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Speaker 4: Hey Daniel, can you pass through walls?

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Speaker 5: No?

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Speaker 1: Keep trying and just keep getting more bumps on my head?

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Speaker 4: How about can you be in two plays at the

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Speaker 4: same time?

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Speaker 1: Sometimes it feels like I'm supposed to be, but I've

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Speaker 1: never actually managed it.

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Speaker 4: So I guess you're not a quantum object.

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Speaker 1: No, actually, I'm quite classical.

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Speaker 4: But you're a particle physicist. Aren't you made of particles?

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Speaker 4: And aren't those particles quantum mechanical? I study particles and

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Speaker 4: I'm made of particles. But I follow the rules of

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Speaker 4: classical physics. Classic. Do I mean you're classic, Daniel?

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Speaker 1: I'm not new Coke Daniel.

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Speaker 4: I am Horehem, a cartoonist and the creator of PhD comics.

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Speaker 1: I'm Daniel. I'm a particle physics but I'm quite classical

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Speaker 1: in my tastes.

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Speaker 4: Are you a fan of classical music.

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Speaker 1: Then it's better than quantum music. Let me tell you.

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Speaker 4: Oh, that's a new genre to make a new category

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Speaker 4: at the Grammys.

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Speaker 1: Oh, I wish it was a new genre. But I'm

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Speaker 1: sure if we type it into Google we will find

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Speaker 1: something for quantum music.

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Speaker 4: I feel like that's all music these days. It's both

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Speaker 4: good and bad. It's kind of incoherence. It's both original

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Speaker 4: and stale. Welcome to our podcast, Daniel and Jorge Explain

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Speaker 4: the Universe, a production of iHeartRadio.

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Speaker 1: In which we explore everything in the universe and try

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Speaker 1: to make sense of it. We try to understand how

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Speaker 1: things move in our world and how tiny particles move.

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Speaker 1: We try to understand the rules of the universe, whether

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Speaker 1: they govern supernovas and black holes or tiny little electrons,

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Speaker 1: and we try to make sure that you understand them.

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Speaker 4: Yeah, because we try to make this podcast a superposition

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Speaker 4: of both fun and real.

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Speaker 1: Science, physics and banana jokes.

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Speaker 4: People often think those two can't be in the same

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Speaker 4: place at the same time.

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Speaker 1: What makes say that you haven't met any fun physicists.

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Speaker 4: You mean the physicists is fun, or they know how

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Speaker 4: to have fun, or.

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Speaker 1: Just doing physics is fun. Why doesn't everybody see that?

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Speaker 4: Come on, I think that's the problem, Daniel, that's the problem.

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Speaker 4: But yeah, it's a weird and strange universe out there,

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Speaker 4: and so we like to talk about all of the

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Speaker 4: things that make it weird and strange. It's pretty unintuitive

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Speaker 4: to universe it is, and physics has done a great

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Speaker 4: job of building this edifice to help us understand the

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Speaker 4: way the universe really is, not the way we think

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Speaker 4: the universe should be or might be, or the way

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Speaker 4: that makes sense to us based on our limited experience,

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Speaker 4: but actually revealing to us the true nature of reality.

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Speaker 4: But sometimes what we learn is pretty hard to swallow. Yeah,

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Speaker 4: and specifically quantum mechanics. I feel like that really trips

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Speaker 4: people up. It trips me up, for sure, And it's

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Speaker 4: kind of hard to wrap your head around all of

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Speaker 4: the weird, kind of unintuitive phenomenon that happens at the

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Speaker 4: quantum level.

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Speaker 1: Yeah, it is pretty weird because quantum particles seem to

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Speaker 1: be following different rules. They see to be able to

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Speaker 1: break rules that are hard and fast for things like

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Speaker 1: baseballs and basketballs and scoops of ice cream. And that's

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Speaker 1: a hard thing to understand because it's weird and it's new.

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Speaker 1: It's also hard to understand, like why are there different rules?

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Speaker 1: And you know, what's the difference between an electron and

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Speaker 1: a baseball? You know, where's the sort of threshold between

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Speaker 1: those two where the quantum rules take over or the

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Speaker 1: classical rules take over.

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Speaker 4: Yeah, it is kind of weird that, you know, things

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Speaker 4: are so weird at that level, at the microscopic level,

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Speaker 4: but then once you scale up, things feel more gosh normal,

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Speaker 4: more solid, less uncertain, or.

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Speaker 1: At least more familiar. Right. Science is all about delving

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Speaker 1: into the unknown, and typically we try to explain the

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Speaker 1: unknown in terms of the known. But that fails if

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Speaker 1: the unknown is something really new, something different, something that

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Speaker 1: fundamentally can't be described by what we already know. We've

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Speaker 1: often talked about how physics is like exploring the universe,

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Speaker 1: But it's just been studying the tail of the elephant,

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Speaker 1: and when you look at the rest of the elephant,

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Speaker 1: it's not true that what you learn from the tail

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Speaker 1: can help you understand the rest of the elephant. Sometimes

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Speaker 1: you really do discover something weird and different.

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Speaker 4: Yeah, but is that elephant quantum mechanical, Daniel, Is it

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Speaker 4: really there or not there?

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Speaker 1: It's a theoretical thought experiment elephant. So it's just totally

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Speaker 1: not there. That's classically non existent.

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Speaker 4: All right. Well, that connection between the quantum world and

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Speaker 4: our regular, everyday world is what we'll be exploring today

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Speaker 4: on this episode. Today on the podcast, we'll be asking

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Speaker 4: the question what is quantum decoherence? That's hopefully a coherent question.

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Speaker 1: Yes, And quantum decoherence is the key concept to understanding

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Speaker 1: the answer to this question. Why do big objects not

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Speaker 1: seem to follow quantum rules? What is the difference between

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Speaker 1: quantum objects and big objects? Where is the threshold? Why

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Speaker 1: do we seem to have two sets of rules or

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Speaker 1: is it just that one set of rules sort of

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Speaker 1: morphs into the other.

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Speaker 4: Right, it's an important concept, and it seems to be

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Speaker 4: sort of related to this idea of quantum measurements. I

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Speaker 4: think maybe that's something that if you've heard of quantum

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Speaker 4: mechanics or have talked about it or seen any videos

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Speaker 4: about it or read about it, it's something that seems

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Speaker 4: to be important that you know things are quantum, but

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Speaker 4: then when you poke at them or measure them or

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Speaker 4: try to look at them, things collapse for some reason.

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Speaker 1: Yeah, this is a big and still totally unsolved problem

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Speaker 1: in quantum mechanics. Quantum mechanical things can have like multiple possibilities,

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Speaker 1: but we don't observe multiple possibilities. When you poke an electron,

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Speaker 1: as you say, it picks one of them, and we

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Speaker 1: don't really understand how that happens, how one of them

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Speaker 1: gets picked, and actually when that picking happens, you know,

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Speaker 1: does it happen when your finger touches the electron, does

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Speaker 1: it happen when you look at the results, does it

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Speaker 1: happen somewhere in between. That's a really interesting and hard problem,

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Speaker 1: and it's related to quantum decoherence. But they're not quite

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Speaker 1: the same thing. So today we'll try to explain what

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Speaker 1: quantum decoherence is is how it helps us understand the

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Speaker 1: difference between quantum and classical objects. But it's important to

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Speaker 1: understand that it doesn't actually solve this problem of the

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Speaker 1: quantum measurement.

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Speaker 4: Mmmmm, is that what happens when you pull on the

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Speaker 4: tail of the elephant? Things get real real quick.

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Speaker 1: You get quantum stumped. It makes quantum music out of you.

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Speaker 4: All right, well, this is an interesting question what is

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Speaker 4: quantum decoherence? And so as usual we were wondering how

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Speaker 4: many people out there in the real world know what

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Speaker 4: it means. So, as usual, Daniel went o, they're into

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Speaker 4: the wilds of the internet to ask what is quantum decoherence?

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Speaker 1: So thank you very much to everybody who volunteered your

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Speaker 1: speculation for the podcast. If you would like to volunteer

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Speaker 1: for a future podcast, please write to us two questions

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Speaker 1: at Daniel and Jorge dot com.

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Speaker 4: Think about it for a second and someone asks you

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Speaker 4: what quantum decoherence is, what would you say it is,

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Speaker 4: or at least guess it is. Here's what people had

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Speaker 4: to say.

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Speaker 6: I'm not sure if I recognize this right, But I

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Speaker 6: think teakeoherence is about how the quantum and the normal

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Speaker 6: fu colide, so how we can map quantum effects into

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Speaker 6: our reality.

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Speaker 7: Since coherent means to make sense, I'm thinking quantum decoherence

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Speaker 7: is when quantum particles can't logically follow the rules of

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Speaker 7: the universe, the constant of the universe, or something of

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Speaker 7: the nature.

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Speaker 5: I'm not sure what quantum decoherence is, but I think

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Speaker 5: it might be wave function collapse, which is how the

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Speaker 5: wave function of a quantity and a quantum system collapses

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Speaker 5: when you measure that quantity.

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Speaker 8: I don't know what quantum decoherence is, but my guess

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Speaker 8: would be that it is the occurrence of something totally

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Speaker 8: inconsistent that disrupts the quantum realm.

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Speaker 6: It has got me thinking of something to do with

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Speaker 6: quantum entitlement.

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Speaker 4: All right, pretty coherent answers for the most part, or

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Speaker 4: at least coherent in there not knowing what it is.

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Speaker 1: Yeah, nobody actually quite nailed it, but you know, are

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Speaker 1: in the vicinity. They seem to understand that there's a

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Speaker 1: concept of coherence, at least in quantum mechanics.

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Speaker 4: Somebody said that it is sort of where the real

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Speaker 4: world and the normal world collide. I guess they do,

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Speaker 4: maybe think it has something to do with the connection

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Speaker 4: between the quantum world and our everyday experience.

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Speaker 1: Yeah, and that one's the closest I think to the

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Speaker 1: right answer, to the right way of thinking about it.

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Speaker 1: Quantum decoherence, in brief, is the idea that explains how

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Speaker 1: quantum objects look like classical objects when they get really

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Speaker 1: big and messy.

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Speaker 4: All right, well, let's jump into it, Daniel, and I

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Speaker 4: guess let's start with just a quick recap of quantum

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Speaker 4: of a small subject called quantum physics. You know, what

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Speaker 4: is it that we actually call quantum and how can

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Speaker 4: we kind of describe those effects?

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Speaker 1: So the thing to understand is that when you look

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Speaker 1: at really small objects, things like electrons or photons or individuals,

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Speaker 1: tiny particles, they seem to be following rules that don't

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Speaker 1: apply to bigger objects like baseballs and basketballs. Right, And

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Speaker 1: the key concept to understand when thinking about these tiny

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Speaker 1: particles is that they're not just particles. They're not like

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Speaker 1: tiny versions of a baseball, They're not just like miniaturized

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Speaker 1: little blobs of stuff flying through space. Right. When people

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Speaker 1: were first thinking about the atom, for example, they were

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Speaker 1: thinking about the electron like orbiting the nucleus like a

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Speaker 1: tiny planet around a star. But we pretty quickly figured

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Speaker 1: out that was impossible because if an electron orbits a nucleus,

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Speaker 1: then it's going to give off radiation because it's accelerating,

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Speaker 1: it's giving off radiation. And they did the calculation and discovered, well,

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Speaker 1: that would collapse in like one hundred billionth of a

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Speaker 1: second because they would lose all of its energy. And

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Speaker 1: so instead they had to have a new idea for

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Speaker 1: what controls an electron, what defines what an electron does

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Speaker 1: and how it interacts, and so instead they try to

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Speaker 1: use like wave like properties to describe it. So you've

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Speaker 1: probably heard this phrase called the wave function. The wave

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Speaker 1: function is just a mathematical tool that helps us understand

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Speaker 1: what an electron is likely to do. And the key

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Speaker 1: concept is that the wave function tells you where a

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Speaker 1: particle is likely to be and where it's not likely

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Speaker 1: to be. Sean Carroll says that the wave function is

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Speaker 1: the dopiest name in the world for one of the

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Speaker 1: most profound things in the universe, which really made me laugh.

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Speaker 4: Well, dope and profound go hand in hand.

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Speaker 1: I think like physics and fun. Right.

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Speaker 4: Yeah, well, yeah, I think that is maybe the hardest

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Speaker 4: thing to grasp about quantum mechanics and physics. You know,

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Speaker 4: I think everyone sort of grows up at least in's

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Speaker 4: early in school and definitely in popular culture. You know,

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Speaker 4: the depiction like pictures of an atom always look like

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Speaker 4: little planetary systems, you know, like a bunch of little

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Speaker 4: balls in the middle cluster together, and then other little

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Speaker 4: balls kind of swinging around in large orbits and rings

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Speaker 4: around that. And that's the picture that we have about

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Speaker 4: the atom. But you're saying, at some point we figured

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Speaker 4: out that's not possible, like that doesn't make sense.

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Speaker 1: Yeah, exactly. It's not like the electron has a trajectory,

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Speaker 1: has a path, and we just don't I don't know it.

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Speaker 1: It doesn't actually have a path. It doesn't have like

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Speaker 1: a position at every moment in time. Instead, what it

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Speaker 1: has is this quantum wave. Now, the quantum wave behaves

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Speaker 1: all sorts of normal wave like rules, but what it

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Speaker 1: does is tell us where the electron is likely to be,

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Speaker 1: and so the electron is likely to be here and

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Speaker 1: it's likely to be there. Now, sometimes people say that

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Speaker 1: means that electron is in two places at once, but

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Speaker 1: that's not actually correct. It means it has the probability

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Speaker 1: to be here or there, and those in both probabilities

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Speaker 1: can exist at the same time. It doesn't mean it's

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Speaker 1: actually in both places at once. If you ask the

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Speaker 1: electron where are you, then it collapses as we talked

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Speaker 1: about earlier, It picks one place or the other. But

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Speaker 1: the wave function describes what's likely to happen.

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Speaker 4: Well, I guess you mentioned before that it has a

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Speaker 4: dopey name. Why do you think it's a bad name,

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Speaker 4: And what would you have called the if not the

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Speaker 4: wave function?

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Speaker 1: And why is it called the wave function? Well, wave,

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Speaker 1: I suppose because it follows a wave equation shorting equation

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Speaker 1: is very much like equations for other waves that we'd

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Speaker 1: seen before, that electromagnetism, And it's just waves in water. Right,

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Speaker 1: there's a certain differential equation which just looks like a

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Speaker 1: wave equation.

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Speaker 4: Like a wiggle, like a like a like a rippling wiggle.

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Speaker 1: Yeah, it's like a rippling wiggle, but you know it's

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Speaker 1: not a rippling wiggle in anything physical, right, Like sound

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Speaker 1: waves are a wiggle in air like air pressure. Right, Yeah,

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Speaker 1: light waves are a wiggle in the electromagnetic field, which

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Speaker 1: even if it's hard to imagine, is a physical thing.

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Speaker 1: The wave function is complex, it's imaginary values. It's like

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Speaker 1: you know, one plus three I and so it's not

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Speaker 1: a wiggle in a physical thing itself. So it's hard

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Speaker 1: to understand because it's like this sort of abstract literally

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Speaker 1: complex things in the sense that it exists in the

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Speaker 1: imaginary plane, but it controls something real. So I wouldn't

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Speaker 1: have called it the wave function, you know, I like

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Speaker 1: the word wave, but function to me is sort of confusing.

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Speaker 4: Would you have called it the imaginary function? Well, I

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Speaker 4: feel like alluding to the imaginary complex plain that is

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Speaker 4: not helping me here, I guess. And you just brought

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Speaker 4: up maybe a source of confusion, which is that you know,

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Speaker 4: you just said that light or a photon is like

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Speaker 4: a ripple in the electromagnetic field, right, So it's a

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Speaker 4: ripple like kind of like a sound waving that It's like,

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Speaker 4: it's more intense here on this intense here are you

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Speaker 4: saying that there's also like a photon would also have

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Speaker 4: another kind of wavness, which is imaginary.

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Speaker 1: Absolutely, the photon also has a wave function, right, and

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Speaker 1: that wave function determines where the photon is likely to go,

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Speaker 1: like which parts of the electromagnetic field are likely to ripple?

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Speaker 8: You know?

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Speaker 1: For example, you know, the classical situation is, imagine you

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Speaker 1: shoot a photon at two slits in a screen. You

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Speaker 1: know which one is it going to go through. It

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Speaker 1: has a probability to go through one and a probability

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Speaker 1: to go through the other. The wave function controls what

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Speaker 1: those probabilities are, right, And if it collapses and picks

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Speaker 1: the one on the left, then you get an electromagnetic

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Speaker 1: wave through the one on the left. So the probability

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Speaker 1: wave and the electromagnetic wave are sort of two different

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Speaker 1: things to keep in your.

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Speaker 4: Mind, and they both spread differently. Like why did they

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Speaker 4: call them waves in the first place, Like, do these

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Speaker 4: like probabilities ripple out into space also, or do they

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Speaker 4: just look like a ripple that moves around.

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Speaker 1: They do ripple, and they do follow wave mechanics, and

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Speaker 1: that's why they call it a wave. And that's why

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Speaker 1: they can do really amazing and fascinating things. Because the

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Speaker 1: location of the electron is controlled by something which is

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Speaker 1: fundamentally a wave, it can do things that waves can do,

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Speaker 1: like it can interfere, right, you can have probabilities interfering

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Speaker 1: with themselves. Probability being here and there can interfere with

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Speaker 1: each other and create probabilities in other places, just like

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Speaker 1: actual waves can. Right, you put two hands in a

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Speaker 1: lake or in a bathtub and you make two sources

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Speaker 1: of waves. Those waves can interfere with each other, meaning

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Speaker 1: just that they can add up or cancel out.

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Speaker 4: So, for example, if I have like an electron here,

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Speaker 4: it has like a ripple of probability emanating from it,

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Speaker 4: or is it kind of static if the electron is static.

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Speaker 1: Well, electrons can't actually be totally static, right, because they're

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Speaker 1: quantum objects. So you can't just like say an electron

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Speaker 1: is here and it's not moving. That would violate the

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Speaker 1: Heisenberg and certainly principle would effectively be an electron at

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Speaker 1: absolute zero. But if you have an electron you shoot

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Speaker 1: it out of like an electron gun or something, and

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Speaker 1: you want to describe what's it likely to do, where

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Speaker 1: is it likely to go, then you have a probability

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Speaker 1: for all those various outcomes, right, And the key thing

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Speaker 1: to understand is like there's not a real history that's

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Speaker 1: happening between when you shoot the electron and when it

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Speaker 1: hits the wall and you're just learning about it. It's uncertain, right,

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Speaker 1: It has both possibilities existing simultaneously until you measure it.

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Speaker 1: And that's the key thing that's hard to understand about

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Speaker 1: quantum mechanics. It's like how this measurement changes it from

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Speaker 1: like having two possibilities to actually existing in one place,

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Speaker 1: but doesn't exist between the places you measure it only

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Speaker 1: exists where you measure it. In between. They're just probability,

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Speaker 1: all right.

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Speaker 4: So you're saying that maybe, like an electron is like

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Speaker 4: a little tiny baseball, but we just don't know where

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Speaker 4: it is, and where it is is determined by this

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Speaker 4: ripple in probability.

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Speaker 1: Yeah, I'm saying an electron is like a little tiny baseball,

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Speaker 1: but it doesn't have a place where it is. It's

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Speaker 1: not like it is someplace and we don't know its

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Speaker 1: place is not determined. The probability of it being in

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Speaker 1: one place or another is determined by the wave function.

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Speaker 1: It's like forty two percent probability to be there, seventy

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Speaker 1: one percent probability to be here, or whatever, so they

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Speaker 1: add up to one. But the probabilities are determined by

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Speaker 1: the wave function, but doesn't actually have a location. It

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Speaker 1: just has those probabilities again until you measure it, which

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Speaker 1: is the weird bit, and.

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Speaker 4: Then when you measure it, then then it feels like

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Speaker 4: you were hit by a baseball.

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Speaker 1: It certainly does, and that's why we see these weird

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Speaker 1: quantum effects because these particles like electrons, can do things

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Speaker 1: that waves can do, like if you have two sources

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Speaker 1: of them, you get these interference effects, or they can

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Speaker 1: like tunnel through walls. These are things that waves can do.

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Speaker 1: Probability waves can do, and you get effects because you

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Speaker 1: have these wave like properties of the electrons wave function.

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Speaker 4: These probabilities can go through walls like the wall doesn't

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Speaker 4: affect it, like it just goes through them.

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Speaker 1: The wall does affect it. We have a whole fun

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Speaker 1: podcast on quantum tunneling, and it's possible to go through walls,

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Speaker 1: right because you can have a probability to be on

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Speaker 1: one side of the wall and then a probability to

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Speaker 1: be on the other side of the wall, and you

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Speaker 1: can do that without going through the wall. The probability

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Speaker 1: can leak through the wall, giving you a chance to

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Speaker 1: be on the other side of the wall, even if

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Speaker 1: you're never actually in the wall.

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Speaker 4: All right, And so that means that the baseball would

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Speaker 4: just appear on the other side, or that it is

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Speaker 4: found a way through the wall.

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Speaker 1: It just appears on the other side. Remember that quantum

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Speaker 1: particles don't have to have paths between where you've seen them.

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Speaker 1: You see it at A and you see it at

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Speaker 1: B doesn't mean it went from A to B. Doesn't

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Speaker 1: have like a secret history how it got from A

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Speaker 1: to B. It was at A and then it was

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Speaker 1: at B. Remember they follow fundamentally different rules. It was

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Speaker 1: at A, then it had lots of probabilities for maybe

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Speaker 1: how it got to be, not like one of them

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Speaker 1: is true and we just don't know it. There are

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Speaker 1: those probabilities. It's undetermined. It's not unknown, it's undetermined. And

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Speaker 1: then later it's at B. So it doesn't have to

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Speaker 1: go from A to B in order to be at

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Speaker 1: A and then be at B. And this is highlighted

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Speaker 1: by the quantum tunneling experiment because you can't go from

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Speaker 1: A to B. There's a barrier there.

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Speaker 4: All right, Well, let's get into quantum coherence and how

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Speaker 4: that relates or how that ties this uncertainty and this

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Speaker 4: wave function to real things like baseball. But first let's

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Speaker 4: take a quick break.

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Speaker 4: All right, we're talking about quantum decoherence, and hopefully, Daniel

463
00:23:18,600 --> 00:23:22,960
Speaker 4: will we're not. We're not breaking down into decoherence talking

464
00:23:23,000 --> 00:23:26,439
Speaker 4: about it. But okay, So particles have a wave function

465
00:23:26,760 --> 00:23:31,680
Speaker 4: which tells you it's like a ripple in the imaginary space.

466
00:23:31,800 --> 00:23:35,719
Speaker 4: That tells you the probability where that little tiny baseball

467
00:23:35,840 --> 00:23:38,400
Speaker 4: where you will find it if you were to poke it. Yes,

468
00:23:38,480 --> 00:23:41,239
Speaker 4: exactly right. So then what does coherence and decoherence mean?

469
00:23:41,400 --> 00:23:45,560
Speaker 1: So quantum coherence is when you have two possible outcomes

470
00:23:45,560 --> 00:23:48,080
Speaker 1: for what's going to happen to your particle, and those

471
00:23:48,119 --> 00:23:51,399
Speaker 1: possibilities sort of line up, like the wave functions for

472
00:23:51,520 --> 00:23:55,520
Speaker 1: those two possibilities line up. Now, any solution to the

473
00:23:55,560 --> 00:23:58,639
Speaker 1: wave equation, any quantum state, you can take it and

474
00:23:58,720 --> 00:24:00,800
Speaker 1: add it to another quantum same to get a third

475
00:24:00,880 --> 00:24:03,239
Speaker 1: quantum state, which is a mixture of the two. So

476
00:24:03,280 --> 00:24:06,240
Speaker 1: you can mix two possible wave functions, Like if you

477
00:24:06,240 --> 00:24:07,959
Speaker 1: have one that says the electron is gonna arrive at

478
00:24:07,960 --> 00:24:09,960
Speaker 1: point A, and you have another one that says the

479
00:24:10,000 --> 00:24:11,960
Speaker 1: electron is gonna rivee at point B, you can have

480
00:24:12,000 --> 00:24:14,879
Speaker 1: a mixture that like mixes A and B with fifty

481
00:24:14,880 --> 00:24:18,159
Speaker 1: to fifty odds. So that's a coherent combination. It just

482
00:24:18,200 --> 00:24:21,199
Speaker 1: says you have two possibilities and you've added them together,

483
00:24:21,720 --> 00:24:24,560
Speaker 1: and they're coherent because their wave functions are sort of

484
00:24:24,600 --> 00:24:26,760
Speaker 1: syncd up. They start in the same place and they

485
00:24:26,760 --> 00:24:28,960
Speaker 1: sort of wiggle in time together.

486
00:24:28,800 --> 00:24:30,840
Speaker 4: Right, but they don't end up in the same place.

487
00:24:31,080 --> 00:24:33,679
Speaker 4: Isn't there some kind of cancelation or some kind of

488
00:24:34,560 --> 00:24:36,600
Speaker 4: or are you saying coherence is when they don't cancel.

489
00:24:36,680 --> 00:24:38,879
Speaker 1: They can cancel, right. The fact that they can cancel

490
00:24:39,000 --> 00:24:42,480
Speaker 1: is because they are coherent. You only get interference effects

491
00:24:42,520 --> 00:24:45,520
Speaker 1: from coherent sources of waves. Like go back to the

492
00:24:45,600 --> 00:24:48,760
Speaker 1: example of like bathtubs. Right, say you put your hand

493
00:24:48,800 --> 00:24:50,480
Speaker 1: in the water and you slap it, so you make

494
00:24:50,840 --> 00:24:52,840
Speaker 1: a rhythm and you get waves in the water. You

495
00:24:52,880 --> 00:24:55,320
Speaker 1: do the same thing with your other hand if you're

496
00:24:55,359 --> 00:24:57,480
Speaker 1: doing it in the same way, right, If you're like

497
00:24:57,520 --> 00:25:00,520
Speaker 1: slapping the water in time, then you get the waves

498
00:25:00,600 --> 00:25:04,000
Speaker 1: which either add up or cancel out coherently. If your

499
00:25:04,040 --> 00:25:07,000
Speaker 1: secondhand instead is just like random just like randomly slapping it,

500
00:25:07,200 --> 00:25:08,879
Speaker 1: then they're not going to add up nicely. It's just

501
00:25:08,880 --> 00:25:10,719
Speaker 1: going to be a big emotion. It's going to spread

502
00:25:10,720 --> 00:25:14,080
Speaker 1: out to nothing. So you only get these interference effects

503
00:25:14,440 --> 00:25:18,159
Speaker 1: when the quantum waves are in sync. That's quantum coherence,

504
00:25:18,400 --> 00:25:22,000
Speaker 1: and that's what allows quantum things to be sort of quantumy.

505
00:25:21,680 --> 00:25:24,760
Speaker 4: Hmmm, meaning that they're in sync in time. So what

506
00:25:24,800 --> 00:25:26,439
Speaker 4: you're saying, or in time and space.

507
00:25:26,520 --> 00:25:29,520
Speaker 1: Yeah, they're in sync in time, and so at every

508
00:25:29,600 --> 00:25:33,480
Speaker 1: point in space they can interfere. At one point in space,

509
00:25:33,480 --> 00:25:37,159
Speaker 1: you might get cancelation because they're waving in opposite directions,

510
00:25:37,640 --> 00:25:40,480
Speaker 1: and at another point in space they might support each

511
00:25:40,480 --> 00:25:43,400
Speaker 1: other because they're waving in the same direction. But they

512
00:25:43,400 --> 00:25:47,400
Speaker 1: can only do that consistently if they're in sync in time.

513
00:25:47,200 --> 00:25:50,800
Speaker 4: So it sounds like, you know, particles have these wave functions,

514
00:25:50,840 --> 00:25:53,520
Speaker 4: and they some have to sync up in order for

515
00:25:53,560 --> 00:25:55,680
Speaker 4: them to interact with each other, because if they don't

516
00:25:55,680 --> 00:25:58,520
Speaker 4: sync up, then then what happens They just cancel each

517
00:25:58,520 --> 00:26:01,520
Speaker 4: other out, or they can't or what happens if they

518
00:26:01,520 --> 00:26:02,119
Speaker 4: don't sink up.

519
00:26:02,160 --> 00:26:04,360
Speaker 1: If they don't sync up, then you don't get any

520
00:26:04,359 --> 00:26:08,760
Speaker 1: of these interference effects. It's like if your noise cancelation headphones, right,

521
00:26:09,119 --> 00:26:11,600
Speaker 1: if those were sort of just like randomly putting out

522
00:26:11,680 --> 00:26:14,639
Speaker 1: sounds instead of like syncing up to the sounds that

523
00:26:14,680 --> 00:26:17,919
Speaker 1: are coming at your ear and producing exactly the opposite

524
00:26:18,119 --> 00:26:21,160
Speaker 1: sound to cancel them out. Right, your noise canceling headphones

525
00:26:21,240 --> 00:26:25,280
Speaker 1: only work because they produce a coherent noise which cancels

526
00:26:25,280 --> 00:26:28,600
Speaker 1: out the ambient noise. Otherwise, if they put out just random,

527
00:26:28,680 --> 00:26:31,040
Speaker 1: arbitrary noise, they wouldn't cancel each other out, and you

528
00:26:31,160 --> 00:26:32,960
Speaker 1: just get sort of normal stuff you could have like

529
00:26:33,200 --> 00:26:36,360
Speaker 1: A and B. You wouldn't have like weird interference effects

530
00:26:36,520 --> 00:26:39,359
Speaker 1: between the incoming noise and the noise produced by the headphones,

531
00:26:39,760 --> 00:26:43,800
Speaker 1: and all the weird quantumness comes from those like interference effects.

532
00:26:43,800 --> 00:26:46,920
Speaker 1: These effects of the probability wave, and if you don't

533
00:26:46,920 --> 00:26:49,560
Speaker 1: have coherence, then you don't get those effects.

534
00:26:49,640 --> 00:26:52,359
Speaker 4: M okay, So you need coherence in order to have

535
00:26:52,640 --> 00:26:56,520
Speaker 4: interference is a little maybe counter in twitter. But it's

536
00:26:56,560 --> 00:26:58,800
Speaker 4: not a frequency thing, right, It's not like they have

537
00:26:58,880 --> 00:27:01,760
Speaker 4: to be the same frequency or fit the same number

538
00:27:01,800 --> 00:27:04,440
Speaker 4: of wavelengths within the same space. It's something a little

539
00:27:04,440 --> 00:27:05,000
Speaker 4: bit more than that.

540
00:27:05,160 --> 00:27:06,960
Speaker 1: It's more than that they have to be linked up.

541
00:27:06,960 --> 00:27:09,679
Speaker 1: They have to like sync up in time. Otherwise you

542
00:27:09,680 --> 00:27:12,440
Speaker 1: could have like coherence just for a moment, right, but

543
00:27:12,560 --> 00:27:14,640
Speaker 1: have to sink up in time to be like consistently

544
00:27:14,840 --> 00:27:17,679
Speaker 1: giving out these probability waves that interfere. Then they have

545
00:27:17,760 --> 00:27:20,040
Speaker 1: to be sort of syncd up, which is linked in time.

546
00:27:20,040 --> 00:27:21,960
Speaker 1: That's to like start at the same place and go

547
00:27:22,080 --> 00:27:24,120
Speaker 1: down the same time or up at the same time.

548
00:27:24,440 --> 00:27:27,480
Speaker 1: Either way, they have to like match each other in phase.

549
00:27:27,359 --> 00:27:29,600
Speaker 4: Right, But they can also cancel each other out and

550
00:27:29,680 --> 00:27:33,440
Speaker 4: be coherent, right, Like you can be coherent and destructive

551
00:27:33,560 --> 00:27:36,439
Speaker 4: at the same time. It's different than decoherent.

552
00:27:36,000 --> 00:27:38,760
Speaker 1: Just like noise canceling headphones. Right. The cool thing about

553
00:27:38,760 --> 00:27:40,679
Speaker 1: the quantum wave function is that we actually have a

554
00:27:40,760 --> 00:27:44,400
Speaker 1: lot of intuition for how waves work, right, All these effects,

555
00:27:44,440 --> 00:27:48,000
Speaker 1: interference and cancelation, these are normal things. It's just weird

556
00:27:48,080 --> 00:27:51,760
Speaker 1: when you apply it to the probability for something to happen.

557
00:27:52,240 --> 00:27:54,760
Speaker 1: So we're very familiar and happy to talk about waves

558
00:27:54,800 --> 00:27:56,959
Speaker 1: and that. None of that is weird, Like noise canceling

559
00:27:56,960 --> 00:27:59,359
Speaker 1: headphones are not quantum magic. It's just weird when you

560
00:27:59,359 --> 00:28:02,119
Speaker 1: apply it to the probability for an experiment to have

561
00:28:02,119 --> 00:28:02,920
Speaker 1: a certain outcome.

562
00:28:03,160 --> 00:28:06,400
Speaker 4: Right, And lasers are also coherent, right, Like, that's kind

563
00:28:06,400 --> 00:28:07,240
Speaker 4: of what a laser is.

564
00:28:07,240 --> 00:28:09,760
Speaker 1: Yes, exactly, a laser is a coherent source of light.

565
00:28:09,800 --> 00:28:11,760
Speaker 1: All the photons are like in phase and have the

566
00:28:11,800 --> 00:28:15,000
Speaker 1: same frequency, so they add up together. Right, So it's

567
00:28:15,000 --> 00:28:17,200
Speaker 1: a very intense source of coherent light.

568
00:28:17,320 --> 00:28:20,560
Speaker 4: Okay, So that's at the microscopic level, like electrons and

569
00:28:20,600 --> 00:28:24,280
Speaker 4: photons and quarks. They can have this coherence. But then

570
00:28:24,320 --> 00:28:27,639
Speaker 4: something happens when you go up to the bigger things,

571
00:28:27,680 --> 00:28:29,479
Speaker 4: like when don't we have to worry about coherence at

572
00:28:29,480 --> 00:28:30,200
Speaker 4: the baseball level?

573
00:28:30,280 --> 00:28:32,520
Speaker 1: Right, Well, we don't have to worry about interference of

574
00:28:32,600 --> 00:28:36,400
Speaker 1: bass balls because they're not coherent quantum objects, like all

575
00:28:36,440 --> 00:28:39,600
Speaker 1: of their particles are not wiggling in phase. They're all

576
00:28:39,600 --> 00:28:42,920
Speaker 1: scrambled and random. It's like a huge choir of children

577
00:28:42,960 --> 00:28:45,760
Speaker 1: all singing different songs at different volumes and different speeds,

578
00:28:46,040 --> 00:28:48,920
Speaker 1: and so what we see is like a big average goomush.

579
00:28:49,040 --> 00:28:51,560
Speaker 1: We don't see any sort of like interference effects when

580
00:28:51,560 --> 00:28:54,200
Speaker 1: two baseballs bounce off each other because they don't have

581
00:28:54,280 --> 00:28:57,200
Speaker 1: coherent quantum waves. Their phases are all scrambled.

582
00:28:57,200 --> 00:28:59,480
Speaker 4: All right, Well, let's talk about that scrambling, because I

583
00:28:59,480 --> 00:29:02,800
Speaker 4: think maybe that's at the key of what makes things

584
00:29:02,920 --> 00:29:05,720
Speaker 4: quantumy or not. Like this, maybe step us through, Like, okay,

585
00:29:05,760 --> 00:29:09,920
Speaker 4: we start with one atom, and the particles inside the

586
00:29:09,960 --> 00:29:13,600
Speaker 4: atom do have this wave function, and presumably they're coherent,

587
00:29:13,840 --> 00:29:16,440
Speaker 4: Like are the protons and neutrons and quarks inside of

588
00:29:16,440 --> 00:29:19,480
Speaker 4: a an atom coherent together or is there already some

589
00:29:19,600 --> 00:29:21,160
Speaker 4: kind of smooshing at that level?

590
00:29:21,200 --> 00:29:24,360
Speaker 1: They can be coherent. Absolutely, there's no limit to how

591
00:29:24,480 --> 00:29:27,000
Speaker 1: large a coherent system can be. It just gets harder

592
00:29:27,040 --> 00:29:29,840
Speaker 1: and harder to do because it has to be isolated.

593
00:29:30,160 --> 00:29:32,760
Speaker 1: The key is that anytime you interact with something, then

594
00:29:32,800 --> 00:29:35,400
Speaker 1: it becomes part of your system, and so the system

595
00:29:35,400 --> 00:29:37,720
Speaker 1: sort of grows and grows and grows, so it's easier

596
00:29:37,720 --> 00:29:40,000
Speaker 1: to start from like a single particle. Take a single

597
00:29:40,040 --> 00:29:43,600
Speaker 1: electron or a single photon, right, it has a certain

598
00:29:43,640 --> 00:29:46,120
Speaker 1: wave function, and that wave function is coherent. It has

599
00:29:46,240 --> 00:29:48,680
Speaker 1: like two possibilities for what it can do, and those

600
00:29:48,720 --> 00:29:52,480
Speaker 1: possibilities are coherent, and so you get like interesting interference effects.

601
00:29:52,680 --> 00:29:55,920
Speaker 1: That's why, for example, a single photon going through the

602
00:29:55,920 --> 00:29:59,960
Speaker 1: famous double slit experiment can interfere with itself. Right, It's

603
00:30:00,080 --> 00:30:04,160
Speaker 1: two possibilities are interfering. So single photon with two coherent

604
00:30:04,160 --> 00:30:08,440
Speaker 1: possibilities can interfere with itself. Now things get messy once

605
00:30:08,480 --> 00:30:11,440
Speaker 1: that photon starts to interact with other stuff because now

606
00:30:11,480 --> 00:30:15,240
Speaker 1: the two possibilities for the photon interact differently with the environment.

607
00:30:15,560 --> 00:30:17,720
Speaker 1: You know this interact with the wall or interact with

608
00:30:17,920 --> 00:30:20,480
Speaker 1: the tool whatever you're using to measure it, and they

609
00:30:20,600 --> 00:30:23,720
Speaker 1: change the phases of those two different outcomes, and now

610
00:30:23,760 --> 00:30:26,760
Speaker 1: it's decoherent. So a particle can be coherent. You can

611
00:30:26,840 --> 00:30:29,240
Speaker 1: even have two particles coherent, but once you touch it,

612
00:30:29,280 --> 00:30:32,240
Speaker 1: once you interact with it, then you can break that coherence.

613
00:30:32,360 --> 00:30:34,400
Speaker 4: Right. But you know, we're trying to build up from

614
00:30:34,440 --> 00:30:37,880
Speaker 4: like particles up to a baseball, and so like if

615
00:30:37,880 --> 00:30:41,560
Speaker 4: I assemble you know, three quarts together into a proton.

616
00:30:41,800 --> 00:30:44,840
Speaker 4: Are they still coherent together or do they start to

617
00:30:45,040 --> 00:30:47,120
Speaker 4: kind of get out of sync Once I put them

618
00:30:47,120 --> 00:30:48,600
Speaker 4: together into a proton.

619
00:30:48,400 --> 00:30:50,640
Speaker 1: They can be coherent together, and you can have a

620
00:30:50,680 --> 00:30:53,719
Speaker 1: single wave function that describes just those particles. Now, if

621
00:30:53,760 --> 00:30:55,440
Speaker 1: you want to have a wave function that describes just

622
00:30:55,520 --> 00:30:58,880
Speaker 1: those particles, it can't be interacting with anything else, because

623
00:30:58,920 --> 00:31:01,280
Speaker 1: then you'd need to include that in the wave function.

624
00:31:01,360 --> 00:31:02,760
Speaker 1: If you want to have a wave function for just

625
00:31:02,800 --> 00:31:05,760
Speaker 1: your atom, you have to keep it isolated, right, And

626
00:31:05,800 --> 00:31:08,480
Speaker 1: that gets harder and harder to do as things get bigger.

627
00:31:08,600 --> 00:31:12,480
Speaker 1: Like it's possible to imagine a photon in an experiment

628
00:31:12,520 --> 00:31:15,240
Speaker 1: that doesn't interact with anything you've built a special trap

629
00:31:15,360 --> 00:31:18,800
Speaker 1: or whatever. It's harder to imagine a baseball that doesn't

630
00:31:18,840 --> 00:31:22,360
Speaker 1: interact with anything, no air, molecules, no photons, no nothing.

631
00:31:22,560 --> 00:31:25,400
Speaker 1: There's so many particles in there. It becomes harder and

632
00:31:25,440 --> 00:31:29,560
Speaker 1: harder to keep it isolated. That's why decoherence appears as

633
00:31:29,600 --> 00:31:31,920
Speaker 1: soon as things get big, because it's really hard to

634
00:31:32,040 --> 00:31:36,280
Speaker 1: keep larger, realistic sized things isolated and coherent.

635
00:31:36,440 --> 00:31:36,600
Speaker 9: Right.

636
00:31:36,720 --> 00:31:39,840
Speaker 4: I guess I'm trying to understand when that comes in. So, Like,

637
00:31:39,960 --> 00:31:42,680
Speaker 4: if I build a nucleus out of protons that are

638
00:31:42,720 --> 00:31:46,760
Speaker 4: all in sync inside. Then are they all also together

639
00:31:46,800 --> 00:31:49,280
Speaker 4: in sync like you know, like carbon has twelve of

640
00:31:49,320 --> 00:31:51,800
Speaker 4: them in the nucleus and they're all compent there together,

641
00:31:51,960 --> 00:31:55,120
Speaker 4: held by the strong nuclear force. Are they still coherent

642
00:31:55,280 --> 00:31:57,080
Speaker 4: or are they starting to kind of fuzz out?

643
00:31:57,120 --> 00:32:00,200
Speaker 1: If you keep it isolated, it can stay coherent. Absolutely, Okay.

644
00:32:00,280 --> 00:32:02,920
Speaker 4: So then I build an atom, I throw in some electrons,

645
00:32:02,920 --> 00:32:05,920
Speaker 4: and that also gets synced up. And at what point

646
00:32:05,960 --> 00:32:08,040
Speaker 4: do things start to kind of go awry?

647
00:32:08,320 --> 00:32:10,800
Speaker 1: At the point where it becomes impossible to keep it

648
00:32:10,880 --> 00:32:12,800
Speaker 1: isolated from the rest of the universe.

649
00:32:12,840 --> 00:32:14,640
Speaker 4: But then couldn't I be in sync with the rest

650
00:32:14,640 --> 00:32:16,000
Speaker 4: of the universe Daniel.

651
00:32:16,160 --> 00:32:19,040
Speaker 1: Yes, exactly. Some people think that there is a wave

652
00:32:19,080 --> 00:32:22,479
Speaker 1: function for the whole universe, right. The problem is that

653
00:32:22,480 --> 00:32:24,760
Speaker 1: now we're inside the wave function. Now the wave function

654
00:32:24,840 --> 00:32:28,040
Speaker 1: includes us, and so it's hard to see these quantum

655
00:32:28,080 --> 00:32:30,840
Speaker 1: effects now because we are part of the experiment.

656
00:32:30,880 --> 00:32:33,320
Speaker 4: All right, So I got an atom and it's coherent

657
00:32:33,360 --> 00:32:35,840
Speaker 4: and it's syncd up, and now I add another atom.

658
00:32:36,200 --> 00:32:38,880
Speaker 4: Is that a problem or does it just get bigger?

659
00:32:39,000 --> 00:32:41,400
Speaker 1: It's not a problem. It gets bigger. It's just harder

660
00:32:41,440 --> 00:32:43,240
Speaker 1: to keep it coherent because you have to keep it

661
00:32:43,280 --> 00:32:46,360
Speaker 1: isolated from the system. Remember one time we talked about

662
00:32:46,600 --> 00:32:50,560
Speaker 1: building a macroscopic like big size stuff that behaves in

663
00:32:50,600 --> 00:32:53,320
Speaker 1: a quantum mechanical way. This is done in a special

664
00:32:53,360 --> 00:32:57,800
Speaker 1: way using Bose Einstein condensates special form of matter that

665
00:32:57,840 --> 00:33:00,520
Speaker 1: can be coherent, that can stay together and can stay

666
00:33:00,600 --> 00:33:03,360
Speaker 1: isolated from the rest of the system. These things don't

667
00:33:03,440 --> 00:33:05,520
Speaker 1: last very long. They last like, you know, seconds or

668
00:33:05,600 --> 00:33:08,320
Speaker 1: minutes because it's hard to keep them isolated. So it's

669
00:33:08,360 --> 00:33:11,840
Speaker 1: like real experimental bravado if you can put more than

670
00:33:11,840 --> 00:33:15,479
Speaker 1: a few atoms together in a quantum coherence system and

671
00:33:15,680 --> 00:33:18,960
Speaker 1: keep them coherent, keep them from interacting with the rest

672
00:33:18,960 --> 00:33:21,160
Speaker 1: of the universe and getting their wave functions sort of

673
00:33:21,360 --> 00:33:23,040
Speaker 1: muddled up with the rest of the universe.

674
00:33:23,160 --> 00:33:25,040
Speaker 4: Yeah, well, I guess maybe a big part of it

675
00:33:25,080 --> 00:33:27,920
Speaker 4: seems to be this idea of an experiment, and like

676
00:33:28,040 --> 00:33:31,240
Speaker 4: who's in on the know and who's outside of the experiment,

677
00:33:31,320 --> 00:33:33,640
Speaker 4: and what does it mean for something to be kind

678
00:33:33,680 --> 00:33:36,440
Speaker 4: of pristine or not pristine? So maybe let's get a

679
00:33:36,480 --> 00:33:38,640
Speaker 4: little bit into that, which is I think basically the

680
00:33:38,680 --> 00:33:41,360
Speaker 4: idea of decoherence, right, all right, let's get into that,

681
00:33:41,440 --> 00:33:43,320
Speaker 4: but first let's take another quick break.

682
00:33:47,520 --> 00:33:49,320
Speaker 1: When you pop a piece of cheese into your mouth

683
00:33:49,440 --> 00:33:52,560
Speaker 1: or enjoy a rich spoonful of Greek yogurt, you're probably

684
00:33:52,600 --> 00:33:56,640
Speaker 1: not thinking about the environmental impact of each and every bite.

685
00:33:56,680 --> 00:33:59,280
Speaker 1: But the people in the dairy industry are. US Dairy

686
00:33:59,320 --> 00:34:03,640
Speaker 1: has set themselves some ambitious sustainability goals, including being greenhouse

687
00:34:03,680 --> 00:34:06,240
Speaker 1: gas neutral by twenty to fifty. That's why they're working

688
00:34:06,280 --> 00:34:08,600
Speaker 1: hard every day to find new ways to reduce waste,

689
00:34:08,680 --> 00:34:12,919
Speaker 1: conserve natural resources, and drive down greenhouse gas emissions. Take water,

690
00:34:12,960 --> 00:34:16,040
Speaker 1: for example, most dairy farms reuse water up to four

691
00:34:16,080 --> 00:34:19,560
Speaker 1: times the same water cools the milk, cleans equipment, washes

692
00:34:19,600 --> 00:34:22,400
Speaker 1: the barn, and irrigates the crops. How is US dairy

693
00:34:22,440 --> 00:34:26,160
Speaker 1: tackling greenhouse gases? Many farms use anaerobic digestors that turn

694
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Speaker 1: the methane from maneuver into renewable energy that can power farms, towns,

695
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Speaker 1: and electric cars. So the next time you grab a

696
00:34:32,239 --> 00:34:34,279
Speaker 1: slice of pizza or lick an ice cream cone, know

697
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Speaker 1: that dairy farmers and processors around the country are using

698
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Speaker 1: the latest practices and innovations to provide the nutrient dense

699
00:34:40,680 --> 00:34:43,399
Speaker 1: dairy products we love with less of an impact. Visit

700
00:34:43,480 --> 00:34:46,279
Speaker 1: us dairy dot com slash sustainability to learn more.

701
00:34:46,480 --> 00:34:50,120
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702
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716
00:35:34,880 --> 00:35:37,359
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717
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719
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720
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Speaker 4: All right, we're talking about quantum decoherence, which is kind

721
00:35:56,320 --> 00:35:59,000
Speaker 4: of at the heart of this kind of headache that

722
00:35:59,080 --> 00:36:03,600
Speaker 4: people have quantum mechanics and trying to understand it at

723
00:36:03,600 --> 00:36:07,600
Speaker 4: an intuitive level. So you know, small particles can have

724
00:36:07,719 --> 00:36:13,400
Speaker 4: quantum effects and wave functions and weird probability existences, but

725
00:36:13,480 --> 00:36:17,160
Speaker 4: once you start piling them on together, it gets harder

726
00:36:17,560 --> 00:36:22,120
Speaker 4: to kind of keep pristine, I guess, right, untouched from

727
00:36:22,680 --> 00:36:25,160
Speaker 4: to an observer from the outside or just to the

728
00:36:25,280 --> 00:36:28,440
Speaker 4: universe in general, the same, right, because the universe, I imagine

729
00:36:28,360 --> 00:36:31,000
Speaker 4: doesn't care, right, like the universe if there is a

730
00:36:31,080 --> 00:36:34,399
Speaker 4: quantum wave function for the entire universe, Like, it doesn't care,

731
00:36:34,920 --> 00:36:37,600
Speaker 4: Like it doesn't know the difference between something that you

732
00:36:38,000 --> 00:36:39,799
Speaker 4: would think is incoherent or not.

733
00:36:40,000 --> 00:36:42,480
Speaker 1: Yeah, that's right. And the tricky thing here is that

734
00:36:42,520 --> 00:36:44,480
Speaker 1: we want to have a wave function just for our

735
00:36:44,600 --> 00:36:47,920
Speaker 1: experiment because we want to see quantum effects. If we

736
00:36:47,960 --> 00:36:51,080
Speaker 1: become part of the experiment, then we no longer see

737
00:36:51,080 --> 00:36:53,399
Speaker 1: the quantum effects because we only are like on one

738
00:36:53,480 --> 00:36:54,520
Speaker 1: branch of that history.

739
00:36:54,560 --> 00:36:56,200
Speaker 4: What do you mean we don't see the effects Like

740
00:36:56,239 --> 00:36:58,879
Speaker 4: we're also existing in multiple places at the same time

741
00:36:59,040 --> 00:37:01,120
Speaker 4: to somebody outside of our universe.

742
00:37:01,200 --> 00:37:04,080
Speaker 1: Yeah, somebody outside of our universe sees a wave function

743
00:37:04,160 --> 00:37:06,000
Speaker 1: for the whole universe and they see lots of different

744
00:37:06,040 --> 00:37:10,120
Speaker 1: possible outcomes, right, and those things can exist simultaneously until

745
00:37:10,160 --> 00:37:12,960
Speaker 1: like if they observe the universe. But we're on just

746
00:37:13,000 --> 00:37:15,200
Speaker 1: sort of one branch of that history the way we

747
00:37:15,239 --> 00:37:19,400
Speaker 1: are existing, and so we don't see those other branches necessarily.

748
00:37:19,600 --> 00:37:21,440
Speaker 1: And so if you want to see a quantum effect,

749
00:37:21,480 --> 00:37:24,760
Speaker 1: you have to be like outside of that quantum system

750
00:37:25,080 --> 00:37:28,000
Speaker 1: and take some measurements of it. Right now, as soon

751
00:37:28,040 --> 00:37:29,960
Speaker 1: as you take those measurements of it, you've sort of

752
00:37:30,000 --> 00:37:34,400
Speaker 1: inserted yourself in that quantum system and it becomes much muddier.

753
00:37:34,440 --> 00:37:36,520
Speaker 4: I think you just blew my mind here, because, like,

754
00:37:36,600 --> 00:37:39,560
Speaker 4: if we are all part of the quantum function of

755
00:37:39,600 --> 00:37:43,960
Speaker 4: the universe, that means that there are like multiples of

756
00:37:44,000 --> 00:37:47,680
Speaker 4: me out there to some alien observer outside of the universe.

757
00:37:47,800 --> 00:37:51,360
Speaker 4: M Like, I only think that I exist as one person,

758
00:37:52,200 --> 00:37:57,520
Speaker 4: because what because I am observing myself, I guess.

759
00:37:57,600 --> 00:38:00,120
Speaker 1: Yeah, it's complicated, and this whole question of like who

760
00:38:00,160 --> 00:38:02,960
Speaker 1: is an observer who can collapse the wave function when

761
00:38:03,000 --> 00:38:05,799
Speaker 1: does the wave function get collapsed. It's very complicated. It's

762
00:38:05,800 --> 00:38:09,200
Speaker 1: a whole other philosophical question that it hasn't been resolved.

763
00:38:09,200 --> 00:38:10,920
Speaker 1: We don't know the answer to it. It's like the

764
00:38:10,920 --> 00:38:14,040
Speaker 1: biggest problem in the foundations of quantum mechanics. We're not

765
00:38:14,080 --> 00:38:16,319
Speaker 1: going to figure it out today on the podcast, but

766
00:38:16,520 --> 00:38:19,520
Speaker 1: it is connected to this question of quantum decoherence and

767
00:38:19,600 --> 00:38:23,719
Speaker 1: quantum coherence because we're interested in observing quantum effects, like

768
00:38:23,960 --> 00:38:26,440
Speaker 1: when do things look quantumy, and when do things not

769
00:38:26,640 --> 00:38:31,040
Speaker 1: look quantumy, and if you are inside the experiment, things

770
00:38:31,040 --> 00:38:33,680
Speaker 1: don't look quantumy. Like I've never talked to a photon.

771
00:38:33,719 --> 00:38:35,240
Speaker 1: I don't know what it's like to be a photon

772
00:38:35,520 --> 00:38:38,440
Speaker 1: in a double slit experiment that has experienced one path

773
00:38:38,560 --> 00:38:41,560
Speaker 1: is it experienced some weird combination of multiple paths. But

774
00:38:41,600 --> 00:38:42,960
Speaker 1: I know what it's like to be me, and I

775
00:38:42,960 --> 00:38:46,120
Speaker 1: don't experience superpositions, right, I don't live two lives at

776
00:38:46,160 --> 00:38:48,160
Speaker 1: the same time. Sometimes it feels like it.

777
00:38:48,160 --> 00:38:50,799
Speaker 4: Yeah, okay, so it kind of depends on who you

778
00:38:50,960 --> 00:38:54,640
Speaker 4: ask whether something feels quantumy or not. Like, you know,

779
00:38:54,680 --> 00:38:57,040
Speaker 4: we can have a little experiment here in front of

780
00:38:57,160 --> 00:39:01,120
Speaker 4: us that looks and feels quantity, but the particles inside

781
00:39:01,120 --> 00:39:03,840
Speaker 4: it doesn't feel quantomy or to an observer outside of

782
00:39:03,840 --> 00:39:05,759
Speaker 4: our universe, we feel quantumy to them.

783
00:39:05,840 --> 00:39:08,200
Speaker 1: Oh absolutely, Like there's a very simple thought experiment to

784
00:39:08,200 --> 00:39:11,200
Speaker 1: think about that. Say I set up a quantum experiment

785
00:39:11,239 --> 00:39:13,400
Speaker 1: that can have you know, two outcomes A or B,

786
00:39:13,760 --> 00:39:16,239
Speaker 1: and I run the experiment. Now, before I read the

787
00:39:16,239 --> 00:39:18,680
Speaker 1: outcome of the experiment, you could say there's two possibilities

788
00:39:18,760 --> 00:39:21,680
Speaker 1: A or B. Cool. What if you're running an experiment

789
00:39:21,719 --> 00:39:24,880
Speaker 1: and your experiment is me running that experiment. So you

790
00:39:24,920 --> 00:39:27,880
Speaker 1: put me in a box and I do the experiment,

791
00:39:27,920 --> 00:39:30,080
Speaker 1: and I know the outcome, but you don't yet know

792
00:39:30,160 --> 00:39:34,600
Speaker 1: the outcome, right, So I am your experiment. Well you know,

793
00:39:34,680 --> 00:39:37,800
Speaker 1: am I living in the outcomes of both experiments until

794
00:39:37,840 --> 00:39:40,960
Speaker 1: you ask me what's the outcome of my experiment? Right?

795
00:39:41,000 --> 00:39:44,480
Speaker 1: So absolutely? Like the quantumans depends on who's doing the

796
00:39:44,560 --> 00:39:47,840
Speaker 1: asking and who's doing the observing and who is collapsed

797
00:39:47,880 --> 00:39:50,200
Speaker 1: the wave function, And that's like that deep question of

798
00:39:50,280 --> 00:39:52,640
Speaker 1: quantum mechanics that we don't know the answer to is

799
00:39:52,640 --> 00:39:55,440
Speaker 1: like when do wave functions get collapsed and how did

800
00:39:55,480 --> 00:39:56,240
Speaker 1: they get collapsed?

801
00:39:56,320 --> 00:39:58,600
Speaker 4: Right? Like if the cat ensure the Ainger's box was

802
00:39:58,600 --> 00:40:03,399
Speaker 4: a physicist, Like, the cat knows whether or not it's

803
00:40:03,440 --> 00:40:06,960
Speaker 4: dead or alive, or you know, the radioactive particle clicked

804
00:40:07,080 --> 00:40:09,600
Speaker 4: or not. But to us, the cat is dead and alive,

805
00:40:09,719 --> 00:40:10,600
Speaker 4: But to the cat it's not.

806
00:40:10,760 --> 00:40:12,920
Speaker 1: That's right. And so that's why I say you can

807
00:40:12,960 --> 00:40:16,400
Speaker 1: observe quantum effects if you're outside the experiment, Like you

808
00:40:16,440 --> 00:40:18,560
Speaker 1: observe a quantum effect on me, because I'm part of

809
00:40:18,600 --> 00:40:21,600
Speaker 1: your experiment. I observe a quantum effect on the little

810
00:40:21,600 --> 00:40:24,080
Speaker 1: experiment that I'm running with the cat or whatever. Right,

811
00:40:24,200 --> 00:40:27,520
Speaker 1: I don't experience the quantum effects that you observe in me.

812
00:40:27,960 --> 00:40:30,280
Speaker 4: Right, So then how does that apply to our baseball?

813
00:40:30,360 --> 00:40:32,120
Speaker 4: Like is it a thing kind of like as you

814
00:40:32,239 --> 00:40:36,920
Speaker 4: pile on more particles that are interacting with more things,

815
00:40:37,120 --> 00:40:39,960
Speaker 4: you're sort of opening up those throlled in group boxes.

816
00:40:40,080 --> 00:40:41,920
Speaker 1: Yeah, exactly. And there's two ways to think about it,

817
00:40:42,000 --> 00:40:44,680
Speaker 1: sort of. One is intuitive and the other's mathematical. The

818
00:40:44,760 --> 00:40:47,760
Speaker 1: intuitive way is that as the baseball starts to interact

819
00:40:47,800 --> 00:40:50,840
Speaker 1: with more stuff, that stuff becomes part of the baseball's

820
00:40:50,920 --> 00:40:53,640
Speaker 1: quantum wave function, right, Like, now you have a wave

821
00:40:53,640 --> 00:40:56,480
Speaker 1: function for the bat and the baseball together, and so

822
00:40:56,719 --> 00:40:59,440
Speaker 1: the bat can no longer do like quantum experiments on

823
00:40:59,520 --> 00:41:02,880
Speaker 1: the baseball, because it's like entangled with the baseball the

824
00:41:02,920 --> 00:41:05,960
Speaker 1: same way they're like, I'm inside your experiment. And so

825
00:41:06,000 --> 00:41:08,680
Speaker 1: the intuitive way is like, as a particle starts to

826
00:41:08,719 --> 00:41:11,160
Speaker 1: interact with the system around it, it gets sort of

827
00:41:11,280 --> 00:41:14,480
Speaker 1: enmeshed quantum mechanically with the wave function of the larger system.

828
00:41:14,719 --> 00:41:18,080
Speaker 1: So that system is now part of that you know,

829
00:41:18,200 --> 00:41:21,319
Speaker 1: particle or baseball's quantum wave function, and it can no

830
00:41:21,400 --> 00:41:24,960
Speaker 1: longer see the quantum effects of those things. So that's decoherence.

831
00:41:25,520 --> 00:41:28,239
Speaker 1: And so the mathematical way to think about it is

832
00:41:28,280 --> 00:41:31,040
Speaker 1: that when a particle interacts with something, what happens is

833
00:41:31,040 --> 00:41:33,680
Speaker 1: that its phase gets shifted a little bit, and the

834
00:41:33,719 --> 00:41:37,520
Speaker 1: phases of the different possibilities get shifted differently based on

835
00:41:37,560 --> 00:41:41,000
Speaker 1: how you're interacting. And so what happens is that all

836
00:41:41,000 --> 00:41:43,399
Speaker 1: the phases of the baseball when it hits the bat

837
00:41:43,640 --> 00:41:46,360
Speaker 1: gets shifted a tiny little bit and they all get scrambled.

838
00:41:46,640 --> 00:41:48,600
Speaker 1: And so now the phases are like out of sync

839
00:41:48,640 --> 00:41:51,560
Speaker 1: and they can't do quantum stuff together because they have

840
00:41:51,680 --> 00:41:54,280
Speaker 1: decoher because they're all like random phases.

841
00:41:54,400 --> 00:41:57,400
Speaker 4: Wait, so you know I was building this baseball from atoms,

842
00:41:57,920 --> 00:42:01,120
Speaker 4: and so it isn't it possible to build a baseball

843
00:42:01,400 --> 00:42:04,719
Speaker 4: that is still coherent, like all of the wave functions

844
00:42:04,719 --> 00:42:08,879
Speaker 4: inside are in sync and happy and quantumy, in which

845
00:42:08,960 --> 00:42:10,840
Speaker 4: case the whole baseball is quantumy.

846
00:42:10,880 --> 00:42:14,279
Speaker 1: Theoretically possible, practically very very difficult because you'd have to

847
00:42:14,320 --> 00:42:17,480
Speaker 1: isolate it from the entire universe. Nobody could interact with

848
00:42:17,640 --> 00:42:18,920
Speaker 1: or observe that baseball.

849
00:42:19,000 --> 00:42:20,600
Speaker 4: Right, Let's say I put it inside of a short

850
00:42:20,680 --> 00:42:24,600
Speaker 4: finger's box. It's there, it's not interacting. Yeah, that baseball

851
00:42:24,920 --> 00:42:25,560
Speaker 4: is quantumy.

852
00:42:25,600 --> 00:42:28,399
Speaker 1: That baseball is quantum me. Now, like practically shortingers box

853
00:42:28,440 --> 00:42:31,400
Speaker 1: is impossible because you know, no box is impervious to

854
00:42:31,480 --> 00:42:34,239
Speaker 1: heat and all sorts of other interactions. But let's say

855
00:42:34,280 --> 00:42:37,400
Speaker 1: theoretically you've built some way to isolate the baseball completely,

856
00:42:37,520 --> 00:42:40,400
Speaker 1: then yes, it is still quantumy. It has not interacted

857
00:42:40,400 --> 00:42:41,279
Speaker 1: with anything else.

858
00:42:41,440 --> 00:42:43,759
Speaker 4: Right, But I think maybe a key limitation here is

859
00:42:43,800 --> 00:42:45,960
Speaker 4: that it's not that the baseball can be here or

860
00:42:46,000 --> 00:42:50,560
Speaker 4: in Mars. The probability of where it is isn't that big,

861
00:42:50,680 --> 00:42:54,640
Speaker 4: because you know, you're just adding tiny little probabilities, right,

862
00:42:55,239 --> 00:42:58,080
Speaker 4: Like it can't be here or a meter away that

863
00:42:58,200 --> 00:43:01,360
Speaker 4: quantum meanness of the isolated baseila is like it's here,

864
00:43:01,520 --> 00:43:03,480
Speaker 4: or it's a few angs from to the right.

865
00:43:03,640 --> 00:43:07,040
Speaker 1: It could actually have quite different possible locations. It depends

866
00:43:07,080 --> 00:43:09,200
Speaker 1: on how you set it up inside the box. It

867
00:43:09,200 --> 00:43:12,160
Speaker 1: could be sensitive to one quantum fluctuation which sends it

868
00:43:12,160 --> 00:43:14,719
Speaker 1: in one direction or the other direction. I think what

869
00:43:14,719 --> 00:43:17,279
Speaker 1: you're referring to, though, is more like the classical sense

870
00:43:17,280 --> 00:43:20,279
Speaker 1: of the decohered baseball, a baseball that's like that you're

871
00:43:20,280 --> 00:43:22,200
Speaker 1: familiar with, that's flying through the air in a normal

872
00:43:22,239 --> 00:43:25,440
Speaker 1: baseball game. We don't see those quantum effects because they

873
00:43:25,520 --> 00:43:28,640
Speaker 1: all average out. Because all the quantum effects of all

874
00:43:28,640 --> 00:43:31,279
Speaker 1: those particles in the baseball are not pulling like in

875
00:43:31,280 --> 00:43:34,320
Speaker 1: the same directions. You never see like weird interference effects

876
00:43:34,719 --> 00:43:38,000
Speaker 1: or weird probability distributions because they've all averaged out. They're

877
00:43:38,040 --> 00:43:41,480
Speaker 1: all decoherent. If they were coherent, then yes, the baseball

878
00:43:41,480 --> 00:43:44,839
Speaker 1: could do quantum things the way like Schruenninger's cat can

879
00:43:44,880 --> 00:43:47,960
Speaker 1: do quantum things like be dead or alive. Have those

880
00:43:48,000 --> 00:43:49,520
Speaker 1: possibilities at the same time.

881
00:43:50,000 --> 00:43:53,080
Speaker 4: Okay, so now you're saying that, like if I has

882
00:43:53,160 --> 00:43:55,319
Speaker 4: this baseball in the box and I open it. That's

883
00:43:55,360 --> 00:43:57,000
Speaker 4: the same thing as hitting it with a bat.

884
00:43:57,200 --> 00:44:00,160
Speaker 1: Yes, because now photons are hitting it and you are

885
00:44:00,200 --> 00:44:01,640
Speaker 1: seeing those photons.

886
00:44:01,120 --> 00:44:03,080
Speaker 4: And like, the bat is connected to the batter, and

887
00:44:03,120 --> 00:44:04,879
Speaker 4: the batter is connected to the ground, and the ground

888
00:44:04,920 --> 00:44:07,880
Speaker 4: is connected to me, and there's air in between, and

889
00:44:07,920 --> 00:44:11,279
Speaker 4: there are photons flying back and forth, meaning that like,

890
00:44:11,480 --> 00:44:15,319
Speaker 4: I am kind of inextricably tied to this baseball, which

891
00:44:15,320 --> 00:44:17,840
Speaker 4: means that I am now inside of a larger box

892
00:44:17,920 --> 00:44:20,239
Speaker 4: with the baseball exactly. Then that's why you don't see

893
00:44:20,280 --> 00:44:23,320
Speaker 4: quantum effects on big things, because big things are always interacting,

894
00:44:23,719 --> 00:44:26,720
Speaker 4: you know. Einstein famously asked somebody like, do you believe

895
00:44:26,760 --> 00:44:29,520
Speaker 4: the moon isn't there when you're not looking, because he

896
00:44:29,600 --> 00:44:31,920
Speaker 4: was thinking, like, it's silly to imagine that the universe

897
00:44:32,040 --> 00:44:34,920
Speaker 4: like is uncertain when you're not existing. And the answer

898
00:44:35,040 --> 00:44:37,280
Speaker 4: is like, of course the moon is there because photons

899
00:44:37,280 --> 00:44:39,400
Speaker 4: are hitting it and bouncing off of it, and so

900
00:44:39,520 --> 00:44:42,600
Speaker 4: the universe is always looking because the universe is filled

901
00:44:42,600 --> 00:44:45,160
Speaker 4: with particles and they're always sort of bouncing off of

902
00:44:45,200 --> 00:44:48,759
Speaker 4: things in gravity too, right, it's interacting through gravity with us.

903
00:44:48,840 --> 00:44:51,279
Speaker 1: Ooh, that's tricky because we don't know if gravity is

904
00:44:51,360 --> 00:44:54,600
Speaker 1: quantum mechanical and if they are gravitons bouncing around through space.

905
00:44:54,800 --> 00:44:57,960
Speaker 1: But in principle yes, and so quantum decoherence is just

906
00:44:58,040 --> 00:45:01,040
Speaker 1: like when an object no longer becomes isolated and its

907
00:45:01,080 --> 00:45:04,480
Speaker 1: wave function is now like complicatedly mixed up with the

908
00:45:04,520 --> 00:45:06,879
Speaker 1: rest of the environment so that they don't like add

909
00:45:06,920 --> 00:45:09,239
Speaker 1: up coherently anymore. Like this little bit of the wave

910
00:45:09,280 --> 00:45:10,960
Speaker 1: function is mixed up with that part of the wave

911
00:45:10,960 --> 00:45:12,919
Speaker 1: function from the bat, and that part of the wave

912
00:45:12,920 --> 00:45:14,560
Speaker 1: function from the ball is mixed up with this other

913
00:45:14,600 --> 00:45:16,319
Speaker 1: bit of the wave function from the bat. And if

914
00:45:16,360 --> 00:45:18,279
Speaker 1: you were outside the baseball game, you could view the

915
00:45:18,280 --> 00:45:20,879
Speaker 1: whole baseball games wave function. Then you could say, oh,

916
00:45:20,920 --> 00:45:23,480
Speaker 1: I still see quantum effects, right, because I'm looking at

917
00:45:23,480 --> 00:45:25,839
Speaker 1: the wave function of the whole baseball game. But if

918
00:45:25,840 --> 00:45:28,719
Speaker 1: you're inside, if you are the batter, right, then now

919
00:45:28,800 --> 00:45:30,400
Speaker 1: you are only seeing one slice of it.

920
00:45:31,000 --> 00:45:33,719
Speaker 4: All right. Well it's weird because you know, I feel

921
00:45:33,760 --> 00:45:37,640
Speaker 4: like the word decoherence means that things get out of sync,

922
00:45:38,080 --> 00:45:41,160
Speaker 4: but really it means I got sucked into the box.

923
00:45:42,480 --> 00:45:46,480
Speaker 1: Yeah, you are entangled, right, and decoherence right, yeah, exactly,

924
00:45:46,560 --> 00:45:47,600
Speaker 1: I see how that's confusing.

925
00:45:47,680 --> 00:45:50,400
Speaker 4: Yeah, it's more like I got sucked into the box.

926
00:45:50,800 --> 00:45:53,640
Speaker 4: But the word decoherence kind of, you know, implies like

927
00:45:53,719 --> 00:45:55,880
Speaker 4: some kind of like noise or some kind of like

928
00:45:55,960 --> 00:45:56,879
Speaker 4: breakdown of things.

929
00:45:57,000 --> 00:45:58,640
Speaker 1: And I think the key there is that, you know,

930
00:45:58,920 --> 00:46:01,880
Speaker 1: just the ball itself not become decoherent, right. You no

931
00:46:01,960 --> 00:46:04,279
Speaker 1: longer have just a wave function that describes the ball.

932
00:46:04,320 --> 00:46:06,799
Speaker 1: You have to describe the ball and the bat, or

933
00:46:06,880 --> 00:46:10,000
Speaker 1: Jorge and the cat. There's no wave function by itself

934
00:46:10,040 --> 00:46:12,960
Speaker 1: that now describes the ball because the ball is entangled

935
00:46:12,960 --> 00:46:17,040
Speaker 1: with the bat, and so the ball's isolated individual wave

936
00:46:17,040 --> 00:46:20,160
Speaker 1: function is no longer coherent. It's like a part of

937
00:46:20,200 --> 00:46:22,920
Speaker 1: a larger wave function. It can't be isolated. And so

938
00:46:22,960 --> 00:46:25,840
Speaker 1: that's why you can't get quantum effects on the ball anymore,

939
00:46:25,880 --> 00:46:28,239
Speaker 1: because it's complicatedly tied up with the things you want

940
00:46:28,280 --> 00:46:29,920
Speaker 1: to use to measure those quantum effects.

941
00:46:29,960 --> 00:46:32,640
Speaker 4: Because we are the ball now, Daniels, The ball and

942
00:46:32,800 --> 00:46:35,640
Speaker 4: us are one. That's what decoherence means, right, kind of

943
00:46:35,840 --> 00:46:38,680
Speaker 4: like it gets so complicated. I guess that's why we

944
00:46:38,800 --> 00:46:42,760
Speaker 4: use the word decoherence, just because it gets complicated beyond

945
00:46:43,000 --> 00:46:46,120
Speaker 4: our ability to be outside the box. It's like we're

946
00:46:46,160 --> 00:46:49,319
Speaker 4: in the box now, and we can't make out what

947
00:46:49,400 --> 00:46:52,000
Speaker 4: these quantumness effects are.

948
00:46:52,320 --> 00:46:54,799
Speaker 1: Yeah, exactly, it's too much for us to calculate. It's

949
00:46:54,800 --> 00:46:57,320
Speaker 1: too much for us to understand. And so what happens

950
00:46:57,920 --> 00:47:01,000
Speaker 1: is that quantum mechanics doesn't fail, doesn't go. This is

951
00:47:01,080 --> 00:47:04,600
Speaker 1: just what quantum mechanics looks like at a big scale.

952
00:47:04,760 --> 00:47:08,520
Speaker 1: Quantum mechanics over zillions and zillions of objects looks different

953
00:47:08,520 --> 00:47:11,160
Speaker 1: because you don't see those coherence effects anymore. They only

954
00:47:11,200 --> 00:47:13,279
Speaker 1: exist when you have like one or two or three

955
00:47:13,320 --> 00:47:15,520
Speaker 1: little things that you can keep separated, so you can

956
00:47:15,600 --> 00:47:18,919
Speaker 1: have a wave function just for that. When you're part

957
00:47:18,960 --> 00:47:21,960
Speaker 1: of the wave function, quantum mechanics says that things look different.

958
00:47:21,960 --> 00:47:24,560
Speaker 1: They look more smeared and averaged out. So it's not

959
00:47:24,600 --> 00:47:27,680
Speaker 1: like classical physics is in disagreement with quantum mechanics. It's

960
00:47:27,680 --> 00:47:29,759
Speaker 1: what quantum mechanics looks like, sort of from a high

961
00:47:29,800 --> 00:47:31,200
Speaker 1: altitude right.

962
00:47:31,080 --> 00:47:34,239
Speaker 4: Like to an alien observer outside of our universe, we

963
00:47:34,280 --> 00:47:37,080
Speaker 4: are still all coherent. We are you and I in

964
00:47:37,280 --> 00:47:40,400
Speaker 4: this podcast, and that baseball it still looks like a

965
00:47:40,480 --> 00:47:43,080
Speaker 4: Priestine quantum universe.

966
00:47:43,480 --> 00:47:45,200
Speaker 1: Yeah, and I hope that alien that has that deep

967
00:47:45,280 --> 00:47:48,040
Speaker 1: understanding of quantum mechanics has a coherent understanding of what

968
00:47:48,040 --> 00:47:50,959
Speaker 1: we've been talking about today, because it's gotten pretty tricky.

969
00:47:53,000 --> 00:47:56,040
Speaker 4: All right, Well, I think hopefully that gives people a

970
00:47:56,080 --> 00:47:58,600
Speaker 4: sense of kind of the issues involved. You know, it's

971
00:47:58,680 --> 00:48:01,879
Speaker 4: kind of about what you consider the box to be,

972
00:48:02,120 --> 00:48:06,360
Speaker 4: what's interacting with what, and how these kind of probabilities

973
00:48:06,440 --> 00:48:07,840
Speaker 4: add up or don't add up.

974
00:48:08,239 --> 00:48:10,200
Speaker 1: And it's not just like an academic question or a

975
00:48:10,200 --> 00:48:14,359
Speaker 1: philosophical question. It's actually really important for quantum computing. If

976
00:48:14,400 --> 00:48:17,000
Speaker 1: you want to build a quantum computer, you need cubits.

977
00:48:17,040 --> 00:48:20,239
Speaker 1: You need weird particles that follow quantum rules so you

978
00:48:20,239 --> 00:48:23,359
Speaker 1: can have them do quantum computations. And to do that,

979
00:48:23,400 --> 00:48:26,200
Speaker 1: you need to keep them isolated. And that's okay to

980
00:48:26,280 --> 00:48:29,560
Speaker 1: do for one cubit, two cubits, three cubits, But imagine

981
00:48:29,600 --> 00:48:32,920
Speaker 1: having a really big quantum computer with thousands and thousands

982
00:48:32,960 --> 00:48:35,960
Speaker 1: of cubits or millions or trillions, right, you got to

983
00:48:36,040 --> 00:48:39,680
Speaker 1: keep them all isolated and all individually coherent. It becomes

984
00:48:39,719 --> 00:48:42,759
Speaker 1: really difficult. So this is something people are literally working on,

985
00:48:42,880 --> 00:48:45,600
Speaker 1: is building larger coherent quantum systems.

986
00:48:45,920 --> 00:48:50,000
Speaker 4: M yeah, I can't wait for that quantum phone, so

987
00:48:50,040 --> 00:48:53,800
Speaker 4: I can take quantum pictures of my kid playing quantum baseball.

988
00:48:53,880 --> 00:48:55,920
Speaker 1: So you can ignore that email and answer it at

989
00:48:55,960 --> 00:48:56,560
Speaker 1: the same time.

990
00:48:56,920 --> 00:49:00,200
Speaker 4: Yeah, that's right, So I can do everything at the

991
00:49:00,239 --> 00:49:02,120
Speaker 4: same time exactly.

992
00:49:02,160 --> 00:49:05,040
Speaker 1: And this is really closely connected to deep issues in

993
00:49:05,080 --> 00:49:07,759
Speaker 1: the philosophy of quantum mechanics. You know, who is doing

994
00:49:07,800 --> 00:49:10,239
Speaker 1: the observing, why does it matter? When does the wave

995
00:49:10,239 --> 00:49:12,640
Speaker 1: function collapse? And I want to have another episode where

996
00:49:12,680 --> 00:49:15,239
Speaker 1: we talk about wave function collapse and the measurement problem.

997
00:49:15,280 --> 00:49:16,719
Speaker 1: But this is sort of like a warm up to

998
00:49:16,760 --> 00:49:20,160
Speaker 1: that because it helps you understand, you know why sometimes

999
00:49:20,320 --> 00:49:23,840
Speaker 1: the probabilities are more classical instead of quantum mechanical. Quantum

1000
00:49:23,880 --> 00:49:27,000
Speaker 1: coherence tells you, like, you know what's likely to happen.

1001
00:49:27,040 --> 00:49:31,040
Speaker 1: It doesn't explain why it collapses from two possibilities down

1002
00:49:31,040 --> 00:49:32,120
Speaker 1: to one actual thing.

1003
00:49:32,200 --> 00:49:34,600
Speaker 4: Mmmm. That's the tricky part.

1004
00:49:34,719 --> 00:49:37,239
Speaker 1: That's one of the tricky parts. That's the trickiest part.

1005
00:49:37,320 --> 00:49:39,080
Speaker 4: It's all tricky, but you have to get inside the

1006
00:49:39,080 --> 00:49:41,120
Speaker 4: box and then it's not tricky.

1007
00:49:41,200 --> 00:49:41,800
Speaker 1: Yeah, exactly.

1008
00:49:41,920 --> 00:49:44,760
Speaker 4: Then you understand or you don't understand, just like the cat.

1009
00:49:44,719 --> 00:49:46,680
Speaker 1: Yeah exactly. If you want quant mechanics to go away,

1010
00:49:46,800 --> 00:49:49,680
Speaker 1: just you know, only work on big complicated systems. Where

1011
00:49:49,719 --> 00:49:52,239
Speaker 1: those effects don't appear because they're all decoherent.

1012
00:49:52,520 --> 00:49:55,640
Speaker 4: All right, Well, we hope you enjoyed dad and got

1013
00:49:55,680 --> 00:49:59,160
Speaker 4: a better sense of quantum mechanics. Thanks for joining us,

1014
00:50:00,160 --> 00:50:00,919
Speaker 4: See you next time.

1015
00:50:08,840 --> 00:50:11,640
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

1016
00:50:11,680 --> 00:50:15,640
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1017
00:50:15,719 --> 00:50:20,360
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