at almost the speed of light.

838
00:40:45,560 --> 00:40:47,080
Speaker 3: You're seeing. They're faster than lights I neil.

839
00:40:47,480 --> 00:40:50,239
Speaker 1: They are not faster than light. They leave sooner. The

840
00:40:50,280 --> 00:40:52,880
Speaker 1: photons spend more time packing, but they do travel a

841
00:40:52,920 --> 00:40:56,440
Speaker 1: little faster. But you're exactly right that there's the possibility

842
00:40:56,480 --> 00:40:59,279
Speaker 1: that there could be some weird heavy neutrinos, So not

843
00:40:59,360 --> 00:41:01,799
Speaker 1: the neutrinos that we're familiar with. But if there is

844
00:41:01,840 --> 00:41:05,000
Speaker 1: another kind of neutrino, a fourth neutrino, or many other

845
00:41:05,120 --> 00:41:08,160
Speaker 1: kinds of neutrinos that are very heavy, then those are

846
00:41:08,160 --> 00:41:11,120
Speaker 1: still valid candidates for the dark matter, and those go

847
00:41:11,160 --> 00:41:14,680
Speaker 1: by the terms like sterile neutrinos because called sterile because

848
00:41:14,680 --> 00:41:17,600
Speaker 1: maybe they interact with our kind of matter even less.

849
00:41:17,800 --> 00:41:20,120
Speaker 3: Whoa, it's like a neutral neutrino.

850
00:41:20,320 --> 00:41:22,920
Speaker 1: Yeah, that's right. It's like an even more standoffish and

851
00:41:23,000 --> 00:41:25,960
Speaker 1: snobbish particle than the neutrino. And that's a hard standard

852
00:41:26,000 --> 00:41:26,279
Speaker 1: to meet.

853
00:41:26,480 --> 00:41:28,880
Speaker 3: Oh, I was just thinking like shy or you know,

854
00:41:29,320 --> 00:41:31,759
Speaker 3: through interact with other particles.

855
00:41:31,320 --> 00:41:33,480
Speaker 1: They have the introvert neutrinos.

856
00:41:33,040 --> 00:41:34,920
Speaker 3: Right, but you just assume that, you know, it's just not.

857
00:41:35,920 --> 00:41:38,319
Speaker 1: My apologies sterile neutrinos.

858
00:41:37,960 --> 00:41:39,839
Speaker 3: I take it back, right, So that tells it they

859
00:41:39,960 --> 00:41:44,040
Speaker 3: can't be neutrinos because neutrinos usually go really fast, but

860
00:41:44,080 --> 00:41:46,759
Speaker 3: they could be. Basically, that doesn't leave you much, does

861
00:41:46,800 --> 00:41:48,920
Speaker 3: It just tells you that it's another kind of part

862
00:41:48,920 --> 00:41:50,320
Speaker 3: of it. Yeah, and that we don't know about it.

863
00:41:50,400 --> 00:41:52,680
Speaker 1: That's an important clue because that means that there's no

864
00:41:52,800 --> 00:41:55,959
Speaker 1: particle on our current list that fits the requirements. There's

865
00:41:55,960 --> 00:42:00,000
Speaker 1: no particle out there that doesn't have electromagnetic or strong

866
00:42:00,080 --> 00:42:04,200
Speaker 1: interactions and is heavy, right. There just isn't one. The

867
00:42:04,320 --> 00:42:07,080
Speaker 1: only particle in our current list that had any chance

868
00:42:07,239 --> 00:42:10,399
Speaker 1: of being the dark matter or neutrinos, and this piece

869
00:42:10,440 --> 00:42:12,920
Speaker 1: of evidence rules that out. It says it can't be

870
00:42:13,040 --> 00:42:15,360
Speaker 1: one of the neutrinos we know. So it has to

871
00:42:15,440 --> 00:42:18,400
Speaker 1: be a new particle. And that's exciting. A heavy particle,

872
00:42:18,440 --> 00:42:21,400
Speaker 1: a new heavy particle exactly. It means that there's something

873
00:42:21,440 --> 00:42:23,560
Speaker 1: new to discover. It's not just oh, there are more

874
00:42:23,680 --> 00:42:25,880
Speaker 1: of this particle than we thought. It means there's a

875
00:42:25,960 --> 00:42:28,400
Speaker 1: new particle. And a new particle is interesting because you

876
00:42:28,440 --> 00:42:30,279
Speaker 1: want to like, why does it exist? How many new

877
00:42:30,280 --> 00:42:32,719
Speaker 1: particles are there? Where did it come from? Why is

878
00:42:32,719 --> 00:42:35,160
Speaker 1: it different from these other particles? You know, it gives

879
00:42:35,160 --> 00:42:37,000
Speaker 1: you a whole new set of questions to ask, a

880
00:42:37,000 --> 00:42:38,640
Speaker 1: whole new way to look at the universe.

881
00:42:38,719 --> 00:42:40,759
Speaker 3: Right, And you guys are looking for these in the

882
00:42:40,800 --> 00:42:44,319
Speaker 3: particle colliders, right, you're smashing particles hoping that a new

883
00:42:44,400 --> 00:42:46,520
Speaker 3: kind of particle will pop out. And you might say, hey,

884
00:42:46,560 --> 00:42:47,520
Speaker 3: that's dark matter.

885
00:42:47,640 --> 00:42:50,359
Speaker 1: That's right. And we have specific ideas for what this

886
00:42:50,440 --> 00:42:53,880
Speaker 1: new particle could be. We have ideas like the wimp particle,

887
00:42:54,160 --> 00:42:58,280
Speaker 1: weekly interacting massive particle. It's just a generic name meaning

888
00:42:58,719 --> 00:43:02,239
Speaker 1: some big, heavy party that doesn't interact very much, and

889
00:43:02,280 --> 00:43:04,040
Speaker 1: it has to not interact very much in order to

890
00:43:04,080 --> 00:43:06,320
Speaker 1: be the dark matter, and it has to be massive

891
00:43:06,640 --> 00:43:09,080
Speaker 1: in order to be cold because of the structure of

892
00:43:09,080 --> 00:43:13,000
Speaker 1: the universe. And another idea is the axion. The axion

893
00:43:13,120 --> 00:43:16,360
Speaker 1: could be the dark matter, and we have specific experiments

894
00:43:16,400 --> 00:43:19,759
Speaker 1: to look for WIMPs and for axions. We just did

895
00:43:19,760 --> 00:43:21,680
Speaker 1: a podcast episode about axions.

896
00:43:22,040 --> 00:43:22,839
Speaker 3: They're not the same thing.

897
00:43:22,920 --> 00:43:25,000
Speaker 1: They are not the same thing. They're two very different

898
00:43:25,080 --> 00:43:27,920
Speaker 1: kinds of particles. The axion is like a heavier version

899
00:43:27,960 --> 00:43:30,400
Speaker 1: of the photon, and the wimp is like it's like

900
00:43:30,400 --> 00:43:33,760
Speaker 1: a heavier version of the neutrino, but maybe interacts even less.

901
00:43:34,120 --> 00:43:37,719
Speaker 1: And we have experiments underground to look for WIMPs, these

902
00:43:37,760 --> 00:43:41,480
Speaker 1: big tanks of liquid argon, for example, or liquid xenon

903
00:43:41,960 --> 00:43:45,600
Speaker 1: that look for one wimp coming through and knocking into

904
00:43:45,960 --> 00:43:48,040
Speaker 1: a bunch of particles and then giving us a signal.

905
00:43:48,520 --> 00:43:52,080
Speaker 1: We're using space telescopes to look to see if occasionally

906
00:43:52,320 --> 00:43:54,640
Speaker 1: WIMPs bounce into each other and give off a little

907
00:43:54,719 --> 00:43:56,680
Speaker 1: flash of light that we could see, which would be

908
00:43:56,680 --> 00:43:59,759
Speaker 1: really really rare because dark matter is dark. But you know,

909
00:44:00,160 --> 00:44:02,319
Speaker 1: we look at places where there's a lot of dark

910
00:44:02,360 --> 00:44:05,080
Speaker 1: matter and try to see the occasional blip and then

911
00:44:05,080 --> 00:44:07,880
Speaker 1: we try to make dark matter in the collider to

912
00:44:07,960 --> 00:44:10,360
Speaker 1: see if we can create it and play with it there.

913
00:44:10,719 --> 00:44:13,279
Speaker 1: So far, none of these experiments have turned up any

914
00:44:13,360 --> 00:44:16,919
Speaker 1: evidence for dark matter that anybody believes, and so we're

915
00:44:17,000 --> 00:44:19,600
Speaker 1: still in the hunt. But you know, even though we

916
00:44:19,680 --> 00:44:21,560
Speaker 1: don't know what dark matter is, we're able to say

917
00:44:21,600 --> 00:44:23,120
Speaker 1: some things about what it isn't.

918
00:44:23,360 --> 00:44:26,040
Speaker 3: Is it weird that you haven't found dark matter in

919
00:44:26,080 --> 00:44:29,239
Speaker 3: these colliders. I mean, like, in the universe there's five

920
00:44:29,360 --> 00:44:32,839
Speaker 3: times more dark matter than regular matter, which might make

921
00:44:32,880 --> 00:44:35,880
Speaker 3: you think that it's it's more likely to happen, But

922
00:44:35,960 --> 00:44:38,360
Speaker 3: in our colliders you can't seem to make even a

923
00:44:38,360 --> 00:44:38,920
Speaker 3: little bit of it.

924
00:44:39,000 --> 00:44:41,879
Speaker 1: That's right, It is a little weird. Now. On one hand,

925
00:44:42,200 --> 00:44:44,359
Speaker 1: it may be that dark matter is everywhere, but we

926
00:44:44,440 --> 00:44:47,280
Speaker 1: can't make it because we're playing with our kind of matter,

927
00:44:47,560 --> 00:44:50,239
Speaker 1: Like our kind of matter might not interact with dark matter,

928
00:44:50,280 --> 00:44:53,640
Speaker 1: which means that we can't use our matter to look

929
00:44:53,680 --> 00:44:55,920
Speaker 1: for dark matter, and we can't use our matter to

930
00:44:56,040 --> 00:44:58,520
Speaker 1: make dark matter like for that to work for any

931
00:44:58,520 --> 00:45:01,840
Speaker 1: of the experiments I just describe to work to discover

932
00:45:02,000 --> 00:45:04,200
Speaker 1: the particle nature of dark matter means there has to

933
00:45:04,200 --> 00:45:07,279
Speaker 1: be some way for our particles to talk to the

934
00:45:07,360 --> 00:45:10,480
Speaker 1: dark matter particles to share some sort of new dark

935
00:45:10,520 --> 00:45:14,080
Speaker 1: photon or some new force has to exist that works

936
00:45:14,080 --> 00:45:17,640
Speaker 1: on both particles. And it could be that it just doesn't.

937
00:45:17,760 --> 00:45:19,680
Speaker 1: It could be that dark matter's out there, it's a

938
00:45:19,719 --> 00:45:22,960
Speaker 1: particle and it just feels nothing except for gravity, in

939
00:45:22,960 --> 00:45:26,239
Speaker 1: which case it's basically hopeless for us to discover its

940
00:45:26,280 --> 00:45:29,520
Speaker 1: particle nature because gravity is so weak that we can

941
00:45:29,600 --> 00:45:33,560
Speaker 1: only detect dark matter when you have enormous, like galaxy

942
00:45:33,600 --> 00:45:36,080
Speaker 1: sized blobs of it, which makes it pretty hard to

943
00:45:36,120 --> 00:45:37,080
Speaker 1: do particle experiments.

944
00:45:37,160 --> 00:45:39,399
Speaker 3: But I thought when you smash particles, it turns into

945
00:45:39,680 --> 00:45:42,000
Speaker 3: pure energy and then anything can come out of it.

946
00:45:42,080 --> 00:45:44,080
Speaker 3: Are you saying that maybe it's possible that not even

947
00:45:44,160 --> 00:45:45,439
Speaker 3: dark matter can come out of that.

948
00:45:45,440 --> 00:45:48,040
Speaker 1: That's right. When you smash particles together, it's not exactly

949
00:45:48,080 --> 00:45:51,480
Speaker 1: pure energy. It turns into one of the bosons of

950
00:45:51,520 --> 00:45:54,440
Speaker 1: the forces that can interact with those particles. So, for example,

951
00:45:54,600 --> 00:45:56,800
Speaker 1: when you smash a quark and an anti quark together,

952
00:45:57,080 --> 00:45:58,960
Speaker 1: you can get a glue on, or you can get

953
00:45:58,960 --> 00:46:02,200
Speaker 1: a photon, you can get a w boson. But if

954
00:46:02,239 --> 00:46:05,400
Speaker 1: those forces, the weak and the strong force and electromagnetism

955
00:46:05,600 --> 00:46:09,000
Speaker 1: don't interact with dark matter, then those bosons which represent

956
00:46:09,120 --> 00:46:12,560
Speaker 1: that energy can't then turn into dark matter. And so

957
00:46:12,640 --> 00:46:14,759
Speaker 1: that is one limitation I know that I like to

958
00:46:14,760 --> 00:46:16,799
Speaker 1: say on this podcast that we can use colliders to

959
00:46:16,880 --> 00:46:19,680
Speaker 1: explore the universe because anything that can be made will

960
00:46:19,719 --> 00:46:22,560
Speaker 1: be made. But there is an important caveat there that

961
00:46:22,640 --> 00:46:26,000
Speaker 1: whatever can be made has to somehow interact with the

962
00:46:26,040 --> 00:46:29,040
Speaker 1: particles that we're smashing. If there's no way to interact,

963
00:46:29,360 --> 00:46:30,360
Speaker 1: then you just can't make it.

964
00:46:30,360 --> 00:46:33,480
Speaker 3: So you need a dark matter collider, Daniel, obviously.

965
00:46:34,160 --> 00:46:36,360
Speaker 1: To discover dark matter. Yeah, you have to build a

966
00:46:36,440 --> 00:46:37,440
Speaker 1: dark collider.

967
00:46:38,120 --> 00:46:41,279
Speaker 3: All right. Well, it sounds like we don't know what

968
00:46:41,440 --> 00:46:44,520
Speaker 3: dark matter is still, but we know that it's pretty cool.

969
00:46:44,840 --> 00:46:47,720
Speaker 3: It's a pretty cool thing in the universe. It's cold,

970
00:46:47,760 --> 00:46:49,479
Speaker 3: that's right. Dark matter is pretty chill.

971
00:46:50,120 --> 00:46:50,359
Speaker 9: You know.

972
00:46:50,480 --> 00:46:52,319
Speaker 1: It wants to come over and watch Netflix with you,

973
00:46:52,640 --> 00:46:53,759
Speaker 1: even if you don't think it's hot.

974
00:46:55,680 --> 00:46:58,440
Speaker 3: Yeah, all right, Well again, just makes you think about

975
00:46:58,520 --> 00:47:00,680
Speaker 3: all the crazy things we don't know, you know, and

976
00:47:00,719 --> 00:47:03,439
Speaker 3: all the sort of fun and clever ways we can

977
00:47:03,880 --> 00:47:06,839
Speaker 3: tell about things we don't know even though we don't

978
00:47:06,840 --> 00:47:07,560
Speaker 3: know anything about it.

979
00:47:07,960 --> 00:47:10,600
Speaker 1: Yeah, And this is what science does, is we probe

980
00:47:10,600 --> 00:47:13,560
Speaker 1: things from every direction. We're trying to uncover a real

981
00:47:13,640 --> 00:47:16,160
Speaker 1: truth about the universe, and that has lots of facets.

982
00:47:16,560 --> 00:47:18,920
Speaker 1: And so if we get stumped in one direction, like

983
00:47:18,960 --> 00:47:21,120
Speaker 1: we can't seem to find it in our detectors, then

984
00:47:21,160 --> 00:47:22,799
Speaker 1: we go another route and say, well, can we say

985
00:47:22,800 --> 00:47:25,279
Speaker 1: anything about it from this perspective or from that perspective?

986
00:47:25,320 --> 00:47:27,880
Speaker 1: And we're trying to be clever in the field of

987
00:47:27,880 --> 00:47:30,680
Speaker 1: particle physics and science in general is filled with clever

988
00:47:30,760 --> 00:47:34,000
Speaker 1: people having new ideas about ways to answer these questions,

989
00:47:34,320 --> 00:47:35,600
Speaker 1: and so to me, this is one of the most

990
00:47:35,640 --> 00:47:39,880
Speaker 1: elegant ways to put a really important, really insightful constraint

991
00:47:39,880 --> 00:47:41,880
Speaker 1: on what dark matter is and isn't.

992
00:47:42,280 --> 00:47:44,960
Speaker 3: All right, Well, I think we answered that question pretty good,

993
00:47:45,040 --> 00:47:46,560
Speaker 3: and I think we can all learn a little bit

994
00:47:46,600 --> 00:47:50,360
Speaker 3: from dark matter to just be cool. Don't get too excited.

995
00:47:50,680 --> 00:47:52,880
Speaker 3: Thanks for joining us, See you next time.

996
00:48:00,960 --> 00:48:03,800
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

997
00:48:03,840 --> 00:48:07,839
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

998
00:48:07,840 --> 00:48:12,480
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