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Speaker 1: Hey, Jorhan Daniel here, and we want to tell you

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Speaker 1: about our new book. It's called Frequently Asked Questions about

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Speaker 1: the Universe because you have questions about the universe, and

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Speaker 1: so we decided to write a book all about them.

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Speaker 1: We talk about your questions, we give some answers, we

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Speaker 1: make a bunch of silly jokes as usual, and we

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Speaker 1: tackle all kinds of questions, including what happens if I

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Speaker 1: fall into a black hole? Or is there another version

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Speaker 1: of you out there that's right? Like usual, we tackle

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Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.

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Speaker 1: If you want to support the podcast, please get the

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Speaker 1: book and get a copy, not just for yourself, but

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Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,

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Speaker 1: and for the aliens. So get your copy of Frequently

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Speaker 1: Asked Questions about the Universe is available for pre order now,

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Speaker 1: coming out November two. You can find more details at

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Speaker 1: the book's website, Universe f a Q dot com. Thanks

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Speaker 1: for your support, and if you have a hamster that

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Speaker 1: can read, please let us know. We'd love to have

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Speaker 1: them on the podcast. Hey Daniel, what kind of floors

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Speaker 1: do you have in your office. Actually, I'm glad you asked,

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Speaker 1: because I'm kind of proud of them. I put wood

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Speaker 1: floors into my office last year. What you like, you

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Speaker 1: did it yourself in your university office? Yeah, I did it,

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Speaker 1: just snuck in and did it on the weekend. Did

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Speaker 1: you ask permission to do it? I figured better to

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Speaker 1: ask forgivenness than permission. Oh man, well, I guess you.

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Speaker 1: You better not mention it on a podcast or anything.

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Speaker 1: I would never be so shortsighted. And let me guys,

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Speaker 1: did the floors you put in? Are they made out

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Speaker 1: of particle boards since you're a particle physicists? But they

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Speaker 1: are particularly snazzy? Are they made out of florine florinos?

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Speaker 1: Or are they fluorescent? They are scintillating. I think reached

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Speaker 1: the floor of the pun space. They're glad to know

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Speaker 1: this a bottom. Hi am or hammy cartoonists and the

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Speaker 1: creator of PhD comics. Hi. I'm Daniel. I'm a particle

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Speaker 1: physicist and a professor UC Irvine, and technically I'm an experimentalist,

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Speaker 1: but I don't actually like to build things. But you

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Speaker 1: are an amateur carpenter, would you say, or a florist

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Speaker 1: I'm definitely an amateur. Nobody is paying me to put

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Speaker 1: in their floors. Welcome to our podcast Daniel and Jorge

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Speaker 1: Explain the Universe, a production of I Heart Radio, in

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Speaker 1: which we dig through the floor of your understanding and

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Speaker 1: into all of the mysteries of the universe. We try

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Speaker 1: to understand everything that's out there above our heads and

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Speaker 1: below our feet and all around us, from the crazy

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Speaker 1: mysteries inside black holes, to the swirling insanity that is

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Speaker 1: our galaxy, to the tiniest particles that are flying through

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Speaker 1: our bodies. That's right. We try to break through the

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Speaker 1: ceilings and the floors of our brains and our human

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Speaker 1: understanding of how the verse works, because there is a

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Speaker 1: lot more than what is immediately around us, beyond our

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Speaker 1: floors and ceilings. Do you think it's possible to hear

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Speaker 1: an idea which would break your mind, which would like

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Speaker 1: literally make you go insane. You mean, like it makes

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Speaker 1: you insane and then you hear it, or you hear

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Speaker 1: it right before you go insane. Yeah, it makes you

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Speaker 1: go insane. Like if I reveal to you the true

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Speaker 1: nature of the universe and it blew your mind in

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Speaker 1: such a way that you just couldn't function afterwards. Oh boy, Well,

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Speaker 1: let's hope it doesn't happen today because we got to

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Speaker 1: record this podcast live on the air. We blow over

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Speaker 1: his mind. It could be like a weapon of mass destruction,

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Speaker 1: almost like an earworm that disables your brain somehow. I

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Speaker 1: think I read a book like that. It was called lexicon.

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Speaker 1: Actually there was a word that if you heard it

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Speaker 1: or if you saw it written, it would blow your mind.

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Speaker 1: Was it particle wood floors. I don't know what it

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Speaker 1: was because if I had read it then it would

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Speaker 1: have blown my mind. So I didn't finish the book. Really,

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Speaker 1: it was like a warning doesn't tell you what the

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Speaker 1: word is. It can't, man, it can't. Oh boy. But anyways,

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Speaker 1: we do try to talk about everything in the universe

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Speaker 1: that's interesting and that might be hiding out there for

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Speaker 1: humans to discover and to blow our minds with. Once

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Speaker 1: we sort of figure out how everything works, because it

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Speaker 1: is a pretty mysterious and interesting universe, that's right, and

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Speaker 1: we want to know how it works, and more specifically,

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Speaker 1: we want to know what's in it, what's it made

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Speaker 1: out of. We look at this universe with wonder and admiration,

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Speaker 1: but we also look at it with curiosity. We wonder

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Speaker 1: what makes it up and what makes it tick, And

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Speaker 1: as a particle physicist, I'm always trying to break it

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Speaker 1: down into the smallest pieces to understand, like what are

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Speaker 1: the lego bricks of the universe and how do they work? Yeah,

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Speaker 1: and do they hurt when you step on them as well?

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Speaker 1: But it is an interesting question, this question of what

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Speaker 1: is the universe made out of? And it turns out

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Speaker 1: that it's made out of things we have no idea about.

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Speaker 1: It turns out most of the universes is made out

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Speaker 1: of mysterious things and mysterious energies. So there's still a

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Speaker 1: lot of work left for particle physicists. Yeah, the mystery

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Speaker 1: is not solved. You can never retire, Daniel, I don't

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Speaker 1: know why you're celebrating. Well. On one hand, is disappointing

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Speaker 1: and frustrating to not know the answer to this great

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Speaker 1: mystery of the universe. On the other hand, it's exciting.

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Speaker 1: It's an opportunity because it means that we have crazy

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Speaker 1: discoveries ahead of us. I think that one day humans

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Speaker 1: will know what the universe is made out of, and

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Speaker 1: they will hold that knowledge in their little brains. I

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Speaker 1: hope it doesn't blow their minds and melt their brains

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Speaker 1: out of their noses. Yeah. So, when you think about

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Speaker 1: what the universe is made out of, it turns out

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Speaker 1: that physicists have figured out that most of the stuff

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Speaker 1: in the universe, like the stuff that the matter in

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Speaker 1: the universe, is apparently not the regular kind of stuff

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Speaker 1: that we're used to, like the atoms and all of

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Speaker 1: the corks and electrons that you and I are made

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Speaker 1: out of, and that cats and bananas are made out of.

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Speaker 1: It turns out most of the stuff in the universe

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Speaker 1: is something completely different and mysterious. That's right, And we

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Speaker 1: make this mistake all the time in science and in physics,

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Speaker 1: that we see one kind of thing around us or

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Speaker 1: one kind of behavior around us, and we assume that

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Speaker 1: that's it, that everything follows these rules, that the whole

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Speaker 1: universe obeys these principles that we see around us, and

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Speaker 1: then we discover, Oops, it turns out this is unusual.

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Speaker 1: It doesn't hold generally, and there are lots of circumstances

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Speaker 1: where the rules are totally different, from relativity to quantum mechanics.

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Speaker 1: And here's another scenario where we have spent hundreds or

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Speaker 1: thousands of years studying the nature of matter, only to

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Speaker 1: learn that the kind of stuff we've been studying that

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Speaker 1: makes up me and you and hamsters and ice cream

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Speaker 1: and lava is only five per cent of the stuff

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Speaker 1: in the universe, and that most of the universe is

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Speaker 1: something totally different. Yeah, well, most of the universe, it

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Speaker 1: turns out, is it's something called dark energy. But about

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Speaker 1: twenty of the rest of the things in the universe,

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Speaker 1: the energy and matter is something that business is called

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Speaker 1: dark matter, right, Daniel, that's right. It's a kind of

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Speaker 1: matter that we know is out there. We know it's matter.

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Speaker 1: We know it's some kind of stuff. It feels gravity,

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Speaker 1: it causes gravity, it's shaped the structure of the universe.

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Speaker 1: We know it's there, but we don't know what it is.

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Speaker 1: We don't know what is made out of. We don't

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Speaker 1: know how it's made or what rules it follows. Yeah,

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Speaker 1: it's kind of like a giant, cosmic elephant in the room. Right.

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Speaker 1: That's that's invisible at the same time, like the whole

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Speaker 1: universe knows it's there. It feels its presence, it's it's

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Speaker 1: being affected by it. It's definitely there, but nobody can

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Speaker 1: see it. So it's like having a giant elephant invisible

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Speaker 1: elephant in the room. Yeah, and it's a reminder of

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Speaker 1: a really important point that the universe that you see

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Speaker 1: in the universe that we know is just one slice

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Speaker 1: of the universe. That there's a lot going on around

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Speaker 1: us that is invisible to us. That doesn't mean it

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Speaker 1: isn't there, And in fact, what we see is a

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Speaker 1: little tiny fraction of what's out there in the universe.

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Speaker 1: So it's not just dark matter this out there. There's

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Speaker 1: lots of particles out there in the universe that are

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Speaker 1: invisible or almost invisible to us. For example, new trinos

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Speaker 1: are these tiny little particles that are flying everywhere produced

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Speaker 1: from the Sun, but you don't see them even though

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Speaker 1: there are billions flying through your fingers. So the universe

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Speaker 1: is mostly dark and invisible to us. Yeah, it seems

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Speaker 1: to be hiding for most. But do you think it's

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Speaker 1: hiding then? What? What doesn't it want us to see?

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Speaker 1: Why are you so suspicious? Man? Maybe it's just like

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Speaker 1: gently walking us down the garden path to reveal its

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Speaker 1: beautiful secrets. It's just leading us down the path to

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Speaker 1: hopefully it is not going to blow our minds and

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Speaker 1: kill us at the end. I trust the universe alright.

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Speaker 1: So dark matter is something that is big and mysterious,

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Speaker 1: a big part of the universe, but we actually don't

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Speaker 1: know what it is. The name dark matter is just

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Speaker 1: kind of a placeholder, right, Like dark just means it's invisible,

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Speaker 1: and matter just means you know, we feel it's gravity,

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Speaker 1: but we don't actually know what it is, even though

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Speaker 1: we are sort of actively wondering what it is and

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Speaker 1: we're trying to find ways to study it. Yeah, it's

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Speaker 1: a bit of a fine point. Some people say dark

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Speaker 1: matter exists, other people say, we haven't discovered dark matter yet.

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Speaker 1: How can both of those things be possible? Well, we

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Speaker 1: know that dark matter exists, but we don't really understand

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Speaker 1: what it's made out of or what it is. So

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Speaker 1: what we're looking to do is understand, like, is dark

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Speaker 1: matter made of a new kind of particle, and if so,

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Speaker 1: what we're dark matter made out of something else entirely.

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Speaker 1: So we know it exists, but we have been able

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Speaker 1: to isolate it. Yeah, we've been looking for a while now.

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Speaker 1: I mean dark matter was discovered kind of in the nineties, right,

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Speaker 1: and people have been thinking about it looking for devising experiments,

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Speaker 1: and without success, we haven't sort of seen anything that

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Speaker 1: can tell is more concretely like, hey, that was made

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Speaker 1: by a little bit of dark matter. We actually have

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Speaker 1: clues about the existence of dark matter dating all the

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Speaker 1: way back to the nineteen thirties, and then in the

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Speaker 1: nineteen seventies it really became mainstream when VERA. Reubens saw

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Speaker 1: how galaxies were rotating, and since then there's been a

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Speaker 1: very exciting and active program to try to understand what

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Speaker 1: dark matter is made out of. But yeah, we haven't

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Speaker 1: seen it yet. Yeah, and part of the problem is

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Speaker 1: that it's invisible. Right, It's invisible and you can't see

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Speaker 1: it or touch it, and so it's really hard to

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Speaker 1: study something that you know, you can't see or touch.

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Speaker 1: That's right. So far, the only way we know how

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Speaker 1: to interact with dark matter is through gravity, and gravity

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Speaker 1: is the weakest force in the universe, which makes it

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Speaker 1: a very very bad way to discover particles because particles

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Speaker 1: have almost no mass and so they have very very

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Speaker 1: weak gravity. Yeah, that gravity is really weak. And but

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Speaker 1: also I think one of the things that might be

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Speaker 1: preventing us from seeing and studying dark matter better is

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Speaker 1: this concept that we're going to talk about today. That

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Speaker 1: has to do with neutrinos, which are also kind of

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Speaker 1: elusive in invisible particles. That's right. So we're looking for

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Speaker 1: something elusive and almost invisible, and it might be hiding

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Speaker 1: behind something else, also elusive and also almost invisible. So

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Speaker 1: today on the program, we'll be tackling the question our

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Speaker 1: neutrinos hiding dark matter. Oh man, this is such a

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Speaker 1: mistrustful episode exactly, so much suspicion, like who's hiding one,

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Speaker 1: who's keeping the truth from us? Man, Let's just have

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Speaker 1: like a universe truthtelling commission where everybody comes to table

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Speaker 1: and says what they got and what they know, and

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Speaker 1: everybody can just share all the information. Maybe a better

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Speaker 1: title would have been our Neutrinos walking us down the

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Speaker 1: poorest path of knowledge and enlightenment. Maybe neutrinos just have

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Speaker 1: a brand plan and this is just part of the plan,

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Speaker 1: you know, keep us in darkness for a while and

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Speaker 1: then boom, reveal the truth that blows our minds without

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Speaker 1: actually melting our brains. Wow, these neutrinos man, all right.

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Speaker 1: And this has to do with this concept called the

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Speaker 1: neutrino floor that physicists talk about, and that might be

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Speaker 1: the thing that is hiding or kind of preventing us

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Speaker 1: from seeing or experimenting with dark matter. Yeah, exactly, we

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Speaker 1: have these experiments to look for a dark matter, and

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Speaker 1: they're worried that dark matter might be hiding for them

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Speaker 1: by hiding under the neutrino floor in the what the

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Speaker 1: universe basement or what's under the trino floor? I guess

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Speaker 1: that's the question we'll be tackling today. All right, Well,

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Speaker 1: we were, as usual, wondering how many people out there

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Speaker 1: had heard of the neutrino floor or had any guesses

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Speaker 1: as to what it could be. So Daniel went out

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Speaker 1: there and asked people on the internet this question. That's right.

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Speaker 1: We are still in pandemic mode. So if you'd like

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Speaker 1: to participate in euro out there on the internet, please

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Speaker 1: don't hesitate to right to me two questions at Daniel

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Speaker 1: and Jorge dot com. I know you want to hear

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Speaker 1: your voice in the podcast. You desperately want to participate,

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Speaker 1: you just haven't yet, so send us that email. It's easy,

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Speaker 1: it's fun. Yeah, So think about it for a second.

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Speaker 1: If I say the words neutrino floor, what does it

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Speaker 1: make you think of? Here's what people have to say.

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Speaker 1: I know what a neutrino is, and I know what

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Speaker 1: a floor is. But putting those two things together, neutrino

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Speaker 1: and floor, and assuming there's only one of them, makes

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Speaker 1: it feel like we're talking about some kind of minimum,

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Speaker 1: a global minimum in something to do with neutrinos. So

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Speaker 1: I don't know that like the lowest energy that a

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Speaker 1: neutrino could possibly have, or in the distribution of neutrinos

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Speaker 1: energy which we observe, what is the smallest one, or like,

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Speaker 1: what is the lightest neutrino that can possibly exist? Well,

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Speaker 1: we know what that is. The neutrino floor I don't know,

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Speaker 1: so probably trinos is the floor of neutrinos. Floor is

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Speaker 1: the bottom of something, right, Yes, the bottom of what

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Speaker 1: they're composing. And okay, but what are they composing? Particles?

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Speaker 1: This is a kind of particle. But the neutrino floor

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Speaker 1: means probably something like the bottom of something to do

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Speaker 1: with neutrinos. Let's say, the smallest possible neutrino or the

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Speaker 1: lowest energy neutrino or something like that. I think the

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Speaker 1: neutrino floor is the baseline saturation of neutrinos. Throughout the universe,

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Speaker 1: and perturbations in that floor would indicate something weird going

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Speaker 1: on if you detect extra neutrinos. Maybe this is the

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Speaker 1: absolute lowest state of energy that the neutrino can't be in.

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Speaker 1: Is there like something weird about neutrinos where they have

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Speaker 1: to have some energy and they just approach the floor

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Speaker 1: where they don't get any less energy? I don't know, Uh,

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Speaker 1: neutrino floor, I'm guessing is the the lowest amount of

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Speaker 1: neutrinos that could exist in the universe, so on that

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Speaker 1: that would be the theoretical lower limit of of how

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Speaker 1: many would have to exist in order for the universe

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Speaker 1: to be stable. The first thing that comes to mind

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Speaker 1: is neutrinos are small, and perhaps that's the floor is

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Speaker 1: defining a smallest particle that we can know of. So

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Speaker 1: maybe the neutrino floor is the smallest particle that we

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Speaker 1: know of at the moment. Maybe that's UM basically maybe

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Speaker 1: a base like a like a baseplate of neutrinos where

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Speaker 1: UM we can basically detected measurements according to what neutrinos

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Speaker 1: hit that area. Neutron e knows I've learned in the

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Speaker 1: podcast are pretty much everywhere, and many, many of them.

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Speaker 1: So I guess if you don't have another source of neutrinos,

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Speaker 1: the neutrinow flaw would be the sort of normal or

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Speaker 1: median neutrino density um that that you would find. All Right,

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Speaker 1: a lot of great answers. I feel like any of

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Speaker 1: these could be the real answer. These are great speculative answers.

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Speaker 1: None of them are right, but they are great examples

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Speaker 1: of people brainstorming and using their physics knowledge and coming

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Speaker 1: up with totally reasonable ideas for what this crazy concept

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Speaker 1: could be. Well, that these all seem plausible, and I

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Speaker 1: think everyone sort of latching onto the word floor as

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Speaker 1: it's kind of like the bottom of something, or like

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Speaker 1: the minimum of something, or like the point at which

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Speaker 1: you can't go below exactly. And that's reasonable, and that's

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Speaker 1: why floor is in there. But as you'll hear us

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Speaker 1: talk about today, that's not exactly what we're talking about.

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Speaker 1: We're not talking about the lowest energy date of neutrinos

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Speaker 1: or literal floors made out of neutrinos. Do you have

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Speaker 1: a neutrino house? Is that possible? Well, it wouldn't give

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Speaker 1: you much privacy, and it wouldn't shield you from the weather,

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Speaker 1: but you still have to pay taxes on it. So

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Speaker 1: I don't think it's a great idea. Oh boy, but

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Speaker 1: it's neutral taxes though, right is weak taxes. You have

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Speaker 1: to pay it in dark matter dollars. Maybe maybe you

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Speaker 1: could pay in weak dollars as the US dollar might

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Speaker 1: be these things all right, Well, the topic is to

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Speaker 1: the general topic though, is dark matter and why we

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Speaker 1: can't measure it as well as we should be able to.

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Speaker 1: And so let's maybe recap for folks what is dark

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Speaker 1: matter and how we know it's there? Yeah, so, very briefly,

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Speaker 1: dark matter is most of the stuff in the universe.

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Speaker 1: We know that out there, deep in space and also

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Speaker 1: around us here there is some kind of matter which

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Speaker 1: has gravity, and so it affects the way things move

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Speaker 1: and the way the universe has been shaped and evolved.

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Speaker 1: But we don't know exactly where it is and what

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Speaker 1: it is, but we are sure that it's there and

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Speaker 1: that it's here. It was discovered initially because we were

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Speaker 1: looking at how galaxies rotate. When galaxy spin, you might wonder,

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Speaker 1: like why don't the stars fly off into intergalactic space

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Speaker 1: like ping pong balls would on a Merry go Round,

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Speaker 1: and the answer is gravity. Gravity holds them into the galaxy.

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Speaker 1: But you can ask is there enough gravity to hold

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Speaker 1: the galaxy together, because we can measure how fast the

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Speaker 1: galaxy is spinning, and we can count up how many

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Speaker 1: stars there are to estimate how much gravity there is,

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Speaker 1: so you can do this kind of cross check. This

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Speaker 1: is a great kind of thing to do in science.

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Speaker 1: It's just like double check that things make sense and

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Speaker 1: nine at the time they do and you move on,

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Speaker 1: and it's really boring. But sometimes they reveal, like a

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Speaker 1: cosmic mystery, a clue that there's something missing in our understanding.

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Speaker 1: And that's what happened here. Because the galaxies are spinning

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Speaker 1: way too fast, there's not nearly enough gravity to hold

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Speaker 1: them together if you just count the mass of the

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Speaker 1: stars that we can see. So people thought, well, there

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Speaker 1: must be some other kind of stuff out there in

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Speaker 1: the galaxy. And people had other ideas to like maybe

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Speaker 1: we just don't understand gravity or something wrong with our

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Speaker 1: theory of gravity. But pretty soon we had other evidence

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Speaker 1: of dark matter that convinced us it was real and

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Speaker 1: it was matter. For example, we understand that dark matter

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Speaker 1: has shaped the whole evolution of the universe, since it's

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Speaker 1: most of the matter of the universe, it's most of

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Speaker 1: the gravity, which changes how the stuff in the universe flows.

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Speaker 1: You know that there are galaxies and filaments of galaxies

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Speaker 1: and superclusters and this all this structure in the universe

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Speaker 1: that's controlled by dark matter. If dark matter hadn't been around,

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Speaker 1: we wouldn't have had that structure. We wouldn't have galaxies

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Speaker 1: and stars today. So we have lots of evidence for

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Speaker 1: dark matter in the universe, but we don't yet know

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Speaker 1: exactly what it's made out of. Yeah, we definitely know

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Speaker 1: it's there. Like, like we've mentioned before, it's like having

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Speaker 1: an elephant in the room. It's like you can feel

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Speaker 1: its presence in the universe, and like you're saying, like,

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Speaker 1: we know it's there because it explains to the rotation

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Speaker 1: of galaxies. And also, like I think we've covered this

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Speaker 1: in another episode that it's sort of the only way

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Speaker 1: to explain how the universe is the way it is now.

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Speaker 1: Like if you took out dark matter from the beginning

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Speaker 1: of the universe, like we wouldn't end up with the

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Speaker 1: same universe. Yeah, you wouldn't at all. The universe wouldn't

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Speaker 1: have galaxies and stars form as early as they did

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Speaker 1: in our universe. So we're pretty sure that that gravity

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Speaker 1: is there. We just don't know what it is that's

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Speaker 1: generating that gravity, all right. So we know the elephant

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Speaker 1: is there in the room. We can smell the you know,

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Speaker 1: elephant done, and we know we can feel its attraction

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Speaker 1: or repulsion. But what do we actually know about dark matter? Like,

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Speaker 1: do we know anything about it except other than its

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Speaker 1: effects in terms of it's matter and gravity. We do

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Speaker 1: know some things because we've been looking for it, and

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Speaker 1: we know, for example, that it doesn't feel some of

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Speaker 1: the forces like electromagnetism, the force that makes things reflect

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Speaker 1: light or it makes things glow. Doesn't feel that force

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Speaker 1: at all. It has no electric charge. If it did,

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Speaker 1: it would reflect light or it would glow because it

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Speaker 1: has some temperature. But it doesn't, so it doesn't feel electromagnetism.

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Speaker 1: We know that it doesn't feel the weak force. We've

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Speaker 1: also looked for using the weak force, and that's actually

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Speaker 1: what we'll talk about today, experiments that tried to look

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Speaker 1: for it using the weak force, and it also doesn't

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Speaker 1: feel a strong force. Similarly, if it felt a strong force,

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Speaker 1: it would have crazy interactions with our matter that we

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Speaker 1: could see. But it does feel gravity, which means that

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Speaker 1: it has mass. Right, it changes the shape of space,

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Speaker 1: means it has mass. It has some energy to it,

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Speaker 1: but we also know a little bit more about how

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Speaker 1: much energy it has. We actually know something about the

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Speaker 1: temperature of dark matter. You might think like, well, how

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Speaker 1: could you measure the temperature of dark matter. You can't

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Speaker 1: like take a thermometer and stick it in there because

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Speaker 1: it can't interact with the dark matter. What we do

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Speaker 1: is we look at how dark matter is clumped and

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Speaker 1: spread through the universe. If dark matter was hot, if

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Speaker 1: it's particles were moving really really fast, it would spread

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Speaker 1: out a lot, and that would change the shape of

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Speaker 1: the universe how things were distributed, like the galaxies and

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Speaker 1: where they are. And if dark matter was cold, if

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Speaker 1: it was slow moving, you would tend to clump a

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Speaker 1: little bit more and that would give you a different

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Speaker 1: shape for the universe. And what we see is that

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Speaker 1: dark matter is pretty cold. It's not like some fast

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Speaker 1: moving little particle that spreads out a lot tends to

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Speaker 1: be cold and clumpy. Dark matter is pretty cool, for sure,

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Speaker 1: But we also sort of know kind of where it

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Speaker 1: is right, or the kind of the distribution of it

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Speaker 1: or the shape of it throughout the universe, Like we

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Speaker 1: know it's sort of like a giant cloud, or some

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Speaker 1: people call it a halo around our galaxy. And when

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Speaker 1: you look out into the the universe, you can see

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Speaker 1: that there's sort of ripples and clumps of it here,

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Speaker 1: and they're like, it's not evenly distributed throughout the universe.

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Speaker 1: It seems to clump to things, and there's clumps of

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Speaker 1: it out there in space. That's right, and describing it

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Speaker 1: as a halo is accurate, but it suggests sort of

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Speaker 1: that dark matter follows the normal matter that you know

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Speaker 1: dark matter is there where normal matter is, when actually

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Speaker 1: it's the opposite. Normal matter follows the dark matter because

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Speaker 1: dark matter it's much more gravity. The reasons in galaxy

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Speaker 1: right here is because there was a big clump of

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Speaker 1: dark matter and so all the normal matter fell into

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Speaker 1: that gravitational well and was then squeezed together into a galaxy.

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Speaker 1: So yes, it's not everywhere through space. It's in these

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Speaker 1: big clumps. And we can tell where the really big

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Speaker 1: clumps are because they have enough gravity, but we can't

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Speaker 1: tell example, is there a blob of it right here

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Speaker 1: in the room with me, because it's really hard to

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Speaker 1: measure the gravity of smaller objects, so we can't tell

429
00:22:06,880 --> 00:22:09,359
Speaker 1: where the dark matter is with like really fine resolution,

430
00:22:09,680 --> 00:22:11,840
Speaker 1: smaller than like, you know, a chunk of the galaxy.

431
00:22:12,080 --> 00:22:14,240
Speaker 1: We can't even tell, like down to the Solar System

432
00:22:14,400 --> 00:22:16,840
Speaker 1: where the dark matter is. Right But the big mystery

433
00:22:16,880 --> 00:22:18,960
Speaker 1: of dark matter is that we sort of don't know

434
00:22:19,520 --> 00:22:22,199
Speaker 1: what it is, right like, we know it's there. We

435
00:22:22,280 --> 00:22:25,520
Speaker 1: know there's something or some something we I don't know

436
00:22:25,520 --> 00:22:27,640
Speaker 1: if the thing is even the right word, but there's

437
00:22:27,680 --> 00:22:30,520
Speaker 1: something there that's pulling us gravitationally. But it could be

438
00:22:30,560 --> 00:22:33,600
Speaker 1: like a particle, or could be something non particle. It

439
00:22:33,600 --> 00:22:35,639
Speaker 1: could be, like I don't know, some kind of like

440
00:22:35,800 --> 00:22:38,679
Speaker 1: new kind of stuff. Right, absolutely it could, and we

441
00:22:38,720 --> 00:22:40,680
Speaker 1: need to keep an open mind because all of our

442
00:22:40,800 --> 00:22:43,800
Speaker 1: ideas about what matter is come from studying the kind

443
00:22:43,800 --> 00:22:45,800
Speaker 1: of matter we are made out of. But we know

444
00:22:45,880 --> 00:22:48,200
Speaker 1: that dark matter is different. It has to be different.

445
00:22:48,200 --> 00:22:50,880
Speaker 1: It's not made out of atoms, and so it might

446
00:22:50,960 --> 00:22:54,560
Speaker 1: follow very different rules and whole different concepts. So on

447
00:22:54,560 --> 00:22:56,879
Speaker 1: one hand, we could try to extrapolate from what we

448
00:22:56,920 --> 00:22:59,399
Speaker 1: know and say everything out here is made a particle.

449
00:22:59,480 --> 00:23:02,520
Speaker 1: So maybe dark matter is also, but maybe dark matters

450
00:23:02,520 --> 00:23:04,320
Speaker 1: made of lots of different kind of particles or as

451
00:23:04,359 --> 00:23:07,440
Speaker 1: you say, even something weirder, something that's not a particle.

452
00:23:07,840 --> 00:23:09,800
Speaker 1: And we did a whole fun podcast episode about what

453
00:23:09,840 --> 00:23:13,320
Speaker 1: an unparticle might be. It's weird new kind of matter

454
00:23:13,400 --> 00:23:16,120
Speaker 1: that people are playing with conceptually. But it also could

455
00:23:16,160 --> 00:23:18,920
Speaker 1: be something that nobody has thought of at all, something

456
00:23:19,040 --> 00:23:22,080
Speaker 1: totally new and weird that blows our minds. Right, it

457
00:23:22,119 --> 00:23:24,520
Speaker 1: could be an unparticle, or maybe it's a fun particle,

458
00:23:24,760 --> 00:23:29,000
Speaker 1: who know, Or it's an unidea waiting to join the party.

459
00:23:29,160 --> 00:23:31,800
Speaker 1: All right, That's what dark matter is. It's something that's there.

460
00:23:31,840 --> 00:23:33,800
Speaker 1: We know it's there, but we don't know what it is.

461
00:23:33,920 --> 00:23:37,520
Speaker 1: And because it's invisible, it doesn't interact with the electromagnetic force,

462
00:23:37,600 --> 00:23:39,399
Speaker 1: And so how do you study something like that? How

463
00:23:39,440 --> 00:23:41,920
Speaker 1: do you look for something that's invisible and doesn't want

464
00:23:41,920 --> 00:23:44,600
Speaker 1: to be touched. So let's get into that, but first

465
00:23:44,880 --> 00:24:00,040
Speaker 1: let's take a quick break. Alright, we're talking about the

466
00:24:00,080 --> 00:24:04,480
Speaker 1: neutrino floor and how somehow that floor is preventing us

467
00:24:04,640 --> 00:24:09,400
Speaker 1: from or hiding maybe dark matter and our understanding of

468
00:24:09,440 --> 00:24:11,679
Speaker 1: what it's made out of So we talked about what

469
00:24:11,840 --> 00:24:14,639
Speaker 1: dark matter is. And now, Daniel, how are people, I guess,

470
00:24:15,040 --> 00:24:17,479
Speaker 1: trying to study dark matter. I mean, it's invisible and

471
00:24:17,520 --> 00:24:19,560
Speaker 1: you can't touch it with your finger or any kind

472
00:24:19,560 --> 00:24:23,800
Speaker 1: of instrument really, because it only feels certain forces. How

473
00:24:23,800 --> 00:24:26,919
Speaker 1: do you look for something that elusive? It's overwhelming, you know,

474
00:24:27,000 --> 00:24:28,720
Speaker 1: to say, I want to look for something I don't

475
00:24:28,720 --> 00:24:30,800
Speaker 1: really know what it is, if it's even a particle,

476
00:24:30,880 --> 00:24:33,240
Speaker 1: if it's something I haven't imagined yet, I don't know

477
00:24:33,280 --> 00:24:36,679
Speaker 1: how to interact with it. In general, that's an unsolvable problem.

478
00:24:36,800 --> 00:24:39,120
Speaker 1: We just don't know in science how to tackle such

479
00:24:39,160 --> 00:24:41,400
Speaker 1: a big problem. So what we do is we break

480
00:24:41,440 --> 00:24:44,119
Speaker 1: it into pieces and we say, well, let's assume that

481
00:24:44,160 --> 00:24:47,199
Speaker 1: we're lucky. Let's assume that dark matter is something that

482
00:24:47,240 --> 00:24:50,240
Speaker 1: we do know how to discover, and that we're lucky

483
00:24:50,520 --> 00:24:52,679
Speaker 1: and it can talk to us. So we make a

484
00:24:52,680 --> 00:24:56,800
Speaker 1: bunch of totally unjustified assumptions and hope that they're correct. So,

485
00:24:56,840 --> 00:24:59,600
Speaker 1: for example, we assume that dark matter is made of

486
00:24:59,640 --> 00:25:02,560
Speaker 1: particle because that's basically all we know how to do.

487
00:25:03,040 --> 00:25:05,440
Speaker 1: And we assume that dark matter is made of one

488
00:25:05,600 --> 00:25:08,280
Speaker 1: kind of particle because that's just simpler, And as you

489
00:25:08,280 --> 00:25:11,480
Speaker 1: said earlier, there's no justification for assuming that dark matter

490
00:25:11,560 --> 00:25:13,719
Speaker 1: is made of particles other than everything so far has

491
00:25:13,760 --> 00:25:16,800
Speaker 1: been made of particles, And there's no justification for assuming

492
00:25:16,800 --> 00:25:19,560
Speaker 1: it's one kind of particle, because you know, our matters

493
00:25:19,560 --> 00:25:21,600
Speaker 1: made of lots of different kinds of particles. But it's

494
00:25:21,600 --> 00:25:24,000
Speaker 1: just sort of like the simplest place to start, I see,

495
00:25:24,040 --> 00:25:26,240
Speaker 1: because you know, most of the stuff we are familiar

496
00:25:26,280 --> 00:25:28,359
Speaker 1: with and that we that we have at our disposal

497
00:25:28,680 --> 00:25:31,520
Speaker 1: and that we know about is made out of particles, right,

498
00:25:31,680 --> 00:25:33,880
Speaker 1: and not just sort of like any particles, but sort

499
00:25:33,880 --> 00:25:37,320
Speaker 1: of like a certain range of sizes of particles, right, yeah, exactly.

500
00:25:37,359 --> 00:25:39,679
Speaker 1: And we think that dark matter is heavy. We do

501
00:25:39,760 --> 00:25:42,200
Speaker 1: have some evidence there because we know that it's cold.

502
00:25:42,560 --> 00:25:45,720
Speaker 1: If dark matter was really really low mass, then it

503
00:25:45,760 --> 00:25:48,399
Speaker 1: would have enough energy to be zipping around at higher speed.

504
00:25:48,480 --> 00:25:50,680
Speaker 1: So we have some evidence that dark matter, if it

505
00:25:50,760 --> 00:25:53,800
Speaker 1: is a particle, is probably on the heavier side. But

506
00:25:53,880 --> 00:25:57,359
Speaker 1: we don't know if that particle feels any forces other

507
00:25:57,400 --> 00:25:59,680
Speaker 1: than gravity, Like we know it feels gravity, but if

508
00:25:59,680 --> 00:26:02,240
Speaker 1: it only feels gravity, it would make it very very

509
00:26:02,280 --> 00:26:06,399
Speaker 1: difficult to ever discover a particle of dark matter. Because

510
00:26:06,760 --> 00:26:09,159
Speaker 1: even if it's heavy, it might weigh, you know, like

511
00:26:09,320 --> 00:26:13,080
Speaker 1: as much as a gold nucleus. But how much gravity

512
00:26:13,160 --> 00:26:16,960
Speaker 1: does a gold nucleus have? Almost zero. It's very difficult

513
00:26:17,000 --> 00:26:20,000
Speaker 1: to measure the gravity of a single particle. So in

514
00:26:20,080 --> 00:26:23,440
Speaker 1: order to discover dark matter, we also make another almost

515
00:26:23,520 --> 00:26:27,520
Speaker 1: totally unjustified assumption, which is that there's some new force

516
00:26:27,600 --> 00:26:31,080
Speaker 1: out there that dark matter feels and we also feel,

517
00:26:31,160 --> 00:26:35,080
Speaker 1: and we can use that to discover dark matter. What Okay,

518
00:26:35,119 --> 00:26:36,919
Speaker 1: I got stuck a little bit while ago because you

519
00:26:36,960 --> 00:26:38,960
Speaker 1: said that it has to be heavy because it's cold.

520
00:26:39,040 --> 00:26:41,520
Speaker 1: Can't it also be a small or light particle and

521
00:26:41,560 --> 00:26:44,000
Speaker 1: also be cold. It can be. It's possible. We think

522
00:26:44,000 --> 00:26:46,359
Speaker 1: it's more likely because it's cold that it's heavy. That

523
00:26:46,400 --> 00:26:48,439
Speaker 1: would make it easier for it to be slow moving,

524
00:26:48,520 --> 00:26:51,040
Speaker 1: right when we know something about its velocity, And if

525
00:26:51,080 --> 00:26:52,880
Speaker 1: it's light, then it would have to be even low

526
00:26:53,119 --> 00:26:56,000
Speaker 1: energy to be cold. So yeah, it's possible to have

527
00:26:56,200 --> 00:26:59,000
Speaker 1: cold light particles, but they're less likely, we think, all right,

528
00:26:59,080 --> 00:27:00,600
Speaker 1: And so then you said you have to assume it

529
00:27:00,920 --> 00:27:03,639
Speaker 1: interacts through a new kind of force that we have

530
00:27:03,760 --> 00:27:06,359
Speaker 1: no idea about, and I guess maybe explain why that

531
00:27:06,480 --> 00:27:09,199
Speaker 1: is is it. Couldn't it also be interacting through the

532
00:27:09,240 --> 00:27:12,080
Speaker 1: weak or strong forces, maybe in a different way than

533
00:27:12,119 --> 00:27:15,120
Speaker 1: you thought, but it could also be interacting through those forces. Yeah,

534
00:27:15,160 --> 00:27:17,840
Speaker 1: And we've looked for it interacting through those forces, and

535
00:27:17,880 --> 00:27:20,360
Speaker 1: we haven't seen it. You know, if dark matter interacted

536
00:27:20,400 --> 00:27:23,160
Speaker 1: with the strong force, then everything that feels a strong

537
00:27:23,200 --> 00:27:25,720
Speaker 1: force would interact with dark matter, and it should be

538
00:27:25,760 --> 00:27:28,560
Speaker 1: pretty easy to find because the strong force is very strong.

539
00:27:28,960 --> 00:27:31,880
Speaker 1: Like any blob of matters out there, every rock, for example,

540
00:27:32,200 --> 00:27:34,920
Speaker 1: should be hit by dark matter, should be interacting with

541
00:27:35,000 --> 00:27:36,960
Speaker 1: dark matter. But we don't see that, you know, we

542
00:27:36,960 --> 00:27:40,280
Speaker 1: don't see those things. We study particles really carefully. And

543
00:27:40,320 --> 00:27:42,919
Speaker 1: the strong force, again is very very strong. So if

544
00:27:42,960 --> 00:27:46,480
Speaker 1: dark matter was interacting with matter using the strong force,

545
00:27:46,640 --> 00:27:49,800
Speaker 1: we would see weird, unexplained effects. We would discover dark

546
00:27:49,800 --> 00:27:52,040
Speaker 1: matter years and years ago. The same thing for the

547
00:27:52,080 --> 00:27:54,760
Speaker 1: weak force. We have looked for dark matter interacting with

548
00:27:54,800 --> 00:27:57,960
Speaker 1: our particles using the weak force, and we haven't seen it.

549
00:27:58,200 --> 00:28:00,880
Speaker 1: And we know these forces really really well, like very

550
00:28:00,920 --> 00:28:04,000
Speaker 1: precise measurements of these forces and colliders and other experiments,

551
00:28:04,119 --> 00:28:07,399
Speaker 1: So any deviations from our theories of these forces would

552
00:28:07,400 --> 00:28:09,119
Speaker 1: be hints of dark matter and we've looked for that

553
00:28:09,160 --> 00:28:11,280
Speaker 1: and we just haven't seen it. I see, there's no

554
00:28:11,359 --> 00:28:14,120
Speaker 1: evidence that it feels a weak or strong force so far.

555
00:28:14,280 --> 00:28:16,920
Speaker 1: That's right, And we've studied those in the wazoo, out

556
00:28:16,920 --> 00:28:18,920
Speaker 1: the wazoo, and around the wazoo. I don't want to

557
00:28:18,920 --> 00:28:21,440
Speaker 1: know where the wazoo of an elephant is. So then

558
00:28:22,200 --> 00:28:24,560
Speaker 1: is that where we're at now? Like we've given up

559
00:28:24,560 --> 00:28:27,720
Speaker 1: on the weak force and the strong force for dark matter,

560
00:28:28,160 --> 00:28:30,480
Speaker 1: we've given up on those, and so we said, well,

561
00:28:30,520 --> 00:28:33,879
Speaker 1: what if there's another force? Right? What if there's another

562
00:28:34,040 --> 00:28:37,560
Speaker 1: force that dark matter can use to interact with our matter?

563
00:28:37,760 --> 00:28:39,840
Speaker 1: And if there is, then we can use that to

564
00:28:39,960 --> 00:28:43,880
Speaker 1: discover it. The argument for that existing is mostly boy,

565
00:28:43,960 --> 00:28:46,440
Speaker 1: I hope it exists because that would make it possible

566
00:28:46,480 --> 00:28:49,640
Speaker 1: to discover dark matter. There are some other hand wavy

567
00:28:49,720 --> 00:28:53,000
Speaker 1: arguments to suggest that maybe it's reasonable, but mostly it's

568
00:28:53,040 --> 00:28:55,040
Speaker 1: the first one. It's just out of desperation. It's the

569
00:28:55,080 --> 00:28:56,840
Speaker 1: only way we would be able to see it. So

570
00:28:56,920 --> 00:28:59,680
Speaker 1: let's hope it's true. Yeah, exactly, let's start there. And

571
00:28:59,720 --> 00:29:01,600
Speaker 1: you know, if we don't find it, then we need

572
00:29:01,640 --> 00:29:04,240
Speaker 1: to re examine these assumptions and go back and think well,

573
00:29:04,240 --> 00:29:06,760
Speaker 1: what if there's another way, let's be more clever about it.

574
00:29:06,800 --> 00:29:09,120
Speaker 1: But it also makes sense in science to try the

575
00:29:09,120 --> 00:29:11,960
Speaker 1: simplest thing first. Hey, maybe we'll get lucky and dark

576
00:29:12,000 --> 00:29:15,040
Speaker 1: matter will be some heavy kind of particle that has

577
00:29:15,080 --> 00:29:17,840
Speaker 1: a new force that interacts with our detectors and we

578
00:29:17,840 --> 00:29:19,680
Speaker 1: can discover it that way. It would be silly not

579
00:29:19,760 --> 00:29:22,080
Speaker 1: to try the simplest thing first, right, But I guess

580
00:29:22,120 --> 00:29:24,320
Speaker 1: it doesn't sound that simple, right, like making up a

581
00:29:24,320 --> 00:29:26,520
Speaker 1: whole new we're assuming a whole new force in the

582
00:29:26,600 --> 00:29:29,400
Speaker 1: universe that nobody has ever seen or or felt before.

583
00:29:29,440 --> 00:29:32,200
Speaker 1: It seems a bit of a stretch because like, if

584
00:29:32,240 --> 00:29:36,600
Speaker 1: such a force existed, then our matter can interact through it,

585
00:29:36,760 --> 00:29:38,720
Speaker 1: wouldn't we have noticed by now? Yes, And so it

586
00:29:38,760 --> 00:29:40,880
Speaker 1: has to be a weak force, not weak with a

587
00:29:40,920 --> 00:29:43,720
Speaker 1: capital W, like the weak force, but it has to

588
00:29:43,720 --> 00:29:47,720
Speaker 1: be like a feeble force. So you're right, exactly, if

589
00:29:47,760 --> 00:29:50,880
Speaker 1: there is this other force and our particles can feel it,

590
00:29:51,120 --> 00:29:53,160
Speaker 1: then we should see it in experiments. We have other

591
00:29:53,240 --> 00:29:56,120
Speaker 1: experiments also that are looking for these kinds of forces,

592
00:29:56,320 --> 00:29:58,560
Speaker 1: and so we hope it's out there. But if it's true,

593
00:29:58,600 --> 00:30:01,120
Speaker 1: it would have to be very, very feeble and that's

594
00:30:01,120 --> 00:30:04,280
Speaker 1: why these experiments are very difficult. Is that the official name.

595
00:30:04,280 --> 00:30:07,520
Speaker 1: Have you guys christened the feeble force? No, we haven't

596
00:30:07,560 --> 00:30:11,360
Speaker 1: christened it fantastic force. And it's very confusing, of course,

597
00:30:11,400 --> 00:30:14,600
Speaker 1: because it's particle physics. Naming. This particle we're talking about

598
00:30:14,680 --> 00:30:19,000
Speaker 1: is called the WHIMP weakly interacting massive particle. But weakly

599
00:30:19,080 --> 00:30:22,240
Speaker 1: interacting there does not mean interacting through the weak force.

600
00:30:22,360 --> 00:30:25,760
Speaker 1: It means interacting through some new, not very powerful force.

601
00:30:26,040 --> 00:30:27,960
Speaker 1: So they should have called it, like the FIMP, the

602
00:30:28,080 --> 00:30:31,240
Speaker 1: feebly interacting massive particle. Yeah, because you don't want to

603
00:30:31,240 --> 00:30:35,400
Speaker 1: call it the powerful interacting massive particle. That would be

604
00:30:35,520 --> 00:30:40,000
Speaker 1: inappropriate for any podcast, that's right, or the limp or something, right,

605
00:30:40,160 --> 00:30:43,840
Speaker 1: the lightly interacting massive particle. There you go, all right, Well,

606
00:30:43,920 --> 00:30:47,400
Speaker 1: so if dark matter is interactive through this new imaginary

607
00:30:47,480 --> 00:30:50,480
Speaker 1: force we're hoping to see, um, how would we see it?

608
00:30:50,640 --> 00:30:56,000
Speaker 1: It's not imaginary? Is hypothetical? I see? There's a difference

609
00:30:56,160 --> 00:30:59,400
Speaker 1: right between hypothetical and imaginary. It's all about spin. I mean,

610
00:30:59,440 --> 00:31:02,320
Speaker 1: you say, it's like making it very complicated. On the

611
00:31:02,360 --> 00:31:05,080
Speaker 1: other hand, it's sort of ambitious, right, Like this way,

612
00:31:05,440 --> 00:31:08,280
Speaker 1: if we discover dark matter, we get two discoveries for

613
00:31:08,320 --> 00:31:11,160
Speaker 1: the price of one. We find a new particle and boom,

614
00:31:11,400 --> 00:31:14,280
Speaker 1: new force. At the same time. It's like Nobel prize

615
00:31:14,440 --> 00:31:17,920
Speaker 1: with the side of another Nobel prize. I see. It's like,

616
00:31:18,240 --> 00:31:20,440
Speaker 1: how are we going to find the big invisible elephant

617
00:31:20,480 --> 00:31:22,800
Speaker 1: in the room? Well, I'm glad you asked. We're going

618
00:31:22,880 --> 00:31:27,760
Speaker 1: to use invisible camels. Yes, exactly, exactly, And in this

619
00:31:27,840 --> 00:31:30,000
Speaker 1: case you need the invisible camels to show you where

620
00:31:30,000 --> 00:31:32,640
Speaker 1: the invisible elephant is. And so you assume both exist

621
00:31:32,680 --> 00:31:37,480
Speaker 1: and then when you discover them, boom, two discoveries, two

622
00:31:37,520 --> 00:31:39,600
Speaker 1: animals for the price of one. That's right. So we're

623
00:31:39,600 --> 00:31:42,680
Speaker 1: looking for the zimp, the zoo interacting massive particle. All right,

624
00:31:42,760 --> 00:31:45,520
Speaker 1: So then what are these experiments? What do they look like?

625
00:31:45,560 --> 00:31:46,880
Speaker 1: How do you look for a force you don't even

626
00:31:46,920 --> 00:31:49,840
Speaker 1: know it exists? So there's actually three different ways that

627
00:31:50,000 --> 00:31:52,400
Speaker 1: we look for the whimp. They're called make it, shake it,

628
00:31:52,600 --> 00:31:54,440
Speaker 1: or break it. But today we're gonna talk about just

629
00:31:54,600 --> 00:31:56,360
Speaker 1: one of them because it's the one that's related to

630
00:31:56,480 --> 00:31:59,680
Speaker 1: neutrinos and the neutrino floor, and that's the shake it.

631
00:32:00,320 --> 00:32:02,920
Speaker 1: And this is a strategy of looking for dark matter

632
00:32:03,120 --> 00:32:07,480
Speaker 1: by basically making a really big chunk of stuff and

633
00:32:07,560 --> 00:32:10,280
Speaker 1: putting in a really quiet place so you don't expect

634
00:32:10,320 --> 00:32:12,680
Speaker 1: anything to happen, and then looking to see if dark

635
00:32:12,720 --> 00:32:16,080
Speaker 1: matter ever bumps into part of your really big chunk

636
00:32:16,120 --> 00:32:20,400
Speaker 1: of stuff. This is one of those like xenon detectors, right,

637
00:32:20,960 --> 00:32:23,720
Speaker 1: so it's a huge tank of liquid and actually gashes

638
00:32:23,920 --> 00:32:27,680
Speaker 1: zenon that's deep deep underground and zenon because Zenon is

639
00:32:27,720 --> 00:32:29,680
Speaker 1: one of the noble elements. So if you have a

640
00:32:29,720 --> 00:32:32,400
Speaker 1: big tank of xenon, it basically does nothing, doesn't like

641
00:32:32,600 --> 00:32:35,800
Speaker 1: give off flashes of light or interact. And so if

642
00:32:35,880 --> 00:32:39,000
Speaker 1: something does cause the zenon to do something, it means

643
00:32:39,160 --> 00:32:42,000
Speaker 1: something has penetrated somethings like kicked the zenon or giving

644
00:32:42,040 --> 00:32:43,760
Speaker 1: it a little boost or something. Do you take your

645
00:32:43,800 --> 00:32:47,040
Speaker 1: big vast tank of xenon, you bury deep deep underground

646
00:32:47,440 --> 00:32:50,000
Speaker 1: so that particles from space don't hit it, and then

647
00:32:50,040 --> 00:32:52,960
Speaker 1: you put basically cameras they'll photo multiplier tubes to watch

648
00:32:53,040 --> 00:32:55,719
Speaker 1: it and ask like did any of my xenon atoms

649
00:32:55,840 --> 00:32:59,160
Speaker 1: get bumped? Right? But doesn't Zenon sort of move or

650
00:32:59,520 --> 00:33:01,960
Speaker 1: does thing by itself? Like how do you know? You

651
00:33:02,000 --> 00:33:03,120
Speaker 1: know what I mean? Like if you put something in

652
00:33:03,160 --> 00:33:05,240
Speaker 1: a room. How do you know it's something moved it

653
00:33:05,400 --> 00:33:07,880
Speaker 1: or if it moved by itself. Yeah, So it's cryogenic,

654
00:33:08,160 --> 00:33:11,520
Speaker 1: so it's very very cold liquid xenon. And they do

655
00:33:11,640 --> 00:33:14,200
Speaker 1: a lot of work to try to isolate other sources

656
00:33:14,280 --> 00:33:16,600
Speaker 1: of noise. This is the kind of detector where they're

657
00:33:16,640 --> 00:33:20,440
Speaker 1: hoping to see one dark matter particle come through over

658
00:33:20,600 --> 00:33:23,880
Speaker 1: like several years. Right. So in order to claim discovery

659
00:33:23,960 --> 00:33:26,360
Speaker 1: when you see like one example, you need to make

660
00:33:26,400 --> 00:33:29,120
Speaker 1: sure there are no other ways for this kind of

661
00:33:29,200 --> 00:33:31,440
Speaker 1: thing to happen, no other things that might look like

662
00:33:31,560 --> 00:33:34,040
Speaker 1: you're invisible camel. And so they do a lot of

663
00:33:34,080 --> 00:33:36,680
Speaker 1: work to shield this thing from particles from the outside,

664
00:33:37,040 --> 00:33:40,600
Speaker 1: from radiation from the rock, and also to cool this

665
00:33:40,720 --> 00:33:43,720
Speaker 1: thing down so there's no internal noise. Right. And I

666
00:33:43,760 --> 00:33:46,120
Speaker 1: think the idea is not that there's only one particle

667
00:33:46,240 --> 00:33:48,960
Speaker 1: dark matter there per year. It's more like it's full

668
00:33:49,040 --> 00:33:51,720
Speaker 1: of dark matter particles, but only like once in a

669
00:33:51,760 --> 00:33:55,160
Speaker 1: blue moon do they sort of interact with the zenon

670
00:33:55,280 --> 00:33:58,520
Speaker 1: particles exactly. We think that the Earth is moving through

671
00:33:58,640 --> 00:34:01,800
Speaker 1: a dark matter wind, like we think that dark matter

672
00:34:01,960 --> 00:34:04,960
Speaker 1: is this big halo that surrounds the galaxy, or the

673
00:34:05,040 --> 00:34:07,880
Speaker 1: galaxy is embedded in the halo of dark matter. So

674
00:34:08,040 --> 00:34:11,160
Speaker 1: we think that dark matter is probably everywhere, and so

675
00:34:11,360 --> 00:34:13,839
Speaker 1: we have dark matter in our room with us right now,

676
00:34:14,360 --> 00:34:16,600
Speaker 1: probably a good bit of it. And so this is

677
00:34:16,640 --> 00:34:19,200
Speaker 1: this wind of dark matter. But as you say, we

678
00:34:19,239 --> 00:34:22,000
Speaker 1: don't have a high probability to interact with that dark matter.

679
00:34:22,120 --> 00:34:24,600
Speaker 1: Most of the time when dark matter passes through normal matter,

680
00:34:24,880 --> 00:34:27,320
Speaker 1: nothing happens. So you need to do a lot of that.

681
00:34:27,400 --> 00:34:29,600
Speaker 1: You need to shoot dark matter through your detector a

682
00:34:29,719 --> 00:34:31,920
Speaker 1: lot of times, and that's why you wait a long

683
00:34:32,000 --> 00:34:34,759
Speaker 1: time and you have really big detector, and you're exactly right.

684
00:34:34,800 --> 00:34:37,399
Speaker 1: We expect like thousands and millions and billions of dark

685
00:34:37,440 --> 00:34:40,120
Speaker 1: matter particles to pass through. But this is a very

686
00:34:40,280 --> 00:34:44,239
Speaker 1: weak interaction. It's very feeble, and so only occasionally will

687
00:34:44,280 --> 00:34:46,799
Speaker 1: the dark matter particle bump into Zenon in a way

688
00:34:46,840 --> 00:34:48,840
Speaker 1: that we can see, right, Because I think when you

689
00:34:48,920 --> 00:34:51,600
Speaker 1: say like weak or feeble, you don't necessarily mean like

690
00:34:51,880 --> 00:34:54,080
Speaker 1: it hits it and it doesn't create an effect. It's

691
00:34:54,120 --> 00:34:57,919
Speaker 1: more like the probability of this interaction is very low

692
00:34:58,280 --> 00:35:02,600
Speaker 1: because it is, after all, presumably a quantum interaction. It

693
00:35:02,719 --> 00:35:04,840
Speaker 1: is a quantum interaction, and we talk about it in

694
00:35:05,000 --> 00:35:07,759
Speaker 1: terms of cross sections, because we'd like to use like

695
00:35:07,840 --> 00:35:11,840
Speaker 1: a classical physical analogy. Imagine that you're shooting two particles

696
00:35:11,920 --> 00:35:14,719
Speaker 1: at each other, or two balls at each other, right,

697
00:35:14,800 --> 00:35:16,960
Speaker 1: the chances that those balls will hit each other depends

698
00:35:17,000 --> 00:35:19,719
Speaker 1: on their cross sectional areas. If you shoot two like

699
00:35:19,880 --> 00:35:22,520
Speaker 1: basketballs at each other, it's much easier for them to

700
00:35:22,600 --> 00:35:24,680
Speaker 1: hit than if you shoot two ping pong balls at

701
00:35:24,719 --> 00:35:27,200
Speaker 1: each other. And so we think that dark matter has

702
00:35:27,239 --> 00:35:30,279
Speaker 1: a very low cross section with the zenon nucleus, which

703
00:35:30,360 --> 00:35:32,919
Speaker 1: means basically, it sees the zeno nucleus as a tiny,

704
00:35:33,000 --> 00:35:35,240
Speaker 1: tiny little dot and most of the time just flies

705
00:35:35,360 --> 00:35:38,400
Speaker 1: right by, whereas other particles, you know, like corks, have

706
00:35:38,480 --> 00:35:41,319
Speaker 1: a very large cross section with the zenon nucleus. If

707
00:35:41,360 --> 00:35:43,480
Speaker 1: you shout a cork through a tank of zenon, it

708
00:35:43,480 --> 00:35:45,960
Speaker 1: would interact with basically everything, right, So that that's the

709
00:35:46,000 --> 00:35:48,480
Speaker 1: basicic experiment that you're saying. You take a block of

710
00:35:48,640 --> 00:35:51,320
Speaker 1: really cold zenon, you put it under a lot of

711
00:35:51,480 --> 00:35:53,880
Speaker 1: installations so nothing else can reach it, and then you

712
00:35:54,080 --> 00:35:57,000
Speaker 1: just wait. As we're moving through the universe, we're moving

713
00:35:57,080 --> 00:36:01,600
Speaker 1: through a cloud or haze of dark matter, and hopefully eventually,

714
00:36:01,760 --> 00:36:04,279
Speaker 1: maybe one day this dark matter will interact with your

715
00:36:04,360 --> 00:36:06,600
Speaker 1: zene on in some way that you can detect, and

716
00:36:06,640 --> 00:36:08,600
Speaker 1: then you'll be like, hey, there is the dark matter,

717
00:36:08,760 --> 00:36:11,200
Speaker 1: that's right. And we look for these little flashes of

718
00:36:11,320 --> 00:36:14,080
Speaker 1: light that indicate that dark matter might have come through

719
00:36:14,480 --> 00:36:16,960
Speaker 1: and kicked one of these senon atoms which caused it

720
00:36:17,000 --> 00:36:19,759
Speaker 1: to either like lose an electron or to give off

721
00:36:19,760 --> 00:36:22,600
Speaker 1: a little scintillation flash of light. So that's the signal

722
00:36:22,680 --> 00:36:25,399
Speaker 1: that we're looking for. All right, Well, it sounds simple enough,

723
00:36:25,440 --> 00:36:27,719
Speaker 1: but there is apparently a sort of a hiccup in

724
00:36:27,840 --> 00:36:30,440
Speaker 1: this schematic, in this idea, and it has to do

725
00:36:30,600 --> 00:36:33,719
Speaker 1: with the nutrino floor. So let's get into that or

726
00:36:33,920 --> 00:36:49,440
Speaker 1: under that. But first let's take a quick break. All right.

727
00:36:49,520 --> 00:36:52,520
Speaker 1: We're trying to find dark matter, Daniel, and it's invisible

728
00:36:52,600 --> 00:36:54,799
Speaker 1: and it doesn't want us to a theater or touch

729
00:36:54,880 --> 00:36:57,600
Speaker 1: it or bump into it. But it might have a weakness,

730
00:36:57,760 --> 00:37:01,080
Speaker 1: which is a totally new kind of for yeah, exactly,

731
00:37:01,400 --> 00:37:03,760
Speaker 1: and so we are hoping that it will reveal itself

732
00:37:04,200 --> 00:37:08,040
Speaker 1: in this very quiet tank of liquid zenon deep underground.

733
00:37:08,040 --> 00:37:10,760
Speaker 1: There's actually several of them. There's one underground in Canada,

734
00:37:10,960 --> 00:37:14,680
Speaker 1: there's one underground in China. And there's one underground in Italy,

735
00:37:14,920 --> 00:37:18,800
Speaker 1: and these are all competing tanks of liquid zenon. M interesting.

736
00:37:18,960 --> 00:37:21,200
Speaker 1: It's interesting to think there are three places in the

737
00:37:21,239 --> 00:37:24,040
Speaker 1: world where there's a block of zenon just waiting for

738
00:37:24,160 --> 00:37:27,319
Speaker 1: something to happen and trying to ignore everything else that's

739
00:37:27,320 --> 00:37:30,319
Speaker 1: going on in the universe basically, right, Yeah, yeah, it's

740
00:37:30,360 --> 00:37:33,000
Speaker 1: not exactly a block. It's liquid zenon. Mostly there's a

741
00:37:33,080 --> 00:37:35,840
Speaker 1: gaseous face on the top. But yes, this tank of zenon.

742
00:37:36,120 --> 00:37:38,120
Speaker 1: And it must be interesting to be sitting there and

743
00:37:38,280 --> 00:37:41,279
Speaker 1: babysitting at you know, because it could be that one

744
00:37:41,360 --> 00:37:44,520
Speaker 1: day when you're on shift, that's the day you see

745
00:37:44,600 --> 00:37:48,080
Speaker 1: the signal that dark matter makes itself obvious. Most days

746
00:37:48,239 --> 00:37:50,800
Speaker 1: nothing happens, so most days you hope nothing happens. You

747
00:37:51,000 --> 00:37:53,440
Speaker 1: just sit there, and the end result of sitting there

748
00:37:53,440 --> 00:37:55,680
Speaker 1: for eight hours is yet we saw nothing today. So

749
00:37:55,840 --> 00:37:59,200
Speaker 1: it's very strange, like gambling with the universe, wondering if

750
00:37:59,239 --> 00:38:01,920
Speaker 1: today is gonna be the day you see something. It's

751
00:38:01,960 --> 00:38:04,279
Speaker 1: like you're staring down dark matter. It's like who's gonna

752
00:38:04,280 --> 00:38:07,400
Speaker 1: blink first. It's like you're staking out dark matter. You're

753
00:38:07,400 --> 00:38:09,960
Speaker 1: sitting outside of dark Matter's house and it's never left

754
00:38:10,000 --> 00:38:12,520
Speaker 1: to buy groceries, and you've been there for years and

755
00:38:12,600 --> 00:38:14,440
Speaker 1: you're wondering if it's ever going to come out. You're

756
00:38:14,440 --> 00:38:15,840
Speaker 1: waiting for it to peek out of its blind and

757
00:38:15,880 --> 00:38:18,239
Speaker 1: you're like, I knew somebody was home, all right. So

758
00:38:18,320 --> 00:38:20,640
Speaker 1: we're waiting for a dark matter to bump into a

759
00:38:20,760 --> 00:38:23,840
Speaker 1: zenon atom in one of these tanks around the world.

760
00:38:23,960 --> 00:38:26,839
Speaker 1: But there's sort of a confusing factor here. There's something

761
00:38:26,920 --> 00:38:31,080
Speaker 1: that might prevent us forever maybe finding in any of

762
00:38:31,160 --> 00:38:33,799
Speaker 1: these dark matter bumps exactly, or at least a complication.

763
00:38:34,200 --> 00:38:36,040
Speaker 1: And you brought up one of them earlier, which is

764
00:38:36,320 --> 00:38:38,880
Speaker 1: aren't there other ways for zeno and to get bumped

765
00:38:38,920 --> 00:38:41,960
Speaker 1: over to bump into itself? You know, this is an

766
00:38:42,040 --> 00:38:44,759
Speaker 1: indirect experiment. It's not like we capture the dark matter

767
00:38:44,880 --> 00:38:46,480
Speaker 1: and we can like see it and look at it

768
00:38:46,560 --> 00:38:48,759
Speaker 1: and study it and parade it around the world in

769
00:38:48,840 --> 00:38:51,640
Speaker 1: a dark matter zoo. Right. All we see is that

770
00:38:51,719 --> 00:38:55,080
Speaker 1: the xenon atom got bumped. We don't ever directly see

771
00:38:55,400 --> 00:38:58,520
Speaker 1: what bumped it, right, And so there are other things

772
00:38:58,600 --> 00:39:01,640
Speaker 1: that might be able to bump zenon, and we try

773
00:39:01,719 --> 00:39:03,960
Speaker 1: to shield the detector from that by having a deep

774
00:39:04,080 --> 00:39:08,000
Speaker 1: underground under many layers of rock. So for example, muans

775
00:39:08,040 --> 00:39:10,560
Speaker 1: and other cosmic ray particles from space don't bump it.

776
00:39:10,960 --> 00:39:13,920
Speaker 1: But there is one kind of cosmic ray, a particle

777
00:39:14,040 --> 00:39:16,560
Speaker 1: from space, which can get through all of that rock

778
00:39:16,840 --> 00:39:20,319
Speaker 1: and can bump Zenon and can mimic this dark matter signal. Yeah,

779
00:39:20,360 --> 00:39:23,080
Speaker 1: because dark matter is not the only elusive and invisible

780
00:39:23,200 --> 00:39:26,680
Speaker 1: particle or stuff in universe. There are also neutrinos, which

781
00:39:26,760 --> 00:39:31,080
Speaker 1: we know are invisible and don't interact with the electromagnetic force,

782
00:39:31,239 --> 00:39:33,719
Speaker 1: that's right, And they can penetrate through the entire Earth

783
00:39:34,120 --> 00:39:36,920
Speaker 1: without thinking twice, and so it's no big deal for

784
00:39:37,000 --> 00:39:39,720
Speaker 1: them that we shield these tanks of Xenon with layers

785
00:39:39,760 --> 00:39:41,919
Speaker 1: and layers and layers of rock. They just fly right through.

786
00:39:42,480 --> 00:39:44,839
Speaker 1: And most of the time they also fly right through

787
00:39:44,920 --> 00:39:48,799
Speaker 1: that tank of Zenon without interacting or causing anybody any trouble. Right,

788
00:39:49,280 --> 00:39:53,120
Speaker 1: But neutrinos do feel the weak force, and the nucleus

789
00:39:53,160 --> 00:39:56,640
Speaker 1: of the atom also feels the weak force, and so sometimes,

790
00:39:56,920 --> 00:39:59,799
Speaker 1: very rarely neutrino will bump into Zenon and it will

791
00:39:59,840 --> 00:40:02,600
Speaker 1: look a lot like what would happen if dark matter

792
00:40:02,680 --> 00:40:05,160
Speaker 1: bumped into Zenon. It would bump the zenon through the

793
00:40:05,239 --> 00:40:09,319
Speaker 1: weak force or through maybe this new hypothetical I imaginary

794
00:40:10,080 --> 00:40:12,759
Speaker 1: force that you guys are hypothesizing. It might bump it

795
00:40:12,760 --> 00:40:15,320
Speaker 1: through the imaginary camel force. I don't know, but it

796
00:40:15,320 --> 00:40:18,239
Speaker 1: would definitely bump it through the weak force. Neutrinos feel

797
00:40:18,239 --> 00:40:20,239
Speaker 1: the weak force, and so do the components of a

798
00:40:20,320 --> 00:40:24,000
Speaker 1: zeno atom, and so we definitely expect these neutrinos to

799
00:40:24,239 --> 00:40:26,319
Speaker 1: bump the zenon at some rate. And you can't tell

800
00:40:26,320 --> 00:40:29,319
Speaker 1: the difference between a neutrino bump and a potential dark

801
00:40:29,360 --> 00:40:31,960
Speaker 1: matter bump. We can't for an individual bump. We can't

802
00:40:32,000 --> 00:40:33,719
Speaker 1: look at an individual bump and say, oh, this one

803
00:40:33,800 --> 00:40:35,600
Speaker 1: was a neutrino, this one was a dark matter. But

804
00:40:35,680 --> 00:40:38,040
Speaker 1: we do have some handles for telling, like is it

805
00:40:38,120 --> 00:40:40,000
Speaker 1: more likely to have been dark matter or is it

806
00:40:40,120 --> 00:40:42,320
Speaker 1: more likely to have been a neutrino based on what

807
00:40:42,480 --> 00:40:45,319
Speaker 1: time of year it was? So interesting it's seasonal. It's

808
00:40:45,320 --> 00:40:48,000
Speaker 1: seasonal because you know, the Earth goes around the Sun,

809
00:40:48,080 --> 00:40:51,319
Speaker 1: which changes, for example, how much dark matter we are

810
00:40:51,360 --> 00:40:55,120
Speaker 1: flowing through. Our velocity through the dark matter halo of

811
00:40:55,239 --> 00:40:59,080
Speaker 1: the galaxy changes during the year, right, and so dark

812
00:40:59,120 --> 00:41:02,200
Speaker 1: matters natural flux which comes from the motion of the

813
00:41:02,280 --> 00:41:04,840
Speaker 1: actual the Sun, the whole Solar System to the Milky

814
00:41:04,880 --> 00:41:08,320
Speaker 1: Way peaks in June and then it reaches its lowest

815
00:41:08,360 --> 00:41:11,279
Speaker 1: point in December. But neutrinos have a different pattern because

816
00:41:11,280 --> 00:41:14,560
Speaker 1: neutrinos are produced by the Sun and so they have

817
00:41:14,640 --> 00:41:17,319
Speaker 1: a different pattern. Oh that's interesting. But I guess I'm

818
00:41:17,360 --> 00:41:19,799
Speaker 1: confused because I thought we didn't know that much about

819
00:41:19,880 --> 00:41:21,879
Speaker 1: where dark matter was. How do we know that dark

820
00:41:21,920 --> 00:41:24,760
Speaker 1: matter is even seasonal if we can really see or touchet.

821
00:41:24,760 --> 00:41:27,040
Speaker 1: We're assuming the dark matter is distributed through the galaxy

822
00:41:27,320 --> 00:41:30,839
Speaker 1: fairly evenly, and we know something about its rotation because

823
00:41:30,880 --> 00:41:34,000
Speaker 1: we know something about it's like distribution, and that requires

824
00:41:34,040 --> 00:41:36,200
Speaker 1: it to be rotating at some rate, And so we

825
00:41:36,280 --> 00:41:38,160
Speaker 1: know something about where the dark matter is. We can't

826
00:41:38,200 --> 00:41:40,719
Speaker 1: resolve it down to like here's a piece of dark matter,

827
00:41:40,920 --> 00:41:43,719
Speaker 1: or even there's a clumpier piece of space that has

828
00:41:43,760 --> 00:41:45,600
Speaker 1: more dark matter in it. But we just assumed the

829
00:41:45,680 --> 00:41:48,480
Speaker 1: dark matter is like evenly distributed through the galaxy. And

830
00:41:48,520 --> 00:41:50,960
Speaker 1: you're also assuming that it's spinning. I hadn't heard that

831
00:41:51,000 --> 00:41:53,160
Speaker 1: one before. You're assuming that the dark matter and the

832
00:41:53,280 --> 00:41:55,440
Speaker 1: galaxy is spinning with the galaxy. It has to be,

833
00:41:55,560 --> 00:41:58,160
Speaker 1: because if it wasn't spinning, it would just fall towards

834
00:41:58,200 --> 00:41:59,920
Speaker 1: the center. And the reason that the dark matter is

835
00:42:00,000 --> 00:42:03,240
Speaker 1: in a halo is because it's spinning. If it wasn't spinning,

836
00:42:03,239 --> 00:42:05,120
Speaker 1: it would just fall into the black hole at the

837
00:42:05,160 --> 00:42:07,759
Speaker 1: center of the galaxy. I see. So when you say

838
00:42:07,800 --> 00:42:10,560
Speaker 1: it's seasonal, I guess what you mean is like, you know,

839
00:42:10,640 --> 00:42:13,359
Speaker 1: as this Earth goes around the Sun, sometimes we're kind

840
00:42:13,400 --> 00:42:17,000
Speaker 1: of swimming upstream of the dark matter currents, and sometimes

841
00:42:17,040 --> 00:42:19,800
Speaker 1: we were swimming downstream of the dark matter wind or

842
00:42:19,880 --> 00:42:22,279
Speaker 1: current exactly. And just like on a boat, if you're

843
00:42:22,320 --> 00:42:24,680
Speaker 1: moving with the wind, you don't feel it, and if

844
00:42:24,719 --> 00:42:26,799
Speaker 1: you're moving up wind, you do feel it. Or maybe

845
00:42:26,840 --> 00:42:29,080
Speaker 1: like more like on a bicycle, the wind is at

846
00:42:29,120 --> 00:42:30,880
Speaker 1: your back, you don't really feel the wind. And when

847
00:42:30,920 --> 00:42:33,239
Speaker 1: you're going uphill and the wind is down your face,

848
00:42:33,320 --> 00:42:35,680
Speaker 1: you feel it more strongly, and so you have a

849
00:42:35,760 --> 00:42:38,759
Speaker 1: higher flux of wind. And so if more dark matter

850
00:42:38,840 --> 00:42:41,600
Speaker 1: particles are passing through our detectives, we expect to see

851
00:42:41,640 --> 00:42:43,879
Speaker 1: more of them. Remember we had this podcast episode about

852
00:42:43,880 --> 00:42:46,680
Speaker 1: the Dama experiment. This is another dark matter experiment that

853
00:42:46,800 --> 00:42:49,680
Speaker 1: actually claimed to have discovered dark matter and saw a

854
00:42:49,800 --> 00:42:53,080
Speaker 1: seasonal variation, just like you would expect. Turns out there

855
00:42:53,160 --> 00:42:55,680
Speaker 1: other reasons not to believe that experiment, but that's the

856
00:42:55,719 --> 00:42:57,479
Speaker 1: kind of thing we see. If we ever do see

857
00:42:57,560 --> 00:43:00,400
Speaker 1: a lot of interactions, then we would expect them, if

858
00:43:00,440 --> 00:43:02,600
Speaker 1: they are a dark matter, to come in this pattern

859
00:43:02,680 --> 00:43:04,480
Speaker 1: where there's more in one part of the year and

860
00:43:04,680 --> 00:43:07,560
Speaker 1: fewer in another part of the year. I see, But

861
00:43:07,840 --> 00:43:11,200
Speaker 1: generally speaking, that's what the Nutrina floor is. It's like,

862
00:43:11,840 --> 00:43:13,920
Speaker 1: you know, we're trying to look for dark matter and

863
00:43:14,000 --> 00:43:16,160
Speaker 1: we're trying to find it when it bumps into zeno tanks.

864
00:43:16,239 --> 00:43:19,240
Speaker 1: But the neutrinos could also be they're bumping into zenon,

865
00:43:19,360 --> 00:43:21,799
Speaker 1: and so that's when you say like the neutrina floor,

866
00:43:21,840 --> 00:43:24,319
Speaker 1: it's it's more like you're saying sort of like there's

867
00:43:24,320 --> 00:43:28,399
Speaker 1: a base level of noise that we expect from neutrinos. Yeah,

868
00:43:28,520 --> 00:43:32,680
Speaker 1: and if dark matter interacted with zenon more than this

869
00:43:32,760 --> 00:43:35,640
Speaker 1: neutrino floor right at a higher rate than this neutrina floor,

870
00:43:35,840 --> 00:43:37,800
Speaker 1: it wouldn't be a big deal. The rate would be

871
00:43:37,840 --> 00:43:40,080
Speaker 1: above the floor. We could see dark matter interaction with

872
00:43:40,160 --> 00:43:42,920
Speaker 1: zenon be all great. We collect our Nobel Prize. If

873
00:43:42,960 --> 00:43:45,960
Speaker 1: the dark matter rate is low is small. The probability

874
00:43:46,040 --> 00:43:48,319
Speaker 1: for dark matter to hit Xenon is small enough, then

875
00:43:48,360 --> 00:43:50,840
Speaker 1: it's going to be below the neutrina floor, meaning that

876
00:43:50,920 --> 00:43:54,000
Speaker 1: we expect to get more interactions from the neutrino interacting

877
00:43:54,040 --> 00:43:56,359
Speaker 1: with Xenon than we do from dark matter, and that's

878
00:43:56,360 --> 00:43:58,960
Speaker 1: going to make it very difficult to disentangle this dark

879
00:43:59,040 --> 00:44:01,800
Speaker 1: matter signal from the new trino floor. That looks just

880
00:44:01,920 --> 00:44:04,240
Speaker 1: like it, right, it's like a base level of noise

881
00:44:04,400 --> 00:44:06,440
Speaker 1: or like you know, it's like there's a little bit

882
00:44:06,480 --> 00:44:08,040
Speaker 1: of fog on the floor and you're trying to find

883
00:44:08,080 --> 00:44:10,719
Speaker 1: your keys that you dropped, or like, if you're trying

884
00:44:10,719 --> 00:44:12,839
Speaker 1: to find your keys, it's hard on a foggy floor,

885
00:44:12,880 --> 00:44:14,680
Speaker 1: But if you're trying to find a basketball, maybe that

886
00:44:14,680 --> 00:44:17,920
Speaker 1: would stick more. Yeah, or if your keys are floating

887
00:44:18,040 --> 00:44:20,439
Speaker 1: or something. All right, So then that's the netrino floor.

888
00:44:20,600 --> 00:44:23,160
Speaker 1: It's sort of like fuzzing up our view of dark

889
00:44:23,200 --> 00:44:26,320
Speaker 1: matter through this hypothetical new fourth But you're saying the

890
00:44:26,400 --> 00:44:29,200
Speaker 1: seasonality of these two things, maybe we'll let us kind

891
00:44:29,200 --> 00:44:31,520
Speaker 1: of break through that fog. It's gonna be tricky, right,

892
00:44:31,640 --> 00:44:33,800
Speaker 1: because in order to make these arguments, you need to

893
00:44:33,840 --> 00:44:36,359
Speaker 1: see more than one interaction, Like if you just see

894
00:44:36,480 --> 00:44:39,279
Speaker 1: one and it comes in June, you might say, well,

895
00:44:39,640 --> 00:44:41,520
Speaker 1: dark matter is most likely to come in June. So

896
00:44:41,560 --> 00:44:44,640
Speaker 1: I guess this is more likely dark matter than new trinos,

897
00:44:44,680 --> 00:44:47,200
Speaker 1: which tend to peek in January when the Earth is

898
00:44:47,239 --> 00:44:49,920
Speaker 1: closest to the Sun. But it's not a great argument.

899
00:44:50,000 --> 00:44:51,440
Speaker 1: When you need to do is see like a hundred

900
00:44:51,480 --> 00:44:53,920
Speaker 1: of these things and show that they tend to cluster

901
00:44:54,040 --> 00:44:56,239
Speaker 1: in June, that there are more in June than there

902
00:44:56,280 --> 00:44:59,120
Speaker 1: are in January in December, because otherwise you could just

903
00:44:59,200 --> 00:45:02,920
Speaker 1: be seeing like a rare newtrino interaction in June. So

904
00:45:03,160 --> 00:45:04,640
Speaker 1: it means that we need to see a lot more

905
00:45:04,680 --> 00:45:07,760
Speaker 1: than to really be confident. I see, But the problem

906
00:45:07,840 --> 00:45:10,400
Speaker 1: is that the experiment is really feeble, and so you

907
00:45:10,440 --> 00:45:12,600
Speaker 1: don't get hundreds of him, or you would at least

908
00:45:12,640 --> 00:45:14,640
Speaker 1: have to wait hundreds of years maybe to get a

909
00:45:14,719 --> 00:45:16,879
Speaker 1: hundred of them. Yeah, and so far we haven't seen any.

910
00:45:17,160 --> 00:45:19,560
Speaker 1: So we've been running these tanks and the plan is

911
00:45:19,600 --> 00:45:22,040
Speaker 1: to make them bigger and bigger and bigger. So they

912
00:45:22,120 --> 00:45:24,160
Speaker 1: got the technology to work on a smaller tank, and

913
00:45:24,200 --> 00:45:26,040
Speaker 1: then they scaled it up and up and up, and

914
00:45:26,200 --> 00:45:29,320
Speaker 1: right now they're running these tanks with many tons of

915
00:45:29,440 --> 00:45:32,800
Speaker 1: liquid zen on underground, and you're right, the idea is

916
00:45:32,920 --> 00:45:36,600
Speaker 1: to either run them for years or decades or make

917
00:45:36,680 --> 00:45:39,840
Speaker 1: them bigger. So we're impatient to see dark matter, and

918
00:45:39,920 --> 00:45:42,440
Speaker 1: so we're making them bigger and bigger and bigger. And

919
00:45:42,719 --> 00:45:45,400
Speaker 1: right now we're at the point where we should start

920
00:45:45,520 --> 00:45:48,719
Speaker 1: to see the new trino floor very very soon. We

921
00:45:48,800 --> 00:45:51,040
Speaker 1: were all hoping to discover dark matter before we hit

922
00:45:51,080 --> 00:45:53,759
Speaker 1: the floor, but we didn't see anything. And so now

923
00:45:53,800 --> 00:45:56,520
Speaker 1: we're like right at the new trino floor and we

924
00:45:56,800 --> 00:45:59,279
Speaker 1: might spot it just before we get there, but we

925
00:45:59,360 --> 00:46:01,759
Speaker 1: might also have to dig into the neutrino floor. I

926
00:46:01,800 --> 00:46:03,400
Speaker 1: guess what do you mean? Like hitting the floor? That

927
00:46:03,480 --> 00:46:07,080
Speaker 1: means that you have enough zenon out there that if

928
00:46:07,120 --> 00:46:09,080
Speaker 1: there was dark matter, you would have seen it by now.

929
00:46:09,239 --> 00:46:12,160
Speaker 1: And we know how neutrinos interact, so we know when

930
00:46:12,280 --> 00:46:15,360
Speaker 1: we should expect to see neutrinos interacting with our zenon,

931
00:46:15,920 --> 00:46:18,720
Speaker 1: and neutrinos don't interact very often, and so far tanks

932
00:46:18,760 --> 00:46:21,680
Speaker 1: have been smaller, but now we have these much bigger tanks,

933
00:46:21,840 --> 00:46:24,799
Speaker 1: and so we expect to see neutrinos interacting with them

934
00:46:24,920 --> 00:46:28,560
Speaker 1: pretty soon, meaning like we're out there, we're running these detectors,

935
00:46:28,640 --> 00:46:31,120
Speaker 1: were gathering the data, we're analyzing it. You know, the

936
00:46:31,280 --> 00:46:33,600
Speaker 1: year or two these experiments will come out with the

937
00:46:33,920 --> 00:46:36,600
Speaker 1: results and they will be sensitive to neutrinos like they

938
00:46:36,640 --> 00:46:39,800
Speaker 1: should have seen neutrinos. Interesting. All right, Well, then I

939
00:46:39,840 --> 00:46:42,120
Speaker 1: guess what are the possible outcomes there? It could be

940
00:46:42,239 --> 00:46:44,800
Speaker 1: that how you build these giant tanks and then you

941
00:46:44,920 --> 00:46:47,919
Speaker 1: find nothing except neutrinos? What would that mean about dark matter?

942
00:46:48,040 --> 00:46:49,759
Speaker 1: What would that mean about the darkroa matter? That would

943
00:46:49,760 --> 00:46:53,359
Speaker 1: be disappointing. It would mean either that dark matter does

944
00:46:53,480 --> 00:46:56,560
Speaker 1: exist and is a whimp and does interact with denon,

945
00:46:57,120 --> 00:47:00,239
Speaker 1: just at a lower level than we're capable of seeing, right,

946
00:47:00,400 --> 00:47:04,320
Speaker 1: just like even more feeble than the interactions with neutrinos.

947
00:47:04,480 --> 00:47:07,800
Speaker 1: So that's one possibility. Another possibility is dark matter is

948
00:47:07,880 --> 00:47:10,120
Speaker 1: real and it's a particle, but it doesn't have this

949
00:47:10,320 --> 00:47:13,160
Speaker 1: invisible camel force that we made up to give us

950
00:47:13,200 --> 00:47:15,080
Speaker 1: a window to interact with it. That the only thing

951
00:47:15,120 --> 00:47:17,919
Speaker 1: it feels is gravity, And that would mean it would

952
00:47:17,920 --> 00:47:21,240
Speaker 1: be very, very difficult to ever discover the particle nature

953
00:47:21,400 --> 00:47:24,120
Speaker 1: of dark matter, because particles don't feel a lot of gravity.

954
00:47:24,239 --> 00:47:26,200
Speaker 1: But I mean we definitely know it's there it which

955
00:47:26,239 --> 00:47:28,759
Speaker 1: is maybe confirmed that we could maybe never see it

956
00:47:29,120 --> 00:47:32,800
Speaker 1: or really experiment with it, at least from using these ideas,

957
00:47:33,040 --> 00:47:35,879
Speaker 1: using these ideas, and so we'll have to be more clever,

958
00:47:36,239 --> 00:47:38,640
Speaker 1: and people are working on other ideas. They're working on

959
00:47:38,760 --> 00:47:41,680
Speaker 1: other ways to detect dark matter that would be more sensitive.

960
00:47:41,840 --> 00:47:44,680
Speaker 1: One of my favorites is an idea for directional dark

961
00:47:44,760 --> 00:47:47,319
Speaker 1: matter that can see dark matter if only if it's

962
00:47:47,400 --> 00:47:49,840
Speaker 1: moving in one direction and not in the other. And

963
00:47:49,920 --> 00:47:53,040
Speaker 1: that helps like remove the neutrino background, because neutrinos tend

964
00:47:53,080 --> 00:47:55,120
Speaker 1: to be moving from the Sun. So if you can

965
00:47:55,160 --> 00:47:58,840
Speaker 1: tell the direction that something bumped your zenon or zenion equivalent,

966
00:47:59,120 --> 00:48:01,719
Speaker 1: you can help understand if it's neutrino or something else.

967
00:48:01,760 --> 00:48:03,759
Speaker 1: And we have an idea for the direction we think

968
00:48:03,800 --> 00:48:06,760
Speaker 1: that dark matter wind is going, so that's one way forward.

969
00:48:06,920 --> 00:48:09,120
Speaker 1: And then there are other crazier ideas like maybe dark

970
00:48:09,200 --> 00:48:12,000
Speaker 1: matters not a wind, Maybe it's an axon and go

971
00:48:12,200 --> 00:48:15,440
Speaker 1: check out our podcast episode about how to discover axons.

972
00:48:15,560 --> 00:48:18,279
Speaker 1: Or maybe it's made of primordial black holes, or maybe

973
00:48:18,320 --> 00:48:21,239
Speaker 1: it's made of weird crazy elephants. We just don't know.

974
00:48:21,440 --> 00:48:23,200
Speaker 1: So we've got to be more creative. But this is

975
00:48:23,239 --> 00:48:25,759
Speaker 1: the first thing to try, is this heavy particle that

976
00:48:25,840 --> 00:48:29,239
Speaker 1: has a new, weak kind of interaction, And so it

977
00:48:29,360 --> 00:48:30,920
Speaker 1: makes sense to try. But if we don't see it,

978
00:48:31,000 --> 00:48:32,920
Speaker 1: it just means we need to sort of broaden our

979
00:48:33,000 --> 00:48:35,560
Speaker 1: ideas a little bit. It could be an invisible rhino,

980
00:48:35,680 --> 00:48:38,719
Speaker 1: not an elephant this whole time. You've been holding onto

981
00:48:38,760 --> 00:48:41,040
Speaker 1: this idea this whole time. You just now drop it

982
00:48:41,120 --> 00:48:44,320
Speaker 1: on us. But it seems I guess kind of crazy

983
00:48:44,320 --> 00:48:46,720
Speaker 1: that you would build all these I mean, I'm guessing

984
00:48:46,800 --> 00:48:49,560
Speaker 1: billions of dollars in experiments based on an idea that

985
00:48:49,760 --> 00:48:51,640
Speaker 1: is so hypothetical, you know what I mean. But I

986
00:48:51,680 --> 00:48:53,239
Speaker 1: guess you have to. You have to do it because

987
00:48:53,280 --> 00:48:55,160
Speaker 1: you have to check off that box. Yeah. Well, there

988
00:48:55,160 --> 00:48:57,839
Speaker 1: are people in the theoretical physics community who say it's

989
00:48:57,880 --> 00:49:00,279
Speaker 1: ridiculous and it's a huge waste of money. These rants

990
00:49:00,280 --> 00:49:02,759
Speaker 1: don't cost billions of dollars. They do cost tens of

991
00:49:02,880 --> 00:49:05,800
Speaker 1: millions of dollars, and I think the idea is strong

992
00:49:05,960 --> 00:49:08,640
Speaker 1: enough that it's worth checking. Other people do think that

993
00:49:08,719 --> 00:49:11,880
Speaker 1: it's a very narrow idea, has a lot of assumptions

994
00:49:11,920 --> 00:49:14,120
Speaker 1: that are not justified, and it's a lot of money

995
00:49:14,160 --> 00:49:16,120
Speaker 1: to spend on those kinds of experiments. So there's some

996
00:49:16,239 --> 00:49:18,799
Speaker 1: very vocal people out there who think that the whole

997
00:49:18,800 --> 00:49:20,920
Speaker 1: thing is a waste of time. I am very curious.

998
00:49:21,239 --> 00:49:23,040
Speaker 1: My judgment is, do I want to go to this

999
00:49:23,120 --> 00:49:26,680
Speaker 1: seminar and see the results. Every time these experiments xenon

1000
00:49:27,080 --> 00:49:30,160
Speaker 1: Lux and Panda x put out new results, I'm desperately

1001
00:49:30,200 --> 00:49:32,759
Speaker 1: curious to see what they say. So I'm willing to

1002
00:49:32,800 --> 00:49:36,760
Speaker 1: spend my taxpayer dollars on funding these experiments on the camels.

1003
00:49:38,040 --> 00:49:39,719
Speaker 1: I want to know if the camels are out there,

1004
00:49:40,160 --> 00:49:42,399
Speaker 1: yes or no, will be a whole new particle zoo

1005
00:49:43,320 --> 00:49:45,600
Speaker 1: for the universe to lead us to and maybe we can,

1006
00:49:45,800 --> 00:49:48,040
Speaker 1: you know, recover some of the expenses by charging admission.

1007
00:49:48,160 --> 00:49:50,799
Speaker 1: There you go. You can pick up those dark, battered

1008
00:49:50,840 --> 00:49:54,280
Speaker 1: dollars from the floor. So yeah, I'm learning to monetize. Monetized, monetize.

1009
00:49:54,320 --> 00:49:58,319
Speaker 1: Man become a patreon of our invisible camels. Please, there

1010
00:49:58,400 --> 00:50:02,080
Speaker 1: you go. As physicists ever using Catron to fund the research,

1011
00:50:02,200 --> 00:50:04,080
Speaker 1: I don't know, and I don't think anybody's ever kick

1012
00:50:04,160 --> 00:50:07,480
Speaker 1: started a particle physics experiment either. Zero out of forty

1013
00:50:07,480 --> 00:50:12,200
Speaker 1: million dollars pledged, Well it's not too late, all right. Well,

1014
00:50:12,400 --> 00:50:15,359
Speaker 1: that gives us an answer. Here are neutrinos hiding dark

1015
00:50:15,400 --> 00:50:18,440
Speaker 1: matter potentially, It kind of sounds like maybe the answer

1016
00:50:18,520 --> 00:50:20,600
Speaker 1: is yes. I mean, we're getting pretty close to the floor,

1017
00:50:20,920 --> 00:50:23,680
Speaker 1: and it sounds like if dark matter is there and

1018
00:50:23,800 --> 00:50:26,399
Speaker 1: we'll never see it because of these neutrinos. Neutrinos are

1019
00:50:26,600 --> 00:50:29,080
Speaker 1: definitely clouding the issue and can make it harder to

1020
00:50:29,360 --> 00:50:31,719
Speaker 1: find dark matter. But I'm still holding out hope. We're

1021
00:50:31,760 --> 00:50:33,840
Speaker 1: not at the floor yet, and it could be that

1022
00:50:33,960 --> 00:50:36,799
Speaker 1: one of these detectors reveals results that are above the floor,

1023
00:50:37,280 --> 00:50:40,239
Speaker 1: that are at a rate the neutrinos couldn't reproduce and

1024
00:50:40,520 --> 00:50:42,840
Speaker 1: is a much more convincing sign of dark matter. But

1025
00:50:42,920 --> 00:50:44,880
Speaker 1: we'll find out in a year or so. Al Right,

1026
00:50:45,120 --> 00:50:48,480
Speaker 1: stay tuned in the meantime, Thanks for joining us. We

1027
00:50:48,560 --> 00:50:58,920
Speaker 1: hope you enjoyed that. See you next time. Thanks for listening,

1028
00:50:58,960 --> 00:51:01,680
Speaker 1: and remember that Dan lan Jorge Explain the Universe is

1029
00:51:01,719 --> 00:51:05,239
Speaker 1: a production of I Heart Radio. For more podcast from

1030
00:51:05,239 --> 00:51:08,920
Speaker 1: my Heart Radio, visit the I Heart Radio Apple Apple Podcasts,

1031
00:51:09,120 --> 00:51:17,239
Speaker 1: or wherever you listen to your favorite shows. Yeah,