Daniel and Jorge Explain the UniverseDaniel talks to Prof. Valia Allori about the theory of Bohmian Mechanics, a deterministic alternative to traditional Quantum Mechanics.
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Quantum mechanics just doesn't seem to make sense. It tells us that the universe is fundamentally random, that some questions just don't have answers, that there's a limit to what can be known about reality, and that things change when we look at them. More than that, it tells us that reality is fundamentally different from what we have imagined. But what if that's not true? What if that's wrong? What if it were possible to build a theory of quantum mechanics that doesn't describe the universe as bizarrely random, that doesn't have any special role for observers, that doesn't suffer from the famous measurement problem, and that lets us think of the microscopic world as very similar to our familiar intuitive world. And what if this theory actually worked and was able to describe and predict experiments? That is, what if there's an intuitive alternative to mainstream quantum mechanics. If there were, why on Earth wouldn't it be embraced. Hi, I'm Daniel. I'm a particle physicist and a professor of physics that you see Irvine, and I want to believe that the world makes sense. We are all drawn to basic questions about the nature of the universe. How does it work, Why is it this way and not some other way? How did it all begin? And how will it all end? Physics is supposed to be a way to get answers to those questions, and so welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio, where this is precisely the kind of question we ask and the kind of answer we reach for. And the amazing thing is that physics kind of seems to work. It offers explanations, explanations that not only work because they can predict what happens in experiments, but explanations that usually make some kind of sense. The stories they tell us are mathematical and could be very different from the stories we guessed at. It turns out the Earth is millions of years old and not thousands, that stars are massive balls of fusion in the sky rather than tiny pinpricks in a screen. But in the end, these mathematical stories, if physics tells us about the universe, they are coherent, they are sensible. We can use them to understand how the universe really is. Except in one area, quantum mechanics. While we do have a working theory, we struggle to make sense of it. What does it really mean? What is it telling us about how the world really is? And while we have lots of different interpretations, we struggle to accept the story that they tell us. Is the universe really random? Is everything really described by the wave function? Does it collapse when you observe it or split into millions of meta universes? Or do objects not really have any properties on their own to observe or all properties relative to the observer. None of these are easy to absorb, to click into our minds and let you say, oh, yeah, I get it, that's how the universe is. But what if there was a version of quantum mechanics that was more intuitive, that was deterministic, that didn't need some observer effect or multiple universes or a redefinition of the nature of reality. Well, today we will be exploring a less popular theory of quantum mechanics that doesn't rely on randomness and uncertainty. It tells us that what is happening to tiny particles is much simpler and easier to swallow, and we'll talk about why it's been overlooked by mainstream physics. So today on the podcast, we'll be asking the question does quantum mechanics have to be so random? My friend and co host Jorges on a break. So I'm continuing our series of conversations with experts in quantum mechanics. We spoke to Adam Becker about mainstream quantum mechanics, to Carlo Rovelli about his theory of relational quantum mechanics, to Sean Carroll about the Many world's interpretation, and today we are speaking to an expert on pilot wave theory, also known as Bomian mechanics. So it's my great pleasure today to introduce all of you to Professor Valia Alori, who, if I understand correctly, holds two PhDs, one in physics and one in philosophy, so she's the perfect person for us to talk to about the crazy philosophical consequences of quantum mechanics. She's also a full professor in the Department of Philosophy at Northern Illinois University and a fellow at the John Bell Institute for Foundations of Physics. Professor Alori, welcome to the podcast. Thank you for having me, well, thank you for coming here to talk to us about the mysteries of quantum mechanics. Before we get into the details of pilot wave theory, I thought we should take a step back and remind ourselves why we have so many theories of quantum mechanics and why there are still so many questions about it. To me, the basic question we have about quantum mechanics is what is going on? How do we understand the story that it's telling us. Our intuition is to think of particles as tiny dots of matter, but quantum mechanics usually tells us that they are basically different, that they are fundamentally different kinds of things because they can maintain two contradictory possibilities at once. There's also this wave function that seems to control what happens, but then it collapses when you touch it, but it's not clear what the rules of that collapse are. It's so hard to get a mental picture of what's going on with the little particles. So how do you approach this question of trying to understand what quantum mechanics means?
So first of all, let me just say that I'm not sure that we should understand quantum mechanics philosophically. There is a sense in which we don't understand quantum mechanics even physically as a physical theory, because I mean, the theory seems to be talking about you know, electrons and protons and men better in general and fields, but when you actually look at the formalism, it's unclear exactly what plays the rollos of what. So we do have an equation, the Shootinger equation, which is a question of evolution for the wave function. Should we understand the wave function as a physical object if the wave function is a physical object, what does it represent? Does it represent particles, does it represent fields? Since I was a student, just to put it bluntly, I really had trouble relating to the theory as a physics student. But even granting that it's acra to talk about that as a theory about something, Let's put it this way. The theory, I would say, is either empiredically inadequate or it's incomplete.
Why is that?
Well, because I just said that, you do have this equation, which is the Shreadinger equation, which is a again the question of evolution of an article the wave function, and the wave function is a call like that because it's a wave. So and wave can superimpose. You know, you throw a rock in the pond, right, throw another rock in the pond, and you see waves from one rock, and then you see waves from the other rock. They superimposed. You have interference in the fraction of this kind of behavior that you would attribute two waves. Okay, And so since they do superimpose, if you think of the wave functions that are presenting objects of physical objects right at the microscopic level, they could be in a superposition state, right, and nucleus or radioactive substance of subsort could be in the superposition of a decayed state or a non decayed state.
And by superposition you mean that there's two possibilities for an object that could be spin up or spin down, or decayed or not decayed. There's two options for the situation it can actually be in.
Yes in a sense, yes, more generally, I mean mathematically, this is the mathematical property of the equation.
Right.
I mean the prototype example is the problem of the Shuldinger cat, right, in which you do have this cat which is in a box. In the box that is this vial of poison. The vial of poison will break because it's connected to this radioactive substance. So it will break if the substance will decay, but nothing happens, it will not break. So what happens is that if the nucleus decays, dile of poison breaks and the cat dies.
Okay.
So that's a possible state of affairs. Otherwise, nothing happens and the cat stays alive, okay. And so what happens is that, however, given the superposition state, possibly given the fact that there is a possibility of having a superposition state as a true physical state for the system, then you could also have this microscopic superposition of decayed and non decayed which actually spread out of the cat. And so the theory predicts this microscopic superposition which will never ever observe. They are not observable. That's not what we have experienced us. So there is a very strong sense in which theory as it is is empirically inadequate, because when we open the box and when we check on the cat, the cat is either dad or alive.
So what I'm hearing you saying is that quantum mechanics is useful as a description of these microscopic states, by which I think you mean like quantum particles, electrons, and photons, et cetera, But that we don't really understand what it means and we can't access it directly. We can't like see these things. We have to interact with them using macroscopic objects like detectors or our fingers or cats, et cetera, which don't have the same quantum properties, and so it doesn't really answer the question of like what's actually going on in the microscopic level. Is that a summary of the problem.
Yes, actually it's more than that. So not only doesn't explain what's going on intuitively at the microscopic level, but also if you try to apply the theory to everything, including cats and detectors and stuff like that, the theory doesn't give you what you observe. So it's really bad for the theory. The theory doesn't. I mean, it is actually falsified directly by the fact that the straining question is it's.
A linear I think, because you're saying that they suggest that cats should also be in superpositions, and fingers and detectors and everything should be in superpositions. But that's not what we observe. That's what you mean by experimentally falsifying.
Yes, exactly.
And of course, I mean you know, the founding fathers were not a naive, and they newness, okay, and that's why they proposed at least that's what to Nouman did, right. He proposed that there is actually a second evolution equation for the wave function. And so they say, okay, right, you don't want microscopic superposition, Okay, So when do you get them again? Oh, when there is a measurement, aha, So when the measurement is performed, then there is a different evolution equation. Okay, the wave function randomly collapses in one of the terms, the superposition, and when you open the door and you see the cat haha, the wave function actually collapses. So you right, in a sense right as the detector right, you collapse the wave function.
An issue there is that we don't have a clear definition of what a measurement is and when it happens. Because you can imagine, you know, if I'm poking something with my finger, the tip of my finger is still a microscopic particle, so why should it collapse the wave function and two particles on the tip of my finger should still be a quantum mechanical system. So there's no like clear line when something becomes classical or microscopic when the wave function should collapse.
Yes, exactly.
I mean we don't know who does the collapsing, who kills the cat?
Right?
So is it me when I open the door, or is it my consciousness? We don't really want to enter into that. So it is a problem that you're suggesting. Namely, it's not a precise physical theory doesn't really define what a measurement is because I mean, this is puzzling because we just would like measurement just to be physical processes like anything else, right, I mean, they're made of particles, quantum particles, and so why are they special. So there is a sense in which started from this, which is called the measurement problem, because I mean, we are actually measuring what is the state of the cat, and the cat is actually measuring what is the state of the particle. Another way of putting this would be that measurements when you're performing a measurement, Quantum theory says that measurements do not have a precise result. Okay, so like the cat doesn't have a precise state, and so various. I mean people call them interpretation, but I actually think that they are different theories, but they have different solutions of these problem so to speak. So booming mechanics is one of those. It does solve this problem, even if I do think that's not the way the reason why it was proposed. So this theory was proposed by I mean, the first version of this was proposed by the Brody in nineteen twenty three as part of its dissertation.
So according to.
This theory, what happens is that I mean, just like very very Some people like to put it unromantic, right, something very plain and boring in a sense obvious because it according to this theory, matter is made of particles. It's like in classical mechanics, but they do have a different evolution equation than quantum theories. In this theory there is this object which is the wave function, which is the same guy as ordinary quantum theory, but it evolves according to Streadinger equation. So you do have an evolution equation for the particles, which is first order, and then you have an object which is the wave function, which evolves like in regular quantum mechanics, according to the Streadinger equation.
So then in the Copenhagen interpretation, the one most people are familiar with, the wave function is supposed to be everything is supposed to describe the whole system, and particles when we're not looking at them sort of operate according to this wave function, which evolves according to the Shorter equation. But then there's this weird second bit where things collapse to particle like behavior that we observe when you look at them. So, for example, you have a particle that's supposed to hit a screen, the whole wave hits the whole screen, but at some point when it interacts, when that measurement happens, then it becomes a single point, a flash of light on that screen. And so you're saying that boy and can exist different because not only do you have the wave function, but you also have the particles. It's not like this. There's sometimes waves and then sometimes particles. They're always particles, but they're governed by this wave that sort of guides them through their path.
Yes, so there are always particles. That's what matter is made of. Tables and chairs and people and screens and detectors and whatever are all made of particles. So what happens is that these particles their trajectories is mathematically written down in terms of this wave function, and this way function in itself evolves according to a given equation. Okay, So usually what you said is kind of important because the very common way of describing the theory, which is also called because of this reason, the pilot wave theory, is that this particle are pushed.
Around by this wave.
Okay, So the usual slogan is, oh, it's not particle and waves or waves, it's particle end waves.
Okay.
So there is a sense in which this is true, in the sense that there are particles and there is also this wave function. However, I think that it is kind of misleading to think of that in these terms, because if you think about what kind of entity the wave function is, it is a wave, but not a wave in three dimensional space. Okay, if you think of how to represent the wave function, what the wave function really is? It's a function of all the particles, right, it is a function of the configuration, in the case of bomb me mechanics, the function of the configuration of all the particles. So it has three dimensions for every particle. So in total it has three n dimensions if the universe is composed of n particles, so it's not a field in three dimensional space.
The way function, then, just to be clear, talks about the trajectory of all the particles in the universe, and so they're all sort of combined into this one grand object.
The way function Bob me Mechanics talks about is the wave function of the universe. So the one that evolves according to the Shottinger question is the way function of the universe. So I do have two things to clarify here. So The first thing is, so how we should interpret this wave function physically? It's an open question. I mean, philosophers and physicists start talking about this.
All the time.
But I do think if you describe Bomber mechanics as I just did, namely, is the theory of particles with the wave function defining that trajectory. And you can understand the wave function has pushing the particles just in the same way as you understand gravity is pulling stuff right on the ground. Okay, So it's I think that the best and this is my personal take on this, is that the best way of understanding the way function in Bomia mechanics is to think of that as law. Like right, It's part of the ingredients of the law of nature, something that you need right in order to specify the right trajectory, the one that you observe. And so the other thing was about the wave function of the universe. So the fact that the way the function is a function of all these particles is something that leads to a very important feature of bombing mechanics, which is it's no locality.
And I want to talk about non locality in a minute, but first I just want to make sure that we have a clear sense of what's going on here. So we talked about how the problem with quantum mechanics was this measurement problem that what happens when you measure this wave and it collapses into a particle. So how exactly does Bomian mechanics solve that problem? Is it because things are always a particle and so when you look at them, they were a particle and it's no big deal, and this is where it was, and it has like a well defined trajectory that in Boe Mean mechanics you really can think about like electrons as tiny little dots of matter flying through the universe, the way planets fly through the Solar system.
Yes, I think that's right.
In the case of the cat, the cat is made of particles like everything else, so it is either.
Dead or alive.
Okay, the cat is either dead or alive at all times. Okay, So the microscopic superposition should not belong to the wave function, but the wavefunct, which is not what cat is made of. The cat was made of particles in particles of a precise location, which is what it is.
Right, either in the dead camp or in a life camp.
So This is really different from the way people are sort of taught to think about quantum mechanics, that information isn't there until you measure it, that there's a fuzziness to the universe, that there is fundamentally random all these really alien elements of quantum mechanics that make it so weird. Boemi mechanics seems to sort of like chuck that out the window and say, no, everything actually is determined. There is no randomness or uncertainty. There's just some information you sometimes haven't measured yet, but it's really there. That the cat really is dead or is alive. It's never sort of uncertain. Is that true that there's really no randomness, no true randomness in Bomian mechanics.
It depends on what is meant by that. So it is true that the cat is either dead or alive. It is true that the particles even passes through one sleet or the other slate. It is true that when you observe a flash on the screen that was coming from a particle that traveled all the way from the source to the green.
And it is true that there is no fuzziness.
That's why I think that boomy mechanics is physically clear, and the question is okay, so is there no randomness? Well, now there is randomness because the prediction of Boomer mechanics are provable to be the same as quantum mechanics, and quantum mechanics predicts probabilities.
Right.
The traditional story is that you do get only the probabilities of the results. Right, you obtain this, this or that not with the definite outcome. For sure, you have a probability distribution of the experimental results. So the legitimate question is where is this probability is coming from? In Bomian mechanics, they come from the fact that So, I mean, this is a more general question about how is it possible to get probabilities? If you have a deterministic theory. Deterministic theory, you have one past, one future, right.
If you know the law.
If you not the initial condition, you know everything. Right, everything is the termine. If you have this Laplacian demon knows it all and everything. He knows everything. So this is a deterministic theory. So what are probability is coming from. They're coming from the initial conditions. Okay, so there are two elements here, right. In determinism is something like that given the initial conditions and given the laws, you know everything. So if you do know the laws and you do know that I mean principle, you can predict anything.
I want to talk more about this randomness and initial conditions, but first let's take a quick break. With big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price you thought you were paying magically skyrockets. With Mint Mobile, You'll never have to worry about gotcha's ever again. When min Mobile says fifteen dollars a month for a three month plan, they really mean it. I've used Mint Mobile and the call quality is always so crisp and so clear. I can recommend it to you. So say bye by your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. You can use your own phone any Mint Mobile plan and bring your phone number along with your existing contacts. So dig your overpriced wireless with Mint Mobiles deal and get three months a premium wireless service for fifteen bucks a month. To get this new customer offer and your new three month premium wireless plan for just fifteen bucks a month, go to mintmobile dot com slash universe. That's mintmobile dot com slash universe. Cut your wireless build of fifteen bucks a month At mintmobile dot com slash Universe, forty five dollars upfront payment required equivalent to fifteen dollars per month new customers on first three month plan only. Speeds slower about forty gigabytes on unlimited plan. Additional taxi, s, fees, and restrictions apply. See mint mobile for details.
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So yes?
So so if you say that you do have this distribution of the particles, the particles of distributed according to quantum eclibum distribution, and it is an equilibrium distribution and nothing changes anymore, then that's the most complete information that you may have about these particles. And see, we do not have more knowledge than this about the particles. Then we have absolute uncertainty about the precise positions of the particles. And so this plays out into having a distribution of the outcomes at the end of the experiment.
I see. So we have particles which go through the experiment using deterministic laws. So the entire outcome is determined for each particle based on how it came into the experiment. But we have some distribution of inputs that the particles when they come into the experiment, they're never all actually at the same angle or location or whatever. There's some variation there and that gives a variation in the output. So not a randomness, but you have sort of variation and the inputs gets translated to a variation on the outputs, sort of like you know that game where you drop a ball and it goes left and right and left and right and left and right. It's sort of chaotic. It's very hard to predict exactly what slot it's going to go into. But in theory, if you did drop it exactly the same place twice, it should end up in the same slot twice. So Boemian mechanics describes the universe that way that you have some like variation in how the balls start to drop, which is how you get a variation in the output. But each trajectory of each one really is like a tiny, classical little baseball. That's crazy to me. I mean that requires like a whole rethinking of the idea of quantum mechanics, because I've spent twenty years getting used to this concept of the universe being random and unavailable and fuzzy, and this is now saying, oh, no, you actually don't have to take that whole weird route after all.
Yes, that's right, So you don't have to, and so why go for it? So, I mean, there is this uncertainty that you have regarding then the configuration, right, the initial configuration but that's it, right, You don't have to transform that into necessarily into somehow random trajectories or randomness more radical levels.
But where's the fuzziness come from in the beginning? I mean, does the universe start with fuzziness? Because the standard picture we have, like why the universe is not totally smooth while we have galaxies here and not over there, is that we had some like quantum fluctuations in the early universe that gave us densities which you know, dot dot dot. Billions of years later we have galaxies. Where do those fluctuations in the density of the early universe come from? If not from quantum randomness, is it some pre pre initial condition or the big thing?
Yeah, well, I have no idea, so I mean, but I mean this is I think it's a very very important thing to notice.
Right.
So if you do have a theory, which is like moving mechanics, is precise mathematically and physically, meaning you do have equations right written there, they apply every time. Right, it's not like oh, you use this or use that measurement, No measurement. No, it's precise, okay, and it's precise physically. It gives you a picture of what's going on, which is exactly how it was in the classical you know, when we're thinking about classical physics, and one of the you know, the merit is that you can visualize.
Okay.
So but if you do have this theory and there are crazy things about it, you know how to which questions are needed? Right?
Which questions are really the ones that we should focus on? Okay?
So one question is where is this absolute uncertain thing coming from? Another question, right, is what about the fact the way function is a function of all the configuration. There is a sense in which you may say that, you know, boombing mechanics removes all the romance from from physics, and that I think that's a merit romance.
I would say, removes all the headaches the head.
Oh yeah, exactly. I mean to me, it removes all the headaches.
But some people, you know, they think of that, Oh yeah, but I mean the observer, you know, gains again, right, the center of the attention. I'm not sympathetic at all about this kind of talk, but I mean some people are attracted by the craziness, right, and so when they hear about bombing mechanics, they think, oh, where is all the fun where is this? I mean, physics is fun, but maybe in a different way.
I'm sympathetic to that because I think we want physics to teach us the truth of the universe, and we hope in our hearts somehow the truth of the universe is not what we imagine, that we're going to be learning something that requires some sort of like mental revolution to be like, wow, the universe is so weird and different from what we imagine. And so if you're just telling me, know, the universe at the tiny scale, it's just a tiny little bunch of baseballs, the way it is sort of like the atomic scale and the macroscopic scale and the scale of planets and stars, then yeah, I guess that does remove a little bit of the mystery. But you know what, I was struggling to learn quantum mechanics and absorb it intuitively as a college student. The thing that really got me over the hump were these bells theorems, and these bells inequalities that really seemed like definitive proof that quantum mechanics was random. And we have these experiments and very clever people have shown that there are these correlations among entangled particles that simply cannot happen if quantum mechanics was not fundamentally random, that you can't like secretly hide all the information that it can't be the things are really just one way or not the other way that you know before you look at the electron. It always was spin up in my mind. Those bells in equality really sort of like killed that possibility. Said, no, you have to accept fundamental randomness. Why don't these theorems, these bells and equalities and those experiments, why don't they kill Bomian mechanics.
They did kill it for a long time. Actually, you know, the first theorem that was the theory which allegedly proved that hidden variables are impossible, was due to for Noymann in nineteen thirty five or something like that, and so he basically wanted to put an end to all for reasons that are you know, maybe historically interesting, but I mean what he wanted to provide was a proof and mathematical proof that you cannot do better than quantum theory. So that was just like kind of you know, oh, we all would like to have a pictorial view of visualizeable theory, right, but we cannot. That's what he wanted to prove, and so he went by contradiction. Okay, so he said, okay, let's pretend for a second that we can complete quantum mechanics. Let's pretend for a second that we can add these hidden variables right to the theory. The theory is not complete, right it is. There are these even variables. At first, they're hidden for them in the sense that quantum theory doesn't specify what they are. And so he said, okay, let's pretend let's start with this theory, let's work it out, let's work the consequences out. And what he obtained was that there is some sort of a contradiction, like you know, five is greater than seven. I mean, it's not really the case, but I mean you can imagine.
Something like that. Okay.
So he said, okay, what are the assumptions? I mean the reasonable assumption. So the only assumption that we have, So we had reasonable assumption, we started from this Hiddene viable theory. We get contradictions. So the only way out is just to say there are no hidden variables.
The quantum world is weird.
For those of you who don't know, Van Noyman is one of the great mathematical geniuses of the century and really credited with like pulling together the mathematics of modern quantum theory. And so when he said something, people tended to listen, and you know, it was sort of difficult to stand up to Van Noyman, you know, back in the forties when he was in his heyday, he was very influential.
Exactly. I mean, this is actually something normal.
It's not like you can charge these people to have listened and just relied on the authority. It was just like kind of normals. It's for nomen process theory. I mean, there is not much of a reason to suspect fact that he was wrong. But he was wrong because he assumed something which is a standard assumption of quantum theory. The experiment doesn't really change the system, Okay, the interaction is small enough that the property that you're trying to measure is left the same. Okay, Like I was talking about before, I do believe I have a fever. Say okay, I want to measure my temperature and making an experiment, put the thermometer under my arm. Wait a second, wait for the interaction. Then the mercury or whatever, the galium or whatever, it is expense and it gives me the temperature. Okay, so, but the temperature that I read is not really my temperature before I actually put the thermometer under my arm. It's actually the equilibrium temperature between the thermomytery and me. Okay, so, but what I read is we forget about this all the time because we believe that I mean, this is the property of the thermometer, which is thermometer in such a way that it doesn't affect too much that the equilibrium temperature is really close to original temperature.
So you're saying that, for example, when you measure your temperature, you actually measure slightly lower temperature than your actual temperature because the thermometer is slightly cooler than you and you guys have come into equilibrium, and it's sort of like putting a tiny little piece of ice on you and it's cooled you down a little bit. And in the same way, you need to take that into account. And band Noyman ignored the impact of the measurement on the system when he was making all of his calculations and proof that quantum mechanics had to be random, that you couldn't have any hidden variables so right.
It's actually worse than that, because I mean, this is a general assumption that we all make when you're doing quantum theory. Right, we do assume that, I mean, the operators represent properties. The problem is that most of the time the experiments are such that they perturbed the system so much that they don't measure anything about the system. They tell you something about the interaction. Think about you want to know where the table is, Okay, so you switch on the light. Basically what happens you hit the table surface with footons. The photons go into your retina, and the retina records the result. Right, but I mean the photon bounce back, but also the table recoils. It to be you forget about that, okay, because the mass and blah blah blah. Okay, it's much bigger. However, instead if instead of willing to try and find the position of the table, you want to try and find the position of an electron, Okay, you switch on the light. The photon hits the electron, and the electron goes So what you measure the electron is going to click somewhere in some detector.
Somewhere, So the position what you're measuring is.
Not the position of the electron before, it's the position afterwards. Okay, which is totally fine, But I mean what is tricky sometimes what you want is that not What for Noemen actually proved was not that the variables are impossible, but that he proved that not all experiments are actually measurement, so all the certain experiments are able to measure, namely those experiments where the interaction is not that high to destroy the system or perturbic too much.
And how does that connect with hidden variables? Like I get that he's showing that you can only make a measurement if you're making a very small, negligible interaction on the system, that you're extracting information from what happened before you measured it. How does that connect to the question of whether quantum mechanics is really random or whether there's sort of hidden information in there that controls what's happening.
It doesn't have much to do with hidden variables. But for sure, his theorem was supposed to be showing that hidden variables are impossible, Okay, but he didn't show that because he had this assumption in it. He came out with the contradiction because he was assuming this, and so he was assuming that there are properties and these properties have actually weird behavior.
So he set out to prove that hidden variables couldn't exist, and he did it by contradiction. But he considered a false assumption into his proof, which is the thing that led to the contradiction. So his conclusion about hidden variables was therefore invalid because the contradiction came from somewhere else. And then this stood for decades. Right, people thought, oh, by norm improved, the quantum mechanics must be random. So this burglar theory, this, this deterministic idea of quantum mechanics, we shouldn't even think about that. And then what happened? When did people realize, oh, hold on a second, Van Normen was wrong and it's possible to have determinist quantum mechanics.
Yeah, well, some people actually figured this out immediately, but we're ignored either because they were, you know, not very well known figure, or because they did really want to batter.
I mean, according to some.
People, did Einstein figured this out immediately, but he didn't bother to reply. And it is also true that the original proof of h. Normen had other issues, which, however, we're you know, taking care of in proofs that came later. But the person who actually figured this out was Bell, John Bell, who actually came back to this Phenoyemen proof and figure out where he was wrong, namely the assumption that operators necessarily mean you can understand experiments always as measurement, which is not necessarily the case.
So the same Bell who's responsible for most people thinking that quontomic has to be random because he showed these crazy inequalities is the one who also revealed that Noyman was wrong in proving the quantum mechanics is random. So this Bell guy had a pretty big role to play in our understanding quem mechanics.
Yes, yes, and I mean, and also just the case that he was often misunderstood for many years, even if he clearly wrote down what he was trying to prove. So I mean, indeed he was writing about for Noyman's proof, and very shortly after he came up with his own bels inequality. So he did try to provide it did invariable theory. So he was trying to do the same as for Noymann and say, okay, so if we do have this is an ar variable theory, what do we get there is a sense in which you can take as you were doing at the beginning, Right, He's inequality just like a different variety of impossibility proof against the invariable. But actually, as many people would say, even if there is a sense in which it's controversial, I mean it's controversial whether he actually proved it. What is not controversial is what he sought. Namely, he sought to have proven that, at the end of the day, if you have a theory which respects the prediction of quantum mechanics, that this theory has to be non local.
Right, So let's unpack what that means for a moment, Because Bell's inequality tells us that the universe has to be random, there can't be any hidden variables. But it turns out there's a caveat. That's only true if you're talking about so called local information, right, and information which is accessible to somebody like in their immediate environment. You know, like I can know what's near me, I can measure something nearby, but I don't know anything about what's happening in Andromeda right now because this sort of limited passage of information. And I want to talk more about entanglement and locality. But first, let's take another quick break. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love. With less of an impact. Visit us dairy dot com slash sustainability to learn more.
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Okay, we're back and we are talking about whether quantum mechanics is what we call local. We know that there's a limit on how fast information can move, that there's this speed limit of information in the universe, and that information cannot move instantaneously. But this gets confusing when we talk about in angled particles, you create two electrons so that they have to have opposite spin, but you don't know which electron is spin up and which one is spinned down. But as soon as you measure one to be spin up, for example, you know instantaneously that the other one has to be spinned down. And that seems sort of non local because the particles can be entangled, but they can also be really far apart. So all of a sudden, when you measure the spin of one particle, the other one, which is many many kilometers or maybe light years away, instantaneously collapses to have the other possibility.
So I would put it slightly differently in the sense that I would say that in general what Bell proofs tools that you do have no locality. In general, at the beginning, particle one didn't have any spin property because of the entire state. When it's measured, instead, oh it turns up up so and the other immediately down.
And the issue there, of course, is that these things can be separated. Right, So if these two particles, they have to have opposite spins, and classical or in the traditional quanom mechanics tells us that both of them have the possibility to be up and down. And so when you measure one of them and becomes up, then the other one now hundreds of miles away or thousands of miles away, somehow instantaneously goes from being up or down to only being down. And that's this question of non locality, right, How does the information get from one particle, you know, to the other particle faster than the speed of light.
Yes, that's a problem.
That's something that they regarded as a non starter. It was just like thinking about I mean, that's one possibility and the other possibilities instead that they really had a property of spin since the beginning, right, So you measure spin up because the first guy always had spin up from the start, okay, And so they don't actually talk, right, They were prepared in up and down, and you detect them up and down.
And that's this hidden variables interpretation that they always are something. It's just you don't know about it, hidden from you until you measure it. But that there's no actual uncertainty. It's not like there's the particles actually in up and down until you measure it. And so that's this problem with non locality, right. And you're saying Einstein and collaborators were suggesting this is ridiculous because it requires a theory that's non local, that somehow these things have to coordinate to make sure that they're always opposite spins. And so what did Bell show? Bell showed that every theory of quantum mechanics has to be non local.
Yes, because I mean he started off with a theory like that and he predicts inequality, and so they eat the variables. You have to imagine something like this, so you have quantum mechanics. Quantum mechanics implies that there has to been variables.
So one of the main objections people might have to this theory of deterministic particles being guided by the wave function, that information is actually there, it's just we don't know it. Sometimes is that we thought the quantum mechanics have to be random because of these arguments by Bell and these experiments that showed that you couldn't explain these experiments using some hidden variables. But it turns out that you couldn't explain those experiments using local hidden variables, but you can explain those experiments using non local hidden variables. So Boneian mechanics works and is consistent with experiments if you have non locality, this idea that particles that are not in the same place, that are not near each other can somehow you know, communicate or coordinate their arrangements. And you might think, well, that's crazy, that's bonkers, how could that be possible? And that seems like a pretty big objection. But I think as you were saying, Bell showed that this is actually true and required for all theories of quantum mechanics, not just Boomian mechanics, And so it's not really a strike against Bonian mechanics to say that requires non local information.
Yes, that's true, because I mean, he did prove his inequality, and if you're right, then down in the appropriate way you will see that the hidden variable is just a passage in the deduction, but it's actually something that you don't require. So that arguably what's going on is that every single theory that has the same prediction as fund to mechanics will turn out to be non local.
But doesn't non locality seem sort of crazy? I mean, special relativity tells us that information takes time to propagate through the universe, that what's happening in Andromeda can't influence me right now because I'm outside of its light cone. So if you're telling me that not only does Bonian mechanics which seems like a beautiful description of the universe and nicely deterministic, require non locality. But all theories of quantum mechanics require non locality. How do I then accept that? How do I think about the universe as non local? Does it mean that every particle in Andromeda potentially can influence me? Right now?
Yeah? Okay, so that's the craziness. Right.
So that's a good thing about Bona mechanics because in this theory the non locality is obvious. It's clear right there in the wave functions. So the next thing that we need to do as physicists is to investigate how it's possible for a theory like that to be compatible with relativity theory.
Right.
We just directs us to the right questions again before I actually talk about that. I mean, so you don't really have to go into the interpretation and show that all the other interpretations are non local. Just think about the regular theory, okay, with the collapse. When you do have the collapse, the collapse is no local, right, I mean, think about the original EPR argument. Right, how do you explain the compere relation over there? It's no local, right? You measure one the other has to tell the first one has to tell the other one. Right, that's no locality right there. It's not a problem of the hidden variables. I mean the regular I mean the textbook theory has it right there. Indeed, Heisenberg accepted that, and he has there are some lectures that I forgot the year, the precise year, in which he talks about exactly this. Right, the collapse is no local, but then he says it doesn't contradict relativity.
He didn't really take it seriously.
That much because he thought that it can accuse the no locality of the collapse to transfer information. So if you think of relativity as a theory of signals, there is not I mean, you can get around this's.
Not locality, right.
And so for listeners who are curious, it does seem like there's some weird non local features of quantum mechanics, but it is not possible to use that non locality to send information faster than the speed of light. And Jorge and I did a whole podcast on that, so check that out in detail. We don't have time to get into all of that today, but if you're curious about why you can't send information faster, than the speed of light using quantum entanglement. We did cover that in a whole podcast episode. All right, so this is really fascinating and I don't want to use too much more of your time, So I just want to ask you if Boney and Mechanics, you know, is a nice, beautiful picture of the universe and explains all the experiments that we have and doesn't require us to accept some strange alien uncertainty and randomness that's counterintuitive and only requires the acceptance of this concept of non locality, which already is present in all other quantum theories. Then why isn't it the dominant quantum theory? What are the objections against it? Is it's still sort of like historical inertia because von Neuman didn't like it, or are there you know, real philosophical objections to it.
So, I mean, I think that part of the problem has to do with the fact that historically it was blocked. I mean there is all this you know, historical accidents that happened one after the other. I mean, first Ball was you know, ostracized for various reasons, and then for Noymann contributed to this. There seems to be no real reason to reject this theory from a rational point of view. I mean it provides a clear mathematical picture. It's a clear physical picture as well. You do have to accept no locality, as you said, but I mean it's something that we have to deal with. Some people sometimes mentioned that, oh, it's not testable in the sense that provably the prediction of the Boomian mechanics are the same as quantum theory. That's not a good objection for a variety of reasons. First, because I mean you have a piece of evidence. You have two theories, right, and so which one of the theory is the evidence confirming, assuming that you can confirm a theory the first.
Okay, so who came first?
Then brow in nineteen thirty twenty twenty three, right, and some of Cole No, no, no, But it's simpler, right you quan to mechanics is simpler.
That's just one equation.
Booe mechanicis has two equations, one equation with two evolution equations. Okay, so what about time of flight? You have particle physicists, right, you measure time of flight, you measure where the particle how long they take to go from here to there? But there is no time operit and so what are this time of flight results? Well, I mean the regular quantum theory have resorts to this kind of approximation. Right, If you approximate the time measurement in one way or in another way, you get.
Different distribution of results.
Bomby mechanics gives you you know, the particles, right, so you don't need the operators, right, you just do you use the particle trajectories and do the calculation that you would do classically.
But we quantum trajectories, and.
So there is the possibility of actually making an experiment. So there are some cases in which you can you can put yourself in a situation in which the prediction from quantums are different from booming mechanics. This can happen because you know, quantum mechanics is not precise. It's ambiguos in this respect, so you can test out. So there is a strong sense in which you can you know, falsify quantum theial or quantum mechanics. So even if your physicists are usually strong about this undetectability business, but I mean no, you can detect. So I mean, I really don't understand that much about the reasons why booming mechanics hasn't been taken more seriously by physicists, and I hope the situation will change.
Well, what it might require for to change is maybe for us to meet alien intelligence and talk to them about quantum mechanics and you know, maybe their way in and they'll say, sorry, folks, we think it's many worlds or no, what you call boomy mechanics is what makes most sense to us. So on the topic, let me ask you totally off the wall question, what do you think are the chances of that that if we meet alien intelligence that they will have sort of similar concepts about the universe? I mean, really, another way to ask the question, do you think what we're doing here are playing games inside our own minds to try to tell mathematical stories about the universe it makes sense to us, or do you think we're actually probing something deep and universal which we could present without embarrassment at the first Interstellar Physics meeting after we meet the aliens.
I really do hope that we can meaningfully talk about the universe, and it seems like we are actually succeeding in that right. We explained so many things since the beginning that we started doing science, not We've made many hypotheses and constructed many theories, and some of them were bad ideas, some of them were better ideas. I think that the fact that we are explaining so much is an indication that maybe we are.
Onto something, but I don't know.
I hope that we can contribute to the alien meeting in some way.
Maybe they have their own version of von Noyman and they've made their own mistakes along the way. We can help them understand some of the things that we have learned. I hope also that when we meet the aliens, we can talk physics with them, because I hope that they are advanced and that millions of years ago they were struggling with these questions and now to them it's child's play. But I fear, honestly that everything we've learned is sort of centered in the human mind. We're asking human questions, we're telling human stories using mathematical tools that make sense to humans, and that it might be frankly impossible to translate into this knowledge to any other intelligence. But it remains to be seen, and the universe is filled with surprises. So I look forward to having hard quantum mechanics conversations with alien physicists, all right, And with that, I'll say thank you very much for coming on a podcast and talking to us about this crazy concept of boney and mechanics. It seems to me like sort of a beautiful theory that lets us recover the sense that the universe makes sense. That these particles are flying through the air, and they have trajectories, and they were here and then they're there, which means that they were sort of in between in the middle. That you can still think about the universe in a way that's intuitive to you, and that you can sort of get rid of a lot of this quantum weirdness and uncertainty. In some ways, it even hangs together better than other theories, and it's sort of unfortunate that it was cast aside for so many decades because of the mistake of eminent physicists. But we'll see what the future holds and how much progress we have to make. So thanks again very much for coming on the podcast. It was a pleasure.
Thank you, Thank you very much.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts, from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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