Daniel and Kelly’s Extraordinary Universe - Why does measuring a quantum object change it?

Episode Date: June 1, 2021

Daniel chats with Adam Becker about the "measurement problem" in quantum mechanics: does the wavefunction collapse, and what causes it? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want or gone.

Now, hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy,

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Apple Podcasts, or wherever you get your podcasts. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people, an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. Take a listen. Sue and I were like riding the line.

I'm bikes the other day, and we're like, we're like, people write bikes because it's fun. We got more incredible guests like Megan in store, plus news of the day and more. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network. Once upon a time, physicists seemed to have the world figured out, almost. There were one or two loose threads to be tidied up, but a solid idea about how the universe worked had emerged. And it made sense. At a particle level, physicists thought, the universe worked basically the same way it did at the human level and at the planetary level,

little balls moving around, orbiting each other, occasionally even careening off of each other. How wonderful and symmetric and simple it seemed. that the same concepts worked from the very small to the very large. What a deep satisfying truth about the universe we had revealed that explained almost everything other than a few pesky experimental results. And then those remaining loose threads unraveled the whole picture. To explain those weird experiments, we needed to break that symmetry and come up with a new vision for how the microscopic world works.

At the smallest level, the world wasn't made of little spinning balls, but of something new and quite alien. Quantum objects have followed a weird set of rules that gave headaches to even the geniuses of the 20th century. So then, what is real? Is the world made of stuff that moves through space like basketballs and planets, or does it follow some crazy new weird quantum rules? And if the quantum rules are real,

does that mean that the universe doesn't make any sense deep down? Hi, I'm Daniel. I'm a particle physicist, and I'm desperate to know what is real about the universe. And with me today is a special guest, astrophysicist Adam Becker, and an expert on reality, given that he's written a wonderful book about quantum mechanics titled What Is Real? Adam, welcome to the program. Say hello. Hi, yeah, thanks for having to have. me, Daniel. This is a lot of fun. Well, I'm especially pleased to have you on today because when

listeners write in and ask me what they can read to get a better understanding of the thorny problems of quantum mechanics, I always recommend your book. So thanks for joining us and for helping us unravel a little bit about what we know and what we don't know about the universe. Well, that's great. I'm really glad to hear that you're plugging my book. And welcome, everybody, to the podcast, Daniel and Jorge Explain the Universe, where we try to do just that. Embrace our knowledge and admit our ignorance. We do a deep dive into what things really mean and admit when words in science are being used to describe our lack of knowledge rather than our actual understanding. We're here to explain all of it to you.

And on today's program, we're going to attempt to do something very hard to tackle one of the trickiest topics in modern physics, the meaning of quantum mechanics. But our goal isn't to find the solution today, but instead to help guide you through the current situation, the status of our knowledge and science. ignorance to show you where the tricky bits are why they have been so persistently tricky and what the various ideas are for making progress. I mean, we know that quantum mechanics works, right? The math is correct. It can predict the results of experiments with incredible precision. It seems like our universe is quantum mechanical, but we want to know what that means about the universe. We want to know what is real. To me, that's what physics is explaining the unknown in terms of the known, is grappling with it and getting our intuition around it.

So my first question to you, Adam, is do you think that's possible? Do we even have the tools, the mental tools, to explain and understand something this alien, to understand what is real? I mean, hopefully, I guess that's the short answer. The longer answer is, you know, so far we seem to be doing a pretty okay job. I am certainly open to the possibility that the human mind is just not capable of comprehending some basic features of reality. On the other hand, you know, throughout the history of science, we've got a pretty good track record of, you know, banging our heads against a problem and eventually coming up with a pretty good theory of what's going on and a pretty good mathematical, you know, description to go along with that theory. Quantum mechanics, of course, is deeply strange, but there's no rule against reality being strange, right? In fact, it'd be kind of weird if the world were not weird.

It'd be disappointing. Yeah, exactly. Yeah. And also, come on, have you been here? Have you seen this place? Of course, it's weird. But you're touting sort of the history of our accomplishments, and those are wonderful. But a lot of those are limited to sort of the narrow regime in which our intuition works, right?

Because we grew up experiencing it things. These are familiar questions we have. Why does the thing roll down the hill? What are these stars moving around us? Does that necessarily mean it's possible to, like, extrapolate to other weird realms where we just have not grown up with any sort of natural experience? Yeah, I mean, not necessarily. it's possible that we'll hit some sort of limit. I'm just not convinced that quantum mechanics represents that limit.

I mean, first of all, we have this phenomenally accurate and precise theory in quantum mechanics, in quantum physics more generally, you know, arguably the most accurate scientific theory ever in terms of, you know, how well it matches experiment. And it's not as if we've looked at the theory and thrown up our hands and said, you know, this is impossible to understand. We have, you know, mathematical tools, but there's no way. way that the human mind can comprehend the reality behind the math. If anything, it's the opposite. We have too many ideas about how to understand the reality behind the math. So that doesn't

sound like a failure of human intuition to me, at least not yet. Yeah, I'm totally open to the idea that we'll get there at some point. All right. Well, you sound like a supporter of quantum mechanics. In fact, it sounds like you're a shill for big quantum. You know, I don't think anyone has ever accused me of being a shill for big quantum. for, but I can't say that you're wrong. I'm just not exactly a paid shell. There's no money in it. Oh, you're not getting your checks? Oh, man.

Yeah, well, not from Big Quantum, just from the publisher. Well, we can't tackle all of quantum mechanics in a single episode. So today I want to focus on one issue in particular, which is, I think, at the heart of it all, and sometimes known as the measurement problem. So on today's program, we're asking the question.

What makes the wave function collapse? What is measurement in quantum mechanics? And Adam, before we dig into it, we do something fun on the program, which is that I ask our listeners to answer this question, just to get a sense for like, what out there are people thinking? How much of a grasp of people have on this question? It helps orient us to know where to aim our answer. So I have for us some clips from listeners. And if you out there listening would like to participate for future episodes to answer really hard. physics questions with no preparation,

please write to me to questions at danielandhorpe.com. It's a lot more fun than it sounds. Here's what our listeners had to say. Okay, I have been learning about wave functions in quantum physics, and I know that's a really important part of measuring

something, and I have heard about it collapsing, but I'm not sure what makes it collapse. I'm going to guess that what makes a wave function collapse is when something's measured. I would say once the energy in the wave is reduced to a certain point, the wave can no longer support itself and it collapses.

I'm just going to guess here probably something that intervenes from outside. So on outside intervie. direction. All right. So those are the answers from our awesome listeners. Adam, what do you think about those speculations? I mean, they mostly sound like the kinds of things that you would see in a quantum mechanics textbook, actually, which is to say kind of vague. Right. There's a lot of talk in there about like, well, I'm not sure something about measurement, but I don't really know what that means. And like, that's really the heart of the problem, right? Like, nobody really knows what we mean by measurement or by

observation. So we like have a word for it. We have a phrase for, but we don't really know exactly what that means is happening deep down. Yeah, that's exactly right. All right. So I think maybe we should start just by orienting ourselves, just by getting sort of like using the same vocabulary and making sure everybody out there knows what we're talking about when we say the wave function. Can you give us a short definition of what the wave function is and why it's so important to this question? I mean, there's a sense in which the question of what the wave function is kind of what's at the heart of all this too. But yeah, I can take a stab at that. So in sort of classical physics, the physics of Isaac Newton, the physics of everyday life,

the physics of, you know, billiard balls and car crashes, the way that we describe where things are, we usually use three numbers to describe where something is, or at least where the center of mass of something is. You know, we say, okay, well, here's where it is in the X, Y, and Z. Here's how high off the ground it is. Here's how far in front of it. me it is and here's how far it is off to one side. And that's all you really need to describe where something is. Because we live in a three-dimensional world. Exactly right. But in quantum mechanics, if you want to do the same thing, if you want to take all the information we have about where something is, like if you want to talk about where an electron is, you need more than three

numbers. You actually need an infinity of numbers spread out across all of space. And that's the wave function. So the numbers are high. higher in some spots and lower in others. And usually what we say the wave function represents is that it's to do with the probability of finding the electron in a particular spot when we look, which makes it sound like the wave function isn't really a thing in nature and it's just a lot more about our information. Yeah, so hold on. Let me ask you about that because you're making an analogy to a classical particle where

we're talking about like where it actually is. And you're saying that you need more information to talk about where an electron is. But now you're describing the wave function in terms not of where the object is or what it is, but about our measurements of it already. So like we've already sort of snuck into the electron. That's exactly right. I mean, there's, there are, I wasn't kidding when I said that, you know, the question of what the wave function is is sort of part of the controversy here and part of what's at stake.

We'll see if we get past this one question in the whole episode. Exactly. Yeah. I'm not convinced we'll succeed. But yeah, I mean, the reason I say, oh, this is sort of the quantum analog of, you know, the three numbers describing where something is in Newton's physics is that, you know, it sort of plays the same role in the same sorts of physical laws in quantum physics. So the question of whether the wave function is a thing out in the world or if it's just something about our information about, about. stuff out in the world is, you know, a live question and a subject of active debate. But it's not just as simple as saying, oh, it's just our information about what's out there. It's just that in the most simple way imaginable. Because wave functions, I mean, like the name sort of implies, the wave functions wave. They behave in ways that we actually tend to associate with physical objects.

they undulate smoothly. The numbers change smoothly from one place to another. They change over time. And they can even perform some of the same tricks that waves perform. You can send them through a narrow slit and they'll diffract outward on the other side. They can interfere with themselves and cause patterns of light and darkness on a photographic plate, that sort of thing. So we call it a wave function because mathematically it's described by similar equations that describe other kind of classical waves we're familiar with. That's right. Yeah. And it also performs some of the same tricks as classical waves that we're familiar with physically. So, you know, we don't tend to think of our information about a thing as doing that. And it doesn't mean that it can't. It just means that if we want an account of wave functions in terms of our information about the world, as opposed to saying, you know, the wave function's actually a wave that's out there. We need to do some extra work.

So you're saying the wave function tells us how to predict the outcomes of our experiments. like if I'm going to find the electron over here, or if I'm going to find it spin up, or if I'm going to find it spin up, or if I'm going to find it spin down. It tells me what I'm likely to observe, but we're not sure whether it's actually real and distinct, separate from our ability to measure it and interact with it. We don't know sort of philosophically whether we can take that step. Yeah, yeah. I mean, there are theorems that suggest that there's something like the wave function out in the world, but it's not, you know, this is an open question and has been since the beginning of quantum physics, almost 100 years. years ago. And I think that's sort of one of the most fascinating points. I mean, you talk about classical physics. There's no distinction there between the thing exists and we measure it to

exist there. It's just like those two things are just part of the same idea. You see the ball there because it is there. And it would be there if you weren't here to look at it, all this kind of stuff. So I love these discoveries in physics that make us sort of crack open to ideas we thought were so naturally entangled. So like deeply connected. And now we realize there's a possibility for these two things to be actually separate and distinct. Observing something is there doesn't mean that it is there in some deeper sense. It's like totally crazy. Yeah.

No, that's absolutely true. And one of the strange things about wave functions and measurement is just the idea that, you know, measurement and observation are coming into what's supposed to be a fundamental theory at all. Because, you know, measurement is not a well-defined thing. What do we mean when we say measurement? Right. And I think that a key concept we need to tackle before we get into measurement is this question of superposition, right? Because quantum mechanical objects can do something that like our baseballs can do, which is that they can for a long time have two possible outcomes and maintain those two possibilities simultaneously, right? So the way function can incorporate various possible outcomes inside of itself. Yeah, no, that's exactly right. If you send a ping pong ball into a maze, it's just going to go down. have one path in that maze and you can watch it take one path. But if you send an electron or a photon

or some other, you know, tiny quantum object into, you know, some sort of maze like send a photon into a set of mirrors and prisms on an optical bench, you know, in basement of a physics department somewhere, it's not going to take just one path. Quantum mechanics says, no, it's going to take a superposition of all of those paths. It's going to go down two or three or four different paths at the same time or its wave function will. But then when we measure it at the end, right, we say, all right, I'm going to put a device in here. I'm going to ask the question, which one did it actually go down? I can't measure all those paths, right? I get one answer. That's right. You get one answer. If you put a detector on one of the paths, then you'll get an

answer saying, you know, yes, it went down this path or no, it didn't. But if instead you set up your optical bench, your maze, whatever you want to call it, or your double slit experiment, so that there's an interference pattern on the other side, you will get, interference. So when you're not asking the question of which way the photon went when it went into your setup, it sort of goes down all of those paths and then interferes with itself. But if you ask, wait, which way did you go? Well, then it says, oh, no, I went this way and then it doesn't interfere with itself. And so we know that the way function does this superposition thing, having two possible outcomes at the same time, because we see the interference that's

proof of superposition. But then when we try to measure the photon, the superposition sneaks away. And for you, is that like the clearest encapsulation of this question, this measurement problem, like how the wave function goes from having like various quantum mechanical possibilities for the paths of a photon to basically picking one? How the universe like ends up rolling that die choosing, oh, this path or that path or the other path. I think it's a very clear example of that. The way that I usually talk about it is a little different, you know, I say, okay, this is one example of the measurement problem, but in general, the measurement problem is more about that sort of undulating property of the wave functions that I was

talking about before, right? We have this very nice equation, the Schrodinger equation. It's a law of physics, right? We think of it as a law of nature, and that describes how wave functions wave, right? It says that they always wave sort of smoothly and evenly, and, you know, they don't make any abrupt transitions. But sometimes the Schrodinger equation is temporarily suspended. Well, you can't do that. You can't just pause the laws of physics. Yeah, sometimes it's as if someone just hits pause on the Schrodinger equation. And instead, you have to use this other thing called the Bourne rule, which says, okay, take the wave function. and look at all the different possibilities it gives you for the way that your experiment is going to turn out.

And that gives you the probabilities for the different outcomes. That's what the wave function does when you use the Bourne Rule. And then, whichever one you actually observe, cut out all the other parts of the wave function. That's the only one that's left. All the others just instantly go to zero. And that violates the Schrodinger equation? And that violates the Schrodinger equation. The Schrodinger equation doesn't have anything in it like that.

And then when you stop looking, that's what happens when you make a measurement. And then when you stop looking, the Schrodinger equation applies again. And so then the question is, okay, well, so if you have these two different rules and they contradict each other, then first of all, why? And second, we better be really, really, really clear about when to use one and when to use the other. and this is the collapse of the wave function. And so the usual answer to the question, when do we use one and when do we use the other? When does the wave function collapse?

The usual answer to that is when we make a measurement. And so now the fact that the word measurement is kind of vague goes from, you know, a little troublesome or annoying to a really serious problem. Right. So that's a great encapsulation of the question we're facing. Like we have this beautiful equation, the Schrodinger equation, that tells us how this wave function moves and changes and squishes through the world and we verified it to zillions of degrees of accuracy, except that, as you say, sometimes it seems to be ignored. And sometimes it doesn't seem to apply.

And so we have this question of like how a wave function goes from this smooth underlending property to like collapsing into just a point when we make a measurement, what that measurement even means. So I want to dig into that in much more detail. First, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass.

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Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't. trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly

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All right, we're back and we're talking to astrophysicist Adam Becker, author of What Is Real, about the nature of the quantum wave function and what happens to it when we look at it. And I have this quote that I love from Bell who says, either the wave function as given by the Schrodinger equation is everything or it's not right. What do you make of that? I see what he's getting at there. And I think he's kind of right. I mean, there's got to be something more that tells us, okay, when do we apply the Schrodinger equation and when don't we? Because otherwise, you know, and I think Bell said something along these lines as well,

we're stuck in this situation where these laws of physics that are supposed to be fundamental are just kind of hopelessly vague. So we have to take the shorteninger equation and the way function, all of which seems wonderful and perfect and beautiful and we love it. And we need to add something else. We need to say, plus there's this other mechanism that makes things collapse. And this, I think, is where people disagree how to describe this weird combination of ideas in sort of a holistic concept. And so first let's talk about maybe the most mainstream way to attack this, the most common, the one that people most read about in their textbooks and that I think a lot of our listeners refer to, which is basically the Copenhagen interpretation where you add something to the Schrodinger equation that makes

the wave function collapse when you look at it. So how does that actually happen? Like, what do you add to your system, you know, mathematically to make that happen? You can't just have like a thing that says, and by the way, if there's a measurement. I mean, doesn't everything have to be like, you know, written down in some sort of equation? The thing is it is just kind of added on. They do basically just say, yeah, use the Schrodinger equation except when a measurement occurs and what a measurement occurs, use this other thing instead, use this collapse rule

called the Bourne rule named after Max Born one of the architects of quantum physics and it's just got a completely different mathematical form and it says, okay, you know, like I said before, it lets you use the wave function to calculate probabilities and then says and then the rest of the wave function

other than the part that you saw collapses. So if you're looking for an electron somewhere and you've got the wave function of the electron which is you know this sort of nice smooth thing that's maybe got three or four different peaks you look for the electron you find it near one of the peaks the born rule says okay well then what happens to the electron's wave function is you know now it just has one extremely narrow peak exactly where you found it and it goes to zero everywhere else and then when you stop looking the schrodinger equation just applies again, which is kind of incredible. And it requires us to sort of insert

ourselves into the equation, right? It needs like the measurement part is when we are interacting with this thing. And I think the most common question is what counts as a measurement? If I put a particle detector in there but don't turn it on, does it count? If I turn it on but don't connect it to my computer, does it count? If I hook it all up, but then don't look at the computer screen, does it count as a measurement? And what's special about my particle? detector. Isn't that particle constantly interacting with other things? Does that count as a measurement? So can we tackle it by thinking about so the quantum particles we're using to make the measurement? You know, because we don't just like look at an electron, right? We like bounce a photon off of it or something like that.

Yeah, yeah. I mean, the Copenhagen interpretation sort of lives or dies on what you mean by measurement, right? And so it is tempting to say, okay, well, maybe we can get around this problem by saying that, you know, the measurement devices itself also quantum. But the problem is that if you use the Schrodinger equation and, you know, wave functions and the mathematical machinery of quantum mechanics to describe the measurement device as well, then all that happens when you make a measurement is you go from your measured system in a superposition and your measuring device sort of ready to make a measurement to a state where both the measured system and the measuring device are in a superposition. And so, you know, if you wanted to say, okay, did the electron go left or did it go right and then you use your measuring device to answer that question, then the Schrodinger equation says at the end of that measurement, what you're going to end up with is a superposition of the electron went left and the measuring device says left and the electron went right and the measuring device says right.

So the measuring device has become sort of part of the experiment. Exactly, yeah. And so that's not going to get you out of it. eventually you have to, according to the Copenhagen interpretation, you have to say, well, then a measurement occurs, and so the Schrodinger equation doesn't apply anymore, and we have to use the collapse rule, the born rule. And so you really need to get comfortable with whatever it is that a measurement means, which the Copenhagen interpretation is kind of famously vague about. So let's break that down a little bit more. So we have our electron, and we probe it with the tip of

some very, very narrow tool and the tip is just like a single particle that's interacting with the electron. Now, we might say, okay, the tool is touching the electron, so it's being measured. It should collapse. It should just collapse right there. But somebody else coming in and looking in the experiment the same way could say, no, no, no, I think the system is the electron plus the tip of the tool and the rest of the tool is the measuring device. So the tip of the tool plus the electron, that's your experiment. That's what you're probing. The measurement happens when like the next particle over reads off the information from the tip of the tool. And somebody else could come along and say, no, no, no, I think the original electron plus

the first two things on the tip of the tool are part of the experiment, and the rest of it is the measurement. And you could just basically do this forever, right? All the way down the tool, including as many particles as you like, or even including the experimenter, him or herself. Yeah, I mean, quantum mechanics has this weird propensity to just sort of generate these sorts of thought experiments, like the one that you're talking about, that sound like. like something out of like an ancient Greek philosophical dialogue or something.

Zeno's quantum experiment. Exactly. Yeah. I mean, there even is a Zeno experiment, though not that one. But yeah, the problem here is, you know, it'd be easy to say when a measurement occurs if we could say, well, there's a quantum world and then there's a non-quantam world. And when a non-quantam thing interacts with a quantum thing, that's a measurement. Thing is nobody believes that anymore.

Because all non-quantam things are made of quantum things, right? Exactly, yeah. We believe that the world is made of everything in the world is made of molecules, which are made of atoms, which are made of subatomic particles, all of which are subject to the loss of quantum mechanics. And quantum mechanics doesn't have a real size limit. I mean, certainly there are sizes at which some of its features are more obvious than others. But in principle, there's no limit to the size of a system that you can use quantum mechanics to describe. And we believe that the whole world is made of particles subject to the laws of quantum physics. So, yeah, the question becomes if there's no border between the quantum world and the non-quantum world because the whole world is quantum, then when does a measurement occur? Is it when the measurement device touches the object? Well, in that case, does that mean that quantum mechanics doesn't apply to the measurement device? Okay, well, maybe it's when somebody looks at the measurement device. Maybe it's when I look at the measurement device. Okay, but does that mean that quantum mechanics doesn't apply to me? I'm made of

quantum stuff. You know, I'm made of cells, which are made of molecules, which are made of subatomic particles and so on. You know, there's no reason to think that quantum mechanics doesn't apply to all of the stuff in my body and brain. In fact, every time we've checked on something like that, we've found that, you know, every biochemical process is fully explained by quantum mechanics. All right, but there is one wrinkle there, right? Like, you are different from, you know, the oscilloscope or the probe we're using the touch the electron. We think in that you are conscious, right? You are a self-aware. You are a living, thinking, breathing person. I don't know about the oscilloscope. I didn't invite the oscilloscope to be a guest on the podcast

to speak up for itself. But, you know, I think a lot of people imagine that that might be the moment when the measurement happens, when the information like goes through the tool and up the computer and into your brain and it's like known by a conscious observer. What about that? Why can't we use that as a distinction? Well, so there's a few issues there, right? One is, you know, consciousness is something that we don't understand well, what do we mean by consciousness? You know, you were sort of getting at that before when you were bringing in this thought experiment of, you know, okay, well, when I look, is that the measurement? No, well, then when you come in the room and you look at me, is that the measurement? This was put together by this famous physicist Eugene Vigner

and it's called the Vigner's friend experiment. And I'm conscious, right? My friend is conscious. So maybe the measurement happens when I look or is it when my friend looks at me or, you know, does it have to be a human? What if we put a chimp in there? Right? What about a dog or a crow? Right? Crows are really smart. Hold on. Let's break down the Vignus friend experiment because I think this is worth describing like essentially the idea is you are doing this experiment. You are measuring this electron. You're using a tool and you do the evaluation and you get a number. Now, I don't know the answer yet. And so in some sense, I can look at you and say, well, you are part of my tool, Adam. I haven't asked you yet what happened. So I don't know the.

answer. So you are still in a quantum superposition of the electron went left and the electron went right. So in that sense, like a conscious person can be in a quantum state, right? You can have like the wave function of Adam Becker having two different possibilities. Yeah, I mean, that's a problem, right? Because that's the sort of thing that feels like you could lead to an infinite regress, right? You know, okay, but then you're in a superposition until your friend talks to you. And then we start having problems like, okay, but then why does everybody agree about the outcome of the experiment? Right. What was it like to be in a superposition?

What did it feel like? Yeah, what was it like to be in a superposition? Exactly. What does it feel like? I don't think that I've ever been in two places at once or that I've ever believed that an experiment. I felt like I needed to be in two places or once. Yes, exactly. I never achieved it.

Yeah. And I certainly don't think that I've ever like, you know, looked at the outcome of an experiment and thought, oh, that went both of the two mutual contradictory ways that it could go. You know, the electron went left and it also went right, and I saw the measurement device say left and also say right at the same time. That's not an experience I remember having. And that kind of rules out this notion of consciousness being the threshold, because you can put a conscious observer into your experiment and still have the wave function not collapse until after the conscious observer reports their results, right? Just at a conscious observer observing something doesn't necessarily make the way.

wave function collapse. Isn't that right? Yeah, with an asterisk. Tell us about the asterisk. Yeah. So, I mean, you can set up a system where you've got a quantum wave function and superposition and you can sort of verify that it's in a superposition and that verification does not itself lead to the collapse of the wave function. Wait, how do you do that? How do you verify that? Is that by observing interference? Yeah, that's by observing interference. You can see that there's interference. But what you can't do, or at least what we don't have the ability to do right now, is put a human in there as part of the system that is exhibiting interference, right? Oh, I see.

I can't see the various modes of atom interfering with themselves. Exactly, yeah. But there are other reasons to think that consciousness is probably not what's going on here, or if it is, you need a really good account of how that's possible, right? Because one of the things that we want to be able to use quantum physics to do, and, you know, as a cosmologist by training, this is near and dear to my heart, we want to use quantum physics to describe the very early universe who want to do quantum cosmology. And, you know, that means talking about things like the wave function of the universe. And indeed, you know, we talk about that when we talk about things like, you know, patterns in the cosmic microwave background radiation, the old light in the universe, an echo of the big bang. We see the imprint of quantum mechanics in the

sky. And now I am going to almost directly quote John Bell, was the wave function of the universe waiting for billions and billions of years for, you know, a paramecium to arrive and collapse the wave function? Or did it need a better qualified observer? You know, someone with a PhD. The first PhD collapsed the universe's wave function. Exactly. Yeah. I don't think that that's how that worked. I don't think that conscious beings are necessary in order for quantum mechanics to work. So if the wave function collapses, and we don't really know if the way function is real and exists outside the mind of humans, but if it is real and it does collapse, it seems like it must have been collapsing for billions of years before we showed up. That's right. And if it doesn't

collapse, we need to figure out why it looks like it does. It does seem important. And I think that you mentioned something really interesting about how we know that a. asymmetries do exist, right? Like, this question is important not just for philosophers, but for like quantum cosmologists. How do you go from the beginning of a universe where you, I assume, have a symmetric wave function because anything else would be bonkers and somehow get asymmetries, right? How do you get a universe that's not exactly the same in every direction? Where do those things come from?

Those come from quantum fluctuations, which are quantum collapses, right? Yeah, that's right. Quantum fluctuations happen when you might have equal probability. abilities to go left or right, but like one of them is chosen. The universe does roll a die. And so the fact that we exist here and not a billion light years to the left is evidence that quantum mechanics does fluctuate, that there are these collapses, that these things are real somehow. Yeah, exactly. Or at least that's something like collapse or something that imitates collapse or gives the appearance of collapse happens. All right. So it seems like this Copenhagen

interpretation is pretty problematic, right? Like there's a basic fundamental unknown in it, like what this even means by measurement. We need measurement to get the wave function to collapse or to get to look like it collapses, but we don't even really know what that means and what triggers it. So how could this possibly be the most mainstream core idea in the most fundamental concept in physics? That's a great question, and it unfortunately has a very simple answer. The answer is when people ask these sorts of questions, they were just sort of waved away. It's more complex than that. I wrote a whole book about how this happened. And before I did, I used to say, well, I could write a book about it.

And then it turns out that I made good on that. That wave function did collapse into a book. Yes, it did. But yeah, the answer is, you know, people ask, well, what do we mean by measurement? We have to get more specific about this. How could this possibly be this vague and ill-defined and contradictory? And the answer that was usually given was it works, so don't worry about it. This was sort of summed up famously by the physicist David Merman as shut up and calculate.

That's basically like, don't worry about what it means. It works. It predicts our experiments. Who cares? Yeah. Don't pay any attention to the man behind the curtain. Just, you know, do the calculations and you'll be able to build most of the technology that the modern world is based on, which is, you know, absolutely true.

You know, you don't need to answer this question in order to do things like design, semiconductor transistors and build computer chips and lasers and LEDs and, you know, nuclear power and all of the other incredible and, you know, awesome in the most literal sense technologies that quantum physics has enabled over the last century. But science and physics is not just about delivering technological improvements for humanity, right? Like, I love that all our listeners can hear this podcast on various devices enabled by quantum mechanics, but I didn't go into physics to make a better iPhone. I went into physics to understand the universe, right? So doesn't that really fly in the face of sort of the core mission of the entire discipline to

like gain some understanding? I think so. I completely agree with you, but apparently not everyone does. All right. Well, I'm glad we agree on that. And I want to dig into some other possibilities, some other ways people have attacked this problem, some crazy, totally different ways for thinking about what might be real about the universe. But first, let's take another break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage,

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Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus. to a threat that hides in plain sight that's harder to predict and even harder to stop. Listen to the new season of law and order criminal justice system

on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Well, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon.

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And you'll meet the team behind the scenes at Othrum, the Houston Lab that takes on the most hopeless cases. to finally solve the unsolvable. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, sis, what if I could promise you you never had to listen to a condescending finance, bro, tell you how to manage your money again.

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And we've been talking about the way. function and how the Copenhagen, the mainstream interpretation of quantum mechanics has a basic problem in it, in that it can't define what a measurement is, but a measurement is essential to making the theory work. So it can't be the only idea that's out there. Surely people have thought of some other approaches. And so if you're a listener to Sean Carroll, for example, you probably heard him as a big proponent of this Everettian many worlds interpretation. So Adam, how does a many world's interpretation. How does manufacturing billions and billions of branching universes solve this measurement problem or does it? That's a great question. I want to say before I answer

that, this is something that I get a lot of email and people asking me about it back when, you know, in person, back when, you know, we could do things in person. For whatever reason, a lot of people came away from my book thinking that I agree with Sean Carroll. And I like Sean. Sean's a great guy. I'm sensing a butt coming. Yeah, but I think that his position is a reasonable one, but I don't think that it's the only reasonable one. And I think that I am not here as a shill of big many worlds. I'm just a shill of big quantum. Many worlds is already big. You don't say big in front of it. Yeah, that's true. No, many worlds, I think, is pretty clearly the next most popular interpretation after this sort of jumble that is the Copenhagen interpretation.

All right. So break it down for us. What is the mini world's interpretation? So the many world's interpretation gets out of the measurement problem by saying, oh, yeah, collapse doesn't happen. It just sort of looks like it does. It takes the sort of infectious property of superposition where, you know, if a measurement device measures something that's in superposition, then it will go into superposition. It takes that property and sort of embraces it wholeheartedly and turns it into a strength. It says, okay, well, collapse never happens. The Bourne rule is, you know, not a fundamental thing in nature that describes what's actually happening in the world. It's just something we need to make predictions. And in reality, the Schrodinger equation or, you know,

the relativistic extensions thereof, always apply. And so wave functions always just evolve smoothly, which means that when you make a measurement of an electron or something in a superposition, you know, the classic example here is Schrodinger's cat. You set it up with a quantum device where, you know, if it goes one way the cat lives and if it goes the other way, the cat dies. So when you open the box, you find a cat that is both dead and alive. It's in a superposition of dead and alive. And then, you know, in the process of opening the box, you enter into a superposition.

position yourself of seeing a dead cat and seeing a living cat. And then someone else comes in the room and they enter a superposition of, you know, seeing you crying over this dead cat and seeing you, you know, playing with the living cat and so on. And this just sort of spreads out into the universe. So you're saying the wave function never actually collapses and picks one of these branches. It just keep branching. And we are only in one of those branches, which is why it looks like. it collapses.

Sort of. The question of where we are in the theory is definitely something that's contentious, but I think that what Sean would say, well, I don't want to put words into Sean's mouth. If I put on my many worlds hat and say, okay, I'm going to pretend to be a real advocate of many worlds, I would say, no, we're in both branches. But once we split a quantum process called decoherence ensures that the two branches, you know, once they involve large objects made of many quantum parts, articles can't interfere or communicate with each other in any way very, very quickly. And so we

split. And so, you know, if you ask one of the copies of you that is in either branch, hey, how many cats do you see? How many outcomes do you see for this cat? Both of them would say, oh, I only see one outcome. They just disagree about what that outcome is. And so this is why it's called many worlds, because it imagines that multiple versions of the universe are existing decoherently, that they've decohered from each other, and that they're all out there. They're real, but they're sort of like not accessible to us anymore because we're only in one branch of the wave function. Yeah, or this copy of ourselves is only in this branch, but there are other near identical

copies in all of the other branches. And so I was trying to lead you down the garden path there, I think, to my major objection to the many world's interpretation, which is like, why are we? are we in this one? Because as you say, like, there's a copy of me in all of those universes that have observed every possible outcome of the Schrodinger's box experiment. But still, I'm this one. And I know that in the other universe, the other me thinks that it's that one.

And that's fine. But why is it in that universe and I'm in this universe? Like, there is still something special about this universe because I'm in it, right? Well, you know, your copy in the other universe where the cat died would say the same. thing. I know, but it also has a reasonable objection, right? There is still something different about this universe because I'm in it and there's something different about that universe because it's in that one. It seems to me like does not really avoid this problem because it still takes one universe to be special in some sense because this is the only one that I'm experiencing.

Anyway, what are your concerns about the many world interpretation? Well, the classic concern about it is that you still actually need the born rule, right? Because quantum mechanics doesn't issue forth certain predictions. It doesn't say this is, you know, 100% definitely what's going to happen. It says that sometimes. But most of the time, the predictions of quantum mechanics come in the form of probabilities. It says, well, there's a 20% chance that this is going to happen, a 30% chance. That's going to happen. A 50% chance that that's going to happen. And, you know, those are the possible outcomes. But in a world where the Schrodinger equation always applies, well, the Schrodinger equation has no probability in it. The Schrodinger equation is actually like

Newton's physics in that it's completely deterministic, you know, when you ask a many world's person, well, what's going to happen when you open the box? They'd say, well, with 100% probability, I will split into two copies, one of which we'll see a living cat and the other will see a dead cat. That's definitely what's going to happen. And so then, you know, the next question, which is, you know, what's the probability that you're going to see a living cat? Because I don't want a dead cat. The answer to that has to be, well, you need to use the Bourne rule. You need to use this collapse rule because that collapse rule is how we get predictions out of quantum physics. It's what makes it so phenomenally accurate and powerful. And so

you need to figure out, okay, how do we introduce probability into a theory in which literally anything that can happen does happen? That's a little thorny. And one way of going about it, and this is actually a position that I know for sure Sean holds. So now I am going to like do my best Sean Carroll impression. Sean says that, well, the probability comes from basically exactly your concern, that we don't know where in this branching multiverse of worlds we're located. And so we have uncertainty about where we are. And that uncertainty is where the probabilities come from. When we do the experiment and we see an outcome, what we're actually doing is learning where in the many worlds we are, and then you can look at the structure of this multiverse and sort of derive the

born rule from it. You can say, okay, well, this is the right way to answer questions about probabilities. So the problem with the many worlds interpretation then is that it keeps the wave function sort of too long. The wave function itself doesn't actually make predictions, as you say, it can be used to make predictions. but if you just keep the wave function going forever, then how do you actually predict the outcome of an experiment?

All right, that's fascinating. Yeah, you need to answer that. And I want to be clear, the many advocates of many worlds generally have answers to that. Although I don't think that there's consensus around one single answer to that among all of the many advocates of, you know, this kind of interpretation.

They're aware of this problem and they've addressed it and they have answers to it. So the question isn't, you know, how do you answer it? The question is, does one or several of the answers that have been provided work? And that is an open question. Awesome. And so before we wrap up, I want to touch on a couple of other ideas. So it's totally different directions people are taking about attacking this deep question about the meaning of the wave function and what measurement means. And one of my favorites is this hidden variable theory or these categories of theories called hidden variable theories. Because when I was

learning about quantum mechanics, I remember thinking like, well, sure, but how do we know it's not like just actually determined by something we're not aware of? You know, it feels like maybe our lack of information, this uncertainty in the universe doesn't just come from inherent uncertainty, but it just comes from like our not seeing the full picture. So maybe there's like something going on behind the scenes that's controlling everything. How do we know that's not the case? How do we know that it's not just like more to the universe that makes it actually deterministic? I mean, that's a great question. And you're in really good company there. As I'm sure you know, Albert Einstein basically had exactly the same question. It's a myth that he never accepted quantum physics. He knew that it worked

and he fully accepted that it worked. He just thought it couldn't be the whole story for basically the same reason that you're giving. And in particular, he was very unhappy about the idea that things depended on observation and that you couldn't talk about what was happening when you weren't looking. He thought that this was, you know, as you were saying, just kind of avoiding the whole point of science. Science is about figuring out what's in the world and how it works. And he was also really concerned about the possibility introduced in quantum physics for what he called spooky action at a distance, these long distance connections between objects. And that is actually directly related as it turns out to the answer to your question. You know, the question is there's

something going on that we don't know about some, you know, hidden properties, what we usually call hidden variables of these particles that, you know, determine their behavior and we just don't know what they are. And that's where the uncertainty comes from. The answer to that that we know is, yes, it's possible, but you have to pay a price. The price is spooky action at a distance. And that was proven by experiments that were done to test a theorem by John Bell. So we can have a super deterministic universe, but it can't be local. We can't also have like everything be determined by what's happening right here. So yeah, I got to be like really pedantic and nitpicky. There is actually a class of interpretations called super determinism. And that's

something else. But yes, we can have a deterministic universe. We can have hidden variables that determine everything that's going on, but the price we have to pay is that, you know, things that happen right here can instantaneously influence stuff that happens arbitrarily far away and do so in a way that provably can't be used to send anything, information or material, faster than the speed of light. All right. So that's super deterministic with a lowercase S and two words. Yes. What's super determinism? The single word with a capital S. Is that Superman is determining the outcome of all these quantum experiments? Super determinism is the idea of like a hardcore clockwork universe. It's this idea that, oh, we can explain the outcome of these bell experiments without

sacrificing locality and without, you know, without sacrificing the idea that, you know, instantaneous action at a distance can't happen. We can also do it without sacrificing the idea of determinism. But to do that, instead, we have to say, oh, at the beginning of time in the Big Bang, a whole bunch of really fine-grained information was encoded into every particle in the universe about the outcomes of those experiments, those Bell experiments that would be conducted, you know, 13.8 billion years later, that would arrange for them to turn out in a way that would trick us into thinking that, you know, the universe was non-local.

So we do these experiments, and they seem to suggest the universe is non-local, but that's just because they've been cleverly arranged 14 billion years ago to look that way. Yeah, that's super determinism, yeah. That's super nuts. Yeah, I'm not super sympathetic to superdeterminism. But, you know, all these ideas are kind of crazy. All of them have things you might object to. I guess in the end, the question I have for you is, are we going to figure this out?

Or how could we figure this out? Are there experiments we can do to figure out which of these things are real? Or is it just going to rely on philosopher, smoking banana peels and organizing their minds? Yeah, no, this is a great question. So the answer depends on what you mean by, is there an experiment that we can do, right? So if you're asking, is there an experiment that we can do to figure out which of these different interpretations of quantum physics is the right way to think about quantum physics right now? The answer to that is no because they all give the same, or almost all give almost all the same outcomes for all experiments provably. I mean, there are some proposals for solving the measurement problem that aren't just new interpretations, but are actually completely different theories.

There's a class of theories called objective collapse theories that modify the Schrodinger equation. Those can be tested. So, yes, some of them can just be directly tested, and those tests are sort of ongoing. But for most of these, like the many worlds interpretation or the best known and most developed of the hidden variables interpretations called Bohemian Mechanics, or DeBoi-Bome Theory, or Pilotwave Theory, has a few different names, which is, you know, non. local and they think that that's like a good thing about the theory and that's a whole other story. I'm not saying that to disparage them. I understand why they say that and I think that that's also a reasonable position. But the point is those two and, you know, many of the other interpretations of quantum mechanics are just that. They're interpretations. They all provably give rise to

exactly the same outcomes in all of these experiments. And so if you ask them, well, what's the experimental evidence? They'd say all experimental evidence for quantum physics, you know, is experimental evidence for this interpretation as well. So in that sense, no, there's no experimental way to distinguish between them. Doesn't that mean we just haven't been clever enough? I mean, if we have seven theories that all fit the data, it just means we need to come up with a more clever experiment

that can distinguish between those seven theories, right? Otherwise, you have to accept the possibility that there could be multiple theories of physics that work perfectly to describe our universe, in which case, like the whole project of physics of coming up with a unique idea, to describe the universe and then interpreting what that idea means is sort of cast into doubt. I have some good news and some bad news.

Let's start with the bad news. The bad news is all of these theories provably give rise to exactly the same mathematics and provably spit out the same results for the same experiments. And in fact, you can even prove that given the... the mathematical structure of any scientific theory you could ever devise, there is an infinite number of interpretations that you could come up with to, you know, explain what's going on in that theory. So that does sound bad from the perspective of, you know, physics and the project of trying to understand what's going on in the world. The good news is that's not actually how

physics works. You know, we don't sit down and say, okay, well, there's an infinite space. of possible theories for the mathematical structure that we devised, and so now we need to try to narrow that infinite space. That's not how we do physics. How we do physics and how we do science more generally is we say, okay, well, look, we have these ideas about how nature works, and these ideas come from a variety of places. They come from the results of experiments. They come from older theories that we had that worked and now seem to be breaking down. They come from new theoretical ideas that we've been kicking around because we like them. And they come from, you know, preconceived cultural and social norms and, you know, mythology and storytelling and whatnot,

you know, just ideas that we have about the world. And all of that goes into the process of judgment that is made when new theories are developed and choices are made about how to interpret those theories. It sounds like you're talking about a meta level of measurement where we're like measuring the ability of an experiment to satisfy our need to understand the universe. Exactly. Yeah, that's not wrong. But the thing is, that's actually good news when it comes to the question of interpreting quantum physics and finding out which, if any of these, is the best way to think about quantum physics, because we know we're not done. You know, the one thing, aside from the success of quantum physics, that I think that you could get everyone in,

the world of quantum foundations and the world of physics more generally to agree upon is that we are not done in our search for the fundamental laws of the universe. We know if nothing else that we have not found a way to get our best theory of gravity, general relativity, to work with our best theories of quantum physics, quantum field theory and the standard model of particle physics. And we also know that that standard model is not just missing gravity, but is also missing things like dark energy and dark matter. So we know that we're not done. And so that means we're still on the hunt for new theories. And one of the things that goes into the mix when coming up with new theories is the interpretations of old theories. So the way we think about

quantum physics now can influence the hunt for the next theory that will go beyond our current understanding of physics, and it also goes backwards. If and when we come up with that theory, it will probably suggest to us an experiment that can be conducted that would distinguish between some or all of the existing options on the table for interpreting quantum mechanics. Yay, I have faith in the future of experimental physicists to get us out of this jam by coming up with a clever new experiment. Yeah, we should.

All right. Well, that's wonderful. Thank you very much, Adam. I think it's been a delightful journey through the problems and possible solutions to the questions at the heart of quantum mechanics. And I'm glad that there's still a lot of work to do because us quantum physicists will still have a job. So thanks, Adam, very much for joining us and for explaining these things so clearly. Before we go, do you want to tell our listeners about any upcoming projects you have or places they can find you other than your excellent book, What is Real? First, I just want to encourage people. Go find my book. If you like hearing about these things, I like talking about them, but I like writing about them even more. And there's, you know, 300 pages of it available wherever fine books are sold. If you want to find me on Twitter or really almost anywhere else, my Twitter name and online handle is freelance astro. So I'm, you know, on most social media under that name. And my website is freelance astro.com. and you can find links to my latest work there. And yeah, aside from that, I am working on another book about science and Silicon Valley, but it will not be out for another couple of years. It's still in the very early stages. But yeah, if this sort of thing is interesting to you, please have a look at my book. All right. Well, thanks again for coming on. And I hope your next book collapses into a very readable pile, just like the first one. Thank you. Best of luck with that.

And thanks again for coming on. Thanks. Thanks for having me. This was a lot of fun. And thanks to all you listeners for coming along on another ride of curiosity where we investigate what the universe actually means and try to explain it all to you. Tune in next time. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHeart Radio, visit the IHeart Radio app, Apple podcasts or wherever you listen to your favorite shows. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged. Terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back-to-school week on the OK-Stra. Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot.

He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you.

When you think about emotion regulation, we're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials easier. Complex problem solving. It takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

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