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Speaker 1: Imagine you're taking a test. You sit down, pencils sharpened,

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Speaker 1: and your nice notepad, ready to bend your mind to

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Speaker 1: the task. Your goal for each question is, of course,

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Speaker 1: to find the answer, because every question has an answer

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Speaker 1: one that just needs to be revealed or discovered. And

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Speaker 1: whether you get question seventeen right shouldn't depend on your

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Speaker 1: answer to question thirty eight or whether the test writers

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Speaker 1: included question ten or cut it, because that's just how

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Speaker 1: tests work. They have fixed, predetermined answers, and that's how

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Speaker 1: most of us think that the universe works. Something happens,

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Speaker 1: and it's our goal to figure out what happened and why.

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Speaker 1: Doesn't matter what order you ask the questions or what

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Speaker 1: other questions you asked, the answers are all ready set.

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Speaker 1: Stuff happened. But the universe is quantum mechanical, it works differently.

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Speaker 1: The answer to a question, the result of a physics

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Speaker 1: measurement does actually depend on which other measurements you've made.

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Speaker 1: But this is not because of the famous Heisenberg n

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Speaker 1: certainty principle or quantum fuzziness, or because measurements disturb the system.

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Speaker 1: It's because fundamentally, quantum systems don't have a ground truth

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Speaker 1: a bedrock reality. Even if you avoid the Heisenberg uncertainty principle.

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Speaker 1: Quantum measurements are contextual. They depend on the context the

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Speaker 1: other measurements you've made in a way that our classical

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Speaker 1: brains really struggle to into it. The answer to quantum

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Speaker 1: question seventeen does depend on your answer to question thirty eight.

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Speaker 1: Welcome to Daniel and Kelly's extraordinarily contextual universe. Hello.

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Speaker 2: I'm Kelly Wiener Smith.

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Speaker 3: I study parasites and space, and today we are in

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Speaker 3: for a really incredible explanation from Daniel.

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Speaker 2: Why are you laughing?

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Speaker 1: Daniel, Wow, would have set me upisode early in.

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Speaker 2: The episode, setting the bar high.

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Speaker 1: Hi, I'm Daniel. I study particles and aliens, and I

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Speaker 1: do my best to understand quant mechanics and to explain

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Speaker 1: all of it to you.

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Speaker 3: That's right, and quantum mechanics can be pretty tough to understand,

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Speaker 3: but we are lucky to have Daniel to explain it

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Speaker 3: to us. And so today we're talking a lot about measurements.

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Speaker 3: And so I was wondering, as a scientist, Daniel, what

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Speaker 3: is the hardest thing that you have had to try

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Speaker 3: to measure?

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Speaker 1: Oh? My gosh, the hardest thing that I've tried to measure.

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Speaker 2: I guess it's a guy, have you I'm.

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Speaker 1: Not a theory guy. What as a theory guy? Oh

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Speaker 1: that hurts.

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Speaker 4: Oh that hurts.

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Speaker 1: Oh I'm experimentalists.

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Speaker 2: Okay, never mind, I pull it back.

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Speaker 1: I pull No. Well, that's fascinating because I get that

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Speaker 1: a lot. Even some people in my department I discovered

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Speaker 1: thought that I was a particle theorist, and I was like,

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Speaker 1: what are you talking about? Remember that time I was

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Speaker 1: away Tocern for two years to work on the experiment.

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Speaker 1: I don't know what it is. I just give off

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Speaker 1: theory vibes or something like Daniel doesn't seem like he

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Speaker 1: could work with his hands? Is that what's going on?

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Speaker 3: You know? Okay, So in retrospect I realized, I I

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Speaker 3: don't know why I said that, because I know you

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Speaker 3: work Ancern. You've had my family get a tour of cern.

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Speaker 3: But I guess so in my field though, when when

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Speaker 3: you mean when we say we work with our hands,

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Speaker 3: we mean we are up to our knees in mud

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Speaker 3: and dirts. But when you all work with your hands,

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Speaker 3: you get like data sent through the internet and it

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Speaker 3: shows up on your computer, and so I still feel

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Speaker 3: like you're like theoretically dealing with particles.

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Speaker 2: I see, but that's not fair of me. Sorry.

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Speaker 1: Would you be more impressed if I had to like

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Speaker 1: pull on elbow length of gloves before I sat down

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Speaker 1: on my computer to make a measurement?

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Speaker 3: Man, at least, then you're like imagining you could get messy.

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Speaker 3: But I'm sorry, you're an experimentalist.

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Speaker 1: No, it's fine, it's fine.

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Speaker 3: Well.

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Speaker 1: As an example, the measurement that I did when I

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Speaker 1: was a postoc so after I got my PhD and

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Speaker 1: before I was the professor, was trying to make a

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Speaker 1: very precise measurement of the mass of the top quark.

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Speaker 1: And that's hard because the top quark doesn't last very long,

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Speaker 1: and so you never see it directly. You only see

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Speaker 1: the stuff it blows up into, and you have to

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Speaker 1: make measurements of that and then infer what was the

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Speaker 1: top quark mass. And there's all sorts of stuff that

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Speaker 1: makes that measurement fuzzy. And some of the work of

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Speaker 1: experimental physics is how to make that measurement more clean,

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Speaker 1: how to remove those sources of fuzziness so we get

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Speaker 1: the most information from the universe. And so me and

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Speaker 1: my colleagues invent a new statistical technique to extract as

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Speaker 1: much information as possible from the data and to reduce

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Speaker 1: our sensitivity to some sources of uncertainty, so we could

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Speaker 1: force the universe to reveal information to us. And to me,

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Speaker 1: that's the heart of experimental science. I mean, being a

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Speaker 1: theorist requires cleverness and creativity and sort of mathematical chops.

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Speaker 1: Being an experimentalist means figuring out ways to force the

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Speaker 1: universe to reveal its answer to you. That's what an

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Speaker 1: experiment is really is setting up a situation where if

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Speaker 1: the truth is A, then something happens, and if the

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Speaker 1: truth is be, something else happens, and you can tell

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Speaker 1: the difference. So yeah, that's maybe the hardest measurement I

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Speaker 1: ever did, and that's what got me my job here

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Speaker 1: at Earth Line Well.

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Speaker 3: But it still sounds to me like to get your

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Speaker 3: answer you needed mathematical or maybe statistical chops, because what

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Speaker 3: you did was figure out a new statistical technique.

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Speaker 2: It wasn't like put on the glove. But it still counts.

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Speaker 2: It still counts.

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Speaker 1: Wow, I feel like interviewing from my job all over again.

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Speaker 2: You get the job, Daniel Well.

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Speaker 1: Let me say a couple of things about that. Particle

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Speaker 1: physics has really big collaborations, which means that everybody does

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Speaker 1: their bit, and they all get to do their favorite bit.

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Speaker 1: So there's some folks who really like climbing around the

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Speaker 1: detector with bolts and screwdrivers and getting dirty and wearing gloves,

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Speaker 1: and they get to do their bit, and they think

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Speaker 1: that's the most important bit, and some of us get

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Speaker 1: to nerd out about the statistics and we think that's

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Speaker 1: the most important bit. And so you know, I think

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Speaker 1: specialization is progress and I'm a fan of that. And

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Speaker 1: so I get to work on the thing that to

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Speaker 1: me is the most interesting, and everybody else gets to

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Speaker 1: work on the thing that they think is the most interesting.

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Speaker 1: So yeah, that's my contribution. And it is statistical and

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Speaker 1: it is computational, but I think it's also still experimental.

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Speaker 3: Yes, And I'm not going to argue with you at all.

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Speaker 3: I'm totally giving you that just for comparison. Though.

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Speaker 1: Your tone is the tone that you use when you're

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Speaker 1: like talking to a crazy old man and you don't

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Speaker 1: want to anger him.

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Speaker 2: No. No, maybe when I'm talking to my kids, but.

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Speaker 1: No, I'm definitely getting Kelly's mom voice.

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Speaker 2: Well, I think this is just a culture difference.

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Speaker 3: Okay, So let me tell, okay, the hardest thing I

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Speaker 3: ever had to measure. So you might remember in the

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Speaker 3: Zombie Fish episode, I talked about how there's a free

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Speaker 3: living stage of the parasite I study that emerges from

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Speaker 3: snails in salt marshes and swims around to look for fish.

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Speaker 3: I was trying to figure out if there were parts

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Speaker 3: of a salt marsh where you'd find more of those parasites,

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Speaker 3: Like were they clumping and forming dense clouds at the

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Speaker 3: top of the water, where they kind of near the bottom.

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Speaker 3: Were they in some parts of the salt marsh more

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Speaker 3: than others? And so some engineering students had developed this

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Speaker 3: device that would like suck little bits of water out

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Speaker 3: of different heights of the water column. And I was

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Speaker 3: supposed to move it from one part of the salt

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Speaker 3: marsh to another and like suck little water samples out

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Speaker 3: and then civet and die what I got and try

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Speaker 3: to find and count the parasite. So I could figure out, well,

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Speaker 3: where are the parasites, where do you find the most

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Speaker 3: of them? Where is it riskiest for the fish?

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Speaker 1: So what was especially hard about this measurement.

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Speaker 3: Anytime I would try to take a little water sample,

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Speaker 3: I was creating too much turbulence. These parasites are very

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Speaker 3: delicate and they would get ripped to shreds, and so

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Speaker 3: I could never get them intact enough so that I

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Speaker 3: could count them. And the other problem is that I

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Speaker 3: needed iodine to try to dye them.

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Speaker 2: And it turns out iodine is.

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Speaker 3: A controlled substance, oh, in very high quantities, which I

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Speaker 3: didn't know, And so I had to get all of

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Speaker 3: this like security access, and I couldn't get it done

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Speaker 3: by the end of the summer. So anyway, I was

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Speaker 3: in salt marshes trying to count parasites and it just

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Speaker 3: wasn't working for me. And so I imagine measurements require

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Speaker 3: like mud and security clearance and stuff like that.

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Speaker 1: Oh okay, well, I can tell you a similar story. Before

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Speaker 1: I became a particle physicist, I was trying to be

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Speaker 1: a condensed matter physicist and I spent a summer in

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Speaker 1: a basement working with a laser. And this laser has

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Speaker 1: like seventy five components to it, each of which works

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Speaker 1: like ninety eight percent of the time, which means the

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Speaker 1: laser never works. Oh no, because there's always something broken.

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Speaker 1: I spent the whole summer repairing this laser and tweaking

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Speaker 1: this and then tweaking that and the other thing. And

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Speaker 1: I think we got like nineteen seconds in the whole

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Speaker 1: summer when everything was working, and we got a little

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Speaker 1: bit of data. And some people love that and they're like, ooh,

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Speaker 1: this is really fun. We get to debug the laser.

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Speaker 1: My reaction was like, this is really frustrating and annoying,

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Speaker 1: which is why I didn't go into condensed matter experiment.

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Speaker 1: And I prefer, you know, digital puzzles. And I don't

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Speaker 1: say that to be negative about people who do that

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Speaker 1: kind of experiment, just as an example of like, hey,

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Speaker 1: this is very personal. What's frustrating and no fun for

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Speaker 1: one person is an exciting challenge for somebody else. And

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Speaker 1: that's why curiosity and science is so personal. And we

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Speaker 1: have people who go into parasites and other people who

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Speaker 1: go into particles and that's wonderful.

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Speaker 2: I totally agree.

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Speaker 3: And Daniel is super excited about mechanics and measuring quantum

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Speaker 3: phenomena and he's going to tell us all about it today.

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Speaker 3: And so today we're going to learn about quantum contextuality exactly.

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Speaker 1: An excellent job with a transition. Thank you very much

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Speaker 1: Kelly for keeping track.

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Speaker 3: Yes, I mean I took us about ten minutes off

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Speaker 3: off path, but I'm bringing us back eventually.

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Speaker 1: But I'm very excited to talk about this topic today

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Speaker 1: because it's something very few people have heard about. I

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Speaker 1: think at the pop side level. You know, we've heard

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Speaker 1: about quantum mechanics. We've heard about measurement and quantum mechanics.

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Speaker 1: We've heard about uncertainty and the challenge of how one

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Speaker 1: measurement can upset another measurement. That's not what quantum contextuality

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Speaker 1: is about. It's a deeper concept in quantum mechanics which

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Speaker 1: you've probably learned about without realizing about it when we

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Speaker 1: talked about Bell's theorem. But we're going to go to

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Speaker 1: the heart of the matter today and it's going to

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Speaker 1: show you something fundamental about quantum mechanics beyond the Heisenberg

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Speaker 1: uncertainty principle.

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Speaker 3: Is this the kind of thing where folks should go

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Speaker 3: back and listen to our episode on Bell's Theorem before

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Speaker 3: listen to this one, or are we gonna summarize it

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Speaker 3: enough that they'll be fine.

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Speaker 1: We'll give an encapsulated explanation of Bell's experiment. But Bell's

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Speaker 1: experiment is just one example of quantum contextuality. But it's

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Speaker 1: not actually the greatest example of it. So we're going

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Speaker 1: to talk about other measurements. But before we dig into it,

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Speaker 1: I was wondering how much people knew about quantum contextuality.

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Speaker 1: It's always wonderful for me to get sort of a

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Speaker 1: level of understanding out there. What do people think? What

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Speaker 1: do they already know, so we can aim these episodes

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Speaker 1: at the right level and get you the best possible understanding.

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Speaker 1: If you'd like to participate for future episodes, please don't

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Speaker 1: be shy. Write to us questions at Danielankelly dot org.

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Speaker 1: You can throw your guesses into the mix. So think

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Speaker 1: about it for a minute. Do you know what quantum

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Speaker 1: contextuality is? Here's what listeners had to say, Well, I

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Speaker 1: have no idea.

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Speaker 2: Sounds like the name for a new book. I had

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Speaker 2: no idea what quantum contextuality is.

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Speaker 4: When you finally explain quantum mechanics in a way that

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Speaker 4: all of us can understand. I have ever heard the

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Speaker 4: phrase quantum contextuality, but taking from context, I would imagine

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Speaker 4: it is a theory that talks about how the rules

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Speaker 4: governing quantum systems can change depending on the context that

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Speaker 4: system finds itself in.

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Speaker 5: I have no idea, but I think I would say

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Speaker 5: that it's some scene that you try to mention at

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Speaker 5: the quantum level. I think that would be my best guess.

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Speaker 1: Maybe it's trying to find the line between quantum and classical,

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Speaker 1: like when it's in which context.

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Speaker 4: I'm just going to guess that it's a way to

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Speaker 4: specify what quantum someone's talking about in science fiction movies.

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Speaker 3: All right, Well, if listener questions are meant to help

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Speaker 3: you understand where you should start, it sounds like you

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Speaker 3: should start at the beginning. And I appreciate that the

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Speaker 3: listeners are at the same point that I am. Thank

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Speaker 3: you everybody, and so yeah, Daniel, where do we start.

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Speaker 1: Let's start by remembering what measurement is and focusing in

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Speaker 1: on this. You know, every time we dig into the

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Speaker 1: philosophy is something you always got to start with crisp definitions,

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Speaker 1: so we know what are we talking about. Let's use

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Speaker 1: language in a clear way, and let's start with something

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Speaker 1: that's intuitive, which is measurement in classical systems, just like

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Speaker 1: in your ordinary everyday life when you go out to

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Speaker 1: measure something. You're measuring the number of parasites or the

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Speaker 1: amount of seawater or something. You imagine that there's an

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Speaker 1: answer there. The world is a certain way, and you're

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Speaker 1: just measuring it. You're observing it. Observation and measurement in

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Speaker 1: a classical world is sort of passive. You're just gathering information.

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Speaker 1: You're not changing the world. It's revelation, it's not interaction, right,

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Speaker 1: you're not messing with it. Like if you go out

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Speaker 1: and you measure somebody's height, right, Okay, Daniel is five

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Speaker 1: to ten or whatever, and then you measure Daniel's weight. Right.

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Speaker 1: The order in which you make these measurements doesn't matter.

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Speaker 1: It doesn't matter if you measure weight first and then height,

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Speaker 1: or height and then weight, because there's an answer to

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Speaker 1: each of them. Right. There is a number that reflects

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Speaker 1: my height, there's a number that reflects my weight, and

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Speaker 1: all we're doing is trying to measure it. And maybe

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Speaker 1: somebody comes along and invents a new statistical technique to

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Speaker 1: make it more precise or whatever. But there is a

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Speaker 1: truth there that we're aiming for. All right, still with me?

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Speaker 2: Totally intuitive?

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Speaker 1: Yep? Okay, yes, So that's the way classical systems work. Right,

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Speaker 1: measurements are non contextual. In a classical system, it doesn't

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Speaker 1: matter the context, what other measurements you've made, the order

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Speaker 1: in which you make the measurements. Right, Classical systems are

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Speaker 1: non contextual. All right. Now, let's talk about quantum systems,

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Speaker 1: and the quantum system measurement requires interaction. It's not like

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Speaker 1: you can just sit back and gather information about a

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Speaker 1: quantum system. In order to gather information, you have to

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Speaker 1: probe the system. You have an electron flying along. You

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Speaker 1: want information about that electron, you have to gather up

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Speaker 1: particles that have been emitted by that electron or have

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Speaker 1: bounced off of that electron, Like maybe the electron is

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Speaker 1: turning and so it emits photons which you gather, and

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Speaker 1: then you can use that to know something about where

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Speaker 1: the electron was or what its velocophy was, or you

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Speaker 1: can shoot photons at the electron to deflect it. Right.

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Speaker 1: In every case, you're interacting with the system in order

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Speaker 1: to gather information from it.

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Speaker 3: So I'm going to go ahead and try to make

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Speaker 3: this way more complicated, just in case there are other

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Speaker 3: people out there like me who are trying to overcomplicate things.

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Speaker 3: But you know, like so when I'm when I go

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Speaker 3: to the doctor's office and they make me stand on

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Speaker 3: the thing to get my height, Like you know, there

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Speaker 3: are photons that are you know, like bouncing off of

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Speaker 3: the meter stick and into the eyes of the person

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Speaker 3: who's making the measurement. Yeah, is that in any way

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Speaker 3: analogous to what you're talking about? Or no, because it's

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Speaker 3: much more interactive in this second case.

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Speaker 1: No, it's a great question, and it goes to the

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Speaker 1: heart of like the quantum mechanical measurement problem because essentially

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Speaker 1: you're saying, Hey, can't I think about the classical measurement

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Speaker 1: in a quantum way? Isn't it really the same, because

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Speaker 1: even a classical measurement requires photons bouncing off of things

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Speaker 1: like if I'm reading off the scale, somebody has to

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Speaker 1: shine a light on the scale, right, And you're absolutely right,

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Speaker 1: And because everything is quantum in the end, but in

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Speaker 1: the classical system, we're assuming that all of those quantum

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Speaker 1: effects cancel out, that they average out, that your height

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Speaker 1: or your weight is not affected by the measurement at all.

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Speaker 1: And that's mostly true for classical systems, right, Like, yes,

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Speaker 1: photons do push on the scale, and that might change

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Speaker 1: the measurement, but not within the level at which we're

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Speaker 1: talking about. So those quantum effects can be ignored for

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Speaker 1: a classical system because when you zoom out, they average

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Speaker 1: out and they go away. But for a tiny system

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Speaker 1: they're really important and they cannot be ignored. So that's

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Speaker 1: really the distinction.

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Speaker 2: Okay, great, what's next.

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Speaker 1: Cool? And so when you dig into these quantum systems,

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Speaker 1: you have to give up your classical intuition, this feeling

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Speaker 1: that you're just observing passively the universe. You're interacting with it.

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Speaker 1: You're changing it, right, and so you can't measure something

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Speaker 1: without changing it. And we're we're used to this because

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Speaker 1: we already know about things like the Heisenbergen certainty principle

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Speaker 1: that if you measure the position of an electron, that

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Speaker 1: you can't also know it's momentum very precisely because those

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Speaker 1: two things are coupled in quantum mechanics. And that's not

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Speaker 1: what we mean by contextuality. It's not the topic of

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Speaker 1: today's episode, but let's just explain it really briefly so

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Speaker 1: that people understand what the Heisenbergen certainty principle does and

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Speaker 1: doesn't say. So we don't get confused later. The Heisenberg

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Speaker 1: and certainty principle says that certain pairs of measurements the

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Speaker 1: order does matter. So like position and momentum. If you

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Speaker 1: measure momentum, it changes the position. If you measure the position,

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Speaker 1: it changes the momentum. These things are coupled, and they're

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Speaker 1: coupled in this very specific way. Like also energy is

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Speaker 1: coupled to time, or spin in one axis is coupled

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Speaker 1: to spin in another axis. And the Heisenberg and certainty

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Speaker 1: principle doesn't say, like, you measure one of these things

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Speaker 1: and they all change. It says that there's specific relationships.

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Speaker 1: So you measure position and momentum changes doesn't change spin

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Speaker 1: or doesn't change energy, doesn't change time. Position and momentum

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Speaker 1: are linked, energy and time are linked. There are these

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Speaker 1: Heisenberg pairs, okay, And that's a fuzziness that's inherent in

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Speaker 1: quant mechanics. And it's another example of how classical measurements

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Speaker 1: are different from quantum measurements, right, And it gets you

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Speaker 1: part of the way, sort of philosophically or intuitive to

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Speaker 1: accepting that quantum mechanics describes a world that sort of

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Speaker 1: can't be pinned down. But there's another layer to that,

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Speaker 1: the sense that quantum measurements are contextual even if you

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Speaker 1: remove Heisenberg uncertainty, or if you avoid making measurements of

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Speaker 1: quantities that are paired by Heisenberg uncertainty principle, Even if

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Speaker 1: you avoid all of that uncertainty, there's still a contextual

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Speaker 1: nature to quantum measurements, meaning that the measurements you make

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Speaker 1: depend on the other measurements you have made. The answer

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Speaker 1: to question eighteen on the test depends on the answer

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Speaker 1: to sixteen and to fourteen, not because of Heisenberg uncertainty principle,

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Speaker 1: but because quantume CANAI does not describe a bedrock ground

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Speaker 1: truth to the universe. The answer you get follows a

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Speaker 1: bunch of rules and constraints, but there's no way to

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Speaker 1: satisfy all of the constraints simultaneously. There is no ground

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Speaker 1: truth that's being revealed. You're just interacting with the system

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Speaker 1: and you're getting one view of it.

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Speaker 3: Let me just okay, so for the ground truth thing thing,

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Speaker 3: let me just try to understand so, like you know,

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Speaker 3: in quantum mechanics, things could be in a couple different states,

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Speaker 3: and so when you say there's not like a ground truth.

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Speaker 3: But when you look at something at one moment, it

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Speaker 3: collapses to one state. Aren't you seeing like the ground

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Speaker 3: truth of what's happening like at that moment after you've

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Speaker 3: interacted with it, even if you're only seeing one piece

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Speaker 3: of the whole truth, is that still not a truth?

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Speaker 3: Why is that not a ground truth? Or am I

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Speaker 3: just getting tied up in the language.

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Speaker 1: That's a really good point, and let's pull that apart.

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Speaker 1: You're right that once you've collapse the state, once you've

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Speaker 1: made a measurement, there is a state in which the

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Speaker 1: system is in. Right, by the point of quantum contextuality,

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Speaker 1: is that measurement you've made depends on other measurements that

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Speaker 1: have already been made, and there's no ground truth before

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Speaker 1: you make the measurement that determines the measurement. Right, The

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Speaker 1: measurement depends not on the ground truth, but on the

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Speaker 1: other measurements you've made. And we'll dig into that in

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Speaker 1: more detail when we talk about Bell's experiment and non

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Speaker 1: locality and how that's an example of contextuality and quantum mechanics.

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Speaker 3: Well, then let's take a break and go ahead and

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Speaker 3: jump right into that.

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Speaker 2: When we get back.

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Speaker 3: And we're back, and let's go ahead and start by

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Speaker 3: jumping into a refresher on Bell's experiments.

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Speaker 1: So Bell's theorem and the experiments to test it are

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Speaker 1: a great example of how we know that quantum mechanics

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Speaker 1: is non local and really random. If you remember, the

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Speaker 1: setup is that you have a particle and it decays

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Speaker 1: into two particles, and because the two particles were produced together,

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Speaker 1: they're correlated. They have to satisfy some constraints like if

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Speaker 1: one is spin up, the other one is spinned down,

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Speaker 1: or if one is charged plus, the other one has

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Speaker 1: to be charged minus. You know, there's some quantum mechanical

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Speaker 1: rule that's applied there that says there's a connection between

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Speaker 1: the two and that correlation is local when the two

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Speaker 1: particles are created. But then the particles can drift apart, right,

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Speaker 1: and they can be miles away, one in California and

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Speaker 1: one in Virginia, But that correlation is preserved if you've

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Speaker 1: been really careful aby keeping them isolated. And the confusing

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Speaker 1: thing about quantum mechanics is that it says that the

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Speaker 1: particle's actual state doesn't exist. It's not like my particle

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Speaker 1: is spin up and Kelly's is spinned down and it's

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Speaker 1: just waiting for us to measure it. That would be

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Speaker 1: the classical of you that there's some thing that has

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Speaker 1: determined it. But instead, my particle has a chance to

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Speaker 1: be spin up or a chance to be spinned down,

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Speaker 1: and Kelly's has a chance to be spinned up and

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Speaker 1: a chance to be spinned down. And it's not till

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Speaker 1: I make my measurement that Kelly's particle is determined. Right,

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Speaker 1: This is what Bell's experiment is all about. Is it

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Speaker 1: really true that there's no hidden information there really controlling

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Speaker 1: the outcome? There's no ground truth that just depends on

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Speaker 1: the measurement. And so in the language contextuality, does Kelly's

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Speaker 1: measurement depend on my measurement? There's no like actual truth

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Speaker 1: to her particle? Or is there some hidden variable that

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Speaker 1: we just haven't measured yet? And Bell's theorem is a

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Speaker 1: way to test that, to distinguish between the two hypotheses.

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Speaker 1: One that there's some hidden variable, some ground truth to

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Speaker 1: the experiment that's controlling everything. We just haven't sensed it,

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Speaker 1: or there isn't And Bell's experiment is really clever, but

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Speaker 1: a little bit subtle, because there's no like one shot

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Speaker 1: experiment a smoking gun that proves that the particles were

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Speaker 1: not determined, that there's no hidden variable there. It's instead

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Speaker 1: about correlations. Bell's experiment works because you can't just measure

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Speaker 1: it along one axis, where it'd be hard to tell,

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Speaker 1: like was my particle actually determined before I measured it?

436
00:23:14,240 --> 00:23:16,640
Speaker 1: Or does it depend on whether or not Kelly has

437
00:23:16,680 --> 00:23:20,359
Speaker 1: made her a measurement. You pick three different axes, and

438
00:23:20,400 --> 00:23:24,080
Speaker 1: it relies on the correlations of the measurements across those axes.

439
00:23:24,480 --> 00:23:27,000
Speaker 1: So Kelly and I both pick three axes, and then

440
00:23:27,040 --> 00:23:30,359
Speaker 1: at random we choose which access we're going to measure,

441
00:23:30,760 --> 00:23:34,320
Speaker 1: and then we compare results. And quantum mechanics gives one

442
00:23:34,359 --> 00:23:38,560
Speaker 1: prediction for how correlated our answers should be and hidden variables.

443
00:23:38,560 --> 00:23:42,600
Speaker 1: A classical theory gives a different prediction. And so again,

444
00:23:42,720 --> 00:23:44,879
Speaker 1: it's not like one measurement you're making. We're like I

445
00:23:44,920 --> 00:23:47,520
Speaker 1: got up, you got down? What does that mean? Nothing?

446
00:23:47,880 --> 00:23:50,280
Speaker 1: It's about the patterns of ups and downs when we

447
00:23:50,359 --> 00:23:53,960
Speaker 1: measure along different axes or similar axis or related axes.

448
00:23:54,280 --> 00:23:57,040
Speaker 1: That's why the experiment is so subtle and so powerful

449
00:23:57,080 --> 00:23:57,960
Speaker 1: and so clever.

450
00:23:58,480 --> 00:24:04,399
Speaker 3: Okay, and the results suggests that there aren't hidden variables.

451
00:24:04,440 --> 00:24:06,520
Speaker 3: When it's all said and done, that's right, And so

452
00:24:06,560 --> 00:24:10,200
Speaker 3: does that suggest that there is not contextuality?

453
00:24:10,440 --> 00:24:11,560
Speaker 2: Is that the connection here?

454
00:24:11,640 --> 00:24:15,480
Speaker 1: So that suggests the opposite. It suggests that there is contextuality. Right.

455
00:24:15,640 --> 00:24:19,120
Speaker 1: Then it tells you that there's no way to preassign

456
00:24:19,600 --> 00:24:22,440
Speaker 1: spin to all the particles that are going to satisfy

457
00:24:22,560 --> 00:24:26,440
Speaker 1: all of the measurements. Right, there's no like actual value

458
00:24:26,840 --> 00:24:29,400
Speaker 1: of these things that you can preassign in advance. That's

459
00:24:29,400 --> 00:24:31,960
Speaker 1: going to say, here, I can determine without knowing what

460
00:24:32,040 --> 00:24:35,440
Speaker 1: Daniel measures. I can determine what Kelly's going to measure. Right.

461
00:24:35,440 --> 00:24:38,400
Speaker 1: There's no information that's carried along with the particles that's

462
00:24:38,400 --> 00:24:40,560
Speaker 1: going to determine what Kelly's going to measure. It depends

463
00:24:40,600 --> 00:24:43,240
Speaker 1: on Daniel's measurement. Has he made his measurement or not?

464
00:24:43,400 --> 00:24:46,359
Speaker 1: What is the outcome of Daniel's measurement. There's no local

465
00:24:46,400 --> 00:24:50,240
Speaker 1: hidden variable that can meet all the requirements, right, Okay,

466
00:24:50,280 --> 00:24:52,760
Speaker 1: So what this tells us is that the measurement is

467
00:24:52,840 --> 00:24:56,160
Speaker 1: non local. That's usually the focus of understanding Bell's experiment,

468
00:24:56,359 --> 00:24:59,240
Speaker 1: the weirdness of quantum mechanics. That Kelly's measurement depends on

469
00:24:59,320 --> 00:25:02,840
Speaker 1: Daniel's measure and that's really cool. But in the context

470
00:25:02,840 --> 00:25:06,840
Speaker 1: of this conversation, let's reinterpret that. Let's interpret it as

471
00:25:06,960 --> 00:25:11,520
Speaker 1: Kelly's measurement depends on its quantum context, and in this case,

472
00:25:11,520 --> 00:25:15,280
Speaker 1: it's quantum context is Daniel's measurement, right, And that's this

473
00:25:15,400 --> 00:25:19,560
Speaker 1: question of contextuality. Your measurement depends on other measurements because

474
00:25:19,600 --> 00:25:21,880
Speaker 1: of constraints, you know, like one has to be spin

475
00:25:22,000 --> 00:25:24,239
Speaker 1: up and the other has to be spinned down. And

476
00:25:24,280 --> 00:25:27,359
Speaker 1: in a classical world, you can satisfy these constraints just

477
00:25:27,400 --> 00:25:29,000
Speaker 1: by like, well, I'm going to sign one to be

478
00:25:29,040 --> 00:25:31,480
Speaker 1: spin up and another one to be spinned down. But

479
00:25:31,600 --> 00:25:34,880
Speaker 1: in these systems, there is no way to satisfy all

480
00:25:34,920 --> 00:25:38,480
Speaker 1: of the measurements by making these pre assigned values. Just

481
00:25:38,520 --> 00:25:42,280
Speaker 1: like in Bell's experiment, any individual test you could explain

482
00:25:42,359 --> 00:25:44,760
Speaker 1: by assigning a spin up or spin down in advance.

483
00:25:45,000 --> 00:25:48,600
Speaker 1: But the pattern across these many experiments, that's smoking gun

484
00:25:49,040 --> 00:25:52,240
Speaker 1: of no hidden variables of the quantum nature cannot be

485
00:25:52,359 --> 00:25:56,080
Speaker 1: explained by any assignment of hidden variables. There's no ground

486
00:25:56,119 --> 00:26:00,960
Speaker 1: to truth there. The measurements depend not on some rock reality,

487
00:26:01,320 --> 00:26:04,160
Speaker 1: but on the other measurements that have been made.

488
00:26:04,560 --> 00:26:05,840
Speaker 2: Okay, I understand that.

489
00:26:06,320 --> 00:26:09,159
Speaker 3: And so now to take a step back and connect

490
00:26:09,240 --> 00:26:12,640
Speaker 3: what you said about the Heisenberg enn certainty principle being

491
00:26:12,720 --> 00:26:15,720
Speaker 3: sort of an example of contextuality but not being an

492
00:26:15,720 --> 00:26:17,640
Speaker 3: example of contextuality.

493
00:26:17,840 --> 00:26:19,879
Speaker 1: No, that's a good point, though, because here there's no

494
00:26:19,960 --> 00:26:24,040
Speaker 1: Heisenbergen certainty principle. This is not an issue of measurements

495
00:26:24,040 --> 00:26:28,280
Speaker 1: commuting one fuzzing the other. My measurement of my particle

496
00:26:28,680 --> 00:26:31,119
Speaker 1: is not coupled by the Heisenbergen certainty to yours. That

497
00:26:31,160 --> 00:26:34,240
Speaker 1: doesn't mess up your measurement the way like measuring position

498
00:26:34,320 --> 00:26:37,399
Speaker 1: messes up momentum. Right, these two things we can both know.

499
00:26:37,960 --> 00:26:39,760
Speaker 1: I can know my particle spin and you can know

500
00:26:39,800 --> 00:26:42,680
Speaker 1: your particle spin. They're not fuzzed up by the Heisenberg

501
00:26:42,680 --> 00:26:46,320
Speaker 1: and certainty principle. The bizarreness here quantum mechanics is not

502
00:26:46,400 --> 00:26:48,879
Speaker 1: about the Heisenberg and certainty principle. It's about how my

503
00:26:49,040 --> 00:26:53,480
Speaker 1: measurement depends on your measurement. So Bell's experiment is the

504
00:26:53,480 --> 00:26:57,040
Speaker 1: most familiar example of contextuality, but it's a little bit

505
00:26:57,040 --> 00:26:59,359
Speaker 1: hard to tease out the contextuality from that one. So

506
00:26:59,560 --> 00:27:02,840
Speaker 1: let's take step back and try to build a classical

507
00:27:03,000 --> 00:27:06,920
Speaker 1: intuition for contextuality, and I think there are useful examples

508
00:27:06,920 --> 00:27:09,399
Speaker 1: that are easier to think about, maybe even familiar, that

509
00:27:09,440 --> 00:27:13,199
Speaker 1: are geographical, that I think help people understand what we

510
00:27:13,320 --> 00:27:14,600
Speaker 1: mean by contextuality.

511
00:27:15,000 --> 00:27:17,320
Speaker 3: Okay, I have a feeling I'm gonna end up thinking

512
00:27:17,560 --> 00:27:22,480
Speaker 3: we should have started here, and then we can and

513
00:27:22,520 --> 00:27:24,960
Speaker 3: then we can say, Kelly, why didn't you realize that

514
00:27:25,000 --> 00:27:26,280
Speaker 3: when you read the outline earlier?

515
00:27:26,320 --> 00:27:27,280
Speaker 2: But let's go Okay, let's go.

516
00:27:27,280 --> 00:27:29,040
Speaker 3: Ahead, and let's let's go ahead and start with the

517
00:27:29,080 --> 00:27:30,760
Speaker 3: easy example then, Daniel.

518
00:27:30,480 --> 00:27:33,040
Speaker 1: Because it's context dependent, right, you have to hear it first.

519
00:27:33,040 --> 00:27:34,280
Speaker 1: It depends on what I said.

520
00:27:34,440 --> 00:27:34,760
Speaker 2: Okay.

521
00:27:35,359 --> 00:27:38,800
Speaker 1: So imagine your job is to take a world map,

522
00:27:38,840 --> 00:27:41,199
Speaker 1: and you have the outlines of all the countries and

523
00:27:41,280 --> 00:27:45,680
Speaker 1: to color them. Okay, and you only have three colors, right,

524
00:27:45,800 --> 00:27:49,639
Speaker 1: you have blue, red, and green. Okay, And there are

525
00:27:49,680 --> 00:27:52,040
Speaker 1: no rules other than you have to color every country.

526
00:27:52,400 --> 00:27:55,880
Speaker 1: It doesn't matter what color you give the United States green, red, blue, whatever,

527
00:27:56,320 --> 00:28:00,359
Speaker 1: doesn't matter if adjacent countries have the same color. The

528
00:28:00,440 --> 00:28:02,520
Speaker 1: easy version of this game is just go and you

529
00:28:02,640 --> 00:28:06,200
Speaker 1: color right, And that's not a problem. You're going assign

530
00:28:06,320 --> 00:28:08,200
Speaker 1: every country a color. You can make the whole world green.

531
00:28:08,280 --> 00:28:10,359
Speaker 1: You can make the whole world blue. You can do

532
00:28:10,400 --> 00:28:13,000
Speaker 1: whatever you like, not a problem. You can give every

533
00:28:13,040 --> 00:28:15,480
Speaker 1: country a color, right, still with me?

534
00:28:15,880 --> 00:28:18,000
Speaker 2: Yeah, this is really easy, all right, easy so far.

535
00:28:18,200 --> 00:28:21,600
Speaker 1: Now, quantum mechanics adds constraints, right, if we're going to

536
00:28:21,680 --> 00:28:24,920
Speaker 1: make this a quantum measurement, there's always some rules here,

537
00:28:25,200 --> 00:28:27,520
Speaker 1: Like the way that my particle is spin up, then

538
00:28:27,560 --> 00:28:29,960
Speaker 1: yours has to be spinned down. Have to be opposites, right,

539
00:28:30,520 --> 00:28:33,000
Speaker 1: and so what let's add some constraints. And the typical

540
00:28:33,040 --> 00:28:35,280
Speaker 1: constraint when you're coloring a map is you don't want

541
00:28:35,320 --> 00:28:38,800
Speaker 1: adjacent countries to have the same color. It's confusing. Yeah, right,

542
00:28:38,840 --> 00:28:40,800
Speaker 1: if a country is red, you want none of its

543
00:28:40,800 --> 00:28:42,920
Speaker 1: neighbors to be red, because otherwise it's hard to tell

544
00:28:42,960 --> 00:28:46,040
Speaker 1: when it ends. Right, And this is a famous problem

545
00:28:46,080 --> 00:28:49,200
Speaker 1: in map coloring. Right, how many colors does it take

546
00:28:49,600 --> 00:28:51,840
Speaker 1: to color a two dimensional map and then have no

547
00:28:51,920 --> 00:28:54,960
Speaker 1: adjacent countries have the same color? Right? Really fun math

548
00:28:55,000 --> 00:28:57,320
Speaker 1: puzzle that Actually as a kid, I spent a lot

549
00:28:57,320 --> 00:28:59,720
Speaker 1: of time trying to come up with maps that required

550
00:28:59,760 --> 00:29:02,440
Speaker 1: more than four colors. But it's an interesting thing that

551
00:29:02,480 --> 00:29:06,040
Speaker 1: with four colors you can color every single country and

552
00:29:06,120 --> 00:29:08,600
Speaker 1: have no neighbors have the same color, so you need

553
00:29:08,640 --> 00:29:09,360
Speaker 1: four colors.

554
00:29:09,760 --> 00:29:12,240
Speaker 2: So with me, you're the right kind of nerd. Daniel.

555
00:29:14,360 --> 00:29:17,160
Speaker 1: It's just so fun as a puzzle because one example

556
00:29:17,160 --> 00:29:17,800
Speaker 1: will misprove it.

557
00:29:17,880 --> 00:29:18,000
Speaker 5: Right.

558
00:29:18,000 --> 00:29:20,800
Speaker 1: There's this theorem that says four colors is enough to

559
00:29:20,840 --> 00:29:23,760
Speaker 1: color any map. So if any little seven year old

560
00:29:23,800 --> 00:29:26,280
Speaker 1: nerd comes with a map that you can't color, boom,

561
00:29:26,360 --> 00:29:28,480
Speaker 1: you disprove the whole theorem. So that seems to me

562
00:29:28,560 --> 00:29:30,200
Speaker 1: like an easy challenge, and I spend a lot of

563
00:29:30,200 --> 00:29:32,400
Speaker 1: time in the afternoons just like, what if I bend

564
00:29:32,400 --> 00:29:34,400
Speaker 1: this one and make a really narrow thing over here

565
00:29:34,400 --> 00:29:36,760
Speaker 1: and it loops around it anyway, Obviously I never figured

566
00:29:36,760 --> 00:29:39,080
Speaker 1: it out or would be much more famous. But in

567
00:29:39,120 --> 00:29:43,160
Speaker 1: this example, let's say somebody gives you the impossible task

568
00:29:43,560 --> 00:29:46,880
Speaker 1: of coloring a map with only three colors. So now

569
00:29:46,880 --> 00:29:49,040
Speaker 1: you have a map no adjacent countries can have the

570
00:29:49,080 --> 00:29:52,480
Speaker 1: same color, but you only have three colors, right, So

571
00:29:52,640 --> 00:29:55,200
Speaker 1: you can start by like, Okay, this one's green, I'm

572
00:29:55,240 --> 00:29:58,040
Speaker 1: going to make this neighbors red and blue. But eventually

573
00:29:58,040 --> 00:30:01,240
Speaker 1: you're going to run into a problem. No way to

574
00:30:01,440 --> 00:30:05,000
Speaker 1: color this map using only three colors, And so every

575
00:30:05,040 --> 00:30:06,520
Speaker 1: time you color a new country, you're gonna have to

576
00:30:06,600 --> 00:30:10,360
Speaker 1: change a previous country, right, And there's no global assignment

577
00:30:10,440 --> 00:30:13,680
Speaker 1: you can make. There's no solution. There's no perfect truth

578
00:30:13,880 --> 00:30:16,160
Speaker 1: where you can assign the right color to every country.

579
00:30:16,160 --> 00:30:18,600
Speaker 1: And then later Kelly comes along and asks, Daniel, oh,

580
00:30:18,680 --> 00:30:20,880
Speaker 1: what do you color turk Menistan? And I can tell

581
00:30:20,920 --> 00:30:25,480
Speaker 1: you right, the answer to turk Menistan depends on its neighbors.

582
00:30:25,960 --> 00:30:32,640
Speaker 3: Right, quantum mechanics is impossible. Stop trying, no.

583
00:30:31,440 --> 00:30:34,560
Speaker 1: No, no. What this tells you is that if you

584
00:30:34,640 --> 00:30:37,760
Speaker 1: have this constraint that adjacent countries can't have the same color,

585
00:30:37,800 --> 00:30:40,360
Speaker 1: and you only have three colors, then there is no

586
00:30:40,480 --> 00:30:44,360
Speaker 1: way to color the map right. There is no solution. Okay, Now,

587
00:30:44,440 --> 00:30:46,719
Speaker 1: you can have little local solutions. You can say, well,

588
00:30:46,720 --> 00:30:48,680
Speaker 1: i'm gonna color this one red and I'm gonna color

589
00:30:48,720 --> 00:30:52,440
Speaker 1: its neighbors differently, and that'll work for this over here.

590
00:30:52,680 --> 00:30:54,320
Speaker 1: But then if we want to color a different part

591
00:30:54,360 --> 00:30:56,360
Speaker 1: of the globe, we're gonna have to switch it up. Right.

592
00:30:56,440 --> 00:31:00,240
Speaker 1: I can't just give this country a fixed color because

593
00:31:00,240 --> 00:31:02,800
Speaker 1: there's no way to make a global assignment to all

594
00:31:02,840 --> 00:31:06,040
Speaker 1: the countries where every country has one of three colors,

595
00:31:06,440 --> 00:31:08,920
Speaker 1: and no neighboring countries have the same color. It takes

596
00:31:08,960 --> 00:31:11,640
Speaker 1: four colors to do that, so if you're given only three,

597
00:31:11,800 --> 00:31:13,120
Speaker 1: you just can't do it.

598
00:31:13,520 --> 00:31:17,880
Speaker 3: Okay, So now there's no one answer that works for everything,

599
00:31:18,520 --> 00:31:21,040
Speaker 3: and so you can get a local answer. But as

600
00:31:21,080 --> 00:31:24,719
Speaker 3: soon as you start looking somewhere else, then the local

601
00:31:24,800 --> 00:31:29,640
Speaker 3: answer that you had before change. So if Turkmenistan was

602
00:31:29,680 --> 00:31:33,000
Speaker 3: green before you understood what was happening with the electrons

603
00:31:33,040 --> 00:31:35,400
Speaker 3: that were over in the above the part of your

604
00:31:35,440 --> 00:31:38,280
Speaker 3: map where Turkmenistan was, and then you go over and

605
00:31:38,320 --> 00:31:41,760
Speaker 3: you look at what was happening above America? Does that

606
00:31:42,280 --> 00:31:45,040
Speaker 3: change the electrons or did you know, change what was

607
00:31:45,040 --> 00:31:49,320
Speaker 3: happening over above Turkmenistan. I'm like mixing metaphors now, but like,

608
00:31:49,760 --> 00:31:52,640
Speaker 3: does this make sense? Every time you measure electrons, does

609
00:31:52,680 --> 00:31:55,280
Speaker 3: that change everything about all the other electrons you've ever

610
00:31:55,320 --> 00:31:55,720
Speaker 3: looked at?

611
00:31:55,880 --> 00:31:58,920
Speaker 1: Ooh, yes, you are on the right track. Think again

612
00:31:58,960 --> 00:32:03,719
Speaker 1: about Turkmenistan? Does it have a fixed ground truth color?

613
00:32:04,240 --> 00:32:06,320
Speaker 1: Is there a color you can assign to it that

614
00:32:06,440 --> 00:32:09,720
Speaker 1: satisfies all of the quantum rules when you look at

615
00:32:09,720 --> 00:32:12,320
Speaker 1: its neighbors? Could you do that all the way across

616
00:32:12,360 --> 00:32:15,800
Speaker 1: the globe so that every country just has a single color. No,

617
00:32:16,000 --> 00:32:19,360
Speaker 1: you can't, not if you only have three colors. So

618
00:32:19,440 --> 00:32:22,960
Speaker 1: in that case, Turkmenistan doesn't have a single color. It

619
00:32:23,040 --> 00:32:25,600
Speaker 1: might have to be blue in the context where you

620
00:32:25,680 --> 00:32:29,280
Speaker 1: first colored its neighbor Afghanistan, or red if you first

621
00:32:29,280 --> 00:32:33,920
Speaker 1: colored Kazakhstan, etc. There's no global solution for everyone, And

622
00:32:33,960 --> 00:32:36,280
Speaker 1: so the answer what is the color of turk Ministan

623
00:32:36,400 --> 00:32:39,720
Speaker 1: depends on what else you have already colored. It has

624
00:32:39,760 --> 00:32:43,200
Speaker 1: to shift depending on what colors you've already chosen. That's

625
00:32:43,240 --> 00:32:46,760
Speaker 1: the context. That's why this is now a contextual issue.

626
00:32:47,280 --> 00:32:50,080
Speaker 1: So both sets of measurements satisfied the constraints, right. You

627
00:32:50,080 --> 00:32:52,800
Speaker 1: can't get some of the conflicts with itself the way

628
00:32:52,880 --> 00:32:54,800
Speaker 1: like if I get spin up, you have to get

629
00:32:54,840 --> 00:32:59,280
Speaker 1: spinned down, right, absolutely, But if I measure first or

630
00:32:59,320 --> 00:33:01,880
Speaker 1: you measure first, we might get different answers. Okay, But

631
00:33:02,000 --> 00:33:03,840
Speaker 1: if I measure it and then you measure it, your

632
00:33:03,880 --> 00:33:07,280
Speaker 1: measurement doesn't change my measurement, right, because we still have

633
00:33:07,360 --> 00:33:11,440
Speaker 1: to have a consistent result that satisfies the quantum mechanical constraints.

634
00:33:11,920 --> 00:33:15,960
Speaker 3: And this only depends on whether or not the electrons

635
00:33:16,120 --> 00:33:19,560
Speaker 3: are connected in some way, right, Because they don't have

636
00:33:19,680 --> 00:33:20,680
Speaker 3: to be that's right.

637
00:33:20,720 --> 00:33:24,160
Speaker 1: This only happens if there's a quantum mechanical constraint. Right

638
00:33:24,240 --> 00:33:26,800
Speaker 1: in our case, they're entangled and they come from the

639
00:33:26,840 --> 00:33:29,240
Speaker 1: same origin, and we're in the case of the map analogy,

640
00:33:29,280 --> 00:33:32,000
Speaker 1: we've imposed this artificial constraint. You're only allowed to use

641
00:33:32,040 --> 00:33:34,920
Speaker 1: three colors because we knew that. That made it impossible,

642
00:33:34,960 --> 00:33:37,240
Speaker 1: and that made it a good analogy. If you didn't

643
00:33:37,240 --> 00:33:39,280
Speaker 1: have that constraint, if you could do do any color

644
00:33:39,360 --> 00:33:41,760
Speaker 1: or whatever, you had an infinite number of colors, or

645
00:33:41,960 --> 00:33:45,760
Speaker 1: you didn't care about the neighbors, then this wouldn't apply, right, Okay,

646
00:33:45,800 --> 00:33:47,480
Speaker 1: But the idea here is to give you the intuition

647
00:33:47,880 --> 00:33:50,640
Speaker 1: that there are some problems where there is no global

648
00:33:50,640 --> 00:33:53,440
Speaker 1: solution and the answer you get for one country depends

649
00:33:53,440 --> 00:33:54,840
Speaker 1: on the countries you've done so far.

650
00:33:55,400 --> 00:33:56,160
Speaker 2: Got it? Got it?

651
00:33:56,200 --> 00:33:58,400
Speaker 3: So you know, I feel like this should be something

652
00:33:58,400 --> 00:34:00,239
Speaker 3: that makes sense to all of us. Because Kell has

653
00:34:00,280 --> 00:34:02,760
Speaker 3: been saying it depends on the show for such a

654
00:34:02,760 --> 00:34:06,280
Speaker 3: long time. We should have internalized this long ago.

655
00:34:06,680 --> 00:34:07,080
Speaker 2: Okay.

656
00:34:07,360 --> 00:34:10,520
Speaker 3: I feel like that map example has now totally clicked

657
00:34:10,520 --> 00:34:13,520
Speaker 3: for me. And let's take a break, and when we

658
00:34:13,600 --> 00:34:16,600
Speaker 3: come back, let's do another example looking at just a

659
00:34:16,640 --> 00:34:19,600
Speaker 3: single particle to try to make this all click even more.

660
00:34:39,400 --> 00:34:40,120
Speaker 2: All right, we are.

661
00:34:40,040 --> 00:34:44,560
Speaker 3: Talking about quantum contextuality on the show today, and we

662
00:34:44,680 --> 00:34:47,480
Speaker 3: are going through examples to try to make this complicated

663
00:34:47,520 --> 00:34:50,359
Speaker 3: idea click. And so now we're going to go through

664
00:34:50,400 --> 00:34:52,640
Speaker 3: a single particle example.

665
00:34:53,360 --> 00:34:54,000
Speaker 2: Go for it.

666
00:34:54,719 --> 00:34:57,600
Speaker 1: Yeah. So the cool thing about Bell's experiment, right, is

667
00:34:57,640 --> 00:35:01,000
Speaker 1: this connection between the particles. And it's famous because of

668
00:35:01,040 --> 00:35:06,080
Speaker 1: this business of entanglement. But contextuality doesn't require entanglement between

669
00:35:06,200 --> 00:35:10,400
Speaker 1: two particles. The weird thing about Bell's experiment is the

670
00:35:10,440 --> 00:35:13,560
Speaker 1: non locality, the fact that the two particle measurements depend

671
00:35:13,800 --> 00:35:16,440
Speaker 1: on each other. And you can actually set up quantum

672
00:35:16,480 --> 00:35:19,720
Speaker 1: systems that exhibit this weird behavior where one measurement depends

673
00:35:19,760 --> 00:35:22,920
Speaker 1: on another measurement and it's just a single particle. It

674
00:35:22,960 --> 00:35:27,240
Speaker 1: doesn't require entanglement across space and time. And that's helpful

675
00:35:27,239 --> 00:35:30,160
Speaker 1: because it shows you that it's not about entanglement. It's

676
00:35:30,200 --> 00:35:32,960
Speaker 1: actually something else. It's this contextuality.

677
00:35:33,280 --> 00:35:38,960
Speaker 3: Okay, And as a physics person who doesn't know all

678
00:35:38,960 --> 00:35:41,240
Speaker 3: the ins and out of the Heisenberg n certainty principle,

679
00:35:41,640 --> 00:35:45,799
Speaker 3: is the Heisenberg uncertainty principle about pairs of particles, or

680
00:35:45,840 --> 00:35:48,400
Speaker 3: is that about one particle and not being able to

681
00:35:48,400 --> 00:35:50,040
Speaker 3: measure multiple things about one particle.

682
00:35:50,360 --> 00:35:53,080
Speaker 1: Yeah, it's about one particle, right, and not being able

683
00:35:53,120 --> 00:35:57,120
Speaker 1: to measure the momentum and location of one particle for example.

684
00:35:57,360 --> 00:36:00,480
Speaker 1: But again, this contextuality thing is not about the Heisenberg

685
00:36:00,560 --> 00:36:04,000
Speaker 1: uncertainty principle. So here we're going to focus on multiple

686
00:36:04,040 --> 00:36:07,000
Speaker 1: measurements of a single particle, but where the Heisenberg and

687
00:36:07,080 --> 00:36:09,879
Speaker 1: certainty principle does not apply. You know, the same way

688
00:36:09,920 --> 00:36:12,440
Speaker 1: I can measure like position and then I can measure spin,

689
00:36:12,600 --> 00:36:16,279
Speaker 1: and Heisenberg has nothing to say about that. Right, Those

690
00:36:16,280 --> 00:36:19,239
Speaker 1: are two measurements you can make in any order. We're

691
00:36:19,239 --> 00:36:22,320
Speaker 1: going to remove Heisenberg from the conversation by only making

692
00:36:22,360 --> 00:36:25,560
Speaker 1: measurements where the uncertainty principle does not apply. But there

693
00:36:25,560 --> 00:36:28,560
Speaker 1: are going to be constraints about these measurements. That shows

694
00:36:28,680 --> 00:36:31,640
Speaker 1: us that the context in which you measure it changes

695
00:36:31,680 --> 00:36:34,600
Speaker 1: the answer you get. That there's no true answer, there's

696
00:36:34,600 --> 00:36:37,920
Speaker 1: no true state to this quantum system. The measurements you

697
00:36:38,000 --> 00:36:41,000
Speaker 1: make depend on the other measurements you've made because of

698
00:36:41,040 --> 00:36:42,680
Speaker 1: these quantum rules that do apply.

699
00:36:43,040 --> 00:36:45,239
Speaker 2: All right, set this up for me and keep your

700
00:36:45,280 --> 00:36:46,360
Speaker 2: mouth shut, Heisenberg.

701
00:36:48,520 --> 00:36:50,040
Speaker 1: All right, So we're going to talk about a particle

702
00:36:50,239 --> 00:36:52,400
Speaker 1: and we're going to talk about its spin. And in

703
00:36:52,440 --> 00:36:54,520
Speaker 1: the past we've talked about particles that can be spinned

704
00:36:54,600 --> 00:36:57,719
Speaker 1: up or spin down. But imagine instead a particle that

705
00:36:57,760 --> 00:37:02,360
Speaker 1: has three possible spin states up, zero, or down. And

706
00:37:02,400 --> 00:37:04,440
Speaker 1: so this is like a spin one particle, like a

707
00:37:04,520 --> 00:37:07,800
Speaker 1: z or a photon or any kind of boson. You

708
00:37:07,880 --> 00:37:12,240
Speaker 1: can have three possible spins, okay, instead of just two outcomes. Okay,

709
00:37:12,320 --> 00:37:15,920
Speaker 1: So now you pick three random directions X, Y, and z,

710
00:37:16,080 --> 00:37:18,240
Speaker 1: and those are your axes, and because you know space

711
00:37:18,320 --> 00:37:20,880
Speaker 1: is relative, you can pick those in any way as

712
00:37:20,880 --> 00:37:23,560
Speaker 1: long as they're permendicular to each other. And then you

713
00:37:23,640 --> 00:37:26,719
Speaker 1: make a measurement of the spin of this particle along X,

714
00:37:26,840 --> 00:37:31,200
Speaker 1: along y, and along z. Okay, And listeners who know

715
00:37:31,200 --> 00:37:33,480
Speaker 1: about the Heisenberg and certainty principle will be like, hold

716
00:37:33,520 --> 00:37:36,160
Speaker 1: on a second, Daniel. You said, we're making measurements where

717
00:37:36,160 --> 00:37:39,480
Speaker 1: Heisenberg does not apply, but it does apply to spins.

718
00:37:39,480 --> 00:37:41,759
Speaker 1: What's going on? And you're right, But if you make

719
00:37:41,800 --> 00:37:44,120
Speaker 1: a tweak to this, you can lock Heisenberg out of

720
00:37:44,160 --> 00:37:46,879
Speaker 1: the discussion. If you measure the spin, and you don't

721
00:37:46,920 --> 00:37:49,319
Speaker 1: ask what is the spin? You just ask is the

722
00:37:49,400 --> 00:37:50,360
Speaker 1: spin zero?

723
00:37:50,880 --> 00:37:51,200
Speaker 3: Right? Like?

724
00:37:51,320 --> 00:37:53,920
Speaker 1: Is it zero? Or is it plus or minus? Turns

725
00:37:53,920 --> 00:37:56,360
Speaker 1: out that that measurement, for complicated reasons we don't need

726
00:37:56,400 --> 00:37:59,400
Speaker 1: to get into, can ignore the Heisenberg and certainty principle.

727
00:37:59,880 --> 00:38:02,480
Speaker 1: You have your particle, You measure the spin along three

728
00:38:02,640 --> 00:38:05,319
Speaker 1: axis and you ask is it zero long x? Is

729
00:38:05,320 --> 00:38:08,080
Speaker 1: it zero long? Why is it zero along z right?

730
00:38:08,080 --> 00:38:10,920
Speaker 1: So you have three yes or no questions you're asking

731
00:38:10,920 --> 00:38:11,800
Speaker 1: about this particle.

732
00:38:12,160 --> 00:38:15,359
Speaker 3: I am wondering if it is going to be intuitive

733
00:38:15,400 --> 00:38:18,120
Speaker 3: to someone who's like a biologist to think of, like

734
00:38:18,200 --> 00:38:21,000
Speaker 3: what does it mean to say that you are negative

735
00:38:21,040 --> 00:38:24,280
Speaker 3: along the Z axis and positive along the X axis

736
00:38:24,320 --> 00:38:25,080
Speaker 3: in your spin?

737
00:38:25,640 --> 00:38:29,239
Speaker 1: For biologists or people with classical intuition, you're probably thinking, like,

738
00:38:29,800 --> 00:38:32,839
Speaker 1: all right, the particle has some spin. It's spinning in

739
00:38:32,880 --> 00:38:36,480
Speaker 1: some direction. So what do we mean by spin in

740
00:38:36,480 --> 00:38:39,480
Speaker 1: some direction or positive or negative spin? This is a

741
00:38:39,480 --> 00:38:41,839
Speaker 1: bit of a physics thing. We think of spin, even

742
00:38:41,840 --> 00:38:45,200
Speaker 1: in classical systems like a planet, as being along the

743
00:38:45,239 --> 00:38:49,960
Speaker 1: axis of rotation, the line around which it's spinning. So

744
00:38:50,040 --> 00:38:53,120
Speaker 1: the Earth, for example, is spinning and it spins around

745
00:38:53,160 --> 00:38:55,960
Speaker 1: the north south pole. Right, draw a line between the

746
00:38:56,000 --> 00:38:58,880
Speaker 1: north pole and the south pole, So that's the spin axis,

747
00:38:58,920 --> 00:39:02,120
Speaker 1: and then there's a direction clockwise spin is positive and

748
00:39:02,160 --> 00:39:07,799
Speaker 1: counterclockwise spin is negative. No spin is zero. So if

749
00:39:07,840 --> 00:39:10,560
Speaker 1: you have an object that's spinning, you can define some

750
00:39:10,680 --> 00:39:14,000
Speaker 1: axis and ask how is it spinning along these axes?

751
00:39:14,440 --> 00:39:16,640
Speaker 1: Or if you're a vector like kind of person, you

752
00:39:16,640 --> 00:39:19,160
Speaker 1: can think about that spin is having a vector along

753
00:39:19,239 --> 00:39:21,960
Speaker 1: the spin axis. And then if you define x, y,

754
00:39:22,000 --> 00:39:24,760
Speaker 1: and z axis, you're asking how much do those axes

755
00:39:24,840 --> 00:39:28,600
Speaker 1: overlap with the spin vector. So back to the Earth,

756
00:39:28,680 --> 00:39:31,680
Speaker 1: if you lined up your x, y, z axis so

757
00:39:31,719 --> 00:39:34,359
Speaker 1: that X was along the north south pole, you'd say

758
00:39:34,400 --> 00:39:37,840
Speaker 1: the Earth has positive spin along x and zero along

759
00:39:38,040 --> 00:39:40,840
Speaker 1: y and z. If the axis didn't line up with

760
00:39:40,880 --> 00:39:43,799
Speaker 1: the north south pole, they would like skewed somehow. You'd

761
00:39:43,840 --> 00:39:47,080
Speaker 1: say the Earth has spin along multiple axes. It has

762
00:39:47,120 --> 00:39:51,000
Speaker 1: spin along some direction north south and these axes are

763
00:39:51,000 --> 00:39:53,839
Speaker 1: each capturing a part of it all right, So that's

764
00:39:53,880 --> 00:39:56,319
Speaker 1: what happens when you have an actual object that's really

765
00:39:56,360 --> 00:40:00,160
Speaker 1: classically spinning. Just to think about like the math of spin. Now,

766
00:40:00,239 --> 00:40:02,280
Speaker 1: let's think about the quantum version and what it means

767
00:40:02,320 --> 00:40:05,279
Speaker 1: to measure the spin of a particle, and now I'm

768
00:40:05,360 --> 00:40:09,200
Speaker 1: like measuring its spin along some axis. It's maybe capturing

769
00:40:09,320 --> 00:40:11,719
Speaker 1: some fraction of it, and I want to imagine that

770
00:40:11,719 --> 00:40:14,399
Speaker 1: there's a real answer here. It's really spinning in some

771
00:40:14,480 --> 00:40:17,560
Speaker 1: direction and I'm just capturing it along some angle. But

772
00:40:17,680 --> 00:40:20,560
Speaker 1: remember the number one. This is quantum spin. So these

773
00:40:20,560 --> 00:40:23,560
Speaker 1: things are not like actually spinning. We call it spin

774
00:40:23,600 --> 00:40:26,000
Speaker 1: because it has some relationship to spin. There is like

775
00:40:26,200 --> 00:40:28,640
Speaker 1: the math of it is similar to the math of spin.

776
00:40:29,000 --> 00:40:31,160
Speaker 1: But you shouldn't think of it as actually spinning. Just

777
00:40:31,160 --> 00:40:34,920
Speaker 1: think about as some weird quantum process. These things can do.

778
00:40:35,680 --> 00:40:37,320
Speaker 1: The X, Y, and zero important because that's where the

779
00:40:37,360 --> 00:40:41,560
Speaker 1: quantum constraint comes in. Okay, the quantum mechanics says that

780
00:40:41,760 --> 00:40:45,000
Speaker 1: only one of these directions can have zero spin. So

781
00:40:45,160 --> 00:40:47,839
Speaker 1: you can measure zero along X, you can measure zero

782
00:40:47,880 --> 00:40:51,000
Speaker 1: along Y, or you can measure zero along Z. But

783
00:40:51,080 --> 00:40:53,360
Speaker 1: you can't get zero along X and Z at the

784
00:40:53,360 --> 00:40:56,680
Speaker 1: same time. That's the quantum constraint. So we make these

785
00:40:56,719 --> 00:40:59,239
Speaker 1: three measurements along our X, Y, and Z. We ask

786
00:40:59,440 --> 00:41:01,479
Speaker 1: is it zero X? Is it zero? Why is it zero?

787
00:41:01,480 --> 00:41:01,759
Speaker 4: On Z?

788
00:41:02,120 --> 00:41:05,560
Speaker 1: We can only get a yes along one of those axes. Okay,

789
00:41:05,560 --> 00:41:09,040
Speaker 1: so that's the equivalent of like the map coloring rule. Right,

790
00:41:09,080 --> 00:41:10,800
Speaker 1: there's some quantum constraint here.

791
00:41:11,120 --> 00:41:14,120
Speaker 3: Is it interesting to know why only one of those

792
00:41:14,200 --> 00:41:18,040
Speaker 3: values can be zero? Or is that just an arbitrary thing?

793
00:41:18,120 --> 00:41:21,200
Speaker 1: In this example, it's totally not arbitrary. It comes like

794
00:41:21,280 --> 00:41:24,319
Speaker 1: out of the mathematics of spin. It's sort of what

795
00:41:24,480 --> 00:41:28,920
Speaker 1: spin one means. The mathematical details I think are not helpful,

796
00:41:29,040 --> 00:41:31,640
Speaker 1: but it's not just a rule that we've chosen. Right.

797
00:41:31,640 --> 00:41:34,680
Speaker 1: This is the nature of spin one particles that they

798
00:41:34,719 --> 00:41:37,479
Speaker 1: can only have zero along one direction at a time.

799
00:41:38,320 --> 00:41:40,840
Speaker 1: And so Kelly or the biologist or the hidden variable

800
00:41:40,880 --> 00:41:44,160
Speaker 1: proponent might be like, okay, look, my particle has spin

801
00:41:44,239 --> 00:41:47,759
Speaker 1: in some direction, and there are predetermined answers to the

802
00:41:47,840 --> 00:41:50,400
Speaker 1: question of like is it zero a lung X, is

803
00:41:50,400 --> 00:41:53,120
Speaker 1: it zero loung? Why is it zero lung z? And

804
00:41:53,160 --> 00:41:55,440
Speaker 1: when I go and make my measurements, it just reveals

805
00:41:55,600 --> 00:41:58,960
Speaker 1: the secret, pre existing answer that the universe had all along,

806
00:41:59,000 --> 00:42:02,040
Speaker 1: that there is a truth there. Right. The problem is

807
00:42:02,040 --> 00:42:04,960
Speaker 1: that you are not the only person making measurements, all right.

808
00:42:05,040 --> 00:42:08,040
Speaker 3: So I have an X, Y and z and I've

809
00:42:08,040 --> 00:42:11,000
Speaker 3: got my zero yeah, and you have an X, Y

810
00:42:11,040 --> 00:42:13,560
Speaker 3: and z and you have a zero in a different spot.

811
00:42:13,719 --> 00:42:17,359
Speaker 3: Is that because we have different particles that we're looking at,

812
00:42:17,840 --> 00:42:20,200
Speaker 3: or like, what do I know now that I know

813
00:42:20,239 --> 00:42:21,360
Speaker 3: that we have different answers?

814
00:42:21,640 --> 00:42:24,440
Speaker 1: Yeah, so we're looking at the same particle. Right. You

815
00:42:24,520 --> 00:42:26,479
Speaker 1: measure your X, Y and z, you have your zero.

816
00:42:26,640 --> 00:42:28,840
Speaker 1: I measure my X, Y and Z, I have a zero.

817
00:42:29,520 --> 00:42:31,920
Speaker 1: And you might think, all right, well, there's some way

818
00:42:32,040 --> 00:42:37,040
Speaker 1: to satisfy Kelly's answer and Daniel's answer simultaneously. Right, there's

819
00:42:37,040 --> 00:42:40,200
Speaker 1: some hidden truth here that they're both consistent with. But

820
00:42:40,280 --> 00:42:42,680
Speaker 1: you can keep adding people who choose their X, Y

821
00:42:42,760 --> 00:42:45,400
Speaker 1: and z, And for example, somebody might come along who

822
00:42:45,440 --> 00:42:47,799
Speaker 1: has the same X as me and a different Y

823
00:42:47,880 --> 00:42:51,000
Speaker 1: and z. Right, So, now X belongs to two different

824
00:42:51,040 --> 00:42:55,040
Speaker 1: triples and has to satisfy two different constraints, right, And

825
00:42:55,120 --> 00:42:59,000
Speaker 1: it's not possible to have an assignment to all of

826
00:42:59,040 --> 00:43:01,840
Speaker 1: these things that's con distant across all of the triples

827
00:43:01,840 --> 00:43:05,200
Speaker 1: that anybody might measure. And so whether I get a

828
00:43:05,280 --> 00:43:07,480
Speaker 1: zero for X depends on the answer I got for

829
00:43:07,680 --> 00:43:10,319
Speaker 1: Y and z. And whether somebody else gets a zero

830
00:43:10,480 --> 00:43:13,320
Speaker 1: for their X which is the same as mine, depends

831
00:43:13,320 --> 00:43:15,960
Speaker 1: on their y and z, and so even though our

832
00:43:16,120 --> 00:43:17,840
Speaker 1: x is the same, I could get a zero and

833
00:43:17,880 --> 00:43:20,600
Speaker 1: somebody else might not get a zero. Maybe they already

834
00:43:20,640 --> 00:43:23,400
Speaker 1: have a zero for their y and so it's impossible

835
00:43:23,400 --> 00:43:25,960
Speaker 1: to come up with an assignment that satisfies all of

836
00:43:26,000 --> 00:43:30,120
Speaker 1: the triples simultaneously, that all the triples only have one zero.

837
00:43:30,920 --> 00:43:33,680
Speaker 1: The answer you get always depends on the other y

838
00:43:33,760 --> 00:43:35,960
Speaker 1: and z. You chose the measurements you made in the

839
00:43:36,040 --> 00:43:37,040
Speaker 1: other directions.

840
00:43:37,400 --> 00:43:40,080
Speaker 3: And are we all looking at the same particle at

841
00:43:40,120 --> 00:43:42,480
Speaker 3: the same time and getting different answers about it, or

842
00:43:42,520 --> 00:43:43,720
Speaker 3: we're all looking at difference?

843
00:43:43,960 --> 00:43:45,720
Speaker 2: Oh how does that happen?

844
00:43:46,200 --> 00:43:48,839
Speaker 1: We're all looking at the same particle at the same time,

845
00:43:48,880 --> 00:43:51,680
Speaker 1: and we're making measurements that don't mess up the other measurements. Right,

846
00:43:51,840 --> 00:43:54,560
Speaker 1: Remember we locked Heisenberg out of this conversation. It's not

847
00:43:54,760 --> 00:43:57,759
Speaker 1: like a momentum and location thing. The fact is that

848
00:43:57,800 --> 00:44:01,200
Speaker 1: the quantum system doesn't have a ground truth that we're probing.

849
00:44:01,560 --> 00:44:05,560
Speaker 1: The answers you get depend on the other answers you got,

850
00:44:05,600 --> 00:44:08,120
Speaker 1: because it has to satisfy these quantum rules. And the

851
00:44:08,200 --> 00:44:11,800
Speaker 1: quantum rules are such that there is no global solution

852
00:44:11,920 --> 00:44:15,200
Speaker 1: that you can satisfy It's like making an impossible requirement

853
00:44:15,200 --> 00:44:17,239
Speaker 1: on a system, like saying, look, I'm gonna color this

854
00:44:17,320 --> 00:44:20,360
Speaker 1: map with only three colors, and I no adjacent country

855
00:44:20,400 --> 00:44:22,879
Speaker 1: is going to have the same color. It's an impossible constraint, right,

856
00:44:23,239 --> 00:44:26,200
Speaker 1: Quantum mechanics says, Okay, that's no problem. I'm just gonna

857
00:44:26,239 --> 00:44:28,799
Speaker 1: give everybody who asks a different color. Right. There is

858
00:44:28,880 --> 00:44:32,440
Speaker 1: no true color to Turkmenistan. Right, I'm just gonna say, well,

859
00:44:32,480 --> 00:44:34,479
Speaker 1: depending on what you color it as neighbors, I'm gonna

860
00:44:34,520 --> 00:44:37,480
Speaker 1: tell you what you need to notice satisfy the constraints. Right,

861
00:44:37,520 --> 00:44:41,640
Speaker 1: But there is no true global assignment for everybody, and

862
00:44:41,760 --> 00:44:45,760
Speaker 1: so the properties of quantum systems are contextual. They depend

863
00:44:45,840 --> 00:44:50,799
Speaker 1: on other measurements you have made to satisfy the quantum constraints.

864
00:44:51,280 --> 00:44:55,000
Speaker 3: Okay, so now my brain is like going to the

865
00:44:55,080 --> 00:44:58,120
Speaker 3: implications and like, how do you learn from a system

866
00:44:58,160 --> 00:45:01,440
Speaker 3: where everybody looks at the same thing but gets different outcomes?

867
00:45:01,840 --> 00:45:03,839
Speaker 3: And I guess the answer is you just do it

868
00:45:03,920 --> 00:45:06,760
Speaker 3: statistically and probabilistically or.

869
00:45:07,360 --> 00:45:11,520
Speaker 1: Ah, yeah, no, I love that. And it turns out

870
00:45:11,719 --> 00:45:17,399
Speaker 1: to not be important that systems have like fixed true values. Right.

871
00:45:17,480 --> 00:45:21,839
Speaker 1: The universe can just be undetermined in that way can

872
00:45:21,920 --> 00:45:24,960
Speaker 1: be contextual still follows rules, and as long as it's

873
00:45:24,960 --> 00:45:28,440
Speaker 1: following rules, we can discover those rules. Right, as long

874
00:45:28,480 --> 00:45:30,600
Speaker 1: as we give up on our like sort of hidden

875
00:45:30,680 --> 00:45:35,400
Speaker 1: philosophical assumptions that there is a singular hidden truth that

876
00:45:35,440 --> 00:45:39,399
Speaker 1: we're probing and accept that measurements are interactions and those

877
00:45:39,400 --> 00:45:44,000
Speaker 1: interactions are contextual in this really weird way. Right. And

878
00:45:44,120 --> 00:45:48,080
Speaker 1: this is not like the observers creating your reality, or

879
00:45:48,520 --> 00:45:52,759
Speaker 1: you know, quantum mechanics is consciousness, or that quantum mechanics

880
00:45:52,800 --> 00:45:56,239
Speaker 1: is nonsensical. Right, it comes actually out of quantum mechanics

881
00:45:56,360 --> 00:46:02,200
Speaker 1: requiring constraints, right, respecting conservation law, and what's real here

882
00:46:02,280 --> 00:46:06,720
Speaker 1: are the relationships. Right. Properties of objects are not fixed.

883
00:46:06,960 --> 00:46:10,239
Speaker 1: They depend on the context, and they're determined by relationships.

884
00:46:10,320 --> 00:46:12,719
Speaker 1: So that's sort of the same way that like, you

885
00:46:12,760 --> 00:46:16,440
Speaker 1: don't have a velocity. Your velocity depends on who's measuring.

886
00:46:16,480 --> 00:46:20,520
Speaker 1: You have multiple velocities simultaneously, Right, I have a velocity

887
00:46:20,560 --> 00:46:22,480
Speaker 1: with respect to my chair, and a different one with

888
00:46:22,520 --> 00:46:24,520
Speaker 1: respect to the sun, and a different one with respect

889
00:46:24,600 --> 00:46:28,200
Speaker 1: to some asteroid in space. It's cool to have many velocities, right.

890
00:46:28,400 --> 00:46:31,440
Speaker 1: It depends on the context. The observer who's making the measurement.

891
00:46:31,920 --> 00:46:35,920
Speaker 1: In the same way, properties of particles are contextual. Even

892
00:46:35,960 --> 00:46:37,719
Speaker 1: though we like to think of the universe as like

893
00:46:37,800 --> 00:46:40,799
Speaker 1: having an answer being a certain way, there are some

894
00:46:40,960 --> 00:46:43,239
Speaker 1: properties of the universe that are not like that. They

895
00:46:43,280 --> 00:46:45,760
Speaker 1: are just contextual, They are not fixed.

896
00:46:46,120 --> 00:46:48,880
Speaker 3: I feel like you had the nub of your like

897
00:46:49,400 --> 00:46:52,440
Speaker 3: quantum self help book in there somewhere.

898
00:46:51,920 --> 00:46:53,600
Speaker 2: Like the only thing that's real or the.

899
00:46:53,640 --> 00:46:58,360
Speaker 3: Relationships, and I think your million lies somewhere in the

900
00:46:58,440 --> 00:47:00,000
Speaker 3: last five minutes of things that you said.

901
00:47:00,160 --> 00:47:01,440
Speaker 2: Anyway, think about that.

902
00:47:02,160 --> 00:47:04,279
Speaker 1: Well, my agent tells me that self help books are

903
00:47:04,320 --> 00:47:06,280
Speaker 1: all that's selling in the nonfiction category.

904
00:47:06,360 --> 00:47:08,359
Speaker 3: So that's what I've heard as well, and so that's

905
00:47:08,360 --> 00:47:10,760
Speaker 3: why I'm always listening for the next self help book.

906
00:47:11,360 --> 00:47:11,760
Speaker 2: Anyway.

907
00:47:11,840 --> 00:47:16,400
Speaker 3: So what are some like misinterpretations, What are some things

908
00:47:16,440 --> 00:47:19,960
Speaker 3: that doesn't mean that people get confused about.

909
00:47:20,640 --> 00:47:24,120
Speaker 1: Yeah, this is not an open door to consciousness or

910
00:47:24,440 --> 00:47:27,319
Speaker 1: to you know, quantum wu or anything like that. This

911
00:47:27,360 --> 00:47:29,880
Speaker 1: is a path to a deeper understanding of what quantum

912
00:47:29,920 --> 00:47:33,919
Speaker 1: mechanics says about the universe, which is that there isn't

913
00:47:33,960 --> 00:47:37,560
Speaker 1: a fixed, assigned truth that we're observing, right, that the

914
00:47:37,600 --> 00:47:41,160
Speaker 1: measurements we make depend on the other measurements. Question eighteen

915
00:47:41,239 --> 00:47:45,640
Speaker 1: depends on question sixteen and the answer you gave. And

916
00:47:45,719 --> 00:47:48,160
Speaker 1: that's just a different way of thinking about what's out

917
00:47:48,200 --> 00:47:51,719
Speaker 1: there and what's real, if anything is real, And I

918
00:47:51,760 --> 00:47:54,520
Speaker 1: think it tells you that we are not separate from

919
00:47:54,560 --> 00:47:57,200
Speaker 1: the universe. We are part of it, and that our

920
00:47:57,239 --> 00:48:00,520
Speaker 1: interactions with the universe are measurements of it. Don't reveal

921
00:48:01,000 --> 00:48:05,960
Speaker 1: some fundamental objective reality. They reveal the laws that the

922
00:48:06,040 --> 00:48:08,839
Speaker 1: universe follow, and those laws are quite different from the

923
00:48:08,840 --> 00:48:11,880
Speaker 1: intuition that we've built up from, like walking around on

924
00:48:11,880 --> 00:48:13,200
Speaker 1: this Earth and interacting with.

925
00:48:13,200 --> 00:48:15,399
Speaker 3: Goats or whatever, which is one of the best things

926
00:48:15,400 --> 00:48:16,920
Speaker 3: that you can do with this lifetime of.

927
00:48:16,880 --> 00:48:22,720
Speaker 1: Ours, especially quantum goats. So tell me, is your goat

928
00:48:22,880 --> 00:48:26,080
Speaker 1: still in a superposition of having given birth and not

929
00:48:26,080 --> 00:48:27,640
Speaker 1: having given birth or has that collapsed?

930
00:48:27,960 --> 00:48:30,720
Speaker 2: It hasn't collapsed yet. It hasn't collapsed yet, Daniel.

931
00:48:32,520 --> 00:48:34,600
Speaker 1: And that is Kelly's context right.

932
00:48:34,480 --> 00:48:38,560
Speaker 3: Now, that's right, that's right. It's the only context in

933
00:48:38,600 --> 00:48:42,560
Speaker 3: my life. Everything depends on whether or not Lottie has

934
00:48:42,600 --> 00:48:47,520
Speaker 3: given birth yet. So before we started the show, I

935
00:48:47,600 --> 00:48:52,840
Speaker 3: knew that you could entangle particles, and what happened you know,

936
00:48:52,840 --> 00:48:54,960
Speaker 3: if you looked at one of them, what happened to

937
00:48:54,960 --> 00:48:57,839
Speaker 3: the other one depended on what happened to this one.

938
00:48:58,040 --> 00:49:01,560
Speaker 3: And so that's an example of contextuality, right, yes, exactly.

939
00:49:01,760 --> 00:49:04,200
Speaker 3: And so the new thing in this case is that

940
00:49:04,239 --> 00:49:08,480
Speaker 3: we're trying to tell people that there's lots of instances

941
00:49:08,520 --> 00:49:11,760
Speaker 3: where what you see happening in the quantum world depends

942
00:49:11,840 --> 00:49:15,400
Speaker 3: on what happens somewhere else, or.

943
00:49:15,280 --> 00:49:18,840
Speaker 1: Even other measurements of the same particle, not just somewhere.

944
00:49:18,440 --> 00:49:21,920
Speaker 3: Else, right, or even other measurements of the same particle,

945
00:49:22,040 --> 00:49:26,439
Speaker 3: but not We're not talking about Heisenberg uncertainty principle, that's right.

946
00:49:26,480 --> 00:49:28,000
Speaker 2: We're talking about.

947
00:49:28,320 --> 00:49:32,400
Speaker 3: Other people looking at the exact same particle exactly, not

948
00:49:32,480 --> 00:49:35,759
Speaker 3: getting the same measurements exactly. And these are just two

949
00:49:35,920 --> 00:49:39,720
Speaker 3: examples of the many ways that contextuality happens, or these

950
00:49:39,840 --> 00:49:42,560
Speaker 3: are the examples of contextuality.

951
00:49:42,880 --> 00:49:46,880
Speaker 1: These are two examples of a fundamental principle in quantum mechanics,

952
00:49:46,880 --> 00:49:48,040
Speaker 1: which is contextuality.

953
00:49:48,400 --> 00:49:49,239
Speaker 2: All right, got it?

954
00:49:49,400 --> 00:49:51,680
Speaker 3: Okay, So then I think that's what I got out

955
00:49:51,680 --> 00:49:53,920
Speaker 3: of the episode. So it sounds like we did it.

956
00:49:54,239 --> 00:49:57,240
Speaker 1: Thank you very much, Kelly for describing in two minutes

957
00:49:57,400 --> 00:50:00,040
Speaker 1: what I took an hour to explain it.

958
00:50:00,080 --> 00:50:01,960
Speaker 3: But I only was able to do that because you

959
00:50:02,000 --> 00:50:03,920
Speaker 3: explained it so clearly over the hour.

960
00:50:04,320 --> 00:50:06,000
Speaker 2: So hooray for Daniel.

961
00:50:07,239 --> 00:50:11,279
Speaker 1: Go TDKU, and thank you everybody for going on this

962
00:50:11,400 --> 00:50:15,640
Speaker 1: crazy quantum journey with us understanding the weird nature of

963
00:50:15,719 --> 00:50:16,719
Speaker 1: quantum measurements.

964
00:50:17,000 --> 00:50:18,680
Speaker 2: Thanks everybody, see you next time.

965
00:50:25,320 --> 00:50:27,759
Speaker 1: Thanks everybody for listening. Please go and do us a

966
00:50:27,760 --> 00:50:31,040
Speaker 1: favor and rate the show on whatever podcast app you're using.

967
00:50:31,120 --> 00:50:32,680
Speaker 1: It really helps people find us.

968
00:50:33,239 --> 00:50:37,160
Speaker 3: Daniel and Kelly's Extraordinary Universe is edited by the amazing

969
00:50:37,200 --> 00:50:37,920
Speaker 3: Matt Kesselman.

970
00:50:38,160 --> 00:50:41,399
Speaker 1: He really is a wizard. You can also find us

971
00:50:41,480 --> 00:50:46,560
Speaker 1: online on Blue Sky, Instagram and x D and K Universe.

972
00:50:46,640 --> 00:50:47,879
Speaker 1: Come engage with us.

973
00:50:48,120 --> 00:50:50,840
Speaker 3: You can email us at questions at Daniel and Kelly

974
00:50:50,920 --> 00:50:51,440
Speaker 3: dot org.

975
00:50:51,560 --> 00:50:53,080
Speaker 2: We really do want to hear.

976
00:50:53,000 --> 00:50:55,680
Speaker 1: From you, and you can find our website www dot

977
00:50:55,800 --> 00:50:59,640
Speaker 1: danieland Kelly dot org, where you'll also find an invitation

978
00:50:59,680 --> 00:51:02,800
Speaker 1: to join in our discord where everybody comes and talks

979
00:51:02,840 --> 00:51:04,880
Speaker 1: about the amazing universe.

980
00:51:04,680 --> 00:51:08,640
Speaker 3: And we also have the most amazing moderators. This is

981
00:51:08,680 --> 00:51:11,239
Speaker 3: an iHeart podcast. Thanks for joining us.