How do we know quantum mechanics is really random?

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Speaker 1: Hey, Daniel, do you have a pretty good routine? You mean like a dance routine or like ten tight minutes of stand up comedy? I mean like a schedule, Like do you have the same day plant every day? Or do you wing it every day? Yeah? I'm pretty into my schedules. It's the only way I can really stay on top of everything. Oh man, that is the opposite of what I do. I like to wake up every day not knowing what's gonna happen. Well, I like to plan every day, but in the end, every day turns out totally different because my well laid plans get blown up by something that happens. See, so what's the point of making plans. I like to live in a superposition of organization and chaos. So you're both or neither depends on which day you collapse my wave function and on which day my schedule collapses. Sounds like you're the one who collapses at the end of the day, though. That's how you know him a true quantum mechanic. Hi am or Him and Cartoonists, and the co author of Frequently Asked Questions about the Universe. Hi, I'm Daniel. I'm a particle physicist. And a professor at U C Irvine, And I'm supposed to understand quantum mechanics. You're supposed to do that, I guess because you're a physicist, right, that's right, it's my official job. Particles are definitely quantum objects, and yet it's still something that everybody in the field struggles with. But didn't Richard Fine when famously said that nobody understands quantum mechanics and if you do, then you don't really understand it. And he was one of the top five smartest physicists. So yeah, everybody below him on the ranking can't understand it better than he does. With the top four, dude, I think there are a few people out there that might understand quantum mechanics better than Richard Fineman. Yeah. Do you think it's maybe just a limitation of the human brain or is the quantum mechanics use there not understandable. I think we definitely can understand the mathematics of it, but sometimes translating that mathematics into intuition is really complicated. It's hard to understand things which are very unfamiliar to us. Because in the end, physics is about trying to explain the unfamiliar in terms of the familiar. But sometimes we don't have a good intuitive analog to reach for. Sometimes we find something which really is very different from anything we've experienced before. That's why I don't believe in intuition, either schedules and intuitions. I just leave him at home every day. But anyways, welcome to our podcast Daniel and Jorge Explained the Universe, a production of My Heart Radio in which we attempt to apply our intuition to understanding everything about the universe. For these little squishy brains that evolved on this one rock around one planet. It's an incredible task to try to understand everything that's out there, including phenomena that our ancestors never saw, crazy black holes, incredibly dense neutron stars, any buzzing particles. Is it even possible to grop all of that, to import it somehow into our minds so we can play with it, manipulated and understand it. That's right, because it is a vast and incredible universe full of amazing things that run counter to our intuitions sometimes and that are very difficult to understand. And so the only thing we can schedule on this podcast is the idea that we're gonna talk about it and try to understand it and ask questions about it. Because on the podcast we try to do something which may be impossible, which is to translate all of these ideas, which in the end are expressed mathematically, into concepts that we can deliver into your brain just with chit chat and conversation. It's not always easy to know how to transform these ideas from their essential mathematical principles into an intuitive understanding, a stream of words which land in your ear and build in your mind a little model that makes you go, oh, I get it. But that's what we're going for. Yeah, it's a pretty challenging problem if you think about it, right, because we're trying to take the higher universe, which is at least four dimensions, maybe more, and we're trying to get it down to really one dimension, right, because audio is just one one degree of freedom, right, I suppose though, although in principle there are an infinite number of frequencies along which to convey information. But yeah, that's a good point. We're trying to like serialize the universe into a stream of information which unpacks itself into your mind to give you a mental model of the universe that somehow works. I guess it would help if maybe we're recording stereo, like I could be on people's left ear and you could be on people's right ear, and then we could maybe convey more information that way, like a little angel and devils standing on your shoulders. Or maybe we need to cartoonists and to physicists going simultaneously. How does that help, and we're all talking at the same time exactly, it would be two dimensional podcasting simultaneously. I feel like you would still collapse right under the amount of information. You're still collapsing the information down to one dimensional audio. Yeah. I think probably it's best to stick with one dimension and do best to project these crazy ideas down into a one dimensional audio stream. It is a complex universe, and sometimes it's a seemingly random universe. It's a huge universe, and all kinds of things are happening in it, and it's not quite clear where the things are happening according to a plan or if they are just randomly occurring in the universe. Yeah. One of the most fundamental questions about the nature of the universe is whether you can predict what's going to happen in the future based on the past. Is the universe like a big clock, where if you understood all of the rules and had enough information, you could tell exactly what was going to happen? Or fundamentally, is there something weird going on at the heart of the machine that is running the universe, something different from anything we have ever experienced directly, something truly random? And well, I guess the universe seems pretty random, right, Like if I flip a coin, it's really hard to tell if it's going to be heads or tails. Right, it does, And we often use flipping a coin or rolling a dice as an approximation for some random But those are not actually random processes. Those are just very very complicated processes, things which are hard to predict, but in principle possible to predict if you had enough information and enough computer processing power. What about whether we're going to explain something well or not? Isn't that also kind of random? Hey, sometimes what we talk about on the podcast feels a little random. You know, I'll prepare a whole outline and we'll never get past the first bit. Wait, are you saying I'm the random filter here? I'm saying that Daniel Jorge interaction is a little unpredictable. Sometimes what we end up talking about in the best possible way. I love those episodes when you're like a whole lot of second, slow down, what does that actually mean? And then we spend forty five minutes talking about the definition. We may we just need like a parallel podcast or something. Maybe we need the multi World's podcast where we take every possible branch and every possible digression simultaneously. Well, this idea of whether the universe is random or not with something that sort of came up recently in the last hundred or two hundred years, right, I mean, after Newton, people have figured that the universe was pretty mechanical, pretty much like a machine where everything followed F equals m A, and you could predict what the path of a baseball or dropping a coin, what was going to happen. You could predict that. But then came quantum mechanics, who said, well, maybe things are not that predictable. Yeah, And both of those really are revolutions in our understanding of how the universe works. I mean, before quantum mechanics, even just the idea that the universe was deterministic, that it was like clockwork, that the whole apparatus of reality was somehow following physical laws which you could uncover and understand and used to predict the future. This was a big idea, right. This flew in the face of lots of people sort of spiritual sense that there was somebody out there, unpredictable, in control of the universe. To reduce it to a set of natural laws which governed it, that was a big step forward. And so then to pull the rug out from underneath that and say, actually, no, at the heart of all of it, there might be something unpredictable, some process which determines the outcome but isn't determined by the past, is somehow fundamentally random. That was a crazy, big new idea. Yeah, I guess it was a double sweeping of the rug, right, because before Newton, I guess, and before these fundamental laws of the universe, people kind of thought the universe was random. Right. It was random, or at least at the whim of some gods or some deity that sort of randomly decided things. And then we thought it was all ordered, and then we realized, wait, it is sort of random. Yeah, exactly though random in a very very different way. Right, quantum mechanical randomness, as we'll dig into, it's not arbitrary or at the whims of some god. Right, how do you know, Daniel? You know, we might be at the whims of the writers of the simulation. But whatever code they wrote is what determines how the universe seems to work. What if that code is at the whim of some other writers. Well, maybe it is, but they don't seem to have been changing the code recently. It seems like the code is pretty stable over the fourteen billion years at the universe's history, So there haven't been any updates. Well, it seems like we've done a double take here on the random of the universe. And the latest is that according to quantum mechanics, things are random. But is that really true? And so to be on the podcast we'll be tackling the question how do we know quantum mechanics is really random as opposed to just plane wacky or flaky or at the whim of some quantum mechanical gods. Well, you know, quantum mechanics has probabilities in it, and you can talk about what probabilities means. Sometimes probability just means our lack of information. Things we don't know, but in principle could predict. And sometimes probability means fundamentally random, governed by our process outside of our control. You're gonna bet on the outcome of a Roulette wheel spin, for example, you might think that's random, and in principle, if you knew how the ball bounced and you spun it the same way twice, you should get exactly the same answer, So it's not really random. The probabilities, they're just come from your lack of understanding. The question really is quantum mechanics the same way. Are there details which actually do determine the outcome of these experiments, which is not aware of them? Or is the universe really actually at its core a random number generator? You're asking is it really random or does it just seem random? Because something can seem random, right like I can have a computer code that spits out random numbers, which will look pretty random to anyone, but actually there's sort of card coded on the computer right exactly. Random number generators follow a sequence where computers follow rules. They can't actually generate random numbers. They can only have pseudo random number sequences that sort of look random ish, right, And so we're asking the same question about the entire universe. Is the universe actually random at its core? Or does it just seem random? And I guess we need to go to quantum mechanics to find the answer. And we've been talking around this topic and a few recent episodes and listeners have responded and asked us to dig into the heart of the matter. Yeah, and as usually, we were wondering how many people out there I thought about whether quantum mechanics really is random or not. So thanks to everybody who answers these questions for us. It gives us a great sense for what people know and what they're wondering about, and what you might be thinking out there. And if you would like to lend your voice for a future episode, please don't be shy, all right to us two questions at Daniel and Jorge dot com. So think about it for a second. Do you think quantum mechanics really is random? Here's what people had to say. Actually, I then that's what Einstein thought. He thought there was some hidden variables are controlled all the processes, and we didn't know about that, and that's why we thought it rest them, but I think there have been many experiments where they redeed the same thing over in our work, but in the same conditions, but there's a different result each time, and that's what that's how we know that it is truly random is such a question. We do experiments thousands and thousands of times so that we can get probability curves that show randomness. But he would only know to a certain amount of certainty based on how many experiments you do, and you can't do an infinite number of experiments. So maybe we don't know that it's random, but it's just random enough for purposes. Well, if it's not random, I guess scientists would have figured out how it's really working, and we would have really cool quantum computers by now. We may not know it as an absolute fact, but our models really suggest it is random through many experiments and theories. That model of randomness holds out really, really well. And that's about as good as we can get if the model fits we accepted. I'm a big fan of the idea that there's a hidden variable that we don't understand, But at the same time I realized that all the evidence says that it's really really random. There's that whole thing where you send electrons through a slit experiment, one electron at a time, and they still interfere because, as I've heard you guys say, it's a field, not a point. But I don't really understand damn that um. As a computer programmer, I know that quantum is the gold standard for truly random numbers, but I guess I really don't understand that at all. If you set up an experiment, well so they call it an ensemble, if you set up multiple instances of that experiment and everything is the same, and you produce the electron, say you, I don't know if I were it in a given direction, And then well, since you know its position or the trajectory it's taking, if you then try to measure its momentum while it's moving, even though the experiments are set up in exactly the same way, you get different answers for the momentum, and it doesn't depend on how you've set up the experiment, because the ensembles are exactly the same and there is no like sort of external factor that you can change that somehow correlates with the measured momentum and that's why we say quantum mechanics is random. Well, I guess you could set up the same experiment many many times and if you get different outcomes um with the sort of random distribution, you would know that it's very random. Otherwise I have no idea. Interesting, I feel like some people don't want to know, kind of. It is really hard to accept this idea that the universe is so different from the one you experience. So I think a lot of people resisted. Yeah, and do you think quantum mechanics is random or maybe it was just discovered randomly? It does seem like the history of science is a little bit random, you know, especially in the case of quantum mechanics, because we had a few experiments that people had done and nobody really understood, and then Einstein and Plank came along and sort of put the pieces together years later. Makes you wonder if it could have happened sooner, or maybe if it could have happened decades later. It's fun to think about alternative histories and what we might have discovered or not at all. Right, Like what if Einstein had decided that he wanted to play soccer for a living. Maybe we wouldn't be having this conversation at all. Usually can't say that about historical figures, but Eisen is one of those figures where if he hadn't come along at the moment he did, things would be super different. Things might be different. There are people who say that a lot of the precursors to his ideas came from other people, and so it was sort of inevitable for them to click together. You know, a lot of the math that underpins relativity was developed by other folks. Rimon, for example, developed the rimanny and manifold, which Einstein realized was a great way to describe the curvature of space. Other folks were working on similar ideas and may have brought it together even without Einstein, though it could have taken a few years or decades longer. Well, Eisen did what he did. And here we are talking about quantum mechanics and randomness and whether or not it is actually random at its core. And so I guess, Daniel, let's start with the basics here. Uh, Well, first of all, what do we mean by the word random? So by random we really mean something which is not determined by the experimental setup you'd build an experiment to shoot a ball, or to flip a coin, or to roll a dice or whatever. If it really is random, then you can do the same experiment twice and get different outcomes, right Like For example, a computer random number generator is not really random because it uses a computer formula, right like that. One works by taking a look at the current time, grabbing a bunch of different variables that are changing all the time, and then it processes those and then it spits out what seems like a random number, but it's not really random because venia what all the numbers that went into the random number generator, you could generate the exact same sequence, right yeah, and we do that all the time. You have a random number seeds for example. These are the parameters that control the random number generation. And if you give a computer the same seeds, it will generate the same sequence of random numbers every time. So computer random number generators are deterministic. They can be predicted from their inputs and reproduced. You run the same random number generator with the same inputs get exactly the same outputs, So that's deterministic. That's not random, But they are chaotic. They are hard to predict. Their designed to be complicated the way. For example, a die is designed to be unpredictable, as all these sharp edges which bounce unpredictably against surfaces and makes it really tricky to know if a two or four is going to land upright, It's very sensitive to exactly how you throw it, which makes it hard to predict and appear random but not actually be random, right, because a die with sharp edges sort of like if you stand it on one corner, I guess it might fall to the rider, It might fault to the left, or it might bounce to the right or left, just like a coin if you stand it up on its side, it could maybe um flip or land and either way. Yeah, imagine trying to learn, for example, how to flip a coin so that it always comes up heads. In principle, you could you could learn how to spin it at just the right frequency and toss it in the air just the right velocity, so it has a certain number of flips before it lands on your hand and it's always going to come up heads. That would be a great skill, right, But it's so hard to do because it's so sensitive to all of those details. You'd have to be a master coin flipper to be able to do that same with a dive. Some many knew how to roll sevens every single time. They would make zillions of dollars at casinos every day. Right, The whole game of craps is built on the assumption that nobody can really control what happens to the diet even though they give them to you, they let you roll them, right, And so the whole assumption there is that you can't reproduce the same toss over and over again. So I don't let you into casinos anymore. It may they stop you at the door first, they're like, are you Antonian physicists or a quantum mechanicis may say quantum physicists. They'll let you in. They'll let you in exactly because you've given up. You've allowed the randomness to enter your life, all right. So that's the kind of the difference between random and not random. Random you can't predict given the initial conditions, and not random you can't predict it even if it is really hard. If you can't predict it, then it's possible that you can't predict it, and so it's not random, and everything in your everyday experience is not random. Whether you hit a green light, or whether you trip on the steps, or whether that bird poops on your shoulder or whatever. These things can seem random, whether really just complex. They're actually just chaotic. Even the weather, right, the weather is not fundamentally quantum mechanically random. It's just difficult to predict because it's so complicated. So in our experience, everything that seems random is actually just deterministic and complicated, or at least I think you mean, it's mostly deterministic and chaotic, right, And it's it's just saying that Newtonian dynamics dominate our everyday lives. But there is still a little bit of a quantum at it's hard right at the microscopic level, right like as the coin hits the table, there is some sort of maybe quantum interaction there. They could determine whether it flips to the right or to the left. Well, we do know that microscopically everything we experience is made of quantum objects, and so if quantum mechanics is random, then you know, you might ask why aren't things made of quantum objects also random. The answer is that that randomness mostly averages out, and so even electron is going to like quantum mechanically fluctuate to the left somewhere than an electron quantum mechanically fluctuating to the right. So when you have in big enough groups of quantum objects, these things tend to wash out. It's very difficult to actually pinpoint quantum mechanical impacts on everyday macroscopic classical objects. Otherwise we would have discovered quantum mechanics sooner. You know, it would have been more obvious if there were quantum mechanical impacts on our everyday life. Right, But you just found it a little bit absolute in But then you said you mostly wash this out, right, not completely right. There is still a little bit of tiny, little bit of maybe quantum randomness in our everyday lives too. Yeah, there's a little bit there. Right In the end, these things are averages, so there are probabilities you could in principle disappear and quantum tunnel to the other side of your house. Right, It's not impossible. That's why you should never say things absolutely. Also, this is not something that we a hundred understand, right, How do quantum mechanical objects when they're all tiny, the huge frothing mass of them, how did they come together to make the classical picture that we understand that boundary is kind of fuzzy and not super well understood. So there might be places where quantum effects really do have so of like cascading consequences which lead to macroscopic effects, like the heart of the human brain. Are there quantum effects inside your neurons which change the decisions that you make? We don't really understand that in enough detail to be absolutist about it, right, But I think what you're saying that then, is that our everyday lives that things are mostly deterministic because all the quantum mechanics sort of mostly washes off. But although there's still a little bit of room there for things to be random, but they're not as random as they are at the microscopic level. If you're looking at like one electron that has a as a huge random as factor whether it goes right or left exactly, we think that at the microscopic level, quantum mechanics might be really truly random. Although there are a lot of different interpretations for these weird experiments that we're going to dig into, these bells experiment with entangled particles, right, So, even at the macroscopic level, you can ask the question if an electron is actually actually random or whether it just seems random. Right, that's the question we're asking today. That's the one at the heart of the matter. If the tiniest little bits in the universe can be predicted if you have not all the information, or if the universe is like rolling a truly random die every time an electron has to decide where it's going to go. All right, well, let's dig into whether or not the universe is random at the microscopic level or not, and how we could maybe tell the difference using a famous experiment. First, let's take a quick break. All right, we're asking the question whether the universe really is random, and whether or not Daniel can plan his day with any certainty at all, or is it all a futile exercise. Just give up like I do. Just embrace the chaos. Yeah, embrace the randomness. It's different than kids. Well you should e'mbrace both. I guess just let whatever have happened. Yeah, So that there's a famous way to tell whether or not electrons and things at the microscopic level are truly random, or whether or not they just seem random. Right, And this is the idea of Bell's experiment, And it goes actually back to Einstein again. Einstein, though he had some of the foundational ideas that led us to develop quantum mechanics, he was fundamentally uncomfortable with the idea that the universe was truly random. He thought that perhaps there were just details there that we were not understanding, that when things seemed random, it was just because there was missing information that we didn't have that was actually controlling the outcome of the experiments. So he and a couple of buddies of his came up with a thought experiment because he was like a champion of thought experiments, to demonstrate how weird it would be if quantum mechanics was really random. Yeah, And I think it all sort of goes back to this picture of one electron, right, Like, if you shoot an electron towards a magnet, it has kind of a random equal probability of serving to the right, as does swerving to the left. Right. That's kind of the fundamental random experiment that people picture when they picture quantum mechanics. Right, It's like it has a half a probablegy to go right. Have a probability to go left, and it's totally randomly. There's no way you could maybe predict whether it's going to go right or left. Yeah, And just to clarify, electrons always go the same direction when they hit like a big macroscopic magnet, because magnetic fields turn electrons in a way that we understand it. But electrons also have another quantum mechanical component, the spin, which affects their little magnetic field, and so that can affect whether they go like left or right when they hit like a weird magnetic field. And so you're right. Quantum mechanics says there's an equal probability for it to be spin up or spin down, which means that it goes left or it goes right, and it says that that's not actually determined until somebody measures it, that both possibilities are live simultaneously until you actually measure it, whereas the other view says, no, no, no no, there's some detail that determines whether it's spin up or spin down, whether it's going to go left or right, and it those left or it goes right the whole time until you look at it. Right. That's the idea of the hidden variable right, Like, maybe the electron at its core knows whether it's spinning up or spinning down. It's just that we don't know. And so that's why you call it a hidden variable. And so the question is, does the electron actually know if it's spinning up or down? Or does even the electron not know what's going to happen until somebody comes in and ask it or puts it. Yeah, and you might imagine it's impossible to tell the difference, like how can you know if it's actually determined but you're just not aware of it, or if it's chosen at the time you poke it, because before that nobody's poking it, So how can you tell? So Einstein's big idea was to add another electron, which said, well, what if you have two of these things and you know something about the pair of them. You know that they have to have opposite spins, maybe they come from the same source, so they're constrained somehow. There's a connection between them, so that if one of them is spin up, the other one has to be spinned down. This is the idea of quantum entanglement. And it's not so hard to I understand the general idea For example, you have two bags, one with the red ball, one with a blue ball in it, and you and your friend each take one bag, but you don't know which is which, and you travel like ten miles apart. Now you look at the bag and you say, oh, I have the blue ball. That means my friend has the red ball. Or if your friend has the blue ball, that means you have the red ball. Because you know there's only one blue ball, then you know something about what's happening with the other particle. That's the idea of entanglement connecting these two electrons together, right, Because when you separate the balls in the bags, you take one this way and take the other one that way. They have something that ties their history together, right, some sort of constraint that says if one is blue, the olne spread and if this one is red deal and has to be blue. Right, it's something that ties their histories together exactly. In Einstein's point was if things really aren't determined until you look, that means something really weird. That means that the electrons, which are now five miles apart from each other, if you measure one of them and it determines to be spin up if you're saying that they really weren't determined until you're measured, that means that the other electron, now ten miles apart, instantaneously is from undetermined to spin down without anybody even looking at it. So this was Einstein's complaint that if quantum mechanics really was random, then it was somehow nonlocal. It is somehow instantaneous collapse of the distant electron the other one the way you weren't even looking at. Right. Yeah, you mentioned the idea of local, because that's kind of a big part of it, right, Like if I take one of the balls and I go to New Mexico and you stay in Los Angeles, and I opened my ball and I know and I see that it's red, then I know that your ball is blue. But you don't know that I opened my bag and found a red ball right to you. It's still uh, totally unpredictable what's in your bag. Unless I go and I call you or I send you an email saying, hey, my ball was a certain color, then you would know what color your ball is exactly. But according to quantum mechanics, it is at that point determined once you've measured yours to be red, then mine is blue. So Einstein's big point here was to say, this is ridiculous, This idea that quantum mechanics is random, that there aren't details determining which one is spin up and which one has spin down, requires them to somehow conspire across great distances faster than the speed of light. So we said, obviously this can't be true, but it turned up that it is true. I feel like you were leading me into that, but I don't really know. That's what Einstein I wanted everybody to think. But again you can ask the question, how can you know? Maybe quantum mechanics really is just weird that way and it doesn't sit well in Einstein's brain, doesn't mean it isn't reality. Is there some way we can enhance this experiment so we can tell the difference. We can tell if it really is random and decided at the last minute before you measure it, or if it's all somehow decided in advance using information. We just don't have access to some sort of weird hidden details about these particles that determine which one is spin up or spin down. So that was the great challenge. Is there a way to come up with an experiment to tell the difference. Right, you're saying that as soon as I opened my bag in New Mexico and I see that my ball is read, suddenly your ball goes from being a quant mechanical object that could be anything to a non quantum mechanical object which can only be blue. That's the weird thing that kind of freak instain out. As soon as I opened my bag in New Mexico, So your bag in Los Angeles starts being quantum mechanical instantaneously. Yeah. So people were chewing on this problem, and one other very smart guy who might understand quantum mechanics better than Richard Feynman, he came up with a really ingenious idea for how to tell the difference, for how to know if quantum mechanics was doing this at the last minute, if it was really was left undecided and truly randomly collapsed at the last moment, or if he was determined by some information we just didn't have access to. He actually came up with a way to test that, to build an experiment which would tell you what the universe was doing. Well, what's the alternative? Then, in the case of the two balls, the one in New Mexico and the one in Los Angeles. Like, if Einstein is right, then what actually happened to the balls? You actually knew which one was red and blue the whole time. Yeah, if eine Stein is right, then one was red and one was blue with whole time. We don't have access to the information. We didn't know that until we opened it up. But it actually was read the whole time. And if quantum mechanics is right, then it wasn't read. It was a possibility of being read and a possibility being blue. Right in the quantum mechanical view, both were possibilities until I open minding in Mexico, and in which case both became non possibilities exactly. And if Einstein was right, you get what he calls realism. He says, the universe is a certain way, even if you aren't looking at it. There is a fact of the matter, and the ball is blue or is read regardless of whether we know it or not. That's what Einstein believed. But the typical description of quantum mechanics says that it really is undetermined and there's a random process that chooses it at the last moment, just before you measure it, or as you measure it, or the act of you measuring it collapses it and forces the universe to access its true random number generator. And I think one the Einstein's point is that it's hard to tell the difference between those two scenarios whether they were red and blue the whole time time or whether they decided only when I opened mining New Mexico, because there's no way to tell a difference, which is that simple experiment, So you need to sort of do an experiment two point oh that maybe messages with that to see if actually things were random or not. Yeah, exactly, And that was Bell's big idea. Bell came up with a way to test this, and at first, blush, it feels impossible, right, like how could you tell whether it's undetermined when you don't look without looking, and by looking you collapse it. So it seems sort of like a paradox, like impossible to probe. Bell's big idea was taking advantage of another aspect of quantum mechanics that didn't exist in the hidden variables picture, and that's the fact that it matters along which direction you're measuring the spin. So we're talking about a quantum mechanical property of these electrons. It's called spin, and they can be spin up or spin down. But it can be spin up or spin down along with some direction. Right, if you have like an axis you're defining as X, you can say, is my electron spin up or spin down along this axis? You can also measured along Y or measured along z. Asid anything quantum mechanically is that these things are connected. Like in quantum mechanics, you can't know the spin in X and in Y and in Z simultaneously. They're all weirdly entangled by the Heisenberg uncertainty principle, the same way that like you can't know the position and momentum of an object at the same time those two pieces of information are really connected together. So Bell came up with this experiment where people in different locations might use different axes, they might be measuring the spin in different directions, and quantum mechanics would make a different prediction for the correlations between those measurements than the hidden variable theory would. Yeah, let me just let me go back the little bit on this idea of spin, because this is when I think it's going to be hard to explain over audio. I think maybe a way to picture it is that you know, instead of a red and a blue ball that we put in our and those hidden bags, instead of drawing arrow on our balls, like an arrow pointing up or an arrow pointing down right, or I guess the arrow could be pointing in any direction. Really in the in the ball right, it could be pointing up, down, left, right, diagonal, diagonal down, diagonal up, So it can be pointing in any of those directions. But one thing about quantum mechanics is that you can't ask whether it's pointing up and down and left and right at the same time. That's a weird thing about quantum mechanics, right. The weird thing about quantum mechanics there is that it matters the order in which you do it. Just like if you measure position, you get a number, and then you measure momentum, then your position measurement is no longer valid. Once you measure momentum, you scramble the position. In the same way here, if you measure the spin along one axis, you look to see if the arrow is pointing up or down according to your imaginary Z axis, and then you do it along y or X. It scrambles the first measurement, so you can't know the spin in all three directions simultaneously for a quantum object the way you can for a ball. Right ball, you can just look at and say, oh, it's kind of up in Z and kind of down and X and kind of whatever. You can just know it's determined as possible. These are sort of like orthogonal directions in the hidden variable theory quantum mechanics. They're weirdly connected to each other. Is like let information available. There's like shared information between x, Y and Z and the spin measurements. Right, Like, let's maybe explain it. Like let's say I point an arrow on the face of my ball, and it can be up, down, left, right, the daggon or whatever. Maybe you can picture it as like the hour hand in a clock, So it can be pointing up at twelve o'clock or down at six o'clock, or right at three o'clock or left at nine o'clock, or it could put pointing at one o'clock, four o'clock, eight o'clock, ten o'clock. And you can only sort of ask one thing at a time, whether it's generally pointing up or down or left or right, not both at the same time. So like, if it's actually pointing at two o'clock, I can as well as it pointing up or down, and you would say, well, it's at two o'clock, so it's pointing up. Where I can ask is the pointing left or right? And you say, well, it's pointing right because it's pointing at two o'clock. But I can't ask both of them at the same time to really figure out what the hour was like. Once you ask whether it's up or down, the whole thing collapses and that's it. I can't know anything else about it. Yeah, once you make a measurement, all your previous measurements are now relevant, so you can't like zero in on the exact details. Right, Like you would maybe said your hour clock at a point in your clock right, and then I would ask you is it up or down? And you would see up. And now I can't ask you whether it was right or left because I would tell me exactly where the hand was right, remember that there might not be any where it really was. In the theory of local realism, there is a true position, a total reality, and the clock really is pointed in just one direction, but in the quantum theory without hidden variables, measuring it along one direction scrambles it any other directions, so they're not just not known, they are not determined. And that's really the issue we want to address. The question we want to answer, can we tell if those measurements are undetermined or unknown? And the fact that in quantum mechanics you can't know more than one direction of spin at once is the crucial concept in Bell's theory because it changes how measurements in different directions are core lated measurements along different axes, And this is the exact idea at the heart of Bell's experiment. Bell says, let's take our balls and let's pick three directions in advance. And the people who are doing these measurements, they're gonna pick one of these three directions to make their measurement. As you say, it's like picking two o'clock or nine o'clock or six o'clock on the clock right to make your measurement, to ask whether the arrow is up or down. They're going to pick one of those. And if things really are determined, then the direction they pick doesn't matter, doesn't change the state of the ball at all, it's a very simple relationship between whether or not they're they're likely to see the same answer. You know, if they both pick twelve o'clock, they're going to see the same answer. One of them picks twelve and the other one picks two o'clock, they're almost always going to see the same answer. This kind of stuff. So you can say, if things aren't messed up in that way, measuring in one direction doesn't measure and the other directions, then we understand exactly how often people should get the same answer. But in the quantum mechanics version, if these things are scrambled, if measuring one direction messes up, the measurements in the other directions, get a different relationship with people with the two balls or the two electrons get the same answer sort of more often than you would expect. If things really are determined by hidden variables, these correlations between the different directions quantum mechanically come into play and sort of mess up the otherwise perfect picture, right. I think you're saying that, Like in our original experiment where we have the tool balls in Los Angeles, and I took one of the balls to New Mexico. Now we're going to introduce something new to eights experiment in order to test this quantum randomness, and that is to put people in between Los Angeles and New Mexico and have them asked questions about the ball on the way as it's traveling from Los Angeles to New Mexico, right, and somehow that's going to tell you whether or not things are actually random or not. You measure each ball one time, because once you've measured it, there's no more entanglement with the other ball going in the other direction, and you don't necessarily measure each ball along the same spin axis. Each ball gets measured along one of three directions. You can make the three directions like a Mercedes symbol if you want. Both balls might get measured along the same direction, which case one is up and one and down. That happens a third at the time, but two thirds of the time you don't choose the same axes and bells and equalities all about how often both balls that measured spin up or spin down along the random access that's chosen for a hidden variable model, you get the same answer from both balls less than two thirds of the time, And so when you compare the answers for one ball and the other ball. It just depends on like what angle the ball actually was at. Right, Maybe let's step people through that example in our scenario here of l a Vers is New Mexico. So like, let's say that things are not quantum mechanical, and you actually drew on your ball, you know, an arrow pointing at one o'clock right now. The first person's going to ask is it generally pointing in the twelve o'clock direction, and you would say yes, And when it arrives in New Mexico, it's still going to be pointing at one o'clock like you drew it right exactly. You also have to have people asking the same questions of the other ball and then comparing the answers. That's the key to the experiment. Okay, now that's what it's going to happen. If the universe is not random, if he has hidden variables, if you actually drew the arrow on the ball before putting it into the bag. But now let's paint the quantum mechanical version where it's something. It's not really drawn on the ball, it's just something. It just has the probability of being something. Right, Yeah, So as a probability in any random direction, And the only thing we know is that whatever direction is in the other ball going to the other city is pointing the other way. And so in the quantum mechanical version, you can really only ask one question. You can measure it along one direction. You can say, is it pointing towards two o'clock or is it pointing towards eleven o'clock. Once you've done that, you sort of messed it up. You can't really get any more information about the ball. So you can make one measurement about your ball, and your friend going the other direction you can make one measurement about their ball. If you pick these three directions in advance, then you can predict how often they will get the same answer. Like both people say two o'clock, then you know they're going to get opposite answers. Right, one ball is going to be up with respect to two o'clock, the other one is going to be down. But if one person uses two o'clock and the other person uses eleven am, then they might get different answers. And quantum mechanics tells you how likely they are to get different answers. Well, let's step people through it. What happens if it is a quantum mechanical ball that goes through and gets the question. So the first person says, is it generally pointing towards twelve o'clock? And then that will sort of collapse the ball a little bit, right. I think that's what you're saying, is that now the ball cannot be pointing downwards if I say yes, if you say yes, then the ball cannot be pointing downwards. So that if the next person says, hey, is it pointing three o'clock, they can't tell you. Right. Well, what happens is you've destroyed the entanglement, so you can make the measurement, but it's no longer constrained to be the opposite of what the other ball is. And the whole idea is that these things need to be entangled. Once you've made a measurement, then the entanglement is broken. You can only use up the entanglement sort of one time. That's why you can only really make one interesting measurement. You can make as many measurements as you like, but they're not really as interesting because you no longer measure ring an entangled system. Right. Once you interact with something, you break the entanglement. But wait, is that really a good analogy of Bell's theorem that somebody along the way asks if it's pointing towards twelve o'clock. Sort of if you take one more step. Bell's experiment says, pick three directions in advance. Everybody decides in those three directions, and then when you actually make your measurement, you pick one of those three directions randomly. So you know, Jorge in New Mexico is going to pick the two o'clock direction, and Daniel in l A. Is maybe he's gonna pick the two o'clock direction, maybe he's gonna pick the eleven o'clock. There's a random element there. If we pick the same directions, we're gonna get answers exactly opposite each other. Of course, if we don't pick the same directions, then we might get the same answers. We might not. And that's the part that's predicted by quantum mechanics. Oh, I see, you don't ask it the three times when it's going from l A to New Mexico. You ask it one time, like one of the three people ask their question. That's what you're saying, and the person who gets to ask. The question is decided at random exactly, and in the hidden variables version, you can very easy calculate what are the chances that the one ball is going to give you the same answer as the other ball, And it's all determined, and so you can just do the calculations. You get a very crisp number of prediction. But quantum mechanics adds more connections between these balls because it says measurements in one direction are connected to measurements in another direction, which doesn't exist for the hidden variables versions. So it means you're more likely in the quantum mechanics to get the same answer as the other person. Bell's experiment is not a one off thing. You can't say from one experiment, Oh, definitely, it was random. It's a statistical calculation. Across many iterations of this experiment, you get a correlation between these things which should be impossible. In the hidden variables version, your measurements agree more often than if all the details were specified in advance, and it's because of that quantum mechanical connection between measuring in different directions. All right, Well, dig into this a little bit more, because I feel like maybe you're sort of waving your hand and saying, there's a lot of complex math here that we can't understand on the podcast. But I wonder if there are sort of intuitive ways for us to figure out why they would give you different results if there was there was a hidden variable or not. Let's try to dig into that. But first let's take another quick break. Alright, we're talking about Bell's experiments, which, if it's true, confirms whether or not quantum mechanics really is random or we just think it's random, which would also confirm whether the universe is random. And that's a pretty big deal, right. If the universe is random, then it's totally unpredictable. If the universe is not random, then everything that happens is kind of predetermined. Although to this day there are very strenuous philosophical arguments about what the results of Bell's experiment really means. Is it actually ruling out local hidden variables? And one person who argued very strongly that these experiments don't rule out hidden variables was Bell. Bell was persuaded not that the universe was random, but just that the universe was non local, that it was somehow coordinating the results of these experiments across space and time in a way that we didn't understand. Well, we had this experiment setup where we had some balls and we drew arrows on them, or had them quantum mechanically drawn on the balls, and then we sent them to New Mexico, and you had people asking questions alowing the way. But it seems sort of like you're saying that, really, to understand how Bill's experiment works, we sort of really need to dig into the math, because that's where the differences between a random universe and a non random universe really are. Like, if it's really random, then the math says that you should get one type of result from this experiment, and if it's not random, then the math has you should get another kind of results. Yeah, it does come down to the math. And there are lots of times in quantum mechanics where things don't make intuitive sense to us, but the math is pretty clear and it tells you exactly what's going to happen. And this is one of those scenarios where you're like, well, that would be really weird if that were true. The quantum mechanic predicts it to happen, and then you go and you do it in the experiment, and it does like people have in these experiments starting in the seventies and up till fairly recently, more and more sophisticated versions of them, and the numbers they get agree with quantum mechanics. They disagree with the local hidden variables picture of the universe. And what you want is to, like have a deep understanding of why that is. What is it about quantum mechanics that makes it have a different prediction. So this experiment predicts something different for quantum mechanics and the hidden variables theory, and that's tricky. I mean, it's very clear to just look at the math, like you write out the probabilities, you do the calculation, the number comes out of certain value. But we don't all think mathematically, and so you want sometimes an intuitive understanding. And I think the most intuitive understanding I have of it at least is that quantum mechanics ties up these different measurements, if you're thinking about measurements in one direction, how they're connected to measurements in other directions than sort of in the hidden variables version, everything is clean and crisp and they don't mess up each other, whereas in the quantum mechanical version. You make a measurement in one direction, it's more connected to measurements in other directions. That's what gives you these enhanced mathematical probabilities. All right, well, I think maybe the next and then should be have people actually done this experiment? I mean, we sort of talked about it, and we know that if it comes out one way, it sort of proves quantum mechanics is random or not. And have people actually done this experiment? They have. The first test was in nineteen seventy two, originally done with photons. You can do this kind of experiment with any sort of quantum object, where you can create entanglement, where you create a connection between these two things so that they have to like follow some overall constraint, want to spin up or want to spin down. In the case of photons, they're not spinning one half particles. They don't spin up or down. They have three different states, including like a circuit of polarization. But fundamentally the idea is the same. And so the first test confirmed Bell's experiment in nineteen seventy two. That was just a few years after his original paper. It's actually a funny story about that because Bell chose to publish his theorem in a really cheap journal that didn't charge him to publish it, and it meant that very few people actually read the paper when it first came out. It was such a cheap journal that if Bell wanted copies of his own paper, the journal would even charge large him for his own copies. Usually, if you write a paper, you get like a certain number of free copies. So he published it in this cheap, obscure journal, which meant that not many people saw it. But one guy did and he was really intrigued, and he set up the first experiment in the seventies to test this idea. And it involves kind of pairing up electrons or pairing up photons, and so maybe just to paint us a picture. You know, you've sort of run this bunch of times, right, not just once, and then you can tell the universe is random or not. You have to run it like a hundred times. And if at the end you get you know a certain number of times them both being spin up or spin down, it means that the universe is random. But if at the end you get that there was both spin up or spin down, as a different percentage, then you know that the universe is maybe not random. Right, that's kind of what we're looking at. Yeah, you prepare these particles, you send them off in different directions. Then you have some process to randomly choose the axis along which you're going to measure the spin. Remember, you have to have like three different possibilities and you have to randomly choose which one. Oh, how did they do it? Did they flip a coin? I don't remember the details of the first experiment, but they've become more and more elaborate as time goes on. They use things like telescopes pointed to distant stars, and like the flickering of that star helps determine which when you pick. They've been really really careful about how to determine these things. Sometimes they're linked to cosmic rays, which people think might be fundamentally random. Is there a mu on hitting my detector right now? So they do a lot of work to try to make sure these things are random. Remember in our episode about super determinism, this was the heart of the matter. People were worried about whether that choice really was random, or whether it just appeared to be random, whether the whole universe had been built to conspire to make these things look random when really they weren't. Wait wait, I think you're telling me that this experiment that humans have devised to test whether the universe is random or not depends on us doing something random. It's a little bit funny, isn't it. Absolutely, and people have been digging into these apparent loopholes and Bells experiment and that one of them like, how do we know that the way we constructed the experiment is actually random? Another one is, how do you know these two things actually aren't communicating in some way? The first experiment wasn't that big, you know, the photons, They didn't send them very far apart. And so they've been making these experiments more and more elaborate, trying to make them more actually random in the way they choose the axis, and making the particles further and further apart, so there's no way to transmit information from one to the other unless you do it faster than the speed of light. So they've been slowly working to try to close these loopholes. And every time somebody does want one of these experiments, somebody goes, oh, wait, but what if have you checked? How do you really know in one of the core foundational loopholes that people are trying to close is this one about the randomness. So they come up with these more and more elaborate systems to try to ensure that the construction of the experiment itself is actually random, right, because if the experiment depends on you doing something random, if you're if you're not really random doing it, then the whole experiment sort of falls apart a little bit, right. Yeah, absolutely, that's the base is of super determinism, to say no, things really are determined. It's just that even how you're choosing the apparently random element of this experiment is not random, that itself is determined by things that happened before. All Right. So then people have been doing this experiment for fifty years, and they've been trying harder and harder to make it more and more pure and exact and full proof. And what's the overall result that they've been getting. They've been getting that the universe is really random at the quantum level. They've been getting a result that says that there are no local hidden variables, right, That says that there's no information that's being passed along with these particles that somehow determines whether the ball is red or blue, or you know, what direction is pointed at. There's no information with the particles. Wait, I feel like maybe you're using um sort of lawyers speak here. Absolutely, I am right, Like I asked whether the universe is random or not, and you said there are no local hidden variables, which is not a yes or no answer, not a yes or no answer. So what are what are the lawyerly nuances here? Yeah, because it's possible that there are global hidden variables, that there's something controlling everything that happens in the universe that determines the outcome of this experiment. Bell's experiment only rules out local hidden variables, not global hidden variables. What's the difference, Well, local hidden variables would mean information is being passed along with the electron. Something about the electron itself in the environment of the electron determines whether it goes spin up or spin down. Something global would be coordinating across space time faster than the speed of light. And so. For example, there is an interpretation of quantum mechanics called Bomian mechanics where quantum mechanics is not random. But there's this pilot wave. This thing which controls the whole universe and arranges for these things, coordinates and says, oh, if this one over here spin up, I'm going to go make this one be spin down. And so it's like coordinating globally faster than the speed of light. Wait, so a local hidden viroiable is when the ball you put in the bag has a little pocket inside of it that knows whether it is spinning up or down. That's the local hidden variable. And the Bell's experiment proves that there is no such pocket inside of the the electron or the ball, but there might be a global hidden variable, meaning like there's a giant universe size pocket out there hiding information and coordinating information between here and alpha centric kind of right exactly, And that seems really weird. So the more common interpretation is equantum mechanics is really just random. If you don't like nonlocality, if you don't like things being coordinated across the universe, then the more common interpretation is, well, things are just really random. But it's important to remember that that's one possible interpretation of Bell's experiment. There are other ones which involve non local hidden variables, So it doesn't actually put a nail in the coffin of hidden variables completely, just local hidden variables. Wait, you're saying that like a global hidden viroiable, like the whole universe is coordinated somehow magically. Is this looks the same as a totally random universe. Yes, we cannot tell the difference. Nobody's come up with a way to disting between that view, which is Bowmian mechanics, which actually Bell himself is a huge proponent of and sort of Copenhagen view where these things are not determined and then they collapse when you make this measurement. I guess. Then the next question is if there is a giant universe size hidden pocket viable, you know, thing coordinating everything, is that random or not? In that theory, it's not random, it's deterministic. In that theory, everything that happens is determined by the initial conditions. There's no randomness in it. I feel like this confirms something I've sort of come to believe it for a long time, which is that there's really no difference between a totally random universe and a universe run by all powerful God. Well, we can't tell the difference. Philosophically, it's a very different statement about what's out there, what's real, what's happening in the universe. But it really goes to the heart of the question and like what that means. What does it mean for things to be happening if we can't know the difference, If these particles really are undetermined, or if they were determined the whole time by some crazy pilot function which is controlling the fate of the universe, What really is the difference to us if we can't ever devise an experiment to tell the difference, is there really a difference? I don't know. It's a really interesting question in philosophy, which is one reason why philosophers still have jobs, because people are confused. It sounds like we need to start a new religion called pilotism, maybe pilotism or how would you call it, global hidden vinableism. It's not a religion. It's a totally respectable philosophy of quantum mechanics, and it's not very mainstream because for a long time people thought that Belle's experiment ruled it out, and there was actually a proof by von Neumann that suggested that no hidden variables were allowed, but there was a mistake in it. So it's a sort of a historical accident that Bowman mechanics was sort of cast aside for many years, even though Bell himself was a proponent of it and people thought that his experiments ruled out all hidden variables. And now Bowmian mechanics is sort of like an afterthought. People don't get taught it in schools, not mentioned very often, even though it's totally consistent with our understanding of the universe. It's just maybe even stranger than a random universe. Well, it's interesting to think that maybe we'll never find out right, Like, it's possible that it's impossible to tell the difference between you know, all powerful God or pilot function or pilot wave and a totally random, unpredictable universe. It's possible, or maybe we just need next centuries and John Bell to come up with an even more clever idea for an experiment that can somehow tell the difference. I mean, I remember learning about this experiment as an undergrad in quantum mechanics and thinking, how could you possibly construct an experiment to tell the difference. It's impossible, and then reading his experiment going oh wow, that's clever. I never would have thought of that. So it might just mean that we need another generation of clever scientists. Maybe somebody out there listening has actually understood our description of Bell's experiment and thought, what if you add in this feature to it? What if you did that? What have you changed in this way to come up with a new experiment that might tell us the difference? Well, what's the probability of that somewhere between zero and one? As long as it's not zero, I guess we just gotta keep doing it and eventually somebody will come up with the answer. Right, that's how statistics works. That's right. If we do an infinite number of podcast we will eventually inspire the physical theory of the universe. Yeah, we'll eventually get to take credit for understanding the universe exactly monkeys on typewriters and cartoonists and physicists on podcasts. Well, we're making pretty good progress, right, we'ven We've got a couple of hundred episodes on Under our Belt. Yeah, something north of four hundred. Yea, So now we just need what infinity minus for hundred more exactly? Let me do the calculation to do too. That's infinity but getting close all right, Well, we hope you enjoyed that attempt to try and explain Bell's theorem, which is pretty complicated. It's pretty complicated even if you have the math and the diagrams in front of you. So thanks for bearing with us and this attempt to translate into a one dimensional form for your audio stream. Hope you enjoyed it. Yeah, and please join my new church of pilot Is where Jorge is the God. Are you accepting donations? There you go, that's right, I am the pilot Wave. Thanks for joining us. See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast for my heart Radio, visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. Ye